Discovery of a Large-scale Wall in the Direction of Abell 22

We report on the discovery of a large-scale wall in the direction of Abell 22. Using photometric and spectroscopic data from the Las Campanas Observatory and Anglo-Australian Telescope Rich Cluster Survey, Abell 22 is found to exhibit a highly unusual and striking redshift distribution. We show that Abell 22 exhibits a foreground wall-like structure by examining the galaxy distributions in both redshift space and on the colour-magnitude plane. A search for other galaxies and clusters in the nearby region using the 2dF Galaxy Redshift Survey database suggests that the wall-like structure is a significant large-scale, non-virialized filament which runs between two other Abell clusters either side of Abell 22. The filament stretches over at least >40 Mpc in length and 10 Mpc in width at the redshift of Abell 22.Comment: 6 pages, 4 figures, accepted for publication in MNRAS letter

Public policies for the working poor: The earned income tax credit versus minimum wage legislation

This paper documents the declining relationship between low hourly wages and low household income over the last half-century and how this has reduced the share of minimum wage workers who live in poor households. It then compares recent and prospective increases in the earned income tax credit (EITC) and the minimum wage as methods of increasing the labor earnings of poor workers. Data from the Current Population Survey (CPS) are used to simulate the effects of both programs. Increases in the EITC between 1989 and 1992 delivered a much larger proportion of a given dollar of benefits to the poor than did increases in the minimum wage from $3.35 to$4.25. Scheduled increases in the EITC through 1996 will also do far more for the working poor than raising the minimum wage.

The Stellar Populations of Low-redshift Clusters

We present some preliminary results from an on-going study of the evolution of stellar populations in rich clusters of galaxies. This sample contains core line-strength measurements from 183 galaxies with b_J <= 19.5 from four clusters with ~0.04. Using predictions from stellar population models to compare with our measured line strengths we can derive relative luminosity-weighted mean ages and metallicities for the stellar populations in each of our clusters. We also investigate the Mgb'-sigma and Hbeta_G'-sigma scaling relations. We find that, consistent with previous results, Mgb' is correlated with sigma, the likely explanation being that larger galaxies are better at retaining their heavier elements due to their larger potentials. Hbeta', on the other hand, we find to be anti-correlated with sigma. This result implies that the stellar populations in larger galaxies are older than in smaller galaxies.Comment: 3 pages, 2 figures, to appear in the Proceedings of IAU Colloquium 195: "Outskirts of Galaxy Clusters: intense life in the suburbs", Torino Italy, March 12-16 200

A Search for Low Surface Brightness Structure Around Compact Narrow Emission Line Galaxies

As the most extreme members of the rapidly evolving faint blue galaxy population at intermediate redshift, the compact narrow emission line galaxies (CNELGs) are intrinsically luminous (-22 < M_B < -18) with narrow emission linewidths (30 < \sigma < 125 km/s). Their nature is heavily debated: they may be low-mass starbursting galaxies that will fade to present-day dwarf galaxies or bursts of star formation temporarily dominating the flux of more massive galaxies, possibly related to in situ bulge formation or the formation of cores of galaxies. We present deep, high-quality (~0.6 - 0.8 arcsec) images with CFHT of 27 CNELGs. One galaxy shows clear evidence for a tidal tail; the others are not unambiguously embedded in galactic disks. Approximately 55% of the CNELGS have sizes consistent with local dwarfs of small-to-intermediate sizes, while 45% have sizes consistent with large dwarfs or disks galaxies. At least 4 CNELGs cannot harbor substantial underlying disk material; they are low-luminosity galaxies at the present epoch (M_B > -18). Conversely, 15 are not blue enough to fade to low-luminosity dwarfs (M_B > -15.2). The majority of the CNELGs are consistent with progenitors of intermediate-luminosity dwarfs and low-luminosity spiral galaxies with small disks. CNELGs are a heterogeneous progenitor population with significant fractions (up to 44%) capable of fading into today's faint dwarfs (M_B > -15.2), while 15 to 85% may only experience an apparently extremely compact CNELG phase at intermediate redshift but remain more luminous galaxies at the present epoch.Comment: 16 pages, 14 figures, emulateapj, published in Ap

Cluster Galaxy Evolution from a New Sample of Galaxy Clusters at 0.3 < z < 0.9

(Abridged) We analyze photometry and spectroscopy of a sample of 63 clusters at 0.3<z<0.9 drawn from the Las Campanas Distant Cluster Survey to empirically constrain models of cluster galaxy evolution. Specifically, by combining data on our clusters with those from the literature we parametrize the redshift dependence of 1) M*_I in the observed frame; 2) the V-I color of the E/S0 red sequence in the observed frames; and 3) the I-K' color of the E/S0 red sequence in the observed frame. Using the peak surface brightness of the cluster detection, S, as a proxy for cluster mass, we find no correlation between S and M* or the location of the red envelope in V-I. We suggest that these observations can be explained with a model in which luminous early type galaxies (or more precisely, the progenitors of current day luminous early type galaxies) form the bulk of their stellar populations at high redshift (>~ 5) and in which many of these galaxies, if not all, accrete mass either in the form of evolved stellar populations or gas that causes only a short term episode of star formation at lower redshifts (1.5 < z < 2). Our data are too crude to reach conclusions regarding the evolutionary state of any particular cluster or to investigate whether the morphological evolution of galaxies matches the simple scenario we discuss, but the statistical nature of this study suggests that the observed evolutionary trends are universal in massive clusters.Comment: 35 pages, accepted for publication in Ap

Radial Color Gradients in K+A Galaxies in Distant Clusters of Galaxies

Galaxies in rich clusters with z $\gtrsim$ 0.3 are observed to have a higher fraction of photometrically blue galaxies than their nearby counterparts. This raises the important question of what environmental effects can cause the termination of star formation between z $\approx$ 0.3 and the present. The star formation may be truncated due to ram-pressure stripping, or the gas in the disk may be depleted by an episode of star formation caused by some external perturbation. To help resolve this issue, surface photometry was carried out for a total of 70 early-type galaxies in the cluster Cl1358+62, at z $\sim$ 0.33, using two-color images from the Hubble Archive. The galaxies were divided into two categories based on spectroscopic criteria: 24 are type K+A (e.g., strong Balmer lines, with no visible emission lines), while the remaining 46 are in the control sample with normal spectra. Radial color profiles were produced to see if the K+A galaxies show bluer nuclei in relation to their surrounding disks. Specifically, a linear gradient was fit to the radial color profile of each galaxy. We find that the K+A galaxies on average tend to have slightly bluer gradients towards the center than the normals. A Kolmogorov-Smirnov two-sample test has been applied to the two sets of color gradients. The result of the test indicates that there is only a $\sim$2% probability that the K+A and normal samples are drawn from the same parent distribution. There is a possible complication from a trend in the apparent magnitude vs. color gradient relation, but overall our results favor the centralized star formation scenario as an important process in the evolution of galaxies in dense clusters.Comment: 16 pages, 12 figures, accepted for publication in A