The Ultraviolet Luminosity Density of the Universe from Photometric Redshifts of Galaxies in the Hubble Deep Field

Studies of the Hubble Deep Field (HDF) and other deep surveys have revealed an apparent peak in the ultraviolet (UV) luminosity density, and therefore the star-formation rate density, of the Universe at redshifts 1<z<2. We use photometric redshifts of galaxies in the HDF to determine the comoving UV luminosity density and find that, when errors (in particular, sampling error) are properly accounted for, a flat distribution is statistically indistinguishable from a distribution peaked at z~1.5. Furthermore, we examine the effects of cosmological surface brightness (SB) dimming on these measurements by applying a uniform SB cut to all galaxy fluxes after correcting them to redshift z=5. We find that, comparing all galaxies at the same intrinsic surface brightness sensitivity, the UV luminosity density contributed by high intrinsic SB regions increases by almost two orders of magnitude from z~0 to z~5. This suggests that there exists a population of objects with very high star formation rates at high redshifts that apparently do not exist at low redshifts. The peak of star formation, then, may occur somewhere beyond a redshift z~>5.Comment: 4 pages total, including 3 embedded figures, to appear in the proceedings of the Xth Rencontres de Blois, "The Birth of Galaxies." LaTeX style file include

The Star Formation Rate Intensity Distribution Function--Implications for the Cosmic Star Formation Rate History of the Universe

We address the effects of cosmological surface brightness dimming on observations of faint galaxies by examining the distribution of "unobscured" star formation rate intensities versus redshift. We use the star formation rate intensity distribution function to assess the ultraviolet luminosity density versus redshift, based on our photometry and photometric redshift measurements of faint galaxies in the HDF and the HDF--S WFPC2 and NICMOS fields. We find that (1) previous measurements have missed a dominant fraction of the ultraviolet luminosity density of the universe at high redshifts by neglecting cosmological surface brightness dimming effects, which are important at redshifts larger than z = 2, (2) the incidence of the highest intensity star forming regions increases monotonically with redshift, and (3) the ultraviolet luminosity density plausibly increases monotonically with redshift through the highest redshifts observed. By measuring the spectrum of the luminosity density versus redshift, we also find that (4) previous measurements of the ultraviolet luminosity density at redshifts z < 2 must be reduced by a factor 2 to allow for the spectrum of the luminosity density between rest-frame wavelengths 1500 and 2800 A. And by comparing with observations of high-redshift damped Lyman-alpha absorption systems detected toward background QSOs, we further find that (5) the distribution of star formation rate intensities matches the distribution of neutral hydrogen column densities at redshifts z = 2 through 5, which establishes a quantitative connection between high-redshift galaxies and high column density gas and suggests that high-redshift damped Lyman-alpha absorption systems trace lower star formation rate intensity regions of the same galaxies detected in star light in the HDF and HDF--S.Comment: 28 pages, 9 figures; accepted for publication in the Astrophysical Journa

AN ACOUSTIC / RADAR SYSTEM FOR AUTOMATED DETECTION, LOCALIZATION, AND CLASSIFICATION OF BIRDS IN THE VICINITY OF AIRFIELDS

Bird-aircraft collisions present a significant threat to military and commercial aircraft, and as bird populations and air traffic continue to grow, and airport/airbase operations continue to expand, the problem will steadily get worse. To help mitigate bird strike hazards, we propose a multi-sensor system consisting of ground radar and acoustic sensors that can directly monitor bird activity and provide an alert when a threat condition occurs. Radar offers a large detection range and the ability to detect in all weather conditions, while acoustic sensors allow the ability to detect targets in the midst of clutter and add the capability to classify. A multi-sensor approach ensures that the system can provide bird strike monitoring capability in any situation with a low false alarm rate. As the Phase II effort of an Air Force STTR project, we have constructed and tested a microphone array adapted from state-of-the-art undersea warfare sensor technology that measures accurate angles to any acoustic source (broadband or narrowband) and a parabolic dish microphone which provides high-gain data on targets of interest. A test was conducted near Panama City / Bay County International Airport in conjunction with the Merlin Bird Detection Radar designed by DeTect, Inc. Results of this test will be presented and show that the acoustic array is capable of detecting, localizing in angle, and tracking multiple targets simultaneously, including birds, bats, aircraft, automobiles, people, and boats. The parabolic dish microphone was able to provide very high-gain acoustic data on several of these targets. The radar data was used as truth data for acoustic sensor performance evaluation and to determine situations in which the acoustic data can benefit the radar. Altogether, almost three days of continuous acoustic and radar data were collected, and analysis of these data show that the hybrid radar-acoustic system can provide bird strike avoidance capability