- ID:
- ivo://CDS.VizieR/J/ApJ/846/71
- Title:
- M51 ISM structures from the CO maps of PAWS
- Short Name:
- J/ApJ/846/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare the structure of molecular gas at 40pc resolution to the ability of gas to form stars across the disk of the spiral galaxy M51. We break the PdBI Arcsecond Whirlpool Survey (PAWS; Schinnerer+ 2013ApJ...779...42S) into 370pc and 1.1kpc resolution elements, and within each we estimate the molecular gas depletion time ({tau}_Dep_^mol^), the star-formation efficiency per free-fall time ({epsilon}_ff_), and the mass-weighted cloud-scale (40pc) properties of the molecular gas: surface density, {Sigma}, line width, {sigma}, and b={Sigma}/{sigma}^2^{propto}{alpha}_vir_^-1^, a parameter that traces the boundedness of the gas. We show that the cloud-scale surface density appears to be a reasonable proxy for mean volume density. Applying this, we find a typical star-formation efficiency per free-fall time, {epsilon}_ff_(<{Sigma}_40pc_>)~0.3%-0.36%, lower than adopted in many models and found for local clouds. Furthermore, the efficiency per free-fall time anti-correlates with both {Sigma} and {sigma}, in some tension with turbulent star-formation models. The best predictor of the rate of star formation per unit gas mass in our analysis is b={Sigma}/{sigma}^2^, tracing the strength of self-gravity, with {tau}_Dep_^mol^{propto}b^-0.9^. The sense of the correlation is that gas with stronger self-gravity (higher b) forms stars at a higher rate (low {tau}_Dep_^mol^). The different regions of the galaxy mostly overlap in {tau}_Dep_^mol^ as a function of b, so that low b explains the surprisingly high {tau}_Dep_^mol^ found toward the inner spiral arms found by Meidt et al. (2013ApJ...779...45M).
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Search Results
- 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/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/ApJS/233/15
- Title:
- ND_2_ rotational spectrum
- Short Name:
- J/ApJS/233/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The deuteration mechanism of molecules in the interstellar medium is still being debated. Observations of deuterium-bearing species in several astronomical sources represent a powerful tool to improve our understanding of the interstellar chemistry. The doubly deuterated form of the astrophysically interesting amidogen radical could be a target of detection in space. In this work, the rotational spectrum of the ND_2_ radical in its ground vibrational and electronic X^2^B_1_ state has been investigated between 588 and 1131GHz using a frequency modulation millimeter/submillimeter-wave spectrometer. The ND_2_ molecule has been produced in a free-space glass absorption cell by discharging a mixture of ND_3_ and Ar. Sixty-four new transition frequencies involving J values from 2 to 5 and K_a_ values from 0 to 4 have been measured. A global analysis including all the previous field-free pure rotational data has been performed, allowing for a more precise determination of a very large number of spectroscopic parameters. Accurate predictions of rotational transition frequencies of ND_2_ are now available from a few gigahertz up to several terahertz.
- ID:
- ivo://CDS.VizieR/J/ApJ/883/156
- Title:
- Nobeyama 45m Cygnus-X CO. II. C180 clumps
- Short Name:
- J/ApJ/883/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the statistical physical properties of the C^18^O(J=1-0) clumps present in a prominent cluster-forming region, Cygnus X, using the data set obtained by the Nobeyama 45m radio telescope. This survey covers 9deg^2^ of the northern and southern regions of Cygnus X, and, in total, 174 C^18^O clumps are identified using the dendrogram method. Assuming a distance of 1.4kpc, these clumps have radii of 0.2-1pc, velocity dispersions of <2.2km/s, gas masses of 30-3000M_{sun}_, and H_2_ densities of (0.2-5.5)x10^4^cm^-3^. We confirm that the C^18^O clumps in the northern region have a higher H_2_ density than those in the southern region, supporting the existence of a difference in the evolutionary stages, consistent with the star-formation activity of these regions. The difference in the clump properties of the star-forming and starless clumps is also confirmed by the radius, velocity dispersion, gas mass, and H_2_ density. The average virial ratio of 0.3 supports that these clumps are gravitationally bound. The C^18^O clump mass function shows two spectral index components, {alpha}=-1.4 in 55-140M_{sun}_ and {alpha}=-2.1 in >140M_{sun}_, which are consistent with the low- and intermediate-mass parts of the Kroupa's initial mass function. The spectral index of the star-forming clumps >140M_{sun}_ is consistent with that of the starless clumps ranging from 55-140M_{sun}_, suggesting that the latter will evolve into star-forming clumps while retaining the gas accretion. Assuming a typical star-formation efficiency of molecular clumps (10%), about 10 C^18^O clumps having a gas mass of >10^3^M_{sun}_ will evolve into open clusters containing one or more OB stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/880/138
- Title:
- Observed transitions of CH_3_OH and CH_3_CHO
- Short Name:
- J/ApJ/880/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- IRAM 30m Observations toward eight protostellar outflow sources were taken in the 96-176GHz range. Transitions of CH_3_OH and CH_3_CHO were detected in seven of them. The integrated emissions of the transitions of each species that fell into the observed frequency range were measured and fit using RADEX and LTE models. Column densities and gas properties inferred from this fitting are presented. The ratio of the A and E-type isomers of CH_3_OH indicates that the methanol observed in these outflows was formed on the grain surface. Both species demonstrate a reduction of terminal velocity in their line profiles in faster outflows, indicating destruction in the post-shock gas phase. This destruction, and a near constant ratio of the CH_3_OH and CH_3_CHO column densities, imply it is most likely that CH_3_CHO also forms on the grain surface.
- ID:
- ivo://CDS.VizieR/J/ApJS/252/1
- Title:
- OH and HI data in molecular clouds
- Short Name:
- J/ApJS/252/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a OH 18cm survey toward 141 molecular clouds in various environments, including 33 optical dark clouds, 98 Planck Galactic cold clumps (PGCCs), and 10 Spitzer dark clouds with the Arecibo telescope. The deviations from local thermal equilibrium are common for intensity ratios of both OH main lines and satellite lines. Line intensity of OH 1667MHz is found to correlate linearly with visual extinction A_V_ when A_V_ is less than 3mag. It was converted into OH column density by adopting the excitation temperature derived from Monte Carlo simulations with 1{sigma} uncertainty. The relationship between OH abundance X(OH) relative to H_2_ and A_V_ is found to follow an empirical formula, X(OH)/10^-7^=1.3_-0.4_^+0.4^+6.3_-0.5_^+0.5^*exp(-A_V_/2.9_-0.6_^+0.6^). Linear correlation is found between OH and ^13^CO intensity. Besides, nonthermal velocity dispersions of OH and ^13^CO are closely correlated. These results imply tight chemical evolution and spatial occupation between OH and ^13^CO. No obvious correlation is found between column density and nonthermal velocity dispersion of OH and HI narrow self-absorption (HINSA), indicating different chemical evolution and spatial volume occupation between OH and HINSA. Using the age information of HINSA analysis, OH abundance X(OH) is found to increase linearly with cloud age, which is consistent with previous simulations. Fourteen OH components without corresponding CO emission were detected, implying the effectiveness of OH in tracing the "CO-dark" molecular gas.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/119
- Title:
- O_2_ laboratory atmosphere simulation experiments
- Short Name:
- J/ApJ/858/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous studies of haze formation in the atmosphere of the early Earth have focused on N_2_/CO_2_/CH_4_ atmospheres. Here, we experimentally investigate the effect of O_2_ on the formation and composition of aerosols to improve our understanding of haze formation on the Neoproterozoic Earth. We obtained in situ size, particle density, and composition measurements of aerosol particles produced from N_2_/CO_2_/CH_4_/O_2_ gas mixtures subjected to FUV radiation (115-400nm) for a range of initial CO_2_/CH_4_/O_2_ mixing ratios (O_2_ ranging from 2ppm to 0.2%). At the lowest O_2_ concentration (2ppm), the addition increased particle production for all but one gas mixture. At higher oxygen concentrations (20ppm and greater), particles are still produced, but the addition of O_2_ decreases the production rate. Both the particle size and number density decrease with increasing O_2_, indicating that O_2_ affects particle nucleation and growth. The particle density increases with increasing O_2_. The addition of CO_2_ and O_2_ not only increases the amount of oxygen in the aerosol, but it also increases the degree of nitrogen incorporation. In particular, the addition of O_2_ results in the formation of nitrate-bearing molecules. The fact that the presence of oxygen-bearing molecules increases the efficiency of nitrogen fixation has implications for the role of haze as a source of molecules required for the origin and evolution of life. The composition changes also likely affect the absorption and scattering behavior of these particles but optical property measurements are required to fully understand the implications for the effect on the planetary radiative energy balance and climate.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A57
- Title:
- Oxygen-rich AGB IRAM spectra
- Short Name:
- J/A+A/641/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to determine the abundances of SiO, CS, SiS, SO, and SO_2_ in a large sample of oxygen-rich asymptotic giant branch (AGB) envelopes covering a wide range of mass loss rates to investigate the potential role that these molecules could play in the formation of dust in these environments. We surveyed a sample of 30 oxygen-rich AGB stars in the {lambda} 2mm band using the IRAM 30m telescope. We performed excitation and radiative transfer calculations based on the large velocity gradient (LVG) method to model the observed lines of the molecules and to derive their fractional abundances in the observed envelopes. We detected SiO in all 30 targeted envelopes, as well as CS, SiS, SO, and SO 2 in 18, 13, 26, and 19 sources, respectively. Remarkably, SiS is not detected in any envelope with a mass loss rate below 10^-6^M_{sun}_/yr, whereas it is detected in all envelopes with mass loss rates above that threshold. From a comparison with a previous, similar study on C-rich sources, it becomes evident that the fractional abundances of CS and SiS show a marked differentiation between C-rich and O-rich sources, being two orders of magnitude and one order of magnitude more abundant in C-rich sources, respectively, while the fractional abundance of SiO turns out to be insensitive to the C/O ratio. The abundance of SiO in O-rich envelopes behaves similarly to C-rich sources, that is, the denser the envelope the lower its abundance. A similar trend, albeit less clear than for SiO, is observed for SO in O-rich sources. The marked dependence of CS and SiS abundances on the C/O ratio indicates that these two molecules form more efficiently in C- than O-rich envelopes. The decline in the abundance of SiO with increasing envelope density and the tentative one for SO indicate that SiO and possibly SO act as gas-phase precursors of dust in circumstellar envelopes around O-rich AGB stars.
