Ubercalibration of the Deep Lens Survey

We describe the internal photometric calibration of the Deep Lens Survey, which consists of five widely separated fields observed by two different observatories. Adopting the global linear least-squares ("ubercal") approach developed for the Sloan Digital Sky Survey (SDSS), we derive flatfield corrections for all observing runs, which indicate that the original sky flats were nonuniform by up to 0.13 mag peak to valley in \z band, and by up to half that amount in {\it BVR}. We show that application of these corrections reduces spatial nonuniformities in corrected exposures to the 0.01-0.02 mag level. We conclude with some lessons learned in applying ubercal to a survey structured very differently from SDSS, with isolated fields, multiple observatories, and shift-and-stare rather than drift-scan imaging. Although the size of the error caused by using sky or dome flats is instrument- and wavelength-dependent, users of wide-field cameras should not assume that it is small. Pipeline developers should facilitate routine application of this procedure, and surveys should include it in their plans from the outset.Comment: accepted to MNRA

Tomographic Magnification of Lyman Break Galaxies in The Deep Lens Survey

Using about 450,000 galaxies in the Deep Lens Survey, we present a detection of the gravitational magnification of z > 4 Lyman Break Galaxies by massive foreground galaxies with 0.4 < z < 1.0, grouped by redshift. The magnification signal is detected at S/N greater than 20, and rigorous checks confirm that it is not contaminated by any galaxy sample overlap in redshift. The inferred galaxy mass profiles are consistent with earlier lensing analyses at lower redshift. We then explore the tomographic lens magnification signal by splitting our foreground galaxy sample into 7 redshift bins. Combining galaxy-magnification cross-correlations and galaxy angular auto-correlations, we develop a bias-independent estimator of the tomographic signal. As a diagnostic of magnification tomography, the measurement of this estimator rejects a flat dark matter dominated Universe at > 7.5{\sigma} with a fixed \sigma_8 and is found to be consistent with the expected redshift-dependence of the WMAP7 {\Lambda}CDM cosmology.Comment: 12 pages, 9 figures, Accepted to MNRA

On the absence of radio halos in clusters with double relics

Pairs of radio relics are believed to form during cluster mergers, and are best observed when the merger occurs in the plane of the sky. Mergers can also produce radio halos, through complex processes likely linked to turbulent re-acceleration of cosmic-ray electrons. However, only some clusters with double relics also show a radio halo. Here, we present a novel method to derive upper limits on the radio halo emission, and analyse archival X-ray Chandra data, as well as galaxy velocity dispersions and lensing data, in order to understand the key parameter that switches on radio halo emission. We place upper limits on the halo power below the $P_{\rm 1.4 \, GHz}\, M_{500}$ correlation for some clusters, confirming that clusters with double relics have different radio properties. Computing X-ray morphological indicators, we find that clusters with double relics are associated with the most disturbed clusters. We also investigate the role of different mass-ratios and time-since-merger. Data do not indicate that the merger mass ratio has an impact on the presence or absence of radio halos (the null hypothesis that the clusters belong to the same group cannot be rejected). However, the data suggests that the absence of radio halos could be associated with early and late mergers, but the sample is too small to perform a statistical test. Our study is limited by the small number of clusters with double relics. Future surveys with LOFAR, ASKAP, MeerKat and SKA will provide larger samples to better address this issue.Comment: 12 pages, 7 figures, MNRAS accepte

Weak Lensing Detection of Cl 1604+4304 at z = 0.90

We present a weak lensing analysis of the high-redshift cluster Cl 1604+4304. At z=0.90, this is the highest-redshift cluster yet detected with weak lensing. It is also one of a sample of high-redshift, optically-selected clusters whose X-ray temperatures are lower than expected based on their velocity dispersions. Both the gas temperature and galaxy velocity dispersion are proxies for its mass, which can be determined more directly by a lensing analysis. Modeling the cluster as a singular isothermal sphere, we find that the mass contained within projected radius R is 3.69+-1.47 * (R/500 kpc) 10^14 M_odot. This corresponds to an inferred velocity dispersion of 1004+-199 km/s, which agrees well with the measured velocity dispersion of 989+98-76 km/s (Gal & Lubin 2004). These numbers are higher than the 575+110-85 km/s inferred from Cl 1604+4304 X-ray temperature, however all three velocity dispersion estimates are consistent within ~ 1.9 sigma.Comment: Revised version accepted for publication in AJ (January 2005). 2 added figures (6 figures total

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 < R < 23.4 of \eta_R < 5.2. We report also on our ensemble of astrometrically variable objects, as well as an example of photometric variability with an undetected precursor.Comment: 24 pages, 12 figures, 3 tables. Accepted for publication in ApJ. Variability data available at http://dls.bell-labs.com/transients.htm

Imaging the Cosmic Matter Distribution using Gravitational Lensing of Pregalactic HI

21-cm emission from neutral hydrogen during and before the epoch of cosmic reionisation is gravitationally lensed by material at all lower redshifts. Low-frequency radio observations of this emission can be used to reconstruct the projected mass distribution of foreground material, both light and dark. We compare the potential imaging capabilities of such 21-cm lensing with those of future galaxy lensing surveys. We use the Millennium Simulation to simulate large-area maps of the lensing convergence with the noise, resolution and redshift-weighting achievable with a variety of idealised observation programmes. We find that the signal-to-noise of 21-cm lens maps can far exceed that of any map made using galaxy lensing. If the irreducible noise limit can be reached with a sufficiently large radio telescope, the projected convergence map provides a high-fidelity image of the true matter distribution, allowing the dark matter halos of individual galaxies to be viewed directly, and giving a wealth of statistical and morphological information about the relative distributions of mass and light. For instrumental designs like that planned for the Square Kilometer Array (SKA), high-fidelity mass imaging may be possible near the resolution limit of the core array of the telescope.Comment: version accepted for publication in MNRAS (reduced-resolution figures

Preliminary Results from NEOWISE: An Enhancement to the Wide-field Infrared Survey Explorer for Solar System Science

The Wide-field Infrared Survey Explorer (WISE) has surveyed the entire sky at four infrared wavelengths with greatly improved sensitivity and spatial resolution compared to its predecessors, the Infrared Astronomical Satellite and the Cosmic Background Explorer. NASA's Planetary Science Division has funded an enhancement to the WISE data processing system called "NEOWISE" that allows detection and archiving of moving objects found in the WISE data. NEOWISE has mined the WISE images for a wide array of small bodies in our solar system, including near-Earth objects (NEOs), Main Belt asteroids, comets, Trojans, and Centaurs. By the end of survey operations in 2011 February, NEOWISE identified over 157,000 asteroids, including more than 500 NEOs and ~120 comets. The NEOWISE data set will enable a panoply of new scientific investigations

An elusive radio halo in the merging cluster Abell 781?

Deep radio observations of the galaxy cluster Abell 781 have been carried out using the Giant Metrewave Radio Telescope at 325 MHz and have been compared to previous 610 MHz observations and to archival VLA 1.4 GHz data. The radio emission from the cluster is dominated by a diffuse source located at the outskirts of the X-ray emission, which we tentatively classify as a radio relic. We detected residual diffuse emission at the cluster centre at the level of S(325 MHz)~15-20 mJy. Our analysis disagrees with Govoni et al. (2011), and on the basis of simple spectral considerations we do not support their claim of a radio halo with flux density of 20-30 mJy at 1.4 GHz. Abell 781, a massive and merging cluster, is an intriguing case. Assuming that the residual emission is indicative of the presence of a radio halo barely detectable at our sensitivity level, it could be a very steep spectrum source.Comment: 5 pages, 4 figures, 1 table - Accepted for publication on Monthly Notices of the Royal Astronomical Society Letter