The University of Southampton
University of Southampton Institutional Repository

What drives the radio slopes in radio-quiet quasars?

What drives the radio slopes in radio-quiet quasars?
What drives the radio slopes in radio-quiet quasars?

The origin of the radio emission in radio-quiet (RQ) quasars is not established yet. Important hints can be provided by the spectral slope, and its relation to other emission properties. We compiled the highest resolution 5 and 8.4 GHz Very Large Array observations available of the RQ optically selected Palomar–Green (PG) quasars at z < 0.5. We derive the 5–8.4 GHz spectral slope, αR, for 25 of the complete and well-studied sample of 71 RQ PG quasars. We find a highly significant correlation of αR with L/LEdd, where high L/LEdd(>0.3) quasars have a steep slope (αR < −0.5), indicative of an optically thin synchrotron source. In contrast, lower L/LEdd(<0.3) quasars generally have a flat slope (αR > −0.5), indicative of a compact optically thick synchrotron source. Flat αR quasars also have a low Fe II/Hβ line ratio, and a flat soft X-ray slope. The 16 radio loud (RL) PGs do not follow the RQ quasar set of correlations, and their αR is set by MBH, suggesting that the radio emission mechanisms in RL and RQ quasars are different. A possible interpretation is that high L/LEdd RQ quasars produce a strong outflow and an associated optically thin synchrotron emission. In lower L/LEdd RQ quasars, the strong outflow is missing, and only a compact optically thick radio source remains, possibly associated with the accretion disc coronal emission. A systematic study of RQ quasars at higher frequencies, and higher resolution, can test whether a compact flat source indeed resides in the cores of all RQ quasars, and allows the exploration of its relation with the coronal X-ray emission.

Quasars: General
0035-8711
5513-5523
Laor, Ari
c05ad4c1-3fb4-465a-ab9e-8928b410043c
Baldi, Ranieri D.
c416ed4c-5d1c-48ee-989c-3a8ab38cd124
Behar, Ehud
04fd38d9-e172-4ae9-a530-9418b301e041
Laor, Ari
c05ad4c1-3fb4-465a-ab9e-8928b410043c
Baldi, Ranieri D.
c416ed4c-5d1c-48ee-989c-3a8ab38cd124
Behar, Ehud
04fd38d9-e172-4ae9-a530-9418b301e041

Laor, Ari, Baldi, Ranieri D. and Behar, Ehud (2019) What drives the radio slopes in radio-quiet quasars? Monthly Notices of the Royal Astronomical Society, 482 (4), 5513-5523. (doi:10.1093/mnras/sty3098).

Record type: Article

Abstract

The origin of the radio emission in radio-quiet (RQ) quasars is not established yet. Important hints can be provided by the spectral slope, and its relation to other emission properties. We compiled the highest resolution 5 and 8.4 GHz Very Large Array observations available of the RQ optically selected Palomar–Green (PG) quasars at z < 0.5. We derive the 5–8.4 GHz spectral slope, αR, for 25 of the complete and well-studied sample of 71 RQ PG quasars. We find a highly significant correlation of αR with L/LEdd, where high L/LEdd(>0.3) quasars have a steep slope (αR < −0.5), indicative of an optically thin synchrotron source. In contrast, lower L/LEdd(<0.3) quasars generally have a flat slope (αR > −0.5), indicative of a compact optically thick synchrotron source. Flat αR quasars also have a low Fe II/Hβ line ratio, and a flat soft X-ray slope. The 16 radio loud (RL) PGs do not follow the RQ quasar set of correlations, and their αR is set by MBH, suggesting that the radio emission mechanisms in RL and RQ quasars are different. A possible interpretation is that high L/LEdd RQ quasars produce a strong outflow and an associated optically thin synchrotron emission. In lower L/LEdd RQ quasars, the strong outflow is missing, and only a compact optically thick radio source remains, possibly associated with the accretion disc coronal emission. A systematic study of RQ quasars at higher frequencies, and higher resolution, can test whether a compact flat source indeed resides in the cores of all RQ quasars, and allows the exploration of its relation with the coronal X-ray emission.

Text
radio_slopes2 - Accepted Manuscript
Download (296kB)

More information

Accepted/In Press date: 12 November 2018
e-pub ahead of print date: 16 November 2018
Published date: 1 February 2019
Keywords: Quasars: General

Identifiers

Local EPrints ID: 430595
URI: http://eprints.soton.ac.uk/id/eprint/430595
ISSN: 0035-8711
PURE UUID: 48df6a59-fc31-4cfc-8827-c4cd37f21669

Catalogue record

Date deposited: 03 May 2019 16:30
Last modified: 29 Jan 2020 12:46

Export record

Altmetrics

Contributors

Author: Ari Laor
Author: Ehud Behar

University divisions

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×