CO Maps Research Articles

A Search for Spatially Resolved Infrared Rovibrational Molecular Hydrogen Emission from the Disks of Young Stars

Abstract We present results from a survey searching for spatially resolved near-infrared line emission from molecular hydrogen gas in the circumstellar environments of nine young stars: AA Tau, AB Aur, DoAr 21, GG Tau, GM Aur, LkCa 15, LkHα 264, UY Aur, and V773 Tau. Prior high-resolution spectra of these stars showed the presence of rovibrational H2 line emission at 2.12 μm with characteristics more typical of gas located in protoplanetary disks rather than outflows. In this study, we spatially resolve the H2 emission in the eight stars for which it is detected. LkCa 15 is the only target that exhibits no appreciable H2 despite a prior detection. We find an anticorrelation between H2 and X-ray luminosities, likely indicating that the X-ray ionization process is not the dominant H2 excitation mechanism in these systems. AA Tau, UY Aur, and V773 Tau show discrete knots of H2, as typically associated with shocks in outflowing gas. UY Aur and V773 Tau exhibit spatially resolved velocity structures, while the other systems have spectrally unresolved emission consistent with systemic velocities. V773 Tau exhibits a complex line morphology indicating the presence of multiple excitation mechanisms, including red- and blueshifted bipolar knots of shock-excited outflowing gas. AB Aur, GM Aur, and LkHα 264 have centralized yet spatially resolved H2 emission consistent with a disk origin. The H2 images of AB Aur reveal spiral structures within the disk, matching those observed in ALMA CO maps. This survey reveals new insights into the structure and excitation of warm gas in the circumstellar environments of these young stars.

The Atacama Cosmology Telescope: CO(J = 3 – 2) Mapping and Lens Modeling of an ACT-selected Dusty Star-forming Galaxy

Abstract We report Northern Extended Millimeter Array CO(J = 3 − 2) observations of the dusty star-forming galaxy ACT-S J020941+001557 at z = 2.5528, which was detected as an unresolved source in the Atacama Cosmology Telescope (ACT) equatorial survey. Our spatially resolved spectral line data support the derivation of a gravitational lens model from 37 independent velocity channel maps using a pixel-based algorithm, from which we infer a velocity-dependent magnification factor μ ≈ 7–22 with a luminosity-weighted mean . The resulting source-plane reconstruction is consistent with a rotating disk, although other scenarios cannot be ruled out by our data. After correction for lensing, we derive a line luminosity , a cold gas mass , a dynamical mass , and a gas mass fraction . The line brightness temperature ratio of r 3,1 ≈ 1.6 relative to a Green Bank Telescope CO(J = 1 − 0) detection may be elevated by a combination of external heating of molecular clouds, differential lensing, and/or pointing errors.

DYNAMO: An upclose view of turbulent, clumpy galaxies

AbstractOver 2/3 of all star formation in the Universe occurs in gas-rich, super-high pressure clumpy galaxies in the epoch of redshift z ∼ 1 – 3. However, because these galaxies are so distant we are limited in the information available to study the properties of star formation and gas in these systems. I will present results using a sample of extremely rare, nearby galaxies (called DYNAMO) that are very well matched in gas fraction (fgas ∼ 20 – 80%), kinematics (rotating disks with velocity dispersions ranging 20 – 100 km/s), structure (exponential disks) and morphology (clumpy star formation) to high-z main-sequence galaxies. We therefore use DYNAMO galaxies as laboratories to study the processes inside galaxies in the dominate mode of star formation in the Universe. In this talk I will report on results from our programs with HST, ALMA, Keck, and NOEMA for DYNAMO galaxies that are aimed at testing models of star formation. We have discovered of an inverse relationship between gas velocity dispersion and molecular gas depletion time. This correlation is directly predicted by theories of feedback-regulated star formation; conversely, predictions of models in which turbulence is driven by gravity only are not consistent with our data. I will also show that feedback-regulated star formation can explain the redshift evolution of galaxy star formation efficiency. I will also present results from a recently acquired map of CO(2-1) in a clumpy galaxy with resolution less than 200 pc. With maps such as these we can begin to study these super giant star forming clumps at scales that are more comparable to local surveys. I will show results for the star formation efficiency of clumps, the boundedness of clumps of molecular gas, and discuss links between star formation efficiency and formation of clumps of stellar mass. The details of clumpy systems are a direct constraint of the results of simulations, especially on the nature of feedback in the high density environments of star formation that dominate the early Universe.

CO Outflow Survey of 68 Very Low Luminosity Objects: A Search for Proto-brown-dwarf Candidates

We present the results of a systematic search for molecular outflows in 68 Very Low Luminosity Objects (VeLLOs) from single-dish observations in CO isotopologues which find 16 VeLLOs showing clear outflow signatures in the CO maps. With additional three VeLLOs from the literature, we analyzed the outflow properties for 19 VeLLOs, identifying 15 VeLLOs as proto-Brown Dwarf (BD) candidates and four VeLLOs as likely faint protostar candidates. The proto-BD candidates are found to have a mass accretion rate ($\sim 10^{-8} - 10^{-7}$ $\rm M_{\odot}$ yr$^{-1}$) lower than that of the protostar candidates ($\gtrsim 10^{-6}$ $\rm M_{\odot}$ yr$^{-1}$). Their accretion luminosities are similar to or smaller than their internal luminosities, implying that many proto-BD candidates might have had either small accretion activity in a quiescent manner throughout their lifetime, or be currently exhibiting a relatively higher (or episodic) mass accretion than the past. There are strong trends that outflows of many proto-BDs are less active if they are fainter or have less massive envelopes. The outflow forces and internal luminosities for more than half of the proto-BD candidates seem to follow an evolutionary track of a protostar with its initial envelope mass of $\sim$0.08 $\rm M_{\odot}$, indicating that some BDs may form in less massive dense cores in a way similar to normal stars. But, because there also exists a significant fraction (about 40%) of proto-BDs with much weaker outflow force than expected by the relations for protostars, we should not rule out the possibility of other formation mechanism for the BDs.

Joint Power Spectrum and Voxel Intensity Distribution Forecast on the CO Luminosity Function with COMAP

Abstract We develop a framework for joint constraints on the CO luminosity function based on power spectra (PS) and voxel intensity distributions (VID) and apply this to simulations of CO Mapping Array Pathfinder (COMAP), a CO intensity mapping experiment. This Bayesian framework is based on a Markov chain Monte Carlo (MCMC) sampler coupled to a Gaussian likelihood with a joint PS + VID covariance matrix computed from a large number of fiducial simulations and re-calibrated with a small number of simulations per MCMC step. The simulations are based on dark matter halos from fast peak patch simulations combined with the L CO(M halo) model of Li et al. We find that the relative power to constrain the CO luminosity function depends on the luminosity range of interest. In particular, the VID is more sensitive at large luminosities, while the PS and the VID are both competitive at small and intermediate luminosities. The joint analysis is superior to using either observable separately. When averaging over CO luminosities ranging between , and over 10 cosmological realizations of COMAP Phase 2, the uncertainties (in dex) are larger by 58% and 30% for the PS and VID, respectively, when compared to the joint analysis (PS + VID). This method is generally applicable to any other random field, with a complicated likelihood, as long a fast simulation procedure is available.

Molecular Gas and Star Formation Properties in Early Stage Mergers: SMA CO(2-1) Observations of the LIRGs NGC 3110 and NGC 232

Abstract Mergers of galaxies are an important mode for galaxy evolution because they serve as an efficient trigger of powerful starbursts. However, observational studies of molecular gas properties during their early stages are scarce. We present interferometric CO(2–1) maps of two luminous infrared galaxies, NGC 3110 and NGC 232, obtained with the Submillimeter Array with ∼1 kpc resolution. While NGC 3110 is a spiral galaxy interacting with a minor (14:1 stellar mass) companion, NGC 232 is interacting with a similarly sized object. We find that such interactions in these galaxies have likely induced enhancements in the molecular gas content and central concentrations, partly at the expense of atomic gas. The obtained molecular gas surface densities in their circumnuclear regions are Σmol ≳ 102.5 M ⊙ pc−2, higher than in noninteracting objects by an order of magnitude. Gas depletion times of 0.5–1 Gyr are found for the different regions, lying in between noninteracting disk galaxies and the starburst sequence. In the case of NGC 3110, the spiral arms show on average 0.5 dex shorter depletion times than in the circumnuclear regions if we assume a similar H2–CO conversion factor. We show that even in the early stages of the interaction with a minor companion, a starburst is formed along the circumnuclear region and spiral arms, where a large population of SSCs is found (∼350), and at the same time a large central gas concentration is building up that might be the fuel for an active galactic nucleus. The main morphological properties of the NGC 3110 system are reproduced by our numerical simulations and allow us to estimate that the current epoch of the interaction is at ∼150 Myr after closest approach.

The Arizona Radio Observatory CO Mapping Survey of Galactic Molecular Clouds. VI. The Cep OB3 Cloud (Cepheus B and C) in CO J = 2–1, 13CO J = 2–1, and CO J = 3–2

Abstract We present (1) new fully sampled maps of CO and J = 2–1 emission and CO J = 3–2 emission toward the molecular clouds Cep B and C, associated with the Cep OB3 association; (2) a map of extinction, A V , derived from IR colors of background stars; and (3) the distribution of young stellar objects (YSOs) over the same field as the molecular maps. An LTE analysis of the CO and maps yields the distribution of molecular column densities and temperatures. Substantial variations are evident across the clouds; smaller subregions show correlations between molecular properties and dust extinction, consistent with a picture of outer photodissociation regions with a layer of CO-dark molecular gas, a CO self-shielded interior, and an inner cold dense region where CO is largely depleted onto grains. Comparing the distribution of YSOs with molecular gas surface density shows a power-law relation very similar in slope to that for the giant molecular cloud associated with the H ii region Sh2-235 from a previous paper in this series that employed the same methodology. We note the presence of several compact, isolated CO emission sources in the J = 3–2 maps. The gas temperature and velocity dispersion yield a map of the sonic Mach number, which varies across the cloud but always exceeds unity, confirming the pervasiveness of supersonic turbulence over length scales ≳0.1 pc (the map resolution). We also compute a J = 2–1 CO X-factor that varies with position but is, on average, within 20% of the Galactic average derived from CO J = 1–0 observations.

Correction to: Entropy Stable Finite Volume Approximations for Ideal Magnetohydrodynamics

When we published this article, the biographies of Gregor J Gassner and Stefanie Walch have been mixed up during the type-setting process. Sadly, this mistake remained unnoticed. The correct biographies are: Gregor Gassner is a professor in numerical analysis/scientific computing at the Mathematical Institute at the University of Cologne. Gregor obtained a diploma degree in aerospace engineering (2004) and a diploma degree in mathematics (2005) from the University of Stuttgart. In 2009 he received his doctoral degree at the Institute of Aerodynamics and Gasdynamics, Stuttgart. He got an offer for a Junior professorship at TU Braunschweig in computational fluid dynamics, an offer for scientific computing at the TU Hamburg-Harburg and an offer from University of Cologne, where he joined in 2013. In 2016 he received an ERC starting grant on the topic of adaptive, robust and highly efficient numerical methods for the simulation of non-linear conservation laws. Stefanie Walch is a full professor for theoretical astrophysics at the University of Cologne since 2013. After the diploma in physics in 2004, Stefanie received her doctoral degree in theoretical physics from the Ludwig-Maximilians-Universitat Munchen in 2008. Afterwards she has spent 3 years at Cardiff University in Wales, and approximately 2 years at the Max-Planck-Institute for Astrophysics in Garching as a postdoctoral researcher before being appointed at the University of Cologne. She specialises in the physics of the interstellar medium including star formation and stellar feedback in the form of ionizing radiation, stellar winds, and supernovae. The evolution of gas in galaxies is studied using massively parallel, three-dimensional magneto-hydrodynamics simulations with additional (self-)gravity, radiative transfer, and chemical networks to follow the formation and dissociation of molecules and to bridge the gap to observations in different tracers. Synthetic observations ranging from X-ray emission to CO and dust polarization maps are now used to put modern theories of star formation and feedback to the test. In 2015, she received an ERC Starting Grant on the topic of “The radiative interstellar medium”. The original article has been corrected. The publisher apologises for this mistake.

A case study of triggered star formation in Cygnus X

Radiative feedback from massive stars can potentially trigger star formation in the surrounding molecular gas. Inspired by the case of radiatively driven implosion in M16 or Eagle Nebula, we analyze a similar case of star formation observed in the Cygnus X region. We present new JCMT observations of $^{13}$CO(3-2) and C$^{18}$O(3-2) molecular lines of a cometary feature located at 50 pc north of the Cyg OB2 complex that was previously identified in $^{12}$CO(3-2) mapping. These data are combined with archival H$\alpha$, infrared, and radio continuum emission data, from which we measure the mass to be 110 M$_\odot$. We identify Cyg OB2 as the ionizing source. We measure the properties of two highly energetic molecular outflows and the photoionized rim. From this analysis, we argue the external gas pressure and gravitational energy dominate the internal pressure. The force balance along with previous simulation results and a close comparison with the case of Eagle Nebula favours a triggering scenario.

Dense Gas, Dynamical Equilibrium Pressure, and Star Formation in Nearby Star-forming Galaxies

Abstract We use new ALMA observations to investigate the connection between dense gas fraction, star formation rate (SFR), and local environment across the inner region of four local galaxies showing a wide range of molecular gas depletion times. We map HCN (1–0), HCO+ (1–0), CS (2–1), 13CO (1–0), and C18O (1–0) across the inner few kiloparsecs of each target. We combine these data with short-spacing information from the IRAM large program EMPIRE, archival CO maps, tracers of stellar structure and recent star formation, and recent HCN surveys by Bigiel et al. and Usero et al. We test the degree to which changes in the dense gas fraction drive changes in the SFR. (tracing the dense gas fraction) correlates strongly with I CO (tracing molecular gas surface density), stellar surface density, and dynamical equilibrium pressure, P DE. Therefore, becomes very low and HCN becomes very faint at large galactocentric radii, where ratios as low as become common. The apparent ability of dense gas to form stars, (where Σdense is traced by the HCN intensity and the star formation rate is traced by a combination of Hα and 24 μm emission), also depends on environment. decreases in regions of high gas surface density, high stellar surface density, and high P DE. Statistically, these correlations between environment and both and are stronger than that between apparent dense gas fraction ( ) and the apparent molecular gas star formation efficiency . We show that these results are not specific to HCN.

ALMA view of RX J1131-1231: Sub-kpc CO (2-1) mapping of a molecular disk in a lensed star-forming quasar host galaxy

We present ALMA 2-mm continuum and CO (2-1) spectral line imaging of the gravitationally lensed z = 0.654 star-forming/quasar composite RX J1131-1231 at 240–400 mas angular resolution. The continuum emission is found to be compact and coincident with the optical emission, whereas the molecular gas forms a complete Einstein ring, which shows strong differential magnification. The de-lensed source structure is determined on 400-parsec-scales resolution using a Bayesian pixelated visibility-fitting lens modelling technique. The reconstructed molecular gas velocity-field is consistent with a large rotating disk with a major-axis FWHM ~9.4 kpc at an inclination angle of i = 54° and with a maximum rotational velocity of 280 km s−1. From dynamical model fitting we find an enclosed mass within 5 kpc of M(r < 5 kpc) = (1.46 ± 0.31) × 1011 M⊙. The molecular gas distribution is highly structured, with clumps that are co-incident with higher gas velocity dispersion regions (40–50 km s−1) and with the intensity peaks in the optical emission, which are associated with sites of on-going turbulent star-formation. The peak in the CO (2-1) distribution is not co-incident with the AGN, where there is a paucity of molecular gas emission, possibly due to radiative feedback from the central engine. The intrinsic molecular gas luminosity is L′CO = 1.2 ± 0.3 × 1010 K km s−1 pc2 and the inferred gas mass is MH2 = 8.3 ± 3.0 × 1010 M⊙, which given the dynamical mass of the system is consistent with a CO–H2 conversion factor of α = 5.5 ± 2.0 M⊙ (K km s−1 pc2)−1. This suggests that the star-formation efficiency is dependent on the host galaxy morphology as opposed to the nature of the AGN. The far-infrared continuum spectral energy distribution shows evidence for heated dust, equivalent to an obscured star-formation rate of SFR = 69−25+41 × (7.3/μIR) M⊙ yr−1, which demonstrates the composite star-forming and AGN nature of this system.

The XCO Conversion Factor from Galactic Multiphase ISM Simulations

Abstract line emission is a widely used observational tracer of molecular gas, rendering essential the X CO factor, which is applied to convert CO luminosity to mass. We use numerical simulations to study how X CO depends on numerical resolution, non-steady-state chemistry, physical environment, and observational beam size. Our study employs 3D magnetohydrodynamics (MHD) simulations of galactic disks with solar neighborhood conditions, where star formation and the three-phase interstellar medium (ISM) are self-consistently regulated by gravity and stellar feedback. Synthetic CO maps are obtained by postprocessing the MHD simulations with chemistry and radiation transfer. We find that CO is only an approximate tracer of . On parsec scales, W CO is more fundamentally a measure of mass-weighted volume density, rather than column density. Nevertheless, , which is consistent with observations and insensitive to the evolutionary ISM state or radiation field strength if steady-state chemistry is assumed. Due to non-steady-state chemistry, younger molecular clouds have slightly lower and flatter profiles of X CO versus extinction than older ones. The -dark fraction is 26%–79%, anticorrelated with the average extinction. As the observational beam size increases from 1 to 100 pc, increases by a factor of ∼2. Under solar neighborhood conditions, in molecular clouds is converged at a numerical resolution of 2 pc. However, the total CO abundance and luminosity are not converged even at the numerical resolution of 1 pc. Our simulations successfully reproduce the observed variations of X CO on parsec scales, as well as the dependence of X CO on extinction and the CO excitation temperature.

Binary energy source of the HH 250 outflow and its circumstellar environment

Aims. Herbig-Haro flows are signposts of recent major accretion and outflow episodes. We aim to determine the nature and properties of the little-known outflow source HH 250-IRS, which is embedded in the Aquila clouds. Methods. We have obtained adaptive optics-assisted L-band images with the NACO instrument on the Very Large Telescope (VLT), together with N- and Q-band imaging with VISIR also on the VLT. Using the SINFONI instrument on the VLT we carried out H- and K-band integral field spectroscopy of HH 250-IRS, complemented with spectra obtained with the SpeX instrument at the InfraRed Telescope Facility (IRTF) in the JHKL bands. Finally, the SubMillimeter Array (SMA) interferometer was used to study the circumstellar environment of HH 250-IRS at 225 and 351 GHz with CO (2–1) and CO (3–2) maps and 0.9 mm and 1.3 mm continuum images. Results. The HH 250-IRS source is resolved into a binary with 0.′′53 separation, corresponding to 120 AU at the adopted distance of 225 pc. The individual components show heavily veiled spectra with weak CO absorption indicative of late-type stars. Both are Class I sources, but their spectral energy distributions between 1.5 μm and 19 μm differ markedly and suggest the existence of a large cavity around one of the components. The millimeter interferometric observations indicate that the gas mainly traces a circumbinary envelope or disk, while the dust emission is dominated by one of the circumstellar envelopes. Conclusions. HH 250-IRS is a new addition to the handful of multiple systems where the individual stellar components, the circumstellar disks and a circumbinary disk can be studied in detail, and a rare case among those systems in which a Herbig-Haro flow is present.

CSO CO (2–1) and Spitzer IRAC observations of a bipolar outflow in high-mass star-forming region IRAS 22506+5944

We present Caltech Submillimeter Observatory CO (2–1) and Spitzer IRAC observations toward IRAS 22506+5944, which is a 104 L⊙ massive star-forming region. The CO (2–1) maps show an east-west bipolar molecular outflow originating from the 3 mm dust continuum peak. The Spitzer IRAC color-composite image reveals a pair of bow-shaped tips which are prominent in excess 4.5μm emission and are located at the leading fronts of the bipolar outflow, providing compelling evidence for the existence of bow-shocks as the driving agents of the molecular outflow. By comparing our CO (2–1) observations with previously published CO (1–0) data, we find that the CO (2–1)/(1–0) line ratio increases from low (∼5 kms−1) to moderate (∼8–12 kms−1) velocities, and then decreases at higher velocities. This is qualitatively consistent with the scenario that the molecular outflow is driven by multiple bow-shocks. We also revisit the position-velocity diagram of the CO (1–0) data, and find two spur structures along the outflow axis, which are further evidence for the presence of multiple jet bowshocks. Finally, power-law fittings to the mass spectrum of the outflow gives power law indexes more consistent with the jet bow-shock model than the wide-angle wind model.

Spatially associated clump populations in Rosette from CO and dust maps

Spatial association of clumps from different tracers turns out to be a valuable tool to determine the physical properties of molecular clouds. It provides a reliable estimate for the $X$-factors, serves to trace the density of clumps seen in column densities only and allows to measure the velocity dispersion of clumps identified in dust emission. We study the spatial association between clump populations, extracted by use of the GAUSSCLUMPS technique from $^{12}$CO (1-0), $^{13}$CO (1-0) line maps and Herschel dust-emission maps of the star-forming region Rosette, and analyse their physical properties. All CO clumps that overlap with another CO or dust counterpart are found to be gravitationally bound and located in the massive star-forming filaments of the molecular cloud. They obey a single mass-size relation $M_{\rm cl}\propto R_{\rm cl}^\gamma$ with $\gamma\simeq3$ (implying constant mean density) and display virtually no velocity-size relation. We interpret their population as low-density structures formed through compression by converging flows and still not evolved under the influence of self-gravity. The high-mass parts of their clump mass functions are fitted by a power law ${\rm d}N_{\rm cl}/{\rm d}\,\log M_{\rm cl}\propto M_{\rm cl}^{\Gamma}$ and display a nearly Salpeter slope $\Gamma\sim-1.3$. On the other hand, clumps extracted from the dust-emission map exhibit a shallower mass-size relation with $\gamma=2.5$ and mass functions with very steep slopes $\Gamma\sim-2.3$ even if associated with CO clumps. They trace density peaks of the associated CO clumps at scales of a few tenths of pc where no single density scaling law should be expected.

Towards a three-dimensional distribution of the molecular clouds in the Galactic Centre

We present a study of the three-dimensional structure of the molecular clouds in the Galactic Centre (GC) using CO emission and OH absorption lines. Two CO isotopologue lines, $^{12}$CO ($J$=1$\rightarrow$0) and $^{13}$CO ($J$=1$\rightarrow$0), and four OH ground-state transitions, surveyed by the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), contribute to this study. We develop a novel method to calculate the OH column density, excitation temperature, and optical depth precisely using all four OH lines, and we employ it to derive a three-dimensional model for the distribution of molecular clouds in the GC for six slices in Galactic latitude. The angular resolution of the data is 15.5 arcmin, which at the distance of the GC (8.34 kpc) is equivalent to 38 pc. We find that the total mass of OH in the GC is in the range 2400-5100 Solar mass . The face-on view at a Galactic latitude of b = 0{\deg} displays a bar-like structure with an inclination angle of 67.5 $\pm$ 2.1{\deg} with respect to the line of sight. No ring-like structure in the GC is evident in our data, likely due to the low spatial resolution of the CO and OH maps.

Urban traffic and induced air quality modeling and simulation: Methodology and illustrative example

Modeling vehicular pollution in urban areas is essential in decision-making for urban planning and sustainable transport policies. Indeed, guaranteeing a breathable air quality in the acceptable levels specified by the World Health Organization (WHO) reinforces the road towards a sustainable urban development.In this work, we present the methodology and the different steps for the implementation of a sustainable transport decision tool permitting to perform a macroscopic simulation of road traffic using a first-order approach using the Cell Transmission Model (CTM) approach and a Dynamic Node Transmission Model (DNTM) approach for intersections; an estimation of the linear emission rates of the roads based on fleet statistics and the implementation of the simplified COPERT4 method; and finally the estimation of the near-instantaneous concentration of pollutants in urban areas. This tool is used to estimate the map of CO and NOx pollutants in the vicinity of a roundabout in the city of Sousse-Tunisia for the reference year 2015.

WIDE FIELD CO MAPPING IN THE REGION OF IRAS 19312+1950

ABSTRACT We report the results of wide field CO mapping in the region of IRAS 19312+1950. This Infrared Astronomical Satellite (IRAS) object exhibits SiO/H2O/OH maser emission, and is embedded in a chemically rich molecular component, the origin of which is still unknown. In order to reveal the entire structure and gas mass of the surrounding molecular component for the first time, we have mapped a wide region around IRAS 19312+1950 in the 12CO J = 1–0, 13CO J = 1–0 and C18O J = 1–0 lines using the Nobeyama 45 m telescope. In conjunction with archival CO maps, we investigated a region up to 20′ × 20′ in size around this IRAS object. We calculated the CO gas mass assuming local thermal equilibrium, the stellar velocity through the interstellar medium assuming an analytic model of bow shock, and the absolute luminosity, using the latest archival data and trigonometric parallax distance. The derived gas mass (225 M ⊙–478 M ⊙) of the molecular component and the relatively large luminosity (2.63 × 104 L ☉) suggest that the central SiO/H2O/OH maser source is a red supergiant rather than an asymptotic giant branch (AGB) star or post-AGB star.

A UNIFORM CATALOG OF MOLECULAR CLOUDS IN THE MILKY WAY

ABSTRACT The all-Galaxy CO survey of Dame et al. is by far the most uniform, large-scale Galactic CO survey. Using a dendrogram-based decomposition of this survey, we present a catalog of 1064 massive molecular clouds throughout the Galactic plane. This catalog contains 2.5 × 108 solar masses, or 25 − 5.8 + 10.7 % of the Milky Way's estimated H2 mass. We track clouds in some spiral arms through multiple quadrants. The power index of Larson's first law, the size-linewidth relation, is consistent with 0.5 in all regions—possibly due to an observational bias—but clouds in the inner Galaxy systematically have significantly (∼30%) higher linewidths at a given size, indicating that their linewidths are set in part by the Galactic environment. The mass functions of clouds in the inner Galaxy versus the outer Galaxy are both qualitatively and quantitatively distinct. The inner Galaxy mass spectrum is best described by a truncated power law with a power index of γ = −1.6 ± 0.1 and an upper truncation mass of M 0 = (1.0 ± 0.2) × 107 M ⊙, while the outer Galaxy mass spectrum is better described by a non-truncating power law with γ = −2.2 ± 0.1 and an upper mass of M 0 = (1.5 ± 0.5) × 106 M ⊙, indicating that the inner Galaxy is able to form and host substantially more massive GMCs than the outer Galaxy. Additionally, we have simulated how the Milky Way would appear in CO from extragalactic perspectives, for comparison with CO maps of other galaxies.

Large-scale CO (J = 4–3) mapping toward the Orion-A giant molecular cloud

Abstract We have mapped the Orion-A giant molecular cloud in the CO (J = 4–3) line with the Tsukuba 30 cm submillimeter telescope. The map covered a 7.125 deg2 area with a 9′ resolution, including main components of the cloud such as the Orion Nebula, OMC-2/3, and L1641-N. The most intense emission was detected toward the Orion KL region. The integrated intensity ratio between CO (J = 4–3) and CO (J = 1–0) was derived using data from the Columbia–Universidad de Chile CO survey, which was carried out with a comparable angular resolution. The ratio was r4−3/1−0 ∼ 0.2 in the southern region of the cloud and 0.4–0.8 at star forming regions. We found a trend that the ratio shows higher values at the edges of the cloud. In particular, the ratio at the northeastern edge of the cloud at (l, b) ≈ (208$_{.}^{\circ}$375, −19$_{.}^{\circ}$0) shows the highest value of 1.1. The physical condition of the molecular gas in the cloud was estimated by non-LTE calculation. The result indicates that the kinetic temperature has a gradient from north (Tkin = 80 K) to south (20 K). The estimation shows that the gas associated with the edge of the cloud is warm (Tkin ∼ 60 K), dense ($n_{\mathrm{H_2}}\sim 10^{4}\:$cm−3), and optically thin, which may be explained by heating and sweeping of interstellar materials from OB clusters.