The origin of radio emission in broad absorption line quasars: Results from the LOFAR Two-metre Sky Survey

Abstract

We present a study of the low-frequency radio properties of broad absorption line quasars (BALQSOs) from the LOFAR Two-metre Sky-Survey Data Release 1 (LDR1). The value-added LDR1 catalogue contains Pan-STARRS counterparts, which we match with the Sloan Digital Sky Survey (SDSS) DR7 and DR12 quasar catalogues. We find that BALQSOs are twice as likely to be detected at 144 MHz than their non-BAL counterparts, and BALQSOs with low-ionisation species present in their spectra are three times more likely to be detected than those with only high-ionisation species. The BALQSO fraction at 144 MHz is constant with increasing radio luminosity, which is inconsistent with previous results at 1.4 GHz, indicating that observations at the different frequencies may be tracing different sources of radio emission. We cross-match radio sources between the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey and LDR1, which provides a bridge via the LDR1 Pan-STARRS counterparts to identify BALQSOs in SDSS. Consequently we expand the sample of BALQSOs detected in FIRST by a factor of three. The LDR1-detected BALQSOs in our sample are almost exclusively radio-quiet (log(R144 MHz) < 2), with radio sizes at 144 MHz typically less than 200 kpc; these radio sizes tend to be larger than those at 1.4 GHz, suggesting more extended radio emission at low frequencies. We find that although the radio detection fraction increases with increasing balnicity index (BI), there is no correlation between BI and either low-frequency radio power or radio-loudness. This suggests that both radio emission and BI may be linked to the same underlying process, but are spatially distinct phenomena.

Placing LOFAR-detected quasars in C iv emission space: implications for winds, jets and star formation

“…By investigating the radio properties of Sloan Digital Sky Survey (SDSS) DR7 quasars from the Faint Images of the Radio Sky at Twenty-Centimetres (FIRST) survey (Becker, White & Helfand 1995), Richards et al (2011) were able to show that radio-loud quasars are concentrated at low C IV blueshifts, thus suggesting radio-loud quasars often have little to no outflowing wind. This behaviour is broadly consistent with the relative scarcity of radio-loud BAL quasars (Stocke et al 1992;Becker et al 2000;White et al 2007;Morabito et al 2019). Richards et al (2011) also found radio-quiet quasars with low blueshifts and, in fact, very similar UV spectral energy distributions (SEDs) to the radio-loud quasars.…”

“…With the advent of the highsensitivity Low-Frequency Array (LOFAR; van Haarlem et al 2013), it is now possible to probe the radio-quiet population in more detail (e.g. Gürkan et al 2015Gürkan et al , 2018Gürkan et al , 2019Morabito et al 2019;Rosario et al 2020). By combining LOFAR data with the C IV emission line, we can therefore consider the relative contributions of winds, star formation, and compact jets in the radio-quiet population and their relation to disc and outflow processes.…”

Fundamental differences in the radio properties of red and blue quasars: enhanced compact AGN emission in red quasars

“…An enhanced fraction of broad absorption line QSOs (BALQ-SOs; known to host powerful winds) have been found in red QSOs (Urrutia et al 2009), which could be evidence that red QSOs are more wind dominated than typical QSOs. Although BALQSOs are virtually all radio-quiet, they have also been found to show a remarkably similar enhancement in the radio as that found for red QSOs (Klindt et al 2019;Morabito et al 2019). Further corroborating but independent evidence for wind-dominated sources becoming more relevant at lower R values comes from Mehdipour & Costantini (2019), who showed a significant inverse correlation between the X-ray measured column density of the ionised wind in AGN and the radio-loudness parameter.…”

Stratified disc wind models for the AGN broad-line region: ultraviolet, optical, and X-ray properties

“…LoBAL features are observed when the sightlines traverse denser, lower ionization state regions of the wind. LoBAL quasars, and particularly FeLoBAL quasars, are known to systematically differ from the rest of the BAL quasar population (Urrutia et al 2009;Lazarova et al 2012;Dai et al 2012;Morabito et al 2019) and may correspond to a particular evolutionary stage of quasars (e.g. Farrah et al 2007).…”