This week on HST

HST Programs: February 2 - February 8, 2009

Selected highlights

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

Schematic diagram of an active galactic 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 proposal 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 examine 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 11566: Imaging Saturn's Equinoctal Auroras

Saturnian aurorae

Planetary aurorae are stimulated by the influx of charged particles from the Sun, which travel along magnetic field lines and funnel into the atmosphere near the magnetic poles. Aurorae therefore require that a planet has both a substantial atmosphere and a magnetic field. They are a common phenomenon on Earth, sometimes visible at magnetic latitudes more than 40 degrees from the pole, and have also been seen on Jupiter, Saturn, Uranus and Neptune. In August 2009, Saturn reaches its equinox, with the Sun moving into the northern Saturnian hemisphere, and Earth crosses the ring plane in mid-September. As a result, it is now possible to view both Saturnian poles simultaneously. This proposal aims to use the ACS/SBC to study aurorae in the northern hemisphere, and compare their characteristics against observations of southern aurorae from previous years. In particular, the southern aurorae tend to occur in an oval whose centre is displaced from the south (rotational) pole. Does the northern hemisphere exhibit a similar phenomenon?

GO 11967: WFPC2 Imaging of the Lockman Hole

Spitzer IRAC imaging of the Lockman hole

The Lockman hole is a small region of sky within the constellation of Ursa Major, lying between the two pointer stars in the Big Dipper and approximately 10 degrees from the Hubble Deep Field Originally identified by Lockman, Jahoda and McCammon in the mid-1980s, this ~4 square degree field has an extremely low column density of HI gas, and is therefore highly transparent to radiation at high energy radiation. In the succeeding years, the Lockman field has been targeted for deep observations at X-ray wavelengths by ROSAT, Chandra, ASCA and XMM, at ultraviolet wavelengths by FUSE, at infrared wavelengths by ISO, Spitzer and, in the near future, Herschel, at sub-millimtere wavelengths with SCUBA, and at radio wavelengths by the VLA and the Giant Metrewave Radio Telescope. Extensive ground-based observations have been obtained at optical wavelengths, but, hitherto, HST observations have been limited in scope. The present program will use WFPC2 to survey the central regions of the Lockman hole in the F606W and F814W filters, providing high spatial resolution morphological information on faint galaxies.