- ID:
- ivo://CDS.VizieR/J/A+A/603/A100
- Title:
- 37 GHz observations of NLS1 galaxies
- Short Name:
- J/A+A/603/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations performed at Metsahovi Radio Observatory at 37GHz are presented for a sample of 78 radio-loud and radio-quiet narrow-line Seyfert 1 (NLS1) galaxies, together with additional lower and higher frequency radio data from RATAN-600, Owens Valley Radio Observatory, and the Planck satellite. Most of the data have been gathered between February 2012 and April 2015 but for some sources even longer light curves exist. The detection rate at 37GHz is around 19%, which is comparable to other populations of active galactic nuclei presumed to be faint at radio frequencies, such as BL Lac objects. Variability and spectral indices are determined for sources with enough detections. Based on the radio data, many NLS1 galaxies show a blazar-like radio spectra exhibiting significant variability. The spectra at a given time are often inverted or convex. The source of the high-frequency radio emission in NLS1 galaxies, detected at 37GHz, is most probably a relativistic jet rather than star formation. Jets in NLS1 galaxies are therefore expected to be a much more common phenomenon than earlier assumed.
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Search Results
- ID:
- ivo://CDS.VizieR/J/other/AstBu/74.348
- Title:
- 164 GHz-peaked spectrum sources
- Short Name:
- J/other/AstBu/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gigahertz-Peaked spectrum (GPS) sources are compact active galactic nuclei, presumably young precursors of bright radio sources. The study of GPS radio properties provides information about the features of synchrotron radiation in extragalactic sources. Also in applied research, GPS sources are useful as compact stationary radio sources in the sky for astrometric purposes. This paper presents the results of a multifrequency GPS study based on quasi-simultaneous measurements with the RATAN-600 radio telescope during the 2006-2017 period. A catalog of GPS spectral flux densities at six frequencies - 1.1, 2.3, 4.8, 7.7/8.2, 11.2, and 21.7GHz - is obtained. In addition, for the analysis of radio spectra, data from low-frequency surveysGLEAM(GaLactic and Extragalactic AllskyMurchisonwidefield array survey) and TGSS (Tata institute for fundamental research GMRT Sky Survey) and high-frequency measurements from Planck survey are used. A total number of 164 GPS and candidates have been identified (17 of them are new discoveries), which makes up a small fraction of GPS in the initial sample of bright AGNs - about 2%. The physical properties and formation conditions of synchrotron radiation is found to be quite different in GPS of different AGNs types. The deficit of distant GPS (z>2) with low maximum frequencies (less than 1GHz) has been confirmed. The existing "size-peak frequency" anticorrelation is continuous. The continuum radio spectra are found to become statistically steeper with increasing redshift.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/125
- Title:
- 1.4GHz radio variability in FIRST & SDSS Stripe 82
- Short Name:
- J/ApJ/769/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a blind survey for extragalactic radio variability that was carried out by comparing two epochs of data from the Faint Images of the Radio Sky at Twenty centimeters survey with a third epoch from a new 1.4GHz survey of SDSS Stripe 82. The three epochs are spaced seven years apart and have an overlapping area of 60deg^2^. We uncover 89 variable sources down to the millijansky level, 75 of which are newly identified, and we find no evidence for transient phenomena. This new sample of variable sources allows us to infer an upper limit to the mean characteristic timescale of active galactic nucleus radio variability of 14yr. We find that only 1% of extragalactic sources have fractional variability f_var_>3, while 44% of Galactic sources vary by this much. The variable sample contains a larger fraction of quasars than a comparable non-variable control sample, though the majority of the variable sources appear to be extended galaxies in the optical. This implies that either quasars are not the dominant contributor to the variability of the sample, or that the deep optical data allow us to detect the host galaxies of some low-z quasars. We use the new, higher resolution data to report on the morphology of the variable sources. Finally, we show that the fraction of sources that are variable remains constant or increases at low flux densities. This may imply that next generation radio surveys with telescopes like Australian Square Kilometer Array Pathfinder and MeerKAT will see a constant or even increasing fraction of variable sources down into the sub-millijansky regime.
1274. 1.4 GHz source survey
- ID:
- ivo://CDS.VizieR/J/AJ/99/1071
- Title:
- 1.4 GHz source survey
- Short Name:
- J/AJ/99/1071
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on 1.4GHz continuum observations for 56 contiguous VLA fields, using the D configuration, in a region devoid of nearby, rich galaxy clusters (at z<0.4). 354 continuum sources are tabulated, with fluxes down to about 1.5mJy, in an area of about 12degres^+2^. Only about seven of the 354 radio sources are associated with known rich galaxy clusters at z>0.4 (tabulated by Gunn, Hoessel, and Oke, 1986ApJ...306...30G). We compare source positions with those from an optical catalog (generated from a POSS plate with the use of the Minnesota Automated Plate Scanner) and find mild correlations on angular scales of order 1arcmin. This suggests some association of radio sources with galaxy groups (sizes of order 200 kpc) at redshifts of order z~0.1, even though there are no rich galaxy clusters in this redshift range.
- ID:
- ivo://CDS.VizieR/J/ApJ/533/611
- Title:
- 1.4GHz survey in HDF region
- Short Name:
- J/ApJ/533/611
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a deep radio survey with the Very Large Array at 1.4GHz of a region containing the Hubble Deep Field (HDF). This survey overlaps previous observations at 8.5GHz allowing us to investigate the radio spectral properties of microJansky sources to flux densities greater than 40{mu}Jy at 1.4GHz and greater than 8{mu}Jy at 8.5GHz. A total of 371 sources have been catalogued at 1.4GHz as part of a complete sample within 20 of the HDF.
- ID:
- ivo://CDS.VizieR/J/AJ/80/771
- Title:
- 5-GHz Survey of Bright Galaxies
- Short Name:
- J/AJ/80/771
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 1135 galaxies in the Reference Catalogue of Bright Galaxies (Cat. <VII/16>) with declinations between +10{deg} and +70{deg} were surveyed at 6-cm wavelength with a 3-sigma detection limit of about 30mf.u.; of these 149 were detected. For 90 of these galaxies, spectral indices were obtained. There is a suggestion that the elliptical galaxies have flat spectra more often than the spiral galaxies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/460/1739
- Title:
- Giant HII regions BOND abundances
- Short Name:
- J/MNRAS/460/1739
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Bayesian oxygen and nitrogen abundance determinations (bond) method. bond is a Bayesian code (available at: http://bond.ufsc.br) to simultaneously derive oxygen and nitrogen abundances in giant HII regions. It compares observed emission lines to a grid of photoionization models without assuming any relation between O/H and N/O. Our grid spans a wide range in O/H, N/O and ionization parameter U, and covers different starburst ages and nebular geometries. Varying starburst ages accounts for variations in the ionizing radiation field hardness, which arise due to the ageing of HII regions or the stochastic sampling of the initial mass function. All previous approaches assume a strict relation between the ionizing field and metallicity. The other novelty is extracting information on the nebular physics from semistrong emission lines. While strong lines ratios alone ([OIII]/H{beta}, [OII]/H{beta} and [NII]/H{beta}) lead to multiple O/H solutions, the simultaneous use of [ArIII]/[NeIII] allows one to decide whether an HII region is of high or low metallicity. Adding HeI/H{beta} pins down the hardness of the radiation field. We apply our method to HII regions and blue compact dwarf galaxies, and find that the resulting N/O versus O/H relation is as scattered as the one obtained from the temperature-based method. As in previous strong-line methods calibrated on photoionization models, the bond O/H values are generally higher than temperature-based ones, which might indicate the presence of temperature fluctuations or kappa distributions in real nebulae, or a too soft ionizing radiation field in the models.
- ID:
- ivo://CDS.VizieR/J/ApJ/654/240
- Title:
- Giant molecular clouds in M31
- Short Name:
- J/ApJ/654/240
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometer observations of giant molecular clouds (GMCs) along a spiral arm in M31. The observations consist of a survey using the compact configuration of the interferometer and follow-up, higher resolution observations on a subset of the detections in the survey. The data are processed using an analysis algorithm designed to extract GMCs and correct their derived properties for observational biases, thereby facilitating comparison with Milky Way data. The algorithm identifies 67 GMCs, of which 19 have a sufficient signal-to-noise ratio to accurately measure their properties. The GMCs in this portion of M31 are indistinguishable from those found in the Milky Way, having a similar size-line width relationship and distribution of virial parameters, confirming the results of previous, smaller studies. The velocity gradients and angular momenta of the GMCs are comparable to the values measured in M33 and the Milky Way, and in all cases are below expected values based on the local galactic shear. The studied region of M31 has an interstellar radiation field, metallicity, Toomre Q parameter, and midplane volume density similar to those of the inner Milky Way, so the similarity of GMC populations between the two systems is not surprising.
- ID:
- ivo://CDS.VizieR/J/A+A/542/A108
- Title:
- Giant molecular clouds in M33
- Short Name:
- J/A+A/542/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of a systematic CO(2-1) survey at 12" resolution covering most of the Local Group spiral M33, which, at a distance of 840kpc, is close enough for individual giant molecular clouds (GMCs) to be identified. The goal of this work is to study the properties of the GMCs in this subsolar metallicity galaxy. The CPROPS (Cloud PROPertieS) algorithm was used to identify 337 GMCs in M33, the largest sample to date for an external galaxy. The sample is used to study the GMC luminosity function, or mass spectrum under the assumption of a constant N(H_2_)/I_CO_ ratio.
- ID:
- ivo://CDS.VizieR/J/ApJ/772/107
- Title:
- Giant molecular clouds in nearby galaxies
- Short Name:
- J/ApJ/772/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We resolve 182 individual giant molecular clouds (GMCs) larger than 2.5x10^5^M_{sun}_ in the inner disks of 5 large nearby spiral galaxies (NGC 2403, NGC 3031, NGC 4736, NGC 4826, and NGC 6946) to create the largest such sample of extragalactic GMCs within galaxies analogous to the Milky Way. Using a conservatively chosen sample of GMCs most likely to adhere to the virial assumption, we measure cloud sizes, velocity dispersions, and ^12^CO(J=1-0) luminosities and calculate cloud virial masses. The average conversion factor from CO flux to H_2_ mass (or X_CO_) for each galaxy is 1-2x10^20^/cm2 (K.km/s)^-1^, all within a factor of two of the Milky Way disk value (~2x10^20^/cm2(K.km/s)^-1^). We find GMCs to be generally consistent within our errors between the galaxies and with Milky Way disk GMCs; the intrinsic scatter between clouds is of order a factor of two. Consistent with previous studies in the Local Group, we find a linear relationship between cloud virial mass and CO luminosity, supporting the assumption that the clouds in this GMC sample are gravitationally bound. We do not detect a significant population of GMCs with elevated velocity dispersions for their sizes, as has been detected in the Galactic center. Though the range of metallicities probed in this study is narrow, the average conversion factors of these galaxies will serve to anchor the high metallicity end of metallicity-X_CO_ trends measured using conversion factors in resolved clouds; this has been previously possible primarily with Milky Way measurements.
