1,209 research outputs found
Galaxy Luminosity Functions from Deep Spectroscopic Samples of Rich Clusters
Using a new spectroscopic sample and methods accounting for spectroscopic
sampling fractions that vary in magnitude and surface brightness, we present
R-band galaxy luminosity functions (GLFs) for six nearby galaxy clusters with
redshifts 4000 < cz < 20000 km/s and velocity dispersions 700 < sigma < 1250
km/s. In the case of the nearest cluster, Abell 1060, our sample extends to
M_R=-14 (7 magnitudes below M*), making this the deepest spectroscopic
determination of the cluster GLF to date. Our methods also yield composite GLFs
for cluster and field galaxies to M_R=-17 (M*+4), including the GLFs of
subsamples of star forming and quiescent galaxies. The composite GLFs are
consistent with Schechter functions (M*_R=-21.14^{+0.17}_{-0.17},
alpha=-1.21^{+0.08}_{-0.07} for the clusters, M*_R=-21.15^{+0.16}_{-0.16},
alpha=-1.28^{+0.12}_{-0.11} for the field). All six cluster samples are
individually consistent with the composite GLF down to their respective
absolute magnitude limits, but the GLF of the quiescent population in clusters
is not universal. There are also significant variations in the GLF of quiescent
galaxies between the field and clusters that can be described as a steepening
of the faint end slope. The overall GLF in clusters is consistent with that of
field galaxies, except for the most luminous tip, which is enhanced in clusters
versus the field. The star formation properties of giant galaxies are more
strongly correlated with the environment than those of fainter galaxies.Comment: 53 pages, 8 figures, 1 ASCII table; accepted for publication in Ap
A long-term survivor of Bland-White-Garland syndrome with systemic collateral supply: A case report and review of the literature
BACKGROUND: land-White-Garland syndrome (anomalous origin of the left coronary artery from the pulmonary artery) is a rare disease which may result in myocardial infarction, congestive heart failure and sometimes death during the early infantile period. Case presentation: A succesfully treated case of a 45-year-old mother of 2 children with Bland-White-Garland syndrome and concomitant severe mitral regurgitation is presented. Subsequent therapy consisted of ligation of the anomalous origin of the left coronary artery, anastomosis of the left internal mammary artery to the left anterior descending branch and mitral valve replacement. Continuous blood flow from the left coronary artery ostium during extracorporeal circulation and aorta clamping suggested systemic collateral supply. Conclusions: Recognition and diagnosis of Bland-White-Garland syndrome is important due to its potentially life-threatening complications
Primary mediastinal hemangiopericytoma
BACKGROUND: Hemangiopericytoma is a rare mesenchymal neoplasm, accounting for about 1% of vascular tumors The tumor occurs most commonly in the skin, subcutaneous soft tissues, muscles of the extremities, retroperitoneum but rarely in the lung, trachea or mediastinum. CASE PRESENTATION: A rare case of primary mediastinal hemangiopericytoma is presented. A 72-year-old woman was treated by complete surgical resection of the tumor. Details of the clinical and radiographic feature are presented. The patient's postoperative course was uneventful with no evidence of recurrence 9 months after the operation. CONCLUSION: Hemangiopericytoma is an uncommon, potentially malignant tumor originating from pericytes in the small vessels and surgical radical excision is the treatment of choice, although the criteria for determining the area of resection have not been established. International literature has demonstrated that recurrent disease usually occurs within 2 years and therefore a long-term careful follow-up is required
The U-band Galaxy Luminosity Function of Nearby Clusters
Despite the great potential of the U-band galaxy luminosity function (GLF) to
constrain the history of star formation in clusters, to clarify the question of
variations of the GLF across filter bands, to provide a baseline for
comparisons to high-redshift studies of the cluster GLF, and to estimate the
contribution of bound systems of galaxies to the extragalactic near-UV
background, determinations have so far been hampered by the generally low
efficiency of detectors in the U-band and by the difficulty of constructing
both deep and wide surveys. In this paper, we present U-band GLFs of three
nearby, rich clusters to a limit of M_U=-17.5 (M*_U+2). Our analysis is based
on a combination of separate spectroscopic and R-band and U-band photometric
surveys. For this purpose, we have developed a new maximum-likelihood algorithm
for calculating the luminosity function that is particularly useful for
reconstructing the galaxy distribution function in multi-dimensional spaces
(e.g., the number of galaxies as a simultaneous function of luminosity in
different filter bands, surface brightness, star formation rate, morphology,
etc.), because it requires no prior assumptions as to the shape of the
distribution function.
The composite luminosity function can be described by a Schechter function
with characteristic magnitude M*_U=-19.82+/-0.27 and faint end slope
alpha_U=-1.09+/-0.18. The total U-band GLF is slightly steeper than the R-band
GLF, indicating that cluster galaxies are bluer at fainter magnitudes.
Quiescent galaxies dominate the cumulative U-band flux for M_U<-14. The
contribution of galaxies in nearby clusters to the U-band extragalactic
background is <1% Gyr^-1 for clusters of masses ~3*10^14 to 2*10^15 M_solar.Comment: 44 pages, 11 figures, accepted for publication in Ap
2-D Radiative Transfer in Protostellar Envelopes: II. An Evolutionary Sequence
We present model spectral energy distributions, colors, polarization, and
images for an evolutionary sequence of a low-mass protostar from the early
collapse stage (Class 0) to the remnant disk stage (Class III). We find a
substantial overlap in colors and SEDs between protostars embedded in envelopes
(Class 0-I) and T Tauri disks (Class II), especially at mid-IR wavelengths.
Edge-on Class I-II sources show double-peaked spectral energy distributions,
with a short-wavelength hump due to scattered light and the long-wavelength
hump due to thermal emission. These are the bluest sources in mid-IR
color-color diagrams.
Since Class 0 and I sources are diffuse, the size of the aperture over which
fluxes are integrated has a substantial effect on the computed colors, with
larger aperture results showing significantly bluer colors. This causes overlap
in color-color diagrams between all evolutionary states, especially in the
mid-IR. However the near-IR polarization of the Class 0 sources is much higher
than the Class I-II sources, providing a means to separate these evolutionary
states.
We varied the grain properties in the circumstellar envelope, allowing for
larger grains in the disk midplane and smaller in the envelope. We find that
grain growth in disks of Class I sources can be detected at wavelengths greater
than 100 m.
Our image calculations predict that the diffuse emission from edge-on Class I
and II sources should be detectable in the mid-IR with the Space Infrared
Telescope Facility (SIRTF) in nearby star forming regions (out to several
hundred parsecs).Comment: A version with high-resolution images is available at
http://www.astro.wisc.edu/glimpse/glimpsepubs.htm
Testing the Hubble Law with the IRAS 1.2 Jy Redshift Survey
We test and reject the claim of Segal et al. (1993) that the correlation of
redshifts and flux densities in a complete sample of IRAS galaxies favors a
quadratic redshift-distance relation over the linear Hubble law. This is done,
in effect, by treating the entire galaxy luminosity function as derived from
the 60 micron 1.2 Jy IRAS redshift survey of Fisher et al. (1995) as a distance
indicator; equivalently, we compare the flux density distribution of galaxies
as a function of redshift with predictions under different redshift-distance
cosmologies, under the assumption of a universal luminosity function. This
method does not assume a uniform distribution of galaxies in space. We find
that this test has rather weak discriminatory power, as argued by Petrosian
(1993), and the differences between models are not as stark as one might expect
a priori. Even so, we find that the Hubble law is indeed more strongly
supported by the analysis than is the quadratic redshift-distance relation. We
identify a bias in the the Segal et al. determination of the luminosity
function, which could lead one to mistakenly favor the quadratic
redshift-distance law. We also present several complementary analyses of the
density field of the sample; the galaxy density field is found to be close to
homogeneous on large scales if the Hubble law is assumed, while this is not the
case with the quadratic redshift-distance relation.Comment: 27 pages Latex (w/figures), ApJ, in press. Uses AAS macros,
postscript also available at
http://www.astro.princeton.edu/~library/preprints/pop682.ps.g
Galaxy Clustering and Large-Scale Structure from z = 0.2 to z = 0.5 in Two Norris Redshift Surveys
(abridged) We present a study of the nature and evolution of large-scale
structure based on two independent redshift surveys of faint field galaxies
conducted with the 176-fiber Norris Spectrograph on the Palomar 200-inch
telescope. The two surveys together sparsely cover ~20 sq. degrees and contain
835 r < 21 mag galaxies with redshifts 0.2 < z < 0.5. Both surveys have a
median redshift of z = 0.30. In order to obtain a rough estimate of the cosmic
variance, we analyze the two surveys independently. We measure the comoving
correlation length to be 3.70 +/- 0.13 h^-1 Mpc at z = 0.30 with a power-law
slope gamma = 1.77 +/- 0.05. Dividing the sample into low (0.2 < z < 0.3) and
high (0.32 < z < 0.5) redshift intervals, we see no evidence for a change in
the comoving correlation length over the redshift range 0.2 < z < 0.5. Similar
to the well-established results in the local universe, we find that
intrinsically bright galaxies are more strongly clustered than intrinsically
faint galaxies and that galaxies with little ongoing star formation, as judged
from the rest-frame equivalent width of the [OII]3727, are more strongly
clustered than galaxies with significant ongoing star formation. The rest-frame
pairwise velocity dispersion of the sample is 326^+67_-52 km s^-1, ~25% lower
than typical values measured locally. The appearance of the galaxy
distribution, particularly in the more densely sampled Abell 104 field, is
quite striking. The pattern of sheets and voids which has been observed locally
continues at least to z ~ 0.5. A friends-of-friends analysis of the galaxy
distribution supports the visual impression that > 90% of all galaxies at z <
0.5 are part of larger structures with overdensities of > 5.Comment: 40 pages including 26 Postscript figures; revised version to match
version accepted by Ap
Cosmological Density and Power Spectrum from Peculiar Velocities: Nonlinear Corrections and PCA
We allow for nonlinear effects in the likelihood analysis of galaxy peculiar
velocities, and obtain ~35%-lower values for the cosmological density parameter
Om and the amplitude of mass-density fluctuations. The power spectrum in the
linear regime is assumed to be a flat LCDM model (h=0.65, n=1, COBE) with only
Om as a free parameter. Since the likelihood is driven by the nonlinear regime,
we "break" the power spectrum at k_b=0.2 h/Mpc and fit a power law at k>k_b.
This allows for independent matching of the nonlinear behavior and an unbiased
fit in the linear regime. The analysis assumes Gaussian fluctuations and
errors, and a linear relation between velocity and density. Tests using proper
mock catalogs demonstrate a reduced bias and a better fit. We find for the
Mark3 and SFI data Om_m=0.32+-0.06 and 0.37+-0.09 respectively, with
sigma_8*Om^0.6 = 0.49+-0.06 and 0.63+-0.08, in agreement with constraints from
other data. The quoted 90% errors include cosmic variance. The improvement in
likelihood due to the nonlinear correction is very significant for Mark3 and
moderately so for SFI. When allowing deviations from LCDM, we find an
indication for a wiggle in the power spectrum: an excess near k=0.05 and a
deficiency at k=0.1 (cold flow). This may be related to the wiggle seen in the
power spectrum from redshift surveys and the second peak in the CMB anisotropy.
A chi^2 test applied to modes of a Principal Component Analysis (PCA) shows
that the nonlinear procedure improves the goodness of fit and reduces a spatial
gradient of concern in the linear analysis. The PCA allows addressing spatial
features of the data and fine-tuning the theoretical and error models. It shows
that the models used are appropriate for the cosmological parameter estimation
performed. We address the potential for optimal data compression using PCA.Comment: 18 pages, LaTex, uses emulateapj.sty, ApJ in press (August 10, 2001),
improvements to text and figures, updated reference
Diffraction-Limited Imaging and Photometry of NGC 1068
The nearby Seyfert 2 Galaxy NGC 1068 was observed with speckle imaging
techniques in the near-infrared H-band (1.6 microns) at the Hale 200-inch
Telescope and K-band (2.2 microns) at the 10 m Keck I Telescope.
Images with diffraction limited or near-diffraction limited resolutions of
0.''05 - 0.''1 were obtained and used to search for structure in the nuclear
region. Images of the nucleus of NGC 1068 reveal an extended region of emission
which accounts for nearly 50% of the nuclear flux at K-band. This region
extends 10 pc on either side of an unresolved point source nucleus which is at
most, 0.''02 or 1.4 pc in size. Both the point source and the newly imaged
extended emission are very red, with identical H-K colors corresponding to a
color temperature of 800 K. While the point source is of a size to be
consistent with grains in thermal equilibrium with the nuclear source, the
extended emission is not. It must consist either of nuclear emission which has
been reflected off an extended dusty disk or of small grains raised to
transiently high temperatures by reflected UV photons.Comment: accepted to AJ, AAS LaTeX and epsfig, 22 pages incl. 5 ps figure
Chain Galaxies are Edge-On Low Surface Brightness Galaxies
Deep HST WFPC2 images have revealed a population of very narrow blue galaxies
which Cowie et al. (1996) have interpreted as being a new morphological class
of intrinsically linear star forming galaxies at . We show that the
same population exists in large numbers at low redshifts (z=0.03) and are
actually the edge-on manifestation of low surface brightness disk galaxies.Comment: 18 pages + 3 pages of figures. Uuencoded, gzipped, tar file of 1
latex file, 5 figures, and 2 latex style files. To appear in the
Astrophysical Journal Letter
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