A VLBI survey of compact broad absorption line quasars with balnicity index BI > 0

Abstract

Aims. Outflows manifest as broad absorption lines (BALs) in the quasars spectra. Although outflows are one of the most common astrophysical processes in the Universe, the BAL quasars are rare. Radio emission is another tool that can help to understand the phenomenon of BAL quasars. The aim of this paper is to study their orientation and age by very long baseline interferometry (VLBI) imaging and radio-loudness parameter distribution. Methods. We performed high resolution radio observations of a new sample of ten BAL quasars using both the Very Long Baseline Array (VLBA) and the European VLBI Network (EVN) at 5 GHz. All the selected sources have balnicity indices (BI) more than 0 and radio flux densities less than 80 mJy at 1.4 GHz. They are very compact with linear sizes of the order of a few tens of parsecs and radio luminosities at 1.4 GHz above the FR I-FR II luminosity threshold. Results. Most of the observed objects have been resolved at 5 GHz showing one-sided, probably core-jet structures, typical for quasars. We discuss in detail their age and orientation based on the radio observations. We then used the largest available sample of BAL quasars to study the relationships between the radio and optical properties in these objects. We found that (1) the strongest absorption (high values of the balnicity index BI) is connected with the lower values of the radio-loudness parameter, log R I < 1.5, and thus probably with large viewing angles; (2) the large span of the BI values in each bin of the radio-loudness parameter indicates that the orientation is only one of the factors influencing the measured absorption; (3) most of the radio-loud BAL quasars are compact, low luminosity objects with a wide range of jet power (although the highest values of BI seem to be associated with the lower values of jet power). In addition, we suggest that the short lifetime postulated for some compact active galactic nuclei could also explain the scarcity of the large-scale radio sources among BAL quasars.

Broadband nuclear emission in two radio-loud broad absorption line quasars

“…The BI value amounts to 850 and 52.5 for PG 1004+130 and 3C 270.1, respectively (Wills et al 1999;Gibson et al 2009). As already mentioned, the strong UV absorption seems to be associated with lower values of radio-loudness parameter, log R I < 1.5 and thus large viewing angles (Welling et al 2014;Kunert-Bajraszewska et al 2014). The values of the radio-loudness parameter, log R I , defined as the radio (1.4 GHz)-to-optical (i-band) ratio of the quasar core (Kimball et al 2011) amounts to 0.7 and 2.8 for PG 1004+130 and 3C 270.1, respectively.…”

“…The radio studies of BAL quasars indicate that strong UV C IV BALs are associated with lower values of the radioloudness parameter (Welling et al 2014;Kunert-Bajraszewska et al 2014). Since this parameter is thought to be a good indicator of orientation (Kimball et al 2011), its low values may imply large viewing angles and consequently the orientation dependence of BAL quasars.…”

“…However, there is no correlation between the radio-loudness parameter and the BI, since a large span of values occurs in each bin of the radio-loudness parameter. Therefore, as pointed out by Kunert-Bajraszewska et al (2014), the orientation is only one of the factors influencing absorption.…”

“…Our modelling of the SED of both quasars indicates that the contribution of the jet-linked X-ray emission is possible in both the strong and weak radio sources, but its fraction seems to scale with jet or radio power. Since the majority of BAL quasars are weak compact radio sources without prominent jets (Bruni et al 2012(Bruni et al , 2013Kunert-Bajraszewska et al 2014), such scaling could be responsible for the difference in X-ray emission between radio-loud BAL quasars and non-BAL objects. Additionally Miller et al (2011) suggest that beaming can increase the dominance of jet-linked X-ray emission at low inclinations in radio-loud BAL quasars.…”

“…Finally, the radio variability studies of Appendix A is available in electronic form at http://www.aanda.org some of the BAL quasars imply that there are polar outflows from the inner regions of a thin disk (Zhou et al 2006;Ghosh & Punsly 2007). Nevertheless, according to the radio studies of BAL quasars Kunert-Bajraszewska et al 2014), the majority of them have low radio luminosities and moderate orientations. The observed X-ray weakness of some of them agrees with the above findings.…”