This week on HST

HST Programs: November 24 - November 30 , 2014

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 13677: Fellowship of the Andromeda Dwarf Galaxies: A Census of their Extended Star Formation Histories

M31, the Andromeda spiral galaxy, and its companiosn - from the PANDAS survey

M31, the Andromeda galaxy, is the nearest large spiral system to the Milky Way (d ~ 700 kpc), and, with the Milky Way, dominates the Local Group. The two galaxies are relatively similar, with M31 likely the larger system; thus, Andromeda provides the best opportunity for a comparative assessment of the structural properties of the Milky Way. Like the Milky Way, Andromeda has a number of satellite galaxy companions. At present, some 31 systems have been identified, the majority from the Pan Andromeda Archaeological Survey (PANDAS), a wide-field survey utilising ground-based imaging data. The four most prominent satellites are the dwarf ellipticals NGC 147, NGC 185, NGC 205 and M32; most of the remaining systems are dwarf spheroidals, with absolute visual magnitudes between MV<\sub> =-10 and -6 and masses less than 108 MSun. The present program aims to probe the star formation history of these systems. The Advanced Camera for Surveys (ACS) will be used to obtain deep V (F606W) and I(F814W) imaging of the 19 dwarf spheroidals that currently lack any HST data; the structure of the red giant branch and horizontal branch in the resultant colour-magnitude diagrams will map the metallicity and age of the component stellar populations.

Finding chart for the multiply imaged supernova, SN Refsdal, discovered in November 2014 in cluster MACJ1149

The overwhelming majority of galaxies in the universe are found in clusters. As such, these systems offer an important means of tracing the development of large-scale structure through the history of the universe. Moreover, as intense concentrations of mass, galaxy clusters provide highly efficient gravitational lenses, capable of concentrating and magnifying light from background high redshift galaxies to allow detailed spectropic investigations of star formation in the early universe. Hubble imaging has already revealed lensed arcs and detailed sub-structure within a handful of rich clusters. At the same time, the lensing characteristics provide information on the mass distribution within the lensing cluster. Hubble is currently undertaking deep imaging observations of up to 6 galaxy clusters as part of the Frontier Fields Director's Time program (GO 13495/13496). Those observations have provided a basis for several synergistic programs. The present program is using the Frontier Field observations to search for supernovae at high redshifts, z> 1.5, aiming to set further constraints on dark energy and probing the frequency of supernovae as a function of redshift, the delay time and hence the likely progenitors. Recent observations of the fourth cluster, MACSJ1149.5+2223, resulted in the detection of a particularly unusual object - multiple lensed images of a supernova in a redshift z=1.49 galaxy that is itself multiply lensed. Each of those images results from light following a different path due to the gravitational potential of the foreground cluster and galaxies. Follow-up observations are being obtained to monitor the light-curves of each component, hence determining the time-delay for each light path. Those measured delays can be matched against the predictions of gravitational lensing models. Moreover, since the galaxy itself has multiple images it is possible that future observations may detect images of the supernova in other components. Thus, this supernova can be discovered more than once.

GO 13802: Characterizing the Sun's 4th Closest Neighbor and the Coldest Known Brown Dwarf

The stellar menagerie: Sun to Jupiter, via brown dwarfs

Brown dwarfs are objects that form in the same manner as stars, by gravitational collapse within molecular clouds, but which do not accrete sufficient mass to raise the central temperature above ~2 million Kelvin and ignite hydrogen fusion. As a result, these objects, which have masses less than 0.075 MSun or ~75 MJup, lack a sustained source of energy, and they fade and cool on relatively short astronomical (albeit, long anthropological) timescales. Following their discovery over a decade ago, considerable observational and theoretical attention has focused on the evolution of their intrinsic properties, particularly the details of the atmospheric changes. At their formation, most brown dwarfs have temperatures of ~3,000 to 3,500K, comparable with early-type M dwarfs, but they rapidly cool, with the rate of cooling increasing with decreasing mass. As temperatures drop below ~2,000K, dust condenses within the atmosphere, molecular bands of titanium oxide and vanadium oxide disappear from the spectrum to be replaced by metal hydrides, and the objects are characterised as spectral type L. Below 1,300K, strong methane bands appear in the near-infrared, characteristics of spectral type T. At present, the coolest T dwarfs known have temperatures of ~650 to 700K. At lower temperatures, other species, notably ammonia, are expected to become prominent, and a number of efforts have been undertaken recently to find examples of these "Y" dwarfs. The search is complicated by the fact that such objects are extremely faint instrinsically, so only the nearest will be detectable. Identifying such ultra-ultracool dwarfs was a goal of the WISE satellite mission, which completed an all-sky survey in 2011 (and is currently being employed in a search for Near-Earth Objects, NEOWISE). WISE has identified several Y dwarfs, including several with temperatures lower than 350K. The most interesting source was discovered by Kevin Luhman (Penn State), WISE0855-071, a brown dwarf lying only 2.2 parsecs from the Sun with a surface temperature around 250 K. The object is extremely faint and is only detectable by virtue of its proximity. The present program aims to obtain J-band photometry using the F110W filter on WFC3-IR.