54,499 research outputs found
The Atacama Cosmology Telescope: the stellar content of galaxy clusters selected using the Sunyaev-Zel'dovich effect
We present a first measurement of the stellar mass component of galaxy
clusters selected via the Sunyaev-Zel'dovich (SZ) effect, using 3.6 um and 4.5
um photometry from the Spitzer Space Telescope. Our sample consists of 14
clusters detected by the Atacama Cosmology Telescope (ACT), which span the
redshift range 0.27 < z < 1.07 (median z = 0.50), and have dynamical mass
measurements, accurate to about 30 per cent, with median M500 = 6.9 x 10^{14}
MSun. We measure the 3.6 um and 4.5 um galaxy luminosity functions, finding the
characteristic magnitude (m*) and faint-end slope (alpha) to be similar to
those for IR-selected cluster samples. We perform the first measurements of the
scaling of SZ-observables (Y500 and y0) with both brightest cluster galaxy
(BCG) stellar mass and total cluster stellar mass (M500star). We find a
significant correlation between BCG stellar mass and Y500 (E(z)^{-2/3} DA^2
Y500 ~ M*^{1.2 +/- 0.6}), although we are not able to obtain a strong
constraint on the slope of the relation due to the small sample size.
Additionally, we obtain E(z)^{-2/3} DA^2 Y500 ~ M500star^{1.0 +/- 0.6} for the
scaling with total stellar mass. The mass fraction in stars spans the range
0.006-0.034, with the second ranked cluster in terms of dynamical mass (ACT-CL
J0237-4939) having an unusually low total stellar mass and the lowest stellar
mass fraction. For the five clusters with gas mass measurements available in
the literature, we see no evidence for a shortfall of baryons relative to the
cosmic mean value.Comment: Accepted for publication in MNRAS; 12 pages, 10 figure
High star formation activity in the central region of a distant cluster at z=1.46
We present an unbiased deep [OII] emission survey of a cluster XMMXCS
J2215.9-1738 at z=1.46, the most distant cluster to date with a detection of
extended X-ray emission. With wide-field optical and near-infrared cameras
(Suprime-Cam and MOIRCS, respectively) on Subaru telescope, we performed deep
imaging with a narrow-band filter NB912 (lambda_c=9139A, Delta_lambda=134A) as
well as broad-band filters (B, z', J and Ks). From the photometric catalogues,
we have identified 44 [OII] emitters in the cluster central region of 6'x6'
down to a dust-free star formation rate of 2.6 Msun/yr (3 sigma).
Interestingly, it is found that there are many [OII] emitters even in the
central high density region. In fact, the fraction of [OII] emitters to the
cluster members as well as their star formation rates and equivalent widths
stay almost constant with decreasing cluster-centric distance up to the cluster
core. Unlike clusters at lower redshifts (z<1) where star formation activity is
mostly quenched in their central regions, this higher redshift 2215 cluster
shows its high star formation activity even at its centre, suggesting that we
are beginning to enter the formation epoch of some galaxies in the cluster core
eventually. Moreover, we find a deficit of galaxies on the red sequence at
magnitudes fainter than ~M*+0.5 on the colour-magnitude diagram. This break
magnitude is brighter than that of lower redshift clusters, and it is likely
that we are seeing the formation phase of more massive red galaxies in the
cluster core at z~1. These results may indicate inside-out and down-sizing
propagation of star formation activity in the course of cluster evolution.Comment: 12 pages, 9 figures, 1 table, accepted for publication in MNRA
Properties of star-forming galaxies in a cluster and its surrounding structure at z=1.46
We conduct a narrow-band imaging survey of [OII] emitters over a 32'x23' area
in and around the XMMXCS J2215.9-1738 cluster at z=1.46 with
Subaru/Suprime-Cam, and select 380 [OII] emitting galaxies down to 1.4E-17
erg/s/cm2. Among them, 16 [OII] emitters in the cluster central region are
confirmed by NIR spectroscopy with Subaru/MOIRCS. We find that [OII] emitters
are distributed along filamentary large-scale structures around the cluster.
The z'-K vs K colour-magnitude diagram shows that a significantly higher
fraction of [OII] emitters is seen on the red sequence in the cluster core than
in other environments we define in this paper. It is likely that these red
galaxies are nearly passively evolving galaxies which host [OII] emitting AGNs,
rather than dust-reddened star-forming galaxies. We argue therefore that AGN
feedback may be one of the critical processes to quench star formation in
massive galaxies in high density regions. We also find that the cluster has
experienced high star formation activities at rates comparable to that in the
field at z=1.46. In addition, a mass-metallicity relation exists in the cluster
at z=1.46, which is similar to that of star-forming galaxies in the field at
z~2. These results all suggest that at z~1.5 star formation activity in the
cluster core becomes as high as those in low density environments and there is
apparently not yet a strong environmental dependence, except for the red
emitters.Comment: 19 pages, 17 figures, 4 tables, accepted for publication in MNRA
The XMM Cluster Survey: Active Galactic Nuclei and Starburst Galaxies in XMMXCS J2215.9-1738 at z=1.46
We use Chandra X-ray and Spitzer infrared observations to explore the AGN and
starburst populations of XMMXCS J2215.9-1738 at z=1.46, one of the most distant
spectroscopically confirmed galaxy clusters known. The high resolution X-ray
imaging reveals that the cluster emission is contaminated by point sources that
were not resolved in XMM observations of the system, and have the effect of
hardening the spectrum, leading to the previously reported temperature for this
system being overestimated. From a joint spectroscopic analysis of the Chandra
and XMM data, the cluster is found to have temperature T=4.1_-0.9^+0.6 keV and
luminosity L_X=(2.92_-0.35^+0.24)x10^44 erg/s extrapolated to a radius of 2
Mpc. As a result of this revised analysis, the cluster is found to lie on the
sigma_v-T relation, but the cluster remains less luminous than would be
expected from self-similar evolution of the local L_X-T relation. Two of the
newly discovered X-ray AGN are cluster members, while a third object, which is
also a prominent 24 micron source, is found to have properties consistent with
it being a high redshift, highly obscured object in the background. We find a
total of eight >5 sigma 24 micron sources associated with cluster members (four
spectroscopically confirmed, and four selected using photometric redshifts),
and one additional 24 micron source with two possible optical/near-IR
counterparts that may be associated with the cluster. Examining the IRAC colors
of these sources, we find one object is likely to be an AGN. Assuming that the
other 24 micron sources are powered by star formation, their infrared
luminosities imply star formation rates ~100 M_sun/yr. We find that three of
these sources are located at projected distances of <250 kpc from the cluster
center, suggesting that a large amount of star formation may be taking place in
the cluster core, in contrast to clusters at low redshift.Comment: Accepted for publication in ApJ, 16 pages, 10 figure
Graph products of spheres, associative graded algebras and Hilbert series
Given a finite, simple, vertex-weighted graph, we construct a graded
associative (non-commutative) algebra, whose generators correspond to vertices
and whose ideal of relations has generators that are graded commutators
corresponding to edges. We show that the Hilbert series of this algebra is the
inverse of the clique polynomial of the graph. Using this result it easy to
recognize if the ideal is inert, from which strong results on the algebra
follow. Non-commutative Grobner bases play an important role in our proof.
There is an interesting application to toric topology. This algebra arises
naturally from a partial product of spheres, which is a special case of a
generalized moment-angle complex. We apply our result to the loop-space
homology of this space.Comment: 19 pages, v3: elaborated on connections to related work, added more
citations, to appear in Mathematische Zeitschrif
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