- ID:
- ivo://CDS.VizieR/J/ApJS/249/6
- Title:
- Galactic interstellar ratio ^18^O/^17^O. I.
- Short Name:
- J/ApJS/249/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interstellar oxygen isotopic ratio of ^18^O/^17^O can reflect the relative amount of the secular enrichment by ejecta from high-mass versus intermediate-mass stars. Previous observations found a Galactic gradient of ^18^O/^17^O, i.e., low ratios in the Galactic center and large values in the Galactic disk, which supports the inside-out formation scenario of our Galaxy. However, there are not many observed objects and, in particular, there are not many at large galactocentric distances. For this reason, we started a systematic study on Galactic interstellar ^18^O/^17^O, through observations of C^18^O and C^17^O multi-transition lines toward a large sample of 286 sources (at least one order of magnitude larger than previous ones), from the Galactic center region to the far outer Galaxy (~22kpc). In this article, we present our observations of J=1-0 lines of C^18^O and C^17^O, with the 12m antenna of the Arizona Radio Observatory (ARO 12m) and the Institut de Radio Astronomie Millimetrique (IRAM) 30m telescopes. Among our IRAM 30m sample of 50 targets, we detected successfully both C^18^O and C^17^O 1-0 lines for 34 sources. Similarly, our sample of 260 targets for ARO 12m observations resulted in the detection of both lines for 166 sources. The C^18^O optical depth effect on our ratio results, evaluated by fitting results of C^17^O spectra with hyperfine components (assuming {tau}_C18O_=4{tau}_C17O_) and our radiative transfer and excitation model nonlocal thermodynamic equilibrium (non-LTE) model calculation for the strongest source, was found to be insignificant. Beam dilution does not seem to be a problem either, which was supported by the fact that there is no systematic variation between the isotopic ratio and the heliocentric distance, and ratios are consistently measured from two telescopes for most of those detected sources. With this study we obtained ^18^O/^17^O isotopic ratios for a large sample of molecular clouds with different galactocentric distances. Our results, though there are still very few detections made for sources in the outer Galaxy, confirm the apparent ^18^O/^17^O gradient of ^18^O/^17^O=(0.10+/-0.03)R_GC_+(2.95+/-0.30), with a Pearson's rank correlation coefficient of R=0.69. This is supported by the newest Galactic chemical evolution model including the impact of massive stellar rotators and novae.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/831/73
- Title:
- Galactic MCs associated with HII regions
- Short Name:
- J/ApJ/831/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relations between star formation and properties of molecular clouds (MCs) are studied based on a sample of star-forming regions in the Galactic Plane. Sources were selected by having radio recombination lines to provide identification of associated MCs and dense clumps. Radio continuum emission and mid-infrared emission were used to determine star formation rates (SFRs), while ^13^CO and submillimeter dust continuum emission were used to obtain the masses of molecular and dense gas, respectively. We test whether total molecular gas or dense gas provides the best predictor of SFR. We also test two specific theoretical models, one relying on the molecular mass divided by the free-fall time, the other using the free-fall time divided by the crossing time. Neither is supported by the data. The data are also compared to those from nearby star-forming regions and extragalactic data. The star formation "efficiency," defined as SFR divided by mass, spreads over a large range when the mass refers to molecular gas; the standard deviation of the log of the efficiency decreases by a factor of three when the mass of relatively dense molecular gas is used rather than the mass of all of the molecular gas.
- 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.
- 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/ApJ/899/158
- Title:
- Gas structure comparison; NGC 253 and Milky Way
- Short Name:
- J/ApJ/899/158
- Date:
- 14 Mar 2022 07:10:20
- Publisher:
- CDS
- Description:
- We compare molecular gas properties in the starbursting center of NGC253 and the Milky Way Galactic center (GC) on scales of ~1-100pc using dendrograms and resolution-, area-, and noise-matched data sets in CO(1-0) and CO(3-2). We find that the size-line width relations in NGC253 and the GC have similar slope, but NGC253 has larger line widths by factors of ~2-3. The {sigma}2/R dependency on column density shows that, in the GC, on scales of 10-100pc the kinematics of gas over N>3x1021/cm^2^ are compatible with gravitationally bound structures. In NGC253 this is only the case for column densities N>3x1022/cm^2^. The increased line widths in NGC253 originate in the lower column density gas. This high velocity dispersion, not gravitationally self-bound gas, is likely in transient structures created by the combination of high average densities and feedback in the starburst. The high densities turn the gas molecular throughout the volume of the starburst, and the injection of energy and momentum by feedback significantly increases the velocity dispersion at a given spatial scale over what is observed in the GC.
- 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^.
