Jonathan Perry Gardner

A SPECTROSCOPIC SEARCH FOR LEAKING LYMAN CONTINUUM AT z ∼ 0.7*

We present the results of rest-frame, UV slitless spectroscopic observations of a sample of 32 z ~ 0.7 Lyman break galaxy (LBG) analogs in the COSMOS field. The spectroscopic search was performed with the Solar Blind Channel on the Hubble Space Telescope. We report the detection of leaking Lyman continuum (LyC) radiation from an active galactic nucleus-starburst composite. While we find no direct detections of LyC emission in the remainder of our sample, we achieve individual lower limits (3σ) of the observed non-ionizing UV-to-LyC flux density ratios, f -ν (1500 A)/f _ν(830 A) of 20 to 204 (median of 73.5) and 378.7 for the stack. Assuming an intrinsic Lyman break of 3.4 and an intergalactic medium transmission of LyC photons along the line of sight to the galaxy of 85%, we report an upper limit for the relative escape fraction in individual galaxies of 0.02-0.19 and a stacked 3σ upper limit of 0.01. We find no indication of a relative escape fraction near unity as seen in some LBGs at z ~ 3. Our UV spectra achieve the deepest limits to date at any redshift for the escape fraction in individual sources. The contrast between these z ~ 0.7 low escape fraction LBG analogs with z ~ 3 LBGs suggests that either the processes conducive to high f esc are not being selected for in the z 1 samples or the average escape fraction is decreasing from z ~ 3 to z ~ 1. We discuss possible mechanisms that could affect the escape of LyC photons

Room Temperature, Continuous-Wave Coupled-Cavity InAsP/InP Photonic Crystal Laser with Enhanced Far-field Emission Directionality

We demonstrate room temperature, continuous-wave lasing with enhanced far field emission directionality in coupled-cavity photonic crystal lasers, made with InAsP/InP quantum well material. These surface-emitting lasers can have a very low effective threshold power of 14.6 μW, with a linewidth of 60 pm, and 40% of the surface emitted power concentrated within a small divergence angle of ±30°.

Galaxies Unveiled: Rest-frame UV Clumps at 0.5 < z < 1.5

Studies of high redshift galaxies reveal compact sub-galactic regions of star formation, known as ‘clumps’. These ‘clumpy’ galaxies are useful for the study of galactic outskirts by enabling us to examine the radial progression of clumps over large time scales. We use the first deep high resolution NUV image from the Hubble Space Telescope covering intermediate redshifts to explore the implications this radial progression may have on galaxy evolution. From the analysis of 209 clumpy galaxies, we find that higher redshift clumps dominate the outer regions of galactic outskirts. This indicates that clumps may be migrating from the outskirts inward toward their galactic centers.

Galaxy number counts at 300 nm from WFPC2 images

We have begun analyzing archival WFPC2 F300W images to obtain galaxy counts over a wider area and at brighter magnitudes than those measured in the Hubble Deep Field (HDF), and to develop techniques for analyzing future random-field data. Galaxy counts at 300 nm are sensitive to evolutionary effects on relatively short timescales. Locally, in galaxies with a constant star formation rate, F300W detects stars averaging ∼500u2009Myr in age, as compared to ∼1.6u2009Gyr for B. At a redshift of 0.5, F300W detects stars averaging ∼60u2009Myr in age. In order to determine the galaxy counts, we have developed a semi-automated analysis based on the SExtractor program of Bertin. An IDL program parses input parameters, removes cosmic rays, and invokes SExtractor, which generates the source catalogs. Another IDL program merges selected data from the catalogs after applying photometric zero points and correcting for Galactic extinction. A preliminary comparison of our F300W number counts to those from the HDF will be presented.