106 research outputs found
Cosmic shear statistics in the Suprime-Cam 2.1 sq deg field: Constraints on Omega_m and sigma_8
We present measurements of the cosmic shear correlation in the shapes of
galaxies in the Suprime-Cam 2.1 deg^2 R_c-band imaging data. As an estimator of
the shear correlation originated from the gravitational lensing, we adopt the
aperture mass variance. We detect a non-zero E mode variance on scales between
2 and 40arcmin. We also detect a small but non-zero B mode variance on scales
larger than 5arcmin. We compare the measured E mode variance to the model
predictions in CDM cosmologies using maximum likelihood analysis. A
four-dimensional space is explored, which examines sigma_8, Omega_m, Gamma and
zs (a mean redshift of galaxies). We include three possible sources of error:
statistical noise, the cosmic variance estimated using numerical experiments,
and a residual systematic effect estimated from the B mode variance. We derive
joint constraints on two parameters by marginalizing over the two remaining
parameters. We obtain an upper limit of Gamma0.9 (68% confidence).
For a prior Gamma\in[0.1,0.4] and zs\in[0.6,1.4], we find
sigma_8=(0.50_{-0.16}^{+0.35})Omega_m^{-0.37} for flat cosmologies and
sigma_8=(0.51_{-0.16}^{+0.29})Omega_m^{-0.34}$ for open cosmologies (95%
confidence). If we take the currently popular LCDM model, we obtain a
one-dimensional confidence interval on sigma_8 for the 95.4% level,
0.62<\sigma_8<1.32 for zs\in[0.6,1.4]. Information on the redshift distribution
of galaxies is key to obtaining a correct cosmological constraint. An
independent constraint on Gamma from other observations is useful to tighten
the constraint.Comment: 12 pages, 12 figures, accepted for publication in Ap
The Extraordinary `Superthin' Spiral Galaxy UGC7321. I. Disk Color Gradients and Global Properties from Multiwavelength Observations
We present B- and R-band imaging and photometry, H-alpha narrow-band imaging,
NIR H-band imaging, and HI 21-cm spectroscopy of the nearby Sd spiral galaxy
UGC7321. UGC7321 exhibits a remarkably thin stellar disk with no bulge
component. The galaxy has a very diffuse, low surface brightness disk, which
appears to suffer little internal extinction in spite of its edge-on geometry.
The UGC7321 disk shows significant B-R color gradients in both the radial and
vertical directions. These color gradients cannot be explained solely by dust
and are indicative of changes in the mix of stellar ages and/or metallicity as
a function of both radius and height above the galaxy plane. The outer regions
of the UGC7321 disk are too blue to be explained by low metallicity alone
(B-R<0.6), and must be relatively young. However, the galaxy also contains
stellar populations with B-R>1.1, indicating it is not a young or
recently-formed galaxy. The disk of UGC7321 is not a simple exponential, but
exhibits a light excess at small radii, as well as distinct surface brightness
zones. Together the properties of UGC7321 imply that it is an under-evolved
galaxy in both a dynamical and in a star-formation sense. (Abridged)Comment: Accepted to the Astronomical Journal; 28 pages, 1 table and 21
figures (GIF and postscript
Detection of a Thick Disk in the edge-on Low Surface Brightness Galaxy ESO 342-G017: I. VLT Photometry in V and R Bands
We report the detection of a thick disk in the edge-on, low surface
brightness (LSB), late-type spiral ESO 342-G017, based on ultra-deep images in
the V and R bands obtained with the VLT Test Camera during Science Verification
on UT1. All steps in the reduction procedure are fully described, which,
together with an extensive analysis of systematic and statistic uncertainties,
has resulted in surface brightness photometry that is reliable for the
detection of faint extended structure to a level of V = 27.5 and R = 28.5
mag/square arcsec. The faint light apparent in these deep images is
well-modeled by a thick exponential disk with an intrinsic scale height about
2.5 times that of the thin disk, and a comparable or somewhat larger scale
length. Deprojection including the effects of inclination and convolution with
the PSF allow us to estimate that the thick disk contributes 20-40% of the
total (old) stellar disk luminosity of ESO 342-G017. To our knowledge, this is
the first detection of a thick disk in an LSB galaxy, which are generally
thought to be rather unevolved compared to higher surface brightness galaxies.Comment: Accepted for publication in Astronomy & Astrophysics; 18 pages, 12
figure
The u'g'r'i'z' Standard Star Network
We present the 158 standard stars that define the u'g'r'i'z' photometric
system. These stars form the basis for the photometric calibration of the Sloan
Digital Sky Survey (SDSS). The defining instrument system and filters, the
observing process, the reduction techniques, and the software used to create
the stellar network are all described. We briefly discuss the history of the
star selection process, the derivation of a set of transformation equations for
the UBVRcIc system, and plans for future work.Comment: References to URLs in paper have been updated to reflect moved
website. Accepted by AJ. 50 pages, including 20 pages of text, 9 tables, and
15 figures. Plain ASCII text versions of Tables 8 and 9 can be found at
http://home.fnal.gov/~dtucker/ugriz/index.html (new URL
Statistical Properties of Bright Galaxies in the SDSS Photometric System
We investigate the photometric properties of 456 bright galaxies using
imaging data recorded during the commissioning phase of the Sloan Digital Sky
Survey (SDSS). Morphological classification is carried out by correlating
results of several human classifiers. Our purpose is to examine the statistical
properties of color indices, scale lengths, and concentration indices as
functions of morphology for the SDSS photometric system. We find that ,
, and colors of SDSS galaxies match well with those expected
from the synthetic calculation of spectroscopic energy distribution of template
galaxies and with those transformed from color data of nearby
galaxies. The agreement is somewhat poor, however, for color band with
a discrepancy of mag. With the aid of the relation between surface
brightness and radius obtained by Kent (1985), we estimate the averages of the
effective radius of early type galaxies and the scale length of exponential
disks both to be 2.6 kpc for galaxies. We find that the half light radius
of galaxies depends slightly on the color bands, consistent with the expected
distribution of star-forming regions for late type galaxies and with the known
color gradient for early type galaxies. We also show that the (inverse)
concentration index, defined by the ratio of the half light Petrosian radius to
the 90% light Petrosian radius, correlates tightly with the morphological type;
this index allows us to classify galaxies into early (E/S0) and late (spiral
and irregular) types, allowing for a 15-20% contamination from the opposite
class compared with eye-classified morphology.Comment: 18 pages, LaTeX (aaspp4), 16 PostScript figures. Accepted for
publication in AJ (September issue
The Updated Zwicky Catalog (UZC)
The Zwicky Catalog of galaxies (ZC), with m_Zw<=15.5mag, has been the basis
for the Center for Astrophysics (CfA) redshift surveys. To date, analyses of
the ZC and redshift surveys based on it have relied on heterogeneous sets of
galaxy coordinates and redshifts. Here we correct some of the inadequacies of
previous catalogs by providing: (1) coordinates with <~2 arcsec errors for all
of the Nuzc catalog galaxies, (2) homogeneously estimated redshifts for the
majority (98%) of the data taken at the CfA (14,632 spectra), and (3) an
estimate of the remaining "blunder" rate for both the CfA redshifts and for
those compiled from the literature. For the reanalyzed CfA data we include a
calibrated, uniformly determined error and an indication of the presence of
emission lines in each spectrum. We provide redshifts for 7,257 galaxies in the
CfA2 redshift survey not previously published; for another 5,625 CfA redshifts
we list the remeasured or uniformly re-reduced value. Among our new
measurements, Nmul are members of UZC "multiplets" associated with the original
Zwicky catalog position in the coordinate range where the catalog is 98%
complete. These multiplets provide new candidates for examination of tidal
interactions among galaxies. All of the new redshifts correspond to UZC
galaxies with properties recorded in the CfA redshift compilation known as
ZCAT. About 1,000 of our new measurements were motivated either by inadequate
signal-to-noise in the original spectrum or by an ambiguous identification of
the galaxy associated with a ZCAT redshift. The redshift catalog we include
here is ~96% complete to m_Zw<=15.5, and ~98% complete (12,925 galaxies out of
a total of 13,150) for the RA(1950) ranges [20h--4h] and [8h--17h] and
DEC(1950) range [-2.5d--50d]. (abridged)Comment: 34 pp, 7 figs, PASP 1999, 111, 43
Color separation of galaxy types in the Sloan Digital Sky Survey imaging data
We study the optical colors of 147,920 galaxies brighter than g* = 21, observed in five bands by the Sloan Digital Sky Survey (SDSS) over similar to 100 deg(2) of high Galactic latitude sky along the celestial equator. The distribution of galaxies in the g*-r* versus u*-g* color-color diagram is strongly bimodal, with an optimal color separator of u*-r* = 2.22. We use visual morphology and spectral classification of subsamples of 287 and 500 galaxies, respectively, to show that the two peaks correspond roughly to early- (E, S0, and Sa) and late-type (Sb, Sc, and Irr) galaxies, as expected from their different stellar populations. We also find that the colors of galaxies are correlated with their radial profiles, as measured by the concentration index and by the likelihoods of exponential and de Vaucouleurs' profile fits. While it is well known that late-type galaxies are bluer than early-type galaxies, this is the first detection of a local minimum in their color distribution. In all SDSS bands, the counts versus apparent magnitude relations for the two color types are significantly different and demonstrate that the fraction of blue galaxies increases toward the faint end
Planetary Nebulae as Standard Candles. XII. Connecting the Population I and Population II Distance Scales
We report the results of [OIII] lambda 5007 surveys for planetary nebulae
(PNe) in NGC 2403, 3115, 3351, 3627, 4258, and 5866. Using on-band/off-band
[OIII] and H-alpha images, we identify samples of PNe in these galaxies and
derive distances using the planetary nebula luminosity function (PNLF). We then
combine these measurements with previous data to compare the PNLF, Cepheid, and
surface brightness fluctuation (SBF) distance scales. We use a sample of 13
galaxies to show that the absolute magnitude of the PNLF cutoff is fainter in
small, low-metallicity systems, but the trend is well modelled theoretically.
When this dependence is removed, the scatter between the Cepheid and PNLF
distances becomes consistent with the internal errors of the methods and
independent of any obvious galaxy parameter. We then use the data to
recalibrate the zero point of the PNLF distance scale. We use a sample of 28
galaxies to show that the scatter between the PNLF and SBF distance
measurements agrees with that predicted from the techniques' internal errors,
and that no systematic trend exists between the distance residuals and stellar
population. However, we find the PNLF and SBF methods have a significant scale
offset: Cepheid-calibrated PNLF distances are, on average, ~0.3 mag smaller
than Cepheid-calibrated SBF distances. We discuss the possible causes of this
offset, and suggest that internal extinction in the bulges of the SBF
calibration galaxies is the principle cause of the discrepancy. If this is
correct, the SBF-based Hubble Constant must be increased by ~7%. We use our
distance to NGC 4258 to argue that the short distance scale to the LMC is
correct, and that the global Hubble Constant inferred from the HST Key Project
should be increased by 8 +/- 3% to H_0 = 78 +/- 7 km/s/Mpc. (abridged)Comment: 38 pages, 9 figures included, accepted for publication in the
Astrophysical Journa
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