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The cluster-scale environment of PKS 2155-304.

Farina, E. and Fumagalli, M. and Decarli, R. and Fanidakis, N. (2016) 'The cluster-scale environment of PKS 2155-304.', Monthly notices of the Royal Astronomical Society., 455 (1). pp. 618-625.


PKS 2155−304 is one of the brightest extragalactic source in the X-ray and EUV bands, and is a prototype for the BL Lac class of objects. In this paper, we investigate the large-scale environment of this source using new multi-object as well as long-slit spectroscopy, together with archival spectra and optical images. We find clear evidence of a modest overdensity of galaxies at z = 0.116 10 ± 0.000 06, consistent with previous determinations of the BL Lac redshift. The galaxy group has a radial velocity dispersion of 250+80−40 km s−1 and a virial radius of 0.22 Mpc, yielding a role-of-thumb estimate of the virial mass of Mvir ∼ 1.5 × 1013 M⊙, i.e. one order of magnitude less than that observed in similar objects. This result hints towards a relatively wide diversity in the environmental properties of BL Lac objects.

Item Type:Article
Keywords:BL Lacertae objects: individual: PKS 2155−304, Galaxies: groups: general.
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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:28 September 2015
Date deposited:23 November 2015
Date of first online publication:05 November 2015
Date first made open access:No date available

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