Showing 1–50 of 76 results for author: Tej, A

ALMA-QUARKS: Few-Thousand-Year Hatching out of "Egg": The Supersonic Breakout of a Hypercompact H II Region from Its Parental Hot Core

Authors: Siju Zhang, Guido Garay, Fengwei Xu, Luis F. Rodríguez, Neal J. Evans II, Annie Zavagno, Paul F. Goldsmith, Dongting Yang, Xunchuan Liu, Aiyuan Yang, Tie Liu, Amelia M. Stutz, Hong-Li Liu, Wenyu Jiao, Anandmayee Tej, Lei Zhu, Kee-Tae Kim, Pablo García, Thomas Peters, Thomas Möller, Shanghuo Li, Leonardo Bronfman

Abstract: The kinematic evolution of hypercompact H II (HC H II) regions around young high-mass stars remains poorly understood due to complex interactions with parental environs. We present ALMA QUARKS/ATOMS 1.3 mm/3 mm observations (the highest resolution $\sim0.01$ pc) of a deeply embedded HC H II region (diameter $\sim0.015$ pc, electron density $\sim2\times10^{5}$ cm$^{-3}$) exhibiting a striking… ▽ More The kinematic evolution of hypercompact H II (HC H II) regions around young high-mass stars remains poorly understood due to complex interactions with parental environs. We present ALMA QUARKS/ATOMS 1.3 mm/3 mm observations (the highest resolution $\sim0.01$ pc) of a deeply embedded HC H II region (diameter $\sim0.015$ pc, electron density $\sim2\times10^{5}$ cm$^{-3}$) exhibiting a striking $\gtrsim20$ km s$^{-1}$ global redshift seen in optically thin H30$α$/H40$α$ recombination lines relative to its parental hot molecular core within a hub-filament system. The 1.3 mm continuum data reveal a distinct 0.1-pc arc and a perpendicular 0.04-pc tail. We propose that this morphology arises from a dynamic champagne flow: the slow expansion of HC H II region into a pre-existing filament forms the arc and associated low-velocity (few km s$^{-1}$) SiO shocks. Meanwhile, in the opposite direction ionized gas escapes along a steep density gradient traced by the tail and high-velocity (20 km s$^{-1}$) SiO emission. We reject the bow shock scenario in which ionized gas co-moves with a runaway high-mass star because shocked gas in the arc aligns with the hub velocity, contradicting the bow shock prediction. Non-LTE radiative transfer modeling further rules out infall of ionized gas as the velocity shift origin. We conclude that this exceptional HC H II region is undergoing a few-thousand-year transition phase of "hatching out of the egg": the ionized gas of HC H II region has just broken out of its parental hot core and now is flowing outward supersonically. This work highlights how anisotropic density distributions induce supersonically anisotropic ionized flows that govern HC H II region evolution. △ Less

Submitted 4 December, 2025; originally announced December 2025.

Comments: 18 pages, 14 figures, accepted for publication by ApJ

The ALMA-QUARKS survey: Evidence of a candidate high-mass prestellar core aside a bright-rimmed cloud IRAS 18290-0924

Authors: Dongting Yang, Hong-Li Liu, Shengli Qin, Tie Liu, Anandmayee Tej, Siju Zhang, Xunchuan Liu, Fengwei Xu, Guido Garay, Lei Zhu, Patricio Sanhueza, Xiaofeng Mai, Wenyu Jiao, Paul F. Goldsmith, Sami Dib, Pablo Garcıa, Di Li, Jinhua He, A. Y. Yang, Prasanta Gorai, Suinan Zhang, Yankun Zhang, Jianjun Zhou, Mika Juvela, James O. Chibueze , et al. (10 additional authors not shown)

Abstract: Although frequently reported in observations, the definitive confirmation of high-mass prestellar cores has remained elusive, presenting a persistent challenge in star formation studies. Using two-band observational data from the 3mm ATOMS and 1.3mm QUARKS surveys, we report a high-mass prestellar core candidate, C2, located on the side of the bright-rimmed cloud IRAS 18290-0924. The C2 core ident… ▽ More Although frequently reported in observations, the definitive confirmation of high-mass prestellar cores has remained elusive, presenting a persistent challenge in star formation studies. Using two-band observational data from the 3mm ATOMS and 1.3mm QUARKS surveys, we report a high-mass prestellar core candidate, C2, located on the side of the bright-rimmed cloud IRAS 18290-0924. The C2 core identified from the 3mm continuum data of the ATOMS survey ($\sim$2 arcsecond, $\rm\sim 10000~au$ at 5.3 kpc) has a mass ranging from 27-68 $M_{\odot}$ for temperatures 10-22K within a radius of $\sim$2800 au. The highest-resolution ($\sim$0.3 arcsecond, $\rm\sim 1500 au$) observations of this source presented to date from the QUARKS survey reveal no evidence of further fragmentation. Further analysis of a total $\sim$10 GHz band width of molecular line survey does not find star-formation activity (e.g., outflows, ionized gas) associated with the core, with a few molecular lines of cold gas detected only. Additionally, virial analysis indicates the C2 core is gravitationally bound ($α_{\rm vir} \sim0.1-0.3$) and thus could be undergoing collapse toward star formation. These results strongly establish a candidate for a high-mass prestellar core, contributing to the very limited number of such sources known to date. △ Less

Submitted 20 November, 2025; v1 submitted 18 November, 2025; originally announced November 2025.

Comments: 8 pages, 3 figures, accepted for publication in ApJ

The ALMA-QUARKS survey: Hot Molecular Cores are a long-standing phenomenon in the evolution of massive protostars

Authors: Dezhao Meng, Tie Liu, Jarken Esimbek, Sheng-Li Qin, Guido Garay, Paul F. Goldsmith, Jianjun Zhou, Xindi Tang, Wenyu Jiao, Yan-Kun Zhang, Fengwei Xu, Siju Zhang, Anandmayee Tej, Leonardo Bronfman, Aiyuan Yang, Sami Dib, Swagat R. Das, Jihye Hwang, Archana Soam, Yisheng Qiu, Dalei Li, Yuxin He, Gang Wu, Lokesh Dewangan, James O. Chibueze , et al. (12 additional authors not shown)

Abstract: We present an analysis of the QUARKS survey sample, focusing on protoclusters where Hot Molecular Cores (HMCs, traced by CH3CN(12--11)) and UC HII regions (traced by H30α/H40α) coexist. Using the high-resolution, high-sensitivity 1.3 mm data from the QUARKS survey, we identify 125 Hot Molecular Fragments (HMFs), which represent the substructures of HMCs at higher resolution. From line integrated i… ▽ More We present an analysis of the QUARKS survey sample, focusing on protoclusters where Hot Molecular Cores (HMCs, traced by CH3CN(12--11)) and UC HII regions (traced by H30α/H40α) coexist. Using the high-resolution, high-sensitivity 1.3 mm data from the QUARKS survey, we identify 125 Hot Molecular Fragments (HMFs), which represent the substructures of HMCs at higher resolution. From line integrated intensity maps of CH3CN(12--11) and H30α, we resolve the spatial distribution of HMFs and UC HII regions. By combining with observations of CO outflows and 1.3 mm continuum, we classify HMFs into four types: HMFs associated with jet-like outflow, with wide-angle outflow, with non-detectable outflow, and shell-like HMFs near UC HII regions. This diversity possibly indicates that the hot core could be polymorphic and long-standing phenomenon in the evolution of massive protostars. The separation between HMFs and H30α/H40αemission suggests that sequential high-mass star formation within young protoclusters is not likely related to feedback mechanisms. △ Less

Submitted 3 November, 2025; originally announced November 2025.

Comments: resubmitted to ApJ after taking into account referee's comments

A misaligned protostellar disk fed by gas streamers in a barred spiral-like massive dense core

Authors: Xiaofeng Mai, Tie Liu, Xunchuan Liu, Bo Zhang, Paul F. Goldsmith, Neal J. Evans II, Qizhou Zhang, Kee-Tae Kim, Dongting Yang, Mika Juvela, Fengwei Xu, Wenyu Jiao, Hongli Liu, Patricio Sanhueza, Guido Garay, Xi Chen, Shengli Qin, Jakobus M. Vorster, Anandmayee Tej, Zhiyuan Ren, Sami Dib, Shanghuo Li, Qiuyi Luo, Jihye Hwang, Prasanta Gorai , et al. (20 additional authors not shown)

Abstract: High-mass stars, born in massive dense cores (MDCs), profoundly impact the cosmic ecosystem through feedback processes and metal enrichment, yet little is known about how MDCs assemble and transfer mass across scales to form high-mass young stellar objects (HMYSOs). Using multi-scale (40-2500 au) observations of an MDC hosting an HMYSO, we identify a coherent dynamical structure analogous to barre… ▽ More High-mass stars, born in massive dense cores (MDCs), profoundly impact the cosmic ecosystem through feedback processes and metal enrichment, yet little is known about how MDCs assemble and transfer mass across scales to form high-mass young stellar objects (HMYSOs). Using multi-scale (40-2500 au) observations of an MDC hosting an HMYSO, we identify a coherent dynamical structure analogous to barred spiral galaxies: three 20,000 au spiral arms feed a 7,500 au central bar, which channels gas to a 2,000 au pseudodisk. Further accretion proceeds through the inner structures, including a Keplerian disk and an inner disk (100 au), which are thought to be driving a collimated bipolar outflow. This is the first time that these multi-scale structures (spiral arms, bar, streamers, envelope, disk, and outflow) have been simultaneously observed as a physically coherent structure within an MDC. Our discovery suggests that well-organized hierarchical structures play a crucial role during the gas accretion and angular momentum build-up of a massive disk. △ Less

Submitted 18 September, 2025; originally announced September 2025.

The ALMA-QUARKS Survey: III. Clump-to-core fragmentation and search for high-mass starless cores

Authors: Dongting Yang, Hong-Li Liu, Tie Liu, Xunchuan Liu, Fengwei Xu, Sheng-Li Qin, Anandmayee Tej, Guido Garay, Lei Zhu, Xiaofeng Mai, Wenyu Jiao, Siju Zhang, Sami Dib, Amelia M. Stutz, Aina Palau, Patricio Sanhueza, Annie Zavagno, A. Y. Yang, Xindi Tang, Mengyao Tang, Yichen Zhang, Pablo Garcia, Tianwei Zhang, Anindya Saha, Shanghuo Li , et al. (21 additional authors not shown)

Abstract: The Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures (QUARKS) survey observed 139 infrared-bright (IR-bright) massive protoclusters at 1.3 mm wavelength with ALMA. This study investigates clump-to-core fragmentation and searches for candidate high-mass starless cores within IR-bright clumps using combined ALMA 12-m (C-2) and Atacama Compact… ▽ More The Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures (QUARKS) survey observed 139 infrared-bright (IR-bright) massive protoclusters at 1.3 mm wavelength with ALMA. This study investigates clump-to-core fragmentation and searches for candidate high-mass starless cores within IR-bright clumps using combined ALMA 12-m (C-2) and Atacama Compact Array (ACA) 7-m data, providing $\sim$ 1 arcsec ($\sim\rm0.02~pc$ at 3.7 kpc) resolution and $\sim\rm0.6\,mJy\,beam^{-1}$ continuum sensitivity ($\sim 0.3~M_{\odot}$ at 30 K). We identified 1562 compact cores from 1.3 mm continuum emission using getsf. Observed linear core separations ($λ_{\rm obs}$) are significantly less than the thermal Jeans length ($λ_{\rm J}$), with the $λ_{\rm obs}/λ_{\rm J}$ ratios peaking at $\sim0.2$. This indicates that thermal Jeans fragmentation has taken place within the IR-bright protocluster clumps studied here. The observed low ratio of $λ_{\rm obs}/λ_{\rm J}\ll 1$ could be the result of evolving core separation or hierarchical fragmentation. Based on associated signatures of star formation (e.g., outflows and ionized gas), we classified cores into three categories: 127 starless, 971 warm, and 464 evolved cores. Two starless cores have mass exceeding 16$\,M_{\odot}$, and represent high-mass candidates. The scarcity of such candidates suggests that competitive accretion-type models could be more applicable than turbulent core accretion-type models in high-mass star formation within these IR-bright protocluster clumps. △ Less

Submitted 5 August, 2025; originally announced August 2025.

Comments: 30 pages, 16 figures, accepted by ApJS

The ALMA-ATOMS Survey: Exploring Protostellar Outflows in HC$_3$N

Authors: Ariful Hoque, Tapas Baug, Lokesh K. Dewangan, Mika Juvela, Anandmayee Tej, Paul F. Goldsmith, Pablo García, Amelia M. Stutz, Tie Liu, Chang Won Lee, Fengwei Xu, Patricio Sanhueza, N. K. Bhadari, K. Tatematsu, Xunchuan Liu, Hong-Li Liu, Yong Zhang, Xindi Tang, Guido Garay, Ke Wang, Siju Zhang, L. Viktor Tóth, Hafiz Nazeer, Jihye Hwang, Prasanta Gorai , et al. (3 additional authors not shown)

Abstract: We present the first systematic study of bipolar outflows using HC$_3$N as a tracer in a sample of 146 massive star-forming regions from ALMA-ATOMS survey. Protostellar outflows arise at the initial stage of star formation as a consequence of active accretion. In general, these outflows play a pivotal role in regulating the star formation processes by injecting energetic material in the parent mol… ▽ More We present the first systematic study of bipolar outflows using HC$_3$N as a tracer in a sample of 146 massive star-forming regions from ALMA-ATOMS survey. Protostellar outflows arise at the initial stage of star formation as a consequence of active accretion. In general, these outflows play a pivotal role in regulating the star formation processes by injecting energetic material in the parent molecular clouds. In such process, lower velocity components of outflows contain a significant portion of the energy. However, extraction of those component is difficult as the corresponding gas is often mixed with that of the ambient cloud. In our sample, we identified 44 bipolar outflows and one explosive outflow in HC$_3$N (J=11--10). The host clumps of these outflows are found to be at different evolutionary stages, suggesting that outflows in HC$_3$N are detectable in different stages of star formation. Also, the non-correlation of HC$_3$N outflows with clump evolutionary stages suggests that HC$_3$N is an unbiased tracer of outflows. Analyses revealed that HC$_3$N performs slightly better in detecting low-velocity components of outflows than traditionally employed tracers like SiO. The derived outflow parameters (i.e outflow mass, momentum, and energy) show moderate correlations with clump mass and luminosity. Our analysis of outflow opening angles and position-velocity diagrams across the outflow lobes show that, HC$_3$N is not only a good tracer of low-velocity outflows, but can also detect high-velocity collimated outflows. Overall, this study indicates that HC$_3$N can be used as a complementary outflow tracer along with the traditionally known outflow tracers, particularly in the detection of the low-velocity components of outflows. △ Less

Submitted 7 May, 2025; originally announced May 2025.

Comments: 26 pages, 12 figures, 4 tables, Accepted for publication in ApJ

Detection of an Explosive Outflow in G34.26+0.15

Authors: Namitha Issac, Xing Lu, Tie Liu, Luis A Zapata, Hong-Li Liu, Anandmayee Tej, Yan-Kun Zhang, Wenyu Jiao, Suinan Zhang

Abstract: This paper reports on the detection of a likely explosive outflow in the high-mass star-forming complex G34.26+0.15, adding to the small number (six) of explosive outflows detected so far. ALMA CO(2-1) and SiO(5-4) archival observations reveal multiple outflow streamers from G34.26+0.15, which correlate well with H2 jets identified from Spitzer-IRAC 4.5 um and [4.5]/[3.6] flux ratio maps. These ne… ▽ More This paper reports on the detection of a likely explosive outflow in the high-mass star-forming complex G34.26+0.15, adding to the small number (six) of explosive outflows detected so far. ALMA CO(2-1) and SiO(5-4) archival observations reveal multiple outflow streamers from G34.26+0.15, which correlate well with H2 jets identified from Spitzer-IRAC 4.5 um and [4.5]/[3.6] flux ratio maps. These nearly linear outflow streamers originate from a common center within an ultracompact HII region located in the complex. The velocity spread of the outflow streamers ranges from 0 to 120 km/s. The radial velocities of these streamers follow the Hubble-Lemaître velocity law, indicating an explosive nature. From the CO emission, the total outflow mass, momentum, and outflow energy are estimated to be ~264 M_sun, 4.3*10^3 M_sun km/s, and 10^48 erg, respectively. The event triggering the outflow may have occurred about 19,000 years ago and could also be responsible for powering the expanding UC HII region, given the similar dynamical ages and positional coincidence of the UC HII region with the origin of the outflow. The magnetic field lines in the region associated with G34.26+0.15 also appear to align with the direction of the outflow streamers and jets, possibly being dragged by the explosive outflow. △ Less

Submitted 22 April, 2025; originally announced April 2025.

Comments: 12 pages, 7 figures, 2 appendices, Accepted for publication in AJ

Exploring the non-thermal physics behind the pulsar wind nebula PSR J2030+4415 through radio observations

Authors: J. M. Paredes, P. Benaglia, V. Bosch-Ramon, A. Tej, A. Saha, J. Martí, P. Bordas

Abstract: PSR J2030+4415 is a gamma-ray pulsar with an X-ray pulsar wind nebula elongated along the north-south direction. The system shows a prominent X-ray filament oriented at an angle of 130° to the nebula axis. To improve our understanding of the non-thermal processes occurring in the pulsar wind nebula, we attempted to determine the possible existence of a radio counterpart, study its morphology, and… ▽ More PSR J2030+4415 is a gamma-ray pulsar with an X-ray pulsar wind nebula elongated along the north-south direction. The system shows a prominent X-ray filament oriented at an angle of 130° to the nebula axis. To improve our understanding of the non-thermal processes occurring in the pulsar wind nebula, we attempted to determine the possible existence of a radio counterpart, study its morphology, and obtain restrictive upper limits of the pulsar and filament emission at radio wavelengths. We performed observations of the pulsar PSR J2030+4415 and its surroundings with the upgraded Giant Metrewave Radio Telescope (uGMRT) at two frequency bands, and put the results in context with findings at other wavelengths. We obtained radio images at 736 and 1274 MHz that reveal a structure trailing the pulsar, with a morphology overlapping the X-ray nebula. This radio structure is the radio counterpart of the X-ray pulsar wind nebula. The derived spectral index along this structure shows spatial variation. There are no hints of the pulsar and the filament at any of the explored radio frequencies, but we obtained restrictive upper limits. A physical scenario that combines the radio and the X-ray observations, and consistent with IR data, of the nebula and the filament is presented. We propose that particle acceleration occurs in the nebula tail due to the presence of a re-collimation shock, and the highest energy particles gradually escape from it through energy-dependent diffusion. We also find a lower limit in the energy of the particles escaping along the X-ray filament of ~GeV. △ Less

Submitted 9 January, 2025; originally announced January 2025.

Comments: 8 pages, 6 figures. Accepted for publication in A&A

Research on the Interstellar Medium and Star Formation in the Galaxy: An Indian Perspective

Authors: Bhaswati Mookerjea, Maheswar G., Kinsuk Acharyya, Tapas Baug, Prasun Datta, Jessy Jose, D. K. Ojha, Jagadheep D. Pandian, Nirupam Roy, Manash Samal, Saurabh Sharma, Archana Soam, Sarita Vig, Ankan Das, Lokesh Dewangan, Somnath Dutta, C. Eswariah, Liton Majumdar, Kshitiz Kumar Mallick, Soumen Mondal, Joe P. Ninan, Neelam Panwar, Amit Pathak, Shantanu Rastogi, Dipen Sahu , et al. (2 additional authors not shown)

Abstract: Although the star formation process has been studied for decades, many important aspects of the physics involved remain unsolved. Recent advancement of instrumentation in the infrared, far-infrared and sub-millimetre wavelength regimes have contributed to a significantly improved understanding of processes in the interstellar medium (ISM) leading to star formation. The future of research on the IS… ▽ More Although the star formation process has been studied for decades, many important aspects of the physics involved remain unsolved. Recent advancement of instrumentation in the infrared, far-infrared and sub-millimetre wavelength regimes have contributed to a significantly improved understanding of processes in the interstellar medium (ISM) leading to star formation. The future of research on the ISM and star formation looks exciting with instruments like the JWST, ALMA, etc., already contributing to the topic by gathering high-resolution high-sensitivity data and with several larger ground- and space-bound facilities either being planned or constructed. India has a sizable number of astronomers engaged in research on topics related to the ISM and star formation. In this white paper invited by the Astronomical Society of India to prepare a vision document for Indian astronomy, we review the Indian contributions to the global understanding of the star formation process and suggest areas that require focused efforts both in creating observing facilities and in theoretical front in India, in order to improve the impact of our research in the coming decades. △ Less

Submitted 8 January, 2025; originally announced January 2025.

Comments: Accepted for publication in The Journal of Astrophysics and Astronomy Special Issue: Indian Astronomy in the Global Context: A compendium of white papers submitted towards the Astronomical Society of India Vision Document (2024)

X-ray study of WR 48-6: A possible colliding wind binary

Authors: Vishal Jadoliya, Jeewan C Pandey, Anandmayee Tej

Abstract: This paper presents an investigation of the X-ray emission associated with the Wolf-Rayet star, WR 48-6, using observations from the XMM Newton and Chandra X-ray telescopes covering two epochs separated by eleven months. The X-ray spectrum of WR 48-6 is well explained by a two-temperature plasma model, with cool and hot plasma temperatures of $0.8_{-0.2}^{\,+0.1}$ and $2.86_{-0.66}^{\,+1.01}$ keV.… ▽ More This paper presents an investigation of the X-ray emission associated with the Wolf-Rayet star, WR 48-6, using observations from the XMM Newton and Chandra X-ray telescopes covering two epochs separated by eleven months. The X-ray spectrum of WR 48-6 is well explained by a two-temperature plasma model, with cool and hot plasma temperatures of $0.8_{-0.2}^{\,+0.1}$ and $2.86_{-0.66}^{\,+1.01}$ keV. No significant X-ray variability is observed during these two epochs of observations. However, an increase in the local hydrogen column density accompanied by a decrease in the intrinsic X-ray flux between two epochs of observations is seen. Additionally, the intrinsic X-ray luminosity is found to be more than $10^{33} \rm\,erg\,s^{-1}$ during both epochs of observations. Based on the analysis presented, WR 48-6 is a promising colliding wind binary candidate with a possible companion of spectral type O5-O6. △ Less

Submitted 4 December, 2024; originally announced December 2024.

Comments: Accepted for publication in the Journal of Astrophysics and Astronomy

The ALMA-QUARKS Survey: Fibers' role in star formation unveiled in an intermediate-mass protocluster region of the Vela D cloud

Authors: Dongting Yang, HongLi Liu, Tie Liu, Anandmayee Tej, Xunchuan Liu, Jinhua He, Guido Garay, Amelia Stutz, Lei Zhu, Sheng-Li Qin, Fengwei Xu, Pak-Shing Li, Mika Juvela, Pablo Garcia, Paul F. Goldsmith, Siju Zhang, Xindi Tang, Patricio Sanhueza, Shanghuo Li, Chang Won Lee, Swagat Ranjan Das, Wenyu Jiao, Xiaofeng Mai, Prasanta Gorai, Yichen Zhang , et al. (10 additional authors not shown)

Abstract: In this paper, we present a detailed analysis of the IRS 17 filament within the intermediate-mass protocluster IRAS 08448-4343 (of $\sim\,10^3\,\rm L_{\odot}$), using ALMA data from the ATOMS 3-mm and QUARKS 1.3-mm surveys. The IRS 17 filament, which spans $\sim$54000 au ($0.26\,\rm pc$) in length and $\sim$4000 au ($0.02\,\rm pc$) in width, exhibits a complex, multi-component velocity field, and… ▽ More In this paper, we present a detailed analysis of the IRS 17 filament within the intermediate-mass protocluster IRAS 08448-4343 (of $\sim\,10^3\,\rm L_{\odot}$), using ALMA data from the ATOMS 3-mm and QUARKS 1.3-mm surveys. The IRS 17 filament, which spans $\sim$54000 au ($0.26\,\rm pc$) in length and $\sim$4000 au ($0.02\,\rm pc$) in width, exhibits a complex, multi-component velocity field, and harbours hierarchical substructures. These substructures include three bundles of seven velocity-coherent fibers, and 29 dense ($n\sim 10^8\,\rm cm^{-3}$) condensations. The fibers have a median length of $\sim 4500\,\rm au$ and a median width of $\sim 1400\,\rm au$. Among these fibers, four are identified as ``fertile", each hosting at least three dense condensations, which are regarded as the ``seeds" of star formation. While the detected cores are randomly spaced within the IRS\,17 filament based on the 3-mm dust continuum image, periodic spacing ($\sim1600\,\rm au$) of condensations is observed in the fertile fibers according to the 1.3-mm dust map, consistent with the predictions of linear isothermal cylinder fragmentation models. These findings underscore the crucial role of fibers in star formation and suggest a hierarchical fragmentation process that extends from the filament to the fibers, and ultimately, to the smallest-scale condensations. △ Less

Submitted 22 October, 2024; v1 submitted 20 October, 2024; originally announced October 2024.

Comments: 19 pages, 10 figures, 4 tables, accepted by ApJ

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions $-$ XVII. High-mass star-formation through a large-scale collapse in IRAS 15394$-$5358

Authors: Swagat R. Das, Manuel Merello, Leonardo Bronfman, Tie Liu, Guido Garay, Amelia Stutz, Diego Mardones, Jian-Wen Zhou, Patricio Sanhueza, Hong-Li Liu, Enrique Vázquez-Semadeni, Gilberto C. Gómez, Aina Palau, Anandmayee Tej, Feng-Wei Xu, Tapas Baug, Lokesh K. Dewangan, Jinhua He, Lei Zhu, Shanghuo Li1, Mika Juvela, Anindya Saha, Namitha Issac, Jihye Hwang, Hafiz Nazeer , et al. (1 additional authors not shown)

Abstract: Hub-filament systems are considered as natural sites for high-mass star formation. Kinematic analysis of the surroundings of hub-filaments is essential to better understand high-mass star formation within such systems. In this work, we present a detailed study of the massive Galactic protocluster IRAS 15394$-$5358, using continuum and molecular line data from the ALMA Three-millimeter Observations… ▽ More Hub-filament systems are considered as natural sites for high-mass star formation. Kinematic analysis of the surroundings of hub-filaments is essential to better understand high-mass star formation within such systems. In this work, we present a detailed study of the massive Galactic protocluster IRAS 15394$-$5358, using continuum and molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming Regions (ATOMS) survey. The 3~mm dust continuum map reveals the fragmentation of the massive ($\rm M=843~M_{\odot}$) clump into six cores. The core C-1A is the largest (radius = 0.04~pc), the most massive ($\rm M=157~M_{\odot}$), and lies within the dense central region, along with two smaller cores ($\rm M=7~and~3~M_{\odot}$). The fragmentation process is consistent with the thermal Jeans fragmentation mechanism and virial analysis shows that all the cores have small virial parameter values ($\rm α_{vir}<<2$), suggesting that the cores are gravitationally bound. The mass vs. radius relation indicates that three cores can potentially form at least a single massive star. The integrated intensity map of $\rm H^{13}CO^{+}$ shows that the massive clump is associated with a hub-filament system, where the central hub is linked with four filaments. A sharp velocity gradient is observed towards the hub, suggesting a global collapse where the filaments are actively feeding the hub. We discuss the role of global collapse and the possible driving mechanisms for the massive star formation activity in the protocluster. △ Less

Submitted 27 September, 2024; originally announced September 2024.

Comments: 23 pages, 19 figures, accepted for publication in MNRAS

JCMT 850 $\micron$ continuum observations of density structures in the G35 molecular complex

Authors: Xianjin Shen, Hong-Li Liu, Zhiyuan Ren, Anandmayee Tej, Di Li, Hauyu Baobab Liu, Gary A. Fuller, Jinjin Xie, Sihan Jiao, Aiyuan Yang, Patrick M. Koch, Fengwei Xu, Patricio Sanhueza, Pham N. Diep, Nicolas Peretto, Ram K. Yadav, Busaba H. Kramer, Koichiro Sugiyama, Mark Rawlings, Chang Won Lee, Ken'ichi Tatematsu, Daniel Harsono, David Eden, Woojin Kwon, Chao-Wei Tsai , et al. (10 additional authors not shown)

Abstract: Filaments are believed to play a key role in high-mass star formation. We present a systematic study of the filaments and their hosting clumps in the G35 molecular complex using JCMT SCUBA-2 850 $\micron$ continuum data. We identified five clouds in the complex and 91 filaments within them, some of which form 10 hub-filament systems (HFSs), each with at least 3 hub-composing filaments. We also com… ▽ More Filaments are believed to play a key role in high-mass star formation. We present a systematic study of the filaments and their hosting clumps in the G35 molecular complex using JCMT SCUBA-2 850 $\micron$ continuum data. We identified five clouds in the complex and 91 filaments within them, some of which form 10 hub-filament systems (HFSs), each with at least 3 hub-composing filaments. We also compiled a catalogue of 350 dense clumps, 183 of which are associated with the filaments. We investigated the physical properties of the filaments and clumps, such as mass, density, and size, and their relation to star formation. We find that the global mass-length trend of the filaments is consistent with a turbulent origin, while the hub-composing filaments of high line masses ($m_{\rm l}\,>$\,230\,$\mathrm{M_{\odot}~pc^{-1}}$) in HFSs deviate from this relation, possibly due to feedback from massive star formation. We also find that the most massive and densest clumps (R\,$>$\,0.2\,pc, M\,$>35\,\mathrm{M_{\odot}}$, $\mathrmΣ>\,0.05\,\mathrm{g~cm^{-2}}$) are located in the filaments and in the hubs of HFS with the latter bearing a higher probability of occurrence of high-mass star-forming signatures, highlighting the preferential sites of HFSs for high-mass star formation. We do not find significant variation in the clump mass surface density across different evolutionary environments of the clouds, which may reflect the balance between mass accretion and stellar feedback. △ Less

Submitted 9 September, 2024; originally announced September 2024.

Comments: 34 pages, 17 figures. Accepted for publication in ApJ

Insight into the occurrence of particle acceleration through the investigation of Wolf-Rayet stars using uGMRT observations

Authors: A. B. Blanco, M. De Becker, A. Saha, A. Tej, P. Benaglia

Abstract: Massive stars produce strong stellar winds that consist of continuous outflows of material at speeds of thousands of km/s. These winds convey large amounts of kinetic power, especially in the case of Wolf-Rayet (WR) stars. When these winds interact with nearby material, they will likely produce shocks. Among other processes, particle acceleration is expected to occur. This is particularly well est… ▽ More Massive stars produce strong stellar winds that consist of continuous outflows of material at speeds of thousands of km/s. These winds convey large amounts of kinetic power, especially in the case of Wolf-Rayet (WR) stars. When these winds interact with nearby material, they will likely produce shocks. Among other processes, particle acceleration is expected to occur. This is particularly well established in the case of massive binary systems, where the stellar winds collide, allowing these systems to be identified thanks to the detection of synchrotron radio emission, produced by a population of relativistic particles accelerated in the shocks. Our goal is to investigate the occurrence of particle acceleration among massive stars in their pre-supernova evolution phases. To this end, we observed a subset of five WR stars in the radio domain using the upgraded Giant Metrewave Radio Telescope (uGMRT), located in India. The observations were carried out in bands 4 (550-950 MHz) and 5 (1050-1450 MHz) for all the targets. We detected radio emission for only WR 110 in bands 4 and 5. Its thermal spectrum displays a consistent index of +0.74 down to uGMRT bands. The four other targets were not detected and we derived 3$σ$ upper limits. Our upper limits in Band 4 are the first provided for these targets below 1 GHz. None of the targets was identified as a synchrotron radio emitter in these radio bands. If some synchrotron emission is produced in these systems, the non-detection with uGMRT can be most likely attributed to strong free-free absorption (FFA). This is especially relevant for WR 98a, which is catalogued as a particle accelerator based on previous measurements at higher radio frequencies. We discuss how the prominence of FFA constitutes a severe obstacle to identifying particle accelerators in the radio domain. △ Less

Submitted 14 August, 2024; originally announced August 2024.

Direct observational evidence of multi-epoch massive star formation in G24.47+0.49

Authors: Anindya Saha, Anandmayee Tej, Hong-Li Liu, Tie Liu, Guido Garay, Paul F. Goldsmith, Chang Won Lee, Jinhua He, Mika Juvela, Leonardo Bronfman, Tapas Baug, Enrique Vazquez-Semadeni, Patricio Sanhueza, Shanghuo Li, James O. Chibueze, N. K. Bhadari, Lokesh K. Dewangan, Swagat Ranjan Das, Feng-Wei Xu, Namitha Issac, Jihye Hwang, L. Viktor Toth

Abstract: Using new continuum and molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming Regions (ATOMS) survey and archival VLA, 4.86 GHz data, we present direct observational evidence of hierarchical triggering relating three epochs of massive star formation in a ring-like H II region, G24.47+0.49. We find from radio flux analysis that it is excited by a massive star(s) of… ▽ More Using new continuum and molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming Regions (ATOMS) survey and archival VLA, 4.86 GHz data, we present direct observational evidence of hierarchical triggering relating three epochs of massive star formation in a ring-like H II region, G24.47+0.49. We find from radio flux analysis that it is excited by a massive star(s) of spectral type O8.5V-O8V from the first epoch of star formation. The swept-up ionized ring structure shows evidence of secondary collapse, and within this ring a burst of massive star formation is observed in different evolutionary phases, which constitutes the second epoch. ATOMS spectral line (e.g., HCO$^+$(1-0)) observations reveal an outer concentric molecular gas ring expanding at a velocity of $\sim$ 9 $\rm km\,s^{-1}$, constituting the direct and unambiguous detection of an expanding molecular ring. It harbors twelve dense molecular cores with surface mass density greater than 0.05 $\rm g\,cm^{-2}$, a threshold typical of massive star formation. Half of them are found to be subvirial, and thus in gravitational collapse, making them third epoch of potential massive star-forming sites. △ Less

Submitted 1 July, 2024; originally announced July 2024.

Comments: 18 pages, 7 figures, accepted for publication in The Astrophysical Journal Letters

Study of Wolf-Rayet stars using uGMRT

Authors: Anindya Saha, Anandmayee Tej, Santiago del Palacio, Michaël De Becker, Paula Benaglia, Ishwara Chandra CH, Prachi Prajapati

Abstract: In recent years, systems involving massive stars with large wind kinetic power have been considered as promising sites for investigating relativistic particle acceleration in low radio frequencies. With this aim, we observed two Wolf-Rayet systems, WR 114 and WR 142, using upgraded Giant Meterwave Radio Telescope observations in Band 4 (550-950 MHz) and Band 5 (1050-1450 MHz). None of the targets… ▽ More In recent years, systems involving massive stars with large wind kinetic power have been considered as promising sites for investigating relativistic particle acceleration in low radio frequencies. With this aim, we observed two Wolf-Rayet systems, WR 114 and WR 142, using upgraded Giant Meterwave Radio Telescope observations in Band 4 (550-950 MHz) and Band 5 (1050-1450 MHz). None of the targets was detected at these frequencies. Based on the non-detection, we report 3$σ$ upper limits to the radio flux densities at 735 and 1260 MHz (123 and 66 $μ$Jy for WR 114, and 111 and 96 $μ$Jy for WR 142, respectively). The plausible scenarios to interpret this non-detection are presented. △ Less

Submitted 24 June, 2024; originally announced June 2024.

Comments: 11 pages, 2 figures, Published in the Proceedings of the 3rd BINA Workshop on the Scientific Potential of the Indo-Belgian Cooperation, held at the Graphic Era Hill University, Bhimtal (India),

Journal ref: Bulletin de la Societe Royale des Sciences de Liege, 2024, Volume 93, No 2, 491-503

Investigating the Role of Pre-supernova Massive Stars in the Acceleration of Galactic Cosmic Rays

Authors: Michael De Becker, Santiago del Palacio, Paula Benaglia, Anandmayee Tej, Benito Marcote, Gustavo Esteban Romero, Valenti Bosch-Ramon, C. H. Ishwara-Chandra

Abstract: Galactic cosmic rays (GCRs) constitute a significant part of the energy budget of our Galaxy, and the study of their accelerators is of high importance in modern astrophysics. Their main sources are likely supernova remnants (SNRs). These objects are capable to convert a part of their mechanical energy into accelerated charged particles. However, even though the mechanical energy reservoir of SNRs… ▽ More Galactic cosmic rays (GCRs) constitute a significant part of the energy budget of our Galaxy, and the study of their accelerators is of high importance in modern astrophysics. Their main sources are likely supernova remnants (SNRs). These objects are capable to convert a part of their mechanical energy into accelerated charged particles. However, even though the mechanical energy reservoir of SNRs is promising, a conversion rate into particle energy of 10 to 20% is necessary to feed the population of GCRs. Such an efficiency is however not guaranteed. Complementary sources deserve thus to be investigated. This communication aims to address the question of the contribution to the acceleration of GCRs by pre-supernova massive stars in binary or higher multiplicity systems △ Less

Submitted 20 June, 2024; originally announced June 2024.

Comments: 8 pages, 1 figure, Published in the Proceedings of the 3rd BINA Workshop on the Scientific Potential of the Indo-Belgian Cooperation

Journal ref: Bulletin de la Société Royale des Sciences de Liège, 2024, Volume 93, No 2, 536-543

The ALMA-QUARKS Survey: II. the ACA 1.3 mm continuum source catalog and the assembly of dense gas in massive star-forming clumps

Authors: Fengwei Xu, Ke Wang, Tie Liu, Lei Zhu, Guido Garay, Xunchuan Liu, Paul Goldsmith, Qizhou Zhang, Patricio Sanhueza, Shengli Qin, Jinhua He, Mika Juvela, Anandmayee Tej, Hongli Liu, Shanghuo Li, Kaho Morii, Siju Zhang, Jianwen Zhou, Amelia Stutz, Neal J. Evans, Kim Kee-Tae, Shengyuan Liu, Diego Mardones, Guangxing Li, Leonardo Bronfman , et al. (8 additional authors not shown)

Abstract: Leveraging the high resolution, high sensitivity, and wide frequency coverage of the Atacama Large Millimeter/submillimeter Array (ALMA), the QUARKS survey, standing for "Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures", is observing 139 massive star-forming clumps at ALMA Band 6 ($λ\sim$ 1.3 mm). This paper introduces the Atacama Compact A… ▽ More Leveraging the high resolution, high sensitivity, and wide frequency coverage of the Atacama Large Millimeter/submillimeter Array (ALMA), the QUARKS survey, standing for "Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures", is observing 139 massive star-forming clumps at ALMA Band 6 ($λ\sim$ 1.3 mm). This paper introduces the Atacama Compact Array (ACA) 7-m data. Combining multi-wavelength data, we provide the first edition of QUARKS atlas, offering insights into the multiscale and multiphase interstellar medium in high-mass star formation. The ACA 1.3 mm catalog includes 207 continuum sources that are called ACA sources. Their gas kinetic temperatures are estimated using three formaldehyde (H$_2$CO) transitions with a non-LTE radiation transfer model, and the mass and density are derived from a dust emission model. The ACA sources are massive (16-84 percentile values of 6-160 $M_{\odot}$), gravity-dominated ($M\propto R^{1.1}$) fragments within massive clumps, with supersonic turbulence ($\mathcal{M}>1$) and embedded star-forming protoclusters. We find a linear correlation between the masses of the fragments and the massive clumps, with a ratio of 6% between the two. When considering the fragments as representative of dense gas, the ratio indicates a dense gas fraction (DGF) of 6%, although with a wide scatter ranging from 1% to 10%. If we consider the QUARKS massive clumps to be what is observed at various scales, then the size-independent DGF indicates a self-similar fragmentation or collapsing mode in protocluster formation. With the ACA data over four orders of magnitude of luminosity-to-mass ratio ($L/M$), we find that the DGF increases significantly with $L/M$, which indicates clump evolutionary stage. We observed a limited fragmentation at the subclump scale, which can be explained by dynamic global collapse process. △ Less

Submitted 4 April, 2024; v1 submitted 2 April, 2024; originally announced April 2024.

Comments: 24 pages, 7 figures. Accepted for publication in Research in Astronomy and Astrophysics. QUARKS atlas link: https://drive.google.com/file/d/1KTqXxCDduYepvLd9kIvZVSSytK48OmfL/view?usp=sharing

Search for protostellar jets with UWISH2 in the molecular cloud complexes Vulpecula and IRDC G53.2

Authors: Manish Chauhan, Manash Samal, Anandmayee Tej, Dirk Froebrich

Abstract: Jets and outflows are the early signposts of stellar birth. Using the UKIRT Wide Field Infrared Survey for H2 (UWISH2) at 2.12 micron, 127 outflows are identified in molecular cloud complexes Vulpecula OB1 and IRDC G53.2 covering 12 square degrees of the Galactic plane. Using multi-wavelength datasets, from 1.2 to 70 micron, 79 young stellar objects (YSOs) are proposed as potential driving sources… ▽ More Jets and outflows are the early signposts of stellar birth. Using the UKIRT Wide Field Infrared Survey for H2 (UWISH2) at 2.12 micron, 127 outflows are identified in molecular cloud complexes Vulpecula OB1 and IRDC G53.2 covering 12 square degrees of the Galactic plane. Using multi-wavelength datasets, from 1.2 to 70 micron, 79 young stellar objects (YSOs) are proposed as potential driving sources, where, $\sim$ 79% are likely Class 0/I protostars, 17% are Class II YSOs and the remaining 4% are Class III YSOs. The outflows are characterized in terms of their length, flux, luminosity and knot-spacing. The identified outflows have a median lobe length of 0.22 pc and 0.17 pc for outflows in Vulpecula OB1 and IRDC G53.2, respectively. Our analysis, from the knot spacing, reveals a typical ejection frequency of $\sim$ 1.2 kyr suggesting an intermediate type between the FU-Ori and EX-Ori type of eruptions in both cloud complexes. Furthermore, the physical parameters of the driving sources are obtained by performing radiative transfer modelling to the observed spectral energy distributions (SEDs), which suggest that the outflows are driven by intermediate mass stars. Various observed trends between the outflow properties and the corresponding driving sources, and various interesting outflows and star forming sites, including sites of triggered star formation and protocluster forming clump with clusters of jets, are discussed. The obtained results and the identified jet-bearing protostellar sample will pave the way to understand many aspects of outflows with future high-resolution observations. △ Less

Submitted 21 March, 2024; originally announced March 2024.

Cloud-cloud collision and cluster formation in the W5-NW complex

Authors: Namitha Issac, Anindya Saha, Saanika Choudhary, Aakash Chaudhary, Anandmayee Tej, Hong-Li Liu, Tie Liu, Maheswar Gopinathan

Abstract: We present a detailed structural and gas kinematic study of the star-forming complex W5-NW. A cloud-cloud collision scenario unravels with evidences of collision induced star and cluster formation. Various signatures of cloud-cloud collision such as "complementary distribution" and "bridging-features" are explored. At the colliding region, the two clouds have complementary morphologies, where W5-N… ▽ More We present a detailed structural and gas kinematic study of the star-forming complex W5-NW. A cloud-cloud collision scenario unravels with evidences of collision induced star and cluster formation. Various signatures of cloud-cloud collision such as "complementary distribution" and "bridging-features" are explored. At the colliding region, the two clouds have complementary morphologies, where W5-NWb has a filamentary key-like shape which fits into the U-shaped cavity in W5-NWa that behaves like a keyhole. The interaction region between the two clouds is characterised by bridging features with intermediate velocities connecting the two clouds. A skewed V-shaped bridging feature is also detected at the site of collision. A robust picture of the molecular gas distribution highlighting the bridges is seen in the position-position-velocity diagram obtained using the SCOUSEPY algorithm. Star cluster formation with an over-density of Class I and Class II young stellar objects is also seen towards this cloud complex, likely triggered by the cloud collision event. △ Less

Submitted 11 February, 2024; originally announced February 2024.

Comments: 16 pages, 9 figures, 2 appendices, Accepted for publication in AJ

Constraints on Triton atmospheric evolution from occultations: 1989-2022

Authors: B. Sicardy, A. Tej, A. R. Gomes-Junior, F. D. Romanov, T. Bertrand, N. M. Ashok, E. Lellouch, B. E. Morgado, M. Assafin, J. Desmars, J. I. B. Camargo, Y. Kilic, J. L. Ortiz, R. Vieira-Martins, F. Braga-Ribas, J. P. Ninan, B. C. Bhatt, S. Pramod Kumar, V. Swain, S. Sharma, A. Saha, D. K. Ojha, G. Pawar, S. Deshmukh, A. Deshpande , et al. (27 additional authors not shown)

Abstract: Context - Around the year 2000, Triton's south pole experienced an extreme summer solstice that occurs every about 650 years, when the subsolar latitude reached about 50°. Bracketing this epoch, a few occultations probed Triton's atmosphere in 1989, 1995, 1997, 2008 and 2017. A recent ground-based stellar occultation observed on 6 October 2022 provides a new measurement of Triton's atmospheric pre… ▽ More Context - Around the year 2000, Triton's south pole experienced an extreme summer solstice that occurs every about 650 years, when the subsolar latitude reached about 50°. Bracketing this epoch, a few occultations probed Triton's atmosphere in 1989, 1995, 1997, 2008 and 2017. A recent ground-based stellar occultation observed on 6 October 2022 provides a new measurement of Triton's atmospheric pressure which is presented here. Aims- The goal is to constrain the Volatile Transport Models (VTMs) of Triton's atmosphere that is basically in vapor pressure equilibrium with the nitrogen ice at its surface. Methods - Fits to the occultation light curves yield Triton's atmospheric pressure at the reference radius 1400 km, from which the surface pressure is induced. Results - The fits provide a pressure p_1400= 1.211 +/- 0.039 microbar at radius 1400 km (47 km altitude), from which a surface pressure of p_surf= 14.54 +/- 0.47 microbar is induced (1-sigma error bars). To within error bars, this is identical to the pressure derived from the previous occultation of 5 October 2017, p_1400 = 1.18 +/- 0.03 microbar and p_surf= 14.1 +/- 0.4 microbar, respectively. Based on recent models of Triton's volatile cycles, the overall evolution over the last 30 years of the surface pressure is consistent with N2 condensation taking place in the northern hemisphere. However, models typically predict a steady decrease in surface pressure for the period 2005-2060, which is not confirmed by this observation. Complex surface-atmosphere interactions, such as ice albedo runaway and formation of local N2 frosts in the equatorial regions of Triton could explain the relatively constant pressure between 2017 and 2022. △ Less

Submitted 4 February, 2024; originally announced February 2024.

Comments: 8 pages, 4 figures, accepted for publication in Astronomy and Astrophysics

The ALMA-QUARKS survey: Detection of two extremely dense substructures in a massive prestellar core

Authors: Xiaofeng Mai, Tie Liu, Xunchuan Liu, Lei Zhu, Guido Garay, Paul F. Goldsmith, Mika Juvela, Hongli Liu, Emma Mannfors, Emma Mannfors, Anandmayee Tej, Patricio Sanhueza, Shanghuo Li, Fengwei Xu, Enrique Vazquez Semadeni, Wenyu Jiao, Yaping Peng, T. Baug, Aiyuan Yang, Lokesh Dewangan, Leonardo Bronfman, Gilberto C. Gómez, Aina Palau, Chang Won Lee, Sheng-Li Qin , et al. (11 additional authors not shown)

Abstract: Only a handful of massive starless core candidates have been discovered so far, but none of them have been fully confirmed. Within the MM1 clump in the filamentary infrared dark cloud G34.43+0.24 that was covered by the ALMA-ATOMS survey at Band 3 ($\sim2\arcsec$, 6000\,au) and the ALMA-QUARKS survey at Band 6 ($\sim 0.3\arcsec$, 900\,au), two prestellar core candidates MM1-C and E1 with masses of… ▽ More Only a handful of massive starless core candidates have been discovered so far, but none of them have been fully confirmed. Within the MM1 clump in the filamentary infrared dark cloud G34.43+0.24 that was covered by the ALMA-ATOMS survey at Band 3 ($\sim2\arcsec$, 6000\,au) and the ALMA-QUARKS survey at Band 6 ($\sim 0.3\arcsec$, 900\,au), two prestellar core candidates MM1-C and E1 with masses of 71 and 20 \solarmass~and radii of 2100--4400\,au were discovered. The two cores show no obvious sign of star-formation activities. In particular, MM1-C is a very promising massive prestellar core candidate with a total gas mass of 71\,\solarmass. Within MM1-C, we detected two extremely dense substructures, C1 and C2, as characterized by their high densities of $\rm n_{H_2}\sim 10^{8-9} cm^{-3}$. Moreover, evidence of further fragmentation in C2 was also revealed. We have detected the primordial fragmentation in the earliest stage of massive star formation, and we speculate that MM1-C would be the birthplace of a massive multiple system. However, we cannot fully rule out the possibility that the massive prestellar core MM1-C will just form a cluster of low-mass stars if it undergoes further fragmentation. △ Less

Submitted 8 January, 2024; originally announced January 2024.

Comments: 12 pages, 6 figures

The Giant Molecular Cloud G148.24+00.41: Gas Properties, Kinematics, and Cluster Formation at the Nexus of Filamentary Flows

Authors: Vineet Rawat, M. R. Samal, D. L. Walker, D. K. Ojha, A. Tej, A. Zavagno, C. P. Zhang, Davide Elia, S. Dutta, J. Jose, C. Eswaraiah, E. Sharma

Abstract: Filamentary flows toward the centre of molecular clouds have been recognized as a crucial process in the formation and evolution of stellar clusters. In this paper, we present a comprehensive observational study that investigates the gas properties and kinematics of the Giant Molecular Cloud G148.24+00.41 using the observations of CO (1-0) isotopologues. We find that the cloud is massive (10$^5$ M… ▽ More Filamentary flows toward the centre of molecular clouds have been recognized as a crucial process in the formation and evolution of stellar clusters. In this paper, we present a comprehensive observational study that investigates the gas properties and kinematics of the Giant Molecular Cloud G148.24+00.41 using the observations of CO (1-0) isotopologues. We find that the cloud is massive (10$^5$ M$_\odot$) and is one of the most massive clouds of the outer Galaxy. We identified six likely velocity coherent filaments in the cloud having length, width, and mass in the range of 14$-$38 pc, 2.5$-$4.2 pc, and (1.3$-$6.9) $\times$ 10$^3$ M$_\odot$, respectively. We find that the filaments are converging towards the central area of the cloud, and the longitudinal accretion flows along the filaments are in the range of $\sim$ 26$-$264 M$_\odot$ Myr$^{-1}$. The cloud has fragmented into 7 clumps having mass in the range of $\sim$ 260$-$2100 M$_\odot$ and average size around $\sim$ 1.4 pc, out of which the most massive clump is located at the hub of the filamentary structures, near the geometric centre of the cloud. Three filaments are found to be directly connected to the massive clump and transferring matter at a rate of $\sim$ 675 M$_\odot$ Myr$^{-1}$. The clump hosts a near-infrared cluster. Our results show that large-scale filamentary accretion flows towards the central region of the collapsing cloud is an important mechanism for supplying the matter necessary to form the central high-mass clump and subsequent stellar cluster. △ Less

Submitted 11 January, 2024; v1 submitted 6 January, 2024; originally announced January 2024.

Comments: 21 pages, 20 figures

The ALMA-QUARKS survey: -- I. Survey description and data reduction

Authors: Xunchuan Liu, Tie Liu, Lei Zhu, Guido Garay, Hong-Li Liu, Paul Goldsmith, Neal Evans, Kee-Tae Kim, Sheng-Yuan Liu, Fengwei Xu, Xing Lu, Anandmayee Tej, Xiaofeng Mai, Leonardo Bronfman, Shanghuo Li, Diego Mardones, Amelia Stutz, Ken'ichi Tatematsu, Ke Wang, Qizhou Zhang, Sheng-Li Qin, Jianwen Zhou, Qiuyi Luo, Siju Zhang, Yu Cheng , et al. (9 additional authors not shown)

Abstract: This paper presents an overview of the QUARKS survey, which stands for `Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures'. The QUARKS survey is observing 139 massive clumps covered by 156 pointings at ALMA Band 6 ($λ\sim$ 1.3 mm). In conjunction with data obtained from the ALMA-ATOMS survey at Band 3 ($λ\sim$ 3 mm), QUARKS aims to carry out… ▽ More This paper presents an overview of the QUARKS survey, which stands for `Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures'. The QUARKS survey is observing 139 massive clumps covered by 156 pointings at ALMA Band 6 ($λ\sim$ 1.3 mm). In conjunction with data obtained from the ALMA-ATOMS survey at Band 3 ($λ\sim$ 3 mm), QUARKS aims to carry out an unbiased statistical investigation of massive star formation process within protoclusters down to a scale of 1000 au. This overview paper describes the observations and data reduction of the QUARKS survey, and gives a first look at an exemplar source, the mini-starburst Sgr B2(M). The wide-bandwidth (7.5 GHz) and high-angular-resolution (~0.3 arcsec) observations of the QUARKS survey allow to resolve much more compact cores than could be done by the ATOMS survey, and to detect previously unrevealed fainter filamentary structures. The spectral windows cover transitions of species including CO, SO, N$_2$D$^+$, SiO, H$_{30}α$, H$_2$CO, CH$_3$CN and many other complex organic molecules, tracing gas components with different temperatures and spatial extents. QUARKS aims to deepen our understanding of several scientific topics of massive star formation, such as the mass transport within protoclusters by (hub-)filamentary structures, the existence of massive starless cores, the physical and chemical properties of dense cores within protoclusters, and the feedback from already formed high-mass young protostars. △ Less

Submitted 14 November, 2023; originally announced November 2023.

Comments: 9 figures, 4 tables, accepted by RAA

A High-Mass Young Star-forming Core Escaping from Its Parental Filament

Authors: Zhiyuan Ren, Xi Chen, Tie Liu, Emma Mannfors, Leonardo Bronfman, Fengwei Xu, Siyi Feng, Hongli Liu, Fanyi Meng, Amelia. M. Stutz, Shanghuo Li, Chang Won Lee, Ke Wang, Jianwen Zhou, Di Li, Chen Wang, Chakali Eswaraiah, Anandmayee Tej, Long-Fei Chen, Hui Shi

Abstract: We studied the unique kinematic properties in massive filament G352.63-1.07 at $10^3$-AU spatial scale with the dense molecular tracers observed with the Atacama Large Millimeter/submillimeter Array (ALMA). We find the central massive core M1 (12 $M_\odot$) being separated from the surrounding filament with a velocity difference of $v- {v}_{sys}=-2$ km/s and a transverse separation within 3 arcsec… ▽ More We studied the unique kinematic properties in massive filament G352.63-1.07 at $10^3$-AU spatial scale with the dense molecular tracers observed with the Atacama Large Millimeter/submillimeter Array (ALMA). We find the central massive core M1 (12 $M_\odot$) being separated from the surrounding filament with a velocity difference of $v- {v}_{sys}=-2$ km/s and a transverse separation within 3 arcsec. Meanwhile, as shown in multiple dense-gas tracers, M1 has a spatial extension closely aligned with the main filament and is connected to the filament towards its both ends. M1 thus represents a very beginning state for a massive young star-forming core escaping from the parental filament, within a time scale of $\sim 4000$ years. Based on its kinetic energy ($3.5\times10^{44}$ erg), the core escape is unlikely solely due to the original filament motion or magnetic field, but requires more energetic events such as a rapid intense anisotropic collapse. The released energy also seems to noticeably increase the environmental turbulence. This may help the filament to become stabilized again. △ Less

Submitted 12 October, 2023; originally announced October 2023.

Comments: 15 pages, 6 figures, accepted for publication in the Astrophysical Journal

Search for particle acceleration in two massive Wolf-Rayet stars using uGMRT observations

Authors: Anindya Saha, Anandmayee Tej, Santiago del Palacio, Michaël De Becker, Paula Benaglia, Ishwara Chandra CH, Prachi Prajapati

Abstract: Large wind kinetic power of Wolf-Rayet (WR) stars make them ideal targets in low radio frequencies to search for non-thermal emission due to relativistic particle acceleration. In this paper, we present observations of two WR stars, WR 114 and WR 142, in Band 4 (550-950 MHz) and Band 5 (1050-1450 MHz) using the upgraded Giant Meterwave Radio Telescope (uGMRT). Neither star is detected in the obser… ▽ More Large wind kinetic power of Wolf-Rayet (WR) stars make them ideal targets in low radio frequencies to search for non-thermal emission due to relativistic particle acceleration. In this paper, we present observations of two WR stars, WR 114 and WR 142, in Band 4 (550-950 MHz) and Band 5 (1050-1450 MHz) using the upgraded Giant Meterwave Radio Telescope (uGMRT). Neither star is detected in the observed frequency bands, nor extended emission associated with them. The upper limit to the free-free radio emission from the stellar wind enables us to constrain the mass-loss rate of WR 114 to $\lesssim \rm 10^{-5}\,M_{ \odot}\,yr^{-1}$; this is a factor three smaller than previously estimated using spectroscopic modelling. If we further assume that the WR stars are binaries, the non-detection of synchrotron emission from the putative wind collision region implies that the stars are either in very wide binary systems away from periastron, or that the stars are in close binary systems with an orbital separation $<70$ AU for WR 114 and $<20$ AU for WR 142. The non-detection of low-frequency radio emission from these two systems thus provides evidence that narrows their nature, though it does not rule them out as bonafide particle-accelerating colliding-wind binaries. △ Less

Submitted 9 September, 2023; originally announced September 2023.

Comments: 8 pages, 3 figures, accepted for publication in MNRAS

Direct observational evidence of the multi-scale, dynamical mass accretion toward a high-mass star forming hub-filament system

Authors: Dongting Yang, Hong-Li Liu, Anandmayee Tej, Tie Liu, Patricio Sanhueza, Sheng-Li Qin, Xing Lu, Ke Wang, Sirong Pan, Feng-Wei Xu, Enrique Vazquez-Semadeni, Shanghuo Li, Gilberto C. Gomez, Aina Palau, Guido Garay, Paul F. Goldsmith, Mika Juvela, Anindya Saha, Leonardo Bronfman, Chang Won Lee, Kenichi Tatematsu, Lokesh Dewangan, Jianwen Zhou, Yong Zhang, Amelia Stutz , et al. (6 additional authors not shown)

Abstract: There is growing evidence that high-mass star formation and hub-filament systems (HFS) are intricately linked. The gas kinematics along the filaments and the forming high-mass star(s) in the central hub are in excellent agreement with the new generation of global hierarchical high-mass star formation models. In this paper, we present an observational investigation of a typical HFS cloud, G310.142+… ▽ More There is growing evidence that high-mass star formation and hub-filament systems (HFS) are intricately linked. The gas kinematics along the filaments and the forming high-mass star(s) in the central hub are in excellent agreement with the new generation of global hierarchical high-mass star formation models. In this paper, we present an observational investigation of a typical HFS cloud, G310.142+0.758 (G310 hereafter) which reveals unambiguous evidence of mass inflow from the cloud scale via the filaments onto the forming protostar(s) at the hub conforming with the model predictions. Continuum and molecular line data from the ATOMS and MALT90 surveys are used that cover different spatial scales. Three filaments (with total mass $5.7\pm1.1\times 10^3~M_{\odot}$) are identified converging toward the central hub region where several signposts of high-mass star formation have been observed. The hub region contains a massive clump ($1280\pm260~M_{\odot}$) harbouring a central massive core. Additionally, five outflow lobes are associated with the central massive core implying a forming cluster. The observed large-scale, smooth and coherent velocity gradients from the cloud down to the core scale, and the signatures of infall motion seen in the central massive clump and core, clearly unveil a nearly-continuous, multi-scale mass accretion/transfer process at a similar mass infall rate of $\sim 10^{-3}~M_{\odot}~yr^{-1}$ over all scales, feeding the central forming high-mass protostar(s) in the G310 HFS cloud. △ Less

Submitted 17 June, 2023; originally announced June 2023.

Comments: Accepted to publish in ApJ. 10 pages with 6 figures and 2 tables

Probing the Global Dust Properties and Cluster Formation Potential of the Giant Molecular Cloud G148.24+00.41

Authors: Vineet Rawat, M. R. Samal, D. L. Walker, A. Zavagno, A. Tej, G. Marton, D. K. Ojha, Davide Elia, W. P. Chen, J. Jose, C Eswaraiah

Abstract: Clouds more massive than about $10^5$ M$_\odot$ are potential sites of massive cluster formation. Studying the properties of such clouds in the early stages of their evolution offers an opportunity to test various cluster formation processes. We make use of CO, Herschel, and UKIDSS observations to study one such cloud, G148.24+00.41. Our results show the cloud to be of high mass ($\sim$… ▽ More Clouds more massive than about $10^5$ M$_\odot$ are potential sites of massive cluster formation. Studying the properties of such clouds in the early stages of their evolution offers an opportunity to test various cluster formation processes. We make use of CO, Herschel, and UKIDSS observations to study one such cloud, G148.24+00.41. Our results show the cloud to be of high mass ($\sim$ $1.1\times10^5$ M$_\odot$), low dust temperature ($\sim$ 14.5 K), nearly circular (projected radius $\sim$ 26 pc), and gravitationally bound with a dense gas fraction of $\sim 18$% and a density profile with a power-law index of $\sim -1.5$. Comparing its properties with those of nearby molecular clouds, we find that G148.24+00.41 is comparable to the Orion-A molecular cloud in terms of mass, size, and dense gas fraction. From our analyses, we find that the central area of the cloud is actively forming protostars and is moderately fractal with a Q-value of $\sim$ 0.66. We also find evidence of global mass-segregation in the cloud, with a degree of mass-segregation ($Λ_{MSR}) \approx3.2$. We discuss these results along with the structure and compactness of the cloud, the spatial and temporal distribution of embedded stellar population, and their correlation with the cold dust distribution, in the context of high-mass cluster formation. Comparing our results with models of star cluster formation, we conclude that the cloud has the potential to form a cluster in the mass range $\sim$ 2000--3000 M$_\odot$ through dynamical hierarchical collapse and assembly of both gas and stars. △ Less

Submitted 9 March, 2023; originally announced March 2023.

Comments: It is accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS). The unedited version of the manuscript has been published

Evidence of high-mass star formation through multi-scale mass accretion in hub-filament-system clouds

Authors: Hong-Li Liu, Anandmayee Tej, Tie Liu, Patricio Sanhueza, Shengli Qin, Jinhua He, Paul F. Goldsmith, Guido Garay, Sirong Pan, Kaho Morii, Shanghuo Li, Amelia Stutz, Keníchi Tatematsu, Feng-Wei Xu, Leonardo Bronfman, Anindya Saha, Namitha Issac, Tapas Baug, L. Viktor Toth, Lokesh Dewangan, Ke Wang, Jianwen Zhou, Chang Won Lee, Dongting Yang, Anxu Luo , et al. (8 additional authors not shown)

Abstract: We present a statistical study of a sample of 17 hub-filament-system (HFS) clouds of high-mass star formation using high-angular resolution ($\sim$1-2 arcsecond) ALMA 1.3mm and 3mm continuum data. The sample includes 8 infrared (IR)-dark and 9 IR-bright types, which correspond to an evolutionary sequence from the IR-dark to IR-bright stage. The central massive clumps and their associated most mass… ▽ More We present a statistical study of a sample of 17 hub-filament-system (HFS) clouds of high-mass star formation using high-angular resolution ($\sim$1-2 arcsecond) ALMA 1.3mm and 3mm continuum data. The sample includes 8 infrared (IR)-dark and 9 IR-bright types, which correspond to an evolutionary sequence from the IR-dark to IR-bright stage. The central massive clumps and their associated most massive cores are observed to follow a trend of increasing mass ($M$) and mass surface density ($Σ$) with evolution from IR-dark to IR-bright stage. In addition, a mass-segregated cluster of young stellar objects (YSOs) are revealed in both IR-dark and IR-bright HFSs with massive YSOs located in the hub and the population of low-mass YSOs distributed over larger areas. Moreover, outflow feedback in all HFSs are found to escape preferentially through the inter-filamentary diffuse cavities, suggesting that outflows would render a limited effect on the disruption of the HFSs and ongoing high-mass star formation therein. From the above observations, we suggest that high-mass star formation in the HFSs can be described by a multi-scale mass accretion/transfer scenario, from hub-composing filaments through clumps down to cores, that can naturally lead to a mass-segregated cluster of stars. △ Less

Submitted 8 January, 2023; originally announced January 2023.

Comments: Accepted for publication in MNRAS; 16 pages, 8 figures, and 3 tables

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -XIII. Ongoing triggered star formation within clump-fed scenario found in the massive ($\sim1500$ $\rm M_\odot$) clump

Authors: S. Zhang, K. Wang, T. Liu, A. Zavagno, M. Juvela, H. Liu, A. Tej, A. M. Stutz, S. Li, L. Bronfman, Q. Zhang, P. F. Goldsmith, C. W. Lee, E. Vázquez-Semadeni, K. Tatematsu, W. Jiao, F. Xu, C. Wang, J. -W. Zhou

Abstract: Whether ionization feedback triggers the formation of massive stars is highly debated. Using ALMA 3 mm observations with a spatial resolution of $\sim 0.05$ pc and a mass sensitivity of 1.1 $\rm M_\odot$ beam$^{-1}$ at 20 K, we investigate the star formation and gas flow structures within the ionizing feedback-driven structure, a clump-scale massive ($\gtrsim 1500$ $\rm M_\odot$) bright-rimmed clo… ▽ More Whether ionization feedback triggers the formation of massive stars is highly debated. Using ALMA 3 mm observations with a spatial resolution of $\sim 0.05$ pc and a mass sensitivity of 1.1 $\rm M_\odot$ beam$^{-1}$ at 20 K, we investigate the star formation and gas flow structures within the ionizing feedback-driven structure, a clump-scale massive ($\gtrsim 1500$ $\rm M_\odot$) bright-rimmed cloud (BRC) associated with IRAS 18290-0924. This BRC is bound only if external compression from ionized gas is considered. A small-scale ($\lesssim1$ pc) age sequence along the direction of ionizing radiation is revealed for the embedded cores and protostars, which suggests triggered star formation via radiation-driven implosion (RDI). Furthermore, filamentary gas structures converge towards the cores located in the BRC's center, indicating that these filaments are fueling mass towards cores. The local core-scale mass infall rate derived from H$^{13}$CO$^+$ $J=1-0$ blue profile is of the same order of magnitude as the filamentary mass inflow rate, approximately 1 $\rm M_\odot$ kyr$^{-1}$. A photodissociation region (PDR) covering the irradiated clump surface is detected in several molecules, such as CCH, HCO$^+$, and CS whereas the spatial distribution stratification of these molecules is indistinct. CCH spectra of the PDR possibly indicate a photoevaporation flow leaving the clump surface with a projected velocity of $\sim2$ km s$^{-1}$. Our new observations show that RDI accompanied by a clump-fed process is operating in this massive BRC. Whether this combined process works in other massive BRCs is worth exploring with dedicated surveys. △ Less

Submitted 5 January, 2023; originally announced January 2023.

Comments: 34 pages with 20 figures, Accepted by MNRAS on 2022 December 28

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- XV. Steady Accretion from Global Collapse to Core Feeding in Massive Hub-filament System SDC335

Authors: Feng-Wei Xu, Ke Wang, Tie Liu, Paul F. Goldsmith, Qizhou Zhang, Mika Juvela, Hong-Li Liu, Sheng-Li Qin, Guang-Xing Li, Anandmayee Tej, Guido Garay, Leonardo Bronfman, Shanghuo Li, Yue-Fang Wu, Gilberto C. Gómez, Enrique Vázquez-Semadeni, Ken'ichi Tatematsu, Zhiyuan Ren, Yong Zhang, L. Viktor Toth, Xunchuan Liu, Nannan Yue, Siju Zhang, Tapas Baug, Namitha Issac , et al. (15 additional authors not shown)

Abstract: We present ALMA Band-3/7 observations towards "the Heart" of a massive hub-filament system (HFS) SDC335, to investigate its fragmentation and accretion. At a resolution of $\sim0.03$ pc, 3 mm continuum emission resolves two massive dense cores MM1 and MM2, with $383(^{+234}_{-120})$ $M_\odot$ (10-24% mass of "the Heart") and $74(^{+47}_{-24})$ $M_\odot$, respectively. With a resolution down to 0.0… ▽ More We present ALMA Band-3/7 observations towards "the Heart" of a massive hub-filament system (HFS) SDC335, to investigate its fragmentation and accretion. At a resolution of $\sim0.03$ pc, 3 mm continuum emission resolves two massive dense cores MM1 and MM2, with $383(^{+234}_{-120})$ $M_\odot$ (10-24% mass of "the Heart") and $74(^{+47}_{-24})$ $M_\odot$, respectively. With a resolution down to 0.01 pc, 0.87 mm continuum emission shows MM1 further fragments into six condensations and multi-transition lines of H$_2$CS provide temperature estimation. The relation between separation and mass of condensations at a scale of 0.01 pc favors turbulent Jeans fragmentation where the turbulence seems to be scale-free rather than scale-dependent. We use the H$^{13}$CO$^+$ (1-0) emission line to resolve the complex gas motion inside "the Heart" in position-position-velocity space. We identify four major gas streams connected to large-scale filaments, inheriting the anti-clockwise spiral pattern. Along these streams, gas feeds the central massive core MM1. Assuming an inclination angle of $45(\pm15)^{\circ}$ and a H$^{13}$CO$^+$ abundance of $5(\pm3)\times10^{-11}$, the total mass infall rate is estimated to be $2.40(\pm0.78)\times10^{-3}$ $M_\odot$ yr$^{-1}$, numerically consistent with the accretion rates derived from the clump-scale spherical infall model and the core-scale outflows. The consistency suggests a continuous, near steady-state, and efficient accretion from global collapse, therefore ensuring core feeding. Our comprehensive study of SDC335 showcases the detailed gas kinematics in a prototypical massive infalling clump and calls for further systematic and statistical analyses in a large sample. △ Less

Submitted 4 January, 2023; originally announced January 2023.

Comments: 29 pages, 7 figures, Accepted for publication in MNRAS

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -XIV. Properties of resolved UC Hii regions

Authors: C. Zhang, Feng-Yao Zhu, Tie Liu, Z. -Y. Ren, H. -L. Liu, Ke Wang, J. -W. Wu, Y. Zhang, J. -W. Zhou, K. Tatematsu, Guido Garay, Anandmayee Tej, Shanghuo Li, W. F. Xu, Chang Won Lee, Leonardo Bronfman, Archana Soam, D. Li

Abstract: Hydrogen recombination lines (RRLs) are one of the major diagnostics of the physical properties of H{\sc ii} regions. We use RRL H40$α$, He40$α$ and 3 mm continuum emission to investigate the properties of a large sample of resolved UC H{\sc ii} regions identified in the ATOMS survey. In total, we identify 94 UC H{\sc ii} regions from H40$α$ emission. The basic parameters for these UC H{\sc ii} re… ▽ More Hydrogen recombination lines (RRLs) are one of the major diagnostics of the physical properties of H{\sc ii} regions. We use RRL H40$α$, He40$α$ and 3 mm continuum emission to investigate the properties of a large sample of resolved UC H{\sc ii} regions identified in the ATOMS survey. In total, we identify 94 UC H{\sc ii} regions from H40$α$ emission. The basic parameters for these UC H{\sc ii} regions such as electron density, emission measure, electron temperature, ionic abundance ratio (n$_{\rm He^+}$/n$_{\rm H^+}$), and line width are derived. The median electron density and the median n$_{\rm He^+}$/n$_{\rm H^+}$ ratio of these UC H{\sc ii} regions derived from RRLs are $\sim$9000 cm$^{-3}$ and 0.11, respectively. Within UC H{\sc ii} regions, the n$_{\rm He^+}$/n$_{\rm H^+}$ ratios derived from the intensity ratio of the He40$α$ and H40$α$ lines seems to be higher in the boundary region than in the center. The H40$α$ line width is mainly broadened by thermal motion and microturbulence. The electron temperature of these UC H{\sc ii} regions has a median value of $\sim$6700 K, and its dependence on galactocentric distance is weak. △ Less

Submitted 4 January, 2023; originally announced January 2023.

Imaging of HH80-81 jet in the NIR shock tracers H$_2$ and [Fe II]

Authors: Sreelekshmi Mohan, Sarita Vig, Watson P. Varricatt, Anandmayee Tej

Abstract: The HH80-81 system is one of the most powerful jets driven by a massive protostar. We present new near-infrared (NIR) line imaging observations of the HH80-81 jet in the H$_2$ (2.122 $μ$m) and [Fe II] (1.644 $μ$m) lines. These lines trace not only the jet close to the exciting source but also the knots located farther away. We have detected nine groups of knot-like structures in the jet including… ▽ More The HH80-81 system is one of the most powerful jets driven by a massive protostar. We present new near-infrared (NIR) line imaging observations of the HH80-81 jet in the H$_2$ (2.122 $μ$m) and [Fe II] (1.644 $μ$m) lines. These lines trace not only the jet close to the exciting source but also the knots located farther away. We have detected nine groups of knot-like structures in the jet including HH80 and HH81 spaced $0.2-0.9$ pc apart. The knots in the northern arm of the jet show only [Fe II] emission closer to the exciting source, a combination of [Fe II] and H$_2$ at intermediate distances, and solely H$_2$ emission farther outwards. Towards the southern arm, all the knots exhibit both H$_2$ and [Fe II] emission. The nature of the shocks is inferred by assimilating the NIR observations with radio and X-ray observations from literature. In the northern arm, we infer the presence of strong dissociative shocks, in the knots located close to the exciting source. The knots in the southern arm that include HH80 and HH81 are explicable as a combination of strong and weak shocks. The mass-loss rates of the knots determined from [Fe II] luminosities are in the range $\sim 3.0\times 10^{-7}-5.2\times 10^{-5}$ M$_{\odot}$ yr$^{-1}$, consistent with those from massive protostars. Towards the central region, close to the driving source of the jet, we have observed various arcs in H$_2$ emission which resemble bow shocks, and strings of H$_2$ knots which reveal traces of multiple outflows. △ Less

Submitted 15 November, 2022; originally announced November 2022.

Comments: 20 pages, 5 figures, 3 tables, Accepted for publication in The Astrophysical Journal

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- XII: Fragmentation and multi-scale gas kinematics in protoclusters G12.42+0.50 and G19.88-0.53

Authors: Anindya Saha, Anandmayee Tej, Hong-Li Liu, Tie Liu, Namitha Issac, Chang Won Lee, Guido Garay, Paul F. Goldsmith, Mika Juvela, Sheng-Li Qin, Amelia Stutz, Shanghuo Li, Ke Wang, Tapas Baug, Leonardo Bronfman, Feng-Wei Xu, Yong Zhang, Chakali Eswaraiah

Abstract: We present new continuum and molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey for the two protoclusters, G12.42+0.50 and G19.88-0.53. The 3 mm continuum maps reveal seven cores in each of the two globally contracting protoclusters. These cores satisfy the radius-mass relation and the surface mass density criteria for high-mass star form… ▽ More We present new continuum and molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey for the two protoclusters, G12.42+0.50 and G19.88-0.53. The 3 mm continuum maps reveal seven cores in each of the two globally contracting protoclusters. These cores satisfy the radius-mass relation and the surface mass density criteria for high-mass star formation. Similar to their natal clumps, the virial analysis of the cores suggests that they are undergoing gravitational collapse ($\rm α_{vir} << 2$). The clump to core scale fragmentation is investigated and the derived core masses and separations are found to be consistent with thermal Jeans fragmentation. We detect large-scale filamentary structures with velocity gradients and multiple outflows in both regions. Dendrogram analysis of the H$^{13}$CO$^{+}$ map identifies several branch and leaf structures with sizes $\sim$ 0.1 and 0.03 pc, respectively. The supersonic gas motion displayed by the branch structures is in agreement with the Larson power-law indicating that the gas kinematics at this spatial scale is driven by turbulence. The transition to transonic/subsonic gas motion is seen to occur at spatial scales of $\sim$0.1 pc indicating the dissipation of turbulence. In agreement with this, the leaf structures reveal gas motions that deviate from the slope of Larson's law. From the large-scale converging filaments to the collapsing cores, the gas dynamics in G12.42+0.50 and G19.88-0.53 show scale-dependent dominance of turbulence and gravity and the combination of these two driving mechanisms needs to be invoked to explain massive star formation in the protoclusters. △ Less

Submitted 21 August, 2022; originally announced August 2022.

Comments: 23 pages, 17 figures, accepted for publication in MNRAS

Investigating star-formation activity towards the southern HII region RCW 42

Authors: Vipin Kumar, S. Vig, V. S. Veena, S. Mohan, S. K. Ghosh, A. Tej, D. K. Ojha

Abstract: The star-forming activity in the HII region RCW 42 is investigated using multiple wavebands, from near-infrared to radio wavelengths. Located at a distance of 5.8 kpc, this southern region has a bolometric luminosity of 1.8 $\times$ 10$^6$ L$_{\odot}$. The ionized gas emission has been imaged at low radio frequencies of 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India and shows a… ▽ More The star-forming activity in the HII region RCW 42 is investigated using multiple wavebands, from near-infrared to radio wavelengths. Located at a distance of 5.8 kpc, this southern region has a bolometric luminosity of 1.8 $\times$ 10$^6$ L$_{\odot}$. The ionized gas emission has been imaged at low radio frequencies of 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India and shows a large expanse of the HII region, spanning $20\times 15$ pc$^2$. The average electron number density in the region is estimated to be $\sim70$ cm$^{-3}$, which suggests an average ionization fraction of the cloud to be $11\%$. An extended green object EGO G274.0649-01.1460 and several young stellar objects have been identified in the region using data from the 2MASS and Spitzer surveys. The dust emission from the associated molecular cloud is probed using Herschel Space Telescope, which reveals the presence of 5 clumps, C1-C5, in this region. Two millimetre emission cores of masses 380 and 390 M$_{\odot}$ towards the radio emission peak have been identified towards C1 from the ALMA map at 1.4 mm. The clumps are investigated for their evolutionary stages based on association with various star-formation tracers, and we find that all the clumps are in active/evolved stage. △ Less

Submitted 29 July, 2022; v1 submitted 28 July, 2022; originally announced July 2022.

Comments: 14 pages, 13 figures, 3 tables, Accepted by MNRAS

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- XI. From inflow to infall in hub-filament systems

Authors: Jian-Wen Zhou, Tie Liu, Neal J. Evans II, Guido Garay, Paul F. Goldsmith, Gilberto C. Gomez, Enrique Vazquez-Semadeni, Hong-Li Liu, Amelia M. Stutz, Ke Wang, Mika Juvela, Jinhua He, Di Li, Leonardo Bronfman, Xunchuan Liu, Feng-Wei Xu, Anandmayee Tej, L. K. Dewangan, Shanghuo Li, Siju Zhang, Chao Zhang, Zhiyuan Ren, Kenichi Tatematsu, Pak Shing Li, Chang Won Lee , et al. (15 additional authors not shown)

Abstract: We investigate the presence of hub-filament systems in a large sample of 146 active proto-clusters, using H$^{13}$CO$^{+}$ J=1-0 molecular line data obtained from the ATOMS survey. We find that filaments are ubiquitous in proto-clusters, and hub-filament systems are very common from dense core scales ($\sim$0.1 pc) to clump/cloud scales ($\sim$1-10 pc). The proportion of proto-clusters containing… ▽ More We investigate the presence of hub-filament systems in a large sample of 146 active proto-clusters, using H$^{13}$CO$^{+}$ J=1-0 molecular line data obtained from the ATOMS survey. We find that filaments are ubiquitous in proto-clusters, and hub-filament systems are very common from dense core scales ($\sim$0.1 pc) to clump/cloud scales ($\sim$1-10 pc). The proportion of proto-clusters containing hub-filament systems decreases with increasing dust temperature ($T_d$) and luminosity-to-mass ratios ($L/M$) of clumps, indicating that stellar feedback from H{\sc ii} regions gradually destroys the hub-filament systems as proto-clusters evolve. Clear velocity gradients are seen along the longest filaments with a mean velocity gradient of 8.71 km s$^{-1}$pc$^{-1}$ and a median velocity gradient of 5.54 km s$^{-1}$pc$^{-1}$. We find that velocity gradients are small for filament lengths larger than $\sim$1~pc, probably hinting at the existence of inertial inflows, although we cannot determine whether the latter are driven by large-scale turbulence or large-scale gravitational contraction. In contrast, velocity gradients below $\sim$1~pc dramatically increase as filament lengths decrease, indicating that the gravity of the hubs or cores starts to dominate gas infall at small scales. We suggest that self-similar hub-filament systems and filamentary accretion at all scales may play a key role in high-mass star formation. △ Less

Submitted 16 June, 2022; originally announced June 2022.

Comments: 16 pages

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions-IX. A pilot study towards IRDC G034.43+00.24 on multi-scale structures and gas kinematics

Authors: Hong-Li Liu, Anandmayee Tej, Tie Liu, Paul F. Goldsmith, Amelia Stutz, Mika Juvela, Sheng-Li Qin, Feng-Wei Xu, Leonardo Bronfman, Neal J. Evans, Anindya Saha, Namitha Issac, Ken'ichi Tatematsu, Ke Wang, Shanghuo Li, Siju Zhang, Tapas Baug, Lokesh Dewangan, Yue-Fang Wu, Yong Zhang, Chang Won Lee, Xun-Chuan Liu, Jianwen Zhou, Archana Soam

Abstract: We present a comprehensive study of the gas kinematics associated with density structures at different spatial scales in the filamentary infrared dark cloud, G034.43+00.24 (G34). This study makes use of the H13CO+ (1-0) molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey, which has spatial and velocity resolution of 0.04 pc and 0.2 km/s, r… ▽ More We present a comprehensive study of the gas kinematics associated with density structures at different spatial scales in the filamentary infrared dark cloud, G034.43+00.24 (G34). This study makes use of the H13CO+ (1-0) molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey, which has spatial and velocity resolution of 0.04 pc and 0.2 km/s, respectively. Several tens of dendrogram structures have been extracted in the position-position-velocity space of H13CO+, which include 21 small-scale leaves and 20 larger-scale branches. Overall, their gas motions are supersonic but they exhibit the interesting behavior where leaves tend to be less dynamically supersonic than the branches. For the larger-scale, branch structures, the observed velocity-size relation (i.e., velocity variation/dispersion versus size) are seen to follow the Larson scaling exponent while the smaller-scale, leaf structures show a systematic deviation and display a steeper slope. We argue that the origin of the observed kinematics of the branch structures is likely to be a combination of turbulence and gravity-driven ordered gas flows. In comparison, gravity-driven chaotic gas motion is likely at the level of small-scale leaf structures. The results presented in our previous paper and this current follow-up study suggest that the main driving mechanism for mass accretion/inflow observed in G34 varies at different spatial scales. We therefore conclude that a scale-dependent combined effect of turbulence and gravity is essential to explain the star-formation processes in G34. △ Less

Submitted 22 February, 2022; originally announced February 2022.

Comments: 11 pages, 6 figures, and 1 table. To appear in MNRAS

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- VIII. A search for hot cores by using C$_2$H$_5$CN, CH$_3$OCHO and CH$_3$OH lines

Authors: Sheng-Li Qin, Tie Liu, Xunchuan Liu, Paul F. Goldsmith, Di Li, Qizhou Zhang, Hong-Li Liu, Yuefang Wu, Leonardo Bronfman, Mika Juvela, Chang Won Lee, Guido Garay, Yong Zhang, Jinhua He, Shih-Ying Hsu, Zhi-Qiang Shen, Jeong-Eun Lee, Ke Wang, Ningyu Tang, Mengyao Tang, Chao Zhang, Yinghua Yue, Qiaowei Xue, Shang-Huo Li, Yaping Peng , et al. (7 additional authors not shown)

Abstract: Hot cores characterized by rich lines of complex organic molecules are considered as ideal sites for investigating the physical and chemical environments of massive star formation. We present a search for hot cores by using typical nitrogen- and oxygen-bearing complex organic molecules (C$_2$H$_5$CN, CH$_3$OCHO and CH$_3$OH), based on ALMA Three-millimeter Observations of Massive Star-forming regi… ▽ More Hot cores characterized by rich lines of complex organic molecules are considered as ideal sites for investigating the physical and chemical environments of massive star formation. We present a search for hot cores by using typical nitrogen- and oxygen-bearing complex organic molecules (C$_2$H$_5$CN, CH$_3$OCHO and CH$_3$OH), based on ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS). The angular resolutions and line sensitivities of the ALMA observations are better than 2 arcsec and 10 mJy/beam, respectively. A total of 60 hot cores are identified with 45 being newly detected, in which the complex organic molecules have high gas temperatures ($>$ 100 K) and small source sizes ($<$ 0.1 pc). So far this is the largest sample of hot cores observed with similar angular resolution and spectral coverage. The observations have also shown nitrogen and oxygen differentiation in both line emission and gas distribution in 29 hot cores. Column densities of CH$_3$OH and CH$_3$OCHO increase as rotation temperatures rise. The column density of CH$_3$OCHO correlates tightly with that of CH$_3$OH. The pathways for production of different species are discussed. Based on the spatial position difference between hot cores and UC~H{\sc ii} regions, we conclude that 24 hot cores are externally heated while the other hot cores are internally heated. The observations presented here will potentially help establish a hot core template for studying massive star formation and astrochemistry. △ Less

Submitted 25 January, 2022; v1 submitted 24 January, 2022; originally announced January 2022.

Comments: 52 pages; Accepted by MNRAS

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- VII. A catalogue of SiO clumps from ACA observations

Authors: Rong Liu, Tie Liu, Gang Chen, Hong-Li Liu, Ke Wang, Jin-Zeng Li, Xun-Chuan Liu, Chang Won Lee, Paul F. Goldsmith, Mika Juvela, Guido Garay, Leonardo Bronfman, Tapas Baug, Jinhua He, Si-Ju Zhang, Yong Zhang, Feng-Wei Xu, Archana Soam, Zhi-Qiang Shen, Shanghuo Li, Lokesh Dewangan, Chakali Eswaraiah, Yue-Fang Wu, Sheng-Li Qin, L. Viktor Tóth , et al. (6 additional authors not shown)

Abstract: To understand the nature of SiO emission, we conducted ACA observations of the SiO (2-1) lines toward 146 massive star-forming regions, as part of the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey. We detected SiO emission in 128 (87.7$\%$) sources and identified 171 SiO clumps, 105 of which are spatially separated from 3 mm continuum emission. A large amount of… ▽ More To understand the nature of SiO emission, we conducted ACA observations of the SiO (2-1) lines toward 146 massive star-forming regions, as part of the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey. We detected SiO emission in 128 (87.7$\%$) sources and identified 171 SiO clumps, 105 of which are spatially separated from 3 mm continuum emission. A large amount of the SiO line profiles (60$\%$) are non-Gaussian. The velocity dispersion of the SiO lines ranges from 0.3 to 5.43 km s$^{-1}$. In 63 sources the SiO clumps are associated with H$_\rm{II}$ regions characterized by H40$α$ emission. We find that 68$\%$ (116) of the SiO clumps are associated with strong outflows. The median velocity dispersion of the SiO line for outflow sources and non-outflow sources is 1.91 km s$^{-1}$ and 0.99 km s$^{-1}$, respectively. These results indicate that outflow activities could be connected to strongly shocked gas. The velocity dispersion and [SiO]/[H$^{13}$CO$^+$] intensity ratio do not show any correlation with the dust temperature and particle number density of clumps. We find a positive correlation between the SiO line luminosity and the bolometric luminosity, implying stronger shock activities are associated with more luminous proto-clusters. The SiO clumps in associations with H$_\rm{II}$ regions were found to show a steeper feature in $L_\rm{sio}$/$L_\rm{bol}$. The SiO line luminosity and the fraction of shocked gas have no apparent evidence of correlation with the evolutionary stages traced by luminosity to mass ratio ($L_\rm{bol}/M$). △ Less

Submitted 19 January, 2022; originally announced January 2022.

Comments: 18 pages, 10 figures

Pluto's atmosphere in plateau phase since 2015 from a stellar occultation at Devasthal

Authors: Bruno Sicardy, Nagarhalli M. Ashok, Anandmayee Tej, Ganesh Pawar, Shishir Deshmukh, Ameya Deshpande, Saurabh Sharma, Josselin Desmars, Marcelo Assafin, Jose Luis Ortiz, Gustavo Benedetti-Rossi, Felipe Braga-Ribas, Roberto Vieira-Martins, Pablo Santos-Sanz, Krishan Chand, Bhuwan C. Bhatt

Abstract: A stellar occultation by Pluto was observed on 6 June 2020 with the 1.3-m and 3.6-m telescopes located at Devasthal, Nainital, India, using imaging systems in the I and H bands, respectively. From this event, we derive a surface pressure for Pluto's atmosphere of $p_{\rm surf}= 12.23^{+0.65}_{-0.38} $~$μ$bar. This shows that Pluto's atmosphere is in a plateau phase since mid-2015, a result which i… ▽ More A stellar occultation by Pluto was observed on 6 June 2020 with the 1.3-m and 3.6-m telescopes located at Devasthal, Nainital, India, using imaging systems in the I and H bands, respectively. From this event, we derive a surface pressure for Pluto's atmosphere of $p_{\rm surf}= 12.23^{+0.65}_{-0.38} $~$μ$bar. This shows that Pluto's atmosphere is in a plateau phase since mid-2015, a result which is in excellent agreement with the Pluto volatile transport model of Meza et al. (2019}. This value does not support the pressure decrease reported by independent teams, based on occultations observed in 2018 and 2019, see Young et al. (2021} and Arimatu et al. (2020), respectively. △ Less

Submitted 14 December, 2021; originally announced December 2021.

Comments: 8 pages, 3 figures, revised and accepted version for ApJL

Galatic HII region IRAS 17149$-$3916 -- A multiwavelength study

Authors: Ajay Potdar, Swagat R Das, Namitha Issac, Anandmayee Tej, Sarita Vig, C. H. Ishwara Chandra

Abstract: This paper presents a multiwavelength investigation of the Galactic HII IRAS 17149$-$3916. Using the Giant Meterwave Radio Telescope, India, first low-frequency radio continuum observations at 610 and 1280 MHz for this region are presented. The ionized gas emission displays an interesting cometary morphology which is likely powered by the early type source, E4 (IRS-1). The origin of the cometary m… ▽ More This paper presents a multiwavelength investigation of the Galactic HII IRAS 17149$-$3916. Using the Giant Meterwave Radio Telescope, India, first low-frequency radio continuum observations at 610 and 1280 MHz for this region are presented. The ionized gas emission displays an interesting cometary morphology which is likely powered by the early type source, E4 (IRS-1). The origin of the cometary morphology is discussed under the framework of the widely accepted bow shock, champagne flow, and clumpy cloud mechanisms. The mid- and far-infrared data from Spitzer-GLIMPSE and Herschel-Hi-GAL reveal a complex network of pillars, clumps, bubble, filaments, and arcs suggesting the profound influence of massive stars on the surrounding medium. Triggered star formation at the tip of an observed pillar structure is reported. High-resolution ALMA continuum data show a string of cores detected within the identified clumps. The core masses are well explained by thermal Jeans fragmentation and support the hierarchical fragmentation scenario. Four `super-Jeans' cores are identified which, at the resolution of the present data set, are suitable candidates to form high-mass stars. △ Less

Submitted 27 November, 2021; originally announced November 2021.

Comments: 17 pages, 10 figures, accepted for publication in MNRAS

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- V. Hierarchical fragmentation and gas dynamics in IRDC G034.43+00.24

Authors: Hong-Li Liu, Anandmayee Tej, Tie Liu, Namitha Issac, Anindya Saha, Paul F. Goldsmith, Jun-Zhi Wang, Qizhou Zhang, Sheng-Li Qin, Ke Wang, Shanghuo Li, Archana Soam, Lokesh Dewangan, Chang Won Lee, Pak-Shing Li, Xun-Chuan Liu, Yong Zhang, Zhiyuan Ren, Mika Juvela, Leonardo Bronfman, Yue-Fang Wu, Ken'ichi Tatematsu, Xi Chen, Di Li, Amelia Stutz , et al. (14 additional authors not shown)

Abstract: We present new 3-mm continuum and molecular lines observations from the ATOMS survey towards the massive protostellar clump, MM1, located in the filamentary infrared dark cloud (IRDC), G034.43+00.24 (G34). The lines observed are the tracers of either dense gas (e.g. HCO+/H13CO+ J = 1-0) or outflows (e.g. CS J = 2-1). The most complete picture to date of seven cores in MM1 is revealed by dust conti… ▽ More We present new 3-mm continuum and molecular lines observations from the ATOMS survey towards the massive protostellar clump, MM1, located in the filamentary infrared dark cloud (IRDC), G034.43+00.24 (G34). The lines observed are the tracers of either dense gas (e.g. HCO+/H13CO+ J = 1-0) or outflows (e.g. CS J = 2-1). The most complete picture to date of seven cores in MM1 is revealed by dust continuum emission. These cores are found to be gravitationally bound, with virial parameter, $α_{vir}<2$. At least four outflows are identified in MM1 with a total outflowing mass of $\sim 45 M_\odot$, and a total energy of $\sim 1\times 10^{47}$ erg, typical of outflows from a B0-type star. Evidence of hierarchical fragmentation, where turbulence dominates over thermal pressure, is observed at both the cloud and the clump scales. This could be linked to the scale-dependent, dynamical mass inflow/accretion on clump and core scales. We therefore suggest that the G34 cloud could be undergoing a dynamical mass inflow/accretion process linked to the multiscale fragmentation, which leads to the sequential formation of fragments of the initial cloud, clumps, and ultimately dense cores, the sites of star formation. △ Less

Submitted 3 November, 2021; originally announced November 2021.

Comments: 14 pages with 6 figures, and in press

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- IV. Radio Recombination Lines and evolution of star formation efficiencies

Authors: C. Zhang, Neal J. Evans II, T. Liu, J. -W. Wu, Ke Wang, H. -L. Liu, F. -Y. Zhu, Z. -Y. Ren, L. K. Dewangan, Chang Won Lee, Shanghuo Li, L. Bronfman, A. Tej, D. Li

Abstract: We report detection of radio recombination line (RRL) H$_{40α}$ toward 75 sources, with data obtained from ACA observations in the ATOMS survey of 146 active Galactic star forming regions. We calculated ionized gas mass and star formation rate with H40U line emission. The mass of ionized gas is significantly smaller than molecular gas mass, indicating that ionized gas is negligible in the star for… ▽ More We report detection of radio recombination line (RRL) H$_{40α}$ toward 75 sources, with data obtained from ACA observations in the ATOMS survey of 146 active Galactic star forming regions. We calculated ionized gas mass and star formation rate with H40U line emission. The mass of ionized gas is significantly smaller than molecular gas mass, indicating that ionized gas is negligible in the star forming clumps of the ATOMS sample. The star formation rate (SFR$_{{\rm H}_{40α}}$) estimated with RRL H$_{40α}$ agrees well with that (SFR$_{\rm L_{bol}}$) calculated with the total bolometric luminosity (L$_{\rm bol}$) when SFR $\gtrsim 5 {\rm M_\odot My}r^{-1}$, suggesting that millimeter RRLs could well sample the upper part of the initial mass function (IMF) and thus be good tracers for SFR. We also study the relationships between L$_{\rm bol}$ and the molecular line luminosities (L0mol) of CS J=2-1 and HC$_3$N J=11-10 for all the 146 ATOMS sources. The Lbol-L0mol correlations of both the CS J=2-1 and HC3N J=11-10 lines appear approximately linear and these transitions have success in predicting L$_{\rm bol}$ similar to that of more commonly used transitions. The L$_{\rm bol}$-to-L$_{\rm mol}$ ratios or SFR-to-mass ratios (star formation efficiency; SFE) do not change with galactocentric distances (R$_{\rm GC}$). Sources with H$_{40α}$ emission (or H$_{\rm II}$ regions) show higher L$_{\rm bol}$-to-L$_{\rm mol}$ than those without H$_{40α}$ emission, which may be an evolutionary effect. △ Less

Submitted 29 September, 2021; originally announced October 2021.

An ALMA study of outflow parameters of protoclusters: outflow feedback to maintain the turbulence

Authors: T. Baug, Ke Wang, Tie Liu, Yue-Fang Wu, Di Li, Qizhou Zhang, Mengyao Tang, Paul F. Goldsmith, Hong-Li Liu, Anandmayee Tej, Leonardo Bronfman, L. Viktor Toth, Kee-Tae Kim, Shang-Huo Li, Chang Won Lee, Ken'ichi Tatematsu, Tomoya Hirota

Abstract: With the aim of understanding the role of outflows in star formation, we performed a statistical study of the physical parameters of outflows in eleven massive protoclusters associated with ultra-compact HII regions. A total of 106 outflow lobes are identified in these protoclusters using the ALMA CO (3-2), HCN (4-3) and HCO+ (4-3) line observations. Although the position angles of outflow lobes d… ▽ More With the aim of understanding the role of outflows in star formation, we performed a statistical study of the physical parameters of outflows in eleven massive protoclusters associated with ultra-compact HII regions. A total of 106 outflow lobes are identified in these protoclusters using the ALMA CO (3-2), HCN (4-3) and HCO+ (4-3) line observations. Although the position angles of outflow lobes do not differ in these three tracers, HCN and HCO+ tend to detect lower terminal velocity of the identified outflows compared to CO. The majority of the outflows in our targets are young with typical dynamical time-scales of 10^2-10^4 years, and are mostly composed of low-mass outflows along with at least one high-mass outflow in each target. An anti-correlation of outflow rate with dynamical time-scale indicates that the outflow rate possibly decreases with time. Also, a rising trend of dynamical time-scale with the mass of the associated core hints that the massive cores might have longer accretion histories than the low mass cores. Estimation of different energies in these protoclusters shows that outflows studied here cannot account for the generation of the observed turbulence, but can sustain the turbulence at the current epoch as the energy injection rate from the outflows is similar to the estimated dissipation rate. △ Less

Submitted 30 June, 2021; originally announced June 2021.

Comments: 14 pages (5 additional pages of Appendix), 8 figures (4 additional figures in Appendix), 3 tables; accepted for publication in MNRAS

ATOMS:ALMA Three-millimeter Observations of Massive Star-forming regions -- III :Catalogues of candidate hot molecular cores and Hyper/Ultra compact HII regions

Authors: Hong-Li Liu, Tie Liu, Neal J. Evans, Ke Wang, Guido Garay, Sheng-Li Qin, Shanghuo Li, Amelia Stutz, Paul F. Goldsmith, Sheng-Yuan Liu, Anandmayee Tej, Qizhou Zhang, Mika Juvela, Di Li, Jun-Zhi Wang, Leonardo Bronfman, Zhiyuan Ren, Yue-Fang Wu, Kee-Tae Kim, Chang-Won Lee, Kenichi Tatematsu, Maria. R. Cunningham, Xun-Chuan Liu, Jing-Wen Wu, Tomoya Hirota , et al. (29 additional authors not shown)

Abstract: We have identified 453 compact dense cores in 3 mm continuum emission maps in the ATOMS (ALMA Three-millimeter Observations of Massive Star-forming regions) survey, and compiled three catalogues of high-mass star forming cores. One catalogue, referred to as H/UC-HII catalogue, includes 89 cores that enshroud hyper/ultra compact (H/UC) HII regions as characterized by associated compact H40alpha emi… ▽ More We have identified 453 compact dense cores in 3 mm continuum emission maps in the ATOMS (ALMA Three-millimeter Observations of Massive Star-forming regions) survey, and compiled three catalogues of high-mass star forming cores. One catalogue, referred to as H/UC-HII catalogue, includes 89 cores that enshroud hyper/ultra compact (H/UC) HII regions as characterized by associated compact H40alpha emission. A second catalogue, referred to as pure s-cHMC, includes 32 candidate Hot Molecular Cores (HMCs) showing rich spectra (N>20lines) of complex organic molecules (COMs) but not associated with H/UC-HII regions. The third catalogue, referred to as pure w-cHMC, includes 58 candidate HMCs with relatively low levels of COM richness and not associated with H/UC-HII regions. These three catalogues of dense cores provide an important foundation for future studies of the early stages of high-mass star formation across the Milky Way. We also find that nearly half of H/UC-HII cores are candidate HMCs. From the number counts of COM-containing and H/UC-HII cores, we suggest that the duration of high-mass protostellar cores showing chemically rich features is at least comparable to the lifetime of H/UC-HII regions. For cores in the H/UC-HII catalogue, the width of the H40alpha line increases as the core size decreases, suggesting that the non-thermal dynamical and/or pressure line-broadening mechanisms dominate on the smaller scales of the H/UC-HII cores. △ Less

Submitted 7 May, 2021; originally announced May 2021.

Comments: 17 pages, five tables, and 11 figures. Accepted for publication at MNRAS

G133.50+9.01: A likely cloud-cloud collision complex triggering the formation of filaments, cores and a stellar cluster

Authors: Namitha Issac, Anandmayee Tej, Tie Liu, Yuefang Wu

Abstract: We present compelling observational evidence of G133.50+9.01 being a bona fide cloud-cloud collision candidate with signatures of induced filament, core, and cluster formation. The CO molecular line observations reveal that the G133.50+9.01 complex is made of two colliding molecular clouds with systemic velocities, -16.9 km s-1 and -14.1 km s-1. The intersection of the clouds is characterised by b… ▽ More We present compelling observational evidence of G133.50+9.01 being a bona fide cloud-cloud collision candidate with signatures of induced filament, core, and cluster formation. The CO molecular line observations reveal that the G133.50+9.01 complex is made of two colliding molecular clouds with systemic velocities, -16.9 km s-1 and -14.1 km s-1. The intersection of the clouds is characterised by broad bridging features characteristic of collision. The morphology of the shocked layer at the interaction front resembles an arc like structure with enhanced excitation temperature and H2 column density. A complex network of filaments is detected in the SCUBA 850 μm image with 14 embedded dense cores, all well correlated spatially with the shocked layer. A stellar cluster revealed through an over-density of identified Class I and II young stellar objects is found located along the arc in the intersection region corroborating with a likely collision induced origin. △ Less

Submitted 28 September, 2020; originally announced September 2020.

Comments: 11 pages, 10 figures, Accepted for publication in the Main Journal of MNRAS

Multiwavelength investigation of extended green object G19.88-0.53: Revealing a protocluster

Authors: Namitha Issac, Anandmayee Tej, Tie Liu, Watson Varricatt, Sarita Vig, Ishwara Chandra C. H., Mathias Schultheis, Govind Nandakumar

Abstract: A multiwavelength analysis of star formation associated with the extended green object, G19.88-0.53 is presented in this paper. With multiple detected radio and millimetre components, G19.88-0.53 unveils as harbouring a protocluster rather than a single massive young stellar object. We detect an ionized thermal jet using the upgraded Giant Meterwave Radio Telescope, India, which is found to be ass… ▽ More A multiwavelength analysis of star formation associated with the extended green object, G19.88-0.53 is presented in this paper. With multiple detected radio and millimetre components, G19.88-0.53 unveils as harbouring a protocluster rather than a single massive young stellar object. We detect an ionized thermal jet using the upgraded Giant Meterwave Radio Telescope, India, which is found to be associated with a massive, dense and hot ALMA 2.7 mm core driving a bipolar CO outflow. Near-infrared spectroscopy with UKIRT-UIST shows the presence of multiple shock-excited H2 lines concurrent with the nature of this region. Detailed investigation of the gas kinematics using ALMA data reveals G19.88-0.53 as an active protocluster with high-mass star forming components spanning a wide evolutionary spectrum from hot cores in accretion phase to cores driving multiple outflows to possible UCHII regions. △ Less

Submitted 29 July, 2020; originally announced July 2020.

Comments: 20 pages, 16 figures, Accepted for publication in the Main Journal of MNRAS

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- I. Survey description and a first look at G9.62+0.19

Authors: Tie Liu, Neal J. Evans, Kee-Tae Kim, Paul F. Goldsmith, Sheng-Yuan Liu, Qizhou Zhang, Kenichi Tatematsu, Ke Wang, Mika Juvela, Leonardo Bronfman, Maria. R. Cunningham, Guido Garay, Tomoya Hirota, Jeong-Eun Lee, Sung-Ju Kang, Di Li, Pak-Shing Li, Diego Mardones, Sheng-Li Qin, Isabelle Ristorcelli, Anandmayee Tej, L. Viktor Toth, Jing-Wen Wu, Yue-Fang Wu, Hee-weon Yi , et al. (20 additional authors not shown)

Abstract: The "ATOMS," standing for {\it ALMA Three-millimeter Observations of Massive Star-forming regions}, survey has observed 146 active star forming regions with ALMA Band 3, aiming to systematically investigate the spatial distribution of various dense gas tracers in a large sample of Galactic massive clumps, to study the roles of stellar feedback in star formation, and to characterize filamentary str… ▽ More The "ATOMS," standing for {\it ALMA Three-millimeter Observations of Massive Star-forming regions}, survey has observed 146 active star forming regions with ALMA Band 3, aiming to systematically investigate the spatial distribution of various dense gas tracers in a large sample of Galactic massive clumps, to study the roles of stellar feedback in star formation, and to characterize filamentary structures inside massive clumps. In this work, the observations, data analysis, and example science of the "ATOMS" survey are presented, using a case study for the G9.62+0.19 complex. Toward this source, some transitions, commonly assumed to trace dense gas, including CS $J = 2-1$, HCO$^+$ $J = 1-0$ and HCN $J = 1-0$, are found to show extended gas emission in low density regions within the clump; less than 25\% of their emission is from dense cores. SO, CH$_3$OH, H$^{13}$CN and HC$_3$N show similar morphologies in their spatial distributions and reveal well the dense cores. Widespread narrow SiO emission is present (over $\sim$1 pc), which may be caused by slow shocks from large--scale colliding flows or H{\sc ii} regions. Stellar feedback from an expanding H{\sc ii} region has greatly reshaped the natal clump, significantly changed the spatial distribution of gas, and may also account for the sequential high-mass star formation in the G9.62+0.19 complex. The ATOMS survey data can be jointly analyzed with other survey data, e.g., "MALT90", "Orion B", "EMPIRE", "ALMA\_IMF", and "ALMAGAL", to deepen our understandings of "dense gas" star formation scaling relations and massive proto-cluster formation. △ Less

Submitted 8 July, 2020; v1 submitted 2 June, 2020; originally announced June 2020.

Comments: published on MNRAS

Journal ref: MNRAS, 496, 2790 (2020)

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- II. Compact objects in ACA observations and star formation scaling relations

Authors: Tie Liu, Neal J. Evans, Kee-Tae Kim, Pail F. Goldsmith, Sheng-Yuan Liu, Qizhou Zhang, Kenichi Tatematsu, Ke Wang, Mika Juvela, Leonardo Bronfman, Maria. R. Cunningham, Guido Garay, Tomoya Hirota, Jeong-Eun Lee, Sung-Ju Kang, Di Li, Pak-Shing Li, Diego Mardones, Sheng-Li Qin, Isabelle Ristorcelli, Anandmayee Tej, L. Viktor Toth, Jing-Wen Wu, Yue-Fang Wu, Hee-weon Yi , et al. (19 additional authors not shown)

Abstract: We report studies of the relationships between the total bolometric luminosity ($L_{\rm bol}$ or $L_{\rm TIR}$) and the molecular line luminosities of $J=1-0$ transitions of H$^{13}$CN, H$^{13}$CO$^+$, HCN, and HCO$^+$ with data obtained from ACA observations in the "ATOMS" survey of 146 active Galactic star forming regions. The correlations between $L_{\rm bol}$ and molecular line luminosities… ▽ More We report studies of the relationships between the total bolometric luminosity ($L_{\rm bol}$ or $L_{\rm TIR}$) and the molecular line luminosities of $J=1-0$ transitions of H$^{13}$CN, H$^{13}$CO$^+$, HCN, and HCO$^+$ with data obtained from ACA observations in the "ATOMS" survey of 146 active Galactic star forming regions. The correlations between $L_{\rm bol}$ and molecular line luminosities $L'_{\rm mol}$ of the four transitions all appear to be approximately linear. Line emission of isotopologues shows as large scatters in $L_{\rm bol}$-$L'_{\rm mol}$ relations as their main line emission. The log($L_{\rm bol}$/$L'_{\rm mol}$) for different molecular line tracers have similar distributions. The $L_{\rm bol}$-to-$L'_{\rm mol}$ ratios do not change with galactocentric distances ($R_{\rm GC}$) and clump masses ($M_{\rm clump}$). The molecular line luminosity ratios (HCN-to-HCO$^+$, H$^{13}$CN-to-H$^{13}$CO$^+$, HCN-to-H$^{13}$CN and HCO$^+$-to-H$^{13}$CO$^+$) all appear constant against $L_{\rm bol}$, dust temperature ($T_{\rm d}$), $M_{\rm clump}$ and $R_{\rm GC}$. Our studies suggest that both the main lines and isotopologue lines are good tracers of the total masses of dense gas in Galactic molecular clumps. The large optical depths of main lines do not affect the interpretation of the slopes in star formation relations. We find that the mean star formation efficiency (SFE) of massive Galactic clumps in the "ATOMS" survey is reasonably consistent with other measures of the SFE for dense gas, even those using very different tracers or examining very different spatial scales. △ Less

Submitted 8 July, 2020; v1 submitted 25 May, 2020; originally announced May 2020.

Comments: Published on MNRAS. The full tables are included in Tables.pdf or Tables.tex files, which can be downloaded from source files

Journal ref: MNRAS, 496, 2821 (2020)

Distance, magnetic field and kinematics of a filamentary cloud LDN 1157

Authors: Ekta Sharma, G. Maheswar, A. Soam, Changwon Lee, Shinyoung Kim, Tuhin Ghosh, A. Tej, G. Kim, S. Neha, Piyali Saha

Abstract: LDN 1157, is one of the several clouds situated in the cloud complex, LDN 1147/1158, represents a coma-shaped morphology with a well-collimated bipolar outflow emanating from a Class 0 protostar, LDN 1157-mm. The main goals of this work are (a) to map the inter-cloud magnetic field (ICMF) geometry of the region surrounding LDN 1157 to investigate its relationship with the cloud morphology, with th… ▽ More LDN 1157, is one of the several clouds situated in the cloud complex, LDN 1147/1158, represents a coma-shaped morphology with a well-collimated bipolar outflow emanating from a Class 0 protostar, LDN 1157-mm. The main goals of this work are (a) to map the inter-cloud magnetic field (ICMF) geometry of the region surrounding LDN 1157 to investigate its relationship with the cloud morphology, with the outflow direction and with the core magnetic field (CMF) geometry inferred from the mm- and sub-mm polarization results from the literature, and (b) to investigate the kinematic structure of the cloud. We carried out R-band polarization observations of the stars projected on the cloud to map the pc-scale magnetic field geometry and made spectroscopic observations of the entire cloud in 12CO, C18O and N2H+ (J=1-0) lines to investigate its kinematic structure. We obtained a distance of 340$\pm$3 pc to the LDN 1147/1158, complex based on the Gaia DR2 parallaxes and proper motion values of the three YSOs associated with the complex. A single filament of $\sim1.2$ pc in length and $\sim0.09$ pc in width is found to run all along the coma-shaped cloud. Based on the relationships between the ICMF, CMF, filament orientations, outflow direction, and the presence of an hour-glass morphology of the magnetic field, it is likely that the magnetic field had played an important role in the star formation process in LDN 1157. Combining the proper motions of the YSOs and the radial velocity of LDN 1147/1158 and another complex LDN 1172/1174 which is situated $\sim2$\dgr~east of it, we found that both the complexes are moving collectively toward the Galactic plane. The filamentary morphology of the east-west segment of LDN 1157 may have formed as a result of mass lost by ablation due to the interaction of the moving cloud with the ambient interstellar medium. △ Less

Submitted 6 May, 2020; originally announced May 2020.

Comments: 20 pages, Accepted in Astronomy & Astrophysics, Abstract has been shortened due to word limit in arxiv

Journal ref: A&A 639, A133 (2020)