- 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.
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- 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/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.
- ID:
- ivo://CDS.VizieR/J/ApJS/94/615
- Title:
- Molecular outflow sources
- Short Name:
- J/ApJS/94/615
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A K'-band imaging survey with a ~8'x3' field of view of all regions associated with CO molecular outflow from the list of Fukui (1989) has been conducted. We present the individual images and describe individual nebulous objects and star clusters. The vast majority of all outflow sources are associated with nebulosity detectable in K', so such nebulae can be used as tracers for very young stars. We find a significant fraction (one-third) of molecular outflow sources to be associated with clusters of young stars. Most of the young embedded clusters show peaks in their K' magnitude histograms that, if interpreted as an evolutionary effect, indicate average ages of the embedded star population of <1x10^6yr.
- ID:
- ivo://CDS.VizieR/J/ApJ/851/76
- Title:
- Molecular transitions toward NGC5128 with ALMA
- Short Name:
- J/ApJ/851/76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Centaurus A, with its gas-rich elliptical host galaxy, NGC 5128, is the nearest radio galaxy at a distance of 3.8Mpc. Its proximity allows us to study the interaction among an active galactic nucleus, radio jets, and molecular gas in great detail. We present ALMA observations of low-J transitions of three CO isotopologues, HCN, HCO+, HNC, CN, and CCH toward the inner projected 500pc of NGC 5128. Our observations resolve physical sizes down to 40pc. By observing multiple chemical probes, we determine the physical and chemical conditions of the nuclear interstellar medium of NGC 5128. This region contains molecular arms associated with the dust lanes and a circumnuclear disk (CND) interior to the molecular arms. The CND is approximately 400pc by 200pc and appears to be chemically distinct from the molecular arms. It is dominated by dense gas tracers while the molecular arms are dominated by ^12^CO and its rare isotopologues. The CND has a higher temperature, elevated CN/HCN and HCN/HNC intensity ratios, and much weaker ^13^CO and C^18^O emission than the molecular arms. This suggests an influence from the AGN on the CND molecular gas. There is also absorption against the AGN with a low velocity complex near the systemic velocity and a high velocity complex shifted by about 60km/s. We find similar chemical properties between the CND in emission and both the low and high velocity absorption complexes, implying that both likely originate from the CND. If the HV complex does originate in the CND, then that gas would correspond to gas falling toward the supermassive black hole.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A22
- Title:
- Monoceros R2 filament hub FIR observations
- Short Name:
- J/A+A/607/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present far-infrared observations of Monoceros R2 (a giant molecular cloud at approximately 830pc distance, containing several sites of active star formation), as observed at 70um, 160um, 250um, 350um, and 500um by the PACS and SPIRE instruments on the Herschel Space Observatory as part of the HOBYS Key programme. The Herschel data are complemented by SCUBA-2 data in the submillimetre range, and WISE and Spitzer data in the mid-infrared. In addition, C^18^O data from the IRAM 30-m Telescope are presented, and used for kinematic information. Sources were extracted from the maps with getsources, and from the fluxes measured, spectral energy distributions were constructed, allowing measurements of source mass and dust temperature. Of 177 Herschel sources robustly detected in the region (a detection with high signal-to-noise and low axis ratio at multiple wavelengths), including protostars and starless cores, 29 are found in a filamentary hub at the centre of the region (a little over 1% of the observed area). These objects are on average smaller, more massive, and more luminous than those in the surrounding regions (which together suggest that they are at a later stage of evolution), a result that cannot be explained entirely by selection effects. These results suggest a picture in which the hub may have begun star formation at a point significantly earlier than the outer regions, possibly forming as a result of feedback from earlier star formation. Furthermore, the hub may be sustaining its star formation by accreting material from the surrounding filaments.
- ID:
- ivo://CDS.VizieR/J/A+A/453/923
- Title:
- Morphologies in the Cepheus Flare region
- Short Name:
- J/A+A/453/923
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- These tables contain the data of the cloud sample on which the study of the relationships between cloud morphology, optical and IR properties, and star formation is based. The sample was defined using the extinction map of the Cepheus Flare region covering ~256 square degrees created from the B band star counts of the USNO-A2.0 catalogue (Cat. <I/252>) with a typical resolution of 3 arcminutes on a 1.5 arcminute grid. Cloud definition and description was carried out using automatized methods. The main table lists the positions, peak extinctions, sizes, morphological parameters and classes, distances, mass estimations, parent cloud complexes, and the number of YSO candidates associated. An additional table with the names of the previously catalogued associated clouds and their references is also available.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A163
- Title:
- Mrk 231 CO(1-0) and CN(1-0) line observations
- Short Name:
- J/A+A/633/A163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present interferometric observations of the CN(1-0) line emission in Mrk 231 and combine them with previous observations of CO and other H_2_ gas tracers to study the physical properties of the massive molecular outflow. We find a strong boost of the CN/CO(1-0) line luminosity ratio in the outflow of Mrk 231, which is unprecedented compared to any other known Galactic or extragalactic astronomical source. For the dense gas phase in the outflow traced by the HCN and CN emissions, we infer X_CN_=[CN]/[H_2_]>X_HCN_ by at least a factor of three, with H_2_ gas densities of n_H2_~10^5-6^cm^-3^. In addition, we resolve for the first time narrow spectral features in the HCN(1-0) and HCO^+^(1-0) high-velocity line wings tracing the dense phase of the outflow. The velocity dispersions of these spectral features, {sigma}_v_~7-20km/s, are consistent with those of massive extragalactic giant molecular clouds detected in nearby starburst nuclei. The H_2_ gas masses inferred from the HCN data are quite high, M_mol_~0.3-5x10^8^M_{sun}_. Our results suggest that massive complexes of denser molecular gas survive embedded into the more diffuse H_2_ phase of the outflow, and that the chemistry of these outflowing dense clouds is strongly aected by UV radiation.
