155 research outputs found
Dynamical analysis of the cluster pair: A3407 + A3408
We carried out a dynamical study of the galaxy cluster pair A3407 \& A3408
based on a spectroscopic survey obtained with the 4 meter Blanco telescope at
the CTIO, plus 6dF data, and ROSAT All-Sky-Survey. The sample consists of 122
member galaxies brighter than . Our main goal is to probe the galaxy
dynamics in this field and verify if the sample constitutes a single galaxy
system or corresponds to an ongoing merging process. Statistical tests were
applied to clusters members showing that both the composite system A3407 +
A3408 as well as each individual cluster have Gaussian velocity distribution. A
velocity gradient of was identified around
the principal axis of the projected distribution of galaxies, indicating that
the global field may be rotating. Applying the KMM algorithm to the
distribution of galaxies we found that the solution with two clusters is better
than the single unit solution at the 99\% c.l. This is consistent with the
X-ray distribution around this field, which shows no common X-ray halo
involving A3407 and A3408. We also estimated virial masses and applied a
two-body model to probe the dynamics of the pair. The more likely scenario is
that in which the pair is gravitationally bound and probably experiences a
collapse phase, with the cluster cores crossing in less than 1
Gyr, a pre-merger scenario. The complex X-ray morphology, the gas temperature,
and some signs of galaxy evolution in A3408 suggests a post-merger scenario,
with cores having crossed each other Gyr ago, as an
alternative solution.Comment: 17 pages, 12 figures, submitted to MNRAS, accepted 2016 May 9.
Received 2016 May 9; in original form 2016 April 1
Dissecting the RELICS cluster SPT-CLJ0615-5746 through the intracluster light: confirmation of the multiple merging state of the cluster formation
The intracluster light (ICL) fraction, measured at certain specific
wavelengths, has been shown to provide a good marker for determining the
dynamical stage of galaxy clusters, i.e., merging versus relaxed, for small to
intermediate redshifts. Here, we apply it for the first time to a high-redshift
system, SPT-CLJ0615-5746 at z=0.97, using its RELICS (Reionization Lensing
Cluster Survey) observations in the optical and infrared. We find the ICL
fraction signature of merging, with values ranging from 16 to 37%. A careful
re-analysis of the X-ray data available for this cluster points to the presence
of at least one current merger, and plausibly a second merger. These two
results are in contradiction with previous works based on X-ray data, which
claimed the relaxed state of SPT-CLJ0615-5746, and confirmed the evidences
presented by kinematic analyses. We also found an abnormally high ICL fraction
in the rest-frame near ultraviolet wavelengths, which may be attributed to the
combination of several phenomena such as an ICL injection during recent mergers
of stars with average early-type spectra, the reversed star formation-density
relation found at this high redshift in comparison with lower-redshift
clusters, and projection effects.Comment: 15 pages, 12 figures, submitted to A&
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