Stellar Masses of High-Redshift Galaxies

We present constraints on the stellar-mass distribution of distant galaxies. These stellar-mass estimates derive from fitting population-synthesis models to the galaxies' observed multi-band spectrophotometry. We discuss the complex uncertainties (both statistical and systematic) that are inherent to this method, and offer future prospects to improve the constraints. Typical uncertainties for galaxies at z ~ 2.5 are ~ 0.3 dex (statistical), and factors of ~ 3 (systematic). By applying this method to a catalog of NICMOS-selected galaxies in the Hubble Deep Field North, we generally find a lack of high-redshift galaxies (z > 2) with masses comparable to those of present-day ``L*'' galaxies. At z < 1.8, galaxies with L*-sized masses do emerge, but with a number density below that at the present epoch. Thus, it seems massive, present-day galaxies were not fully assembled by z ~ 2.5, and that further star formation and/or merging are required to assemble them from these high-redshift progenitors. Future progress on this subject will greatly benefit from upcoming surveys such as those planned with HST/ACS and SIRTF.Comment: 7 pages, 5 figures. To appear in The Mass of Galaxies at Low and High Redshift, eds. R. Bender & A. Renzini (ESO Astrophysics Symposia, Springer-Verlag), Venice, 24-26 Oct 200

The WFPC2 Archival Parallels Project

We describe the methods and procedures developed to obtain a near-automatic combination of WFPC2 images obtained as part of the WFPC2 Archival Pure Parallels program. Several techniques have been developed or refined to ensure proper alignment, registration, and combination of overlapping images that can be obtained at different times and with different orientations. We quantify the success rate and the accuracy of the registration of images of different types, and we develop techniques suitable to equalize the sky background without unduly affecting extended emission. About 600 combined images of the 1,500 eventually planned have already been publicly released through the STScI Archive. The images released to date are especially suited to study star formation in the Magellanic Clouds, the stellar population in the halo of nearby galaxies, and the properties of star-forming galaxies at $z \sim 3$.Comment: 12 pages, 7 figures, to appear in the PAS

New Constraints on the Lyman Continuum Escape Fraction at z~1.3

We examine deep far-ultraviolet (1600 Angstrom) imaging of the Hubble Deep Field-North (HDFN) and the Hubble Ultra Deep Field (HUDF) to search for leaking Lyman continuum radiation from starburst galaxies at z~1.3. There are 21 (primarily sub-L*) galaxies with spectroscopic redshifts between 1.1<z<1.5 and none are detected in the far-UV. We fit stellar population templates to the galaxies' optical/near-infrared SEDs to determine the starburst age and level of dust attenuation, giving an accurate estimate of the intrinsic Lyman continuum ratio, f_1500/f_700, and allowing a conversion from f_700 limits to relative escape fractions. We show that previous high-redshift studies may have underestimated the amplitude of the Lyman Break, and thus the relative escape fraction, by a factor of ~2. Once the starburst age and intergalactic HI absorption are accounted for, 18 galaxies in our sample have limits to the relative escape fraction, f_esc,rel < 1.0 with some limits as low as f_esc,rel < 0.10 and a stacked limit of f_esc,rel < 0.08. This demonstrates, for the first time, that most sub-L* galaxies at high redshift do not have large escape fractions. When combined with a similar study of more luminous galaxies at the same redshift we show that, if all star-forming galaxies at z~1 have similar relative escape fractions, the value must be less than 0.14 (3 sigma). We also show that less than 20% (3 sigma) of star-forming galaxies at z~1 have relative escape fractions near unity. These limits contrast with the large escape fractions found at z~3 and suggest that the average escape fraction has decreased between z~3 and z~1. (Abridged)Comment: Accepted for publication in ApJ. aastex format. 39 pages, 11 figure

How children become invisible in child protection work: findings from research into day to day social work practice

It is well known that in cases in which abused children have died, social workers and other professionals did not relate to them effectively—the phenomenon now known as the ‘invisible child’. Much less well understood is how often and why such invisibility occurs where there has not been a major inquiry or scandal and this paper draws on research which observed day-to-day encounters between social workers, children and families. In most of the practice, children were seen and related to but, in a small number of home visits, social workers were not child-focused. The paper provides a detailed analysis of those cases and shows how social workers were overcome by the emotional intensity of the work and complex interactions with angry, resistant parents and family friends. Workers were also affected by organisational culture, time limits on their work and insufficient support to enable them to contain their feelings and think clearly. The powerful impact of unbearable levels of complexity and anxiety on social workers requires much greater recognition. Sociological, psycho-dynamic and systemic theories are drawn upon to establish how workers need to be helped to think clearly about children and relate to them in the close, intimate ways that are required to keep them safe

High level, long term delivery of oxytetracycline HC1 from a controlled release device in an artificial rumen

High level, long term release of oxytetracycline HCl into artificial rumens was accomplished by a controlled release device. Three controlled release devices delivered 16.33, 8.15, and 9.31 mg/day for 52, 63, and 63 days, respectively. Theory for the controlled release devices predicted release rates of 13.30, 13.48, and 13.63 mg/day for 59.19, 58.34, and 58.63 days, respectively. The release rates were nearly zero-order. The discrepancies between the experimentally determined release kinetics and those predicted by theory were largely attributed to environmental factors;The artificial rumens were found to be viable representations of in vivo rumens up to 92 days based upon pH measurements and volatile fatty acid production. No significant shifts in volatile fatty acid production were noted for the artificial rumens influenced by oxytetracycline HCl release from the delivery devices;Utilization of this controlled release system to administer oxytetracycline HCl and possibly other beneficial agents to ruminants appears to be feasible