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Sapna Mishra, Hum Chand, Gopal-Krishna & Ravi Joshi

Revisiting the incidence of Mg II absorbers along the blazar sightlines

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Mots-clés : AGN, astronomie, astrophysique, extragalactique, spectroscopie

Abstract

It is believed that the cool gas clouds traced by Mg II absorption, within a velocity offset of 5000 km/s from the background quasar, are associated with the quasar itself, whereas the absorbers seen at larger velocity offsets towards us are intervening systems and hence their existence is completely independent of the background quasar. Recent evidence by Bergeron et al. 2011 (hereafter BBM), however, seriously questions this canonical view, by showing that the number density of intervening Mg II absorbers along the sightlines towards 45 blazars is, on average, ~ 2 times the expectation based on the Mg II absorption systems seen on the sightlines to normal QSOs. Given the serious implications of this finding, it becomes important to revisit this issue by enlarging the source sample and subjecting it to an independent analysis. Here, we first report our results based on a re-analysis of the spectroscopic data for the BBM sample; this has reproduced their factor 2 excess in dN/dz along blazar sightlines, vis-a-vis the normal QSOs. Next, we assemble a 6 times larger sample of blazar sightlines, albeit with lower SNR. Using this enlarged sample together with the BBM sample, our analysis shows that the dN/dz of Mg II absorbers statistically matches that known for normal QSO sightlines.

Keywords : AGN, astronomy, astrophysics, extragalactic, spectroscopy

To cite this article

Sapna Mishra, Hum Chand, Gopal-Krishna & Ravi Joshi, «Revisiting the incidence of Mg II absorbers along the blazar sightlines», 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, 325 - 329 URL : https://popups.uliege.be:443/0037-9565/index.php?id=7760.

About: Sapna Mishra

Aryabhatta Research Institute of Observational SciencES, Manora Peak, Nainital 263002, India, sapna@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: Ravi Joshi

Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411007, India