candidate source responsible (Figure 3). The
source emerges just at the detection limit,
so confirmation requires more contrast at
closer separations from the bright star —
capabilities that the Gemini Planet Imager
can provide.
Full results will appear in Astronomy and Astrophysics; a preprint is available now (arXiv:1310.7092).
Figure 4.
Contours show
the galaxy density
distribution in the
redshift 0.48 cluster
[VMF98] 097, with red
and blue galaxy cluster
members plotted in
color. A cross marks
the location of the
X-ray emission peak.
This cluster is not
relaxed, and shows
several significant
concentrations as well
as a mix of red and
blue galaxies in the
central region.
Observations of Galaxies in
Intermediate-mass Clusters
Do galaxies evolve in intermediate-mass
clusters the same way they do in high-mass
clusters? The environment is a function of
cluster mass, and therefore influences evolutionary processes that reflect “nurture”
as opposed to intrinsic “nature” of galaxies. José Luis Nilo Castellón (IATE-CONICET,
Argentina, and Universidad de La Serena,
Chile) and colleagues present first results
from a sample of seven galaxy clusters
and find that the general trends of these
intermediate-mass clusters match those ob-
served in high-mass clusters, in agreement
with previous related work.
The sample was selected based on low Xray luminosity, and multi-band imaging observations using both Gemini Multi-Object
Spectrograph instruments allows classification of the galaxies. In color-magnitude
plots, the low-redshift examples tend to
show a red cluster sequence of early-type
galaxies that is well-defined over several
orders of magnitude with little scatter and
which contains most of the cluster members. These clusters tend to be centrally concentrated, and nearly 70 percent of the red
galaxies are located in the cluster cores. Similar to the case for richer clusters, the fraction
of blue galaxies increases with redshift. In
the higher-redshift group here, red and blue
peaks are evident in the overall distribution
of galaxy colors. In addition, the higher-redshift examples of the cluster density maps
show multiple concentrations and a mix of
red and blue galaxies in the cores (Figure 4).
This work is in press in Monthly Notices of
the Royal Astronomical Society; a preprint is
available at arXiv:1311.0788.
Nancy A. Levenson is Deputy Director and Head
of Science at Gemini Observatory and can be
reached at: [email protected]
14
GeminiFocus
January2014