This week on HST

HST Programs: August 24 - August 30, 2015

Selected highlights

GO 13645; Galactic Environment of A Twenty-Billion Solar-Mass Black Hole at the End of Reionization

Artist's impression of an accreting super-mass black hole

Quasars are highly energetic sources that can achieve luminosities substantially exceeding 1012 LSun. These objects are generally believed to be powered by accretion onto a central supermassive black hole, with M > 107 MSun. Many QSOs reside within galaxies that are morphologically similar to elliptical galaxies, which are predominantly gas poor at the present epoch. One of the key research areas in galaxy evolution centres on the formation and growth of the central supermassive black hole and how that growth might have influenced the development of the surronding host galaxy. The present program targets a newly-discovered high-redshift quasar for detailed study. The system, J0010+2802, lies at a redshift of z~6.30 and is approximately ten times more luminous than they typical z~6 QSO. This program will combine ACS i, z and WFC3-IR J, H imaging to identify young, star-formign galaxies in the vicinity of the QSO, and probe the UV emission and star formation in the quasar host.

GO 13831: GRB hosts and the search for missing star formation at high redshift

ACS images of GRB host galaxies

Gamma ray bursts are events that tap extraordinary energies (1045 to 1047 joules) in remarkably short periods of time. Several thousands bursts have been detected over the last 30+ years, and analyses indicate that they can be divided into two classes with durations longer or shorter than 2 seconds. The short bursts appear to release more high energy radiation, so the two subsets are known as long/soft and short/hard bursts.The short/hard bursts appear to arise from coalescing binary systems (probably pairs of neutron stars or black holes), but the long/soft bursts appear to originate in the collapse of very massive stars. The latter sources are therefore almost certainly associated with star formation, so they act as signposts to active star-forming regions in the high redshift universe. This program aims to use GRBs to identify young galaxies at redshifts 8.2 > z > 6. The WFC3-IR camera is targetting the locations of GRBs that have been either been spectroscopically confirmed at those redshifts or have high photometric redshifts. In each case, the GRB is long gone, so the WFC3-IR F140W imaging should reveal the underlying host galaxy, allowing a determination of its morphology and luminosity.

GO 13677: See Change: Testing time-varying dark energy with z>1 supernovae and their massive cluster hosts

HST/ACS images of a supernova in a galazy at z=1.2

The last few years of the twentieth century saw a revolution in cosmology, with the measurement of the acceleration term in expansion at high redshifts and the identification of dark energy as a major cosmological component. The overall significance of this result has been recognised through the award of the Nobel prize and, most recently, the Fundamental Physics Breakthrough Prize to Perlmutter, Riess and Schmidt and their respective teams. Type Ia supernovae are the prime yardstick for measuring the rate of expansion at moderate and high redshifts. The seminal work in this field was carried out with ground-based telescopes, but Hubble offers almost the only way of obtaining reliable post-maximum photometry of these objects to determine the full shape of the light curve. Many previous HST supernovae programs have concentrated on field galaxies, but applying appropriate corrections for in situ reddening by dust remains an issue in these systems, while the overall SNe detection rates are relatively low at high redshifts. The present program takes a different tack, and aims to minimise the uncertainties by searching for supernovae in massive, high-redshift clusters. The expectation is that the majority of detections lie within dust-poor elliptical galaxies; moreover, supernova rates may be higher. The program will obtain ACS observations of ten of the most massive galaxy clusters lying at redshifts 1.1 < z < 1.75.

GO 14045: Longitude-resolved maps of Uranus's radio emission

The changing aspect of Uranus

Uranus is the nearer of the Solar System's ice giants, following an orbit that takes it between 18.4 and 20.1 AU from the Sun. As such, it has only been visited by one NASA mission, Voyager 2 in January 1986. At that time, the planet appeared almost featureless to both Voyager and ground-based telescopes. That remained the case until 2006, one year before Uranus passed through the equinox, when Hubble observations revealed a dark spot in addition to equatorial bands. The feature is likely an atmospheric storm, with a similar origin to features visible in Jupietr and Saturn. The overall lower activity likely reflects the much lower insolation level, an order of magnitude less than at Jupiter's orbit. There have been several subsequent outbreaks, with both dark and bright spots visible at a range of wavelengths. This has led to speculation that the increased activity might be related to the change in orientation with respect to the Sun: Uranus has an inclination of close to 90 degrees; as it moves through it's 84-year orbit, the orientation changes from pole-on to the Sun, through an equatorial view, to directing the other pole towards the Sun. The present observations aim to combine multi-wavelength imaging of Uranus with HST and radio observations with the VLA in A configuration to probe the wind structrue in the atmosphere, with the aim of understanding the dynamics and the potential for long-term cyclical variations drivn by the inclination.