29 research outputs found
Spectral Classification of Galaxies Along the Hubble Sequence
We develop a straightforward and quantitative two-step method for
spectroscopically classifying galaxies from the low signal-to-noise (S/N)
optical spectra typical of galaxy redshift surveys. First, using \chi^2-fitting
of characteristic templates to the object spectrum, we determine the relative
contributions of the old stellar component, the young stellar component, and
various emission line spectra. Then, we classify the galaxy by comparing the
relative strengths of the components with those of galaxies of known
morphological type. In particular, we use the ratios of (1) the emission line
to absorption line contribution, (2) the young to old stellar contribution, and
(3) the oxygen to hydrogen emission line contribution. We calibrate and test
the method using published morphological types for 32 galaxies from the
long-slit spectroscopic survey of Kennicutt (1992) and for 304 galaxies from a
fiber spectroscopic survey of nearby galaxy clusters. From an analysis of a
sample of long-slit spectra of spiral galaxies in two galaxy clusters, we
conclude that the majority of the galaxies observed in the fiber survey are
sufficiently distant that their spectral classification is unaffected by
aperture bias. Our spectral classification is consistent with the morphological
classification to within one type (e.g. E to S0 or Sa to Sb) for \gtsim 80% of
the galaxies. Disagreements between the spectral and morphological
classifications of the remaining galaxies reflect a divergence in the
correspondence between spectral and morphological types, rather than a problem
with the data or method.Comment: 13 pages, uuencoded gzip'ed ps-file that includes 8 of 9 Figures,
accepted for publication in A
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 LCO/Palomar 10,000 km/sec Cluster Survey. I. Properties of the Tully-Fisher Relation
The first results from a Tully-Fisher (TF) survey of cluster galaxies are
presented. The galaxies are drawn from fifteen Abell clusters that lie in the
redshift range 9000-12,000 km/sec and are distributed uniformly around the
celestial sky. The data set consists of R-band CCD photometry and long- slit
H-alpha spectroscopy. The rotation curves (RCs) are characterized by a turnover
radius (r_t) and an asymptotic velocity v_a, while the surface brightness
profiles are characterized in terms of an effective exponential surface
brightness I_e and a scale length r_e. The TF scatter is minimized when the
rotation velocity is measured at 2.0 +/- 0.2 r_e; a significantly larger
scatter results when the rotation velocity is measured at > 3 or < 1.5 scale
lengths. This effect demonstrates that RCs do not have a universal form, as has
been suggested by Persic, Salucci, and Stel. In contrast to previous studies, a
modest but statistically significant surface-brightness dependence of the TF
relation is found, log v = const + 0.28*log L + 0.14*log I_e. This indicates a
stronger parallel between the TF relation and the FP relations of elliptical
galaxies than has previously been recognized. Future papers in this series will
consider the implications of this cluster sample for deviations from Hubble
flow on 100-200 Mpc scales.Comment: 35 pages, 8 figures, uses aaspp4.sty. Submitted to ApJ. Also
available at http://astro.stanford.edu/jeff
A Determination of the Hubble Constant from Cepheid Distances and a Model of the Local Peculiar Velocity Field
We present a measurement of the Hubble Constant based on Cepheid distances to
27 galaxies within 20 Mpc. We take the Cepheid data from published measurements
by the Hubble Telescope Key Project on the Distance Scale (H0KP). We calibrate
the Cepheid Period-Luminosity (PL) relation with data from over 700 Cepheids in
the LMC obtained by the OGLE collaboration; we assume an LMC distance modulus
of 18.50 mag (d=50.1 kpc). Using this PL calibration we obtain new distances to
the H0KP galaxies. We correct the redshifts of these galaxies for peculiar
velocities using two distinct velocity field models: the phenomenological model
of Tonry et al. and a model based on the IRAS density field and linear
gravitational instability theory. We combine the Cepheid distances with the
corrected redshifts for the 27 galaxies to derive H_0, the Hubble constant. The
results are H_0 = 85 +/- 5 km/s/Mpc (random error) at 95% confidence when the
IRAS model is used, and 92 +/- 5 km/s/Mpc when the phenomenological model is
used. The IRAS model is a better fit to the data and the Hubble constant it
returns is more reliable. Systematic error stems mainly from LMC distance
uncertainty which is not directly addressed by this paper. Our value of H_0 is
significantly larger than that quoted by the H0KP, H_0 = 71 +/- 6 km/s/Mpc.
Cepheid recalibration explains ~30% of this difference, velocity field analysis
accounts for ~70%. We discuss in detail possible reasons for this discrepancy
and future study needed to resolve it.Comment: 33 pages, 8 embedded figures. New table, 5 new references, text
revision
Homogeneous Velocity-Distance Data for Peculiar Velocity Analysis. I. Calibration of Cluster Samples
We have combined five Tully-Fisher (TF) redshift-distance samples for
peculiar velocity analysis: the cluster data of Han, Mould and coworkers
(1991-93, HM) and Willick (1991, W91CL), and the field data of Aaronson et al.
(1992), Willick (1991), Courteau & Faber (1992), and Mathewson et al. (1992),
totaling over 3000 spiral galaxies. We treat the cluster data in this paper,
which is the first of a series; in Paper II we treat the field TF samples.
These data are to be combined with elliptical data (e.g., Faber et al. 1989) to
form the MARK III CATALOG OF GALAXY PECULIAR VELOCITIES, which we will present
in Paper III. The catalog will be used as input for POTENT reconstruction of
velocity and density fields, described in later papers, as well as for
alternative velocity analyses. Our main goal in Papers I & II is to place the
TF data onto a self-consistent system by (i) applying a uniform set of
corrections to the raw observables, (ii) determining the TF slopes and scatters
separately for each sample, and (iii) adjusting the TF zeropoints to ensure
mutually consistent distances. The global zeropoint is set by the HM sample,
chosen because of its depth and uniformity on the sky and its substantial
overlap with each of the other samples. In this paper, we calibrate the
``forward'' and ``inverse'' TF relations for HM and W91CL. We study the
selection criteria for these samples and correct for the resultant statistical
biases. The bias corrections are validated by comparing forward and inverse
cluster distances. We find that many sample clusters are better modeled as
``expanding'' than relaxed, which significantly affects the TF calibrations.
Proper corrections for internal extinction are derived self-consistently from
the data.Comment: 42 Pages, uuencoded PostScript. Submitted to ApJ. 22 Figures not
included, can be obtained via ftp, contact [email protected]
Constraints on Primordial Nongaussiantiy from the High-Redshift Cluster MS1054--03
The implications of the massive, X-ray selected cluster of galaxies
MS1054--03 at are discussed in light of the hypothesis that the
primordial density fluctuations may be nongaussian. We generalize the
Press-Schechter (PS) formalism to the nongaussian case, and calculate the
likelihood that a cluster as massive as MS1054 would appear in the EMSS. The
probability of finding an MS1054-like cluster depends only on \omegam and the
extent of primordial nongaussianity. We quantify the latter by adopting a
specific functional form for the PDF, denoted which tends to
Gaussianity for and show how is related to the more
familiar statistic the probability of fluctuations for a
given PDF relative to a Gaussian. We find that Gaussian initial density
fluctuations are consistent with the data on MS1054 only if \omegam\simlt
0.2. For \omegam\ge 0.25 a significant degree of nongaussianity is required,
unless the mass of MS1054 has been substantially overestimated by X-ray and
weak lensing data. The required amount of nongaussianity is a rapidly
increasing function of \omegam for 0.25 \le \omegam \le 0.45, with (T \simgt 7) at the upper end of this range. For a fiducial
\omegam=0.3, \omegal=0.7 universe, favored by several lines of evidence we
obtain an upper limit corresponding to a This
finding is consistent with the conclusions of Koyama, Soda, & Taruya (1999),
who applied the generalized PS formalism to low (z\simlt 0.1) and
intermediate (z\simlt 0.6) redshift cluster data sets.Comment: 15 pages, 11 figures, submitted to the Astrophysical Journal, uses
emulateapj.st
Maximum-Likelihood Comparisons of Tully-Fisher and Redshift Data. II. Results from an Expanded Sample
This is the second in a series of papers in which we compare Tully-Fisher
(TF) data from the Mark III Catalog with predicted peculiar velocities based on
the IRAS galaxy redshift survey and gravitational instability theory, using a
rigorous maximum likelihood method called VELMOD. In Paper I (Willick et al.
1997b), we we applied the method to a km/sec, 838-galaxy TF
sample and found where
and is the linear biasing parameter for IRAS galaxies. In this paper we
increase the redshift limit to km/sec, thereby enlarging the
sample to 1876 galaxies. The expanded sample now includes the W91PP and CF
subsamples of the Mark III catalog, in addition to the A82 and MAT subsamples
already considered in Paper I.
We implement VELMOD using both the forward and inverse forms of the TF
relation, and allow for a more general form of the quadrupole velocity residual
detected in Paper I. We find (1-sigma error) at 300
km/sec smoothing of the IRAS-predicted velocity field. The fit residuals are
spatially incoherent for indicating that the IRAS plus
quadrupole velocity field is a good fit to the TF data. If we eliminate the
quadrupole we obtain a worse fit, but a similar value for of Changing the IRAS smoothing scale to 500 km/sec has almost no effect on
the best We find evidence for a density-dependence of the
small-scale velocity dispersion,
km/sec.Comment: Latex, 37 pages, 15 figures, uses modified apjpt4.st