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Search Results: 1 - 10 of 498738 matches for " Michael A. Strauss "
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The Large-Scale Velocity Field
Michael A. Strauss
Physics , 1996,
Abstract: I summarize both observational and theoretical developments in the last few years in measuring and understanding the large-scale velocity field of galaxies, with special attention to the bulk flow, or average peculiar velocity, within spheres centered on the Local Group.
Recent Advances in Redshift Surveys of the Local Universe
Michael A. Strauss
Physics , 1996,
Abstract: I review progress in the past few years in studying the large-scale structure of the universe through redshift surveys of galaxies. Of the many statistical methods used to describe the galaxy distribution, I concentrate here on the power spectrum, and go into some detail about the factors which complicate (and make interesting!) its interpretation, such as redshift space distortions, non-linear effects, and the relative bias of galaxies and dark matter. I also discuss two large redshift surveys which are just starting, the Sloan Digital Sky Survey, and the Two Degree Field Redshift Survey, which promise to increase the number of redshifts measured of galaxies in uniform surveys by more than an order of magnitude.
Large-Scale Structure in the Distribution of Galaxies as a Probe of Cosmological Models
Michael A. Strauss
Physics , 1998,
Abstract: The last 20 years have seen an explosion in our understanding of the large-scale distribution and motions of galaxies in the nearby universe. The field has moved from a largely qualitative, morphological description of the structures seen in the galaxy distribution, to a rich and increasingly rigorous statistical description, which allows us to constrain cosmological models. New surveys just now getting underway will be unprecedented in their uniformity and volume surveyed. The study of the evolution of large-scale structure with time is now becoming feasible.
Questions and Controversies in the Measurement and Interpretation of Large-Scale Flows
Michael A. Strauss
Physics , 1999,
Abstract: This introductory talk to the 1999 Victoria Conference on Large-Scale Flows will present the ``big questions'' which will be discussed in the conference: (a) Does the velocity field converge on the largest scales? (b) Why can't we agree on the value of beta? (c) How can we properly measure the small-scale velocity dispersion? (d) Just how complicated can biasing be? (e) How universal are the distance indicators we are using? (f) How do we design our next generation of surveys to answer the above questions?
Large-Scale Flows As A Cosmological Probe
Michael A. Strauss,Michael Blanton
Physics , 1998,
Abstract: We review the use of peculiar velocities of galaxies as a probe of cosmological models. We put particular emphasis on comparison of the peculiar velocity and density fields, focussing on the discrepancies between various recent analyses. We discuss the limitations of the commonly used linear bias model, which may lie at the heart of some of the current controversies in the field.
Constraining the Dark Matter Distribution With Large-Scale Structure Observations
Michael A. Strauss,Michael Blanton
Physics , 1998,
Abstract: We discuss the use of galaxies to trace the large-scale structure of the universe and thereby to make cosmological inferences. We put special emphasis on our lack of knowledge about the relative distribution of galaxies and the dynamically important dark matter. We end with a discussion of the increasing importance of infrared astronomy to large-scale structure studies.
Testing the Hubble Law with the IRAS 1.2 Jy Redshift Survey
Daniel Koranyi,Michael A. Strauss
Physics , 1996, DOI: 10.1086/303669
Abstract: 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.
The Discovery of a Field Methane Dwarf from Sloan Digital Sky Survey Commissioning Data
SDSS Collaboration,Michael A. Strauss
Physics , 1999, DOI: 10.1086/312218
Abstract: We report the discovery of the coolest field dwarf yet known, selected as a stellar object with extremely red colors from commissioning imaging data of the Sloan Digital Sky Survey. Its spectrum from 0.8 to 2.5 microns is dominated by strong bands of H_2 O and CH_4. Its spectrum and colors over this range are very similar to those of Gliese 229B, the only other known example of a methane dwarf. It is roughly 1.2 mag fainter than Gliese 229B, implying that it lies at a distance of roughly 10 pc. Such a cool object must have a mass well below the hydrogen-burning limit of 0.08 solar masses, and therefore is a genuine brown dwarf, with a probable mass in the range 0.015-0.06 solar masses for an age range of 0.3-5 Gyr.
The density and peculiar velocity fields of nearby galaxies
Michael A. Strauss,Jeffrey A. Willick
Physics , 1995, DOI: 10.1016/0370-1573(95)00013-7
Abstract: We review the quantitative science that can be and has been done with redshift and peculiar velocity surveys of galaxies in the nearby universe. After a brief background setting the cosmological context for this work, the first part of this review focuses on redshift surveys. The practical issues of how redshift surveys are carried out, and how one turns a distribution of galaxies into a smoothed density field, are discussed. Then follows a description of major redshift surveys that have been done, and the local cosmography out to 8,000 km/s that they have mapped. We then discuss in some detail the various quantitative cosmological tests that can be carried out with redshift data. The second half of this review concentrates on peculiar velocity studies, beginning with a thorough review of existing techniques. After discussing the various biases which plague peculiar velocity work, we survey quantitative analyses done with peculiar velocity surveys alone, and finally with the combination of data from both redshift and peculiar velocity surveys. The data presented rule out the standard Cold Dark Matter model, although several variants of Cold Dark Matter with more power on large scales fare better. All the data are consistent with the hypothesis that the initial density field had a Gaussian distribution, although one cannot rule out broad classes of non-Gaussian models. Comparison of the peculiar velocity and density fields constrains the Cosmological Density Parameter. The results here are consistent with a flat universe with mild biasing of the galaxies relative to dark matter, although open universe models are by no means ruled out.
Maximum-Likelihood Comparisons of Tully-Fisher and Redshift Data. II. Results from an Expanded Sample
Jeffrey A. Willick,Michael A. Strauss
Physics , 1998, DOI: 10.1086/306314
Abstract: 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 $cz_{LG} \leq 3000$ km/sec, 838-galaxy TF sample and found $\beta_I=0.49\pm 0.07,$ where $\beta_I\equiv \Omega^{0.6}/b_I$ and $b_I$ is the linear biasing parameter for IRAS galaxies. In this paper we increase the redshift limit to $cz_{LG}=7500$ 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 $\beta_I=0.50\pm 0.04$ (1-sigma error) at 300 km/sec smoothing of the IRAS-predicted velocity field. The fit residuals are spatially incoherent for $\beta_I=0.5,$ 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 $\beta_I$ of $0.54\pm 0.04.$ Changing the IRAS smoothing scale to 500 km/sec has almost no effect on the best $\beta_I.$ We find evidence for a density-dependence of the small-scale velocity dispersion, $\sigma_v(\delta_g)\simeq (100 + 35 \delta_g)$ km/sec.
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