This week on HST

HST Programs: November 24 - November 29, 2008

Some selected highlights

GO 11110: Searching for Lyman alpha Emission from FUSE Lyman Continuum Candidates

The starburst galaxy, M82

Ultraviolet light plays an important role in ionising the interstellar and intergalactic medium. Hot, massive stars are the one of the principal sources of UV flux in the present universe. It is therefore important to understand the efficiency with which that light manages to escape from star forming regions, particularly as a means of estimating the relative improtance of star formation as an ionising source in the early universe. The present program targets a number of star forming galaxies that have been observed by the Far Ultraviolet Satellite Explorer (FUSE) and detected in the Lyman continuum (shortward of 912 Angstroms). The ACS/SBC camera is being used to image those systems at Lyman alpha; ground-based imaging has already been used to map the Balmer line emission. All of these data will be combined in models that will be used to estimate the global effect of star formation on the surrounding gaseous environment.

GO 11130: AGNs with Intermediate-mass Black Holes: Testing the Black Hole-Bulge Paradigm, Part II

Schematic diagram of an active galacioc nucleus

Active galaxies are characterised by bright, compact nuclei that are the source of strong emission lines due highly ionised material. These phenomena are generally believed to arise in hot gas in an accretion disk, centred on a massive (>106 solar mass) hole; indeed, detailed kinematics for a handful of objects have confirmed the presence of a compact, massive object in the core. Most active galactic nuclei (AGNs) are found in spiral galaxies that possess at least a moderately prominent bulge. The present aims to determine whether AGNs exist within later-type spirals, with less prominent bulge components. At the same time, the proposers hope to probe the lower mass limit for black hole formation, specifically testing whether significant numbers of intermediate-mass (~105 colar mass) black holes form. To eamine this issue, this proposal targets lower luminosity galaxies, using WFPC2 to obtain I-band (F814W) images of AGNs selected from SDSS spectroscopy. Those images will be used to characterise the nuclear morphology and determine bulge/disk ratios.

GO 11789: An Astrometric Calibration of Population II Distance Indicators

Measuring trigonometric parallax

Trigonometric parallax measurement remains the fundamental method of determining distances to astronomical objects. The best ground-based parallax measurements can achieve accuracies of ~1 milliarcsecond, comparable with the typical accuracies achieved by the ESA Hipparcos astrometric satellite. This level of accuracy allows us to obtain reliable distances and luminosities for main sequence stars, subgiants, red giants and even a number of metal poor subdwarfs. However, with an effective distance limit of 100-150 parsecs, the sampling volume includes less than a handful of rarer, shorter-lived celestial objects. In particular, there are no RR Lyraes or Cepheids, two of the principal calibrators in the extragalactic distance scale. There is only one instrument currently available that can achieve astrometry of higher accuracy - the Fine Guidance Sensors (FGS) on HST. The present team used the FGS to measure a parallax of 3.82+/10.2 milliarseconds for RR Lyrae, the nearest star of its type. this corresponds to a distance of 262 parsecs. The present program aims to improve the calibration by extending observations to four more relatively nearby RR Lyraes (XZ Cyg, UV Oct, RZ Cep and SU Dra) and two Pop II Cepheids (Kappa Pav and VY Pyx).