arXiv subjects

Matthew A. Bershady

Publications and source records attributed to Matthew A. Bershady.

113 records · Page 7Linked to original sources

arXiv1997

The Luminosity Function for L>L* Galaxies at z > 3

Through use of multiband (U, B, R, I) photometry we have isolated high redshift (3.0 L* luminosity function for z = 3-5 galaxies obtained by a photometric redshift analysis of the Hubble Deep Field (HDF) by Gwyn & Hartwick (1996). Our results at R ~ 23 are more consistent with the photometric redshift analysis of the faint HDF galaxies by Sawicki & Yee (1996), but our present upper limits at the brightest magnitudes (R < 21.5, M(R) < -24) allow more generous volume densities of these super-L* galaxies.

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arXiv1997

Towards More Precise Photometric Redshifts: Calibration Via CCD Photometry

We present the initial results from a deep, multi-band photometric survey of selected high Galactic latitude redshift fields. Previous work using the photographic data of Koo and Kron demonstrated that the distribution of galaxies in the multi-dimensional flux space U B R I is nearly planar. The position of a galaxy within this plane is determined by its redshift, luminosity and spectral type. Using recently acquired deep CCD photometry in existing, published redshift fields, we have redetermined the distribution of galaxies in this four-dimensional magnitude space. Furthermore, from our CCD photometry and the published redshifts, we have quantified the photometric-redshift relation within the standard AB magnitude system. This empirical relation has a measured dispersion of approximately 0.02 for z < 0.4. With this work we are reaching the asymptotic intrinsic dispersions that were predicted from simulated distributions of galaxy colors.

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arXiv1996

Spatially Resolved Kinematics of Distant Galaxies

A Tully-Fisher (TF) relation from H-alpha rotation curves of 19 luminous, star-forming galaxies reveals there is little evidence for evolution in the mass-to-light ratio (M/L) of these galaxies to z~0.3. The near-infrared Tolman surface-brightness test for other luminous galaxies indicates their luminosity also is little changed to z~0.3. In this redshift regime, internal velocity -- luminosity relations like Tully-Fisher may provide a way to measure q0. Discrepant results from several intermediate redshift Tully-Fisher surveys, however, must be understood first. One possibility is that different surveys sample different galaxy types and TF relations. Alternatively, M/L of some spiral galaxies may evolve rapidly with look-back time. Larger surveys are needed to resolve this issue. A different approach is to determine disk and halo M/L separately. Such measurements, even at low redshift, would be sensitive to the star formation histories of disks. We outline plans for lambda/dlambda ~ 10000 integral-field spectroscopy of relatively face-on spirals using the 9m Hobby-Eberly Telescope. Rotation curves and disk stellar velocity dispersions can provide statistical information about the M/L of dark halos as well as luminous disks.

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arXiv1996

The Tully-Fisher Relation at Intermediate Redshifts

Motivated by recent pioneering measurements of galaxy kinematics at intermediate redshifts, we have begun a pilot survey to measure rotation curves for blue, star-forming galaxies between 0.05<z<0.35. The scientific impetus for such measurements is to construct internal velocity - luminosity relations at redshifts substantial enough to make cosmological and evolutionary tests. Departures from a fiducial relation as a function of redshift are sensitive to both space-time curvature and the evolution of the mass-to-light ratio in galaxies. Because of this ambiguity -- curvature vs. evolution -- kinematics should be viewed as a new cosmological tool at intermediate redshifts to be combined with additional measurements. In particular, the apparent internal velocities, colors, surface-brightness, and image shape are all unaffected by curvature, so that this ensemble of observables can be used unambiguously to explore galaxy evolution. Here we discuss a well-defined method of target selection which assures efficient measurement of spatially and spectrally resolved kinematics, namely rotation curves. Spatial resolution is critical since it is difficult to use integrated line-widths to distinguish between, for example, a low-mass star-forming galaxy and a high-mass galaxy with a central star-burst. For 18 of 19 appropriately selected galaxies to B<20.5 from Bershady et al (1994), we have successfully measured rotation curves using the KAST spectrograph on the Lick 3m telescope with 1-2 hour integrations for each target. As a sanity check, we present preliminary results for half of our sample: We measure H0 to be ~75 km/s/Mpc at a median redshift of 0.15.

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arXiv1996

Linear Regression for Astronomical Data with Measurement Errors and Intrinsic Scatter

Two new methods are proposed for linear regression analysis for data with measurement errors. Both methods are designed to accommodate intrinsic scatter in addition to measurement errors. The first (BCES) is a direct extension of the ordinary least squares (OLS) estimator to allow for measurement errors. It is quite general, allowing a) for measurement errors on both variables, b) the measurement errors for the two variables to be dependent, c) the magnitudes of the measurement errors to depend on the measurements, and d) other `symmetric' lines such as the bisector and the orthogonal regression can be constructed. The second method is a weighted least squares (WLS) estimator, which applies only in the case where the `independent' variable is measured without error and the magnitudes of the measurement errors on the 'dependent' variable are independent from the measurements. Several applications are made to extragalactic astronomy: The BCES method, when applied to data describing the color-luminosity relations for field galaxies, yields significantly different slopes than OLS and other estimators used in the literature. Simulations with artificial data sets are used to evaluate the small sample performance of the estimators. Unsurprisingly, the least-biased results are obtained when color is treated as the dependent variable. The Tully-Fisher relation is another example where the BCES method should be used because errors in luminosity and velocity are correlated due to inclination corrections. We also find, via simulations, that the WLS method is by far the best method for the Tolman surface-brightness test, producing the smallest variance in slope by an order of magnitude. Moreover, with WLS it is not necessary to ``reduce'' galaxies to a fiducial surface-brightness, since this model incorporates intrinsic scatter.

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