The current consensus is that galaxies begin as small density fluctuations in the early Universe and grow by in situ star formation and hierarchical merging. Stars begin to form relatively quickly in ...sub-galactic-sized building blocks called haloes which are subsequently assembled into galaxies. However, exactly when this assembly takes place is a matter of some debate. Here we report that the stellar masses of brightest cluster galaxies, which are the most luminous objects emitting stellar light, some 9 billion years ago are not significantly different from their stellar masses today. Brightest cluster galaxies are almost fully assembled 4-5 billion years after the Big Bang, having grown to more than 90 per cent of their final stellar mass by this time. Our data conflict with the most recent galaxy formation models based on the largest simulations of dark-matter halo development. These models predict protracted formation of brightest cluster galaxies over a Hubble time, with only 22 per cent of the stellar mass assembled at the epoch probed by our sample. Our findings suggest a new picture in which brightest cluster galaxies experience an early period of rapid growth rather than prolonged hierarchical assembly.
Using a sample of 123 X-ray clusters and groups drawn from the XMM Cluster Survey first data release, we investigate the interplay between the brightest cluster galaxy (BCG), its black hole and the ...intracluster/group medium (ICM). It appears that for groups and clusters with a BCG likely to host significant active galactic nuclei (AGN) feedback, gas cooling dominates in those with T
X > 2 keV while AGN feedback dominates below. This may be understood through the subunity exponent found in the scaling relation we derive between the BCG mass and cluster mass over the halo mass range 1013 < M
500 < 1015 M⊙ and the lack of correlation between radio luminosity and cluster mass, such that BCG AGN in groups can have relatively more energetic influence on the ICM. The L
X-T
X relation for systems with the most massive BCGs, or those with BCGs co-located with the peak of the ICM emission, is steeper than that for those with the least massive and most offset, which instead follows self-similarity. This is evidence that a combination of central gas cooling and powerful, well fuelled AGN causes the departure of the ICM from pure gravitational heating, with the steepened relation crossing self-similarity at T
X= 2 keV. Importantly, regardless of their black hole mass, BCGs are more likely to host radio-loud AGN if they are in a massive cluster (T
X≳ 2 keV) and again co-located with an effective fuel supply of dense, cooling gas. This demonstrates that the most massive black holes appear to know more about their host cluster than they do about their host galaxy. The results lead us to propose a physically motivated, empirical definition of 'cluster' and 'group', delineated at 2 keV.
The XMM Cluster Survey: X-ray analysis methodology Lloyd-Davies, E. J.; Romer, A. Kathy; Mehrtens, Nicola ...
Monthly Notices of the Royal Astronomical Society,
November 2011, Letnik:
418, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters using all publicly available data in the XMM-Newton Science Archive. Its main aims are to measure cosmological parameters ...and trace the evolution of X-ray scaling relations. In this paper we describe the data processing methodology applied to the 5776 XMM observations used to construct the current XCS source catalogue. A total of 3675 > 4σ cluster candidates with >50 background-subtracted X-ray counts are extracted from a total non-overlapping area suitable for cluster searching of 410 deg2. Of these, 993 candidates are detected with >300 background-subtracted X-ray photon counts, and we demonstrate that robust temperature measurements can be obtained down to this count limit. We describe in detail the automated pipelines used to perform the spectral and surface brightness fitting for these candidates, as well as to estimate redshifts from the X-ray data alone. A total of 587 (122) X-ray temperatures to a typical accuracy of <40 (<10) per cent have been measured to date. We also present the methodology adopted for determining the selection function of the survey, and show that the extended source detection algorithm is robust to a range of cluster morphologies by inserting mock clusters derived from hydrodynamical simulations into real XMMimages. These tests show that the simple isothermal β-profiles is sufficient to capture the essential details of the cluster population detected in the archival XMM observations. The redshift follow-up of the XCS cluster sample is presented in a companion paper, together with a first data release of 503 optically confirmed clusters.
Using observations from the FourStar Galaxy Evolution Survey (ZFOURGE), we obtain the deepest measurements to date of the galaxy stellar mass function (SMF) at 0.2 < z < 3. We combine this with ...Hubble Space Telescope imaging from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey, allowing for the efficient selection of both blue and red galaxies down to stellar masses of ~10 super(9.5) M sub(middot in circle) at z ~ 2.5. The total surveyed area is 316 arcmin super(2) distributed over three independent fields. We supplement these data with the wider and shallower NEWFIRM Medium-Band Survey to provide stronger constraints at high masses. Our data allow us, for the first time, to observe a rapid buildup at the low-mass end of the quiescent SMF. Since z = 2.5, the total stellar mass density of quiescent galaxies (down to 10 super(9) M sub(middot in circle)) has increased by a factor of ~12, whereas the mass density of star-forming galaxies only increases by a factor of ~2.2.
ABSTRACT
The
FourStar
galaxy evolution survey (ZFOURGE) is a 45 night legacy program with the
FourStar
near-infrared camera on Magellan and one of the most sensitive surveys to date. ZFOURGE covers a ...total of 400 arcmin
2
in cosmic fields CDFS, COSMOS and UDS, overlapping CANDELS. We present photometric catalogs comprising >70,000 galaxies, selected from ultradeep
K
s
-band detection images (25.5–26.5 AB mag, 5
σ
, total), and >80% complete to
K
s
< 25.3–25.9 AB. We use 5 near-IR medium-bandwidth filters (
J
1
,
J
2
,
J
3
,
H
s
,
H
l
) as well as broad-band
K
s
at 1.05–2.16
μ
m to 25–26 AB at a seeing of ∼0.″5. Each field has ancillary imaging in 26–40 filters at 0.3–8
μ
m. We derive photometric redshifts and stellar population properties. Comparing with spectroscopic redshifts indicates a photometric redshift uncertainty
σ
z
= 0.010, 0.009, and 0.011 in CDFS, COSMOS, and UDS. As spectroscopic samples are often biased toward bright and blue sources, we also inspect the photometric redshift differences between close pairs of galaxies, finding
σ
z
,pairs
= 0.01–0.02 at 1 <
z
< 2.5. We quantify how
σ
z
,pairs
depends on redshift, magnitude, spectral energy distribution type, and the inclusion of
FourStar
medium bands.
σ
z
,pairs
is smallest for bright, blue star-forming samples, while red star-forming galaxies have the worst
σ
z
,pairs
. Including
FourStar
medium bands reduces
σ
z
,pairs
by 50% at 1.5 <
z
< 2.5. We calculate star formation rates (SFRs) based on ultraviolet and ultradeep far-IR
Spitzer
/MIPS and
Herschel
/PACS data. We derive rest-frame
U
−
V
and
V
−
J
colors, and illustrate how these correlate with specific SFR and dust emission to
z
= 3.5. We confirm the existence of quiescent galaxies at
z
∼ 3, demonstrating their SFRs are suppressed by > ×15.
We report the likely identification of a substantial population of massive M ~ 10sup 11 M galaxies at z ~ 4 with suppressed star formation rates (SFRs), selected on rest-frame optical to near-IR ...colors from the FourStar Galaxy Evolution Survey (ZFOURGE). The observed spectral energy distributions show pronounced breaks, sampled by a set of near-IR medium-bandwidth filters, resulting in tightly constrained photometric redshifts. Fitting stellar population models suggests large Balmer/4000A breaks, relatively old stellar populations, large stellar masses, and low SFRs, with a median specific SFR of 2.9 + or -1.8 10sup -11 yrsup -1. Ultradeep Herschel/PACS 100 mu m, 160 mu m and Spitzer/MIPS 24 mu m data reveal no dust-obscured SFR activity for 15/19(79%) galaxies. The study suggests that most of the star formation in the progenitors of quiescent z ~ 4 galaxies was obscured by dust.
The chameleon gravity model postulates the existence of a scalar field that couples with matter to mediate a fifth force. If it exists, this fifth force would influence the hot X-ray emitting gas ...filling the potential wells of galaxy clusters. However, it would not influence the clusters weak lensing signal. Therefore, by comparing X-ray and weak lensing profiles, one can place upper limits on the strength of a fifth force. This technique has been attempted before using a single, nearby cluster (Coma, z = 0.02). Here we apply the technique to the stacked profiles of 58 clusters at higher redshifts (0.1 < z < 1.2), including 12 new to the literature, using X-ray data from the XMM Cluster Survey and weak lensing data from the Canada–France–Hawaii–Telescope Lensing Survey. Using a multiparameter Markov chain Monte Carlo analysis, we constrain the two chameleon gravity parameters (β and ϕ∞). Our fits are consistent with general relativity, not requiring a fifth force. In the special case of f(R) gravity (where
$\beta = \sqrt{1/6}$
), we set an upper limit on the background field amplitude today of |f
R0| < 6 × 10−5 (95 per cent CL). This is one of the strongest constraints to date on |f
R0| on cosmological scales. We hope to improve this constraint in future by extending the study to hundreds of clusters using data from the Dark Energy Survey.
We study the rest-frame ultraviolet (UV) sizes of massive (~0.8 x 10 super(11)M sub(middot in circle)) galaxies at 3.4 < or =, slant z < 4.2, selected from the FourStar Galaxy Evolution Survey, by ...fitting single Sersic profiles to Hubble Space Telescope/WFC3/ F160W images from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. Massive quiescent galaxies are very compact, with a median circularized half-light radius r sub(e) = 0.63 + or - 0.18 kpc. Removing 5/16 (31%) sources with signs of active galactic nucleus activity does not change the result. Star-forming galaxies have r sub(e) = 2.0 + or - 0.60 kpc, 3.2 + or - 1.3 x larger than quiescent galaxies. Quiescent galaxies at z ~ 4 are on average 6.0 + or - 1.7x smaller than at z ~ 0 and 1.9 + or - 0.7x smaller than at z ~ 2. Star-forming galaxies of the same stellar mass are 2.4 + or - 0.7 x smaller than at z ~ 0. Overall, the size evolution at 0 < z < 4 is well described by a power law, with r sub(e) = 5.08 + or - 0.28(1 + z) super(1.44+ or -0.08) kpc for quiescent galaxies and r sub(e) = 6.02 + or - 0.28(1 + z) super(-0.72+ or -0.05) kpc for star-forming galaxies. Compact star-forming galaxies are rare in our sample; we find only 1/14 (7%) with r sub(e)/(M/10 super(11)M sub(middot in circle)) super(0.75) < 1.5, whereas 13/16 (81%) of the quiescent galaxies are compact. The number density of compact quiescent galaxies at z ~ 4 is 1.8 + or - 0.8 x 10 super(-5) Mpc super(-3) and increases rapidly, by >5x, between 2 < z < 4. The paucity of compact star-forming galaxies at z ~ 4 and their large rest-frame UV median sizes suggest that the formation phase of compact cores is very short and/or highly dust obscured.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) Our understanding of the redshift z > 3 galaxy population relies largely on samples selected using the popular "dropout" technique, ...typically consisting of UV-bright galaxies with blue colors and prominent Lyman breaks. As it is currently unknown if these galaxies are representative of the massive galaxy population, we here use the FOURSTAR Galaxy Evolution (ZFOURGE) survey to create a stellar mass-limited sample at z = 3-4. Uniquely, ZFOURGE uses deep near-infrared medium-bandwidth filters to derive accurate photometric redshifts and stellar population properties. The mass-complete sample consists of 57 galaxies with log M > 10.6, reaching below M* at z = 3-4. On average, the massive z = galaxies are extremely faint in the observed optical with median ... = 27.48 + or - 0.41 (rest-frame M sub(1700) = -18.05 + or - 0.37). They lie far below the UV luminosity-stellar mass relation for Lyman break galaxies and are about ~100x fainter at the same mass. The massive galaxies are red (R - K sub(sAB) = 3.9 + or - 0.2; rest-frame UV-slope beta = -0.2 + or - 0.3) likely from dust or old stellar ages. We classify the galaxy spectral energy distributions by their rest-frame U-V and V-J colors and find a diverse population: ... of the massive galaxies are quiescent, ... are dusty star-forming galaxies, and only ... resemble luminous blue star-forming Lyman break galaxies. This study clearly demonstrates an inherent diversity among massive galaxies at higher redshift than previously known. Furthermore, we uncover a reservoir of dusty star-forming galaxies with 4x lower specific star-formation rates compared to submillimeter-selected starbursts at z > 3. With 5x higher numbers, the dusty galaxies may represent a more typical mode of star formation compared to submillimeter-bright starbursts.
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