Showing 1–50 of 153 results for author: Tsai, S

libyt: an In Situ Interface Connecting Simulations with yt, Python, and Jupyter Workflows

Authors: Shin-Rong Tsai, Hsi-Yu Schive, Matthew J. Turk

Abstract: In the exascale computing era, handling and analyzing massive datasets have become extremely challenging. In situ analysis, which processes data during simulation runtime and bypasses costly intermediate I/O steps, offers a promising solution. We present libyt (https://github.com/yt-project/libyt), an open-source C library that enables astrophysical simulations to analyze and visualize data in par… ▽ More In the exascale computing era, handling and analyzing massive datasets have become extremely challenging. In situ analysis, which processes data during simulation runtime and bypasses costly intermediate I/O steps, offers a promising solution. We present libyt (https://github.com/yt-project/libyt), an open-source C library that enables astrophysical simulations to analyze and visualize data in parallel computation with yt or other Python packages. libyt can invoke Python routines automatically or provide interactive entry points via a Python prompt or a Jupyter Notebook. It requires minimal intervention in researchers' workflow, allowing users to reuse job submission scripts and Python routines. We describe libyt's architecture for parallel computing in high-performance computing environments, including its bidirectional connection between simulation codes and Python, and its integration into the Jupyter ecosystem. We detail its methods for reading AMR simulations and handling in-memory data with minimal overhead, and procedures for yielding data when requested by Python. We describe how libyt maps simulation data to yt frontends, allowing post-processing scripts to be converted into in situ analysis with just two lines of change. We document libyt's API and demonstrate its integration into two astrophysical simulation codes, GAMER and Enzo, using examples including core-collapse supernovae, isolated dwarf galaxies, fuzzy dark matter, the Sod shock tube test, Kelvin-Helmholtz instability, and the AGORA galaxy simulation. Finally, we discuss libyt's performance, limitations related to data redistribution, extensibility, architecture, and comparisons with traditional post-processing approaches. △ Less

Submitted 11 December, 2025; originally announced December 2025.

Comments: Submitted to the Astrophysical Journal Supplement Series (ApJS). 34 pages with 13 figures and 4 tables

JWST-TST DREAMS: The Nightside Emission and Chemistry of WASP-17b

Authors: Jacob Lustig-Yaeger, Kristin S. Sotzen, Kevin B. Stevenson, Shang-Min Tsai, Ryan C. Challener, Jayesh Goyal, Nikole K. Lewis, Dana R. Louie, L. C. Mayorga, Daniel Valentine, Hannah R. Wakeford, Lili Alderson, Natalie H. Allen, Thomas J. Fauchez, Ana Glidden, Amélie Gressier, Sarah M. Hörst, Jingcheng Huang, Zifan Lin, Avi M. Mandell, Elijah Mullens, Sarah Peacock, Edward W. Schwieterman, Jeff A. Valenti, C. Matt Mountain , et al. (2 additional authors not shown)

Abstract: Theoretical studies have suggested using planetary infrared excess (PIE) to detect and characterize the thermal emission of transiting and non-transiting exoplanets, however the PIE technique requires empirical validation. Here we apply the PIE technique to a combination of JWST NIRSpec G395H transit and eclipse measurements of WASP-17b, a hot Jupiter orbiting an F-type star, obtained consecutivel… ▽ More Theoretical studies have suggested using planetary infrared excess (PIE) to detect and characterize the thermal emission of transiting and non-transiting exoplanets, however the PIE technique requires empirical validation. Here we apply the PIE technique to a combination of JWST NIRSpec G395H transit and eclipse measurements of WASP-17b, a hot Jupiter orbiting an F-type star, obtained consecutively (0.5 phase or 1.8 days apart) as part of the JWST-TST program to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS). Using the in-eclipse measured stellar spectrum to circumvent the need for ultra-precise stellar models, we extract the first JWST nightside emission spectrum of WASP-17b using only transit and eclipse data thereby performing a controlled test of the PIE technique. From the WASP-17b nightside spectrum, we measure a nightside equilibrium temperature of $1005 \pm 256$ K and find tentative evidence for nightside SO2 absorption ($\ln B = 1.45$, $2.3σ$). In context with the dayside, the temperature of the nightside is consistent with (1) previous eclipse mapping findings that suggest relatively inefficient day-night heat transport, and (2) a non-zero bond albedo of $0.42^{+0.06}_{-0.10}$. SO2 on the nightside, if confirmed, would represent the first direct evidence for transport-induced chemistry, matching previous model predictions, and opening a new door into the 3D nature of giant exoplanets. Our results suggest that PIE is feasible with JWST/NIRSpec for two epochs separated in time by significantly less than the rotation period of the host star. △ Less

Submitted 7 October, 2025; originally announced October 2025.

Comments: 21 pages, 9 figures, 2 tables, revised in response to ApJL reviewer comments

Dark-Matter-Deficient Galaxies from Collisions: A New Probe of Bursty Feedback and Dark Matter Physics

Authors: Yi-Ying Wang, Daneng Yang, Keyu Lu, Yue-Lin Sming Tsai, Yi-Zhong Fan

Abstract: High-velocity collisions between gas-rich ultra-diffuse galaxies present a promising formation channel for dark-matter-deficient galaxies (DMDGs). Using hydrodynamical simulations, we show that the progenitors' baryonic binding energy, $|E_{\rm bind}|$, critically controls the outcome. Repeated potential fluctuations, e.g., from bursty feedback, inject energy and reduce $|E_{\rm bind}|$ by… ▽ More High-velocity collisions between gas-rich ultra-diffuse galaxies present a promising formation channel for dark-matter-deficient galaxies (DMDGs). Using hydrodynamical simulations, we show that the progenitors' baryonic binding energy, $|E_{\rm bind}|$, critically controls the outcome. Repeated potential fluctuations, e.g., from bursty feedback, inject energy and reduce $|E_{\rm bind}|$ by $\approx 15\%$, yielding fewer but substantially more massive DMDGs. By contrast, elastic self-interacting dark matter (SIDM) produces comparable cores without lowering $|E_{\rm bind}|$, resulting in negligible effect. This differs from the other DMDG formation scenario, where SIDM-induced cores enhance dark matter tidal stripping while keeping baryons compact and resilient to tidal effects. The contrasting roles of SIDM help distinguish feedback-formed halo cores from those created by SIDM. Among 15 paired simulation runs, 13 show higher DMDG masses in the weakened-binding case, and about two thirds exhibit $>100\%$ mass enhancements. The simulations also predict systematically lower gas fractions due to sustained post-collision star formation, yielding a clean observational signature. Upcoming wide-field imaging (CSST, LSST), HI surveys (FAST), and kinematic follow-up will be crucial to test this scenario. △ Less

Submitted 27 November, 2025; v1 submitted 29 September, 2025; originally announced September 2025.

Comments: 14 pages, 9 figures, discussion updated

Limb Asymmetries on WASP-39b: A Multi-GCM Comparison of Chemistry, Clouds, and Hazes

Authors: Maria E. Steinrueck, Arjun B. Savel, Duncan A. Christie, Ludmila Carone, Shang-Min Tsai, Can Akın, Thomas D. Kennedy, Sven Kiefer, David A. Lewis, Emily Rauscher, Dominic Samra, Maria Zamyatina, Kenneth Arnold, Robin Baeyens, Leonardos Gkouvelis, David Haegele, Christiane Helling, Nathan J. Mayne, Diana Powell, Michael T. Roman, Hayley Beltz, Néstor Espinoza, Kevin Heng, Nicolas Iro, Eliza M. -R. Kempton , et al. (5 additional authors not shown)

Abstract: With JWST, observing separate spectra of the morning and evening limbs of hot Jupiters has finally become a reality. The first such observation was reported for WASP-39b, where the evening terminator was observed to have a larger transit radius by about 400 ppm and a stronger 4.3 $μ$m CO$_2$ feature than the morning terminator. Multiple factors, including temperature differences, photo/thermochemi… ▽ More With JWST, observing separate spectra of the morning and evening limbs of hot Jupiters has finally become a reality. The first such observation was reported for WASP-39b, where the evening terminator was observed to have a larger transit radius by about 400 ppm and a stronger 4.3 $μ$m CO$_2$ feature than the morning terminator. Multiple factors, including temperature differences, photo/thermochemistry, clouds and hazes, could cause such limb asymmetries. To interpret these new limb asymmetry observations, a detailed understanding of how the relevant processes affect morning and evening spectra grounded in forward models is needed. Focusing on WASP-39b, we compare simulations from five different general circulation models (GCMs), including one simulating disequilibrium thermochemistry and one with cloud radiative feedback, to the recent WASP-39b limb asymmetry observations. We also post-process the temperature structures of all simulations with a 2D photochemical model and one simulation with a cloud microphysics model. Although the temperatures predicted by the different models vary considerably, the models are remarkably consistent in their predicted morning--evening temperature differences. Several equilibrium-chemistry simulations predict strong methane features in the morning spectrum, not seen in the observations. When including disequilibrium processes, horizontal transport homogenizes methane, and these methane features disappear. However, even after including photochemistry and clouds, our models still cannot reproduce the observed ${\sim}2000$ ppm asymmetry in the CO$_2$ feature. A combination of factors, such as varying metallicity and unexplored parameters in cloud models, may explain the discrepancy, emphasizing the need for future models integrating cloud microphysics and feedback across a broader parameter space. △ Less

Submitted 25 September, 2025; originally announced September 2025.

Comments: submitted to AAS Journals. Supplementary Data available on Zenodo

K2-18b Does Not Meet The Standards of Evidence For Life

Authors: Kevin B. Stevenson, Jacob Lustig-Yaeger, E. M. May, Ravi K. Kopparapu, Thomas J. Fauchez, Jacob Haqq-Misra, Mary Anne Limbach, Edward W. Schwieterman, Kristin S. Sotzen, Shang-Min Tsai

Abstract: K2-18b, a temperate sub-Neptune, has garnered significant attention due to claims of possible biosignatures in its atmosphere. Low-confidence detections of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) have sparked considerable debate, primarily around arguments that their absorption features are not uniquely identifiable. Here, we consider all five questions from the astrobiology standa… ▽ More K2-18b, a temperate sub-Neptune, has garnered significant attention due to claims of possible biosignatures in its atmosphere. Low-confidence detections of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) have sparked considerable debate, primarily around arguments that their absorption features are not uniquely identifiable. Here, we consider all five questions from the astrobiology standards of evidence framework, starting with: Have we detected an authentic signal? To answer this, we analyzed publicly-available JWST observations of K2-18b using independent data reduction and spectral retrieval methodologies. Our comprehensive set of reductions demonstrates that the MIRI transit spectrum is highly susceptible to unresolved instrumental systematics. Applying different wavelength binning schemes yields a potpourri of planet spectra that then lead to a wide assortment of atmospheric interpretations. Consequently, we offer recommendations to help minimize this previously-underappreciated instrument systematic in future MIRI reductions of any exoplanet. While the MIRI binning scheme adopted by Madhusudhan et al. (2025) favors the presence of DMS/DMDS in K2-18b, we find that 87.5% of retrievals using our preferred MIRI binning scheme do not. When considering the full, 0.7 - 12 micron transit spectrum, we confirm the detection of CH4 and favor CO2, and find the presence of DMS and C2H4 to be interchangeable. Moreover, we find that the tentative presence of large features in the MIRI transit spectrum is in tension with the more robust, yet smaller, features observed in the near IR. We conclude that red noise -- rather than an astrophysical signal -- plagues the mid-IR data and there is, as yet, no statistically significant evidence for biosignatures in the atmosphere of K2-18b. △ Less

Submitted 3 September, 2025; v1 submitted 7 August, 2025; originally announced August 2025.

Comments: Accepted for publication in AJ

Constraints on axionlike particles from 16.5 years of Fermi-LAT data and prospects for VLAST

Authors: Zhi-Qi Guo, Yue-Lin Sming Tsai, Lei Wu, Zi-Qing Xia

Abstract: Axionlike particles (ALPs), hypothetical particles beyond the Standard Model, are considered as promising dark matter candidates. ALPs can convert into photons and vice versa in a magnetic field via the Primakoff effect, potentially generating detectable oscillation in $γ$-ray spectra. This study analyzes 16.5 years of data from the Fermi Large Area Telescope (Fermi-LAT) on NGC 1275, the brightest… ▽ More Axionlike particles (ALPs), hypothetical particles beyond the Standard Model, are considered as promising dark matter candidates. ALPs can convert into photons and vice versa in a magnetic field via the Primakoff effect, potentially generating detectable oscillation in $γ$-ray spectra. This study analyzes 16.5 years of data from the Fermi Large Area Telescope (Fermi-LAT) on NGC 1275, the brightest galaxy in the Perseus cluster, to constrain the ALP parameter space. Our results improve the previous 95\% exclusion limits of the photon-ALP coupling $g_{aγ}$ by a factor of 2 in the ALP mass range of $4\times 10^{-10}\,\mathrm{eV}\lesssim m_{a}\lesssim 5\times 10^{-9}\,\mathrm{eV}$. Moreover, we investigate the projected sensitivity of the future Very Large Area $γ$-ray Space Telescope (VLAST) on searching for ALPs. We find that (i) the expected sensitivity on the ALP-photon coupling can be stronger than that from the upcoming International Axion Observatory (IAXO) in the ALP mass range of $2\times 10^{-11}\,\mathrm{eV}\lesssim m_{a}\lesssim 1\times 10^{-7}\,\mathrm{eV}$, with the best sensitivity of $g_{aγ}\sim 7\times 10^{-13}\,\mathrm{GeV^{-1}}$ at $m_{a}\sim 2\times 10^{-10}\,\mathrm{eV}$; (ii) VLAST can extend the sensitivity of the ALP masses below $5\times 10^{-12}\,\mathrm{eV}$, where the ALP-photon coupling $g_{aγ}\gtrsim 1.5\times 10^{-11}\,\mathrm{GeV^{-1}}$ will be excluded; (iii) the entire parameter space of ALP accounting for TeV transparency can be fully tested. These results demonstrate that VLAST will offer an excellent opportunity for ALPs searches. △ Less

Submitted 19 October, 2025; v1 submitted 10 July, 2025; originally announced July 2025.

Comments: 11 pages, 9 figures

Journal ref: Phys. Rev. D 112, 075008 (2025)

Osiris revisited: Confirming a solar metallicity and low C/O in HD 209458b

Authors: N. Bachmann, L. Kreidberg, P. Mollière, D. Deming, S. -M. Tsai

Abstract: HD 209458b is the prototypical hot Jupiter and one of the best targets available for precise atmosphere characterisation. Now that spectra from both Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) are available, we can reveal the atmospheric properties in unprecedented detail. In this study, we perform a new data reduction and analysis of the original HST/WFC3 spectrum, accounti… ▽ More HD 209458b is the prototypical hot Jupiter and one of the best targets available for precise atmosphere characterisation. Now that spectra from both Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) are available, we can reveal the atmospheric properties in unprecedented detail. In this study, we perform a new data reduction and analysis of the original HST/WFC3 spectrum, accounting for the wavelength dependence of the instrument systematics that was not considered in previous analyses. This allows us to precisely and robustly measure the much-debated H$_2$O abundance in HD 209458b's atmosphere. We combine the newly reduced spectrum with archival JWST/NIRCam data and run free chemistry atmospheric retrievals over the 1.0 - 5.1 $μ$m wavelength range, covering possible features of multiple absorbing species, including CO$_2$, CO, CH$_4$, NH$_3$, HCN, Na, SO$_2$, and H$_2$S. We detect H$_2$O and CO$_2$ robustly at above 7 $σ$ significance, and find a 3.6 $σ$ preference for cloudy models compared to a clear atmosphere. For all other absorbers we tested, only upper limits of abundance can be measured. We use Bayesian model averaging to account for a range of different assumptions about the cloud properties, resulting in a water volume mixing ratio of $0.95^{+0.35}_{-0.17} \:\times$ solar and a carbon dioxide abundance of $0.94^{+0.16}_{-0.09} \:\times$ solar. Both results are consistent with solar values and comparable to predictions from the VULCAN 1D photochemistry model. Combining these values with a prior on the CO abundance from ground-based measurements, we derive an overall atmospheric composition comparable to solar metallicity of $\mathrm{[M/H]} = 0.10^{+0.41}_{-0.40}$ and very low C/O of $0.054^{+0.080}_{-0.034}$ with a 3 $σ$ upper limit of 0.454. This indicates a strong enrichment in oxygen and depletion in carbon during HD 209458b's formation. △ Less

Submitted 19 June, 2025; originally announced June 2025.

Comments: 22 pages, 18 figures, 9 tables; accepted for publication in A&A

Journal ref: A&A 700, A105 (2025)

Self-Interacting Dark Matter with Mass Segregation: A Unified Explanation of Dwarf Cores and Small-Scale Lenses

Authors: Daneng Yang, Yi-Zhong Fan, Siyuan Hou, Yue-Lin Sming Tsai

Abstract: In two-component SIDM models with inter-species interactions, mass segregation arises naturally from collisional relaxation, enhancing central densities and gravothermal evolution without requiring large cross sections. We propose a model with velocity-dependent interactions, both within and between species, that connects observations across several halo mass scales while remaining consistent with… ▽ More In two-component SIDM models with inter-species interactions, mass segregation arises naturally from collisional relaxation, enhancing central densities and gravothermal evolution without requiring large cross sections. We propose a model with velocity-dependent interactions, both within and between species, that connects observations across several halo mass scales while remaining consistent with cluster-scale constraints. This combination enables modest mass segregation in low-mass and typical-concentration halos, consistent with recent dwarf galaxy clustering measurements. Using cosmological zoom-in simulations and controlled isolated halo studies, we show that this model produces dwarf galaxy cores that grow over time, explains the structure of dark perturbers observed in strong lensing systems, and significantly increases the number and efficiency of small-scale lenses, consistent with the galaxy-galaxy strong lensing excess reported in clusters. Our results establish mass segregation in two-component SIDM as a self-consistent and testable model capable of simultaneously addressing multiple small-scale challenges in structure formation. △ Less

Submitted 17 June, 2025; originally announced June 2025.

Comments: 11 pages, 8 figures

Scrutinizing the impact of the solar modulation on AMS-02 antiproton excess

Authors: Kai-Kai Duan, Xiao Wang, Wen-Hao Li, Zhi-Hui Xu, Yue-Lin Sming Tsai, Yi-Zhong Fan

Abstract: This study examines the impact of solar modulation on the antiproton excess observed by AMS-02, which may indicate dark matter (DM) annihilation. We analyze three solar modulation models: the force-field approximation (FFA), a time-, charge-, and rigidity-dependent FFA, and a three-dimensional numerical simulation based on the Parker transport equation. Based on AMS-02 latest antiproton data (2025… ▽ More This study examines the impact of solar modulation on the antiproton excess observed by AMS-02, which may indicate dark matter (DM) annihilation. We analyze three solar modulation models: the force-field approximation (FFA), a time-, charge-, and rigidity-dependent FFA, and a three-dimensional numerical simulation based on the Parker transport equation. Based on AMS-02 latest antiproton data (2025), our results show that the significance of the DM signal is sensitive to the chosen modulation model, with a 2$σ$ signal for the FFA (4$σ$ if including data from H, He, C, O, B/C, and B/O) and a reduced significance for more complex models. We also address systematic uncertainties using two methods: the add-in-quadrature method, which assumes uncorrelated uncertainties between energy bins, and the nuisance parameter method, which treats systematic uncertainties as nuisance parameters during the fitting process. Fitted to AMS-02 antiproton data, DM annihilation to the $b\bar{b}$ scenario with three different solar modulation models shows that the add-in-quadrature method causes overfitting, whereas the nuisance parameters approach leads to underfitting. Statistically, the signal region of the FFA model using the add-in-quadrature method is the most reliable. This work highlights the need for refined solar modulation models and a better treatment of uncertainties for a conclusive interpretation of the AMS-02 data. △ Less

Submitted 10 October, 2025; v1 submitted 16 June, 2025; originally announced June 2025.

Comments: 23 pages, 9 figures, accepted for publication in JCAP

Prospects for Probing Sub-GeV Leptophilic Dark Matter with the Future VLAST

Authors: Tian-Peng Tang, Meiwen Yang, Kai-Kai Duan, Yue-Lin Sming Tsai, Yi-Zhong Fan

Abstract: The proposed Very Large Area Space Telescope (VLAST), with its expected unprecedented sensitivity in the MeV-GeV range, can also address the longstanding "MeV Gap" in gamma-ray observations. We explore the capability of VLAST to detect sub-GeV leptophilic dark matter (DM) annihilation, focusing on scalar and vector mediators and emphasizing the resonance region where the mediator mass is approxima… ▽ More The proposed Very Large Area Space Telescope (VLAST), with its expected unprecedented sensitivity in the MeV-GeV range, can also address the longstanding "MeV Gap" in gamma-ray observations. We explore the capability of VLAST to detect sub-GeV leptophilic dark matter (DM) annihilation, focusing on scalar and vector mediators and emphasizing the resonance region where the mediator mass is approximately twice the DM mass. While $s$-wave annihilation is tightly constrained by relic density and cosmic microwave background observations, $p$-wave and mixed $(s+p)$-wave scenarios remain viable, particularly near resonance. Additionally, direct detection experiments, especially those probing DM-electron scattering, significantly constrain nonresonance parameter space but are less effective in the resonance regime. VLAST can uniquely probe this surviving region, outperforming existing and planned instruments, and establishing itself as a crucial tool for indirect detection of thermal relic DM. △ Less

Submitted 6 November, 2025; v1 submitted 8 May, 2025; originally announced May 2025.

Comments: 27 pages, 5 figures

Revisiting open clusters within 200 pc in the solar neighbourhood with Gaia DR3

Authors: Penghui Liu, Min Fang, Yue-Lin Sming Tsai, Xiaoying Pang, Fan Wang, Xiaoting Fu

Abstract: In this study, we develop a membership identification method and apply it for 30 open clusters (OCs) within 200 pc of the Sun using astrometric data of Gaia DR3. By accounting for projection effects that distort apparent stellar motions, our approach converts astrometric data into accurate five-dimensional positions and velocities. This approach enables better identification of members in nearby o… ▽ More In this study, we develop a membership identification method and apply it for 30 open clusters (OCs) within 200 pc of the Sun using astrometric data of Gaia DR3. By accounting for projection effects that distort apparent stellar motions, our approach converts astrometric data into accurate five-dimensional positions and velocities. This approach enables better identification of members in nearby open clusters. We then compare our refined membership lists with previous catalogs, revealing more members in most open clusters, but also the identification of elongated structures in Melotte 25 (Hyades), NGC 2632 (Praesepe), Melotte 111 (Coma Berenices), Platais 3, Melotte 22 (Pleiades), NGC 2451A, Platais 9, IC 2391, Platais 8, UPK 640, HSC 2986, which we studied in detail. An analysis of the ages of their members reveals the members within and outside of the tidal radius are distinctly coeval, further validating our methodology. This study suggests that for OCs in the solar neighborhood, correcting for the projection effect is very important for identification of OC members. △ Less

Submitted 10 April, 2025; originally announced April 2025.

Comments: Accepted for publication in AJ,

Diversifying halo structures in two-component self-interacting dark matter models via mass segregation

Authors: Daneng Yang, Yue-Lin Sming Tsai, Yi-Zhong Fan

Abstract: Self-interacting dark matter (SIDM), through gravothermal evolution driven by elastic self-scatterings, offers a compelling explanation for the observed diversity of inner halo densities. In this work, we investigate SIDM dynamics in a two-component dark matter model with mass ratios of order unity, motivated by an asymmetric dark matter framework that naturally evades constraints from relic abund… ▽ More Self-interacting dark matter (SIDM), through gravothermal evolution driven by elastic self-scatterings, offers a compelling explanation for the observed diversity of inner halo densities. In this work, we investigate SIDM dynamics in a two-component dark matter model with mass ratios of order unity, motivated by an asymmetric dark matter framework that naturally evades constraints from relic abundance and mediator decay, while enabling strong, velocity-dependent self-interactions. We show that cross-component scatterings significantly enhance mass segregation, driving the formation of dense, core collapsed-like halos. This effect couples naturally to SIDM-induced diversity, introducing a new mechanism for generating structural variations beyond those arising from gravothermal evolution alone. Our results reveal a novel mechanism for reconciling SIDM with small-scale observational tensions by enabling shifts in central densities while preserving the flexibility to generate diverse halo structures. We further highlight that halo structural diversity may serve as a diagnostic of dark sector composition, opening a new observational window into the particle nature of SIDM. △ Less

Submitted 23 June, 2025; v1 submitted 3 April, 2025; originally announced April 2025.

Comments: 10 pages, 4 figures. Typos fixed, introduction extended

Journal ref: Phys.Rev.D 112 (2025) 8, 083011

Characterising the Atmosphere of 55 Cancri e: 1D Forward Model Grid for Current and Future JWST Observations

Authors: Mantas Zilinskas, Christiaan van Buchem, Sebastian Zieba, Yamila Miguel, Emily Sandford, Renyu Hu, Jayshil Patel, Aaron Bello-Arufe, Leoni Janssen, Shang-Min Tsai, Diana Dragomir, Michael Zhang

Abstract: Recent JWST observations with NIRCam and MIRI of the ultra-short-period super-Earth 55 Cancri e indicate a possible volatile atmosphere surrounding the planet. Previous analysis of the NIRCam spectra suggested potential absorption features from CO2 or CO and significant sub-weekly variability. The MIRI low-resolution spectrum does not contain substantial features but was found to be consistent wit… ▽ More Recent JWST observations with NIRCam and MIRI of the ultra-short-period super-Earth 55 Cancri e indicate a possible volatile atmosphere surrounding the planet. Previous analysis of the NIRCam spectra suggested potential absorption features from CO2 or CO and significant sub-weekly variability. The MIRI low-resolution spectrum does not contain substantial features but was found to be consistent with effective heat redistribution models. In this work, we computed a grid of over 25000 self-consistent 1D forward models incorporating H-N-O-C-S-P-Si-Ti equilibrium chemistry and assessed plausible atmospheric compositions based on the current JWST data. Despite exhaustive analysis, the composition and properties of the atmosphere remain elusive. While our results statistically favour a global, hydrogen-free, nitrogen-dominated atmosphere enriched in PO and CO2, various alternative compositions, including H2O-,CO-, PH3-, or Si-bearing remain viable explanations. Unconstrained heat redistribution efficiency and absolute NIRCam flux are among the largest sources of uncertainty in our analysis. We also find that the heat redistribution factor and surface pressure are highly degenerate with atmospheric composition, and that these parameters cannot be independently constrained using current JWST observations. Furthermore, we show that the observed variability may arise from dynamic interactions between the atmosphere and an underlying magma ocean, driving rapid shifts in atmospheric chemistry and thermal emission. Our results highlight the importance of using self-consistent forward models when analysing novel JWST spectra with limited signal-to-noise ratios -- such as those of 55 Cancri e -- as it allows for a more comprehensive evaluation of potential atmospheric scenarios while also being less sensitive to subtle spectral differences than retrievals... △ Less

Submitted 20 May, 2025; v1 submitted 20 March, 2025; originally announced March 2025.

Comments: Published version

Journal ref: A&A 697, A34 (2025)

Exploring sub-GeV dark matter via $s$-wave, $p$-wave, and resonance annihilation with CMB data

Authors: Yu-Ning Wang, Xin-Chen Duan, Tian-Peng Tang, Ziwei Wang, Yue-Lin Sming Tsai

Abstract: We revisit constraints on sub-GeV dark matter (DM) annihilation via $s$-wave, $p$-wave, and resonance processes using current and future CMB data from Planck, FIRAS, and upcoming experiments such as LiteBIRD, CMB-S4, PRISTINE, and PIXIE. For $s$-wave annihilation, we provide updated limits for both $e^{+}e^{-}$ and $ππ$ channels, with the profile likelihood method yielding stronger constraints tha… ▽ More We revisit constraints on sub-GeV dark matter (DM) annihilation via $s$-wave, $p$-wave, and resonance processes using current and future CMB data from Planck, FIRAS, and upcoming experiments such as LiteBIRD, CMB-S4, PRISTINE, and PIXIE. For $s$-wave annihilation, we provide updated limits for both $e^{+}e^{-}$ and $ππ$ channels, with the profile likelihood method yielding stronger constraints than the marginal posterior method. In the $p$-wave case, we comprehensively present a model-independent inequality for the $95\%$ upper limits from FIRAS, PRISTINE, and PIXIE, with future experiments expected to surpass current BBN limits. For resonance annihilation, we report -- for the first time -- the $95\%$ upper limits on the decay branching ratio of the mediator particle, when the resonance peaks during the recombination epoch. Overall, our study highlights the complementary strengths of $μ$-distortion and CMB anisotropies in probing sub-GeV DM annihilation. △ Less

Submitted 3 September, 2025; v1 submitted 25 February, 2025; originally announced February 2025.

Examining the Potential for Methyl Halide Accumulation and Detectability in Possible Hycean-Type Atmospheres

Authors: Michaela Leung, Shang-Min Tsai, Edward W Schwieterman, Daniel Angerhausen, Janina Hansen

Abstract: Some sub-Neptune planets may host habitable conditions; for example "Hycean" worlds with H2 envelopes over liquid water oceans can maintain potentially hospitable pressures and temperatures at their surface. Recent JWST observations of K2-18b and TOI-270d have shown that such worlds could be compelling targets for biosignature searches, given their extended scale heights and therefore large atmosp… ▽ More Some sub-Neptune planets may host habitable conditions; for example "Hycean" worlds with H2 envelopes over liquid water oceans can maintain potentially hospitable pressures and temperatures at their surface. Recent JWST observations of K2-18b and TOI-270d have shown that such worlds could be compelling targets for biosignature searches, given their extended scale heights and therefore large atmospheric signatures. Methylated biosignatures, a broad group of gases that can be generated by biological attachment of a CH3 group to an environmental substrate, have been proposed as candidate signs of life for Earth-like exoplanets. However, methyl halides (CH3 + halogen) have not yet been robustly examined with self-consistent photochemical and spectral models for planets with H2-dominated atmospheres. Here we demonstrate that methyl chloride (CH3Cl), predominantly produced by marine microbes, could be detected using JWST in tens of transits or fewer for Hycean planets, comparable to detection requirements for other potential atmospheric biosignatures. The threshold atmospheric mixing ratio for detectability is $\sim$10 ppm, which can accumulate with global fluxes comparable to moderately productive local environments on Earth. △ Less

Submitted 20 February, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: 13 pages, 4 figures, 1 appendix; accepted at ApJL updated version includes clarified color scheme and axis in Figure 4

HCN and C2H2 in the atmosphere of a T8.5+T9 brown dwarf binary

Authors: Elisabeth C. Matthews, Paul Mollière, Helena Kühnle, Polychronis Patapis, Niall Whiteford, Matthias Samland, Pierre-Olivier Lagage, Rens Waters, Shang-Min Tsai, Kevin Zahnle, Manuel Guedel, Thomas Henning, Bart Vandenbussche, Olivier Absil, Ioannis Argyriou, David Barrado, Alain Coulais, Adrian M. Glauser, Goran Olofsson, John P. Pye, Daniel Rouan, Pierre Royer, Ewine F. van Dishoeck, T. P. Ray, Göran Östlin

Abstract: T-type brown dwarfs present an opportunity to explore atmospheres teeming with molecules such as H2O, CH4 and NH3, which exhibit a wealth of absorption features in the mid-infrared. With JWST, we can finally explore this chemistry in detail, including for the coldest brown dwarfs that were not yet discovered in the Spitzer era. This allows precise derivations of the molecular abundances, which in… ▽ More T-type brown dwarfs present an opportunity to explore atmospheres teeming with molecules such as H2O, CH4 and NH3, which exhibit a wealth of absorption features in the mid-infrared. With JWST, we can finally explore this chemistry in detail, including for the coldest brown dwarfs that were not yet discovered in the Spitzer era. This allows precise derivations of the molecular abundances, which in turn informs our understanding of vertical transport in these atmospheres and can provide clues about the formation of cold brown dwarfs and exoplanets. This study presents the first JWST/MRS mid-IR spectrum (R ~ 1500-3000) of a T-dwarf: the T8.5+T9 brown dwarf binary WISE J045853.90+643451.9. We fit the spectrum using a parameterized P-T profile and free molecular abundances (i.e., a retrieval analysis), treating the binary as unresolved. We find a good fit with a cloud-free atmosphere and identify H2O, CH4 and NH3 features. Moreover, we make the first detections of HCN and C2H2 (at 13.4$σ$ and 9.5$σ$ respectively) in any brown dwarf atmosphere. The detection of HCN suggests intense vertical mixing ($K_{zz}\sim10^{11}$cm$^2$s$^{-1}$), challenging previous literature derivations of $K_{zz}$ values for T-type brown dwarfs. Even more surprising is the C2H2 detection, which cannot be explained with existing atmospheric models for isolated objects. This result challenges model assumptions about vertical mixing, and/or our understanding of the C2H2 chemical network, or might hint towards a more complex atmospheric processes such as magnetic fields driving aurorae, or lightning driving ionization. These findings open a new frontier in studying carbon chemistry within brown dwarf atmospheres. △ Less

Submitted 28 February, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: Accepted for publication in The Astrophysical Journal Letters. 13 pages (5 figures) + appendices

GEMS JWST: Transmission spectroscopy of TOI-5205b reveals significant stellar contamination and a metal-poor atmosphere

Authors: Caleb I. Cañas, Jacob Lustig-Yaeger, Shang-Min Tsai, Simon Müller, Ravit Helled, Dana R. Louie, Giannina Guzmán Caloca, Shubham Kanodia, Peter Gao, Jessica Libby-Roberts, Kevin K. Hardegree-Ullman, Knicole D. Colón, Ian Czekala, Megan Delamer, Te Han, Andrea S. J. Lin, Suvrath Mahadevan, Erin M. May, Joe P. Ninan, Anjali A. A. Piette, Guðmundur Stefánsson, Kevin B. Stevenson, Johanna Teske, Nicole L. Wallack

Abstract: Recent discoveries of transiting giant exoplanets around M dwarfs (GEMS) present an opportunity to investigate their atmospheric compositions and explore how such massive planets can form around low-mass stars contrary to canonical formation models. Here, we present the first transmission spectra of TOI-5205b, a short-period ($P=1.63~\mathrm{days}$) Jupiter-like planet ($M_p=1.08~\mathrm{M_J}$ and… ▽ More Recent discoveries of transiting giant exoplanets around M dwarfs (GEMS) present an opportunity to investigate their atmospheric compositions and explore how such massive planets can form around low-mass stars contrary to canonical formation models. Here, we present the first transmission spectra of TOI-5205b, a short-period ($P=1.63~\mathrm{days}$) Jupiter-like planet ($M_p=1.08~\mathrm{M_J}$ and $R_p=0.94~\mathrm{R_J}$) orbiting an M4 dwarf. We obtained three transits using the PRISM mode of the JWST Near Infrared Spectrograph (NIRSpec) spanning $0.6-5.3$ um. Our data reveal significant stellar contamination that is evident in the light curves as spot-crossing events and in the transmission spectra as a larger transit depth at bluer wavelengths. Atmospheric retrievals demonstrate that stellar contamination from unocculted star spots is the dominant component of the transmission spectrum at wavelengths $λ\lesssim3.0$ um, which reduced the sensitivity to the presence of clouds or hazes in our models. The degree of stellar contamination also prevented the definitive detection of any $\mathrm{H_2O}$, which has primary absorption features at these shorter wavelengths. The broad wavelength coverage of NIRSpec PRISM enabled a robust detection of $\mathrm{CH_4}$ and $\mathrm{H_2S}$, which have detectable molecular features between $3.0-5.0$ um. Our gridded and Bayesian retrievals consistently favored an atmosphere with both sub-solar metallicity ($\log\mathrm{[M/H]}\sim-2$ for a clear atmosphere) and super-solar C/O ratio ($\log\mathrm{[C/O]}\sim3$ for a clear or cloudy atmosphere). This contrasts with estimates from planetary interior models that predict a bulk metallicity of 10--20%, which is $\sim100\times$ the atmospheric metallicity, and suggests that the planetary interior for TOI-5205b is decoupled from its atmosphere and not well mixed. △ Less

Submitted 10 February, 2025; originally announced February 2025.

Comments: 27 pages + appendix, includes figure sets that will appear in journal, submitted to AAS. Comments welcome

A Comprehensive Reanalysis of K2-18 b's JWST NIRISS+NIRSpec Transmission Spectrum

Authors: Stephen P. Schmidt, Ryan J. MacDonald, Shang-Min Tsai, Michael Radica, Le-Chris Wang, Eva-Maria Ahrer, Taylor J. Bell, Chloe Fisher, Daniel P. Thorngren, Nicholas Wogan, Erin M. May, Piero Ferrari, Katherine A. Bennett, Zafar Rustamkulov, Mercedes López-Morales, David K. Sing

Abstract: Sub-Neptunes are the most common type of planet in our galaxy. Interior structure models suggest that the coldest sub-Neptunes could host liquid water oceans underneath their hydrogen envelopes -- sometimes called ``hycean'' planets. JWST transmission spectra of the $\sim$ 250 K sub-Neptune K2-18 b were recently used to report detections of CH$_4$ and CO$_2$, alongside weaker evidence of (CH$_3$)… ▽ More Sub-Neptunes are the most common type of planet in our galaxy. Interior structure models suggest that the coldest sub-Neptunes could host liquid water oceans underneath their hydrogen envelopes -- sometimes called ``hycean'' planets. JWST transmission spectra of the $\sim$ 250 K sub-Neptune K2-18 b were recently used to report detections of CH$_4$ and CO$_2$, alongside weaker evidence of (CH$_3$)$_2$S (dimethyl sulfide, or DMS). Atmospheric CO$_2$ was interpreted as evidence for a liquid water ocean, while DMS was highlighted as a potential biomarker. However, these notable claims were derived using a single data reduction and retrieval modeling framework, which did not allow for standard robustness tests. Here we present a comprehensive reanalysis of K2-18 b's JWST NIRISS SOSS and NIRSpec G395H transmission spectra, including the first analysis of the second-order NIRISS SOSS data. We incorporate multiple well-tested data reduction pipelines and retrieval codes, spanning 60 different data treatments and over 250 atmospheric retrievals. We confirm the detection of CH$_4$ ($\approx 4σ$), with a volume mixing ratio range $-2.14 \leq \log_{10} \mathrm{CH_4} \leq -0.53$, but we find no statistically significant or reliable evidence for CO$_2$ or DMS. Finally, we assess the retrieved atmospheric composition using photochemical-climate and interior models, demonstrating that our revised composition of K2-18\,b can be explained by an oxygen-poor mini-Neptune without requiring a liquid water surface or life. △ Less

Submitted 29 August, 2025; v1 submitted 30 January, 2025; originally announced January 2025.

Comments: 42 pages, 21 figures. Revised version; accepted to AJ

Can $ν$DM interactions solve the $S_8$ discrepancy?

Authors: Lei Zu, William Giarè, Chi Zhang, Eleonora Di Valentino, Yue-Lin Sming Tsai, Sebastian Trojanowski

Abstract: We present compelling evidence that Dark Matter (DM)-neutrino interactions can resolve the persistent structure growth parameter discrepancy, $S_8 = σ_8\,\sqrt{Ω_m/0.3}$, between early and late universe observations. By incorporating cosmic shear measurements from current Weak Lensing (WL) surveys and leveraging an emulator based on true $N$-body simulations to account for nonlinear corrections, w… ▽ More We present compelling evidence that Dark Matter (DM)-neutrino interactions can resolve the persistent structure growth parameter discrepancy, $S_8 = σ_8\,\sqrt{Ω_m/0.3}$, between early and late universe observations. By incorporating cosmic shear measurements from current Weak Lensing (WL) surveys and leveraging an emulator based on true $N$-body simulations to account for nonlinear corrections, we demonstrate that an interaction strength of $u \sim 10^{-4}$ not only provides a coherent explanation for the high-multipole observations from the Atacama Cosmology Telescope (ACT), but also alleviates the $S_8$ discrepancy. Combining early universe constraints with DES Y3 cosmic shear data yields a nearly $3σ$ detection of non-zero DM-neutrino interactions, marking a significant breakthrough in cosmological research. Our findings challenge the standard $Λ$CDM paradigm and highlight the potential of future large-scale structure surveys, which can rigorously test this interaction and unveil the fundamental properties of dark matter. △ Less

Submitted 23 January, 2025; originally announced January 2025.

Comments: 28 pages, 10 figures

Network and Kinetics-based Biosignatures: Implications for the Putative Habitable World Observatory Design

Authors: Theresa Fisher, Chester Harman, Estelle Janin, Megan Shabram, Shang-Min Tsai, Nicholas Wogan, Michael Wong

Abstract: The proposed Habitable Worlds Observatory is intended to observe the atmospheres of nearby terrestrial exoplanets with a resolution greater than that of any previous instrument. While these observations present a substantial opportunity for astrobiology, they also incur the risk of false positives and false negatives. Here, we explore the use of systems science (in the form of network theory and t… ▽ More The proposed Habitable Worlds Observatory is intended to observe the atmospheres of nearby terrestrial exoplanets with a resolution greater than that of any previous instrument. While these observations present a substantial opportunity for astrobiology, they also incur the risk of false positives and false negatives. Here, we explore the use of systems science (in the form of network theory and thermochemical kinetics) to mitigate these risks, and briefly describe the technical specifications HWO would require in order to use these methodologies. △ Less

Submitted 12 January, 2025; v1 submitted 7 January, 2025; originally announced January 2025.

Statistical trends in JWST transiting exoplanet atmospheres

Authors: Guangwei Fu, Kevin B. Stevenson, David K. Sing, Sagnick Mukherjee, Luis Welbanks, Daniel Thorngren, Shang-Min Tsai, Peter Gao, Joshua Lothringer, Thomas G. Beatty, Cyril Gapp, Thomas M. Evans-Soma, Romain Allart, Stefan Pelletier, Pa Chia Thao, Andrew W. Mann

Abstract: Our brains are hardwired for pattern recognition as correlations are useful for predicting and understanding nature. As more exoplanet atmospheres are being characterized with JWST, we are starting to unveil their properties on a population level. Here we present a framework for comparing exoplanet transmission spectroscopy from 3 to 5$μ$m with four bands: L (2.9 - 3.7$μ$m), SO$_2$ (3.95 - 4.1$μ$m… ▽ More Our brains are hardwired for pattern recognition as correlations are useful for predicting and understanding nature. As more exoplanet atmospheres are being characterized with JWST, we are starting to unveil their properties on a population level. Here we present a framework for comparing exoplanet transmission spectroscopy from 3 to 5$μ$m with four bands: L (2.9 - 3.7$μ$m), SO$_2$ (3.95 - 4.1$μ$m), CO$_2$ (4.25 - 4.4$μ$m) and CO (4.5 - 4.9$μ$m). Together, the four bands cover the major carbon, oxygen, nitrogen, and sulfur-bearing molecules including H$_2$O, CH$_4$, NH$_3$, H$_2$S, SO$_2$, CO$_2$, and CO. Among the eight high-precision gas giant exoplanet planet spectra we collected, we found strong correlations between the SO$_2$-L index and planet mass (r=-0.41$\pm$0.09) and temperature (r=-0.64$\pm$0.08), indicating SO$_2$ preferably exists (SO$_2$-L$>$-0.5) among low mass ($\sim<$0.3M$_J$) and cooler ($\sim<$1200K) targets. We also observe strong temperature dependency for both CO$_2$-L and CO-L indices. Under equilibrium chemistry and isothermal thermal structure assumptions, we find that the planet sample favors super-solar metallicity and low C/O ratio ($<$0.7). In addition, the presence of a mass-metallicity correlation is favored over uniform metallicity with the eight planets. We further introduce the SO$_2$-L versus CO$_2$-L diagram alike the color-magnitude diagram for stars and brown dwarfs. All reported trends here will be testable and be further quantified with existing and future JWST observations within the next few years. △ Less

Submitted 3 January, 2025; originally announced January 2025.

Comments: Accepted to ApJ, JWST keeps on delivering!

A new pathway to SO$_2$: Revealing the NUV driven sulfur chemistry in hot gas giants

Authors: Wiebe de Gruijter, Shang-Min Tsai, Michiel Min, Rens Waters, Thomas Konings, Leen Decin

Abstract: Context. Photochemistry is a key process driving planetary atmospheres away from local thermodynamic equilibrium. Recent observations of the H$_2$ dominated atmospheres of hot gas giants have detected SO$_2$ as one of the major products of this process. Aims. We investigate which chemical pathways lead to the formation of SO$_2$ in an atmosphere, and we investigate which part of the flux from the… ▽ More Context. Photochemistry is a key process driving planetary atmospheres away from local thermodynamic equilibrium. Recent observations of the H$_2$ dominated atmospheres of hot gas giants have detected SO$_2$ as one of the major products of this process. Aims. We investigate which chemical pathways lead to the formation of SO$_2$ in an atmosphere, and we investigate which part of the flux from the host star is necessary to initiate SO$_2$ production. Methods. We use the publicly available S-N-C-H-O photochemical network in the VULCAN chemical kinetics code to compute the disequilibrium chemistry of an exoplanetary atmosphere. Results. We find that there are two distinct chemical pathways that lead to the formation of SO$_2$. The formation of SO$_2$ at higher pressures is initiated by stellar flux >200 nm, whereas the formation of SO$_2$ at lower pressures is initiated by stellar flux <200 nm. In deeper layers of the atmosphere, OH is provided by the hydrogen abstraction of H$_2$O, and sulfur is provided by the photodissociation of SH and S$_2$, which leads to a positive feedback cycle that liberates sulfur from the stable H$_2$S molecule. In higher layers of the atmosphere, OH is provided by the photodissociation of H$_2$O, and sulfur can be liberated from H$_2$S by either photodissociation of SH and S$_2$, or by the hydrogen abstraction of SH. Conclusions. We conclude that the stellar flux in the 200-350 nm wavelength range as well as the ratio of NUV/UV radiation are important parameters determining the observability of SO$_2$. In addition we find that there is a diversity of chemical pathways to the formation of SO$_2$. This is crucial for the interpretation of SO$_2$ detections and derived elemental abundance ratios and overall metallicities. △ Less

Submitted 7 November, 2024; originally announced November 2024.

Comments: Accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 693, A132 (2025)

Searching for Axion-Like Particles with X-ray Observations of Alpha Centauri

Authors: Yu-Xuan Chen, Lei Lei, Zi-Qing Xia, Ziwei Wang, Yue-Lin Sming Tsai, Yi-Zhong Fan

Abstract: We investigate the production of axion-like particles (ALPs) in stellar cores, where they interact with electromagnetic fields and electrons, with typical masses between $\mathcal O(0.1)$ and $\mathcal O(10)$ keV. These low-energy ALPs are gravitationally trapped in the orbits of stars and subsequently decay into two photons that we detect as monochromatic X-ray lines. We propose to search for the… ▽ More We investigate the production of axion-like particles (ALPs) in stellar cores, where they interact with electromagnetic fields and electrons, with typical masses between $\mathcal O(0.1)$ and $\mathcal O(10)$ keV. These low-energy ALPs are gravitationally trapped in the orbits of stars and subsequently decay into two photons that we detect as monochromatic X-ray lines. We propose to search for these gravitationally trapped ALPs in the Alpha Centauri binary system, our closest stellar neighbor, using sensitive X-ray detectors like Chandra and eROSITA. Our search for ALP decay signals in the energy range of $0.2$ keV to $10$ keV yielded null results, thus establishing the most stringent limits on ALP interactions to date. In the case of ALP-electron coupling $g_{aee}\leq 10^{-15}$, we have improved the limits on the ALP-photon coupling $g_{aγγ}$ in ALP mass range between $0.25~\keV$ and $5~\keV$, compared to previous measurements, including those from GW170817, SN 2023ixf, and other sources, and specially the improvement reaches about 2 orders of magnitude at the mass of 2 keV. Even tighter constraints are set for larger $g_{aee}$. △ Less

Submitted 12 June, 2025; v1 submitted 21 October, 2024; originally announced October 2024.

Comments: 10 pages, 5 figures, PRL Accepted

BOWIE-ALIGN: JWST reveals hints of planetesimal accretion and complex sulphur chemistry in the atmosphere of the misaligned hot Jupiter WASP-15b

Authors: James Kirk, Eva-Maria Ahrer, Alastair B. Claringbold, Maria Zamyatina, Chloe Fisher, Mason McCormack, Vatsal Panwar, Diana Powell, Jake Taylor, Daniel P. Thorngren, Duncan A. Christie, Emma Esparza-Borges, Shang-Min Tsai, Lili Alderson, Richard A. Booth, Charlotte Fairman, Mercedes López-Morales, N. J. Mayne, Annabella Meech, Paul Molliere, James E. Owen, Anna B. T. Penzlin, Denis E. Sergeev, Daniel Valentine, Hannah R. Wakeford , et al. (1 additional authors not shown)

Abstract: We present a transmission spectrum of the misaligned hot Jupiter WASP-15b from 2.8-5.2 microns observed with JWST's NIRSpec/G395H grating. Our high signal to noise data, which has negligible red noise, reveals significant absorption by H$_2$O ($4.2σ$) and CO$_2$ ($8.9σ$). From independent data reduction and atmospheric retrieval approaches, we infer that WASP-15b's atmospheric metallicity is super… ▽ More We present a transmission spectrum of the misaligned hot Jupiter WASP-15b from 2.8-5.2 microns observed with JWST's NIRSpec/G395H grating. Our high signal to noise data, which has negligible red noise, reveals significant absorption by H$_2$O ($4.2σ$) and CO$_2$ ($8.9σ$). From independent data reduction and atmospheric retrieval approaches, we infer that WASP-15b's atmospheric metallicity is super-solar ($\gtrsim 15\times$ solar) and its carbon-to-oxygen ratio is consistent with solar, that together imply planetesimal accretion. Our general circulation model simulations for WASP-15b suggest that the carbon-to-oxygen we measure at the limb is likely representative of the entire photosphere due to the mostly uniform spatial distribution of H$_2$O, CO$_2$ and CO. We additionally see evidence for absorption by SO$_2$ and absorption at 4.9$μ$m, for which the current leading candidate is OCS, albeit with several caveats. If confirmed, this would be the first detection of OCS in an exoplanet atmosphere and point towards complex photochemistry of sulphur-bearing species in the upper atmosphere. These are the first observations from the BOWIE-ALIGN survey which is using JWST's NIRSpec/G395H instrument to compare the atmospheric compositions of aligned/low-obliquity and misaligned/high-obliquity hot Jupiters around F stars above the Kraft break. The goal of our survey is to determine whether the atmospheric composition differs across two populations of planets that have likely undergone different migration histories (disc versus disc-free) as evidenced by their obliquities (aligned versus misaligned). △ Less

Submitted 13 February, 2025; v1 submitted 10 October, 2024; originally announced October 2024.

Comments: 27 pages, 25 figures, 6 tables. Accepted to MNRAS on 30th January 2025

Cosmic Ly$α$ Emission from Diffuse Gas

Authors: Sung-Han Tsai, Ke-Jung Chen, Aaron Smith, Yi-Kuan Chiang

Abstract: The Ly$α$ emission has emerged as a powerful tool for probing diffuse gas within the large-scale structure of the universe. In this paper, we investigate cosmic Ly$α$ emission by post-processing cosmological simulations from \texttt{IllustrisTNG} and \texttt{THESAN} project. Specifically, we calculate the Ly$α$ emission from galaxies, circum-galactic medium (CGM) and inter-galactic medium (IGM) ac… ▽ More The Ly$α$ emission has emerged as a powerful tool for probing diffuse gas within the large-scale structure of the universe. In this paper, we investigate cosmic Ly$α$ emission by post-processing cosmological simulations from \texttt{IllustrisTNG} and \texttt{THESAN} project. Specifically, we calculate the Ly$α$ emission from galaxies, circum-galactic medium (CGM) and inter-galactic medium (IGM) across various redshifts. Our results show that IGM alone is significantly under the current observational upper limits. Meanwhile, CGM overshoots the observed galaxy contribution at $z \lesssim 0.5$ indicating that either the escape fraction for the inner CGM is less than unity or the current photoionization equilibrium treatment with an approximate self-shielding prescription is less accurate. The galaxy component also overshoots at low redshift, indicating that the escape fraction has strong evolution caused by an evolving halo mass function and dust growth distribution, that agrees with observationally inferred escape fractions. Furthermore, our findings suggest that the Ly$α$ emission from diffuse gas (CGM+IGM) peaked at $z \sim 4$ and diminishes toward lower redshift. The Ly$α$ emission from diffuse gas mainly originates through the collisional excitation of hot plasma. By comparing models with observation, our predicted Ly$α$ emission from diffuse gas remains $\sim 6$ times fainter than the observed cosmic Ly$α$ emission at $z=1-3$. However, future large telescopes may hold great promise to detect Ly$α$ emission from diffuse gas toward $z>3$. △ Less

Submitted 29 May, 2025; v1 submitted 1 October, 2024; originally announced October 2024.

Comments: 14 pages, 7 figures, submitted to MNRAS, v2

The Featherweight Giant: Unraveling the Atmosphere of a 17 Myr Planet with JWST

Authors: Pa Chia Thao, Andrew W. Mann, Adina D. Feinstein, Peter Gao, Daniel Thorngren, Yoav Rotman, Luis Welbanks, Alexander Brown, Girish M. Duvvuri, Kevin France, Isabella Longo, Angeli Sandoval, P. Christian Schneider, David J. Wilson, Allison Youngblood, Andrew Vanderburg, Madyson G. Barber, Mackenna L. Wood, Natasha E. Batalha, Adam L. Kraus, Catriona Anne Murray, Elisabeth R. Newton, Aaron Rizzuto, Benjamin M. Tofflemire, Shang-Min Tsai , et al. (7 additional authors not shown)

Abstract: The characterization of young planets (< 300 Myr) is pivotal for understanding planet formation and evolution. We present the 3-5$μ$m transmission spectrum of the 17 Myr, Jupiter-size ($R$ $\sim$10$R_{\oplus}$) planet, HIP 67522 b, observed with JWST/NIRSpec/G395H. To check for spot contamination, we obtain a simultaneous $g$-band transit with SOAR. The spectrum exhibits absorption features 30-50%… ▽ More The characterization of young planets (< 300 Myr) is pivotal for understanding planet formation and evolution. We present the 3-5$μ$m transmission spectrum of the 17 Myr, Jupiter-size ($R$ $\sim$10$R_{\oplus}$) planet, HIP 67522 b, observed with JWST/NIRSpec/G395H. To check for spot contamination, we obtain a simultaneous $g$-band transit with SOAR. The spectrum exhibits absorption features 30-50% deeper than the overall depth, far larger than expected from an equivalent mature planet, and suggests that HIP 67522 b's mass is $<$20 $M_{\oplus}$ irrespective of cloud cover and stellar contamination. A Bayesian retrieval analysis returns a mass constraint of $13.8\pm1.0M_{\oplus}$. This challenges the previous classification of HIP 67522 b as a hot Jupiter and instead, positions it as a precursor to the more common sub-Neptunes. With a density of $<$0.10g/cm$^{3}$, HIP 67522 b is one of the lowest density planets known. We find strong absorption from H$_{2}$O and CO$_{2}$ ($\ge7σ$), a modest detection of CO (3.5$σ$), and weak detections of H$_2$S and SO$_2$ ($\simeq2σ$). Comparisons with radiative-convective equilibrium models suggest supersolar atmospheric metallicities and solar-to-subsolar C/O ratios, with photochemistry further constraining the inferred atmospheric metallicity to 3$\times$10 Solar due to the amplitude of the SO$_2$ feature. These results point to the formation of HIP 67522 b beyond the water snowline, where its envelope was polluted by icy pebbles and planetesimals. The planet is likely experiencing substantial mass loss (0.01-0.03 M$_{\oplus}$ Myr$^{-1}$), sufficient for envelope destruction within a Gyr. This highlights the dramatic evolution occurring within the first 100 Myr of its existence. △ Less

Submitted 24 September, 2024; originally announced September 2024.

Comments: Accepted for publication in The Astronomical Journal; 32 pages, 18 figures, 7 tables

A photochemical PHO network for hydrogen-dominated exoplanet atmospheres

Authors: Elspeth K. H. Lee, Shang-Min Tsai, Julianne I. Moses, John M. C. Plane, Channon Visscher, Stephen J. Klippenstein

Abstract: Due to the detection of phosphine PH3 in the Solar System gas giants Jupiter and Saturn, PH3 has long been suggested to be detectable in exosolar substellar atmospheres too. However, to date, a direct detection of phosphine has proven to be elusive in exoplanet atmosphere surveys. We construct an updated phosphorus-hydrogen-oxygen (PHO) photochemical network suitable for simulation of gas giant hy… ▽ More Due to the detection of phosphine PH3 in the Solar System gas giants Jupiter and Saturn, PH3 has long been suggested to be detectable in exosolar substellar atmospheres too. However, to date, a direct detection of phosphine has proven to be elusive in exoplanet atmosphere surveys. We construct an updated phosphorus-hydrogen-oxygen (PHO) photochemical network suitable for simulation of gas giant hydrogen-dominated atmospheres. Using this network, we examine PHO photochemistry in hot Jupiter and warm Neptune exoplanet atmospheres at Solar and enriched metallicities. Our results show for HD 189733b-like hot Jupiters that HOPO, PO and P2 are typically the dominant P carriers at pressures important for transit and emission spectra, rather than PH3. For GJ1214b-like warm Neptune atmospheres our results suggest that at Solar metallicity PH3 is dominant in the absence of photochemistry, but is generally not in high abundance for all other chemical environments. At 10 and 100 times Solar, small oxygenated phosphorus molecules such as HOPO and PO dominate for both thermochemical and photochemical simulations. The network is able to reproduce well the observed PH3 abundances on Jupiter and Saturn. Despite progress in improving the accuracy of the PHO network, large portions of the reaction rate data remain with approximate, uncertain or missing values, which could change the conclusions of the current study significantly. Improving understanding of the kinetics of phosphorus-bearing chemical reactions will be a key undertaking for astronomers aiming to detect phosphine and other phosphorus species in both rocky and gaseous exoplanetary atmospheres in the near future. △ Less

Submitted 20 October, 2024; v1 submitted 10 September, 2024; originally announced September 2024.

Comments: Submitted to ApJ (12 July 2024) - Accepted ApJ (20 Oct 2024)

Volatile-rich Sub-Neptunes as Hydrothermal Worlds: The Case of K2-18 b

Authors: Cindy N. Luu, Xinting Yu, Christopher R. Glein, Hamish Innes, Artyom Aguichine, Joshua Krissansen-Totton, Julianne I. Moses, Shang-Min Tsai, Xi Zhang, Ngoc Truong, Jonathan J. Fortney

Abstract: Temperate exoplanets between the sizes of Earth and Neptune, known as "sub-Neptunes", have emerged as intriguing targets for astrobiology. It is unknown whether these planets resemble Earth-like terrestrial worlds with a habitable surface, Neptune-like giant planets with deep atmospheres and no habitable surface, or something exotic in between. Recent JWST transmission spectroscopy observations of… ▽ More Temperate exoplanets between the sizes of Earth and Neptune, known as "sub-Neptunes", have emerged as intriguing targets for astrobiology. It is unknown whether these planets resemble Earth-like terrestrial worlds with a habitable surface, Neptune-like giant planets with deep atmospheres and no habitable surface, or something exotic in between. Recent JWST transmission spectroscopy observations of the canonical sub-Neptune, K2-18 b, revealed ~1% CH4, ~1% CO2, and a non-detection of CO in the atmosphere. While previous studies proposed that the observed atmospheric composition could help constrain the lower atmosphere's conditions and determine the interior structure of sub-Neptunes like K2-18 b, the possible interactions between the atmosphere and a hot, supercritical water ocean at its base remain unexplored. In this work, we investigate whether a global supercritical water ocean, resembling a planetary-scale hydrothermal system, can explain these observations on K2-18 b-like sub-Neptunes through equilibrium aqueous geochemical calculations. We find that the observed atmospheric CH4/CO2 ratio implies a minimum ocean temperature of ~710 K, whereas the corresponding CO/CO2 ratio allows ocean temperatures up to ~1070 K. These results indicate that a global supercritical water ocean on K2-18 b is plausible. While life cannot survive in such an ocean, this work represents the first step towards understanding how a global supercritical water ocean may influence observable atmospheric characteristics on volatile-rich sub-Neptunes. Future observations with better constrained CO and NH$_3$ mixing ratios could further help distinguish between possible interior compositions of K2-18 b. △ Less

Submitted 9 December, 2024; v1 submitted 10 September, 2024; originally announced September 2024.

Comments: 17 pages, 5 figures, 1 table

Geodynamics of super-Earth GJ 486b

Authors: Tobias G. Meier, Dan J. Bower, Tim Lichtenberg, Mark Hammond, Paul J. Tackley, Raymond T. Pierrehumbert, José A. Caballero, Shang-Min Tsai, Megan Weiner Mansfield, Nicola Tosi, Philipp Baumeister

Abstract: Many super-Earths are on very short orbits around their host star and, therefore, more likely to be tidally locked. Because this locking can lead to a strong contrast between the dayside and nightside surface temperatures, these super-Earths could exhibit mantle convection patterns and tectonics that could differ significantly from those observed in the present-day solar system. The presence of an… ▽ More Many super-Earths are on very short orbits around their host star and, therefore, more likely to be tidally locked. Because this locking can lead to a strong contrast between the dayside and nightside surface temperatures, these super-Earths could exhibit mantle convection patterns and tectonics that could differ significantly from those observed in the present-day solar system. The presence of an atmosphere, however, would allow transport of heat from the dayside towards the nightside and thereby reduce the surface temperature contrast between the two hemispheres. On rocky planets, atmospheric and geodynamic regimes are closely linked, which directly connects the question of atmospheric thickness to the potential interior dynamics of the planet. Here, we study the interior dynamics of super-Earth GJ 486b ($R=1.34$ $R_{\oplus}$, $M=3.0$ $M_{\oplus}$, T$_\mathrm{eq}\approx700$ K), which is one of the most suitable M-dwarf super-Earth candidates for retaining an atmosphere produced by degassing from the mantle and magma ocean. We investigate how the geodynamic regime of GJ 486b is influenced by different surface temperature contrasts by varying possible atmospheric circulation regimes. We also investigate how the strength of the lithosphere affects the convection pattern. We find that hemispheric tectonics, the surface expression of degree-1 convection with downwellings forming on one hemisphere and upwelling material rising on the opposite hemisphere, is a consequence of the strong lithosphere rather than surface temperature contrast. Anchored hemispheric tectonics, where downwellings und upwellings have a preferred (day/night) hemisphere, is favoured for strong temperature contrasts between the dayside and nightside and higher surface temperatures. △ Less

Submitted 14 January, 2025; v1 submitted 20 August, 2024; originally announced August 2024.

Comments: 36 pages, 13 figures, updated with version accepted for publication in JGR: Planets

Journal ref: JGR: Planets 2024, 129, e2024JE008491

Inhomogeneous terminators on the exoplanet WASP-39 b

Authors: Néstor Espinoza, Maria E. Steinrueck, James Kirk, Ryan J. MacDonald, Arjun B. Savel, Kenneth Arnold, Eliza M. -R. Kempton, Matthew M. Murphy, Ludmila Carone, Maria Zamyatina, David A. Lewis, Dominic Samra, Sven Kiefer, Emily Rauscher, Duncan Christie, Nathan Mayne, Christiane Helling, Zafar Rustamkulov, Vivien Parmentier, Erin M. May, Aarynn L. Carter, Xi Zhang, Mercedes López-Morales, Natalie Allen, Jasmina Blecic , et al. (18 additional authors not shown)

Abstract: Transmission spectroscopy has been a workhorse technique over the past two decades to constrain the physical and chemical properties of exoplanet atmospheres. One of its classical key assumptions is that the portion of the atmosphere it probes -- the terminator region -- is homogeneous. Several works in the past decade, however, have put this into question for highly irradiated, hot (… ▽ More Transmission spectroscopy has been a workhorse technique over the past two decades to constrain the physical and chemical properties of exoplanet atmospheres. One of its classical key assumptions is that the portion of the atmosphere it probes -- the terminator region -- is homogeneous. Several works in the past decade, however, have put this into question for highly irradiated, hot ($T_{eq}\gtrsim 1000$ K) gas giant exoplanets both empirically and via 3-dimensional modelling. While models predict clear differences between the evening (day-to-night) and morning (night-to-day) terminators, direct morning/evening transmission spectra in a wide wavelength range has not been reported for an exoplanet to date. Under the assumption of precise and accurate orbital parameters on WASP-39 b, here we report the detection of inhomogeneous terminators on the exoplanet WASP-39 b, which allows us to retrieve its morning and evening transmission spectra in the near-infrared ($2-5\ μ$m) using JWST. We observe larger transit depths in the evening which are, on average, $405 \pm 88$ ppm larger than the morning ones, also having qualitatively larger features than the morning spectrum. The spectra are best explained by models in which the evening terminator is hotter than the morning terminator by $177^{+65}_{-57}$ K with both terminators having C/O ratios consistent with solar. General circulation models (GCMs) predict temperature differences broadly consistent with the above value and point towards a cloudy morning terminator and a clearer evening terminator. △ Less

Submitted 14 July, 2024; originally announced July 2024.

Comments: Published in Nature at https://www.nature.com/articles/s41586-024-07768-4. All code to produce plots (with data) can be found at https://github.com/nespinoza/wasp39-terminators

Probing Cold-to-Temperate Exoplanetary Atmospheres: The Role of Water Condensation on Surface Identification with JWST

Authors: Ziyu Huang, Xinting Yu, Shang-Min Tsai, Julianne I. Moses, Kazumasa Ohno, Joshua Krissansen-Totton, Xi Zhang, Jonathan Fortney

Abstract: Understanding the surface temperature and interior structure of cold-to-temperate sub-Neptunes is critical for assessing their habitability, yet direct observations are challenging. In this study, we investigate the impact of water condensation on the atmospheric compositions of sub-Neptunes, focusing on the implications for JWST spectroscopic observations. By modeling the atmospheric photochemist… ▽ More Understanding the surface temperature and interior structure of cold-to-temperate sub-Neptunes is critical for assessing their habitability, yet direct observations are challenging. In this study, we investigate the impact of water condensation on the atmospheric compositions of sub-Neptunes, focusing on the implications for JWST spectroscopic observations. By modeling the atmospheric photochemistry of two canonical sub-Neptunes, K2-18 b and LHS 1140 b, both with and without water condensation and with and without thick atmospheres, we demonstrate that water condensation can significantly affect the predicted atmospheric compositions. This effect is driven by oxygen depletion from the condensation of water vapor and primarily manifests as an increase in the C/O ratio within the photochemically active regions of the atmosphere. This change in composition particularly affects planets with thin H2-dominated atmospheres, leading to a transition in dominant nitrogen and carbon carriers from N2 and oxygen-rich species like CO/CO2 towards heavier hydrocarbons and nitriles. While our models do not fully account for the loss mechanisms of these higher-order species, such molecules can go on to form more refractory molecules or hazes. Planets with thin H2-rich atmospheres undergoing significant water condensation are thus likely to exhibit very hazy atmospheres. The relatively flat JWST spectra observed for LHS 1140 b could be consistent with such a scenario, suggesting a shallow surface with extensive water condensation or a high atmospheric C/O ratio. Conversely, the JWST observations of K2-18 b are better aligned with a volatile-rich mini-Neptune with a thick atmosphere. △ Less

Submitted 3 September, 2024; v1 submitted 12 July, 2024; originally announced July 2024.

Comments: 21 pages, 7 figures

Sulphur dioxide in the mid-infrared transmission spectrum of WASP-39b

Authors: Diana Powell, Adina D. Feinstein, Elspeth K. H. Lee, Michael Zhang, Shang-Min Tsai, Jake Taylor, James Kirk, Taylor Bell, Joanna K. Barstow, Peter Gao, Jacob L. Bean, Jasmina Blecic, Katy L. Chubb, Ian J. M. Crossfield, Sean Jordan, Daniel Kitzmann, Sarah E. Moran, Giuseppe Morello, Julianne I. Moses, Luis Welbanks, Jeehyun Yang, Xi Zhang, Eva-Maria Ahrer, Aaron Bello-Arufe, Jonathan Brande , et al. (48 additional authors not shown)

Abstract: The recent inference of sulphur dioxide (SO$_2$) in the atmosphere of the hot ($\sim$1100 K), Saturn-mass exoplanet WASP-39b from near-infrared JWST observations suggests that photochemistry is a key process in high temperature exoplanet atmospheres. This is due to the low ($<$1 ppb) abundance of SO$_2$ under thermochemical equilibrium, compared to that produced from the photochemistry of H$_2$O a… ▽ More The recent inference of sulphur dioxide (SO$_2$) in the atmosphere of the hot ($\sim$1100 K), Saturn-mass exoplanet WASP-39b from near-infrared JWST observations suggests that photochemistry is a key process in high temperature exoplanet atmospheres. This is due to the low ($<$1 ppb) abundance of SO$_2$ under thermochemical equilibrium, compared to that produced from the photochemistry of H$_2$O and H$_2$S (1-10 ppm). However, the SO$_2$ inference was made from a single, small molecular feature in the transmission spectrum of WASP-39b at 4.05 $μ$m, and therefore the detection of other SO$_2$ absorption bands at different wavelengths is needed to better constrain the SO$_2$ abundance. Here we report the detection of SO$_2$ spectral features at 7.7 and 8.5 $μ$m in the 5-12 $μ$m transmission spectrum of WASP-39b measured by the JWST Mid-Infrared Instrument (MIRI) Low Resolution Spectrometer (LRS). Our observations suggest an abundance of SO$_2$ of 0.5-25 ppm (1$σ$ range), consistent with previous findings. In addition to SO$_2$, we find broad water vapour absorption features, as well as an unexplained decrease in the transit depth at wavelengths longer than 10 $μ$m. Fitting the spectrum with a grid of atmospheric forward models, we derive an atmospheric heavy element content (metallicity) for WASP-39b of $\sim$7.1-8.0 $\times$ solar and demonstrate that photochemistry shapes the spectra of WASP-39b across a broad wavelength range. △ Less

Submitted 10 July, 2024; originally announced July 2024.

Comments: Published in Nature

Journal ref: Nature 626, 979-983 (2024)

Searching Accretion-Enhanced Dark Matter Annihilation Signals in the Galactic Centre

Authors: MeiWen Yang, Zhi-Qi Guo, Xiao-Yi Luo, Zhao-Qiang Shen, Zi-Qing Xia, Chih-Ting Lu, Yue-Lin Sming Tsai, Yi-Zhong Fan

Abstract: This study reanalyzes the detection prospects of dark matter (DM) annihilation signals in the Galactic Center, focusing on velocity-dependent dynamics within a spike density near the supermassive black hole (Sgr~A$^{\star}$). We investigate three annihilation processes -- $p$-wave, resonance, and forbidden annihilation -- under semi-relativistic velocities, leveraging gamma-ray data from Fermi and… ▽ More This study reanalyzes the detection prospects of dark matter (DM) annihilation signals in the Galactic Center, focusing on velocity-dependent dynamics within a spike density near the supermassive black hole (Sgr~A$^{\star}$). We investigate three annihilation processes -- $p$-wave, resonance, and forbidden annihilation -- under semi-relativistic velocities, leveraging gamma-ray data from Fermi and DAMPE telescopes. Our analysis integrates a fermionic DM model with an electroweak axion-like particle (ALP) portal, exploring annihilation into two or four photons. Employing a comprehensive six-dimensional integration, we precisely calculate DM-induced gamma-ray fluxes near Sgr~A$^{\star}$, incorporating velocity and positional dependencies in the annihilation cross-section and photon yield spectra. Our findings highlight scenarios of resonance and forbidden annihilation, where the larger ALP-DM-DM coupling constant $C_{aχχ}$ can affect spike density, potentially yielding detectable gamma-ray line spectra within Fermi and DAMPE energy resolution. We set upper limits for $C_{aχχ}$ across these scenarios, offering insights into the detectability and spectral characteristics of DM annihilation signals from the Galactic Center. △ Less

Submitted 24 October, 2024; v1 submitted 9 July, 2024; originally announced July 2024.

Comments: 24 pages, 13 figures

A new lever on exoplanetary B fields: measuring heavy ion velocities

Authors: Arjun B. Savel, Hayley Beltz, Thaddeus D. Komacek, Shang-Min Tsai, Eliza M. -R. Kempton

Abstract: Magnetic fields connect an array of planetary processes, from atmospheric escape to interior convection. Despite their importance, exoplanet magnetic fields are largely unconstrained by both theory and observation. In this Letter, we propose a novel method for constraining the B field strength of hot gas giants: comparing the velocities of heavy ions and neutral gas with high-resolution spectrosco… ▽ More Magnetic fields connect an array of planetary processes, from atmospheric escape to interior convection. Despite their importance, exoplanet magnetic fields are largely unconstrained by both theory and observation. In this Letter, we propose a novel method for constraining the B field strength of hot gas giants: comparing the velocities of heavy ions and neutral gas with high-resolution spectroscopy. The core concept of this method is that ions are directly deflected by magnetic fields. While neutrals are also affected by B fields via friction with field-accelerated ions, ionic gas should be more strongly coupled to the underlying magnetic field than bulk neutral flow. Hence, measuring the difference between the two velocities yields rough constraints on the B field, provided an estimate of the stellar UV flux is known. We demonstrate that heavy ions are particularly well suited for this technique, because they are less likely to be entrained in complex hydrodynamic outflows than their lighter counterparts. We perform a proof-of-concept calculation with Ba II, an ion whose velocity has been repeatedly measured at high confidence with high-resolution spectroscopy. Our work shows that a 10G magnetic field would produce ~ km/s ion--neutral velocity differences at a microbar, whereas a 50G magnetic field would produce ~20km/s velocity difference. With new leverage on magnetic fields, we will be able to investigate magnetic field generation in the extreme edge cases of hot gas giants, with wide-ranging consequences for planetary interior structure, dynamo theory, and habitability. △ Less

Submitted 24 June, 2024; v1 submitted 18 June, 2024; originally announced June 2024.

Comments: Accepted at ApJ Letters. 12 pages; 4 figures; 2 tables

Phase-resolving the absorption signatures of water and carbon monoxide in the atmosphere of the ultra-hot Jupiter WASP-121b with GEMINI-S/IGRINS

Authors: Joost P. Wardenier, Vivien Parmentier, Michael R. Line, Megan Weiner Mansfield, Xianyu Tan, Shang-Min Tsai, Jacob L. Bean, Jayne L. Birkby, Matteo Brogi, Jean-Michel Désert, Siddharth Gandhi, Elspeth K. H. Lee, Colette I. Levens, Lorenzo Pino, Peter C. B. Smith

Abstract: Ultra-hot Jupiters are among the best targets for atmospheric characterization at high spectral resolution. Resolving their transmission spectra as a function of orbital phase offers a unique window into the 3D nature of these objects. In this work, we present three transits of the ultra-hot Jupiter WASP-121b observed with Gemini-S/IGRINS. For the first time, we measure the phase-dependent absorpt… ▽ More Ultra-hot Jupiters are among the best targets for atmospheric characterization at high spectral resolution. Resolving their transmission spectra as a function of orbital phase offers a unique window into the 3D nature of these objects. In this work, we present three transits of the ultra-hot Jupiter WASP-121b observed with Gemini-S/IGRINS. For the first time, we measure the phase-dependent absorption signals of CO and H$_{\text{2}}$O in the atmosphere of an exoplanet, and we find that they are different. While the blueshift of CO increases during the transit, the absorption lines of H$_{\text{2}}$O become less blueshifted with phase, and even show a redshift in the second half of the transit. These measurements reveal the distinct spatial distributions of both molecules across the atmospheres of ultra-hot Jupiters. Also, we find that the H$_{\text{2}}$O signal is absent in the first quarter of the transit, potentially hinting at cloud formation on the evening terminator of WASP-121b. To further interpret the absorption trails of CO and H$_{\text{2}}$O, as well as the Doppler shifts of Fe previously measured with VLT/ESPRESSO, we compare the data to simulated transits of WASP-121b. To this end, we post-processes the outputs of global circulation models with a 3D Monte-Carlo radiative transfer code. Our analysis shows that the atmosphere of WASP-121b is subject to atmospheric drag, as previously suggested by small hotspot offsets inferred from phase-curve observations. Our study highlights the importance of phase-resolved spectroscopy in unravelling the complex atmospheric structure of ultra-hot Jupiters and sets the stage for further investigations into their chemistry and dynamics. △ Less

Submitted 18 July, 2024; v1 submitted 13 June, 2024; originally announced June 2024.

Comments: 24 pages, 16 figures, accepted for publication in PASP

Simultaneous retrieval of orbital phase resolved JWST/MIRI emission spectra of the hot Jupiter WASP-43b: evidence of water, ammonia and carbon monoxide

Authors: Jingxuan Yang, Mark Hammond, Anjali A. A. Piette, Jasmina Blecic, Taylor J. Bell, Patrick G. J. Irwin, Vivien Parmentier, Shang-Min Tsai, Joanna K. Barstow, Nicolas Crouzet, Laura Kreidberg, João M. Mendonça, Jake Taylor, Robin Baeyens, Kazumasa Ohno, Lucas Teinturier, Matthew C. Nixon

Abstract: Spectroscopic phase curves of hot Jupiters measure their emission spectra at multiple orbital phases, thus enabling detailed characterisation of their atmospheres. Precise constraints on the atmospheric composition of these exoplanets offer insights into their formation and evolution. We analyse four phase-resolved emission spectra of the hot Jupiter WASP-43b, generated from a phase curve observed… ▽ More Spectroscopic phase curves of hot Jupiters measure their emission spectra at multiple orbital phases, thus enabling detailed characterisation of their atmospheres. Precise constraints on the atmospheric composition of these exoplanets offer insights into their formation and evolution. We analyse four phase-resolved emission spectra of the hot Jupiter WASP-43b, generated from a phase curve observed with the MIRI/LRS onboard the JWST, to retrieve its atmospheric properties. Using a parametric 2D temperature model and assuming a chemically homogeneous atmosphere within the observed pressure region, we simultaneously fit the four spectra to constrain the abundances of atmospheric constituents, thereby yielding more precise constraints than previous work that analysed each spectrum independently. Our analysis reveals statistically significant evidence of NH3 (4$σ$) in a hot Jupiter's emission spectra for the first time, along with evidence of H2O (6.5$σ$), CO (3.1$σ$), and a non-detection of CH4. With our abundance constraints, we tentatively estimate the metallicity of WASP-43b at 0.6-6.5$\times$solar and its C/O ratio at 0.6-0.9. Our findings offer vital insights into the atmospheric conditions and formation history of WASP-43b by simultaneously constraining the abundances of carbon, oxygen, and nitrogen-bearing species. △ Less

Submitted 5 June, 2024; originally announced June 2024.

Comments: 17 pages, 14 figures, accepted for publication in MNRAS. Comments welcome!

Debris Disks can Contaminate Mid-Infrared Exoplanet Spectra: Evidence for a Circumstellar Debris Disk around Exoplanet Host WASP-39

Authors: Laura Flagg, Alycia J. Weinberger, Taylor J. Bell, Luis Welbanks, Giuseppe Morello, Diana Powell, Jacob L. Bean, Jasmina Blecic, Nicolas Crouzet, Peter Gao, Julie Inglis, James Kirk, Mercedes Lopez-Morales, Karan Molaverdikhani, Nikolay Nikolov, Apurva V. Oza, Benjamin V. Rackham, Seth Redfield, Shang-Min Tsai, Ray Jayawardhana, Laura Kreidberg, Matthew C. Nixon, Kevin B. Stevenson, Jake D. Turner

Abstract: The signal from a transiting planet can be diluted by astrophysical contamination. In the case of circumstellar debris disks, this contamination could start in the mid-infrared and vary as a function of wavelength, which would then change the observed transmission spectrum for any planet in the system. The MIRI/LRS WASP-39b transmission spectrum shows an unexplained dip starting at $\sim$10 $μ$m t… ▽ More The signal from a transiting planet can be diluted by astrophysical contamination. In the case of circumstellar debris disks, this contamination could start in the mid-infrared and vary as a function of wavelength, which would then change the observed transmission spectrum for any planet in the system. The MIRI/LRS WASP-39b transmission spectrum shows an unexplained dip starting at $\sim$10 $μ$m that could be caused by astrophysical contamination. The spectral energy distribution displays excess flux at similar levels to that which are needed to create the dip in the transmission spectrum. In this article, we show that this dip is consistent with the presence of a bright circumstellar debris disk, at a distance of $>$2 au. We discuss how a circumstellar debris disk like that could affect the atmosphere of WASP-39b. We also show that even faint debris disks can be a source of contamination in MIRI exoplanet spectra. △ Less

Submitted 4 June, 2024; originally announced June 2024.

Comments: accepted to ApJL

Relic density and temperature evolution of a light dark sector

Authors: Xin-Chen Duan, Raymundo Ramos, Yue-Lin Sming Tsai

Abstract: We have developed a set of four fully coupled Boltzmann equations to precisely determine the relic density and temperature of dark matter by including three distinct sectors: dark matter, light scalar, and standard model sectors. The intricacies of heat transfer between dark matter (DM) and the standard model sector through a light scalar particle are explored, inspired by stringent experimental c… ▽ More We have developed a set of four fully coupled Boltzmann equations to precisely determine the relic density and temperature of dark matter by including three distinct sectors: dark matter, light scalar, and standard model sectors. The intricacies of heat transfer between dark matter (DM) and the standard model sector through a light scalar particle are explored, inspired by stringent experimental constraints on the scalar-Higgs mixing angle and the DM-scalar coupling. Three distinct sectors emerge prior to DM freeze-out, requiring fully coupled Boltzmann equations to accurately compute relic density. Investigation of forbidden, resonance, and secluded DM scenarios demonstrates significant deviations between established methods and the novel approach with fully coupled Boltzmann equations. Despite increased computational demands, this emphasizes the need for improved precision in relic density calculations, underlining the importance of incorporating these equations in comprehensive analyses. △ Less

Submitted 24 September, 2024; v1 submitted 18 April, 2024; originally announced April 2024.

Comments: 40 pages, 10 figures. Matches PRD accepted version

Journal ref: Phys.Rev.D110: 063535, 2024

Biogenic sulfur gases as biosignatures on temperate sub-Neptune waterworlds

Authors: Shang-Min Tsai, Hamish Innes, Nicholas F. Wogan, Edward W. Schwieterman

Abstract: Theoretical predictions and observational data indicate a class of sub-Neptune exoplanets may have water-rich interiors covered by hydrogen-dominated atmospheres. Provided suitable climate conditions, such planets could host surface liquid oceans. Motivated by recent JWST observations of K2-18 b, we self-consistently model the photochemistry and potential detectability of biogenic sulfur gases in… ▽ More Theoretical predictions and observational data indicate a class of sub-Neptune exoplanets may have water-rich interiors covered by hydrogen-dominated atmospheres. Provided suitable climate conditions, such planets could host surface liquid oceans. Motivated by recent JWST observations of K2-18 b, we self-consistently model the photochemistry and potential detectability of biogenic sulfur gases in the atmospheres of temperate sub-Neptune waterworlds for the first time. On Earth today, organic sulfur compounds produced by marine biota are rapidly destroyed by photochemical processes before they can accumulate to significant levels. Domagal-Goldman et al. (2011) suggest that detectable biogenic sulfur signatures could emerge in Archean-like atmospheres with higher biological production or low UV flux. In this study, we explore biogenic sulfur across a wide range of biological fluxes and stellar UV environments. Critically, the main photochemical sinks are absent on the nightside of tidally locked planets. To address this, we further perform experiments with a 3D GCM and a 2D photochemical model (VULCAN 2D (Tsai et al. 2024)) to simulate the global distribution of biogenic gases to investigate their terminator concentrations as seen via transmission spectroscopy. Our models indicate that biogenic sulfur gases can rise to potentially detectable levels on hydrogen-rich waterworlds, but only for enhanced global biosulfur flux ($\gtrsim$20 times modern Earth's flux). We find that it is challenging to identify DMS at 3.4 $μm$ where it strongly overlaps with CH$_4$, whereas it is more plausible to detect DMS and companion byproducts, ethylene (C$_2$H$_4$) and ethane (C$_2$H$_6$), in the mid-infrared between 9 and 13 $μm$. △ Less

Submitted 26 March, 2024; v1 submitted 21 March, 2024; originally announced March 2024.

Comments: 9 pages, 4 figures, accepted for publication in ApJL

Light Thermal Dark Matter Beyond $p$-Wave Annihilation in Minimal Higgs Portal Model

Authors: Yu-Tong Chen, Shigeki Matsumoto, Tian-Peng Tang, Yue-Lin Sming Tsai, Lei Wu

Abstract: This study explores a minimal renormalizable dark matter (DM) model, incorporating a sub-GeV Majorana DM and a singlet scalar particle $φ$. Using scalar and pseudo-scalar interactions (couplings $c_s$ and $c_p$), we investigate implications for DM detection, considering $s$-wave, $p$-wave, and combined ($s$+$p$ wave) contributions in DM annihilation cross-section, as well as loop-correction contri… ▽ More This study explores a minimal renormalizable dark matter (DM) model, incorporating a sub-GeV Majorana DM and a singlet scalar particle $φ$. Using scalar and pseudo-scalar interactions (couplings $c_s$ and $c_p$), we investigate implications for DM detection, considering $s$-wave, $p$-wave, and combined ($s$+$p$ wave) contributions in DM annihilation cross-section, as well as loop-correction contributions to DM-nucleon elastic scattering. Identifying a broad parameter space ($10 \,\rm{MeV} < m_χ\lesssim m_φ$) within the $2σ$ allowed region, we explore scenarios ($\left|c_s\right|\gg \left|c_p\right|$, $\left|c_s\right|\ll \left|c_p\right|$, and $\left|c_s\right|\approx \left|c_p\right|$). We find that (i) a non-zero pseudo-scalar coupling alleviates direct detection constraints as a comparison with the previous pure scalar coupling case; (ii) CMB observations set stringent limits on pseudo-scalar interaction dominant cases, making $s$-wave annihilation viable only for $m_χ>1\,\rm{GeV}$; (iii) the preferred $φ$-resonance region can be tested in the future indirect detection experiments, such as e-ASTROGAM. △ Less

Submitted 30 May, 2024; v1 submitted 5 March, 2024; originally announced March 2024.

Comments: 35 pages, 4 figures

Modeling the Progenitor Stars of Observed IIP Supernovae

Authors: Kai-An You, Ke-Jung Chen, Yen-Chen Pan, Sung-Han Tsai, Po-Sheng Ou

Abstract: Type IIP supernovae (SNe IIP) are thought to originate from the explosion of massive stars > 10 Msun. Their luminosity is primarily powered by the explosion energy and the radioactive decay energy of 56Co, with the photosphere location regulated by hydrogen recombination. However, the physical connections between SNe IIP and their progenitor stars remain unclear. This paper presents a comprehensiv… ▽ More Type IIP supernovae (SNe IIP) are thought to originate from the explosion of massive stars > 10 Msun. Their luminosity is primarily powered by the explosion energy and the radioactive decay energy of 56Co, with the photosphere location regulated by hydrogen recombination. However, the physical connections between SNe IIP and their progenitor stars remain unclear. This paper presents a comprehensive study of SNe IIP and their progenitor stars by using the one-dimensional stellar evolution code, MESA. Our model grids consider the effects of stellar metallicity, mass, and rotation in the evolution of massive stars, as well as explosion energy and 56Ni production in modeling supernovae. To elucidate the observed SNe IIP and their origins, we compare their light curves (LCs) with our models. Furthermore, we investigate the impact of stellar parameters on LCs by considering stellar mass metallicity, rotation, explosion energy, and 56Ni production. We find that more massive stars exhibit longer plateaus due to increased photon diffusion time caused by massive ejecta. Higher metallicity leads to increased opacity and mass loss of progenitor stars. Rapid rotation affects internal stellar structures, enhancing convective mixing and mass loss, potentially affecting the plateau's brightness and duration. Higher explosion energy results in brighter but shorter plateaus due to faster-moving ejecta. 56Ni mass affects late-time luminosity and plateau duration, with larger masses leading to slower declines. △ Less

Submitted 27 May, 2024; v1 submitted 29 February, 2024; originally announced February 2024.

Comments: 22 pages, 7 figures. Accepted for publication in ApJ

Weak Lensing Constraints on Dark Matter-Baryon Interactions with $N$-Body Simulations and Machine Learning

Authors: Chi Zhang, Lei Zu, Hou-Zun Chen, Yue-Lin Sming Tsai, Yi-Zhong Fan

Abstract: We investigate the elastic scattering cross section between dark matter and protons using the DES Year 3 weak lensing data. This scattering induces a dark acoustic oscillation structure in the matter power spectra. To address non-linear effects at low redshift, we utilize principal component analysis alongside a limited set of $N$-body simulations, improving the reliability of our matter power spe… ▽ More We investigate the elastic scattering cross section between dark matter and protons using the DES Year 3 weak lensing data. This scattering induces a dark acoustic oscillation structure in the matter power spectra. To address non-linear effects at low redshift, we utilize principal component analysis alongside a limited set of $N$-body simulations, improving the reliability of our matter power spectrum prediction. We further perform a robust Markov Chain Monte Carlo analysis to derive the upper bounds on the DM-proton elastic scattering cross-section, assuming different velocity dependencies. Our results, presented as the first Frequentist upper limits, are compared with the ones obtained by Bayesian approach. Compared with the upper limits derived from the Planck cosmic microwave background data, our findings from DES Year 3 data exhibit improvements of up to a factor of five. In addition, we forecast the future sensitivities of the China Space Station Telescope, the upcoming capabilities of this telescope could improve the current limits by approximately one order of magnitude. △ Less

Submitted 6 August, 2024; v1 submitted 29 February, 2024; originally announced February 2024.

Comments: 24 pages, 11 figures, published in JCAP

Journal ref: JCAP08(2024)003

JWST observations of K2-18b can be explained by a gas-rich mini-Neptune with no habitable surface

Authors: Nicholas F. Wogan, Natasha E. Batalha, Kevin Zahnle, Joshua Krissansen-Totton, Shang-Min Tsai, Renyu Hu

Abstract: JWST recently measured the transmission spectrum of K2-18b, a habitable-zone sub-Neptune exoplanet, detecting CH$_4$ and CO$_2$ in its atmosphere. The discovery paper argued the data are best explained by a habitable "Hycean" world, consisting of a relatively thin H$_2$-dominated atmosphere overlying a liquid water ocean. Here, we use photochemical and climate models to simulate K2-18b as both a H… ▽ More JWST recently measured the transmission spectrum of K2-18b, a habitable-zone sub-Neptune exoplanet, detecting CH$_4$ and CO$_2$ in its atmosphere. The discovery paper argued the data are best explained by a habitable "Hycean" world, consisting of a relatively thin H$_2$-dominated atmosphere overlying a liquid water ocean. Here, we use photochemical and climate models to simulate K2-18b as both a Hycean planet and a gas-rich mini-Neptune with no defined surface. We find that a lifeless Hycean world is hard to reconcile with the JWST observations because photochemistry only supports $< 1$ part-per-million CH$_4$ in such an atmosphere while the data suggest about $\sim 1\%$ of the gas is present. Sustaining %-level CH$_4$ on a Hycean K2-18b may require the presence of a methane-producing biosphere, similar to microbial life on Earth $\sim 3$ billion years ago. On the other hand, we predict that a gas-rich mini-Neptune with $100 \times$ solar metallicity should have 4% CH$_4$ and nearly 0.1% CO$_2$, which are compatible with the JWST data. The CH$_4$ and CO$_2$ are produced thermochemically in the deep atmosphere and mixed upward to the low pressures sensitive to transmission spectroscopy. The model predicts H$_2$O, NH$_3$ and CO abundances broadly consistent with the non-detections. Given the additional obstacles to maintaining a stable temperate climate on Hycean worlds due to H$_2$ escape and potential supercriticality at depth, we favor the mini-Neptune interpretation because of its relative simplicity and because it does not need a biosphere or other unknown source of methane to explain the data. △ Less

Submitted 3 February, 2024; v1 submitted 19 January, 2024; originally announced January 2024.

Comments: Accepted for publication at ApJL

Dynamically coupled kinetic chemistry in brown dwarf atmospheres -- II. Cloud and chemistry connections in directly imaged sub-Jupiter exoplanets

Authors: Elspeth K. H. Lee, Xianyu Tan, Shang-Min Tsai

Abstract: With JWST slated to gain high fidelity time dependent data on brown dwarf atmospheres, it is highly anticipated to do the same for directly imaged, sub-Jupiter exoplanets. With this new capability, the need for a full 3D understanding to explain spectral features and their time dependence is becoming a vital aspect for consideration. To examine the atmospheric properties of directly imaged sub-Jup… ▽ More With JWST slated to gain high fidelity time dependent data on brown dwarf atmospheres, it is highly anticipated to do the same for directly imaged, sub-Jupiter exoplanets. With this new capability, the need for a full 3D understanding to explain spectral features and their time dependence is becoming a vital aspect for consideration. To examine the atmospheric properties of directly imaged sub-Jupiter exoplanets, we use the three dimensional Exo-FMS general circulation model (GCM) to simulate a metal enhanced generic young sub-Jupiter object. We couple Exo-FMS to a kinetic chemistry scheme, a tracer based cloud formation scheme and a spectral radiative-transfer model to take into account the chemical and cloud feedback on the atmospheric thermochemical and dynamical properties. Our results show a highly complex feedback between clouds and chemistry onto the 3D temperature structure of the atmosphere, bringing about latitudinal differences and inducing time-dependent stormy features at photospheric pressures. This suggests a strong connection and feedback between the spatial cloud coverage and chemical composition of the atmosphere, with the temperature changes and dynamical motions induced by cloud opacity and triggered convection feedback driving chemical species behaviour. In addition, we also produce synthetic latitude dependent and time dependent spectra of our model to investigate atmospheric variability and periodicity in commonly used photometric bands. Overall, our efforts put the included physics in 3D simulations of exoplanets on par with contemporary 1D radiative-convective equilibrium modelling. △ Less

Submitted 15 February, 2024; v1 submitted 28 November, 2023; originally announced November 2023.

Comments: Accepted MNRAS (Feb 2024), 17 pages

Global Chemical Transport on Hot Jupiters: Insights from 2D VULCAN photochemical model

Authors: Shang-Min Tsai, Vivien Parmentier, João M. Mendonça, Xianyu Tan, Russell Deitrick, Mark Hammond, Arjun B. Savel, Xi Zhang, Raymond T. Pierrehumbert, Edward W. Schwieterman

Abstract: The atmospheric dynamics of tidally-locked hot Jupiters is characterized by strong equatorial winds. Understanding the interaction between global circulation and chemistry is crucial in atmospheric studies and interpreting observations. Two-dimensional (2D) photochemical transport models shed light on how the atmospheric composition depends on circulation. In this paper, we introduce the 2D photoc… ▽ More The atmospheric dynamics of tidally-locked hot Jupiters is characterized by strong equatorial winds. Understanding the interaction between global circulation and chemistry is crucial in atmospheric studies and interpreting observations. Two-dimensional (2D) photochemical transport models shed light on how the atmospheric composition depends on circulation. In this paper, we introduce the 2D photochemical (horizontal and vertical) transport model, VULCAN 2D, which improves on the pseudo-2D approaches by allowing for non-uniform zonal winds. We extensively validate our VULCAN 2D with analytical solutions and benchmark comparisons. Applications to HD 189733 b and HD 209458 b reveal a transition in mixing regimes: horizontal transport predominates below $\sim$0.1 mbar while vertical mixing is more important at higher altitudes above 0.1 mbar. Motivated by the previously inferred carbon-rich atmosphere, we find that HD 209458 b with super-solar carbon-to-oxygen ratio (C/O) exhibits pronounced C$_2$H$_4$ absorption on the morning limb but not on the evening limb, owing to horizontal transport from the nightside. We discuss when a pseudo-2D approach is a valid assumption and its inherent limitations. Finally, we demonstrate the effect of horizontal transport in transmission observations and its impact on the morning-evening limb asymmetry with synthetic spectra, highlighting the need to consider global transport when interpreting exoplanet atmospheres. △ Less

Submitted 25 March, 2024; v1 submitted 26 October, 2023; originally announced October 2023.

Comments: 19 pages, 20 figures, published in ApJ

Journal ref: Tsai et al. (2024), ApJ, 963, 41

Inelastic Scattering of Dark Matter with Heavy Cosmic Rays

Authors: Keyu Lu, Yue-Lin Sming Tsai, Qiang Yuan, Le Zhang

Abstract: We investigate the impact of inelastic collisions between dark matter (DM) and heavy cosmic ray (CR) nuclei on CR propagation. We approximate the fragmentation cross-sections for DM-CR collisions using collider-measured proton-nuclei scattering cross-sections, allowing us to assess how these collisions affect the spectra of CR Boron and Carbon. We derive new CR spectra from DM-CR collisions by inc… ▽ More We investigate the impact of inelastic collisions between dark matter (DM) and heavy cosmic ray (CR) nuclei on CR propagation. We approximate the fragmentation cross-sections for DM-CR collisions using collider-measured proton-nuclei scattering cross-sections, allowing us to assess how these collisions affect the spectra of CR Boron and Carbon. We derive new CR spectra from DM-CR collisions by incorporating their cross-sections into the source terms and solving the diffusion equation for the complete network of reactions involved in generating secondary species. In a specific example with a coupling strength of $b_χ=0.1$ and a DM mass of $m_χ=0.1$ GeV, considering a simplified scenario where DM interacts exclusively with Oxygen, a notable modification in the Boron-to-Carbon spectrum due to the DM-CR interaction is observed. Particularly, the peak within the spectrum, spanning from $0.1$ GeV to $10$ GeV, experiences an enhancement of approximately 1.5 times. However, in a more realistic scenario where DM particles interact with all CRs, this peak can be amplified to twice its original value.Utilizing the latest data from AMS-02 and DAMPE on the Boron-to-Carbon ratio, we estimate a 95\% upper limit for the effective inelastic cross-section of DM-proton as a function of DM mass. Our findings reveal that at $m_χ\simeq 2$ MeV, the effective inelastic cross-section between DM and protons must be less than $\mathcal{O}(10^{-32})~{\rm cm}^2$. △ Less

Submitted 7 June, 2024; v1 submitted 19 October, 2023; originally announced October 2023.

Comments: 19 pages, 8 figures

Journal ref: Research in Astronomy and Astrophysics 24, 065007 (2024)

Primordial magnetic field as a common solution of nanohertz gravitational waves and the Hubble tension

Authors: Yao-Yu Li, Chi Zhang, Ziwei Wang, Ming-Yang Cui, Yue-Lin Sming Tsai, Qiang Yuan, Yi-Zhong Fan

Abstract: The origin of interstellar and intergalactic magnetic fields remains largely unknown. One possibility is that they are related to the primordial magnetic fields (PMFs) produced by, for instance, the phase transitions of the early Universe. In this paper, we show that the PMF-induced turbulence generated at around the QCD phase transition epoch--the characteristic magnetic field strength… ▽ More The origin of interstellar and intergalactic magnetic fields remains largely unknown. One possibility is that they are related to the primordial magnetic fields (PMFs) produced by, for instance, the phase transitions of the early Universe. In this paper, we show that the PMF-induced turbulence generated at around the QCD phase transition epoch--the characteristic magnetic field strength $B_{\rm ch}^* \sim \mathcal{O}(1)~\rm{μG}$ and coherent length scale $\ell_{\rm ch}^* \sim \mathcal{O}(1)~\rm{pc}$--can naturally accommodate nanohertz gravitational waves reported by pulsar timing array (PTA) collaborations. Moreover, the evolution of the PMFs to the recombination era with the form of $B_{\rm ch}\sim \ell_{\rm ch}^{-α}$ can induce baryon density inhomogeneities, alter the recombination history, and alleviate the tension of the Hubble parameter $H_0$ and the matter clumpiness parameter $S_8$ between early- and late-time measurements for $0.88\leq α\leq 1.17$ (approximate 95\% credible region based on three PTA likelihoods). The further evolved PMFs may account for the $\sim {\cal O}(10^{-16})$ Gauss extragalactic magnetic field inferred with GRB 221009A. △ Less

Submitted 4 March, 2024; v1 submitted 29 June, 2023; originally announced June 2023.

Comments: 7 pages, 3 figures, 1 table

Journal ref: Phys. Rev. D 109, 043538 (2024)

Mirror QCD phase transition as the origin of the nanohertz Stochastic Gravitational-Wave Background

Authors: Lei Zu, Chi Zhang, Yao-Yu Li, Yu-Chao Gu, Yue-Lin Sming Tsai, Yi-Zhong Fan

Abstract: Several Pulsar Timing Array (PTA) collaborations have recently provided strong evidence for a nHz Stochastic Gravitational-Wave Background (SGWB). Here we investigate the implications of a first-order phase transition occurring within the early universe's dark quantum chromodynamics (dQCD) epoch, specifically within the framework of the mirror twin Higgs dark sector model. Our analysis indicates a… ▽ More Several Pulsar Timing Array (PTA) collaborations have recently provided strong evidence for a nHz Stochastic Gravitational-Wave Background (SGWB). Here we investigate the implications of a first-order phase transition occurring within the early universe's dark quantum chromodynamics (dQCD) epoch, specifically within the framework of the mirror twin Higgs dark sector model. Our analysis indicates a distinguishable SGWB signal originating from this phase transition, which can explain the measurements obtained by PTAs. Remarkably, a significant portion of the parameter space for the SGWB signal also effectively resolves the existing tensions in both the $H_0$ and $S_8$ measurements in Cosmology. This intriguing correlation suggests a possible common origin of these three phenomena for $0.2 < ΔN_{\rm eff} < 0.5$, where the mirror dark matter component constitutes about $30\%$ of the total dark matter abundance. Next generation CMB experiment such as CMB-S4 is able to test this parameter region. △ Less

Submitted 2 July, 2024; v1 submitted 29 June, 2023; originally announced June 2023.

Comments: 7 pages, 4 figures

Journal ref: Sci.Bull. 69 (2024) 741-746

R-process beta-decay neutrino flux from binary neutron star mergers and collapsars

Authors: Yu An, Meng-Ru Wu, Gang Guo, Yue-Lin Sming Tsai, Shih-Jie Huang, Yi-Zhong Fan

Abstract: This study investigates the antineutrinos production by $β$-decay of $r$-process nuclei in two astrophysical sites that are capable of producing gamma-ray bursts (GRBs): binary neutron star mergers (BNSMs) and collapsars, which are promising sites for heavy element nucleosynthesis. We employ a simplified method to compute the $β$-decay $\barν_e$ energy spectrum and consider a number of different r… ▽ More This study investigates the antineutrinos production by $β$-decay of $r$-process nuclei in two astrophysical sites that are capable of producing gamma-ray bursts (GRBs): binary neutron star mergers (BNSMs) and collapsars, which are promising sites for heavy element nucleosynthesis. We employ a simplified method to compute the $β$-decay $\barν_e$ energy spectrum and consider a number of different representative thermodynamic trajectories for $r$-process simulations, each with four sets of $Y_e$ distribution. The time evolution of the $\barν_e$ spectrum is derived for both the dynamical ejecta and the disk wind for BNSMs and collapsar outflow, based on approximated mass outflow rates. Our results show that the $\barν_e$ has an average energy of approximately 3 to 9~MeV, with a high energy tail of up to 20 MeV. The $\barν_e$ flux evolution is primarily determined by the outflow duration, and can thus remain large for $\mathcal{O}(10)$~s and $\mathcal{O}(100)$~s for BNSMs and collapsars, respectively. For a single merger or collapsar at 40~Mpc, the $\barν_e$ flux is $\mathcal{O}(10-100)$~cm$^{-2}$~s$^{-1}$, indicating a possible detection horizon up to $0.1-1$~Mpc for Hyper-Kamiokande. We also estimate their contributions to the diffuse $\barν_e$ background, and find that both sources should only contribute subdominantly to the diffuse background when compared to that expected from core-collapse supernovae. △ Less

Submitted 15 December, 2023; v1 submitted 13 June, 2023; originally announced June 2023.

Comments: 14 pages, 8 figures

Journal ref: Phys. Rev. D 108, 123038 (2023)

Dynamically coupled kinetic chemistry in brown dwarf atmospheres I. Performing global scale kinetic modelling

Authors: Elspeth K. H. Lee, Xianyu Tan, Shang-Min Tsai

Abstract: The atmospheres of brown dwarfs have been long observed to exhibit a multitude of non-equilibrium chemical signatures and spectral variability across the L, T and Y spectral types. We aim to investigate the link between the large-scale 3D atmospheric dynamics and time-dependent chemistry in the brown dwarf regime, and to assess its impact on spectral variability. We couple the miniature kinetic ch… ▽ More The atmospheres of brown dwarfs have been long observed to exhibit a multitude of non-equilibrium chemical signatures and spectral variability across the L, T and Y spectral types. We aim to investigate the link between the large-scale 3D atmospheric dynamics and time-dependent chemistry in the brown dwarf regime, and to assess its impact on spectral variability. We couple the miniature kinetic chemistry module `mini-chem' to the Exo-FMS general circulation model (GCM). We then perform a series of idealised brown dwarf regime atmospheric models to investigate the dynamical 3D chemical structures produced by our simulations. The GCM output is post-processed using a 3D radiative-transfer model to investigate hemisphere-dependent spectral signatures and rotational variability. Our results show the expected strong non-equilibrium chemical behaviour brought on by vertical mixing as well as global spacial variations due to zonal flows. Chemical species are generally globally homogenised, showing variations of $\pm$10\% or less, dependent on pressure level, and follow the dynamical structures present in the atmosphere. However, we find localised storm regions and eddies can show higher contrasts, up to $\pm$100\%, in mixing ratio compared to the background global mean. This initial study represents another step in understanding the connection between three-dimensional atmospheric flows in brown dwarfs and their rich chemical inventories. △ Less

Submitted 6 June, 2023; originally announced June 2023.

Comments: MNRAS Accepted: 5 June 2023