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Globules and pillars in Cygnus X III. Herschel and upGREAT/SOFIA far-infrared spectroscopy of the globule IRAS 20319+3958 inCygnus X
Authors:
N. Schneider,
M. Roellig,
E. T. Polehampton,
F. Comeron,
A. A. Djupvik,
Z. Makai,
C. Buchbender,
R. Simon,
S. Bontemps,
R. Guesten,
G. White,
Y. Okada,
A. Parikka,
N. Rothbart
Abstract:
IRAS 20319+3958 in Cygnus X South is a rare example of a free-floating globule (mass ~240 Msun, length ~1.5 pc) with an internal HII region created by the stellar feedback of embedded intermediate-mass stars, in particular, one Herbig Be star. Here, we present a Herschel/HIFI CII 158 mu map of the whole globule and a large set of other FIR lines (mid-to high-J CO lines observed with Herschel/PACS…
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IRAS 20319+3958 in Cygnus X South is a rare example of a free-floating globule (mass ~240 Msun, length ~1.5 pc) with an internal HII region created by the stellar feedback of embedded intermediate-mass stars, in particular, one Herbig Be star. Here, we present a Herschel/HIFI CII 158 mu map of the whole globule and a large set of other FIR lines (mid-to high-J CO lines observed with Herschel/PACS and SPIRE, the OI 63 mu line and the CO 16-15 line observed with upGREAT on SOFIA), covering the globule head and partly a position in the tail. The CII map revealed that the whole globule is probably rotating. Highly collimated, high-velocity CII emission is detected close to the Herbig Be star. We performed a PDR analysis using the KOSMA-tau PDR code for one position in the head and one in the tail. The observed FIR lines in the head can be reproduced with a two-component model: an extended, non-clumpy outer PDR shell and a clumpy, dense, and thin inner PDR layer, representing the interface between the HII region cavity and the external PDR. The modelled internal UV field of ~2500 Go is similar to what we obtained from the Herschel FIR fluxes, but lower than what we estimated from the census of the embedded stars. External illumination from the ~30 pc distant Cyg OB2 cluster, producing an UV field of ~150-600 G0 as an upper limit, is responsible for most of the CII emission. For the tail, we modelled the emission with a non-clumpy component, exposed to a UV-field of around 140 Go.
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Submitted 24 August, 2021;
originally announced August 2021.
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The Galactic HII Region Luminosity Function at Radio and Infrared Wavelengths
Authors:
J. L. Mascoop,
L. D. Anderson,
Trey. V. Wenger,
Z. Makai,
W. P. Armentrout,
Dana. S. Balser,
T. M. Bania
Abstract:
The Galactic HII region luminosity function (LF) is an important metric for understanding global star formation properties of the Milky Way, but only a few studies have been done and all use relatively small numbers of HII regions. We use a sample of 797 first Galactic quadrant HII regions compiled from the WISE Catalog of Galactic HII Regions to examine the form of the LF at multiple infrared and…
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The Galactic HII region luminosity function (LF) is an important metric for understanding global star formation properties of the Milky Way, but only a few studies have been done and all use relatively small numbers of HII regions. We use a sample of 797 first Galactic quadrant HII regions compiled from the WISE Catalog of Galactic HII Regions to examine the form of the LF at multiple infrared and radio wavelengths. Our sample is statistically complete for all regions powered by single stars of type O9.5V and earlier. We fit the LF at each wavelength with single and double power laws. Averaging the results from all wavelengths, the mean of the best-fit single power law index is $\langleα\rangle=-1.75\,\pm\,0.01$. The mean best-fit double power law indices are $\langleα_1\rangle=-1.40\,\pm\,0.03$ and $\langleα_2\rangle=-2.33\,\pm\,0.04$. We conclude that neither a single nor a double power law is strongly favored over the other. The LFs show some variation when we separate the HII region sample into subsets by heliocentric distance, physical size, Galactocentric radius, and location relative to the spiral arms, but blending individual HII regions into larger complexes does not change the value of the power law indices of the best-fit LF models. The consistency of the power law indices across multiple wavelengths suggests that the LF is independent of wavelength. This implies that infrared and radio tracers can be employed in place of H$α$.
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Submitted 17 February, 2021;
originally announced February 2021.
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The Origin of [CII] 158um Emission toward the HII Region Complex S235
Authors:
L. D. Anderson,
Z. Makai,
M. Luisi,
M. Andersen,
D. Russeil,
M. R. Samal,
N. Schneider,
P. Tremblin,
A. Zavagno,
M. S. Kirsanova,
V. Ossenkopf-Okada,
A. M. Sobolev
Abstract:
Although the 2P3/2-2P1/2 transition of [CII] at 158um is known to be an excellent tracer of active star formation, we still do not have a complete understanding of where within star formation regions the emission originates. Here, we use SOFIA upGREAT observations of [CII] emission toward the HII region complex Sh2-235 (S235) to better understand in detail the origin of [CII] emission. We compleme…
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Although the 2P3/2-2P1/2 transition of [CII] at 158um is known to be an excellent tracer of active star formation, we still do not have a complete understanding of where within star formation regions the emission originates. Here, we use SOFIA upGREAT observations of [CII] emission toward the HII region complex Sh2-235 (S235) to better understand in detail the origin of [CII] emission. We complement these data with a fully-sampled Green Bank Telescope radio recombination line map tracing the ionized hydrogen gas. About half of the total [CII] emission associated with S235 is spatially coincident with ionized hydrogen gas, although spectroscopic analysis shows little evidence that this emission is coming from the ionized hydrogen volume. Velocity-integrated [CII] intensity is strongly correlated with WISE 12um intensity across the entire complex, indicating that both trace ultra-violet radiation fields. The 22um and radio continuum intensities are only correlated with [CII] intensity in the ionized hydrogen portion of the S235 region and the correlations between the [CII] and molecular gas tracers are poor across the region. We find similar results for emission averaged over a sample of external galaxies, although the strength of the correlations is weaker. Therefore, although many tracers are correlated with the strength of [CII] emission, only WISE 12um emission is correlated on small-scales of the individual HII region S235 and also has a decent correlation at the scale of entire galaxies. Future studies of a larger sample of Galactic HII regions would help to determine whether these results are truly representative.
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Submitted 26 April, 2019;
originally announced April 2019.
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The Infrared and Radio Fluxes Densities of Galactic HII Regions
Authors:
Z. Makai,
L. D. Anderson,
J. L. Mascoop,
B. Johnstone
Abstract:
We derive infrared and radio flux densities of all ~1000 known Galactic HII regions in the Galactic longitude range 17.5 < l < 65 degree. Our sample comes from the Wide-Field Infrared Survey Explorer (WISE) catalog of Galactic \hii regions \citep{anderson2014}. We compute flux densities at six wavelengths in the infrared (GLIMPSE 8 microns, WISE 12 microns and 22 microns, MIPSGAL 24 microns, and H…
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We derive infrared and radio flux densities of all ~1000 known Galactic HII regions in the Galactic longitude range 17.5 < l < 65 degree. Our sample comes from the Wide-Field Infrared Survey Explorer (WISE) catalog of Galactic \hii regions \citep{anderson2014}. We compute flux densities at six wavelengths in the infrared (GLIMPSE 8 microns, WISE 12 microns and 22 microns, MIPSGAL 24 microns, and Hi-GAL 70 microns and 160 microns) and two in the radio (MAGPIS 20 cm and VGPS 21 cm). All HII region infrared flux densities are strongly correlated with their ~20 cm flux densities. All HII regions used here, regardless of physical size or Galactocentric radius, have similar infrared to radio flux density ratios and similar infrared colors, although the smallest regions ($r<1\,$pc), have slightly elevated IR to radio ratios. The colors $\log_{10}(F_{24 micron}/F_{12 micron}) \ge 0$ and $\log_{10}(F_{70 micron}/F_{12 micron}) \ge 1.2$, and $\log_{10}(F_{24 micron}/F_{12 micron}) \ge 0$ and $\log_{10}(F_{160 micron}/F_{70 micron}) \le 0.67$ reliably select HII regions, independent of size. The infrared colors of ~22$\%$ of HII regions, spanning a large range of physical sizes, satisfy the IRAS color criteria of \citet{wood1989} for HII regions, after adjusting the criteria to the wavelengths used here. Since these color criteria are commonly thought to select only ultra-compact HII regions, this result indicates that the true ultra-compact HII region population is uncertain. Comparing with a sample of IR color indices from star-forming galaxies, HII regions show higher $\log_{10}(F_{70 micron}/F_{12 micron})$ ratios. We find a weak trend of decreasing infrared to ~20 cm flux density ratios with increasing $R_{gal}$, in agreement with previous extragalactic results, possibly indicating a decreased dust abundance in the outer Galaxy.
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Submitted 17 August, 2017;
originally announced August 2017.
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C$_2$H observations toward the Orion Bar
Authors:
Z. Nagy,
V. Ossenkopf,
F. F. S. Van der Tak,
A. Faure,
Z. Makai,
E. A. Bergin
Abstract:
C$_2$H is one of the first radicals to be detected in the interstellar medium. Its higher rotational transitions have recently become available with the Herschel Space Observatory. We aim to constrain the physical parameters of the C$_2$H emitting gas toward the Orion Bar. We analyse the C$_2$H line intensities measured toward the Orion Bar CO$^+$ Peak and Herschel/HIFI maps of C$_2$H, CH, and HCO…
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C$_2$H is one of the first radicals to be detected in the interstellar medium. Its higher rotational transitions have recently become available with the Herschel Space Observatory. We aim to constrain the physical parameters of the C$_2$H emitting gas toward the Orion Bar. We analyse the C$_2$H line intensities measured toward the Orion Bar CO$^+$ Peak and Herschel/HIFI maps of C$_2$H, CH, and HCO$^+$, and a NANTEN map of [CI]. We interpret the observed C$_2$H emission using radiative transfer and PDR models. Five rotational transitions of C$_2$H have been detected in the HIFI frequency range toward the CO$^+$ peak. A single component rotational diagram gives a rotation temperature of ~64 K and a beam-averaged C$_2$H column density of 4$\times$10$^{13}$ cm$^{-2}$. The measured transitions cannot be explained by any single parameter model. According to a non-LTE model, most of the C$_2$H column density produces the lower-$N$ C$_2$H transitions and traces a warm ($T_{\rm{kin}}$ ~ 100-150 K) and dense ($n$(H$_2$)~10$^5$-10$^6$ cm$^{-3}$) gas. A small fraction of the C$_2$H column density is required to reproduce the intensity of the highest-$N$ transitions ($N$=9-8 and N=10-9) originating from a high density ($n$(H$_2$)~5$\times$10$^6$ cm$^{-3}$) hot ($T_{\rm{kin}}$ ~ 400 K) gas. The total beam-averaged C$_2$H column density in the model is 10$^{14}$ cm$^{-2}$. Both the non-LTE radiative transfer model and a simple PDR model representing the Orion Bar with a plane-parallel slab of gas and dust suggest, that C$_2$H cannot be described by a single pressure component, unlike the reactive ion CH$^+$, which was previously analysed toward the Orion Bar CO$^+$ peak. The physical parameters traced by the higher rotational transitions ($N$=6-5,...,10-9) of C$_2$H may be consistent with the edges of dense clumps exposed to UV radiation near the ionization front of the Orion Bar.
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Submitted 20 April, 2015; v1 submitted 15 May, 2014;
originally announced May 2014.
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Spatially extended OH+ emission from the Orion Bar and Ridge
Authors:
Floris van der Tak,
Zsofia Nagy,
Volker Ossenkopf,
Zoltan Makai,
John Black,
Alex Faure,
Maryvonne Gerin,
Ted Bergin
Abstract:
We report the first detection of a Galactic source of OH+ line emission: the Orion Bar, a bright nearby photon-dominated region. Line emission is detected over ~1' (0.12 pc), tracing the Bar itself as well as the Southern tip of the Orion Ridge. The line width of ~4 km/s suggests an origin of the OH+ emission close to the PDR surface, at a depth of A_V ~0.3-0.5 into the cloud where most hydrogen i…
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We report the first detection of a Galactic source of OH+ line emission: the Orion Bar, a bright nearby photon-dominated region. Line emission is detected over ~1' (0.12 pc), tracing the Bar itself as well as the Southern tip of the Orion Ridge. The line width of ~4 km/s suggests an origin of the OH+ emission close to the PDR surface, at a depth of A_V ~0.3-0.5 into the cloud where most hydrogen is in atomic form. Steady-state collisional and radiative excitation models require unrealistically high OH+ column densities to match the observed line intensity, indicating that the formation of OH+ in the Bar is rapid enough to influence its excitation. Our best-fit OH+ column density of ~1x10^14 cm^-2 is similar to that in previous absorption line studies, while our limits on the ratios of OH+/H2O+ (>~40) and OH+/H3O+ (>~15) are higher than seen before.
The column density of OH+ is consistent with estimates from a thermo-chemical model for parameters applicable to the Orion Bar, given the current uncertainties in the local gas pressure and the spectral shape of the ionizing radiation field. The unusually high OH+/H2O+ and OH+/H3O+ ratios are probably due to the high UV radiation field and electron density in this object. In the Bar, photodissociation and electron recombination are more effective destroyers of OH+ than the reaction with H2, which limits the production of H2O+. The appearance of the OH+ lines in emission is the result of the high density of electrons and H atoms in the Orion Bar, since for these species, inelastic collisions with OH+ are faster than reactive ones. In addition, chemical pumping, far-infrared pumping by local dust, and near-UV pumping by Trapezium starlight contribute to the OH+ excitation. Similar conditions may apply to extragalactic nuclei where OH+ lines are seen in emission.
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Submitted 8 November, 2013;
originally announced November 2013.
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Excitation and Abundance of C3 in star forming cores:Herschel/HIFI observations of the sight-lines to W31C and W49N
Authors:
B. Mookerjea,
T. Giesen,
J. Stutzki,
J. Cernicharo,
J. R. Goicoechea,
M. De Luca,
T. A. Bell,
H. Gupta,
M. Gerin,
C. M. Persson,
P. Sonnentrucker,
Z. Makai,
J. Black,
F. Boulanger,
A. Coutens,
E. Dartois,
P. Encrenaz,
E. Falgarone,
T. Geballe,
B. Godard,
P. F. Goldsmith,
C. Gry,
P. Hennebelle E. Herbst,
P. Hily-Blant,
C. Joblin
, et al. (25 additional authors not shown)
Abstract:
We present spectrally resolved observations of triatomic carbon (C3) in several ro-vibrational transitions between the vibrational ground state and the low-energy nu2 bending mode at frequencies between 1654-1897 GHz along the sight-lines to the submillimeter continuum sources W31C and W49N, using Herschel's HIFI instrument. We detect C3 in absorption arising from the warm envelope surrounding the…
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We present spectrally resolved observations of triatomic carbon (C3) in several ro-vibrational transitions between the vibrational ground state and the low-energy nu2 bending mode at frequencies between 1654-1897 GHz along the sight-lines to the submillimeter continuum sources W31C and W49N, using Herschel's HIFI instrument. We detect C3 in absorption arising from the warm envelope surrounding the hot core, as indicated by the velocity peak position and shape of the line profile. The sensitivity does not allow to detect C3 absorption due to diffuse foreground clouds. From the column densities of the rotational levels in the vibrational ground state probed by the absorption we derive a rotation temperature (T_rot) of ~50--70 K, which is a good measure of the kinetic temperature of the absorbing gas, as radiative transitions within the vibrational ground state are forbidden. It is also in good agreement with the dust temperatures for W31C and W49N. Applying the partition function correction based on the derived T_rot, we get column densities N(C3) ~7-9x10^{14} cm^{-2} and abundance x(C3)~10^{-8} with respect to H2. For W31C, using a radiative transfer model including far-infrared pumping by the dust continuum and a temperature gradient within the source along the line of sight we find that a model with x(C3)=10^{-8}, T_kin=30-50 K, N(C3)=1.5 10^{15} cm^{-2} fits the observations reasonably well and provides parameters in very good agreement with the simple excitation analysis.
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Submitted 5 July, 2010;
originally announced July 2010.