1,886 research outputs found
Shellflow. I. The Convergence of the Velocity Field at 6000 km/s
We present the first results from the Shellflow program, an all-sky
Tully-Fisher (TF) peculiar velocity survey of 276 Sb-Sc galaxies with redshifts
between 4500 and 7000 km/s. Shellflow was designed to minimize systematic
errors between observing runs and between telescopes, thereby removing the
possibility of a spurious bulk flow caused by data inhomogeneity. A fit to the
data yields a bulk flow amplitude V_bulk = 70{+100}{-70} km/s (1 sigma error)
with respect to the Cosmic Microwave Background, i.e., consistent with being at
rest. At the 95% confidence level, the flow amplitude is < 300 km/s. Our
results are insensitive to which Galactic extinction maps we use, and to the
parameterization of the TF relation. The larger bulk motion found in analyses
of the Mark III peculiar velocity catalog are thus likely to be due to
non-uniformities between the subsamples making up Mark III. The absence of bulk
flow is consistent with the study of Giovanelli and collaborators and flow
field predictions from the observed distribution of IRAS galaxies.Comment: Accepted version for publication in ApJ. Includes an epitaph for
Jeffrey Alan Willick (Oct 8, 1959 - Jun 18, 2000
A Definitive Optical Detection of a Supercluster at z = 0.91
We present the results from a multi-band optical imaging program which has
definitively confirmed the existence of a supercluster at z = 0.91. Two massive
clusters of galaxies, CL1604+4304 at z = 0.897 and CL1604+4321 at z = 0.924,
were originally observed in the high-redshift cluster survey of Oke, Postman &
Lubin (1998). They are separated by 4300 km/s in radial velocity and 17
arcminutes on the plane of the sky. Their physical and redshift proximity
suggested a promising supercluster candidate. Deep BRi imaging of the region
between the two clusters indicates a large population of red galaxies. This
population forms a tight, red sequence in the color--magnitude diagram at (R-i)
= 1.4. The characteristic color is identical to that of the
spectroscopically-confirmed early-type galaxies in the two member clusters. The
red galaxies are spread throughout the 5 Mpc region between CL1604+4304 and
CL1604+4321. Their spatial distribution delineates the entire large scale
structure with high concentrations at the cluster centers. In addition, we
detect a significant overdensity of red galaxies directly between CL1604+4304
and CL1604+4321 which is the signature of a third, rich cluster associated with
this system. The strong sequence of red galaxies and their spatial distribution
clearly indicate that we have discovered a supercluster at z = 0.91.Comment: Accepted for publication in Astrophysical Journal Letters. 13 pages,
including 5 figure
The LCO/Palomar 10,000 km/sec Cluster Survey. II. Constraints on Large-Scale Streaming
The LCO/Palomar 10,000 km/sec (LP10K) Tully-Fisher (TF) data set is used to
test for bulk streaming motions on a ~150 Mpc scale. The sample consists of 172
cluster galaxies in the original target range of the survey, 9000-13,000
km/sec, plus an additional 72 galaxies with cz < 30,000 km/sec. A
maximum-likelihood analysis that is insensitive to Malmquist and selection bias
effects is used to constrain the bulk velocity parameters, and realistic
Monte-Carlo simulations are carried out to correct residual biases and
determine statistical errors. When the analysis is restricted to the original
target range, the bias-corrected bulk flow is v_B=720 +/- 280 km/sec toward
l=266, b=19. When all objects out to z=0.1 are included the result is virtually
unchanged, v_B=700 +/- 250 km/sec toward l=272, b=10. The hypothesis that the
Hubble flow has converged to the CMB frame at distances less than ~ 100 Mpc is
ruled out at the 97% confidence level. The data are inconsistent with the flow
vector found by Lauer & Postman. However, the LP10K bulk flow is consistent
with that obtained from the SMAC survey of elliptical galaxies recently
described by Hudson et al. If correct, the LP10K results indicate that the
convergence depth for the Hubble flow is >~ 150 Mpc.Comment: 14 pages, 7 figures, uses emulateapj, submitted to the Astrophysical
Journal. Also available at http://astro.stanford.edu/jeff
The Evolutionary Status of Clusters of Galaxies at z ~ 1
Combined HST, X-ray, and ground-based optical studies show that clusters of
galaxies are largely "in place" by , an epoch when the Universe was
less than half its present age. High resolution images show that elliptical,
S0, and spiral galaxies are present in clusters at redshifts up to . Analysis of the CMDs suggest that the cluster ellipticals formed their
stars several Gyr earlier, near redshift 3. The morphology--density relation is
well established at , with star-forming spirals and irregulars residing
mostly in the outer parts of the clusters and E/S0s concentrated in dense
clumps. The intracluster medium has already reached the metallicity of
present-day clusters. The distributions of the hot gas and early-type galaxies
are similar in clusters, indicating both have largely virialized in
the deepest potentials wells. In spite of the many similarities between
and present-day clusters, there are significant differences. The
morphologies revealed by the hot gas, and particularly the early-type galaxies,
are elongated rather than spherical. We appear to be observing the clusters at
an epoch when the sub-clusters and groups are still assembling into a single
regular cluster. Support for this picture comes from CL0152 where the gas
appears to be lagging behind the luminous and dark mass in two merging
sub-components. Moreover, the luminosity difference between the first and
second brightest cluster galaxies at is smaller than in 93% of
present-day Abell clusters, which suggests that considerable luminosity
evolution through merging has occurred since that epoch. Evolution is also seen
in the bolometric X-ray luminosity function.Comment: 18 pages, 12 figures, to appear in Penetrating Bars through Masks of
Cosmic Dust: the Hubble Tuing Fork Strikes a New Note, eds. D.L. Block, K.C.
Freeman, I. Puerari & R. Groess. Figures degraded to meet astroph size limit;
a version with higher resolution figures may be downloaded from:
http://acs.pha.jhu.edu/~jpb/z1clusters/ford_clusters.pd
Cluster detection from surface-brightness fluctuations in SDSS data
Galaxy clusters can be detected as surface brightness enhancements in
smoothed optical surveys. This method does not require individual galaxies to
be identifiable, and enables clusters to be detected out to surprisingly high
redshifts, as recently demonstrated by the Las Campanas Distant Cluster Survey
(LCDCS). Here, we investigate redshift limits for cluster detection in the
Sloan Digital Sky Survey (SDSS). Calibrating assumptions about the surface
brightness profile, the mass-to-light ratio, and the spectral energy
distribution of galaxy clusters using available observational data, we show
that it should be possible to detect galaxy groups out to redshifts of ~0.5,
and massive galaxy clusters out to redshifts of ~1.2 in summed r'+i'+z' SDSS
data. Redshift estimates can be derived from the SDSS magnitudes of brightest
cluster members out to redshifts near unity. Over the area of sky it covers,
SDSS should find >~98% of the clusters detectable by the Planck satellite
through the thermal Sunyaev-Zel'dovich effect. The few Planck clusters not
detected in SDSS will almost all be at z>~1.2.Comment: 7 pages, submitted to Astronomy & Astrophysic
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