Michael D. Gladders

VIRIAL MASSES AND THE BARYON FRACTION IN GALAXIES

We have measured the weak-lensing signal as a function of rest-frame B-, V-, and R-band luminosity for a sample of isolated galaxies. These results are based on four-band photometry from the Red-Sequence Cluster Survey, enabling us to determine photometric redshifts for a large number of galaxies. We select a secure sample of lenses with photometric redshifts 0.2 < z < 0.4 and study the relation between the virial mass and baryonic contents. In addition, we discuss the implications of the derived photometric redshift distribution for published cosmic shear studies. The virial masses are derived from a fit to the observed lensing signal. For a galaxy with a fiducial luminosity of 1010 h-2 LB,?, we obtain a mass Mvir = 9.9 ? 1011 M?. The virial mass as a function of luminosity is consistent with a power law L1.5, with similar slopes for the three filters considered here. These findings are in excellent agreement with results from the Sloan Digital Sky Survey and semianalytic models of galaxy formation. We measure the fraction of mass in stars and the baryon fraction in galaxies by comparing the virial mass-to-light ratio to predicted stellar mass-to-light ratios. We find that star formation is inefficient in converting baryons into stars, with late-type galaxies converting ~33% and early-type galaxies converting only ~14% of baryons into stars. Our results imply that the progenitors of early-type galaxies must have low stellar mass fractions, suggestive of a high formation redshift.

The Reverse Shock of SNR 1987A at 18 Years after Outburst

We use low-dispersion spectra obtained at the Magellan Observatory to study the broad Hα emission from the reverse shock of the infant supernova remnant SNR 1987A. These spectra demonstrate that the spatiokinematic structure of the reverse shock can be distinguished from that of the circumstellar ring and hot spots, even at ground-based spatial resolution. We measure a total dereddened Hα flux of 1.99(±0.22) × 10-13 ergs s-1 cm-2 at an epoch 18.00 yr after outburst. At 50 kpc, the total reverse shock luminosity in Hα is roughly 15 L☉, which implies a total flux of neutral hydrogen atoms across the reverse shock of 8.9 × 1046 s-1, or roughly 2.3 × 10-3 M☉ yr-1. This represents an increase by a factor of ~4 since 1997. Lyman continuum radiation from gas shocked by the forward blast wave can ionize neutral hydrogen atoms in the supernova debris before they reach the reverse shock. If the inward flux of ionizing photons exceeds the flux of hydrogen atoms approaching the reverse shock, this preionization will shut off the broad Lyα and Hα emission. The observed X-ray emission of SNR 1987A implies that the ratio of ionizing flux to hydrogen atom flux across the reverse shock is presently at least 0.04. The X-ray emission is increasing much faster than the flux of atoms, and if these trends continue, we estimate that the broad Lyα and Hα emission will vanish in 7 yr.

Submillimeter Imaging of RCS J022434–0002.5: Intense Activity in a High-Redshift Cluster?

We present deep 850 μm imaging of the z = 0.773 strong lensing galaxy cluster RCS J022434-0002.5 from the Red-Sequence Cluster Survey (RCS). These data are part of a larger submillimeter survey of RCS clusters with SCUBA on the JCMT. We find five objects at 850 μm, all of which are also detected at either 1.4 GHz or 450 μm, or both. The number density of objects in this field is in general agreement with the blank-field source counts; however, when combined with other cluster surveys a general tendency of cluster fields toward higher submillimeter number densities is seen, which may be the result of unrecognized submillimeter luminous cluster galaxies. Primarily employing optical photometric redshifts, we show that two of the five submillimeter galaxies in this field are consistent with being cluster members, while two are more likely background systems.

The Optical Afterglow of the Gamma-Ray Burst GRB 011211*

The optical afterglows of gamma-ray bursts can be used to probe the physics, geometry, and environments of gamma-ray bursts. In this article I discuss the how spectra and photometry can be used to constrain fireball parameters, describe several types of breaks that might be observed in the optical decay, and briefly review the late-time bumps and rapid variations in optical light curves.

The EXPLORE project: a deep search for transiting extrasolar planets

Searching for transits provides a very promising technique for finding close-in extra-solar planets. Transiting planets present the advantage of allowing one to determine physical properties such as mass and radius unambiguously. The EXPLORE (EXtra-solar PLanet Occultation REsearch) project is a transit search project carried out using wide-field CCD imaging cameras on 4-m class telescopes, and 8--10m class telescopes for velocity verifications of the photometric candidates. We describe some of the considerations that go into the design of the EXPLORE transit search to maximize the discovery rate and minimize contaminating objects that mimic transiting planets. We show that high precision photometry (2 to 10 millimag) and high time sampling (few minutes) are crucial for sifting out contaminating signatures, such as grazing binaries. We have an efficient data reduction pipeline which allows us to completely reduce the data in less than one month after the imaging observations, allowing us to conduct same-semester velocity follow-up observations, reducing the phase uncertainty. We have completed two searches using the 8k MOSAIC camera at the CTIO4m and the CFH12k camera at CFHT, with runs covering 11 and 16 nights, respectively. Using the 4400 images from the two fields, we obtained light curves for approximately 47,000 stars with better than

Properties of galaxy dark matter halos from weak lensing

\sim1

A submm survey of high-redshift galaxy clusters: a submm Butcher-Oemler effect?

\% photometric precision. A number of light curves with flat-bottomed eclipses consistent with being produced by transiting planets has been discovered. Preliminary results from follow-up spectroscopic observations using the VLT UVES spectrograph and the Keck HIRES spectrograph obtained for a number of the candidates are presented. Data from four of these can be interpreted consistently as possible planet candidates, although further data are still required for definitive confirmations.

The Optical Afterglow of GRB 011211

We present the results of a study of weak lensing by galaxies based on 45.5 deg2 of RC-band imaging data from the Red-Sequence Cluster Survey (RCS). We define a sample of lenses with 19:5 < RC < 21 and a sample of background galaxies with 21:5 < RC < 24. We present the first weak-lensing detection of the flattening of galaxy dark matter halos. We use a simple model in which the ellipticity of the halo is f times the observed ellipticity of the lens. We find a best-fit value of f 1⁄4 0:77þ0:18 0:21, which suggests that the dark matter halos are somewhat rounder than the light distribution. The fact that we detect a significant flattening implies that the halos are well aligned with the light distribution. Given the average ellipticity of the lenses, this implies a halo ellipticity of hehaloi 1⁄4 0:33þ0:07 0:09, in fair agreement with results from numerical simulations of cold dark matter. We note that this result is formally a lower limit to the flattening, since the measurements imply a larger flattening if the halos are not aligned with the light distribution. Alternative theories of gravity (without dark matter) predict an isotropic lensing signal, which is excluded with 99.5% confidence. Hence, our results provide strong support for the existence of dark matter. We also study the average mass profile around the lenses, using a maximum likelihood analysis. We consider two models for the halo mass profile: a truncated isothermal sphere (TIS) and a Navarro-Frenk-White (NFW) profile. We adopt observationally motivated scaling relations between the lens luminosity and the velocity dispersion and the extent of the halo. The TIS model yields a best-fit velocity dispersion of 1⁄4 136 5 3 km s 1 (all errors are 68% confidence limits; the first error bar indicates the statistical uncertainty, whereas the second error bar indicates the systematic error) and a truncation radius s 1⁄4 185þ30 28 h 1 kpc for a galaxy with a fiducial luminosity of LB 1⁄4 10 h 2 LB; (under the assumption that the luminosity does not evolve with redshift). Alternatively, the best-fit NFW model yields a mass M200 1⁄4 (8:4 0:7 0:4) ; 10 h 1 M and a scale radius rs 1⁄4 16:2þ3:6 2:9 h 1 kpc. This value for the scale radius is in excellent agreement with predictions from numerical simulations for a halo of this mass. Subject headings: cosmology: observations — dark matter — galaxies: halos — gravitational lensing

Closing in on a short-hard burst progenitor: Constraints from early-time optical imaging and spectroscopy of a possible host galaxy of GRB 050509b

We present the initial results of a deep submillimeter survey of ten z ∼ 1 galaxy clusters with the SCUBA bolometer array on the JCMT. Recently, an excess number of dust enshrouded starbursts in high-redshift galaxy cluster fields was reported (Best 2002) and has been interpreted as increased star-formation within young clusters. An alternative explanation is that these starbursts are background objects behind clusters with enhanced lensing crosssections, over that predicted from simple lensing models, so-called “super-lenses” seen in recent optical cluster surveys. To investigate this issue, we are studying a set of clusters which show strong optical arcs (super-lenses) and a set of clusters of equal redshift and richness but which are not super-lenses. The preliminary results, based on 50% of the sample, tentatively suggest that, while the dusty starbursts are limited to the super-lensing cluster fields, they are not background objects but lie within the clusters themselves. Cluster-cluster merging offers a means of increasing both the lensing cross-section, thereby accounting for the multiple strong optical arcs, and increasing the star formation within the clusters through galaxy interactions.

A Photometric Redshift Galaxy Catalog from the Red-Sequence Cluster Survey

The optical afterglows of gamma-ray bursts can be used to probe the physics, geometry, and environments of gamma-ray bursts. In this article I discuss the how spectra and photometry can be used to constrain fireball parameters, describe several types of breaks that might be observed in the optical decay, and briefly review the late-time bumps and rapid variations in optical light curves.