Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe PG-RQS survey. Building the radio spectral distribution of radio-quiet quasars. I. The 45-GHz data
87
0
0.0
(
0
)
Added by
Ranieri Diego Baldi
Publication date
2021
fields
Physics
and research's language is
English
Authors
R. D. Baldi
Ask ChatGPT about the research
No Arabic abstract
The origin of the radio emission in radio-quiet quasars (RQQs) remains unclear. Radio photons may be produced by a scaled-down version of the relativistic jets observed in radio-loud (RL) AGN, an AGN-driven wind, the accretion disc corona, AGN photon-ionisation of ambient gas (free-free emission), or star formation (SF). Here, we report a pilot study, part of a radio survey (`PG-RQS) aiming at exploring the spectral distributions of the 71 Palomar-Green (PG) RQQs: high angular resolution observations ($sim$50 mas) at 45~GHz (7 mm) with the Jansky Very Large Array of 15 sources. Sub-mJy radio cores are detected in 13 sources on a typical scale of $sim$100 pc, which excludes significant contribution from galaxy-scale SF. For 9 sources the 45-GHz luminosity, $ u L_{45~{rm GHz}}$, is above the lower frequency ($sim$1--10 GHz) spectral extrapolation, indicating the emergence of an additional flatter-spectrum compact component at high frequencies. The X-ray luminosity and black hole (BH) mass, correlate more tightly with the 45-GHz luminosity than the 5-GHz. The 45GHz-based radio-loudness increases with decreasing Eddington ratio and increasing BH mass. These results suggest that the 45-GHz emission from PG RQQs nuclei originates from the innermost region of the core, probably from the accretion disc corona. Increasing contributions to 45-GHz emission from a jet at higher BH masses and lower Eddington ratios and from a disc wind at large Eddington ratios are still consistent with our results. Future full radio spectral coverage of the sample will help us investigating the different physical mechanisms in place in RQQ cores.
rate research
Read More
We discuss 6 GHz JVLA observations covering a volume-limited sample of 178 low redshift ($0.2 < z < 0.3$) optically selected QSOs. Our 176 radio detections fall into two clear categories: (1) About $20$% are radio-loud QSOs (RLQs) having spectral luminosities $L_6 gtrsim 10^{,23.2} mathrm{~W~Hz}^{-1}$ primarily generated in the active galactic nucleus (AGN) responsible for the excess optical luminosity that defines a emph{bona fide} QSO. (2) The radio-quiet QSOs (RQQs) have $10^{,21} lesssim L_6 lesssim 10^{,23.2} mathrm{~W~Hz}^{-1}$ and radio sizes $lesssim 10 mathrm{~kpc}$, and we suggest that the bulk of their radio emission is powered by star formation in their host galaxies. Radio silent QSOs ($L_6 lesssim 10^{,21} mathrm{~W~Hz}^{-1}$) are rare, so most RQQ host galaxies form stars faster than the Milky Way; they are not red and dead ellipticals. Earlier radio observations did not have the luminosity sensitivity $L_6 lesssim 10^{,21} mathrm{~W~Hz}^{-1}$ needed to distinguish between such RLQs and RQQs. Strong, generally double-sided, radio emission spanning $gg 10 mathrm{~kpc}$ was found associated with 13 of the 18 RLQ cores having peak flux densities $S_mathrm{p} > 5 mathrm{~mJy~beam}^{-1}$ ($log(L) gtrsim 24$). The radio luminosity function of optically selected QSOs and the extended radio emission associated with RLQs are both inconsistent with simple unified models that invoke relativistic beaming from randomly oriented QSOs to explain the difference between RLQs and RQQs. Some intrinsic property of the AGNs or their host galaxies must also determine whether or not a QSO appears radio loud.
Although radio-quiet quasars (RQQs) constitute >90% of optically-identified quasar samples their radio properties are only poorly understood. In this paper we present the results of a multi-frequency VLA study of 27 low-redshift RQQs. We detect radio emission from 20 objects, half of which are unresolved (< 0.24). In cases where significant structure can be resolved, double, triple and linear radio sources on scales of a few kpc are found. The radio emission (typically) has a steep spectrum (alpha ~ 0.7), and high brightness temperatures (T_B > 10^5 K) are measured in some of the radio components. The RQQs form a natural extension to the radio luminosity - absolute magnitude distribution of nearby Seyfert 1s. We conclude that a significant fraction of the radio emission in RQQs originates in a compact nuclear source directly associated with the quasar. There are no significant differences between the radio properties of RQQs with elliptical hosts and those in disc galaxies within the current sample.
Although radio-quiet quasars (RQQs), which constitute the majority of optically-identified quasar samples, are by no means radio silent the properties of their radio emission are only poorly understood. We present the results of a multi-frequency VLA study of 27 low-redshift RQQs. In general, we find that the properties of the radio sources in RQQs are consistent with them being weak, small-scale (~1 kpc) jets similar to those observed in nearby Seyfert galaxies. We conclude that a significant fraction of the radio emission in RQQs is directly associated with the central engine and is not a result of stellar processes in the surrounding galaxy. There appears to be no difference between the radio properties of RQQs in elliptical and disc galaxies, implying that the relationship between the host galaxy and the `radio loudness of the active nucleus is not straightforward.
We investigate the radio emitting structures of radio-quiet active galactic nuclei with an emphasis on radio-quiet quasars to study their connection to Seyfert galaxies. We present and analyse high-sensitivity VLA radio continuum images of 14 radio-quiet quasars and six Seyfert galaxies. Many of the low redshift radio-quiet quasars show radio structures that can be interpreted as jet-like outflows. However, the detection rate of extended radio structures on arcsecond scales among our sample decreases with increasing redshift and luminosity, most likely due to a lack of resolution. The morphologies of the detected radio emission indicate strong interactions of the jets with the surrounding medium. We also compare the radio data of seven quasars with corresponding HST images of the [OIII] emitting narrow-line region (NLR). We find that the scenario of interaction between the radio jet and the NLR gas is confirmed in two sources by structures in the NLR gas distribution as previously known for Seyfert galaxies. The extended radio structures of radio-quiet quasars at sub-arcsecond resolution are by no means different from that of Seyferts. Among the luminosities studied here, the morphological features found are similar in both types of objects while the overall size of the radio structures increases with luminosity. This supports the picture where radio-quiet quasars are the scaled-
We present the results from 685 MHz observations with the upgraded Giant Metrewave Radio Telescope (uGMRT) of 22 quasars belonging to the Palomar-Green (PG) quasar sample. Only four sources reveal extended radio structures on $sim$10-30 kpc scales, while the rest are largely a combination of a radio core unresolved at the uGMRT resolution of $sim$3-5 arcsec, surrounded by diffuse emission on few kpc to $sim$10 kpc scales. A few sources reveal signatures of barely resolved jets and lobes in their spectral index images that are created using the uGMRT 685 MHz data and similar resolution GHz-frequency data from the Very Large Array. On the basis of their position on the radio-IR correlation as well as the spectral index images, we find that the radio emission in the two radio-loud (RL) quasars and nearly one-third of the radio-quiet (RQ) quasars is active galactic nucleus (AGN) dominated whereas the remaining sources appear to have significant contributions from stellar-related processes along with the AGN. While the two RL sources exhibit inverted spectral index in their cores, the RQ sources exhibit a range of spectral indices varying from flat to steep ($-0.1gtrsimalpha_{R}gtrsim-1.1$) indicating the presence of unresolved jets/lobes or winds. Except for a significant correlation between the 685~MHz radio luminosity and the Eddington ratio, we do not find strong correlations between other 685 MHz radio properties and black hole (BH) properties in the RQ PG sources. This lack of correlations could be explained by the contribution of stellar-related emission, or radio emission from previous AGN activity episodes which may not be related to the current BH activity state.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
