- ID:
- ivo://CDS.VizieR/J/ApJ/774/117
- Title:
- HII region kinematic distances
- Short Name:
- J/ApJ/774/117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We make a comprehensive study of H I absorption toward H II regions located within |l|<10{deg}. Structures in the extreme inner Galaxy are traced using the longitude-velocity space distribution of this absorption. We find significant H I absorption associated with the Near and Far 3kpc Arms, the Connecting Arm, Bania's Clump 1, and the HI Tilted Disk. We also constrain the line-of-sight distances to H II regions, by using H I absorption spectra together with the H II region velocities measured by radio recombination lines.
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- ID:
- ivo://CDS.VizieR/J/A+A/621/A127
- Title:
- HII regions synchrotron radiation
- Short Name:
- J/A+A/621/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cosmic rays (CRs) and magnetic fields are dynamically important components in the Galaxy, and their energy densities are comparable to that of the turbulent interstellar gas. The interaction of CRs and Galactic magnetic fields (GMF) produces synchrotron radiation clearly visible in the radio regime. Detailed measurements of synchrotron radiation averaged over the line-of-sight (LOS), so-called synchrotron emissivities, can be used as a tracer of the CR density and GMF strength. Our aim is to model the synchrotron emissivity in the Milky Way using a three-dimensional dataset instead of LOS-integrated intensity maps on the sky. Using absorbed HII regions, we measured the synchrotron emissivity over a part of the LOS through the Galaxy, changing from a two-dimensional to a three-dimensional view. Performing these measurements on a large scale is one of the new applications of the window opened by current low-frequency arrays. Using various simple axisymmetric emissivity models and a number of GMF-based emissivity models, we were able to simulate the synchrotron emissivities and compare them to the observed values in the catalog. We present a catalog of low-frequency absorption measurements of HII regions, their distances and electron temperatures, compiled from literature. These data show that the axisymmetric emissivity models are not complex enough, but the GMF-based emissivity models deliver a reasonable fit. These models suggest that the fit can be improved by either an enhanced synchrotron emissivity in the outer reaches of the Milky Way or an emissivity drop near the Galactic center. Current GMF models plus a constant CR density model cannot explain low-frequency absorption measurements, but the fits improved with slight (ad hoc) adaptations. It is clear that more detailed models are needed, but the current results are very promising.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A106
- Title:
- HI observations of AT 2018cow
- Short Name:
- J/A+A/627/A106
- Date:
- 23 Mar 2022 16:27:48
- Publisher:
- CDS
- Description:
- Unusual stellar explosions represent an opportunity to learn about both stellar and galaxy evolution. Mapping the atomic gas in host galaxies of such transients can lead to an understanding of the conditions triggering them. We provide resolved atomic gas observations of the host galaxy, CGCG137-068, of the unusual, poorly-understood transient AT2018cow searching for clues to understand its nature. We test whether it is consistent with a recent inflow of atomic gas from the intergalactic medium, as suggested for host galaxies of gamma-ray bursts (GRBs) and some supernovae (SNe). We observed the HI hyperfine structure line of the AT2018cow host with the Giant Metrewave Radio Telescope. There is no unusual atomic gas concentration near the position of AT2018cow. The gas distribution is much more regular than those of GRB/SN hosts. The AT2018cow host has an atomic gas mass lower by 0.24dex than predicted from its star formation rate (SFR) and is at the lower edge of the galaxy main sequence. In the continuum we detected the emission of AT2018cow and of a star-forming region in the north-eastern part of the bar (away from AT2018cow). This region hosts a third of the galaxy's SFR. The absence of atomic gas concentration close to AT2018cow, along with a normal SFR and regular HI velocity field, sets CGCG137-068 apart from GRB/SN hosts studied in HI. The environment of AT2018cow therefore suggests that its progenitor may not have been a massive star. Our findings are consistent with an origin of the transient that does not require a connection between its progenitor and gas concentration or inflow: an exploding low-mass star, a tidal disruption event, a merger of white dwarfs, or a merger between a neutron star and a giant star. We interpret the recently reported atomic gas ring in CGCG137-068 as a result of internal processes connected with gravitational resonances caused by the bar.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A120
- Title:
- HL TAU and IRAS04302+2247 H2CS ALMA images
- Short Name:
- J/A+A/644/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Planet formation starts around Sun-like protostars with ages <=1Myr, but the chemical compositions of the surrounding discs remains unknown. We aim to trace the radial and vertical spatial distribution of a key species of S-bearing chemistry, namely H_2_CS, in protoplanetary discs. We also aim to analyse the observed distributions in light of the H_2_CS binding energy in order to discuss the role of thermal desorption in enriching the gas disc component. In the context of the ALMA chemical survey of disk-outflow sources in the Taurus star forming region (ALMA-DOT), we observed five Class I or early Class II sources with the o-H_2_CS(7_1,6_-6_1,5_) line. ALMA-Band 6 was used, reaching spatial resolutions ~=40au, that is, Solar System spatial scales. We also estimated the binding energy of H2CS using quantum mechanical calculations, for the first time, for an extended, periodic, crystalline ice. We imaged H2CS emission in two rotating molecular rings in the HL Tau and IRAS04302+2247 discs, the outer radii of which are ~140au (HL Tau) and 115 au (IRAS 04302+2247). The edge-on geometry of IRAS 04302+2247 allows us to reveal that H2CS emission peaks at radii of 60-115au, at z=+/-50au from the equatorial plane. Assuming LTE conditions, the column densities are 10^14^cm^-2^. We estimate upper limits of a few 10^13^cm^-2^ for the H2CS column densities in DG Tau, DG Tau B, and Haro 6-13 discs. For HL Tau, we derive, for the first time, the [H_2_CS]/[H] abundance in a protoplanetary disc (~10^-14^). The binding energy of H2CS computed for extended crystalline ice and amorphous ices is 4258K and 3000-4600K, respectively, implying thermal evaporation where dust temperatures are 50-80K. H_2_CS traces the so-called warm molecular layer, a region previously sampled using CS and H_2_CO. Thioformaldehyde peaks closer to the protostar than H_2_CO and CS, plausibly because of the relatively high excitation level of the observed 7_1,6_-6_1,5_ line (60K). The H_2_CS binding energy implies that thermal desorption dominates in thin, au-sized, inner and/or upper disc layers, indicating that the observed H2CS emitting up to radii larger than 100au is likely injected in the gas phase due to non-thermal processes.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A42
- Title:
- H2O megamaser galaxies radio continuum 5GHz data
- Short Name:
- J/A+A/624/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc accretion disks. Because of the small linear and angular scales involved, this alignment has not yet been checked in a sufficient number of low luminosity active galactic nuclei (LLAGNs). The project examines the validity of this paradigm by measuring the radio continuum on the same physical scale as the accretion disks to investigate any possible connection between these disks and the radio continuum. We observed a sample of 18 LLAGNs in the 4.8GHz (6cm) radio continuum using the Very Long Baseline Array (VLBA) with 3.3-6.5ms resolution. The sources were selected to show both an edge-on accretion disk revealed by 22GHz H_2_O megamaser emission and signatures of a radio jet. Furthermore, the sources were previously detected in 33GHz radio continuum observations made with the Very Large Array. Five out of 18 galaxies observed were detected at 8{sigma} or higher levels (Mrk 0001, Mrk 1210, Mrk 1419, NGC 2273, and UGC 3193). While these five sources are known to have maser disks, four of them exhibit a maser disk with known orientation. For all four of these sources, the radio continuum is misaligned relative to the rotation axis of the maser disk, but with a 99.1% confidence level, the orientations are not random and are confined to a cone within 32{deg} of the maser disk's normal. Among the four sources the misalignment of the radio continuum with respect to the normal vector to the maser disk is smaller when the inner radius of the maser disk is larger. Furthermore, a correlation is observed between the 5GHz VLBA radio continuum and the [OIII] luminosity and also with the H_2_O maser disk's inner radius.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A110
- Title:
- Hypercompact HII regions
- Short Name:
- J/A+A/645/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The derived physical parameters for young HII regions are normally determined assuming the emission region to be optically-thin. However, this is unlikely to hold for young HII regions such as Hyper-compact HII(HCHII) and Ultra-compact HII(UCHII) regions and leads to the underestimation of their properties. This can be overcome by fitting the SEDs over a wide range of radio frequencies. Two primary goals are (1) determining physical properties from radio SEDs and finding potential HCHII regions; (2) using these physical properties to investigate their evolution. We used Karl G. Jansky Very Large Array (VLA) to make observations of X-band and K-band with angular-resolutions of ~1.7" and ~0.7", respectively, toward 114 HII regions with rising-spectra between 1-5GHz. We complement our observations with VLA archival data and construct SEDs between 1-26GHz and model them assuming an ionisation-bounded HII region with uniform density. The sample has a mean electron density of ne=1.6*10^4^cm^-3^, diameter diam=0.14pc, and emission measure EM=1.9*10^7^pc/cm^6^. We identify 16 HCHII region candidates and 8 intermediate objects between the classes of HCHII and UCHII regions. The ne, diam, and EM change as expected, however, the Lyman continuum flux is relatively constant over time. We find that about 67% of Lyman continuum photons are absorbed by dust within these HII regions and the dust absorption fraction tends to be more significant for more compact and younger HII regions. Young HII regions are commonly located in dusty clumps; HCHII regions and intermediate objects are often associated with various masers, outflows, broad radio recombination lines, and extended green objects, and the accretion at the two stages tends to be quickly reduced or halted.
- ID:
- ivo://CDS.VizieR/J/AJ/149/32
- Title:
- Integrated radio continuum spectra of galaxies
- Short Name:
- J/AJ/149/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the spectral shape of the total continuum radiation, between 74MHz and 5GHz (400-6cm in wavelength), for a large sample of bright galaxies. We take advantage of the overlapping survey coverage of the VLA Low-Frequency Sky Survey, the Westerbork Northern Sky Survey, the NRAO VLA Sky Survey, and the Green Bank 6cm Survey to achieve significantly better resolution, sensitivity, and sample size compared to prior efforts of this nature. For our sample of 250 bright galaxies we measure a mean spectral index, {alpha}, of -0.69 between 1.4 and 4.85GHz, -0.55 between 325MHz and 1.4GHz, and -0.45 between 74 and 325MHz, which amounts to a detection of curvature in the mean spectrum. The magnitude of this curvature is approximately {Delta}{alpha}=-0.2 per logarithmic frequency decade when fit with a generalized function having constant curvature. No trend in low-frequency spectral flattening versus galaxy inclination is evident in our data, suggesting that free-free absorption is not a satisfying explanation for the observed curvature. The ratio of thermal to non-thermal emission is estimated through two independent methods: (1) using the IRAS far-IR fluxes and (2) with the value of the total spectral index. Method (1) results in a distribution of 1.4GHz thermal fractions of 9%+/-3%, which is consistent with previous studies, while method (2) produces a mean 1.4GHz thermal fraction of 51% with dispersion 26%. The highly implausible values produced by method (2) indicate that the sum of typical power-law thermal and non-thermal components is not a viable model for the total spectral index between 325 and 1.4GHz. An investigation into relationships between spectral index, infrared-derived quantities, and additional source properties reveals that galaxies with high radio luminosity in our sample are found to have, on average, a flatter radio spectral index, and early types tend to have excess radio emission when compared to the radio-infrared ratio of later types. Early types also have radio emission that is more compact than later type galaxies, as compared to the optical size of the galaxy. Despite these differences, no relation between spectral index and galaxy type is detected.
- ID:
- ivo://CDS.VizieR/J/ApJ/756/72
- Title:
- IRAC identifications for 510 AEGIS20 radio sources
- Short Name:
- J/ApJ/756/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Infrared 3.6-8{mu}m images of the Extended Groth Strip yield plausible counterpart identifications for all but one of 510 radio sources in the AEGIS20 S(1.4GHz)>50{mu}Jy sample. This is the first such deep sample that has been effectively 100% identified. Achieving the same identification rate at R band would require observations reaching R_AB_>27. Spectroscopic redshifts are available for 46% of the sample and photometric redshifts for an additional 47%. Almost all of the sources with 3.6{mu}m AB magnitudes brighter than 19 have spectroscopic redshifts z<1.1, while fainter objects predominantly have photometric redshifts with 1<~z<~3. Unlike more powerful radio sources that are hosted by galaxies having large stellar masses within a relatively narrow range, the AEGIS20 counterparts have stellar masses spanning more than a factor of 10 at z~1. The sources are roughly 10%-15% starbursts at z<~0.5 and 20%-25% active galactic nuclei mostly at z>1 with the remainder of uncertain nature.
- ID:
- ivo://CDS.VizieR/J/A+A/544/L7
- Title:
- IRAS 16293-2422 ALMA maps
- Short Name:
- J/A+A/544/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We focus on the kinematical properties of a proto-binary to study the infall and rotation of gas toward its two protostellar components. We present ALMA Science Verification observations with high-spectral resolution of IRAS 16293-2422 at 220.2GHz. The wealth of molecular lines in this source and the very high spectral resolution offered by ALMA allow us to study the gas kinematics with unprecedented detail.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/31
- Title:
- IR-radio luminosities & surface densities of galaxies
- Short Name:
- J/ApJ/805/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the global star formation law --the relation between gas and star formation (SF) rates-- in a sample of 181 local galaxies with infrared (IR) luminosities spanning almost five orders of magnitude (10^7.8^-10^12.3^L_{sun}_), which includes 115 normal spiral galaxies and 66 (ultra)luminous IR galaxies ((U)LIRGs, L_IR_>>10^11^L_{sun}_). We derive their atomic, molecular gas, and dense molecular gas masses using newly available HI, CO, and HCN data from the literature, and SF rates are determined both from total IR (8-1000um) and 1.4GHz radio continuum (RC) luminosities. In order to derive the disk-averaged surface densities of gas and SF rates, we have taken a novel approach and used high-resolution RC observations to measure the radio sizes for all 181 galaxies. In our sample, we find that the surface density of dense molecular gas (as traced by HCN) has the tightest correlation with that of SF rates ({Sigma}_SFR_), and is linear in log-log space (power-law slope of N=1.01+/-0.02) across the full galaxy sample. The correlation between surface densities of molecular gas ({Sigma}_H_2__, traced by CO) and {Sigma}_SFR_ is sensitive to the adopted value of the CO-to-H_2_ conversion factor ({alpha}_CO_) used to infer molecular gas masses from CO luminosities. For a fixed Galactic value of {alpha}_CO_, a power law index of 1.14+/-0.02 is found. If instead we adopt values for {alpha}_CO_ of 4.6 and 0.8 for disk galaxies and (U)LIRGs, respectively, we find the two galaxy populations separate into two distinct {Sigma}_SFR_ versus {Sigma}_H_2__ relations. Finally, applying a continuously varying {alpha}_CO_ to our sample, we recover a single {Sigma}_SFR_-{Sigma}_H_2__ relation with slope of 1.60+/-0.03. The {Sigma}_SFR_ is a steeper function of total gas {Sigma}_gas_ (molecular gas with atomic gas) than that of molecular gas {Sigma}_H_2__, and are tighter among low-luminosity galaxies. We find no correlation between global surface densities of SFRs and atomic gas (HI).
