77 research outputs found
A new catalog of photometric redshifts in the Hubble Deep Field
Using the newly available infrared images of the Hubble Deep Field in the J,
H, and K bands and an optimal photometric method, we have refined a technique
to estimate the redshifts of 1067 galaxies. A detailed comparison of our
results with the spectroscopic redshifts in those cases where the latter are
available shows that this technique gives very good results for bright enough
objects (AB(8140) < 26.0). From a study of the distribution of residuals
(Dz(rms)/(1+z) ~ 0.1 at all redshifts) we conclude that the observed errors are
mainly due to cosmic variance. This very important result allows for the
assessment of errors in quantities to be directly or indirectly measured from
the catalog. We present some of the statistical properties of the ensemble of
galaxies in the catalog, and finish by presenting a list of bright
high-redshift (z ~ 5) candidates extracted from our catalog, together with
recent spectroscopic redshift determinations confirming that two of them are at
z=5.34 and z=5.60.Comment: 28 pages, 12PS+4JPEG figures, aaspp style. Accepted for publication
in The Astrophysical Journal. The catalog, together with a clickable map of
the HDF, Tables 4 and 5 (HTML, LaTeX or ASCII format), and the figures, are
available at http://bat.phys.unsw.edu.au/~fsoto/hdfcat.htm
Clusters and Superclusters in the Las Campanas Redshift Survey
Two-dimensional high-resolution density field of galaxies of the Las Campanas
Redshift Survey (LCRS) with a smoothing length 0.8 Mpc/h is used to extract
clusters and groups of galaxies, and a low-resolution field with a smoothing
length 10 Mpc/h to find superclusters of galaxies. Properties of these density
field (DF) clusters and superclusters are studied and compared with the
properties of Abell clusters and superclusters, and LCRS loose groups. We
calculate the DF-cluster luminosity function, and show that most luminous
clusters in high-density environments are about ten times brighter than most
luminous clusters in low-density environments. We present a catalogue of
DF-superclusters and show that superclusters that contain Abell clusters are
richer and more luminous than superclusters without Abell clusters. A pdf file
of the paper with high-resolution figures is available in Tartu Observatory
web-site (http://www.aai.ee/~maret/cosmoweb.html)Comment: 19 pages LaTeX text, 15 PostScript Figures, submitted to Astronomy
and Astrophysic
Vacuum condensates and `ether-drift' experiments
The idea of a `condensed' vacuum state is generally accepted in modern
elementary particle physics. We argue that this should motivate a new
generation of precise `ether-drift' experiments with present-day technology.Comment: Latex file, 12 pages, no figure
Implications for dwarf spheroidal mass content from interloper removal
Using the caustic method, we identify the member stars of five dwarf
spheroidal (dSph) galaxies of the Milky Way, the smallest dark matter (DM)
dominated systems in the Universe. After our interloper rejection, we compute
line-of-sight velocity dispersion profiles that are substantially smoother than
previous results. Moreover, two dSphs have line-of-sight velocity dispersions
20% smaller than previous calculations suggested. Our Jeans modelling confirms
that the DM content interior to 300pc is roughly constant with satellite
luminosity. Finally, if we assume that MOND provides the true law of gravity,
our identification of interlopers implies that four dSphs have mass-to-light
ratios in agreement with stellar population synthesis models, whereas Carina
still has a mass-to-light ratio a factor of two too large and remains a problem
for MOND.Comment: A&A accepted, 13 pages, 14 figures, 4 table
Abell 1451 and 1RXS J131423.6-251521: a multi-wavelength study of two dynamically perturbed clusters of galaxies
We present results from optical, X-ray and radio observations of two X-ray
bright (L_X ~ 10^{45} erg/s) galaxy clusters. A1451 is at redshift z=0.1989 and
has line-of-sight velocity dispersion sigma_v = 1330 km/s as measured from 57
cluster galaxies. It has regular X-ray emission without signs of substructure,
a Gaussian velocity distribution, lack of a cooling flow region and significant
deviations from the observed scaling laws between luminosity, temperature and
velocity dispersion, indicating a possible merging shock. There is only one
spectroscopically confirmed cluster radio galaxy, which is close to the X-ray
peak. 1RXS J131423.6-251521 has z=0.2474 and sigma_v = 1100 km/s from 37
galaxies. There are two distinct galaxy groups with a projected separation of
\~700 kpc. The velocity histogram is bi-modal with a redshift-space separation
of ~1700 km/s, and the X-ray emission is double peaked. Although there are no
spectroscopically confirmed cluster radio galaxies, we have identified a
plausible relic source candidate.Comment: 16 pages, 12 figures, some in colour; A&A accepte
The consequences of nuclear electron capture in core collapse supernovae
The most important weak nuclear interaction to the dynamics of stellar core
collapse is electron capture, primarily on nuclei with masses larger than 60.
In prior simulations of core collapse, electron capture on these nuclei has
been treated in a highly parameterized fashion, if not ignored. With realistic
treatment of electron capture on heavy nuclei come significant changes in the
hydrodynamics of core collapse and bounce. We discuss these as well as the
ramifications for the post-bounce evolution in core collapse supernovae.Comment: Accepted by PRL, 5 pages, 2 figure
The Cluster of Galaxies Abell 970
We present a dynamical analysis of the galaxy cluster Abell 970 based on a
new set of radial velocities measured at ESO, Pic du Midi and Haute-Provence
observatories. Our analysis indicates that this cluster has a substructure and
is out of dynamical equilibrium. This conclusion is also supported by
differences in the positions of the peaks of the surface density distribution
and X-ray emission, as well as by the evidence of a large scale velocity
gradient in the cluster. We also found a discrepancy between the masses
inferred with the virial theorem and with the X-ray emission, what is expected
if the galaxies and the gas inside the cluster are not in hydrostatic
equilibrium. Abell 970 has a modest cooling flow, as is expected if it is out
of equilibrium as suggested by Allen (1998). We propose that cooling flows may
have an intermittent behavior, with phases of massive cooling flows being
followed by phases without significant cooling flows after the acretion of a
galaxy group massive enough to disrupt the dynamical equilibrium in the center
of the clusters. A massive cooling flow will be established again, after a new
equilibrium is achieved.Comment: 24 pages, 9 figures, submitted to A&
Long range neutrino forces in the cosmic relic neutrino background
Neutrinos mediate long range forces among macroscopic bodies in vacuum. When
the bodies are placed in the neutrino cosmic background, these forces are
modified. Indeed, at distances long compared to the scale , the relic
neutrinos completely screen off the 2-neutrino exchange force, whereas for
small distances the interaction remains unaffected.Comment: 8 pages, 2 figure
TeV-scale bileptons, see-saw type II and lepton flavor violation in core-collapse supernova
Electrons and electron neutrinos in the inner core of the core-collapse
supernova are highly degenerate and therefore numerous during a few seconds of
explosion. In contrast, leptons of other flavors are non-degenerate and
therefore relatively scarce. This is due to lepton flavor conservation. If this
conservation law is broken by some non-standard interactions, electron
neutrinos are converted to muon and tau-neutrinos, and electrons - to muons.
This affects the supernova dynamics and the supernova neutrino signal. We
consider lepton flavor violating interactions mediated by scalar bileptons,
i.e. heavy scalars with lepton number 2. It is shown that in case of TeV-mass
bileptons the electron fermi gas is equilibrated with non-electron species
inside the inner supernova core at a time-scale of order of (1-100) ms. In
particular, a scalar triplet which generates neutrino masses through the
see-saw type II mechanism is considered. It is found that supernova core is
sensitive to yet unprobed values of masses and couplings of the triplet.Comment: accepted to Eur.Phys.J.
A Study of Catalogued Nearby Galaxy Clusters in the SDSS-DR4: I. Cluster Global Properties
We have selected a sample of 88 nearby (z<0.1) galaxy clusters from the
SDSS-DR4 with redshift information for the cluster members. We have derived
global properties for each cluster, such as their mean recessional velocity,
velocity dispersion, and virial radii. Cluster galaxies have been grouped in
two families according to their colours. The total sample consists of
10865 galaxies. As expected, the highest fraction of galaxies (62%) turned to
be early-type (red) ones, being located at smaller distances from the cluster
centre and showing lower velocity dispersions than late-type (blue) ones. The
brightest cluster galaxies are located in the innermost regions and show the
smallest velocity dispersions. Early-type galaxies also show constant velocity
dispersion profiles inside the virial radius and a mild decline in the
outermost regions. In contrast, late-type galaxies show always decreasing
velocity dispersions profiles. No correlation has been found between the
fraction of blue galaxies and cluster global properties, such as cluster
velocity dispersion and galaxy concentration. In contrast, we found correlation
between the X-ray luminosity and the fraction of blue galaxies. These results
indicate that early- and late-type galaxies may have had different evolution.
Thus, blue galaxies are located in more anisotropic and radial orbits than
early-type ones. Their star formation seems to be independent of the cluster
global properties in low mass clusters, but not for the most massive ones.
These observational results suggest that the global environment could be
important for driving the evolution of galaxies in the most massive cluster
( km s). However, the local environment could play a key
role in galaxy evolution for low mass clusters.Comment: 19 pages, 11 figures, accepted for publication in A&
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