- ID:
- ivo://CDS.VizieR/J/ApJS/243/13
- Title:
- Massive star-forming clump from MALT90
- Short Name:
- J/ApJS/243/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We selected 90 massive star-forming clumps with strong N2H+(1-0), HCO+(1-0), HCN(1-0), and HNC(1-0) emission from the Millimetre Astronomy Legacy Team 90 GHz survey. We obtained Herschel data for all 90 sources and NRAO VLA Sky Survey data for 51 of them. We convolved and regridded all images to the same resolution and pixel size and derived the temperature, H2 column density, molecules' abundances and abundance, and ratios of each pixel. Our analysis yields three main conclusions. First, the abundances of N2H+, HCO+, HCN, and HNC increase when the column density decreases and the temperature increases, with spatial variations in their abundances dominated by changes in the H2 column density. Second, the abundance ratios between N2H+, HCO+, HCN, and HNC also display systemic variations as a function of the column density due to the chemical properties of these molecules. Third, the sources associated with the 20cm continuum emission can be classified into four types based on the behavior of the abundances of the four molecules considered here as a function of this emission. The variations of the first three types could also be attributed to the variation of the H2 column density.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/719/1104
- Title:
- Massive star forming complexes in GLIMPSE
- Short Name:
- J/ApJ/719/1104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the 13 most luminous sources in the WMAP free-free map using the Spitzer GLIMPSE and Midcourse Space Experiment surveys to identify massive star formation complexes, emitting one-third of the Galactic free-free luminosity. We identify star-forming complexes (SFCs) by a combination of bubble morphology in 8um emission and radio recombination line radial velocities. We find 40 SFCs associated with our WMAP sources and determine unique distances up to 31. We interpret the bubbles as evidence for radial expansion. The radial velocity distribution for each source allows us to measure the intrinsic speed of a complex's expansion. This speed is consistent with the size and age of the bubbles. The high free-free luminosities, combined with negligible synchrotron emission, demonstrate that the bubbles are not driven by supernovae. The kinetic energy of the largest bubbles is a substantial fraction of that measured in the older superbubbles found by Heiles. We find that the energy injected into the interstellar medium by our bubbles is similar to that required to maintain turbulent motion in the gas disk inside 8kpc. We report a number of new SFCs powered by massive (M_*_>10^4^M_{sun}_) star clusters. We measure the scale height of the Galactic O stars to be h_*_=35+/-5pc. We determine an empirical relationship between the 8um and free-free emission of the form F_8um_{propto}F^2^_ff_. Finally, we find that the bubble geometry is more consistent with a spherical shell rather than a flattened disk.
- ID:
- ivo://CDS.VizieR/J/A+A/550/A21
- Title:
- Massive star-forming regions radio lines
- Short Name:
- J/A+A/550/A21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Australia Telescope Compact Array (ATCA) observations of the H_2_O maser line and radio continuum at 18.0GHz and 22.8GHz toward a sample of 192 massive star-forming regions containing several clumps already imaged at 1.2mm. The main aim of this study is to investigate the water maser and centimeter continuum emission (that likely traces thermal free-free emission) in sources at different evolutionary stages, using evolutionary classifications previously published. We used the recently comissioned Compact Array Broadband Backend (CABB) at ATCA that obtains images with 20arcsec resolution in the 1.3cm continuum and H_2_O maser emission in all targets. For the evolutionary analysis of the sources we used millimeter continuum emission from the literature and the infrared emission from the MSX Point Source Catalog. We detect centimeter continuum emission in 88% of the observed fields with a typical rms noise level of 0.45mJy/beam. Most of the fields show a single radio continuum source, while in 20% of them we identify multiple components. A total of 214 centimeter continuum sources have been identified, that likely trace optically thin HII regions, with physical parameters typical of both extended and compact HII regions. Water maser emission was detected in 41% of the regions, resulting in a total of 85 distinct components. The low angular (20arcsec) and spectral (14km/s) resolutions do not allow a proper analysis of the water maser emission, but suffice to investigate its association with the continuum sources. We have also studied the detection rate of HII regions in the two types of IRAS sources defined in the literature on the basis of the IRAS colors: High and Low. No significant differences are found, with high detection rates (>90%) for both High and Low sources. We classify the millimeter and infrared sources in our fields in three evolutionary stages following the scheme presented previously: (Type 1) millimeter-only sources, (Type 2) millimeter plus infrared sources, (Type 3) infrared-only sources. We find that HII regions are mainly associated with Type 2 and Type 3 objects, confirming that these are more evolved than Type 1 sources. The HII regions associated with Type 3 sources are slightly less dense and larger in size than those associated with Type 2 sources, as expected if the HII region expands as it evolves, and Type 3 objects are older than Type 2 objects. The maser emission is mostly found to be associated with Type 1 and Type 2 sources, with a higher detection rate toward Type 2, consistent with the results of the literature. Finally, our results on HII region and H_2_O maser association with different evolutionary types confirm the evolutionary classification proposed previously.
- ID:
- ivo://CDS.VizieR/J/ApJ/876/70
- Title:
- Massive YSOs in the IR dark cloud G79.3+0.3
- Short Name:
- J/ApJ/876/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- G79.3+0.3 is an infrared dark cloud in the Cygnus-X complex that is home to massive deeply embedded young stellar objects (YSOs). We have produced a Submillimeter Array (SMA) 1.3mm continuum image and ^12^CO line maps of the eastern section of G79.3+0.3 in which we detect five separate YSOs. We have estimated physical parameters for these five YSOs and others in the vicinity of G79.3+0.3 by fitting existing photometry from Spitzer, Herschel, and ground-based telescopes to spectral energy distribution models. Through these model fits we find that the most massive YSOs seen in the SMA 1.3mm continuum emission have masses in the 5-6M_{sun}_ range. One of the SMA sources was observed to power a massive collimated ^12^CO outflow extending at least 0.94pc in both directions from the protostar, with a total mass of 0.83M_{sun}_ and a dynamical timescale of 23kyr.
515. Measured DIB 8620
- ID:
- ivo://CDS.VizieR/J/A+A/654/A116
- Title:
- Measured DIB 8620
- Short Name:
- J/A+A/654/A116
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We made use of the measurements from the Giraffe Inner Bulge Survey (GIBS) and the Gaia-ESO survey (GES) to study the kinematics and distance of the carrier of the DIB at 862nm, as well as other properties. We confirmed a tight relation between EW and E(J-Ks) as well as Av, with similar fitting coefficients as found by previous works. With a more accurate sample and the consideration of the solar motion, the rest-frame wavelength of DIB 8620 was redetermined as 8620.83 angstroms. We studied the kinematics of the DIB carriers by tracing their median radial velocities in each field in the local standard of rest and into the galactocentric frame, respectively, as a function of the Galactic longitudes. Based on the median velocity and two Galactic rotation models, we got valid kinematic distances of the DIB carriers for nine GIBS and ten GES fields. We also found a linear relation between the DIB 8620 measured in this work and the near-infrared DIB in APOGEE spectra at 1.5273 micron.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/72
- Title:
- Measurements of 19 DIBs and 8 other interstellar lines
- Short Name:
- J/ApJ/774/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Diffuse interstellar bands (DIBs) can trace different conditions of the interstellar medium (ISM) along the sightline toward the observed stars. A small survey was made in optical wavelengths, producing high-resolution and high signal-to-noise spectra. We present measurements of 19 DIBs' properties in 50 sightlines toward hot stars, distributed at a variety of galactic coordinates and interstellar reddening. Equivalent widths were obtained by fitting asymmetric Gaussian and variable continua to DIBs. Conditions of the ISM were calculated from eight atomic and molecular interstellar lines. Two distinctly different types of DIBs were identified by carefully comparing correlation coefficients between DIBs and reddening and by different behavior in UV-shielded ({zeta}) and nonshielded ({sigma}) sightlines. A ratio of DIBs at 5780{AA} and 5797{AA} proved to be reliable enough to distinguish between two different sightline types. Based on the linear relations between DIB equivalent width and reddening for {sigma} and {zeta} sightlines, we divide DIBs into type I (where both linear relations are similar) and type II (where they are significantly different). The linear relation for {zeta} type sightlines always shows a higher slope and larger x-intercept parameter than the relation for {sigma} sightlines. Scatter around the linear relation is reduced after the separation, but it does not vanish completely. This means that UV shielding is the dominant factor of the DIB equivalent width versus reddening relation shape for {zeta} sightlines, but in {sigma} sightlines other physical parameters play a major role. No similar dependency on gas density, electron density, or turbulence was observed. A catalog of all observed interstellar lines is made public.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/151
- Title:
- METAL Hubble program. I. Initial results
- Short Name:
- J/ApJ/871/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Metal Evolution, Transport, and Abundance in the Large Magellanic Cloud (METAL) is a large cycle 24 program on the Hubble Space Telescope aimed at measuring dust extinction properties and interstellar depletions in the Large Magellanic Cloud (LMC) at half-solar metallicity. The 101-orbit program is composed of Cosmic Origins Spectrograph (COS) and Space Telescope Imaging Spectrograph (STIS) spectroscopy toward 33 LMC massive stars between 1150 and 3180{AA} and parallel Wide Field Camera 3 (WFC3) imaging in seven near-UV to near-IR filters. The fraction of silicon in the gas phase (depletion) obtained from the spectroscopy decreases with increasing hydrogen column density. Depletion patterns for silicon differ between the Milky Way, LMC, and Small Magellanic Cloud (SMC), with the silicon depletion level offsetting almost exactly the metallicity differences, leading to constant gas-phase abundances in those galaxies for a given hydrogen column density. The silicon depletion correlates linearly with the absolute-to-selective extinction, RV, indicating a link between gas depletion and dust grain size. Extinction maps are derived from the resolved stellar photometry in the parallel imaging, which can be compared to far-IR images from Herschel and Spitzer to estimate the emissivity of dust at LMC metallicity. The full METAL sample of depletions, UV extinction curves, and extinction maps will inform the abundance, size, composition, and optical properties of dust grains in the LMC, comprehensively improve our understanding of dust properties, and improve the accuracy with which dust-based gas masses, star formation rates, and star formation histories in nearby and high-redshift galaxies are estimated. This overview paper describes the goals, design, data reduction, and initial results of the METAL survey.
- ID:
- ivo://CDS.VizieR/J/ApJ/737/L20
- Title:
- Metallicity dependent star formation rates
- Short Name:
- J/ApJ/737/L20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive a metallicity-dependent relation between the surface density of the star formation rate ({Sigma}_SFR_) and the gas surface density ({Sigma}_g_) in a feedback-regulated model of star formation in galactic disks. In this model, star formation occurs in gravitationally bound protocluster clumps embedded in larger giant molecular clouds with the protocluster clump mass function following a power-law function with a slope of -2. Metallicity-dependent feedback is generated by the winds of OB stars (M>~5M_{sun}_) that form in the clumps. The quenching of star formation in clumps of decreasing metallicity occurs at later epochs due to weaker wind luminosities, thus resulting in higher final star formation efficiencies (SFE_exp_). By combining SFE_exp_ with the timescales on which gas expulsion occurs, we derive the metallicity-dependent SFR per unit time in this model as a function of {Sigma}_g_. This is combined with the molecular gas fraction in order to derive the global dependence of {Sigma}_SFR_ on {Sigma}_g_. The model reproduces very well the observed star formation laws extending from low gas surface densities up to the starburst regime. Furthermore, our results show a dependence of {Sigma}_SFR_ on metallicity over the entire range of gas surface densities in contrast to other models and can also explain part of the scatter in the observations. We provide a tabulated form of the star formation laws that can easily be incorporated into numerical simulations or semi-analytical models of galaxy formation and evolution.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/110
- Title:
- Metallicity measurements in 70 nearby galaxies
- Short Name:
- J/ApJ/862/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the metallicity dependence of HI surface densities in star-forming regions along many lines of sight within 70 nearby galaxies, probing kiloparsec to 50pc scales. We employ HI, SFR, stellar mass, and metallicity (gradient) measurements from the literature, spanning a wide range (5dex) in stellar and gas mass and (1.6dex) in metallicity. We consider metallicities as observed, or rescaled to match the mass-metallicity relation determined for SDSS galaxies. At intermediate to high metallicities (0.3-2 times solar), we find that the HI surface densities saturate at sufficiently large total gas surface density. The maximal HI columns vary approximately inversely with metallicity, and show little variation with spatial resolution, galactocentric radius, or among galaxies. In the central parts of massive spiral galaxies, the HI gas is depressed by factors of ~2. The observed behavior is naturally reproduced by metallicity dependent shielding theories for the HI-to-H2 transitions in star-forming galaxies. We show that the inverse scaling of the maximal HI columns with metallicity suggests that the area filling fraction of atomic-molecular complexes in galaxies is of the order of unity, and weakly dependent on metallicity.
- ID:
- ivo://CDS.VizieR/J/ApJ/854/170
- Title:
- Methanol (CH_3_OH) and OH masers in NGC 6334I
- Short Name:
- J/ApJ/854/170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first sub-arcsecond VLA imaging of 6GHz continuum, methanol maser, and excited-state hydroxyl maser emission toward the massive protostellar cluster NGC 6334I following the recent 2015 outburst in (sub)millimeter continuum toward MM1, the strongest (sub)millimeter source in the protocluster. In addition to detections toward the previously known 6.7GHz Class II methanol maser sites in the hot core MM2 and the UCHII region MM3 (NGC 6334F), we find new maser features toward several components of MM1, along with weaker features ~1" north, west, and southwest of MM1, and toward the nonthermal radio continuum source CM2. None of these areas have heretofore exhibited Class II methanol maser emission in three decades of observations. The strongest MM1 masers trace a dust cavity, while no masers are seen toward the strongest dust sources MM1A, 1B, and 1D. The locations of the masers are consistent with a combination of increased radiative pumping due to elevated dust grain temperature following the outburst, the presence of infrared photon propagation cavities, and the presence of high methanol column densities as indicated by ALMA images of thermal transitions. The nonthermal radio emission source CM2 (2" north of MM1) also exhibits new maser emission from the excited 6.035 and 6.030GHz OH lines. Using the Zeeman effect, we measure a line-of-sight magnetic field of +0.5 to +3.7mG toward CM2. In agreement with previous studies, we also detect numerous methanol and excited OH maser spots toward the UCHII region MM3, with predominantly negative line-of-sight magnetic field strengths of -2 to -5mG and an intriguing south-north field reversal.
