- ID:
- ivo://CDS.VizieR/J/MNRAS/455/4191
- Title:
- Radio emission from radio-quiet quasars
- Short Name:
- J/MNRAS/455/4191
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radio emission from radio-quiet quasars may be due to star formation in the quasar host galaxy, to a jet launched by the supermassive black hole, or to relativistic particles accelerated in a wide-angle radiatively driven outflow. In this paper, we examine whether radio emission from radio-quiet quasars is a byproduct of star formation in their hosts. To this end, we use infrared spectroscopy and photometry from Spitzer and Herschel to estimate or place upper limits on star formation rates in hosts of ~300 obscured and unobscured quasars at z<1. We find that low-ionization forbidden emission lines such as [NeII] and [NeIII] are likely dominated by quasar ionization and do not provide reliable star formation diagnostics in quasar hosts, while polycyclic aromatic hydrocarbon (PAH) emission features may be suppressed due to the destruction of PAH molecules by the quasar radiation field. While the bolometric luminosities of our sources are dominated by the quasars, the 160{mu}m fluxes are likely dominated by star formation, but they too should be used with caution. We estimate median star formation rates to be 6-29M_{sun}_/yr, with obscured quasars at the high end of this range. This star formation rate is insufficient to explain the observed radio emission from quasars by an order of magnitude, with log(L_radio,obs_/L_radio,SF_)=0.6-1.3 depending on quasar type and star formation estimator. Although radio-quiet quasars in our sample lie close to the 8-1000{mu}m infrared/radio correlation characteristic of the star-forming galaxies, both their infrared emission and their radio emission are dominated by the quasar activity, not by the host galaxy.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/768/37
- Title:
- Radio emission from SDSS quasars
- Short Name:
- J/ApJ/768/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used the 1.4GHz NVSS to study radio sources in two color-selected QSO samples: a volume-limited sample of 1313 QSOs defined by M_i_<-23 in the redshift range 0.2<z<0.45 and a magnitude-limited sample of 2471 QSOs with m_r_<=18.5 and 1.8<z<2.5. About 10% were detected above the 2.4mJy NVSS catalog limit and are powered primarily by active galactic nuclei (AGNs). The space density of the low-redshift QSOs evolves as {rho}{prop.to}(1+z)^6^. In both redshift ranges the flux-density distributions and luminosity functions of QSOs stronger than 2.4mJy are power laws, with no features to suggest more than one kind of radio source. Extrapolating the power laws to lower luminosities predicts the remaining QSOs should be extremely radio quiet, but they are not. Most were detected statistically on the NVSS images with median peak flux densities S_p_(mJy/beam){approx}0.3 and 0.05 in the low- and high-redshift samples, corresponding to spectral luminosities log [L_1.4GHz_(W/Hz)]{approx}22.7 and 24.1, respectively. We suggest that the faint radio sources are powered by star formation at rates dM/dt~20M_{sun}_/yr in the moderate luminosity (median <M_i_>{approx}-23.4) low-redshift QSOs and dM/dt~500M_{sun}_/yr in the very luminous (<M_i_>{approx}-27.5) high-redshift QSOs. Such luminous starbursts [<log(L_IR_/L_{sun}_)>~11.2 and 12.6, respectively] are consistent with "quasar mode" accretion in which cold gas flows fuel both AGN and starburst.
- ID:
- ivo://CDS.VizieR/J/A+A/281/161
- Title:
- Radio emission from stars at 250GHz
- Short Name:
- J/A+A/281/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the IRAM 30 m-telescope together with the Max Planck Institute for Radio Astronomy (MPIfR) bolometer to survey nearly 270 stars of different types for 250GHz continuum emission. We compare these data with their low frequency (cm-range) properties. Early type stars show very often a deviation from the uniformly expanding wind model which we tentatively attribute to temperature and/or density fluctuations in their deeper atmospheric layers. For WR stars this deviation seems to depend on the effective temperature. Pre-main sequence stars usually seem to be surrounded by a shell of warm dust making a substantial contribution to the 250 GHz flux density value. We have found especially for nearby giants and supergiants that a layer at the transition from photosphere to chromosphere emits ample 250 GHz radiation. We show that the present data can still be explained by a simple uniformly illuminated disk model with the known stellar radius. Optically variable stars are not very strong emitters at 250 GHz. We preferentially detected the more exotic ones, a few Beta Lyr-type and symbiotic stars. Comments on many individual objects are given in the appropriate sections.
- ID:
- ivo://CDS.VizieR/J/ApJ/573/306
- Title:
- Radio emission from supernovae
- Short Name:
- J/ApJ/573/306
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report Very Large Array radio observations of 29 supernovae (SNe) with ages ranging from 10 days to about 90yr past explosion. These observations significantly contribute to the existing data pool on such objects. Included are detections of known radio SNe 1950B, 1957D, 1970G, and 1983N, the suspected radio SN 1923A, and the possible radio SN 1961V. None of the remaining 23 observations resulted in detections, providing further evidence to support the observed trend that most SNe are not detectable radio emitters. To investigate the apparent lack of radio emission from the SNe reported here, we have followed standard practice and used Chevalier's "standard model" to derive (upper limits to) the mass-loss rates for the supernova progenitors. These upper limits to the fluxes are consistent with a lack of circumstellar material needed to provide detectable radio emission for SNe at these ages and distances. Comparison of the radio luminosities of these supernovae as a function of age past explosion to other well-observed radio SNe indicates that the Type II SNe upper limits are more consistent with the extrapolated light curves of SN 1980K than of SN 1979C, suggesting that SN 1980K may be a more typical radio emitter than SN 1979C. For completeness, we have included an appendix where the results of analyses of the non-SN radio sources are presented. Where possible, we make (tentative) identifications of these sources using various methods.
1335. Radio emission of SS433
- ID:
- ivo://CDS.VizieR/J/AZh/78/922
- Title:
- Radio emission of SS433
- Short Name:
- J/AZh/78/922
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Two daily sets monitoring data of the galactic X-ray binary SS 433 (V1343 Aql) obtained on the RATAN-600 radio telescope (117 days in 1997 and 120 days in 1999) show variations in its quiescent radio emission with a period of 6.05 days at six frequencies from 0.96 to 22GHz.
- ID:
- ivo://CDS.VizieR/J/MNRAS/478/3848
- Title:
- Radio-emitting AGN environmental prop.
- Short Name:
- J/MNRAS/478/3848
- Date:
- 10 Dec 2021 00:52:31
- Publisher:
- CDS
- Description:
- We study the environmental properties of z<=1.2 radio-selected active galactic nuclei (AGNs) belonging to the ~2deg^2^ of the COSMOS field, finding that about 20 per cent of them appear within overdense structures. AGNs with P_1.4GHz_>10^23.5^W/Hz/sr are twice more likely to be found in clusters with respect to fainter sources (~38 per cent vs ~15 per cent), just as radio-selected AGNs with stellar masses M_*_>10^11^M_{sun}_ are twice more likely to be found in overdense environments with respect to objects of lower mass (~24 per cent vs ~11 per cent). Comparisons with galaxy samples further suggest that radio-selected AGN of large stellar mass tend to avoid underdense environments more than normal galaxies with the same stellar content. Stellar masses also seem to determine the location of radio-active AGN within clusters: ~100 per cent of the sources found as satellite galaxies have M_*_<10^11.3^M_{sun}_, while ~100 per cent of the AGNs coinciding with a cluster central galaxy have M_*_>10^11^M_{sun}_. No different location within the cluster is instead observed for AGN of various radio luminosities. Radio AGN, which also emit in the Mid-Infrared show a marked preference to be found as isolated galaxies (~70 per cent) at variance with those also active in the X-ray that all seem to reside within overdensities. What emerges from our work is a scenario whereby physical processes on sub-pc and kpc scales (e.g. emission, respectively, related to the AGN and to star formation) are strongly interconnected with the large-scale environment of the AGN itself.
- ID:
- ivo://CDS.VizieR/J/ApJ/681/1296
- Title:
- Radio evolution of the PN NGC 7027
- Short Name:
- J/ApJ/681/1296
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a 25yr program to monitor the radio flux evolution of the planetary nebula NGC 7027. We find significant evolution of the spectral flux densities. The flux density at 1465MHz, where the nebula is optically thick, is increasing at a rate of 0.251+/-0.015%/yr, caused by the expansion of the ionized nebula. At frequencies where the emission is optically thin, the spectral flux density is changing at a rate of -0.145+/-0.005%/yr, caused by a decrease in the number of ionizing photons coming from the central star. A distance of 980+/-100pc is derived. By fitting interpolated models of post-AGB evolution to the observed changes, we find that over the 25yr monitoring period, the stellar temperature has increased by 3900+/-900K and the stellar bolometric luminosity has decreased by 1.75+/-0.5%. We derive a distance-independent stellar mass of 0.655+/-0.010M_{sun}_ adopting the Blocker stellar evolution models, or about 0.04M_{sun}_ higher when using models of Vassiliadis & Wood. A Cloudy photoionization model is used to fit all epochs at all frequencies simultaneously. The differences between the radio flux density predictions and the observed values show some time-independent residuals of typically 1%. A possible explanation is inaccuracies in the radio flux scale of Baars and coworkers. We propose an adjustment to the flux density scale of the primary radio flux calibrator 3C 286, based on the Cloudy model of NGC 7027. We also calculate precise flux densities for NGC 7027 for all standard continuum bands used at the VLA, as well as for some new 30 GHz experiments.
- ID:
- ivo://CDS.VizieR/J/A+A/552/A19
- Title:
- Radio-farIR correlation in NGC 6946
- Short Name:
- J/A+A/552/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive the distribution of the synchrotron spectral index across NGC 6946 and investigate the correlation between the radio continuum (synchrotron) and far-infrared (FIR) emission using the KINGFISH Herschel PACS and SPIRE data.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A83
- Title:
- Radio flux densities of neutrino associations
- Short Name:
- J/A+A/650/A83
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Identifying the most likely sources for high-energy neutrino emission has been one of the main topics in high-energy astrophysics ever since the first observation of high-energy neutrinos by the IceCube Neutrino Observatory. Active galactic nuclei with relativistic jets, also known as blazars, have been considered to be one of the main candidates because of their ability to accelerate particles to high energies. We study the connection between radio emission and IceCube neutrino events using data from the Owens Valley Radio Observatory (OVRO) and Metsahovi Radio Observatory blazar monitoring programs. We identify sources in our radio monitoring sample that are positionally consistent with IceCube high-energy neutrino events. We estimate their mean flux density and variability amplitudes around the neutrino arrival time, and compare these with values from random samples to establish the significance of our results. We find radio source associations within our samples with 15 high-energy neutrino events detected by IceCube. Nearly half of the associated sources are not detected in the {gamma}-ray energies, but their radio variability properties and Doppler boosting factors are similar to the {gamma}-ray detected objects in our sample, meaning that they could still be potential neutrino emitters. We find that the number of strongly flaring objects in our statistically complete OVRO samples is unlikely to be a random coincidence (at 2{sigma} level). Based on our results, we conclude that although it is clear that not all neutrino events are associated with strong radio flaring blazars, observations of large-amplitude radio flares in a blazar at the same time as a neutrino event are unlikely to be a random coincidence.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/830
- Title:
- Radio flux density of extremely red quasars
- Short Name:
- J/MNRAS/477/830
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most active galactic nuclei (AGNs) are radio quiet, and the origin of their radio emission is not well understood. One hypothesis is that this radio emission is a byproduct of quasar-driven winds. In this paper, we present the radio properties of 108 extremely red quasars (ERQs) at z=2-4. ERQs are among the most luminous quasars (L_bol_~10^47-48^erg/s^) in the Universe, with signatures of extreme (>>1000km/s) outflows in their [OIII]{lambda}5007{AA} emission, making them the best subjects to seek the connection between radio and outflow activities. All ERQs but one are unresolved in the radio on ~10kpc scales, and the median radio luminosity of ERQs is {nu}L_{nu}_[6GHz]= 10^41.0^erg/s, in the radio-quiet regime, but 1-2 orders of magnitude higher than that of other quasar samples. The radio spectra are steep, with a mean spectral index <{alpha}>=-1.0. In addition, ERQs neatly follow the extrapolation of the low-redshift correlation between radio luminosity and the velocity dispersion of [OIII]-emitting ionized gas. Uncollimated winds, with a power of one per cent of the bolometric luminosity, can account for all these observations. Such winds would interact with and shock the gas around the quasar and in the host galaxy, resulting in acceleration of relativistic particles and the consequent synchrotron emission observed in the radio. Our observations support the picture in which ERQs are signposts of extremely powerful episodes of quasar feedback, and quasar-driven winds as a contributor of the radio emission in the intermediate regime of radio luminosity {nu}L_{nu}_=10^39^-10^42^erg/s.