- ID:
- ivo://CDS.VizieR/J/A+A/627/A95
- Title:
- Molecular DNM in Chamaeleon CO spectra
- Short Name:
- J/A+A/627/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To determine carbon monoxide column densities along sightlines through the Chamaeleon cloud complex where molecular absorption had been observed but CO emission had not been detected. We took ^12^CO J=1-0 absorption profiles toward 6 of 8 members of a group of sightlines in Chamaeleon having abundant dark neutral matter and molecular hydrogen but no detectable CO emission. CO absorption was detected along five of the six sightlines at column densities 4x10^+13^cm^-2^<~N(CO)<~10^15^cm^-2^ that are below typical survey detection limits of 1-2K-km/s. Dark gas absent in CO emission along sightlines in the outskirts of the Chamaeleon complex where molecular gas is readily detected in HCO^+^ absorption results from small CO column densities around the onset of CO formation at the HI/H_2_ transition. Relative abundances N(CO)/H_2_<3x10^-6^ in Chamaeleon are comparable to those seen in UV absorption toward early-type stars and in a CO absorption/emission line survey toward local quasar background targets away from the Galactic plane.
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- ID:
- ivo://CDS.VizieR/J/A+A/570/A109
- Title:
- Molecular gas associated with IRAS 10361-5830
- Short Name:
- J/A+A/570/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the distribution of the molecular gas and dust in the molecular clump linked to IRAS 10361-5830, located in the environs of the bubble-shaped HII region Gum 31 in the Carina region, with the aim of determining the main parameters of the associated material and of investigating the evolutionary state of the young stellar objects identified there.
- ID:
- ivo://CDS.VizieR/J/ApJS/163/282
- Title:
- Molecular hydrogen column densities
- Short Name:
- J/ApJS/163/282
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Measurements of molecular hydrogen (H_2_) column densities are presented for the first six rotational levels (J=0-5) for 73 extragalactic targets observed with the Far Ultraviolet Spectroscopic Explorer (FUSE). All of these have a final signal-to-noise ratio larger than 10 and are located at Galactic latitude |b|>20{deg}. The individual observations were calibrated with the FUSE calibration pipeline CalFUSE version 2.1 or higher and then carefully aligned in velocity. The final velocity shifts for all the FUSE segments are listed. H_2_ column densities or limits are determined for the six lowest rotational (J) levels for each HI component in the line of sight, using a curve-of-growth approach at low column densities (<16.5) and Voigt-profile fitting at higher column densities. Detections include 65 measurements of low-velocity H_2_ in the Galactic disk and lower halo. Eight sight lines yield nondetections for Galactic H_2_.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A26
- Title:
- Molecular ion abundances in diffuse ISM
- Short Name:
- J/A+A/622/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The transition between atomic and molecular hydrogen is associated with important changes in the structure of interstellar clouds, and marks the beginning of interstellar chemistry. Most molecular ions are rapidly formed (in ion-molecule reactions) and destroyed (by dissociative recombination) in the diffuse ISM. Because of the relatively simple networks controlling their abundances, molecular ions are usually good probes of the underlying physical conditions including for instance the fraction of gas in molecular form or the fractional ionization. In this paper we focus on three possible probes of the molecular hydrogen column density, HCO^+^, HOC^+^, and CF^+^. We presented high sensitivity ALMA absorption data toward a sample of compact HII regions and bright QSOs with prominent foreground absorption, in the ground state transitions of the molecular ions HCO^+^, HOC^+^, and CF^+^ and the neutral species HCN and HNC, and from the excited state transitions of C_3_H^+^(4-3) and ^13^CS(2-1). These data are compared with Herschel absorption spectra of the ground state transition of HF and p-H_2_O. We show that the HCO^+^, HOC^+^, and CF^+^ column densities are well correlated with each other. HCO^+^ and HOC^+^ are tightly correlated with p-H_2_O, while they exhibit a different correlation pattern with HF depending on whether the absorbing matter is located in the Galactic disk or in the central molecular zone. We report new detections of C_3_H^+^ confirming that this ion is ubiquitous in the diffuse matter, with an abundance relative to H_2_ of ~7x10^-11^. We confirm that the CF^+^ abundance is lower than predicted by simple chemical models and propose that the rate of the main formation reaction is lower by a factor of about 3 than usually assumed. In the absence of CH or HF data, we recommend to use the ground state transitions of HCO^+^, CCH, and HOC^+^ to trace diffuse molecular hydrogen, with mean abundances relative to H_2_ of 3x10^-9^, 4x10^-8^ and 4x10^-11^ respectively, leading to sensitivity N(H_2_)/{int}{tau}dv of 4x10^20^, 1.5x10^21^, and 6x10^22^cm^-2^/km/s, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/565/A64
- Title:
- Molecular ions in L1157-B1
- Short Name:
- J/A+A/565/A64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we perform a complete census of molecular ions with an abundance larger than ~10^-10^ in the protostellar shock L1157-B1. This allows us to study the ionization structure and chemistry of the shock. An unbiased high-sensitivity survey of L1157-B1 performed with the IRAM-30m and Herschel/HIFI as part of the CHESS and ASAI large programs allows searching for molecular ions emission. Then, by means of a radiative transfer code in the Large Velocity Gradient approximation, the gas physical conditions and fractional abundances of molecular ions are derived. The latter are compared with estimates of steady-state abundances in the cloud and their evolution in the shock calculated with the chemical model Astrochem.
- ID:
- ivo://CDS.VizieR/J/ApJ/892/148
- Title:
- Molecular ISM in nearby star-forming galaxies
- Short Name:
- J/ApJ/892/148
- Date:
- 19 Jan 2022 09:08:29
- Publisher:
- CDS
- Description:
- We compare the observed turbulent pressure in molecular gas, P_turb_, to the required pressure for the interstellar gas to stay in equilibrium in the gravitational potential of a galaxy, P_DE_. To do this, we combine arcsecond resolution CO data from PHANGS-ALMA with multiwavelength data that trace the atomic gas, stellar structure, and star formation rate (SFR) for 28 nearby star-forming galaxies. We find that P_turb_ correlates with--but almost always exceeds--the estimated P_DE_ on kiloparsec scales. This indicates that the molecular gas is overpressurized relative to the large-scale environment. We show that this overpressurization can be explained by the clumpy nature of molecular gas; a revised estimate of P_DE_ on cloud scales, which accounts for molecular gas self-gravity, external gravity, and ambient pressure, agrees well with the observed P_turb_ in galaxy disks. We also find that molecular gas with cloud-scale P_turb_~P_DE_>~10^5^k_B_Kcm^-3^ in our sample is more likely to be self-gravitating, whereas gas at lower pressure it appears more influenced by ambient pressure and/or external gravity. Furthermore, we show that the ratio between P_turb_ and the observed SFR surface density, {Sigma}_SFR_, is compatible with stellar feedback-driven momentum injection in most cases, while a subset of the regions may show evidence of turbulence driven by additional sources. The correlation between {Sigma}_SFR_ and kpc-scale P_DE_ in galaxy disks is consistent with the expectation from self-regulated star formation models. Finally, we confirm the empirical correlation between molecular-to-atomic gas ratio and kpc-scale P_DE_ reported in previous works.
- ID:
- ivo://CDS.VizieR/J/ApJ/710/150
- Title:
- Molecular lines in EGOs
- Short Name:
- J/ApJ/710/150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first systematic survey of molecular lines (including HCO^+^(1-0) and ^12^CO, ^13^CO, C^18^O(1-0) lines at the 3mm band) toward a new sample of 88 massive young stellar object (MYSO) candidates associated with ongoing outflows (known as extended green objects or EGOs) identified from the Spitzer GLIMPSE survey in the northern hemisphere with the Purple Mountain Observatory 13.7m radio telescope. By analyzing the asymmetries of the optically thick line HCO^+^ for 69 of 72 EGOs with HCO^+^ detection, we found 29 sources with "blue asymmetric profiles" and 19 sources with "red asymmetric profiles."
- ID:
- ivo://CDS.VizieR/J/A+A/504/853
- Title:
- Molecular lines in 5 massive dense cores
- Short Name:
- J/A+A/504/853
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Two mid-infrared quiet and two brighter massive cores were observed in various transitions (E_up_ up to 289K) of CS, OCS, H_2_S, SO, and SO_2_ and of their ^34^S isotopologues at mm wavelengths with the IRAM 30m and CSO telescopes. The 1D modeling of the dust continuum is used to derive the density and temperature laws, which were then applied in the RATRAN code to modeling the observed line emission and to deriving the relative abundances of the molecules. All lines are detected, except the highest energy SO_2_ transition. Infall (up to 2.9km/s) may be detected towards the core W43MM1. We propose an evolutionary sequence of our sources (W43MM1 - IRAS18264-1152 - IRAS05358+3543 - IRAS18162-2048), based on the SED analysis. The analysis of the variations in abundance ratios from source to source reveals that the SO and SO_2_ relative abundances increase with time, while CS and OCS decrease. Molecular ratios, such as [OCS/H_2_S], [CS/H_2_S], [SO/OCS], [SO_2_/OCS], [CS/SO], and [SO_2_/SO] may be good indicators of evolution, depending on layers probed by the observed molecular transitions. Observations of molecular emission from warmer layers, so that involving higher upper energy levels must be included.
- ID:
- ivo://CDS.VizieR/J/ApJ/780/85
- Title:
- Molecular line study of infrared dark clouds
- Short Name:
- J/ApJ/780/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is currently assumed that infrared dark clouds (IRDCs) represent the earliest evolutionary stages of high-mass stars (>8M_{sun}_). Submillimeter and millimeter-wave studies performed over the past 15yr show that IRDCs possess a broad variety of properties, and hence a wide range of problems and questions that can be tackled. In this paper, we report an investigation of the molecular composition and chemical processes in two groups of IRDCs. Using the Mopra, APEX, and IRAM radio telescopes over the last four years, we have collected molecular line data for CO, H_2_CO, HNCO, CH_3_CCH, CH_3_OH, CH_3_CHO, CH_3_OCHO, and CH_3_OCH_3_. For all of these species we estimated molecular abundances. We then undertook chemical modeling studies, concentrating on the source IRDC028.34+0.06, and compared observed and modeled abundances. This comparison showed that to reproduce observed abundances of complex organic molecules, a zero-dimensional gas-grain model with constant physical conditions is not sufficient. We achieved greater success with the use of a warm-up model, in which warm-up from 10K to 30K occurs following a cold phase.
- ID:
- ivo://CDS.VizieR/J/A+A/606/A123
- Title:
- Molecular maps of NGC1333
- Short Name:
- J/A+A/606/A123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Are the initial conditions for clustered star formation the same as for non-clustered star formation? To investigate the initial gas properties in young proto-clusters we carried out a comprehensive and high-sensitivity study of the internal structure, density, temperature, and kinematics of the dense gas content of the NGC1333 region in Perseus, one of the nearest and best studied embedded clusters. The analysis of the gas velocities in the Position-Position-Velocity space reveals an intricate underlying gas organization both in space and velocity. We identified a total of 14 velocity-coherent, (tran-)sonic structures within NGC1333, with similar physical and kinematic properties than those quiescent, star-forming (aka fertile) fibers previously identified in low-mass star-forming clouds. These fibers are arranged in a complex spatial network, build-up the observed total column density, and contain the dense cores and protostars in this cloud. Our results demonstrate that the presence of fibers is not restricted to low-mass clouds but can be extended to regions of increasing mass and complexity. We propose that the observational dichotomy between clustered and non-clustered star-forming regions might be naturally explained by the distinct spatial density of fertile fibers in these environments.