- ID:
- ivo://CDS.VizieR/J/ApJ/775/63
- Title:
- Gould's Belt VLA Survey. I. Ophiuchus complex
- Short Name:
- J/ApJ/775/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present large-scale (~2000arcmin^2^), deep (~20{mu}Jy), high-resolution (~1") radio observations of the Ophiuchus star-forming complex obtained with the Karl G. Jansky Very Large Array at {lambda}=4 and 6cm. In total, 189 sources were detected, 56 of them associated with known young stellar sources, and 4 with known extragalactic objects; the other 129 remain unclassified, but most of them are most probably background quasars. The vast majority of the young stars detected at radio wavelengths have spectral types K or M, although we also detect four objects of A/F/B types and two brown dwarf candidates. At least half of these young stars are non-thermal (gyrosynchrotron) sources, with active coronas characterized by high levels of variability, negative spectral indices, and (in some cases) significant circular polarization. As expected, there is a clear tendency for the fraction of non-thermal sources to increase from the younger (Class 0/I or flat spectrum) to the more evolved (Class III or weak line T Tauri) stars. The young stars detected both in X-rays and at radio wavelengths broadly follow a Gudel-Benz relation, but with a different normalization than the most radioactive types of stars. Finally, we detect a ~70mJy compact extragalactic source near the center of the Ophiuchus core, which should be used as gain calibrator for any future radio observations of this region.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/833/88
- Title:
- GRB 160509A VLA monitoring campain results
- Short Name:
- J/ApJ/833/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the second multi-frequency radio detection of a reverse shock in a {gamma}-ray burst. By combining our extensive radio observations of the Fermi-Large Area Telescope {gamma}-ray burst 160509A at z=1.17 up to 20 days after the burst with Swift X-ray observations and ground-based optical and near-infrared data, we show that the afterglow emission comprises distinct reverse shock and forward shock contributions: the reverse shock emission dominates in the radio band at <~10 days, while the forward shock emission dominates in the X-ray, optical, and near-infrared bands. Through multi-wavelength modeling, we determine a circumburst density of n_0_~10^-3^cm^-3^, supporting our previous suggestion that a low-density circumburst environment is conducive to the production of long-lasting reverse shock radiation in the radio band. We infer the presence of a large excess X-ray absorption column, N_H_~1.5x10^22^cm^-2^, and a high rest-frame optical extinction, A_V_~3.4mag. We identify a jet break in the X-ray light curve at t_jet_~6days, and thus derive a jet opening angle of {theta}_jet_~4{deg}, yielding a beaming-corrected kinetic energy and radiated {gamma}-ray energy of E_K_~4x10^50^erg and E_{gamma}_~1.3x10^51^erg (1-10^4^keV, rest frame), respectively. Consistency arguments connecting the forward shocks and reverse shocks suggest a deceleration time of t_dec_~460s~T_90_, a Lorentz factor of {Gamma}(t_dec_)~330, and a reverse-shock-to-forward-shock fractional magnetic energy density ratio of R_B_={epsilon}_B,RS_/{epsilon}_B,FS_~8. Our study highlights the power of rapid-response radio observations in the study of the properties and dynamics of {gamma}-ray burst ejecta.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/136
- Title:
- H{beta} to N2 line fluxes of nearby galaxies
- Short Name:
- J/ApJ/847/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present calibrations for star formation rate (SFR) indicators in the ultraviolet, mid-infrared, and radio-continuum bands, including one of the first direct calibrations of 150MHz as an SFR indicator. Our calibrations utilize 66 nearby star-forming galaxies with Balmer-decrement-corrected H{alpha} luminosities, which span five orders of magnitude in SFR and have absolute magnitudes of -24<M_r_{<}-12. Most of our photometry and spectrophotometry are measured from the same region of each galaxy, and our spectrophotometry has been validated with SDSS photometry, so our random and systematic errors are small relative to the intrinsic scatter seen in SFR indicator calibrations. We find that the Wide-field Infrared Space Explorer W4 (22.8{mu}m), Spitzer 24{mu}m, and 1.4GHz bands have tight correlations with the Balmer-decrement-corrected H{alpha} luminosity, with a scatter of only 0.2dex. Our calibrations are comparable to those from the prior literature for L* galaxies, but for dwarf galaxies, our calibrations can give SFRs that are far greater than those derived from most previous literature.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A5
- Title:
- Hercules A LOFAR and JVLA images
- Short Name:
- J/A+A/658/A5
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The prominent radio source Hercules A features complex structures in its radio lobes. Despite being one of the most comprehensively studied sources in the radio sky, the origin of the ring structures in the Hercules A radio lobes remains an open question. We present the first sub-arcsecond angular resolution images at low frequencies (<300MHZ) of Hercules A, made with the International LOFAR Telescope. With the addition of data from the Karl G. Jansky Very Large Array, we map the structure of the lobes from 144MHz to 7GHz. We explore the origin of the rings within the lobes of Hercules A, and test whether their properties are best described by a shock model where shock waves are produced by the jet propagating in the radio lobe, or an inner-lobe model in which the rings are formed by decelerated jetted plasma. From spectral index mapping, our large frequency coverage reveals that the curvature of the different ring spectra increases with distance away from the central active galactic nucleus. We demonstrate that the spectral shape of the rings is consistent with synchrotron aging, which speaks in favor of an inner-lobe model, where the rings are formed from the deposition of material from past periods of intermittent core activity.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A88
- Title:
- High cadence polarization monitoring of OJ287
- Short Name:
- J/A+A/619/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a multifrequency, dense radio monitoring program of the blazar OJ287 using the 100-m Effelsberg radio telescope. The program aims to test different binary supermassive black hole (SMBH) scenarios and studying the physical conditions in the central region of this bright blazar. Between December 2015 and January 2017 (MJD 57370-57785), the radio electric vector position angle (EVPA) showed a large clockwise (CW) rotation by about 340{deg} with a mean rate of -1.04{deg}/day. Based on concurrent polarized Very Long Baseline Array (VLBA) data, the rotation seems to originate within the jet core at 43GHz. Optical polarization data show a similar monotonic CW EVPA rotation of about -1.1{deg}/day, superposed by shorter and faster rotations of about 7.8{deg}/day, mainly in the CW sense. When combined, the single dish, VLBI and optical polarization data are consistent with a polarized emission component propagating on a helical trajectory within a bent jet. We constrained the helix arc length (0.26pc) and radius (about 0.04pc) and the projected jet bending arc length (about 1.9-7.6pc). The helical trajectory covers only a part of the jet width, possibly its spine. In addition, we found a stable polarized component with EVPA (-10{deg}) perpendicular to the large scale jet, suggesting dominance of the poloidal magnetic field component.
- ID:
- ivo://CDS.VizieR/J/AJ/154/156
- Title:
- High resolution survey of Galactic plane at 408 MHz
- Short Name:
- J/AJ/154/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interstellar medium is a complex "ecosystem" with gas constituents in the atomic, molecular and ionized states, dust, magnetic fields, and relativistic particles. The Canadian Galactic Plane Survey has imaged these constituents at multiple radio and infrared frequencies with angular resolution of the order of arcminutes. This paper presents radio continuum data at 408 MHz over the area of 52{deg}=<l=<193{deg}, -6.5{deg}=<b=<8.5{deg}, with an extension to b=21{deg} in the range of 97{deg}=<l=<120{deg}, with angular resolution 2.8'x2.8' cosec{delta}. Observations were made with the Synthesis Telescope at the Dominion Radio Astrophysical Observatory as part of the Canadian Galactic Plane Survey. The calibration of the survey using existing radio source catalogs is described. The accuracy of 408 MHz flux densities from the data is 6%. Information on large structures has been incorporated into the data using the single-antenna survey of Haslam et al. (1982A&AS...47....1H). The paper presents the data, describes how it can be accessed electronically, and gives examples of applications of the data to ISM research.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A100
- Title:
- HII region G24.78+0.08 A1 images
- Short Name:
- J/A+A/624/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The earliest phases of the evolution of a massive star are closely related to the developement of an HII region. Hypercompact HII regions are the most interesting in this respect because they are very young, and hence best suited to study the beginning of the expansion of the ionised gas inside the parental core. We have analysed the geometrical and physical structure of the hypercompact HII region G24.78+0.08 A1, making use of new continuum and hydrogen recombination line data (H41{alpha}, H63{alpha}, H66{alpha}, H68{alpha}) and data from the literature (H30{alpha}, H35{alpha}). We fit the continuum spectrum with a homogenous, isothermal shell of ionised gas at 10^4^K and derive the size of the HII region and the Lyman continuum luminosity of the ionising star. We also fit the recombination line spectra emitted from the same shell with a model taking into account expansion at constant speed. The best fits to the continuum and line spectra allow the derivation of the Lyman continuum luminosity of the ionising star, HII region size, geometrical thickness of the shell, and expansion velocity. Comparison between the 5cm and 7mm brightness temperature distributions demonstrates that a thin layer of ionised gas of a few 1000K at the surface of the HII region is necessary to reproduce the morphology of the continuum emission at both wavelengths. We confirm that the G24 A1 hypercompact HII region consists of a thin shell ionised by an O9.5 star. The shell is expanding at a speed comparable to the sound speed in the ionised gas. The radius of the HII region exceeds the critical value needed to trap the ionised gas by the gravitational field of the star, consistent with the observed expansion.
- 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.
- 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.