Bibcode
Barrena, R.; Boschin, W.; Girardi, M.; Spolaor, M.
Bibliographical reference
Astronomy and Astrophysics, Volume 469, Issue 3, July III 2007, pp.861-872
Advertised on:
7
2007
Journal
Citations
38
Refereed citations
35
Description
Aims:We present the results of a new spectroscopic and photometric
survey of the hot, binary X-ray cluster A115 at z = 0.193, containing a
radio relic. Methods: Our analysis is based on new spectroscopic
data obtained at the Telescopio Nazionale Galileo for 115 galaxies and
on new photometric data obtained at the Isaac Newton Telescope in a
large field. We combine galaxy velocity and position information to
select 85 galaxies recognized as cluster members, determine global
dynamical properties and detect substructures. Results: We find
that A115 appears as a well isolated peak in the redshift space, with a
global line-of-sight (LOS) velocity dispersion
σ_v=1362-108+126 km s-1. Our
analysis confirms the presence of two structures of cluster-type well
recognizable in the plane of the sky and shows that they differ of 2000
km s-1in the LOS velocity. The northern, high velocity
subcluster (A115N) is likely centred on the second brightest cluster
galaxy (BCM-A, coincident with radio source 3C28) and the northern X-ray
peak. The southern, low velocity subcluster (A115S) is likely centred on
the first brightest cluster galaxy (BCM-B) and the southern X-ray peak.
We estimate that A115S is slightly dynamically more important than A115N
having σv = 900-1100 km s-1 vs.
σv = 750-850 km s-1. Moreover, we find
evidence for two small groups at low velocities. We estimate a global
cluster virial mass of 2.2-3.5 × 1015
h70-1 M&sun;. Conclusions: Our
results agree with a pre-merging scenario where A115N and A115S are
colliding with a LOS impact velocity Δ {{v}_rf} ˜ 1600 km
s-1. The most likely solution to the two-body problem
suggests that the merging axis lies at 20 degrees from the plane of the
sky and that the cores will cross after 0.1 Gyr. The radio relic with
its largest dimension perpendicular to the merging axis is likely
connected to this merger.
Figures 1, 2 and Table 1 are only available in electronic form at
http://www.aanda.org