1,289 research outputs found
A Statistical Treatment of the Gamma-Ray Burst "No Host Galaxy" Problem: II. Energies of Standard Candle Bursts
With the discovery that the afterglows after some bursts are coincident with
faint galaxies, the search for host galaxies is no longer a test of whether
bursts are cosmological, but rather a test of particular cosmological models.
The methodology we developed to investigate the original "no host galaxy"
problem is equally valid for testing different cosmological models, and is
applicable to the galaxies coincident with optical transients. We apply this
methodology to a family of models where we vary the total energy of standard
candle bursts. We find that total isotropic energies of E<2e52~erg are ruled
out while log(E)~53 erg is favored.Comment: To appear in Ap.J., 514, 15 pages + 7 figures, AASTeX 4.0. Revisions
are: additional author, updated data, and minor textual change
Stray-light contamination and spatial deconvolution of slit-spectrograph observations
Stray light caused by scattering on optical surfaces and in the Earth's
atmosphere degrades the spatial resolution of observations. We study the
contribution of stray light to the two channels of POLIS. We test the
performance of different methods of stray-light correction and spatial
deconvolution to improve the spatial resolution post-facto. We model the stray
light as having two components: a spectrally dispersed component and a
component of parasitic light caused by scattering inside the spectrograph. We
use several measurements to estimate the two contributions: observations with a
(partly) blocked FOV, a convolution of the FTS spectral atlas, imaging in the
pupil plane, umbral profiles, and spurious polarization signal in telluric
lines. The measurements allow us to estimate the spatial PSF of POLIS and the
main spectrograph of the German VTT. We use the PSF for a deconvolution of both
spectropolarimetric data and investigate the effect on the spectra. The
parasitic contribution can be directly and accurately determined for POLIS,
amounting to about 5%. We estimate a lower limit of about 10% across the full
FOV for the dispersed stray light. In quiet Sun regions, the stray-light level
from the close surroundings (d< 2") of a given spatial point is about 20%. The
stray light reduces to below 2% at a distance of 20" from a lit area for both
POLIS and the main spectrograph. A two-component model of the stray-light
contributions seems to be sufficient for a basic correction of observed
spectra. The instrumental PSF obtained can be used to model the off-limb stray
light, to determine the stray-light contamination accurately for observation
targets with large spatial intensity gradients such as sunspots, and also
allows one to improve the spatial resolution of observations post-facto.Comment: 14 pages, 16 figures, accepted by A&A. Version V2 revised for
language editin
A Serendipitous Galaxy Cluster Survey with XMM: Expected Catalogue Properties and Scientific Applications
This paper describes a serendipitous galaxy cluster survey that we plan to
conduct with the XMM X-ray satellite. We have modeled the expected properties
of such a survey for three different cosmological models, using an extended
Press-Schechter (Press & Schechter 1974) formalism, combined with a detailed
characterization of the expected capabilities of the EPIC camera on board XMM.
We estimate that, over the ten year design lifetime of XMM, the EPIC camera
will image a total of ~800 square degrees in fields suitable for the
serendipitous detection of clusters of galaxies. For the presently-favored
low-density model with a cosmological constant, our simulations predict that
this survey area would yield a catalogue of more than 8000 clusters, ranging
from poor to very rich systems, with around 750 detections above z=1. A
low-density open Universe yields similar numbers, though with a different
redshift distribution, while a critical-density Universe gives considerably
fewer clusters. This dependence of catalogue properties on cosmology means that
the proposed survey will place strong constraints on the values of Omega-Matter
and Omega-Lambda. The survey would also facilitate a variety of follow-up
projects, including the quantification of evolution in the cluster X-ray
luminosity-temperature relation, the study of high-redshift galaxies via
gravitational lensing, follow-up observations of the Sunyaev-Zel'dovich effect
and foreground analyses of cosmic microwave background maps.Comment: Accepted to ApJ. Minor changes, e.g. presentation of temperature
errors as a figure (rather than as a table). Latex (20 pages, 6 figures, uses
emulateapj.sty
The Effects of Inhomogeneities on Evaluating the mass parameter and the cosmological constant
Analytic expressions for distance-redshift relations which have been
corrected for the effects of inhomogeneities in the
Friedmann-Lema\^itre-Robertson-Walker (FLRW) mass density are given in terms of
Heun functions and are used to illustrate the significance of inhomogeneities
on a determination of the mass parameter and the cosmological
constant . The values of these parameters inferred from a given set of
observations depend on the fractional amount of matter in inhomogeneities and
can significantly differ from those obtained by using the standard
magnitude-redshift (-) result for pure dust FLRW models. As an example a
determination of made by applying the homogeneous distance-redshift
relation to SN 1997ap at could be as much as 50% lower than its true
value.Comment: 39 pages including 8 figures and captions. To appear in ApJ 507 (Nov.
1998
The Dipole Anisotropy of the First All-Sky X-ray Cluster Sample
We combine the recently published CIZA galaxy cluster catalogue with the
XBACs cluster sample to produce the first all-sky catalogue of X-ray clusters
in order to examine the origins of the Local Group's peculiar velocity without
the use of reconstruction methods to fill the traditional Zone of Avoidance.
The advantages of this approach are (i) X-ray emitting clusters tend to trace
the deepest potential wells and therefore have the greatest effect on the
dynamics of the Local Group and (ii) our all-sky sample provides data for
nearly a quarter of the sky that is largely incomplete in optical cluster
catalogues. We find that the direction of the Local Group's peculiar velocity
is well aligned with the CMB as early as the Great Attractor region 40 h^-1 Mpc
away, but that the amplitude of its dipole motion is largely set between 140
and 160 h^-1 Mpc. Unlike previous studies using galaxy samples, we find that
without Virgo included, roughly ~70% of our dipole signal comes from mass
concentrations at large distances (>60 h^-1 Mpc) and does not flatten,
indicating isotropy in the cluster distribution, until at least 160 h^-1 Mpc.
We also present a detailed discussion of our dipole profile, linking observed
features to the structures and superclusters that produce them. We find that
most of the dipole signal can be attributed to the Shapley supercluster
centered at about 150 h^-1 Mpc and a handful of very massive individual
clusters, some of which are newly discovered and lie well in the Zone of
Avoidance.Comment: 15 Pages, 9 Figures. Accepted by Ap
The Tolman Surface Brightness Test for the Reality of the Expansion. I. Calibration of the Necessary Local Parameters
The extensive CCD photometry by Postman & Lauer (1995, ApJ, 440, 28) in the
Cape/Cousins R photometric band for first ranked cluster elliptical and S0
galaxies in 118 low redshift clusters is analyzed for the correlations between
average surface brightness, linear radius, and absolute magnitude. The purpose
is to calibrate the correlations between these three parameters in the limit of
zero redshift. These local correlations provide the comparisons to be made in
Paper IV with the sample of early-type galaxies at high redshift in search of
the Tolman surface brightness signal of (1 + z)^4 if the expansion is real.
Surface brightness averages are calculated at various metric radii in each
galaxy in the sample. The definition of such radii by Petrosian (1976, ApJ,
209, L1) uses ratios of observed surface photometric data. The observed surface
brightnesses are listed for 118 first ranked cluster galaxies at Petrosian eta
radii of 1.0, 1.3, 1.5, 1.7, 2.0, and 2.5 mag. The three local diagnostic
correlation diagrams are defined and discussed. We review the Tolman test and
show that, although recipes from the standard cosmological model that already
have the Tolman signal incorporated are required to calculate linear radii and
absolute magnitudes from the observed data, the test is nevertheless free from
the hermeneutical circularity dilemma occasionally claimed in the literature.
The reasons are the observed mean surface brightness (1) is independent of any
assumptions of cosmological model, (2) does not depend on the existence of a
Tolman signal because it is calculated directly from the data using only
angular radii and apparent magnitudes, and (3) can be used to search for the
Tolman signal because it carries the bulk of that signal.Comment: 34 pages, 4 figures; accepted for publication in Astronomical Journa
Optical and X-ray clusters as tracers of the supercluster-void network. I Superclusters of Abell and X-ray clusters
We study the distribution of X-ray selected clusters of galaxies with respect
to superclusters determined by Abell clusters of galaxies and show that the
distribution of X-ray clusters follows the supercluster-void network determined
by Abell clusters. We find that in this network X-ray clusters are more
strongly clustered than other clusters. Poor, non-Abell X-ray clusters follow
the supercluster-void network as well: these clusters are embedded in
superclusters determined by rich clusters and populate filaments between them.
We present a new catalog of superclusters of Abell clusters out to a redshift
of z_{lim}=0.13, a catalog of X-ray clusters located in superclusters
determined by Abell clusters, and a list of additional superclusters of X-ray
clusters.Comment: LaTex (sty files added), 16 pages, 3 ps figures, submitted to
Astronomical Journal. Animations of the 3D distribution of superclusters of
Abell and X-ray clusters at http://www.aai.ee/~maret/SCLVnet.ht
The Tolman Surface Brightness Test for the Reality of the Expansion. IV. A Measurement of the Tolman Signal and the Luminosity Evolution of Early-Type Galaxies
We review a sample of the early literature in which the reality of the
expansion is discussed, explain Hubble's reticence to accept the expansion as
real, and contrast the Tolman surface brightness test with three other modern
tests. We search for the Tolman surface brightness depression with redshift
using the Hubble Space Telescope (HST) data from Paper III for 34 early-type
galaxies from the three clusters Cl 1324+3011 (z=0.76), Cl 1604+4304 (z=0.90),
and Cl 1604+4321 (z=0.92). Depressions of the surface brightness relative to
the zero-redshift fiducial lines in the mean surface brightness, log linear
radius diagrams of Paper I are found for all three clusters. Expressed as the
exponent, n, in 2.5 log (1 + z)^n mag, the value of n for all three clusters is
n = 2.59 +/- 0.17 in the R band and 3.37 +/- 0.13 in the I band for a q_o = 1/2
model. The sensitivity of the result to the assumed value of q_o is shown to be
less than 23% between q_o = 0 and +1. For a true Tolman signal with n = 4, the
luminosity evolution in the look-back time, expressed as the exponent in 2.5
log (1+z)^(4-n) mag, must then be between 1.72 to 1.19 in the R band and 0.94
to 0.45 in the I band. We show that this is precisely the range expected from
the evolutionary models of Bruzual & Charlot. We conclude that the Tolman
surface brightness test is consistent with the reality of the expansion. We
have also used the high-redshift HST data to test the ``tired light''
speculation for a non-expansion model for the redshift. The HST data rule out
the ``tired light'' model at a significance level of better than 10 sigma.Comment: 36 pages, 6 figures; accepted for publication in the Astronomical
Journa
Tracing cosmic evolution with clusters of galaxies
The most successful cosmological models to date envision structure formation
as a hierarchical process in which gravity is constantly drawing lumps of
matter together to form increasingly larger structures. Clusters of galaxies
currently sit atop this hierarchy as the largest objects that have had time to
collapse under the influence of their own gravity. Thus, their appearance on
the cosmic scene is also relatively recent. Two features of clusters make them
uniquely useful tracers of cosmic evolution. First, clusters are the biggest
things whose masses we can reliably measure because they are the largest
objects to have undergone gravitational relaxation and entered into virial
equilibrium. Mass measurements of nearby clusters can therefore be used to
determine the amount of structure in the universe on scales of 10^14 to 10^15
solar masses, and comparisons of the present-day cluster mass distribution with
the mass distribution at earlier times can be used to measure the rate of
structure formation, placing important constraints on cosmological models.
Second, clusters are essentially ``closed boxes'' that retain all their gaseous
matter, despite the enormous energy input associated with supernovae and active
galactic nuclei, because the gravitational potential wells of clusters are so
deep. The baryonic component of clusters therefore contains a wealth of
information about the processes associated with galaxy formation, including the
efficiency with which baryons are converted into stars and the effects of the
resulting feedback processes on galaxy formation. This article reviews our
theoretical understanding of both the dark-matter component and the baryonic
component of clusters. (Abridged)Comment: 54 pages, 15 figures, Rev. Mod. Phys. (in press
Large-scale periodicity in the distribution of QSO absorption-line systems
The spatial-temporal distribution of absorption-line systems (ALSs) observed
in QSO spectra within the cosmological redshift interval z = 0.0--4.3 is
investigated on the base of our updated catalog of absorption systems. We
consider so called metallic systems including basically lines of heavy
elements. The sample of the data displays regular variations (with amplitudes ~
15 -- 20%) in the z-distribution of ALSs as well as in the eta-distribution,
where eta is a dimensionless line-of-sight comoving distance, relatively to
smoother dependences. The eta-distribution reveals the periodicity with period
Delta eta = 0.036 +/- 0.002, which corresponds to a spatial characteristic
scale (108 +/- 6) h(-1) Mpc or (alternatively) a temporal interval (350 +/- 20)
h(-1) Myr for the LambdaCDM cosmological model. We discuss a possibility of a
spatial interpretation of the results treating the pattern obtained as a trace
of an order imprinted on the galaxy clustering in the early Universe.Comment: AASTeX, 13 pages, with 9 figures, Accepted for publication in
Astrophysics & Space Scienc
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