Bibcode
Boschin, W.; Girardi, M.; Barrena, R.
Bibliographical reference
Astronomy and Astrophysics, Volume 547, id.A44, 13 pp.
Advertised on:
11
2012
Journal
Citations
8
Refereed citations
8
Description
Context. Abell 1995 is a puzzling galaxy cluster hosting a powerful
radio halo, but it has not yet been recognized as a obvious cluster
merger, as usually expected for clusters with diffuse radio emission.
Aims: We aim at an exhaustive analysis of the internal structure
of Abell 1995 to verify that this cluster is really dynamically relaxed,
as reported in previous studies. Methods: We base our analysis on
new and archival spectroscopic and photometric data for 126 galaxies in
the field of Abell 1995. The study of the hot intracluster medium was
performed on X-ray archival data. Results: Based on 87 fiducial
cluster members, we have computed the average cluster redshift
⟨z⟩ = 0.322 and the global radial velocity dispersion
σV ~ 1300 km s-1. We detect two main optical
subclusters separated by 1.5'that cause the known NE-SW elongation of
the galaxy distribution and a significant velocity gradient in the same
direction. As for the X-ray analysis, we confirm that the intracluster
medium is mildly elongated, but we also detect three X-ray peaks. Two
X-ray peaks are offset with respect to the two galaxy peaks and lie
between them, thus suggesting a bimodal merger caught in a phase of post
core-core passage. The third X-ray peak lies between the NE galaxy peak
and a third, minor galaxy peak suggesting a more complex merger. The
difficulty of separating the two main systems leads to a large
uncertainty on the line-of-sight (LOS) velocity separation and the
system mass: ΔVrf,LOS = 600-2000 km s-1and
Msys = 2-5×1015 h70-1
M&sun;, respectively. Simple analytical arguments suggest a
merging scenario for Abell 1995, where two main subsystems are seen just
after the collision with an intermediate projection angle.
Conclusions: The high mass of Abell 1995 and the evidence of merging
suggest it is not atypical among clusters with known radio halos.
Interestingly, our findings reinforce the previous evidence for the
peculiar dichotomy between the dark matter and galaxy distributions
observed in this cluster.
Table 1 is available in electronic form at http://www.aanda.org
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