A multiwavelength continuum characterization of high-redshift broad absorption line quasars

D Tuccillo,G Bruni,K.-H Mack,M A Dipompeo,M S Brotherton,J I González-Serrano,A Kraus,A Pasetto

doi:10.1093/mnras/stx333

Abstract

We present the results of a multi-wavelength study of a sample of high-redshift Radio Loud (RL) Broad Absorption Line (BAL) quasars. This way we extend to higher redshift previous studies on the radio properties, and broadband optical colors of these objects. We have se- lected a sample of 22 RL BAL quasars with 3.6 z 4.8 cross-correlating the FIRST radio survey with the SDSS. Flux densities between 1.25 and 9.5 GHz have been collected with the JVLA and Effelsberg-100m telescopes for 15 BAL and 14 non-BAL quasars used as compar- ison sample. We determine the synchrotron peak frequency, constraining their age. A large number of GigaHertz Peaked Spectrum (GPS) and High Frequency Peakers (HFP) sources has been found in both samples (80% for BAL and 71% for non-BAL QSOs), not suggesting a younger age for BAL quasars. The spectral index distribution provides information about the orientation of these sources, and we find statistically similar distributions for the BAL and non-BAL quasars in contrast to work done on lower redshift samples. Our sample may be too small to convincingly find the same effect, or might represent a real evolutionary effect based on the large fraction of young sources. We also study the properties of broadband colors in both optical (SDSS) and near- and mid-infrared (UKIDSS and WISE) bands, finding that also at high redshift BAL quasars tend to be optically redder than non-BAL quasars. However, these differences are no more evident at longer wavelength, when comparing colors of the two samples by mean of the WISE survey.

Highlights

Intrinsic absorption lines are a common feature in quasar (QSO) spectra, and they are likely produced by outflowing winds along the line of sight that are launched from the accretion disk around the central supermassive black hole (Murray et al 1995; Proga, Stone & Kallman 2000)
Considering the angular resolution of the latter for the 8 Broad Absorption Line (BAL) and 8 non-BAL QSOs detected at 9 GHz (0.2 arcsec), we obtain an upper limit for the projected linear size of 1.4 kpc at the mean redshift of 4.02 and 3.91 for our BAL and non-BAL samples
We studied a sample of 15 RL BAL QSOs and compared our results with the ones obtained for a well matched sample of 14 RL non-BAL QSOs

Summary

Introduction

Intrinsic absorption lines are a common feature in quasar (QSO) spectra, and they are likely produced by outflowing winds along the line of sight that are launched from the accretion disk around the central supermassive black hole (Murray et al 1995; Proga, Stone & Kallman 2000). According to the orientation scenario, BAL QSOs are normal quasars seen at high inclination angles, and the outflows at the origin of the BAL features are located near the equatorial plane of the accretion disk. This model fits naturally in the AGN unification models (Antonucci 1993; Urry & Padovani 1995) and it is supported by the claim that both BAL and non-BAL QSOs appear to be drawn by the same parent population (Reichard et al 2003). The results of the studies at higher wavelength are controversial (Gallagher et al 2007, DiPompeo et al 2013) It has been proved that RL BAL QSOs show a variety of possible radio morphologies (Montenegro-Montes et al 2008; DiPompeo et al 2011; Bruni et al 2012, Bruni et al 2013) and are not always unresolved, as it may be expected for young radio sources (Fanti et al 1990)

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Conclusion