- ID:
- ivo://CDS.VizieR/J/ApJ/655/958
- Title:
- 90-GHz observations in NGC 1333
- Short Name:
- J/ApJ/655/958
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observed the clustered star forming complex NGC 1333 with the BIMA and FCRAO telescopes in the transitions HCO+(1-0) and N_2_H+(1-0) over an area with resolution ~10" (0.015pc). The N_2_H+ emission follows very closely the submillimeter dust continuum emission, while HCO+ emission appears more spatially extended and also traces outflows. We have identified 93 N_2_H+ cores using the CLUMPFIND algorithm, and we derive N_2_H+ core masses between 0.05 and 2.5M_{sun}_ , with uncertainties of a factor of a few, dominated by the adopted N_2_H+ abundance.
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- ID:
- ivo://CDS.VizieR/J/ApJ/835/3
- Title:
- 218GHz obs. of embedded protostars in Ophiuchus
- Short Name:
- J/ApJ/835/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present APEX 218GHz observations of molecular emission in a complete sample of embedded protostars in the Ophiuchus star-forming region. To study the physical properties of the cores, we calculate H_2_CO and c-C_3_H_2_ rotational temperatures, both of which are good tracers of the kinetic temperature of the molecular gas. We find that the H_2_CO temperatures range between 16K and 124K, with the highest H_2_CO temperatures toward the hot corino source IRAS 16293-2422 (69-124K) and the sources in the {rho} Oph A cloud (23-49K) located close to the luminous Herbig Be star S1, which externally irradiates the {rho} Oph A cores. On the other hand, the c-C_3_H_2_ rotational temperature is consistently low (7-17K) in all sources. Our results indicate that the c-C_3_H_2_ emission is primarily tracing more shielded parts of the envelope whereas the H_2_CO emission (at the angular scale of the APEX beam; 3600 au in Ophiuchus) mainly traces the outer irradiated envelopes, apart from in IRAS 16293-2422, where the hot corino emission dominates. In some sources, a secondary velocity component is also seen, possibly tracing the molecular outflow.
- ID:
- ivo://CDS.VizieR/J/A+A/625/A147
- Title:
- 80-116GHz spectrum of L483
- Short Name:
- J/A+A/625/A147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An exhaustive chemical characterization of dense cores is mandatory to our understanding of chemical composition changes from a starless to a protostellar stage. However, only a few sources have had their molecular composition characterized in detail. Here we present a 3mm line survey of L483, a dense core around a Class 0 protostar, which was observed with the IRAM 30m telescope in the 80-116GHz frequency range. We detected 71 molecules (140 including different isotopologs), most of which are present in the cold and quiescent ambient cloud according to their narrow lines (FWHM~0.5km/s) and low rotational temperatures (<~10K). Of particular interest among the detected molecules are the cis isomer of HCOOH, the complex organic molecules HCOOCH_3_, CH_3_OCH_3_, and C_2_H_5_OH, a wide variety of carbon chains, nitrogen oxides like N_2_O, and saturated molecules like CH_3_SH, in addition to eight new interstellar molecules (HCCO, HCS, HSC, NCCNH^+^, CNCN, NCO, H_2_NCO^+^, and NS^+^) whose detection has already been reported. In general, fractional molecular abundances in L483 are systematically lower than in TMC-1 (especially for carbon chains), tend to be higher than in L1544 and B1-b, and are similar to those in L1527. Apart from the overabundance of carbon chains in TMC-1, we find that L483 does not have a marked chemical differentiation with respect to starless/prestellar cores like TMC-1 and L1544, although it does chemically differentiate from Class 0 hot corino sources like IRAS 16293-2422. This fact suggests that the chemical composition of the ambient cloud of some Class 0 sources could be largely inherited from the dark cloud starless/prestellar phase. We explore the use of potential chemical evolutionary indicators, such as the HNCO/C_3_S, SO_2_/C_2_S, and CH_3_SH/C_2_S ratios, to trace the prestellar/protostellar transition. We also derived isotopic ratios for a variety of molecules, many of which show isotopic ratios close to the values for the local interstellar medium (remarkably all those involving ^34^S and ^33^S), while there are also several isotopic anomalies like an extreme depletion in ^13^C for one of the two isotopologs of c-C_3_H_2_, a drastic enrichment in ^18^O for SO and HNCO (SO being also largely enriched in ^17^O), and different abundances for the two ^13^C substituted species of C_2_H and the two ^15^N substituted species of N_2_H^+^. We report the first detection in space of some minor isotopologs and quantify for the first time the deuterium fractionation for HDCCO and c-C_3_D. The exhaustive chemical characterization of L483 presented here, together with similar studies of other prestellar and protostellar sources, should allow us to identify the main factors that regulate the chemical composition of cores along the process of formation of low-mass protostars.
- ID:
- ivo://CDS.VizieR/J/ApJS/149/343
- Title:
- Giant molecular clouds in M33
- Short Name:
- J/ApJS/149/343
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first interferometric ^12^CO (J=1->0) map of the entire H{alpha} disk of M33. The 13" diameter synthesized beam corresponds to a linear resolution of 50pc, sufficient to distinguish individual giant molecular clouds (GMCs). From these data we generated a catalog of 148 GMCs with an expectation that no more than 15 of the sources are spurious. The catalog is complete down to GMC masses of 1.5x10^5^M_{sun}_ and contains a total mass of 2.3x10^7^M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/654/240
- Title:
- Giant molecular clouds in M31
- Short Name:
- J/ApJ/654/240
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometer observations of giant molecular clouds (GMCs) along a spiral arm in M31. The observations consist of a survey using the compact configuration of the interferometer and follow-up, higher resolution observations on a subset of the detections in the survey. The data are processed using an analysis algorithm designed to extract GMCs and correct their derived properties for observational biases, thereby facilitating comparison with Milky Way data. The algorithm identifies 67 GMCs, of which 19 have a sufficient signal-to-noise ratio to accurately measure their properties. The GMCs in this portion of M31 are indistinguishable from those found in the Milky Way, having a similar size-line width relationship and distribution of virial parameters, confirming the results of previous, smaller studies. The velocity gradients and angular momenta of the GMCs are comparable to the values measured in M33 and the Milky Way, and in all cases are below expected values based on the local galactic shear. The studied region of M31 has an interstellar radiation field, metallicity, Toomre Q parameter, and midplane volume density similar to those of the inner Milky Way, so the similarity of GMC populations between the two systems is not surprising.
- ID:
- ivo://CDS.VizieR/J/A+A/542/A108
- Title:
- Giant molecular clouds in M33
- Short Name:
- J/A+A/542/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of a systematic CO(2-1) survey at 12" resolution covering most of the Local Group spiral M33, which, at a distance of 840kpc, is close enough for individual giant molecular clouds (GMCs) to be identified. The goal of this work is to study the properties of the GMCs in this subsolar metallicity galaxy. The CPROPS (Cloud PROPertieS) algorithm was used to identify 337 GMCs in M33, the largest sample to date for an external galaxy. The sample is used to study the GMC luminosity function, or mass spectrum under the assumption of a constant N(H_2_)/I_CO_ ratio.
- ID:
- ivo://CDS.VizieR/J/ApJ/772/107
- Title:
- Giant molecular clouds in nearby galaxies
- Short Name:
- J/ApJ/772/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We resolve 182 individual giant molecular clouds (GMCs) larger than 2.5x10^5^M_{sun}_ in the inner disks of 5 large nearby spiral galaxies (NGC 2403, NGC 3031, NGC 4736, NGC 4826, and NGC 6946) to create the largest such sample of extragalactic GMCs within galaxies analogous to the Milky Way. Using a conservatively chosen sample of GMCs most likely to adhere to the virial assumption, we measure cloud sizes, velocity dispersions, and ^12^CO(J=1-0) luminosities and calculate cloud virial masses. The average conversion factor from CO flux to H_2_ mass (or X_CO_) for each galaxy is 1-2x10^20^/cm2 (K.km/s)^-1^, all within a factor of two of the Milky Way disk value (~2x10^20^/cm2(K.km/s)^-1^). We find GMCs to be generally consistent within our errors between the galaxies and with Milky Way disk GMCs; the intrinsic scatter between clouds is of order a factor of two. Consistent with previous studies in the Local Group, we find a linear relationship between cloud virial mass and CO luminosity, supporting the assumption that the clouds in this GMC sample are gravitationally bound. We do not detect a significant population of GMCs with elevated velocity dispersions for their sizes, as has been detected in the Galactic center. Though the range of metallicities probed in this study is narrow, the average conversion factors of these galaxies will serve to anchor the high metallicity end of metallicity-X_CO_ trends measured using conversion factors in resolved clouds; this has been previously possible primarily with Milky Way measurements.
- ID:
- ivo://CDS.VizieR/J/ApJ/803/16
- Title:
- Giant molecular clouds in NGC4526 based on ^12^CO
- Short Name:
- J/ApJ/803/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a high spatial resolution (~20pc) of ^12^CO(2-1) observations of the lenticular galaxy NGC 4526. We identify 103 resolved giant molecular clouds (GMCs) and measure their properties: size R, velocity dispersion {sigma}_v_, and luminosity L. This is the first GMC catalog of an early-type galaxy. We find that the GMC population in NGC 4526 is gravitationally bound, with a virial parameter {alpha}~1. The mass distribution, dN/dM{propto}M^-2.39+/-0.03^, is steeper than that for GMCs in the inner Milky Way, but comparable to that found in some late-type galaxies. We find no size-line width correlation for the NGC 4526 clouds, in contradiction to the expectation from Larson's relation. In general, the GMCs in NGC 4526 are more luminous, denser, and have a higher velocity dispersion than equal-size GMCs in the Milky Way and other galaxies in the Local Group. These may be due to higher interstellar radiation field than in the Milky Way disk and weaker external pressure than in the Galactic center. In addition, a kinematic measurement of cloud rotation shows that the rotation is driven by the galactic shear. For the vast majority of the clouds, the rotational energy is less than the turbulent and gravitational energy, while the four innermost clouds are unbound and will likely be torn apart by the strong shear at the galactic center. We combine our data with the archival data of other galaxies to show that the surface density {Sigma} of GMCs is not approximately constant, as previously believed, but varies by ~3 orders of magnitude. We also show that the size and velocity dispersion of the GMC population across galaxies are related to the surface density, as expected from the gravitational and pressure equilibrium, i.e., {sigma}_v_R^-1/2^{propto}{Sigma}^1/2^.
- ID:
- ivo://CDS.VizieR/J/ApJS/212/2
- Title:
- Giant molecular clouds in the 4th Galactic quadrant
- Short Name:
- J/ApJS/212/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Columbia University-Universidad de Chile CO Survey of the southern Milky Way is used to separate the CO(1-0) emission of the fourth Galactic quadrant within the solar circle into its dominant components, giant molecular clouds (GMCs). After the subtraction of an axisymmetric model of the CO background emission in the inner southern Galaxy, 92 GMCs are identified, and for 87 of them the twofold distance ambiguity is solved. Their total molecular mass is M(H_2_)=1.14+/-0.05x10^8^M_{sun}_, accounting for around 40% of the molecular mass estimated from an axisymmetric analysis of the H_2_ volume density in the Galactic disk, M(H_2_)_disk_=3.03x10^8^M_{sun}_. The large-scale spiral structure in the southern Galaxy, within the solar circle, is traced by the GMCs in our catalog; three spiral arm segments, the Centaurus, Norma, and 3 kpc expanding arm, are analyzed. After fitting a logarithmic spiral arm model to the arms, tangent directions at 310{deg}, 330{deg}, and 338{deg}, respectively, are found, consistent with previous values from the literature. A complete CS(2-1) survey toward IRAS point-like sources with far-IR colors characteristic of ultracompact H II regions is used to estimate the massive star formation rate per unit H_2_ mass (MSFR) and the massive star formation efficiency ({epsilon}) for GMCs. The average MSFR for GMCs is 0.41+/-0.06L_{sun}_/M_{sun}_, and for the most massive clouds in the Norma arm it is 0.58+/-0.09L_{sun}_/M_{sun}_. Massive star formation efficiencies of GMCs are, on average, 3% of their available molecular mass.
- ID:
- ivo://CDS.VizieR/J/ApJ/661/830
- Title:
- Giant molecular clouds of M33
- Short Name:
- J/ApJ/661/830
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New observations of CO (J=1->0) line emission from M33, using the 25 element BEARS focal plane array at the Nobeyama Radio Observatory 45m telescope, in conjunction with existing maps from the BIMA interferometer and the FCRAO 14m telescope, give the highest resolution (13") and most sensitive ({sigma}_rms_~60mK) maps to date of the distribution of molecular gas in the central 5.5kpc of the galaxy. A new catalog of giant molecular clouds (GMCs) has a completeness limit of 1.3x10^5^M_{sun}_.
