Ian P. Dell'Antonio

BVRI Light Curves for 22 Type 1a Supernovae

We present 1210 Johnson/Cousins B, V, R, and I photometric observations of 22 recent Type Ia supernovae (SNe Ia): SNe 1993ac, 1993ae, 1994M, 1994S, 1994T, 1994Q, 1994ae, 1995D, 1995E, 1995al, 1995ac, 1995ak, 1995bd, 1996C, 1996X, 1996Z, 1996ab, 1996ai, 1996bk, 1996bl, 1996bo, and 1996bv. Most of the photometry was obtained at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics in a cooperative observing plan aimed at improving the database for SNe Ia. The redshifts of the sample range from cz = 1200 to 37,000 km s-1 with a mean of cz = 7000 km s-1.

Detailed Mass Map of CL 0024+1654 from Strong Lensing

We construct a high-resolution mass map of the cluster 00241654, based on a parametric inversion z 0.39 of the associated gravitational lens. The lens creates eight well-resolved subimages of a background galaxy, seen in deep imaging with the Hubble Space Telescope. 1 Excluding mass concentrations centered on visible galaxies, more than 98% of the remaining mass is represented by a smooth concentration of dark matter centered near the brightest cluster galaxies, with a 35 kpc soft core. The asymmetry in the mass distribution is less than 3% 1 h inside 107 h 1 kpc radius. The dark matter distribution we observe in CL 0024 is far more smooth, symmetric, and nonsingular than in typical simulated clusters in either or cold dark matter cosmologies. Q 1 Q 0.3 Integrated to a 107 h 1 kpc radius, the rest-frame mass-to-light ratio is M /. L 276 40 h (M/L ) VV

First results on shear-selected clusters from the deep lens survey : Optical imaging, spectroscopy, and X-ray follow-up

We present the first sample of galaxy clusters selected on the basis of their weak gravitational lensing shear. The shear induced by a cluster is a function of its mass profile and its redshift relative to the background galaxies being sheared; in contrast to more traditional methods of selecting clusters, shear selection does not depend on the clusters star formation history, baryon content, or dynamical state. Because mass is the property of clusters that provides constraints on cosmological parameters, the dependence on these other parameters could induce potentially important biases in traditionally selected samples. Comparison of a shear-selected sample with optically and X-ray-selected samples is therefore of great importance. Here we present the first step toward a new shear-selected sample: the selection of cluster candidates from the first 8.6 deg^2 of the 20 deg^2 Deep Lens Survey (DLS), and tabulation of their basic properties such as redshifts and optical and X-ray counterparts.

The Mass Of The Coma Cluster From Weak Lensing In The Sloan Digital Sky Survey

We present a weak lensing analysis of the Coma Cluster using the Sloan Digital Sky Survey (SDSS) Data Release Five. Complete imaging of a {approx} 200 square degree region is used to measure the tangential shear of this cluster. The shear is fit to an NFW model and we find a virial radius of r{sub 200} = 1.99{sup +0.21}{sub -0.22}h{sup -1}Mpc which corresponds to a virial mass of M{sub 200} = 1.88{sup +0.65}{sub -0.56} x 10{sup 15}h{sup -1}M{circle_dot}. We additionally compare our weak lensing measurement to the virial mass derived using dynamical techniques, and find they are in agreement. This is the lowest redshift, largest angle weak lensing measurement of an individual cluster to date.

Triggered Star Formation in Galaxy Pairs at z = 0.08-0.38

We measure the strength, frequency, and timescale of tidally triggered star formation at redshift z = 0.08-0.38 in a spectroscopically complete sample of galaxy pairs drawn from the magnitude-limited redshift survey of 9825 Smithsonian Hectospec Lensing Survey galaxies with R 1/5) pair galaxies with MR < ?20.8 in the redshift range z = 0.08-0.31. The size and completeness of the spectroscopic survey allow us to focus on regions of low local density. The spectrophotometric calibration enables the use of the 4000 ? break (Dn 4000), the H? specific star formation rate (SSFRH?), and population models to characterize the galaxies. We show that Dn 4000 is a useful population classification tool; it closely tracks the identification of emission line galaxies. The sample of major pair galaxies in regions of low local density with low Dn 4000 demonstrates the expected anti-correlation between pairwise projected separation and a set of star formation indicators explored in previous studies. We measure the frequency of triggered star formation by comparing the SSFRH? in the volume-limited sample in regions of low local density: 32% ? 7% of the major pair galaxies have SSFRH? at least double the median rate of the unpaired field galaxies. Comparison of stellar population models for pair and for unpaired field galaxies implies a timescale for triggered star formation of ~300-400?Myr.

THE TIME DEVELOPMENT OF A RESONANCE LINE IN THE EXPANDING UNIVERSE

The time-dependent spectral profile of a resonance line in a homogeneous expanding medium is studied by numerically solving an improved Fokker-Planck diffusion equation. The solutions are used to determine the time required to reach a quasi-static solution near the line center. A simple scaling law for this relaxation time is derived and is fitted to the numerical results. The results are applied to the case of Lyman alpha scattering during primordial recombination of hydrogen. For a wide range of cosmological models it is found that the relaxation times are smaller than the recombination timescale, although not by a very large factor. Thus the standard assumption of a quasi-static solution in cosmological recombination calculations is reasonably valid, and should not cause substantial errors in the solutions.

SHELS : The Hectospec Lensing Survey

The Smithsonian Hectospec Lensing Survey (SHELS) combines a 10,000 galaxy deep complete redshift survey with a weak-lensing map from the Deep Lens Survey (Wittman et al.). We use maps of the velocity dispersion based on systems identified in the redshift survey to compare the three-dimensional matter distribution with the two-dimensional projection mapped by weak lensing. We demonstrate directly that the lensing map images the three-dimensional matter distribution obtained from the kinematic data.

EVOLUTION OF THE Hα LUMINOSITY FUNCTION

The Smithsonian Hectospec Lensing Survey (SHELS) is a window on the star formation history over the last 4 Gyr. SHELS is a spectroscopically complete survey for Rtot ~ L* in each of the redshift bins. We conclude that triggered star formation is an important influence for star forming galaxies with Halpha emission.

THE FAINT END OF THE LUMINOSITY FUNCTION AND LOW SURFACE BRIGHTNESS GALAXIES

Smithsonian Hectospec Lensing Survey (SHELS) is a dense redshift survey covering a 4 deg2 region to a limiting R = 20.6. In the construction of the galaxy catalog and in the acquisition of spectroscopic targets, we paid careful attention to the survey completeness for lower surface brightness dwarf galaxies. Thus, although the survey covers a small area, it is a robust basis for computation of the slope of the faint end of the galaxy luminosity function to a limiting MR = –13.3 + 5log h. We calculate the faint-end slope in the R band for the subset of SHELS galaxies with redshifts in the range 0.02 ≤z < 0.1, SHELS0.1. This sample contains 532 galaxies with R < 20.6 and with a median surface brightness within the half-light radius of SB50, R = 21.82 mag arcsec–2. We used this sample to make one of the few direct measurements of the dependence of the faint end of the galaxy luminosity function on surface brightness. For the sample as a whole the faint-end slope, α = –1.31 ± 0.04, is consistent with both the Blanton et al. analysis of the Sloan Digital Sky Survey and the Liu et al. analysis of the COSMOS field. This consistency is impressive given the very different approaches of these three surveys. A magnitude-limited sample of 135 galaxies with optical spectroscopic redshifts with mean half-light surface brightness, SB50, R ≥ 22.5 mag arcsec–2 is unique to SHELS0.1. The faint-end slope is α22.5 = –1.52 ± 0.16. SHELS0.1 shows that lower surface brightness objects dominate the faint-end slope of the luminosity function in the field, underscoring the importance of surface brightness limits in evaluating measurements of the faint-end slope and its evolution.

Big Throughput Camera: the first year

The Big Throughput Camera (BTC) recently celebrated its first anniversary as a user instrument on the Blanco 4-meter telescope at Cerro Tololo Interamerican Observatory (CTIO), where it collects more photons per second than any other nighttime astronomical camera in the world. We offer a look at the successes and lessons learned during the first year of operation. After an overview of the hardware, we describe the software from the users point of view, and then offer examples of the observing targets and strategies used. BTC has become very popular among CTIO observers -- more than one- third of dark time is now assigned to BTC -- but the large field of view leads to some new data reduction challenges which we discuss in the final section.