1,606 research outputs found
Role of phi decays for K- yields in relativistic heavy-ion collisions
The production of strange mesons in collisions of Ar+KCl at a kinetic beam
energy of 1.756 AGeV is studied within a transport model of
Boltzmann-\"Uhling-Uhlenbeck (BUU) type. In particular, and
yields and spectra are compared to the data mesured recently by the HADES
collaboration and the yield measured previously by the FOPI
collaboration. Our results are in agreement with these data thus presenting an
interpretation of the subleading role of decays into 's and
confirming the importance of the strangeness-exchange channels for
production.Comment: 24 pages, 19 figure
Anti-Proton Evolution in Little Bangs and Big Bang
The abundances of anti-protons and protons are considered within
momentum-integrated Boltzmann equations describing Little Bangs, i.e.,
fireballs created in relativistic heavy-ion collisions. Despite of a large
anti-proton annihilation cross section we find a small drop of the ratio of
anti-protons to protons from 170 MeV (chemical freeze-out temperature) till 100
MeV (kinetic freeze-out temperature) for CERN-SPS and BNL-RHIC energies thus
corroborating the solution of the previously exposed "ani-proton puzzle". In
contrast, the Big Bang evolves so slowly that the anti-baryons are kept for a
long time in equilibrium resulting in an exceedingly small fraction. The
adiabatic path of cosmic matter in the phase diagram of strongly interacting
matter is mapped out
Galaxy morphology in the rich cluster Abell 2390
We have analysed images of the field of A2390 obtained with the CFHT and HST.
The analysis fits models to bulge and disk components to several hundred
galaxies, with about equal samples from the cluster and field. We also have
assessed and graded asymmetries in the images. The cluster galaxies are
compared in different cluster locations and also compared with field galaxies.
We find that the central old population galaxies are bulge-dominated, while
disk systems have young populations and are found predominantly in the outer
cluster. S0 and bulgy disk galaxies are found throughout, but concentrate in
regions of substructure. Disks of cluster blue galaxies are generally brighter
and smaller than those in the field. We find that the cluster members have a
higher proportion of interacting galaxies than the field sample. Interactions
in the cluster and in the field, as well as cluster infall, appear to inhibit
star-formation in galaxies.Comment: 20 pages including 10 of tables, plus 7 figures; To appear in the
Astronomical Jorurna
A Morphological and Multicolor Survey for Faint QSOs in the Groth-Westphal Strip
Quasars representative of the populous faint end of the luminosity function
are frustratingly dim with m~24 at intermediate redshift; moreover groundbased
surveys for such faint QSOs suffer substantial morphological contamination by
compact galaxies having similar colors. In order to establish a more reliable
ultrafaint QSO sample, we used the APO 3.5-m telescope to take deep groundbased
U-band CCD images in fields previously imaged in V,I with WFPC2/HST. Our
approach hence combines multicolor photometry with the 0.1" spatial resolution
of HST, to establish a morphological and multicolor survey for QSOs extending
about 2 magnitudes fainter than most extant groundbased surveys. We present
results for the "Groth-Westphal Strip", in which we identify 10 high likelihood
UV-excess candidates having stellar or stellar-nucleus+galaxy morphology in
WFPC2. For m(606)<24.0 (roughly B<24.5) the surface density of such QSO
candidates is 420 (+180,-130) per square degree, or a surface density of 290
(+160,-110) per square degree with an additional V-I cut that may further
exclude compact emission line galaxies. Even pending confirming spectroscopy,
the observed surface density of QSO candidates is already low enough to yield
interesting comparisons: our measures agree extremely well with the predictions
of several recent luminosity function models.Comment: 29 pages including 6 tables and 7 figures. As accepted for
publication in The Astronomical Journal (minor revisions
Decomposition of AGN host galaxy images
We describe an algorithm to decompose deep images of Active Galactic Nuclei
into host galaxy and nuclear components. Currently supported are three galaxy
models: A de-Vaucouleurs spheroidal, an exponential disc, and a two-component
disc+bulge model. Key features of the method are: (semi-)analytic
representation of a possibly spatially variable point-spread function; full
two-dimensional convolution of the model galaxy using gradient-controlled
adaptive subpixelling; multiple iteration scheme. The code is computationally
efficient and versatile for a wide range of applications. The quantitative
performance is measured by analysing simulated imaging data. We also present
examples of the application of the method to small test samples of nearby
Seyfert 1 galaxies and quasars at redshifts z < 0.35.Comment: 12 pages, 15 figures, accepted for publication in MNRA
The Luminosity Function Of Field Galaxies And Its Evolution Since z=1
We present the B-band luminosity function and comoving space and luminosity
densities for a sample of 2779 I-band selected field galaxies based on
multi-color data from the CADIS survey. The sample is complete down to I_815 =
22 without correction and with completeness correction extends to I_815=23.0.
By means of a new multi-color analysis the objects are classified according to
their spectral energy distributions (SEDs) and their redshifts are determined
with typical errors of delta z <= 0.03. We have split our sample into four
redshift bins between z=0.1 and z=1.04 and into three SED bins E-Sa,Sa-Sc and
starbursting (emission line) galaxies. The evolution of the luminosity function
is clearly differential with SED. The normalization phi* of luminosity function
for the E-Sa galaxies decreases towards higher redshift, and we find evidence
that the comoving galaxy space density decreases with redshift as well. In
contrast, we find phi* and the comoving space density increasing with redshift
for the Sa-Sc galaxies. For the starburst galaxies we find a steepening of the
luminosity function at the faint end and their comoving space density increases
with redshift.Comment: 15 pages, 14 figures, accepted by Astronomy&Astrophysic
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