This week on HST

HST Programs: July 3 - July 9, 2006

Program Number Principal Investigator Program Title Links
9746 Jean-Luc Margot, Cornell University Binary systems in the Kuiper Belt Abstract
10396 John Gallagher, University of Wisconsin - Madison Star Clusters, Stellar Populations, and the Evolution of the Small Magellanic Cloud Abstract
10494 Leon Koopmans, Kapteyn Astronomical Institut Imaging the mass structure of distant lens galaxies Abstract
10496 Saul Perlmutter, Lawrence Berkeley National Laboratory Decelerating and Dustfree: Efficient Dark Energy Studies with Supernovae and Clusters Abstract
10503 Gary Da Costa, Australian National University The Star Formation Histories of Early Type Dwarf Galaxies in Low Density Environments: Clues from the Sculptor Group Abstract
10504 Richard Ellis, California Institute of Technology Characterizing the Sources Responsible for Cosmic Reionization Abstract
10510 Marcella Longhetti, Osservatorio Astronomico di Brera, Milano Morphology of massive early-type galaxies at z>1.2: constraining galaxy formation models Abstract
10516 Bradley Peterson, The Ohio State University Research Foundation Host Galaxies of Reverberation-Mapped AGNs Abstract
10532 Kai Noeske, University of California - Santa Cruz Kinematics and morphology of the most massive field disk galaxies at z>1 Abstract
10542 Antonella Nota, Space Telescope Science Institute Charting the Sparkling Star Formation in NGC346 Abstract
10545 Michael Brown, California Institute of Technology Icy planetoids of the outer solar system Abstract
10556 David Turnshek, University of Pittsburgh Neutral Gas at Redshift z=0.5 Abstract
10567 Helmut Jerjen, Australian National University Securing the Faint-End Galaxy Luminosity Function with Surface Brightness Fluctuation Distances Abstract
10592 Aaron Evans, State University of New York at Stony Brook An ACS Survey of a Complete Sample of Luminous Infrared Galaxies in the Local Universe Abstract
10629 Sally Oey, University of Michigan Are Field OB Stars Alone? Abstract
10630 Anna Pasquali, Eidgenossiche Technische Hochschule (ETH) The Fine Structure of Elliptical Galaxies in Voids Abstract
10760 Michael Garcia, Smithsonian Institution Astrophysical Observatory Black Hole X-ray Novae in M31 Abstract
10775 Ata Sarajedini, University of Florida An ACS Survey of Galactic Globular Clusters Abstract
10797 Knud Jahnke, Max-Planck-Institut fur Astronomie, Heidelberg HE0450-2958: Lonesome black hole, scantly dressed quasar or massively dust obscured host galaxy? Abstract
10808 Pieter van Dokkum, Yale University Morphologies of spectroscopically-confirmed red and dead galaxies at z~2.5 Abstract
10824 Oleg Gnedin, The Ohio State University Research Foundation Measuring the Shape and Orientation of the Galactic Dark-Matter Halo using Hypervelocity Stars Abstract
10849 Stanimir Metchev, University of California - Los Angeles Imaging Scattered Light from Debris Disks Discovered by the Spitzer Space Telescope around 21 Sun-like Star Abstract
10879 I. Neill Reid, Space Telescope Science Institute A search for planetary-mass companions to the nearest L dwarfs - completing the survey Abstract
10906 Sylvain Veilleux, University of Maryland The Fundamental Plane of Massive Gas-Rich Mergers: II. The QUEST QSOs Abstract
10928 John Subasavage, Georgia State University Research Foundation Calibrating Cosmological Chronometers: White Dwarf Masses Abstract

Some selected highlights

GO 10503: The star formation histories of early type dwarf galaxies in low density environments: Clues from the Sculptor Group

NGC 625 - a dwarf galaxy in the Sculptor group The Sculptor group is a relatively low density aggregate of 12-15 galaxies lying at a distance of approximately 3 Mpc. The dominant member is the spiral galaxy, NGC 253, and the group includes a handful of other relatively low luminosity spiral galaxies, but most members are dwarf irregular or elliptical galaxies. Recent observations have detected HI gas and, perhaps, limited numbers of hot, blue stars, suggesting modest star formation, in several dwarf systems - including systems classed as dE. This suggests that these might be "transition" dwarfs, similar to the nearby Phoenix dwarf and LGS3. This program is using the wide-field camera on ACS to obtain deep F606W and F814W images of five Sculptor dwarfs. The aim is to use the resultant colour-magnitude diagrams, which will encompass the upper reaches of the red giant branch and should reach below the horizontal branch in the nearer dwarfs, to study the star formation history in these relatively isolated systems.

GO 10542 Charting the Sparkling Star Formation in NGC346

WFPC2 image of the SMC cluster, NGC 346 The Small Magellanic Cloud has a mass that is less than 0.5% that of the Milky Way, but it encompasses star-forming complexes that are the equal of any Galactic counterpart. The most massive such system is NGC 346, with a diameter of ~70 parsecs and lying in the main body of the SMC. The cluster includes the eruptive variable, HD 5980, which for a short period in 1994 was the most luminous star in the SMC. Previous ACS observations have revealed many compact star clusters, some still embedded in the parent dust clouds. There are also numerous low mass (< 3 solar masses) pre-main-sequence stars distributed throughout the region. The present proposal will extend observations to cover a broader swathe of the complex, using the ACS images in the V (F606W) and I (F814W) filters to probe the stellar mass function to ~0.6 solar masses, and investigate the degree of mass segregation within this active star-ofrming region.

GO 10545: Icy planetoids of the outer solar system

An artist's impression of the view from Sedna The Kuiper Belt lies beyond the orbit of Neptune, extending from ~30 AU to ~50 AU from the Sun, and includes at least 70,000 objects with diameters exceeding 100 km. Setting aside Pluto, the first trans-Neptunian objects were discovered in the early 1990s. Most were relatively modest in size, with diameters of a few hundred km and photometric properties that suggested an icy composition, similar to Pluto and its main satellite, Charon. Over the last three years, however, a handful of substantially larger bodies have been discovered, with diameters of more than 1000 km; one of the objects, 2003 UB313, is comparable in size to Pluto (2320 km.).Both HST and the Spitzer infrared space telescope have played an important role in these recent discoveries, measuring the angular diameter and the albedo over a wide range of wavelengths. The aim of the present set of observations is to target ~20 trans-Neptunian objects, using red (F606W) images and low-resolution spectra, obtained with the High Resolution Camera on the Advanced Camera for Surveys, to probe their size and chemical composition.

GO 10556: Neutral gas at redshift z=0.5

Hubble WFPC2 images of a faint galaxy near a z=2.81 QSO; the galaxy, lying ~1" from the QSO, is only visible after psf subtraction (lower panel), but produces damped Ly-alpha absorption in the QSO spectrum. Bahcall & Salpeter originally suggested in 1965 that there might be a population of intergalactic hydrogen clouds lying along the line of sight to quasars (or high redshift galaxies) that could be detected through absorption in the QSO spectrum. That prediction was soon confirmed, with the detection of numerous absorption lines blueward of the QSO Lyman alpha emission line - the Lyman alpha forest. Most of those lines are extremely narrow, but a subset are suficiently strong that they are completely opaque at the base. These damped Lyman-alpha absorption lines must arise in systems that have a hydrogen column density exceeding 12019 cm-2, indicating a substantial mass of neutral hydrogen gas. A subset of DLA lines have been identified with particular galaxies (through redshift measurements), many lying far from the QSO line of sight. It is possible that both those systems and DLA systems that lack an optical counterpart are progenitors of spiral or irrgeular galaxies. Ground-based observations of DLA systems are restricted to redshifts z>1.65 by the atmospheric cutoff at 3100 Angstroms, but HST allows observations to extend to lower redshifts. The present proposal is using the PR200L prism on the ACS/HRC to survey 109 targets. These observations will extend the DLA census to redshifts between ~0.37 and ~0.7, and will therefore provide valuable information on the evolution of these systems at intermediate redshifts.

Past weeks:
page by Neill Reid, updated 15/6/2006