885 research outputs found
Redshift-distance Survey of Early-type Galaxies: The D_n-sigma Relation
In this paper R-band photometric and velocity dispersion measurements for a
sample of 452 elliptical and S0 galaxies in 28 clusters are used to construct a
template D_n-sigma relation. This template relation is constructed by combining
the data from the 28 clusters, under the assumption that galaxies in different
clusters have similar properties. The photometric and spectroscopic data used
consist of new as well as published measurements, converted to a common system,
as presented in a accompanying paper. The resulting direct relation, corrected
for incompleteness bias, is log{D_n} =1.203 log{sigma} + 1.406; the zero-point
has been defined by requiring distant clusters to be at rest relative to the
CMB. This zero-point is consistent with the value obtained by using the
distance to Virgo as determined by the Cepheid period-luminosity relation. This
new D_n-sigma relation leads to a peculiar velocity of -72 (\pm 189) km/s for
the Coma cluster. The scatter in the distance relation corresponds to a
distance error of about 20%, comparable to the values obtained for the
Fundamental Plane relation. Correlations between the scatter and residuals of
the D_n-sigma relation with other parameters that characterize the cluster
and/or the galaxy stellar population are also analyzed. The direct and inverse
relations presented here have been used in recent studies of the peculiar
velocity field mapped by the ENEAR all-sky sample.Comment: 46 pages, 20 figures, and 7 tables. To appear in AJ, vol. 123, no. 5,
May 200
Near-Infrared Imaging of Early-Type Galaxies IV. The Physical Origins of the Fundamental Plane Scaling Relations
The physical origins of the Fundamental Plane (FP) scaling relations are
investigated for early-type galaxies observed at optical and near-infrared
wavelengths. The slope for the FP is shown to increase systematically with
wavelength from the U-band through the K-band. A distance-independent
construction of the observables is described which provides an accurate
measurement of the change in the FP slope between any pair of bandpasses. The
variation of the FP slope with wavelength is strong evidence of systematic
variations in stellar content along the elliptical galaxy sequence. The
intercept of the diagnostic relationship between log(D_K/D_V) and log(sigma_0)
shows no significant dependence on environment within the uncertainties of the
Galactic extinction corrections, demonstrating the universality of the stellar
populations contributions at the level of Delta(V-K)=0.03 mag to the zero-point
of the global scaling relations.
Several other constraints on the properties of early-type galaxies --- the
slope of the Mg_2-sigma_0 relation, the effects of stellar populations
gradients, and deviations of early-type galaxies from a dynamically homologous
family --- are included to construct an empirical, self-consistent model which
provides a complete picture of the underlying physical properties which are
varying along the early-type galaxy sequence. This empirical approach
demonstrates that there are significant systematic variations in both age and
metallicity along the elliptical galaxy sequence, and that a small, but
systematic, breaking of dynamical homology (or a similar, wavelength
independent effect) is required. Predictions for the evolution of the slope of
the FP with redshift are described. [abriged]Comment: to appear in The Astronomical Journal; 40 pages, including 10
Postscript figures and 3 tables; uses AAS LaTeX style file
Multicolor photometry of the galaxies in the central region of Abell 2634
An optical photometric observation with the BATC multicolor system is carried
out for the central 56' x 56' region of the nearby cluster of galaxies, Abell
2634. We achieved the spectral energy distributions (SEDs) of 5572 sources
detected down to mag, including 178 previously known galaxies, with
fourteen filters covering a wavelength range from 3600 \AA\ to 10000 \AA. After
excluding the foreground and background galaxies, a sample of 124 known members
is formed for an investigation of the SED properties. Based on the knowledge of
SED properties of member galaxies, we performed the selection of faint galaxies
belonging to Abell 2634. The color-color diagrams are powerful in the
star/galaxy separation, and 359 faint galaxies are selected by their color
features. The technique of photometric redshift and color-magnitude correlation
for the early-type galaxies are applied for these faint galaxies, and a list of
74 faint member galaxies is achieved. Basis on the enlarged sample of member
galaxies, the spatial distribution and color-magnitude relation of the galaxies
in core region of Abell 2634 are discussed. We find a tendency that the color
index dispersion of the early-type members is larger for the outer region,
which might reflect some clues about the environmental effect on the evolution
of galaxies in a cluster.Comment: 35 pages, 21 Postscript figures and tables, LaTeX, using aasms4.st
Flows on scales of 150 Mpc?
We investigate the reality of large-scale streaming on scales of up to 150
Mpc using the peculiar motions of galaxies in three directions. New R-band CCD
photometry and spectroscopy for elliptical galaxies is used. The Fundamental
Plane distance indicator is calibrated using the Coma cluster and an
inhomogeneous Malmquist bias correction is applied. A linear bulk-flow model is
fitted to the peculiar velocities in the sample regions and the results do not
reflect the bulk flow observed by Lauer and Postman (LP). Accounting for the
difference in geometry between the galaxy distribution in the three regions and
the LP clustersconfirms the disagreement; assuming a low-density CDM power
spectrum, we find that the observed bulk flow of the galaxies in our sample
excludes the LP bulk flow at the 99.8% confidence level.Comment: 16 pages, 1 figur
A Cepheid Distance to NGC 4603 in Centaurus
In an attempt to use Cepheid variables to determine the distance to the
Centaurus cluster, we have obtained images of NGC 4603 with the Hubble Space
Telescope on 9 epochs using WFPC2 and the F555W and F814W filters. This galaxy
has been suggested to lie within the ``Cen30'' portion of the cluster and is
the most distant object for which this method has been attempted. Previous
distance estimates for Cen30 have varied significantly and some have presented
disagreements with the peculiar velocity predicted from redshift surveys,
motivating this investigation. Using our observations, we have found 61
candidate Cepheid variable stars; however, a significant fraction of these
candidates are likely to be nonvariable stars whose magnitude measurement
errors happen to fit a Cepheid light curve of significant amplitude for some
choice of period and phase. Through a maximum likelihood technique, we
determine that we have observed 43 +/- 7 real Cepheids and that NGC 4603 has a
distance modulus of 32.61 +0.11/-0.10 (random, 1 sigma) +0.24/-0.25
(systematic, adding in quadrature), corresponding to a distance of 33.3 Mpc.
This is consistent with a number of recent estimates of the distance to NGC
4603 or Cen30 and implies a small peculiar velocity consistent with predictions
from the IRAS 1.2 Jy redshift survey if the galaxy lies in the foreground of
the cluster.Comment: Accepted for publication in the Astrophysical Journal. 17 pages with
17 embedded figures and 3 tables using emulateapj.sty. Additional figures and
images may be obtained from http://astro.berkeley.edu/~marc/n4603
Redshift-Distance Survey of Early-type Galaxies. I. Sample Selection, Properties and Completeness
This is the first in a series of papers describing the recently completed
all-sky redshift-distance survey of nearby early-type galaxies (ENEAR) carried
out for peculiar velocity analysis. The sample is divided into two parts and
consists of 1607 elliptical and lenticular galaxies with cz < 7000 km/s and
with blue magnitudes brighter than m_B=14.5 (ENEARm), and of galaxies in
clusters (ENEARc). Galaxy distances based on the Dn-sigma and Fundamental Plane
(FP) relations are now available for 1359 and 1107 ENEARm galaxies,
respectively, with roughly 80% based on new data gathered by our group. The
Dn-sigma and FP template distance relations are derived by combining 569 and
431 galaxies in 28 clusters, respectively, of which about 60% are based on our
new measurements. The ENEARm redshift-distance survey extends the earlier work
of the 7S and the recent Tully-Fisher surveys sampling a comparable volume. In
subsequent papers of this series we intend to use the ENEAR sample by itself or
in combination with the SFI Tully-Fisher survey to analyze the properties of
the local peculiar velocity field and to test how sensitive the results are to
different sampling and to the distance indicators. We also anticipate that the
homogeneous database assembled will be used for a variety of other applications
and serve as a benchmark for similar studies at high-redshift.Comment: 43 pages, 15 figures, submitted to the Astronomical Journa
The Near-Infrared Fundamental Plane of Elliptical Galaxies
We present results from a near-infrared -band imaging survey of 59
elliptical galaxies in five nearby clusters. We measure photometric parameters
for each galaxy using surface photometry and draw velocity dispersions from the
literature. Three observables define a near-infrared Fundamental Plane (FP) of
elliptical galaxies with . The scatter in the near-infrared relation is small at
\% in distance, which is equivalent to, or less than, the scatter of the
optical FP. We suggest that the small deviation of the near-infrared FP
relation from the optical FP is due to the reduction of metallicity effects in
the near-infrared bandpass. While the small scatter of the optical FP could be
consistent with compensating effects of age and metallicity, the similarly
small scatter of the near-infrared FP is nearly independent of metallicity and
hence places a strong constraint on possible age spreads among elliptical
galaxies at every point along the FP. We suggest that the departure of the
near-infrared FP from the pure virial form , and the corresponding observed relation , may be explained by slight systematic departures of
the structure and dynamics of elliptical galaxies from a homology.Comment: to appear in The Astrophysical Journal (Letters); 12 pages, including
2 Postscript figures and 1 table; uuencoded, compressed format; the paper is
also available in various formats from
http://astro.caltech.edu/~map/map.bibliography.refereed.htm
Detection of Bulk Motions in the ICM of the Centaurus Cluster
Several recent numerical simulations of off-center cluster mergers predict
that significant angular momentum with associated velocities of a few x 10^{3}
km/s can be imparted to the resulting cluster. Such gas bulk velocities can be
detected by the Doppler shift of X-ray spectral lines with ASCA spectrometers.
Using two ASCA observations of the Centaurus cluster, we produced a velocity
map for the gas in the cluster's central regions. We also detected radial and
azimuthal gradients in temperature and metal abundance distributions, which
seem to be associated with the infalling sub-group centered at NGC 4709 (Cen
45). More importantly, we found a significant (>99.8% confidence level)
velocity gradient along a line near-perpendicular to the direction of the
incoming sub-group and with a maximum velocity difference of ~3.4+-1.1 x 10^{3}
km/s. It is unlikely (P < 0.002) that the observed velocity gradient is
generated by gain fluctuations across the detectors. While the observed
azimuthal temperature and abundance variations can be attributed to the
interaction with Cen 45, we argue that the intracluster gas velocity gradient
is more likely due to a previous off-center merging event in the main body of
the Centaurus cluster.Comment: 13 pages in emulateapj5 style, 8 postscript figures; Accepted by ApJ;
Revised version with minor change
Direct Measurements of Gas Bulk Flows in the ICM of the Centaurus Cluster with the Chandra Satellite
We present the analysis of the velocity structure of the intracluster gas
near the core of Abell 3526 obtained with two off-center Chandra observations,
specifically designed to eliminate errors due to spatial variations of the
instrumental gain. We detected a significant velocity gradient along the
direction NE-SW direction, roughly perpendicular to the direction of the
incoming sub-group Cen45, in agreement with previous ASCA SIS measurements. The
presence of gas bulk velocities is observed both with and without the inclusion
of the FeK line complex in the spectral fittings. The configuration and
magnitude of the velocity gradient is consistent with near transonic
circulatory motion, either bulk or eddy-like. The velocity difference obtained
using the best calibrated central regions of ACIS-S3 is found to be
(2.4+-1.0)E03 km/s for rectangular regions 2'.4 x 3' roughly diametrically
opposed around the cluster's core. There are also indications of a high
velocity zone towards the Southern region with similar magnitudes. The
detection of velocity gradients is significant at the >99.4% confidence and
simulations show that intrachip gain fluctuations > 1800 km/s are required to
explain the velocity gradient by chance. The measurements suggest that >1% of
the total merger energy can still be bulk kinetic 0.4 Gyr after the merging
event. This is the first direct confirmation of velocity gradients in the
intracluster gas with independent instruments and indicates that strong
departure from hydrostatic equilibrium is possible even for cool clusters that
do not show obvious signs of merging.Comment: 11 pages, 8 figures, accepted for publication in Astrophysical
Journal. For full version with all figures click on this
http://www.astro.lsa.umich.edu/~rdupke/cent_final.tar.g
Investigating Diurnal Changes in the Normal Albedo of the Lunar Surface at 1064 nm: A New Analysis with the Lunar Orbiter Laser Altimeter
The thermal environment of the lunar surface is extreme. At the equator, temperatures drop ~300 K between local noon and night. Laboratory studies demonstrate that minerals common to the lunar surface (e.g.,pyroxene, olivine) show spectral changes with respect to temperature in near infrared wavelengths. Over temperature changes equivalent to the lunar thermal environment (T 300K), the reflectance of pure pyroxene samples can vary by a factor of two
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