- ID:
- ivo://CDS.VizieR/J/AJ/141/123
- Title:
- Molecular clouds associated with HII regions
- Short Name:
- J/AJ/141/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The properties of molecular clouds associated with 10 HII regions were studied using CO observations. We identified 142 dense clumps within our sample and found that our sources are divided into two categories: those with clumps that show a power-law size-line-width relation (Type I) and those that do not show any relation (Type II). The clumps in the Type I sources have larger power-law indices than found in previous studies. The clumps in the Type II sources have larger line widths than do the clumps in the Type I sources.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/835/278
- Title:
- Molecular clouds in the dwarf galaxy NGC6822
- Short Name:
- J/ApJ/835/278
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Atacama Large Millimeter/submillimeter Array survey of CO(2-1) emission from the 1/5 solar metallicity, Local Group dwarf galaxy NGC 6822. We achieve high (0.9"~2pc) spatial resolution while covering a large area: four 250pcx250pc regions that encompass ~2/3 of NGC 6822's star formation. In these regions, we resolve ~150 compact CO clumps that have small radii (~2-3pc), narrow line width (~1km/s), and low filling factor across the galaxy. This is consistent with other recent studies of low-metallicity galaxies, but here shown with a 15x larger sample. At parsec scales, CO emission correlates with 8{mu}m emission better than with 24{mu}m emission and anticorrelates with H{alpha}, so that polycyclic aromatic hydrocarbon emission may be an effective tracer of molecular gas at low metallicity. The properties of the CO clumps resemble those of similar-size structures in Galactic clouds except of slightly lower surface brightness and with CO-to-H_2_ ratio ~1-2x the Galactic value. The clumps exist inside larger atomic-molecular complexes with masses typical for giant molecular clouds. Using dust to trace H_2_ for the entire complex, we find the CO-to-H_2_ ratio to be ~20-25x the Galactic value, but with strong dependence on spatial scale and variations between complexes that may track their evolutionary state. The H_2_-to-HI ratio is low globally and only mildly above unity within the complexes. The ratio of star formation rate to H_2_ is ~3-5x higher in the complexes than in massive disk galaxies, but after accounting for the bias from targeting star-forming regions, we conclude that the global molecular gas depletion time may be as long as in massive disk galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/839/113
- Title:
- Molecular clouds with GLIMPSE/MIPSGAL data
- Short Name:
- J/ApJ/839/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the star-formation (SF) law in 12 Galactic molecular clouds with ongoing high-mass star-formation (HMSF) activity, as traced by the presence of a bright IRAS source and other HMSF tracers. We define the molecular cloud (MC) associated with each IRAS source using ^13^CO line emission, and count the young stellar objects (YSOs) within these clouds using GLIMPSE and MIPSGAL 24{mu}m Spitzer databases. The masses for high-luminosity YSOs (L_bol_>10L_{sun}_) are determined individually using pre-main-sequence evolutionary tracks and the evolutionary stages of the sources, whereas a mean mass of 0.5M_{sun}_ was adopted to determine the masses in the low-luminosity YSO population. The star-formation rate surface density ({Sigma}SFR) corresponding to a gas surface density ({Sigma}gas) in each MC is obtained by counting the number of the YSOs within successive contours of ^13^CO line emission. We find a break in the relation between {Sigma}SFR and {Sigma}gas, with the relation being a power law ({Sigma}SFR{propto}{Sigma}gas^N^) with the index N varying between 1.4 and 3.6 above the break. The {Sigma}gas at the break is between 150-360M_{sun}_/pc^2^ for the sample clouds, which compares well with the threshold gas density found in recent studies of Galactic star-forming regions. Our clouds treated as a whole lie between the Kennicutt relation and the linear relation for Galactic and extra-galactic dense star-forming regions. We find a tendency for the high- mass YSOs to be found preferentially in dense regions at densities higher than 1200M_{sun}_/pc^2^ (~0.25g/cm^2^).
- 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/A+A/540/A96
- Title:
- Molecular gas in Hickson Compact Groups
- Short Name:
- J/A+A/540/A96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the effect of the extreme environment in Hickson Compact Groups (HCGs) on the molecular gas mass, M_H2_, and the star formation rate (SFR) of galaxies as a function of atomic hydrogen (HI) content and evolutionary phase of the group. We selected a redshift-limited (D<100Mpc) sample of 88 galaxies in 20 HCGs with available atomic hydrogen (HI) VLA maps, covering a wide range of HI deficiencies and evolutionary phases of the groups containing at least one spiral galaxy. We observed the CO(1-0) and CO(2-1) lines with the IRAM 30m telescope for 47 galaxies. Together with literature data, our sample contains CO(1-0) spectra for 86 galaxies. We derived the far-infrared (FIR) luminosity L_FIR_ from IRAS data and used it as a tracer of the star formation rate (SFR). We calculated the HI mass, M_HI_ L_FIR_ and M_H2_ deficiencies, based on the values expected from L_B_ and L_K_ in isolated galaxies from the AMIGA sample. We limited our statistical analysis to spiral galaxies, since the large number of upper limits did not allow drawing strong conclusions about M_H2_ and L_FIR_ in early-type galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/901/L8
- Title:
- Molecular gas properties of 70 PHANGS-ALMA galaxies
- Short Name:
- J/ApJ/901/L8
- Date:
- 23 Feb 2022 00:10:50
- Publisher:
- CDS
- Description:
- Using the PHANGS-ALMA CO(2-1) survey, we characterize molecular gas properties on ~100pc scales across 102,778 independent sightlines in 70 nearby galaxies. This yields the best synthetic view of molecular gas properties on cloud scales across the local star-forming galaxy population obtained to date. Consistent with previous studies, we observe a wide range of molecular gas surface densities (3.4dex), velocity dispersions (1.7dex), and turbulent pressures (6.5dex) across the galaxies in our sample. Under simplifying assumptions about subresolution gas structure, the inferred virial parameters suggest that the kinetic energy of the molecular gas typically exceeds its self-gravitational binding energy at ~100pc scales by a modest factor (1.3 on average). We find that the cloud-scale surface density, velocity dispersion, and turbulent pressure (1) increase toward the inner parts of galaxies, (2) are exceptionally high in the centers of barred galaxies (where the gas also appears less gravitationally bound), and (3) are moderately higher in spiral arms than in inter-arm regions. The galaxy-wide averages of these gas properties also correlate with the integrated stellar mass, star formation rate, and offset from the star-forming main sequence of the host galaxies. These correlations persist even when we exclude regions with extraordinary gas properties in galaxy centers, which contribute significantly to the inter-galaxy variations. Our results provide key empirical constraints on the physical link between molecular cloud populations and their galactic environment.
- 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/575/A9
- Title:
- M17-SW datacubes in C and CO lines
- Short Name:
- J/A+A/575/A9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We probe the column densities and masses traced by the ionized [CII] and neutral [CI] atomic carbon with spectrally resolved maps, and compare them to the diffuse and dense molecular gas traced by [CI] and low-J CO lines toward the star-forming region M17 SW. We mapped a 4.1pcx4.7pc region in the [CI] 609{mu}m line using the APEX telescope, as well as the CO isotopologues with the IRAM 30m telescope. Data are analyzed based on velocity channel maps that are 1km/s wide. We correlate their spatial distribution with that of the [CII] map obtained with SOFIA/GREAT. Optically thin approximations were used to estimate the column densities of [CI] and [CII] in each velocity channel.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A27
- Title:
- Musca APEX 12CO(2-1), 13CO(2-1) and C18O(2-1) data
- Short Name:
- J/A+A/644/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dense molecular filaments are ubiquituous in the interstellar medium, yet their internal physical conditions and the role of gravity, turbulence, the magnetic field, radiation, and the ambient cloud during their evolution remain debated. We study the kinematics and physical conditions in the Musca filament, the ambient cloud, and the Chamaeleon-Musca complex to constrain the physics of filament formation. We produced CO(2-1) isotopologue maps with the APEX telescope that cut through the Musca filament. We further study a NANTEN2 ^12^CO(1-6>0) map of the full Musca cloud, HI emission of the Chamaeleon-Musca complex, a Planck polarisation map, line radiative tranfer models, Gaia data, and synthetic observations from filament formation simulations. The Musca cloud, with a size of ~3-6pc, contains multiple velocity components. Radiative transfer modelling of the CO emission indicates that the Musca filament consists of a cold (~10K), dense (n_H2_~10^4^cm^-3^) crest, which is best described with a cylindrical geometry. Connected to the crest, a separate gas component at T~15K and n_H2_~10^3^cm^-3^ is found, the so-called strands. The velocity-coherent filament crest has an organised transverse velocity gradient that is linked to the kinematics of the nearby ambient cloud. This velocity gradient has an angle >=30{deg} with respect to the local magnetic field orientation derived from Planck, and the magnitude of the velocity gradient is similar to the transonic linewidth of the filament crest. Studying the large scale kinematics, we find coherence of the asymmetric kinematics from the 50pc HI cloud down to the Musca filament. We also report a strong [C^18^O]/[^13^CO] abundance drop by an order of magnitude from the filament crest to the strands over a distance <0.2pc in a weak ambient far-ultraviolet (FUV) field. The dense Musca filament crest is a long-lived (several crossing times), dynamic structure that can form stars in the near future because of continuous mass accretion replenishing the filament. This mass accretion on the filament appears to be triggered by a HI cloud-cloud collision, which bends the magnetic field around dense filaments. This bending of the magnetic field is then responsible for the observed asymmetric accretion scenario of the Musca filament, which is, for instance, seen as a V-shape in the position-velocity (PV) diagram.
