326 research outputs found
CIRS: Cluster Infall Regions in the Sloan Digital Sky Survey I. Infall Patterns and Mass Profiles
We use the Fourth Data Release of the Sloan Digital Sky Survey to test the
ubiquity of infall patterns around galaxy clusters and measure cluster mass
profiles to large radii. We match X-ray cluster catalogs with SDSS, search for
infall patterns, and compute mass profiles for a complete sample of X-ray
selected clusters. Very clean infall patterns are apparent in most of the
clusters, with the fraction decreasing with increasing redshift due to
shallower sampling. All 72 clusters in a well-defined sample limited by
redshift (ensuring good sampling) and X-ray flux (excluding superpositions)
show infall patterns sufficient to apply the caustic technique. This sample is
by far the largest sample of cluster mass profiles extending to large radii to
date. Similar to CAIRNS, cluster infall patterns are better defined in
observations than in simulations. Further work is needed to determine the
source of this difference. We use the infall patterns to compute mass profiles
for 72 clusters and compare them to model profiles. Cluster scaling relations
using caustic masses agree well with those using X-ray or virial mass
estimates, confirming the reliability of the caustic technique. We confirm the
conclusion of CAIRNS that cluster infall regions are well fit by NFW and
Hernquist profiles and poorly fit by singular isothermal spheres. This much
larger sample enables new comparisons of cluster properties with those in
simulations. The shapes (specifically, NFW concentrations) of the mass profiles
agree well with the predictions of simulations. The mass inside the turnaround
radius is on average 2.190.18 times that within the virial radius. This
ratio agrees well with recent predictions from simulations of the final masses
of dark matter haloes.Comment: 34 pages, 24 figures, accepted for publication in AJ, full resolution
version available at http://www.astro.yale.edu/krines
CAIRNS: The Cluster And Infall Region Nearby Survey I. Redshifts and Mass Profiles
The CAIRNS (Cluster And Infall Region Nearby Survey) project is a
spectroscopic survey of the infall regions surrounding eight nearby, rich,
X-ray luminous clusters of galaxies. We collect 15665 redshifts (3471 new or
remeasured) within \sim 5-10 Mpc of the centers of the clusters, making it the
largest study of the infall regions of clusters. We determine cluster
membership and the mass profiles of the clusters based on the phase space
distribution of the galaxies. All of the clusters display decreasing velocity
dispersion profiles. The mass profiles are fit well by functional forms based
on numerical simulations but exclude an isothermal sphere. Specifically, NFW
and Hernquist models provide good descriptions of cluster mass profiles to
their turnaround radii. Our sample shows that the predicted infall pattern is
ubiquitous in rich, X-ray luminous clusters over a large mass range. The
caustic mass estimates are in excellent agreement with independent X-ray
estimates at small radii and with virial estimates at intermediate radii. The
mean ratio of the caustic mass to the X-ray mass is 1.03\pm0.11 and the mean
ratio of the caustic mass to the virial mass (when corrected for the surface
pressure term) is 0.93\pm0.07. We further demonstrate that the caustic
technique provides reasonable mass estimates even in merging clusters.Comment: 54 pages, 18 figures, to appear in The Astronomical Journa
Kinematics and Mass Profile of AWM 7
We have measured 492 redshifts (311 new) in the direction of the poor cluster
AWM~7 and have identified 179 cluster members (73 new). We use two independent
methods to derive a self-consistent mass profile, under the assumptions that
the absorption-line galaxies are virialized and that they trace an underlying
Navarro, Frenk & White (1997) dark matter profile: (1) we fit such an NFW
profile to the radial distribution of galaxy positions and to the velocity
dispersion profile; (2) we apply the virial mass estimator to the cluster. With
these assumptions, the two independent mass estimates agree to \sim 15% within
1.7 h^{-1} Mpc, the radial extent of our data; we find an enclosed mass \sim
(3+-0.5)\times 10^{14} h^{-1} M_\odot. The largest potential source of
systematic error is the inclusion of young emission-line galaxies in the mass
estimate.
We investigate the behavior of the surface term correction to the virial mass
estimator under several assumptions about the velocity anisotropy profile,
still within the context of the NFW model, and remark on the sensitivity of
derived mass profiles to outliers. We find that one must have data out to a
large radius in order to determine the mass robustly, and that the surface term
correction is unreliable at small radii.Comment: LaTeX, 5 tables, 7 figures, appeared as 2000 AJ 119 44; typos and Eq.
9 corrected; results are unaffecte
Discovery of a Ringlike Dark Matter Structure in the Core of the Galaxy Cluster Cl 0024+17
We present a comprehensive mass reconstruction of the rich galaxy cluster Cl
0024+17 at z~0.4 from ACS data, unifying both strong- and weak-lensing
constraints. The weak-lensing signal from a dense distribution of background
galaxies (~120 per square arcmin) across the cluster enables the derivation of
a high-resolution parameter-free mass map. The strongly-lensed objects tightly
constrain the mass structure of the cluster inner region on an absolute scale,
breaking the mass-sheet degeneracy. The mass reconstruction of Cl 0024+17
obtained in such a way is remarkable. It reveals a ringlike dark matter
substructure at r~75" surrounding a soft, dense core at r~50". We interpret
this peculiar sub-structure as the result of a high-speed line-of-sight
collision of two massive clusters 1-2 Gyr ago. Such an event is also indicated
by the cluster velocity distribution. Our numerical simulation with purely
collisionless particles demonstrates that such density ripples can arise by
radially expanding, decelerating particles that originally comprised the
pre-collision cores. Cl 0024+17 can be likened to the bullet cluster 1E0657-56,
but viewed the collision axis at a much later epoch. In addition, we
show that the long-standing mass discrepancy for Cl 0024+17 between X-ray and
lensing can be resolved by treating the cluster X-ray emission as coming from a
superposition of two X-ray systems. The cluster's unusual X-ray surface
brightness profile that requires a two isothermal sphere description supports
this hypothesis.Comment: To appear in the June 1 issue of The Astrophysical Journa
CO Isotopologue Lines as Observational Tracers of Past FUor Outbursts
Изменения в молекулярном излучении протопланетного диска вследствие химических процессов могут быть свидетельством прошлых вспышек светимости в данном диске. С помощью моделирования химического состава протопланетного диска (код ХANDES) и переноса излучения (код RADMC-3D) исследуется изменение потока излучения в линиях изотопологов CO после вспышки фуора на ансамбле случайных моделей. Показано, что в дисках без оболочки обе пары линий 13CO J = 2−1/CO J = 2−1 и C18O J = 2−1/CO J = 2−1 позволяют сформулировать критерии, позволяющие отличить диски с прошедшей вспышкой. В дисках с оболочкой такой критерий возможно сформулировать лишь для пары C18O J = 2 − 1/CO J = 2 − 1.Changes in disc molecular emission due to chemical processes can help identify whether disc experienced FUor outbursts in the past. Using astrochemical modelling of protoplanetary discs (ANDES code) and radiative transfer (RADMC-3D code) on a set of random models we investigate the evolution of CO isotopologues lines emission after the FUor outburst. We find that for non-embedded discs, both 13CO J = 2 − 1/CO J = 2 − 1 and C18O J = 2 − 1/CO J = 2 − 1 line pairs allow to formulate criteria for distinguishing post-outburst discs. For embedded discs only for C18O J = 2 − 1/CO J = 2 − 1 pair it is possible to formulate such a criterion.Работа поддержана грантом Фонда развития теоретической физики и математики «БАЗИС» (20-1-2-20)
Observational Mass-to-Light Ratio of Galaxy Systems: from Poor Groups to Rich Clusters
We study the mass-to-light ratio of galaxy systems from poor groups to rich
clusters, and present for the first time a large database for useful
comparisons with theoretical predictions. We extend a previous work, where B_j
band luminosities and optical virial masses were analyzed for a sample of 89
clusters. Here we also consider a sample of 52 more clusters, 36 poor clusters,
7 rich groups, and two catalogs, of about 500 groups each, recently identified
in the Nearby Optical Galaxy sample by using two different algorithms. We
obtain the blue luminosity and virial mass for all systems considered. We
devote a large effort to establishing the homogeneity of the resulting values,
as well as to considering comparable physical regions, i.e. those included
within the virial radius. By analyzing a fiducial, combined sample of 294
systems we find that the mass increases faster than the luminosity: the linear
fit gives M\propto L_B^{1.34 \pm 0.03}, with a tendency for a steeper increase
in the low--mass range. In agreement with the previous work, our present
results are superior owing to the much higher statistical significance and the
wider dynamical range covered (about 10^{12}-10^{15} M_solar). We present a
comparison between our results and the theoretical predictions on the relation
between M/L_B and halo mass, obtained by combining cosmological numerical
simulations and semianalytic modeling of galaxy formation.Comment: 25 pages, 12 eps figures, accepted for publication in Ap
The Northern Sky Optical Cluster Survey II: An Objective Cluster Catalog for 5800 Square Degrees
We present a new, objectively defined catalog of candidate galaxy clusters
based on the galaxy catalogs from the Digitized Second Palomar Observatory Sky
Survey (DPOSS). This cluster catalog, derived from the best calibrated plates
in the high latitude (|b|>30) Northern Galactic Cap region, covers 5,800 square
degrees, and contains 8,155 candidate clusters. A simple adaptive kernel
density mapping technique, combined with the SExtractor object detection
algorithm, is used to detect galaxy overdensities, which we identify as
clusters. Simulations of the background galaxy distribution and clusters of
varying richnesses and redshifts allow us to optimize detection parameters, and
measure the completeness and contamination rates for our catalog. Cluster
richnesses and photometric redshifts are measured, using integrated colors and
magnitudes for each cluster. An extensive spectroscopic survey is used to
confirm the photometric results.
This catalog, with well-characterized sample properties, provides a sound
basis for future studies of cluster physics and large scale structure.Comment: 49 pages, 16 figures. Accepted to AJ; appearing in April. Version
with full resolution figures, and full length tables available at
http://dposs.caltech.edu:8080/NoSOCS.htm
A Potential Galaxy Threshing System in the Cosmos Field
We report on the discovery of a new potential galaxy threshing system in the
COSMOS 2 square degree field using the prime-focus camera, Suprime-Cam, on the
8.2 m Subaru Telescope. This system consists of a giant elliptical galaxy with
and a tidally disrupted satellite galaxy with at a photometric redshift of . This redshift is
consistent with the spectroscopic redshift of 0.079 for the giant elliptical
galaxy obtained from the Sloan Digital Sky Survey (SDSS) archive. The
luminosity masses of the two galaxies are
and , respectively. The distance between the
two galaxies is greater than 100 kpc. The two tidal tails emanating from the
satellite galaxy extend over 150 kpc. This system would be the second
well-defined galaxy threshing system found so far.Comment: 17 pages, 7 figures, accepted for the COSMOS special issue of ApJ
Stellar structure and compact objects before 1940: Towards relativistic astrophysics
Since the mid-1920s, different strands of research used stars as "physics
laboratories" for investigating the nature of matter under extreme densities
and pressures, impossible to realize on Earth. To trace this process this paper
is following the evolution of the concept of a dense core in stars, which was
important both for an understanding of stellar evolution and as a testing
ground for the fast-evolving field of nuclear physics. In spite of the divide
between physicists and astrophysicists, some key actors working in the
cross-fertilized soil of overlapping but different scientific cultures
formulated models and tentative theories that gradually evolved into more
realistic and structured astrophysical objects. These investigations culminated
in the first contact with general relativity in 1939, when J. Robert
Oppenheimer and his students George Volkoff and Hartland Snyder systematically
applied the theory to the dense core of a collapsing neutron star. This
pioneering application of Einstein's theory to an astrophysical compact object
can be regarded as a milestone in the path eventually leading to the emergence
of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal
Diffuse Light in Hickson Compact Groups: The Dynamically Young System HCG 44
Compact groups are associations of a few galaxies in which the environment
plays an important role in galaxy evolution. The low group velocity dispersion
favors tidal interactions and mergers, which may bring stars from galaxies to
the diffuse intragroup light. Numerical simulations of galaxy clusters in
hierarchical cosmologies show that the amount of the diffuse light increases
with the dynamical evolution of the cluster. We search for diffuse light in the
galaxy group HCG 44 in order to determine its luminosity and luminosity
fraction. Combining with literature data, we aim to constrain the dynamical
status of Hickson compact groups. We use Intra Group planetary nebulae (IGPNe)
as tracers of diffuse light. These are detected by the so-called on band-off
band technique. We found 12 emission line objects in HCG 44, none of them
associated with the galaxies of the group. 6/12 emission line objects are
consistent with being IGPNe in HCG 44, but are also consistent with being
Ly background galaxies. Thus we derive an upper limit to the diffuse
light fraction in HCG 44 of 4.7%. We find a correlation between the fraction of
elliptical galaxies and the amount of diffuse light in Hickson compact groups.
Those with large fraction of diffuse light are those with large fractions in
number and luminosity of E/S0 galaxies. We propose an evolutionary sequence for
Hickson compact groups in which the amount of diffuse light increases with the
dynamical evolution of the group.Comment: 9 pages, 4 figures, accepted for publication at A&
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