7,368 research outputs found
The Ks-band Luminosity and Stellar Mass Functions of Galaxies in z~1 Clusters
We present the near-infrared (Ks-band) luminosity function of galaxies in two
z~1 cluster candidates, 3C336 and Q1335+28. A third cluster, 3C289, was
observed but found to be contaminated by a foreground system. Our wide field
imaging data reach to Ks=20.5 (5sigma), corresponding to ~M*+2.7 with respect
to the passive evolution. The near-infrared luminosity traces the stellar mass
of a galaxy due to its small sensitivity to the recent star formation history.
Thus the luminosity function can be transformed to the stellar mass function of
galaxies using the colours with only a small correction (factor<2) for
the effects of on-going star formation. The derived stellar mass function spans
a wide range in mass from ~3 x 10^{11}Msun down to ~6 x 10^{9}Msun (set by the
magnitude limit). The form of the mass function is very similar to lower
redshift counterparts such as that from 2MASS/LCRS clusters (Balogh et al.
2001) and the z=0.31 clusters (Barger et al. 1998). This indicates little
evolution of galaxy masses from z=1 to the present-day. Combined with colour
data that suggest star formation is completed early (z>>1) in the cluster core,
it seems that the galaxy formation processes (both star formation and mass
assembly) are strongly accerelated in dense environments and has been largely
completed by z=1. We investigate whether the epoch of mass assembly of massive
cluster galaxies is earlier than that predicted by the hierarchical galaxy
formation models. These models predict the increase of characteristic mass by
more than factor ~3 between z=1 and the present day. This seems incompatible
with our data.Comment: 12 pages, including 12 figures, uses mn.sty and epsf.sty. Accepted
for publication in MNRAS Main Journa
Homogeneity of Stellar Populations in Early-Type Galaxies with Different X-ray Properties
We have found the stellar populations of early-type galaxies are homogeneous
with no significant difference in color or Mg2 index, despite the dichotomy
between X-ray extended early-type galaxies and X-ray compact ones. Since the
X-ray properties reflect the potential gravitational structure and hence the
process of galaxy formation, the homogeneity of the stellar populations implies
that the formation of stars in early-type galaxies predat es the epoch when the
dichotomy of the potential structure was established.Comment: 6 pages, 5 figures, accepted for publication in Ap
Reconstructing the History of Star Formation in Rich Cluster Cores
We address the current crucial issues on the formation and evolution of
cluster galaxies: ie., connection between the Butcher-Oemler effect, assembly
of cluster galaxies, truncation of star formation, and the origin of S0
galaxies.
We construct the field corrected colour-magnitude (CM) diagrams for 7 CNOC
clusters (0.23<z<0.43) and Coma, and illustrate the evolution of the complete
cluster population down to the present-day based on the model in which star
formation is truncated when the galaxies infall from the surrounding field.
We show that the blue galaxies are incorporated into the present-day tight CM
relation as they fade and become redder after the truncation, which is possibly
responsible for producing faint S0's (>M*+1). Truncation of star formation is,
however, found to be relatively milder (with a time scale of 1 Gyr) than
suggested by the viorent processes such as ram-pressure stripping and/or
mergers/harassment.
The BO effect is after all found to be a combination of three effects,
namely, increasing field star formation activity, increasing galaxy infall
rate, and the truncatin of star formation after the accretion. Our approach
naturally leads to the history of galaxy assembly and `global' star foramtion
for `cluster' galaxies.Comment: 20 pages, 12 figures, Accepted for Publication in MNRAS (first
submitted on 9th Feb 2000
Perturbative analysis of wave interactions in nonlinear systems
This work proposes a new way for handling obstacles to asymptotic
integrability in perturbed nonlinear PDEs within the method of Normal Forms -
NF - for the case of multi-wave solutions. Instead of including the whole
obstacle in the NF, only its resonant part is included, and the remainder is
assigned to the homological equation. This leaves the NF intergable and its
solutons retain the character of the solutions of the unperturbed equation. We
exploit the freedom in the expansion to construct canonical obstacles which are
confined to te interaction region of the waves. Fo soliton solutions, e.g., in
the KdV equation, the interaction region is a finite domain around the origin;
the canonical obstacles then do not generate secular terms in the homological
equation. When the interaction region is infifnite, or semi-infinite, e.g., in
wave-front solutions of the Burgers equation, the obstacles may contain
resonant terms. The obstacles generate waves of a new type, which cannot be
written as functionals of the solutions of the NF. When an obstacle contributes
a resonant term to the NF, this leads to a non-standard update of th wave
velocity.Comment: 13 pages, including 6 figure
Crossing the Phantom Divide
We consider fluid perturbations close to the "phantom divide" characterised
by p = -rho and discuss the conditions under which divergencies in the
perturbations can be avoided. We find that the behaviour of the perturbations
depends crucially on the prescription for the pressure perturbation delta-p.
The pressure perturbation is usually defined using the dark energy rest-frame,
but we show that this frame becomes unphysical at the divide. If the pressure
perturbation is kept finite in any other frame, then the phantom divide can be
crossed. Our findings are important for generalised fluid dark energy used in
data analysis (since current cosmological data sets indicate that the dark
energy is characterised by p ~ -rho so that p < -rho cannot be excluded) as
well as for any models crossing the phantom divide, like some modified gravity,
coupled dark energy and braneworld models. We also illustrate the results by an
explicit calculation for the "Quintom" case with two scalar fields.Comment: 14 pages, 10 figures, v2: updated to agree with published version:
more readable figures, slightly expanded discussion on modified gravity
models and the interpolation across w=-1, results and conclusions unchange
Thermodynamics of four-dimensional black objects in the warped compactification
We reinvestigate the thermodynamics of black objects (holes and strings) in
four-dimensional braneworld models that are originally constructed by Emparan,
Horowitz and Myers based on the anti-de Sitter (AdS) C-metric. After proving
the uniqueness of slicing the AdS C-metric, we derive thermodynamic quantities
of the black objects by means of the Euclidean formulation and find that we
have no necessity of requiring any regularization to calculate their classical
action. We show that there exist the Bekenstein-Hawking law and the
thermodynamic first law. The thermodynamic mass of the localized black hole on
a flat brane is negative, and it differs from the one previously derived. We
discuss the thermodynamic stabilities and show that the BTZ black string is
more stable than the localized black holes in a canonical ensemble, except for
an extreme case. We also find a braneworld analogue of the Hawking-Page
transition between the BTZ black string and thermal AdS branes. The localized
black holes on a de Sitter brane is discussed by considering Nariai instanton,
comparing the study of "black cigar" in the five-dimensional braneworld model.Comment: 15 pages, 4 figures, RevTex4, typos fixed, minor correction
Multiple-Time Higher-Order Perturbation Analysis of the Regularized Long-Wavelength Equation
By considering the long-wave limit of the regularized long wave (RLW)
equation, we study its multiple-time higher-order evolution equations. As a
first result, the equations of the Korteweg-de Vries hierarchy are shown to
play a crucial role in providing a secularity-free perturbation theory in the
specific case of a solitary-wave solution. Then, as a consequence, we show that
the related perturbative series can be summed and gives exactly the
solitary-wave solution of the RLW equation. Finally, some comments and
considerations are made on the N-soliton solution, as well as on the
limitations of applicability of the multiple scale method in obtaining uniform
perturbative series.Comment: 15 pages, RevTex, no figures (to appear in Phys. Rev. E
Coarse graining scale and effectiveness of hydrodynamic modeling
Some basic questions about the hydrodynamical approach to relativistic heavy
ion collisions are discussed aiming to clarify how far we can go with such an
approach to extract useful information on the properties and dynamics of the
QCD matter created. We emphasize the importance of the coarse-graining scale
required for the hydrodynamic modeling which determines the space-time
resolution and the associated limitations of collective flow observables. We
show that certain kinds of observables can indicate the degree of inhomogeneity
of the initial condition under less stringent condition than the local thermal
equilibrium subjected to the coarse-graining scale compatible to the scenario.Comment: 12 pages, 4 figures, Quark Matter 201
Linearizability of the Perturbed Burgers Equation
We show in this letter that the perturbed Burgers equation is equivalent, through a near-identity transformation and
up to order \epsilon, to a linearizable equation if the condition is satisfied. In the case this
condition is not fulfilled, a normal form for the equation under consideration
is given. Then, to illustrate our results, we make a linearizability analysis
of the equations governing the dynamics of a one-dimensional gas.Comment: 10 pages, RevTeX, no figure
New X-ray Clusters in the EMSS II: Optical Properties
We present optical images for 9 new clusters of galaxies we have found in a
reanalysis of the Einstein IPC images comprising the Extended Medium
Sensitivity Survey (EMSS). Based on the presence of a red sequence of galaxies
in a color-magnitude (CM) diagram, a redshift is estimated for each cluster.
Galaxy overdensities (cluster richnesses) are measured in each field using the
B_gc statistic which allows their plausible identification with the X-ray
emission. The nature of our X-ray detection algorithm suggests that most of
these clusters have low X-ray surface brightness (LSB) compared to the
previously known EMSS clusters. We compare the optical and X-ray observations
of these clusters with the well-studied Canadian Network for Observational
Cosmology (CNOC) subsample of the EMSS, and conclude that the new clusters
exhibit a similar range of optical richnesses, X-ray luminosities, and,
somewhat surprisingly, galaxy populations as the predominantly rich, relaxed
EMSS/CNOC clusters.Comment: Accepted to ApJ, 17 pages, 14 figures, uses emulateapj5.st
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