Dara Norman

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 Deep Lens Survey Transient Search. I. Short Timescale and Astrometric Variability

We report on the methodology and first results from the Deep Lens Survey transient search. We utilize image subtraction on survey data to yield all sources of optical variability down to 24th magnitude. Images are analyzed immediately after acquisition, at the telescope and in near-real time, to allow for followup in the case of time-critical events. All classes of transients are posted to the web upon detection. Our observing strategy allows sensitivity to variability over several decades in timescale. The DLS is the first survey to classify and report all types of photometric and astrometric variability detected, including solar system objects, variable stars, supernovae, and short timescale phenomena. Three unusual optical transient events were detected, flaring on thousand-second timescales. All three events were seen in the B passband, suggesting blue color indices for the phenomena. One event (OT 20020115) is determined to be from a flaring Galactic dwarf star of spectral type dM4. From the remaining two events, we find an overall rate of \eta = 1.4 events deg-2 day-1 on thousand-second timescales, with a 95% confidence limit of \eta<4.3. One of these events (OT 20010326) originated from a compact precursor in the field of galaxy cluster Abell 1836, and its nature is uncertain. For the second (OT 20030305) we find strong evidence for an extended extragalactic host. A dearth of such events in the R passband yields an upper 95% confidence limit on short timescale astronomical variability between 19.5

Weak Lensing-Induced Correlations between 1 Jy QSOs and APM Galaxies on Angular Scales of a Degree

We find angular correlations between high-redshift radio-selected QSOs from the 1 Jy catalog and Automatic Plate Measuring Facility (APM) galaxies on 1° scales. We demonstrate that observed correlations are qualitatively consistent with a gravitational lensing explanation and are inconsistent with a Galactic dust obscuration model. Comparing our results with those of Benitez & Martinez-Gonzalez, who also use 1 Jy sources and APM galaxies, we come to the conclusion that galaxy selection criteria can have a major effect on the angular scale and amplitude of detected correlations.

The role of the US National Office in the Gemini partnership

We follow the history of the US National Gemini Office from its origin when the US National New Technology Telescope was reshaped into two 8m telescopes for the International Gemini Observatory. The development of the office in the decade of the 1990s continues to shape its function to the present. The following decade, 2000–2010, marked major milestones including the dedication of the telescopes, the reshaping of the Gemini instrumentation program, and dissatisfaction of the US community as expressed in the ALTAIR report. Nationally funded facilities are under financial pressure, as new projects must be funded from a nearly fixed budget. We will discuss how the US NGO should be used to advocate for both the US community and the Gemini Observatory. This role could be an essential one in protecting open access to 8m-class facilities.

The NOAO variable-sky project

Modern time-domain surveys have demonstrated that finding variable objects is relatively straightforward. The problem now is one of selecting and following up discoveries. With even larger-scale surveys on the horizon, the magnitude of the problem will inevitably increase. One way to prepare for the coming deluge is to have realistic estimates of the numbers of potential detections so that resources can be developed to meet that need. To that end, astronomers at the National Optical Astronomy Observatory (NOAO) have begun a project to characterize the variable sky in terms of type of objects, distribution on the sky and range of variation.

X-Ray Observations of the Most Massive DLS Shear-Selected Galaxy Clusters

We report on preliminary results of our X-ray survey of the most massive clusters currently identified from the Deep Lens Survey (DLS). The DLS cluster sample is selected based on weak lensing shear, which makes it possible for the first time to study clusters in a baryon-independent way. In this article we present X-ray properties of a subset of the shear-selected cluster sample.