Title:	On the incidence of Mg II absorbers along the blazar sightlines
Authors:	Mishra S, S. Chand, Hum Gopal-Krishna Joshi, R. Shchekinov, Yuri Fatkhullin, T.A.
Keywords:	BL Lacertae objects photometry quasars emission lines
Issue Date:	Feb-2018
Publisher:	Oxford University Press for the Royal Astronomical Society
Citation:	Monthly Notices of the Royal Astronomical Society, 2018, Vol. 473, P5154-5164
Abstract:	It is widely believed that the cool gas clouds traced by Mg ii absorption, within a velocity offset of 5000 km s−1 relative to the background quasar are mostly associated with the quasar itself, whereas the absorbers seen at larger velocity offsets towards us are intervening absorber systems and hence their existence is completely independent of the background quasar. Recent evidence by Bergeron et al. (hereinafter BBM) has seriously questioned this paradigm, by showing that the number density of intervening Mg ii absorbers towards the 45 blazars in their sample is nearly two times the expectation based on the Mg ii absorption systems seen towards normal quasars (QSOs). Given its serious implications, it becomes important to revisit this finding, by enlarging the blazar sample and subjecting it to an independent analysis. Here, we first report the outcome of our re-analysis of the available spectroscopic data for the BBM sample itself. Our analysis of the BBM sample reproduces their claimed factor of 2 excess of dN/dz along blazar sightlines, vis-à-vis normal QSOs. We have also assembled an approxmately three times larger sample of blazars, albeit with moderately sensitive optical spectra. Using this sample together with the BBM sample, our analysis shows that the dN/dz of the Mg ii absorbers statistically matches that known for normal QSO sightlines. Further, the analysis indicates that associated absorbers might be contributing significantly to the estimated dN/dz up to offset speeds Δv ∼ 0.2c relative to the blazar.
Description:	Open Access
URI:	http://hdl.handle.net/2289/6904
ISSN:	0035-8711 1365-2966 - (online)
Alternative Location:	http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1710.04020 https://arxiv.org/abs/1710.04020 http://dx.doi.org/10.1093/mnras/stx2684
Copyright:	2018 The authors & the Royal Astronomical Society
Appears in Collections:	Research Papers (A&A)

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