1,838 research outputs found
Spectroscopic Confirmation of the Cl 1604 Supercluster at z~0.9
We present spectroscopic confirmation of the Cl 1604 supercluster at z~0.9.
Originally detected as two individual clusters, Cl 1604+4304 at z = 0.90 and Cl
1604+4321 at z = 0.92, which are closely separated in both redshift and sky
position, subsequent imaging revealed a complex of red galaxies bridging the
two clusters, suggesting that the region contained a large scale structure. We
have carried out extensive multi-object spectroscopy, which, combined with
previous measurements, provides ~600 redshifts in this area, including 230
confirmed supercluster members. We detect two additional clusters that are part
of this structure, Cl 1604+4314 at z = 0.87 and Cl 1604+4316 at z = 0.94. All
four have properties typical of local clusters, with line-of-sight velocity
dispersions between 489 and 962 km/s. The structure is significantly extended
in redshift space, which, if interpreted as a true elongation in real space,
implies a depth of 93 Mpc. We examine the spatial and redshift distribution of
the supercluster members.Comment: Accepted to ApJ Letters. 4 pages with 3 figure
The Tolman Surface Brightness Test for the Reality of the Expansion. III. HST Profile and Surface Brightness Data for Early-Type Galaxies in Three High-Redshift Clusters
Photometric data for 34 early-type galaxies in the three high-redshift
clusters Cl 1324+3011 (z = 0.76), Cl 1604+4304 (z = 0.90), and Cl 1604+4321 (z
= 0.92), observed with the Hubble Space Telescope (HST) and with the Keck
10-meter telescopes by Oke, Postman & Lubin, are analyzed to obtain the
photometric parameters of mean surface brightness, magnitudes for the growth
curves, and angular radii at various Petrosian eta radii. The angular radii at
eta = 1.3 mag for the program galaxies are all larger than 0.24". All of the
galaxies are well resolved at this angular size using HST whose point-spread
function is 0.05", half width at half maximum. The data for each of the program
galaxies are listed at eta = 1.0, 1.3, 1.5, 1.7, and 2.0 mag. They are
corrected by color equations and K terms for the effects of redshift to the
rest-frame Cape/Cousins I for Cl 1324+3011 and Cl 1604+4304 and R for Cl
1604+4321. The K corrections are calculated from synthetic spectral energy
distributions derived from evolving stellar population models of Bruzual &
Charlot which have been fitted to the observed broad-band (BVRI) AB magnitudes
of each program galaxy. The listed photometric data are independent of all
cosmological parameters. They are the source data for the Tolman surface
brightness test made in Paper IV.Comment: 17 pages, 7 figures; accepted for publication in the Astronomical
Journa
Angular Power Spectrum of the Microwave Background Anisotropy seen by the COBE Differential Microwave Radiometer
The angular power spectrum estimator developed by Peebles (1973) and Hauser &
Peebles (1973) has been modified and applied to the 2 year maps produced by the
COBE DMR. The power spectrum of the real sky has been compared to the power
spectra of a large number of simulated random skies produced with noise equal
to the observed noise and primordial density fluctuation power spectra of power
law form, with . Within the limited range of spatial scales
covered by the COBE DMR, corresponding to spherical harmonic indices 3 \leq
\ell \lsim 30, the best fitting value of the spectral index is with the Harrison-Zeldovich value approximately
0.5 below the best fit. For 3 \leq \ell \lsim 19, the best fit is . Comparing the COBE DMR at small to
the at from degree scale anisotropy experiments
gives a smaller range of acceptable spectral indices which includes .Comment: 22 pages of LaTex using aaspp.sty and epsf.sty with appended
Postscript figures, COBE Preprint 94-0
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
A new Tolman test of a cosmic distance duality relation at 21 cm
Under certain general conditions in an expanding universe, the luminosity
distance (d_L) and angular diameter distance (d_A) are connected by the
Etherington relation as d_L = d_A (1 + z)^2. The Tolman test suggests the use
of objects of known surface brightness, to test this relation. In this letter,
we propose the use of redshifted 21 cm signal from disk galaxies, where neutral
hydrogen (HI) masses are seen to be almost linearly correlated with surface
area, to conduct a new Tolman test. We construct simulated catalogs of
galaxies, with the observed size-luminosity relation and realistic redshift
evolution of HI mass functions, likely to be detected with the planned Square
Kilometer Array (SKA). We demonstrate that these observations may soon provide
the best implementation of the Tolman test to detect any violation of the
Etherington relation.Comment: 4 pages, 2 figures, 1 table, v2: published versio
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