- ID:
- ivo://CDS.VizieR/J/ApJ/723/1019
- Title:
- Galactic SFR and gas surface densities
- Short Name:
- J/ApJ/723/1019
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relation between star formation rate (SFR) and gas surface densities in Galactic star-forming regions using a sample of young stellar objects (YSOs) and massive dense clumps. Our YSO sample consists of objects located in 20 large molecular clouds from the Spitzer cores to disks (c2d; Evans, 2009, Cat. J/ApJS/181/321) and Gould's Belt (GB) survey (L. Allen et al. 2010, in preparation). These data allow us to probe the regime of low-mass star formation, essentially invisible to tracers of high-mass star formation used to establish extragalactic SFR-gas relations. We estimate the gas surface density ({Sigma}_gas_) from extinction (A_V_) maps and YSO SFR surface densities ({Sigma}_SFR_) from the number of YSOs, assuming a mean mass and lifetime. We also divide the clouds into evenly spaced contour levels of A_V_, counting only Class I and Flat spectral energy distribution YSOs, which have not yet migrated from their birthplace. For a sample of massive star-forming clumps, we derive SFRs from the total infrared luminosity and use HCN gas maps to estimate gas surface densities. We find that c2d and GB clouds lie above the extragalactic SFR-gas relations (e.g., Kennicutt-Schmidt law) by factors of up to 17. We use ^12^CO and ^13^CO gas maps of the Perseus and Ophiuchus clouds from the COMPLETE survey (Ridge et al. 2006AJ....131.2921R) to estimate gas surface densities and compare to measurements from A_V_ maps.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/530/A118
- Title:
- G29.96-0.02 and G35.20-1.74 1mm and 3mm maps
- Short Name:
- J/A+A/530/A118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most work on high-mass star formation has focused on observations of young massive stars in protoclusters. Very little is known about the preceding stage. Here, we present a new high-resolution study of pre-protocluster regions in tracers exclusively probing the coldest and dense gas (NH_2_ D). The two target regions G29.96-0.02 and G35.20-1.74 (W48) are drawn from the SCAMPS project, which searches for pre-protoclusters near known ultracompact HII regions. We used our data to constrain the chemical, thermal, kinematic, and physical conditions (i.e., densities) in G29.96e and G35.20w. NH_3_, NH_2_ D, HCO^+^, and continuum emission were mapped using the VLA, PdBI, and BIMA.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A133
- Title:
- Gas and dust in star-forming region rho OphA
- Short Name:
- J/A+A/608/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate to what degree local physical and chemical conditions are related to the evolutionary status of various objects in star-forming media. rho Oph A displays the entire sequence of low-mass star formation in a small volume of space. Using spectrophotometric line maps of H_2_, H_2_O, NH_3_, N_2_H^+^, O_2_, OI, CO, and CS, we examine the distribution of the atomic and molecular gas in this dense molecular core. The physical parameters of these species are derived, as are their relative abundances in rho Oph A. Using radiative transfer models, we examine the infall status of the cold dense cores from their resolved line profiles of the ground state lines of H_2_O and NH_3_, where for the latter no contamination from the VLA 1623 outflow is observed and line overlap of the hyperfine components is explicitly taken into account. The stratified structure of this photon dominated region (PDR), seen edge-on, is clearly displayed. Polycyclic aromatic hydrocarbons (PAHs) and OI are seen throughout the region around the exciting star S1. At the interface to the molecular core 0.05pc away, atomic hydrogen is rapidly converted into H_2_, whereas OI protrudes further into the molecular core. This provides oxygen atoms for the gas-phase formation of O_2_ in the core SM1, where X(O_2_)~5x10^-8^. There, the ratio of the O_2_ to H_2_O abundance [X(H_2_O)~5x10^-9^] is significantly higher than unity. Away from the core, O_2_ experiences a dramatic decrease due to increasing H_2_O formation. Outside the molecular core, on the far side as seen from S1, the intense radiation from the 0.5pc distant early B-type star HD147889 destroys the molecules. Towards the dark core SM1, the observed abundance ratio X(O_2_)/X(H_2_O)>1, which suggests that this object is extremely young, which would explain why O_2_ is such an elusive molecule outside the solar system.
- ID:
- ivo://CDS.VizieR/J/A+A/578/A131
- Title:
- Gas and dust in the star-forming region rho OphA
- Short Name:
- J/A+A/578/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using mapping observations of the very dense rho Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimeter continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N_2_H^+^, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N_2_H^+^(J=3-2) and (J=6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H2), hence the surface density distribution of the gas. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM1. The global average, =88, is not far from the canonical value of 100, however. In rho Oph A, the exponent beta of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class-1 sources to low values close to 0 for the disk-dominated emission in ClassIII objects. beta assumes intermediate values for evolutionary classes in between. Since beta is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C^18^O, also N_2_H^+^ is frozen onto the grains.
- ID:
- ivo://CDS.VizieR/J/A+A/527/A135
- Title:
- Gas dynamics in Massive Dense Cores in Cygnus-X
- Short Name:
- J/A+A/527/A135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We studied the kinematic properties of dense gas surrounding massive protostars in a sample of five Massive Dense Cores (MDCs) in Cygnus-X. The aim is to investigate whether turbulent support plays a major role in stabilizing the cores against a rapid fragmentation into Jeans-mass objects. Alternatively the observed kinematics could indicate a high level of dynamics suggesting that the cores are actually not in equilibrium and dynamical processes could be the main driver to build up the final stellar masses.
- ID:
- ivo://CDS.VizieR/J/ApJ/688/290
- Title:
- GASS HI survey of the lower halo
- Short Name:
- J/ApJ/688/290
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have detected over 400 HI clouds in the lower halo of the Galaxy within the pilot region of the Galactic All-Sky Survey (GASS), a region of the fourth quadrant that spans 18{deg} in longitude, 40{deg} in latitude, and is centered on the Galactic equator. These clouds have a median peak brightness temperature of 0.6K, a median velocity width of 12.8km/s, and angular sizes <~1{deg}. The motion of these clouds is dominated by Galactic rotation with a random cloud-to-cloud velocity dispersion of 18km/s. A sample of clouds likely to be near tangent points was analyzed in detail. These clouds have radii on the order of 30pc and a median HI mass of 630M_{sun}_. The population has a vertical scale height of 400pc and is concentrated in Galactocentric radius, peaking at R=3.8kpc. This confined structure suggests that the clouds are linked to spiral features, while morphological evidence that many clouds are aligned with loops and filaments is suggestive of a relationship with star formation. The clouds might result from supernovae and stellar winds in the form of fragmenting shells and gas that has been pushed into the halo rather than from a galactic fountain.
- ID:
- ivo://CDS.VizieR/J/A+A/595/A88
- Title:
- G345.45+1.50 ^13^CO(3-2) clumps
- Short Name:
- J/A+A/595/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ring-like structures in the interstellar medium (ISM) are commonly associated with high-mass stars. Kinematic studies of large structures in giant molecular clouds (GMCs) toward these ring-like structures may help us to understand how massive stars form. The origin and properties of the ring-like structure G345.45+1.50 is investigated through observations of the ^13^CO(3-2) line. The aim of the observations is to determine the kinematics in the region and to compare physical characteristics estimated from gas emission with those previously determined using dust continuum emission. This area in the sky is well suited for studies like this because the ring is located 1.5{deg} above the Galactic plane at 1.8kpc from the Sun, thus molecular structures are rarely superposed on our line of sight, which minimizes confusion effects that might hinder identifying of individual molecular condensations. The ^13^CO(3-2) line was mapped toward the whole ring using the Atacama Pathfinder Experiment (APEX) telescope. The observations cover 17'x20' in the sky with a spatial resolution of 0.2pc and an rms of ~1K at a spectral resolution of 0.1km/s. The ring is found to be expanding with a velocity of 1.0km/s, containing a total mass of 6.9x10^3^M_{sun}_, which agrees well with that determined using 1.2mm dust continuum emission. An expansion timescale of ~3x10^6^yr and a total energy of ~7x10^46^erg are estimated. The origin of the ring might have been a supernova explosion, since a 35.5cm source, J165920-400424, is located at the center of the ring without an infrared counterpart. The ring is fragmented, and 104 clumps were identified with diameters of between 0.3 and 1.6pc, masses of between 2.3 and 7.5x10^2^M_{sun}_, and densities of between ~10^2^ and ~10^4^cm^-3^. At least 18% of the clumps are forming stars, as is shown in infrared images. Assuming that the clumps can be modeled as Bonnor-Ebert spheres, 13 clumps are collapsing, and the rest of them are in hydrostatic equilibrium with an external pressure with a median value of 4x10^4^K/cm^3^. In the region, the molecular outflow IRAS 16562-3959 is identified, with a velocity range of 38.4km/s, total mass of 13M_{sun}_, and kinematic energy of 7x10^45^erg. Finally, five filamentary structures were found at the edge of the ring with an average size of 3pc, a width of 0.6pc, a mass of 2x10^2^M_{sun}_, and a column density of 6x10^21^cm^-2^.
- ID:
- ivo://CDS.VizieR/J/A+A/656/A101
- Title:
- G305 Giant Molecular Cloud II. Clump properties
- Short Name:
- J/A+A/656/A101
- Date:
- 21 Mar 2022 07:03:46
- Publisher:
- CDS
- Description:
- G305 star-forming complex was observed in the 3-2 lines of 12 & 13CO to investigate the effect of feedback from the central OB stars on the complex. The region was decomposed into clumps using dendrogram analysis. A catalog of clump properties was created. The surface mass densities of the clumps were plotted as a function of the incident 8um flux. A mask of the region with 8um flux >100MJy/sr was created and clumps were categorized based on the extent of overlap with the mask into "mostly inside", "partly inside" & "outside". The surface mass density distribution of each of these populations were plotted. This was followed by comparing G305 clumps with the Galactic average taken from the ATLASGAL and CHIMPS clumps. Finally, the cumulative distribution functions (CDF) of the clump masses in G305 & their L/M ratios were compared to that of the Galactic sample. The surface mass densities of clumps showed a positive correlation with incident 8um flux. The data did not have sufficient velocity resolution to discern the effects of feedback on the linewidths of the clumps. The sub-sample of clumps named "mostly inside" had the highest surface mass densities followed by "partly -inside" and "outside" sub-samples. These differences between the three sub-samples were shown to be statistically significant using the KS test. The "mostly inside" sample also showed the highest level of fragmentation compared to the other two. These prove that clumps inside the G305 region are triggered. The G305 clump population is also statistically different from the Galactic average population rejecting redistribution as a likely consequence of feedback. The CDFs of clump masses and their L/M ratios are both flatter than the Galactic average, indicating that feedback in G305 has triggered star formation. The collect & collapse method is the dominant mechanism at play in G305.
- ID:
- ivo://CDS.VizieR/J/A+A/625/A19
- Title:
- 33 GHz continuum map of M51
- Short Name:
- J/A+A/625/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It remains unclear what sets the efficiency with which molecular gas transforms into stars. Here we present a new VLA map of the spiral galaxy M51 in 33GHz radio continuum, an extinction-free tracer of star formation, at 3" scales (~100pc). We combined this map with interferometric PdBI/NOEMA observations of CO(1-0) and HCN(1-0) at matched resolution for three regions in M51 (central molecular ring, northern and southern spiral arm segments). While our measurements roughly fall on the well-known correlation between total infrared and HCN luminosity, bridging the gap between Galactic and extragalactic observations, we find systematic offsets from that relation for different dynamical environments probed in M51, e.g. the southern arm segment is more quiescent due to low star formation efficiency (SFE) of the dense gas, despite having a high dense gas fraction. Combining our results with measurements from the literature at 100pc scales, we find that the SFE of the dense gas and the dense gas fraction anti-correlate and correlate, respectively, with the local stellar mass surface density. This is consistent with previous kpc-scale studies. In addition, we find a significant anti-correlation between the SFE and velocity dispersion of the dense gas. Finally, we confirm that a correlation also holds between star formation rate surface density and the dense gas fraction, but it is not stronger than the correlation with dense gas surface density. Our results are hard to reconcile with models relying on a universal gas density threshold for star formation and suggest that turbulence and galactic dynamics play a major role in setting how efficiently dense gas converts into stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/3461
- Title:
- 6.7-GHz methanol masers-dust associations
- Short Name:
- J/MNRAS/446/3461
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of 870{mu}m continuum observations, using the Large APEX Bolometer Camera, towards 77 class-II, 6.7-GHz methanol masers identified by the Methanol MultiBeam (MMB) survey to map the thermal emission from cool dust towards these objects. These data complement a study of 630 methanol masers associated with compact dense clumps identified from the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. Compact dust emission is detected towards 70 sources, which implies a dust-association rate of 99 per cent for the full MMB catalogue. Evaluation of the derived dust and maser properties leads us to conclude that the combined sample represents a single population tracing the same phenomenon. We find median clump masses of a few 10^3^M_{sun}_ and that all but a handful of sources satisfy the mass-size criterion required for massive star formation. This study provides the strongest evidence of the almost ubiquitous association of methanol masers with massive, star-forming clumps. The fraction of methanol-maser associated clumps is a factor of ~2 lower in the outer Galaxy than the inner Galaxy, possibly a result of the lower metallicity environment of the former. We find no difference in the clump-mass and maser-luminosity distributions of the inner and outer Galaxy. The maser-pumping and clump formation mechanisms are therefore likely to be relatively invariant to Galactic location. Finally, we use the ratio of maser luminosity and clump mass to investigate the hypothesis that the maser luminosity is a good indicator of the evolutionary stage of the embedded source, however, we find no evidence to support this.
