190 research outputs found
Morphology and Evolution of Simulated and Optical Clusters: A Comparative Analysis
We have made a comparative study of morphological evolution in simulated DM
halos and X-ray brightness distribution, and in optical clusters. Samples of
simulated clusters include star formation with supernovae feedback, radiative
cooling, and simulation in the adiabatic limit at three different redshifts, z
= 0.0, 0.10, and 0.25. The optical sample contains 208 ACO clusters within
redshift, . Cluster morphology, within 0.5 and 1.0 h Mpc
from cluster center, is quantified by multiplicity and ellipticity.
We find that the distribution of the dark matter halos in the adiabatic
simulation appear to be more elongated than the galaxy clusters. Radiative
cooling brings halo shapes in excellent agreement with observed clusters,
however, cooling along with feedback mechanism make the halos more flattened.
Our results indicate relatively stronger structural evolution and more clumpy
distributions in observed clusters than in the structure of simulated clusters,
and slower increase in simulated cluster shapes compared to those in the
observed one.
Within , we notice an interesting agreement in the shapes of
clusters obtained from the cooling simulations and observation. We also notice
that the different samples of observed clusters differ significantly in
morphological evolution with redshift. We highlight a few possibilities
responsible for the discrepancy in morphological evolution of simulated and
observed clusters.Comment: Accepted for publication in MNRAS, 2006; 15 pages, 13 postscript
figure
The environment of AGN dwarf galaxies at z0.7 from the VIPERS survey
Dwarf galaxies are ideal laboratories to study the relationship between the
environment and AGN activity. However, the type of environments in which dwarf
galaxies hosting AGN reside is still unclear and limited to low-redshift
studies (z < 0.5). We use the VIMOS Public Extragalactic Redshift Survey
(VIPERS) to investigate, for the first time, their environments at 0.5 < z <
0.9. We select a sample of 12,942 low-mass
() galaxies and use the emission-line
diagnostic diagram to identify AGN. We characterise their local environments as
the galaxy density contrast, , derived from the fifth nearest neighbour
method. Our work demonstrates that AGN and non-AGN dwarf galaxies reside in
similar environments at intermediate redshift suggesting that the environment
is not an important factor in triggering AGN activity already since z = 0.9.
Dwarf galaxies show a strong preference for low-density environments,
independently of whether they host an AGN or not. Their properties do not
change when moving to denser environments, suggesting that dwarf galaxies are
not gas-enriched due to environmental effects. Moreover, AGN presence does not
alter host properties supporting the scenario that AGN feedback does not impact
the star formation of the host. Lastly, AGN are found to host over-massive
black holes. This is the first study of dwarf galaxies hosting AGN at z > 0.5.
The next generation of deep surveys will reveal whether or not such lack of
environmental trends is common also for faint higher-redshift dwarf galaxy
populations.Comment: Accepted for publication in MNRAS, 19 pages, 14 figure
VIPERS : in search for the solution of the riddle of dark energy (and many others)
We present the "VIMOS Public Extragalactic Redshift Survey" (VIPERS). We discuss the present status of the survey, the data which are already open to the public, and review first scientific results of the project
Searching for rotating galaxy clusters in SDSS and 2dFGRS
We present a result of searching for galaxy clusters that show an indication
of global rotation using a spectroscopic sample of galaxies in SDSS and 2dFGRS.
We have determined the member galaxies of 899 Abell clusters covered in SDSS
and 2dFGRS using the redshift and the positional data of galaxies, and have
estimated the ratio of the cluster rotation amplitude to the cluster velocity
dispersion and the velocity gradient across the cluster. We have found 12
tentative rotating clusters that have large ratios of rotation amplitude to
dispersion and large velocity gradients. We have determined the morphological
parameters for 12 tentative rotating clusters using the positional information
of the member galaxies: the ellipticity of the dispersion ellipse is in the
range of 0.080.57, and the position angle of major or minor axis does not
appear to be related to the position angle of rotation axis. We have
investigated the substructures in the sample of tentative rotating clusters,
finding from the Dressler-Shectman plots that the majority (9 out of 12) of
clusters show an evidence of substructure due to the spatially correlated
velocities of galaxies. We have selected six probable rotating clusters (A0954,
A1139, A1399, A2162, A2169, and A2366) that show a single number density peak
around the cluster center with a spatial segregation of the high and low
velocity galaxies. We have found no strong evidences of a recent merging for
the probable rotating clusters: the probable rotating clusters do not deviate
significantly from the relation of the X-ray luminosity and the velocity
dispersion or the virial mass of the clusters, and two probable rotating
clusters (A0954 and A1399) have small values of the peculiar velocities and the
clustercentric distances of the brightest cluster galaxies.Comment: 33 pages, 9 figures. To appear in Ap
Znaczenie migracji w życiu człowieka na przykładzie biografii Polek emigrujących do Kanady w latach 80
Influencia de la solubilidad del anhÃdrido bórico del sinterizado sobre los vidriados
Not availableNo disponibl
Unsupervised classification reveals new evolutionary pathways
While we already seem to have a general scenario of the evolution of
different types of galaxies, a complete and satisfactory understanding of the
processes that led to the formation of all the variety of today's galaxy types
is still beyond our reach. To solve this problem, we need both large datasets
reaching high redshifts and novel methodologies for dealing with them. The
VIPERS survey statistical power, which observed galaxies at , and the application of an unsupervised clustering algorithm allowed us to
distinguish 12 galaxy classes. Studies of their environmental dependence
indicate that this classification may actually reflect different galaxy
evolutionary paths. For instance, a class of the most passive red galaxies
gathers galaxies smaller than other red galaxies of a similar
stellar mass, revealing the first sample of red nuggets at intermediate
redshift. On the other end, a class of blue dwarf galaxies is composed mainly
of AGN, challenging commonly used mid-infrared AGN selections.Comment: Accepted for publication in the ML4ASTRO (ICML 2022) proceeding boo
- …