- ID:
- ivo://CDS.VizieR/J/A+A/522/A3
- Title:
- M33 CO(2-1) and HI integrated intensity maps
- Short Name:
- J/A+A/522/A3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution large-scale observations of the molecular and atomic gas in the Local Group galaxy M 33. The observations were carried out using the HEterodyne Receiver Array (HERA) at the 30m IRAM telescope in the CO(2-1) line, achieving a resolution of 12"x2.6km/s, enabling individual giant molecular clouds (GMCs) to be resolved. The observed region is 650 square arcminutes mainly along the major axis and out to a radius of 8.5kpc, and covers entirely the 2'x40' radial strip observed with the HIFI and PACS Spectrometers as part of the HERM33ES Herschel key program. The achieved sensitivity in main-beam temperature is 20-50mK at 2.6km/s velocity resolution. The CO(2-1) luminosity of the observed region is 1.7+/-0.1x10^7^K.km/s.pc^2^ and is estimated to be 2.8+/-0.3x10^7^K.km/s.pc^2^ for the entire galaxy, corresponding to H_2_ masses of 1.9x10^8^ and 3.3x10^8^ respectively (including He), calculated with N(H_2_)/I_CO_(1-0) twice the Galactic value due to the half-solar metallicity of M 33. The HI 21cm VLA archive observations were reduced, and the mosaic was imaged and cleaned using the multi-scale task in the CASA software package, yielding a series of datacube with resolutions ranging from 5" to 25". The HI mass within a radius of 8.5kpc is estimated to be 1.4x10^9^. The azimuthally averaged CO surface brightness decreases exponentially with a scale length of 1.9+/-0.1kpc whereas the atomicgas surface density is constant at {Sigma}_HI_=6+/-2pc^-2^ deprojected to face-on. For an (H_2_)/I_CO_(1-0) conversion factor twice that of the Milky Way, the central kiloparsec H2 surface density is {Sigma}_HI_=8.5+/-0.2pc^-2^. The star formation rate per unit moecular gas (SF efficiency, the rate of transformation of molecular gas into stars), as traced by the ratio of CO to H{alpha} and FIR brightness, is constant with radus. The SFE, with a N(H2)/I_CO_(1-0) factor twice galactic, appears 2-4 times greater than for large spiral galaxies. A morphological comparison of molecular and atomic gas with tracers of star formation is presented showing good agreement between these maps both in terms of peaks and holes. A few exceptions are noted. Several spectra, including those of a molecular cloud situated more than 8kpc from the galaxy center, are presented.
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102. M16 CO maps
- ID:
- ivo://CDS.VizieR/J/A+A/627/A27
- Title:
- M16 CO maps
- Short Name:
- J/A+A/627/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to investigate the impact of the ionized radiation from the M16 HII region on the surrounding molecular cloud and on its hosted star formation. To present comprehensive multi-wavelength observations towards the M16 HII region, we used new CO data and existing infrared, optical, and submillimeter data. The ^12^CO J=1-0, ^13^CO J=1-0, and C^18^O J=1-0 data were obtained with the Purple Mountain Observatory (PMO) 13.7m radio telescope. To trace massive clumps and extract young stellar objects (YSOs) associated with the M16 HII region, we used the ATLASGAL and GLIMPSE I catalogs, respectively. From CO data, we discern a large-scale filament with three velocity components. Because these three components overlap with each other in both velocity and space, the filament may be made of three layers. The M16 ionized gas interacts with the largescale filament and has reshaped its structure. In the large-scale filament, we find 51 compact cores from the ATLASGAL catalog, 20 of them being quiescent. The mean excitation temperature of these cores is 22.5K, while this is 22.2K for the quiescent cores. This high temperature observed for the quiescent cores suggests that the cores may be heated by M16 and do not experience internal heating from sources in the cores. Through the relationship between the mass and radius of these cores, we obtain that 45% of all the cores are massive enough to potentially form massive stars. Compared with the thermal motion, the turbulence created by the nonthermal motion is responsible for the core formation. For the pillars observed towards M16, the H II region may give rise to the strong turbulence.
103. M31 CO(2-1) spectra
- ID:
- ivo://CDS.VizieR/J/A+A/549/A27
- Title:
- M31 CO(2-1) spectra
- Short Name:
- J/A+A/549/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With IRAM-30m/HERA, we have detected CO(2-1) gas complexes within 30arcsec (100pc) from the center of M31 that amount to a minimum total mass of 4.2x10^4^M_{sun}_ (one third of the positions are detected). Averaging the whole HERA field, we show that there is no additional undetected diffuse component. Moreover, the gas detection is associated with gas lying on the far side of the M31 center as no extinction is observed in the optical, but some emission is present on infrared Spitzer maps. The kinematics is complex. (1) The velocity pattern is mainly redshifted: the dynamical center of the gas differs from the black hole position and the maximum of optical emission, and only the redshifted side is seen in our data. (2) Several velocity components are detected in some lines of sight. Our interpretation is supported by the reanalysis of the effect of dust on a complete planetary nebula sample. Two dust components are detected with respective position angles of 37deg and -66deg. This is compatible with a scenario where the superposition of the (PA=37deg) disk is dominated by the 10kpc ring and the inner 0.7kpc ring detected in infrared data, whose position angle (-66deg) we measured for the first time. The large-scale disk, which dominates the HI data, is steeply inclined (i=77deg), warped and superposed on the line of sight on the less inclined inner ring. The detected CO emission might come from both components.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A96
- Title:
- Mid-J CO shock tracing observations of IRDCs II
- Short Name:
- J/A+A/587/A96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Infrared dark clouds are kinematically complex molecular structures in the interstellar medium that can host sites of massive star formation. We present maps measuring 4 square arcminutes of the ^12^CO, ^13^CO, and C^18^O J=3 to 2 lines from selected locations within the C and F (G028.37+00.07 and G034.43+00.24) infrared dark clouds (IRDCs), as well as single pointing observations of the ^13^CO and C^18^O J=2 to 1 lines towards three cores within these clouds. We derive CO gas temperatures throughout the maps and find that CO is significantly frozen out within these IRDCs. We find that the CO depletion tends to be the highest near column density peaks with maximum depletion factors between 5 and 9 in IRDC F and between 16 and 31 in IRDC C. We also detect multiple velocity components and complex kinematic structure in both IRDCs. Therefore, the kinematics of IRDCs seem to point to dynamically evolving structures yielding dense cores with considerable depletion factors.
- ID:
- ivo://CDS.VizieR/J/ApJ/834/57
- Title:
- Milky Way molecular clouds from ^12^CO
- Short Name:
- J/ApJ/834/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study presents a catalog of 8107 molecular clouds that covers the entire Galactic plane and includes 98% of the ^12^CO emission observed within b+/-5^{deg}^. The catalog was produced using a hierarchical cluster identification method applied to the result of a Gaussian decomposition of the Dame+ (2001ApJ...547..792D) data. The total H_2_ mass in the catalog is 1.2x10^9^M_{sun}_, in agreement with previous estimates. We find that 30% of the sight lines intersect only a single cloud, with another 25% intersecting only two clouds. The most probable cloud size is R~30pc. We find that M{propto}R^2.2+/-0.2^, with no correlation between the cloud surface density, {Sigma}, and R. In contrast with the general idea, we find a rather large range of values of {Sigma}, from 2 to 300M_{sun}_/pc^2^, and a systematic decrease with increasing Galactic radius, R_gal_. The cloud velocity dispersion and the normalization {sigma}_0_={sigma}_v_/R^1/2^ both decrease systematically with R_gal_. When studied over the whole Galactic disk, there is a large dispersion in the line width-size relation and a significantly better correlation between {sigma}_v_ and {Sigma}R. The normalization of this correlation is constant to better than a factor of two for R_gal_<20kpc. This relation is used to disentangle the ambiguity between near and far kinematic distances. We report a strong variation of the turbulent energy injection rate. In the outer Galaxy it may be maintained by accretion through the disk and/or onto the clouds, but neither source can drive the 100 times higher cloud-averaged injection rate in the inner Galaxy.
- 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).
- ID:
- ivo://CDS.VizieR/J/A+A/568/A56
- Title:
- mm continuum and line images of G0.253+0.016
- Short Name:
- J/A+A/568/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The massive infrared dark cloud G0.253+0.016 projected ~45pc from the Galactic centre contains ~10^5^M_{sun}_ of dense gas whilst being mostly devoid of observed star-formation tracers. Our goals are therefore to scrutinise the physical properties, dynamics and structure of this cloud with reference to its star-forming potential. We have carried out a concerted SMA and IRAM 30m study of this enigmatic cloud in dust continuum, CO isotopologues, several shock tracing molecules, as well as H_2_CO to trace the gas temperature. In addition, we include ancillary far-IR and sub-mm Herschel and SCUBA data in our analysis. We detect and characterise a total of 36 dust cores within G0.253+0.016 at 1.3mm and 1.37mm, with masses between 25 and approximately 250M_{sun}_, and find that the kinetic temperature of the gas traced by H_2_CO ratios is >320K on size-scales of ~0.15pc. Analysis of the position-velocity diagrams of our observed lines show broad linewidths and strong shock emission in the south of the cloud, indicating that G0.253+0.016 is colliding with another cloud at v_LSR_~70km/s. We confirm via an analysis of the observed dynamics in the Central Molecular Zone that it is an elongated structure, orientated with Sgr B2 closer to the Sun than Sgr A*, however our results suggest that the actual geometry may be more complex than an elliptical ring. We find that the column density Probability Distribution Function (PDF) of G0.253+0.016 derived from SMA and SCUBA dust continuum emission is log-normal with no discernible power-law tail, consistent with little star formation, and that its width can be explained in the framework of theory predicting the density structure of clouds created by supersonic, magnetised turbulence. We also present the Delta-variance spectrum of this region, a proxy for the density power spectrum of the cloud, and show it is consistent with that expected for clouds with no current star formation. Finally, we show that even after determining a scaled column density threshold for star formation by incorporating the effects of the increased turbulence in the cloud, we would still expect ten stars with masses >15M_{sun}_ to form in G0.253+0.016. If these cannot be accounted for by new radio continuum observations, then further physical aspects may be important, such as the background column density level, which would turn an absolute column density threshold for star formation into a critical over-density. We conclude that G0.253+0.016 contains high-temperatures and wide-spread shocks, displaying evidence of interaction with a nearby cloud which we identify at v_LSR_~70km/s. Our analysis of the structure of the cloud can be well-explained by theory of magnetised turbulence, and is consistent with little or no current star formation. Using G0.253+0.016 as a test-bed of the conditions required for star formation in a different physical environment to that of nearby clouds, we also conclude that there is not one column density threshold for star formation, but instead this value is dependant on the local physical conditions.
- ID:
- ivo://CDS.VizieR/J/A+A/601/A146
- Title:
- M33 molecular clouds and young stellar clusters
- Short Name:
- J/A+A/601/A146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the association between giant molecular clouds (GMCs) and young stellar cluster candidates (YSCCs) to shed light on the time evolution of local star formation episodes in the nearby galaxy M33. The CO (J=2-1) IRAM all-disk survey was used to identify and classify 566 GMCs with masses between 2x10^4^ and 2x10^6^M_{sun}_ across the whole star-forming disk of M33. In the same area, there are 630 YSCCs that we identified using Spitzer-24um data. Some YSCCs are embedded star-forming sites, while the majority have GALEX-UV and H{alpha} counterparts with estimated cluster masses and ages. The GMC classes correspond to different cloud evolutionary stages: inactive clouds are 32% of the total and classified clouds with embedded and exposed star formation are 16% and 52% of the total, respectively. Across the regular southern spiral arm, inactive clouds are preferentially located in the inner part of the arm, possibly suggesting a triggering of star formation as the cloud crosses the arm. The spatial correlation between YSCCs and GMCs is extremely strong, with a typical separation of 17pc. This is less than half the CO (2-1) beam size and illustrates the remarkable physical link between the two populations. GMCs and YSCCs follow the HI filaments, except in the outermost regions, where the survey finds fewer GMCs than YSCCs, which is most likely due to undetected clouds with low CO luminosity. The distribution of the non-embedded YSCC ages peaks around 5Myr, with only a few being as old as 8-10Myr. These age estimates together with the number of GMCs in the various evolutionary stages lead us to conclude that 14Myr is the typical lifetime of a GMC in M33 prior to cloud dispersal. The inactive and embedded phases are short, lasting about 4 and 2Myr, respectively. This underlines that embedded YSCCs rapidly break out from the clouds and become partially visible in H{alpha} or UV long before cloud dispersal.
- ID:
- ivo://CDS.VizieR/J/ApJS/182/131
- Title:
- Molecular clouds and clumps in the GRS
- Short Name:
- J/ApJS/182/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Boston University-Five College Radio Astronomy Observatory (BU-FCRAO) Galactic Ring Survey (GRS) of ^13^CO J=1->0 emission covers Galactic longitudes 18<l<55.7{deg} and Galactic latitudes |b|<=1{deg}. Using the SEQUOIA array on the FCRAO 14m telescope, the GRS fully sampled the ^13^CO Galactic emission (46" angular resolution on a 22" grid) and achieved a spectral resolution of 0.21km/s. Because the GRS uses ^13^CO, an optically thin tracer, rather than ^12^CO, an optically thick tracer, the GRS allows a much better determination of column density and also a cleaner separation of velocity components along a line of sight. With this homogeneous, fully sampled survey of ^13^CO emission, we have identified 829 molecular clouds and 6124 clumps throughout the inner Galaxy using the CLUMPFIND algorithm. Here we present details of the catalog and a preliminary analysis of the properties of the molecular clouds and their clumps. Moreover, we compare clouds inside and outside of the 5kpc ring and find that clouds within the ring typically have warmer temperatures, higher column densities, larger areas, and more clumps compared with clouds located outside the ring. This is expected if these clouds are actively forming stars. This catalog provides a useful tool for the study of molecular clouds and their embedded young stellar objects.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A104
- Title:
- Molecular clouds and star formation
- Short Name:
- J/A+A/588/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As a part of the Milky Way Imaging Scroll Painting (MWISP) survey, the aim is to study the physical properties of molecular clouds and their associated star formation toward the Galactic plane within 216.25{deg}<=l<=218.75{deg} and -0.75{deg}<=b<=1.25{deg}, which covers the molecular cloud complex S287. Using the 3x3 Superconducting Spectroscopic Array Receiver (SSAR) at the PMO-13.7m telescope, we performed a simultaneous ^12^CO (1-0), ^13^CO (1-0), C^18^O (1-0) mapping toward molecular clouds in a region encompassing 3.75 square degrees. The beam size is 52" for ^12^CO (1-0) and 55" for ^13^CO (1-0) and C^18^O (1-0).
