since 05 February 2011 :
View(s): 80 (3 ULiège)
Download(s): 3 (0 ULiège)
print        
Parveen Kumar, Hum Chand, Gopal-Krishna, Raghunathan Srianand, Chelliah Subramonian Stalin & Patrick Petitjean

Spectroscopic and polarimetric study of radio-quiet weak emission line quasars

Article
Open Access

Attached document(s)

Version PDF originale
Mots-clés : AGN, astronomie, astrophysique, extragalactique, polarimétrie, spectroscopie

Abstract

A small subset of optically selected radio-quiet QSOs with weak or no emission lines may turn out to be the elusive radio-quiet BL Lac objects, or simply be radio-quiet QSOs with an infant/shielded broad line region (BLR). High polarisation (p > 3-4%), a hallmark of BL Lacs, can be used to test whether some optically selected ‘radio-quiet weak emission line QSOs’ (RQWLQs) show a fractional polarisation high enough to qualify as radio-quiet analogues of BL Lac objects. To check this possibility, we have made optical spectral and polarisation measurements of a sample of 19 RQWLQs. Out of these, only 9 sources show a non-significant proper motion (hence very likely extragalactic) and only two of them are found to have p > 1%. For these two RQWLQs, namely J142505.59+035336.2 and J154515.77+003235.2, we found the highest polarization to be 1.59±0.53%, which is again too low to classify them as (radio-quiet) BL Lacs, although one may recall that even genuine BL Lacs sometimes appear weakly polarised. We also present a statistical comparison of the optical spectral index, for a sample of 45 RQWLQs with redshift-luminosity matched control samples of 900 QSOs and an equivalent sample of 120 blazars, assembled from the literature. The spectral index distribution of RQWLQs is found to differ, at a high significance level, from that of blazars. This, too, is consistent with the common view that the mechanism of the central engine in RQWLQs, as a population, is close to that operating in normal QSOs and the primary difference between them is related to the BLR.

Keywords : AGN, astronomy, astrophysics, extragalactic, polarimetry, spectroscopy

To cite this article

Parveen Kumar, Hum Chand, Gopal-Krishna, Raghunathan Srianand, Chelliah Subramonian Stalin & Patrick Petitjean, «Spectroscopic and polarimetric study of radio-quiet weak emission line quasars», Bulletin de la Société Royale des Sciences de Liège [En ligne], Volume 87 - Année 2018, Actes de colloques, First Belgo-Indian Network for Astronomy & Astrophysics (BINA) workshop - November 2016 - Nainital, India, 316 - 320 URL : https://popups.uliege.be:443/0037-9565/index.php?id=7755.

About: Parveen Kumar

Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital, 263002 India, parveen@aries.res.in

About: Hum Chand

Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital, 263002 India

About:  Gopal-Krishna

Centre for Excellence in Basic Sciences, University of Mumbai campus (Kalina), Mumbai 400098, India

About: Raghunathan Srianand

Inter-University Centre for Astronomy and Astrophysics, Postbag 4, Ganeshkhind,, Pune 411 007, India

About: Chelliah Subramonian Stalin

Indian Institute of Astrophysics, Block II, Koramangala, Bangalore-560034, India

About: Patrick Petitjean

Institut d'Astrophysique de Paris, CNRS-UPMC, UMR 7095, 98bis bd Arago, 75014 Paris, France