Bibcode
Barrena, R.; Girardi, M.; Boschin, W.; de Grandi, S.; Eckert, D.; Rossetti, M.
Bibliographical reference
Astronomy and Astrophysics, Volume 529, id.A128
Advertised on:
5
2011
Journal
Citations
13
Refereed citations
13
Description
Context. The mechanisms giving rise to diffuse radio emission in galaxy
clusters, and in particular their connection with cluster mergers, are
still debated. Aims: We seek to explore the internal dynamics of
the cluster Abell 545, which has been shown to host a radio halo. Abell
545 is also peculiar for hosting in its center a very bright, red,
diffuse intracluster light due to an old, presumably metal-rich stellar
population, so bright to be named as "star pile". Methods: Our
analysis is mainly based on redshift data for 110 galaxies acquired at
the Telescopio Nazionale Galileo. We identify 95 cluster members and
analyze the cluster internal dynamics by combining galaxy velocities and
positions. We also use both multiband photometric data acquired at the
Isaac Newton Telescope and X-ray data from the XMM-Newton Science
Archive. Results: We estimate the cluster redshift, ⟨ z
⟩ = 0.1580, a large line-of-sight (LOS) velocity dispersion
σV ~ 1200 km s-1, and ICM temperature
kTX ~ 8 keV. Our optical and X-ray analyses detect
substructures. Optical data reveal three main galaxy clumps (one at the
center hosting the peak of X-ray emission; one at NNW, and one at NE);
and possibly a fourth clump at South. There is not a dominant galaxy and
the four brightest galaxies avoid the cluster core - ≳ 0.4
h70-1 Mpcdistant from the cluster center - and are
≳ 1500 km s-1far from the mean cluster velocity. Two of
these brightest galaxies are located in the NNW and NE clumps. The
analysis of the X-ray surface brightness distribution provides us
evidence of a disturbed dynamical phase: the strong NNW-SSE elongation,
a western excess, and a sharp discontinuity in the northern region which
is the likely signature of a shock. Located in the star pile region
there is the brightest galaxy of the cluster core (CBCG) and a very
compact elliptical galaxy, likely a M32-like dwarf. We show that the
star pile, which has a previously determined redshift, has a similar
redshift to that of the CBCG. Both the star pile and the CBCG are at
rest in the cluster rest frame. The elongation of the star pile and its
relative position with respect to the CBCG indicate the same direction
pointed out by the NE clump. Conclusions: The emerging picture of
Abell 545 is that of a massive, M(R < 1.6 h70-1
Mpc) = (1.1-1.8) × 1015 h70-1
M&sun;, very complex cluster with merging occurring along two
directions. Abell 545 gives another proof in the favor of the connection
between cluster merger and extended, diffuse radio emission. The star
pile, likely due to the process of a brightest galaxy forming in the
cluster core, is related to the accretion along the NE direction. Abell
545 represents a textbook cluster where to study the simultaneous
formation of a galaxy system and its brightest galaxy.
Related projects
Galaxy Evolution in Clusters of Galaxies
Galaxies in the universe can be located in different environments, some of them are isolated or in low density regions and they are usually called field galaxies. The others can be located in galaxy associations, going from loose groups to clusters or even superclusters of galaxies. One of the foremost challenges of the modern Astrophysics is to
Jairo
Méndez Abreu