This week on HST

HST Programs: November 2 - November 8, 2015

Selected highlights

GO 13872: The GOODS UV Legacy Fields: A Full Census of Faint Star-Forming Galaxies at z~0.5-2

ACS images of a section of the GOODS fields

The Great Observatories Origins Deep Survey, GOODS, originated as a Spitzer Legacy program coupled with a Cycle 12 HST Treasury program. The program was designed to probe galaxy formation and evolution at redshifts from z~1 to z~6. GOODS covers two ~150 sq. arcminute fields, one centred on the Hubble Deep Field in Ursa Major and the Chandra Deep Field-South in Fornax. Initially, the program combined deep optical/far-red imaging (F435W, F606W, F775W and F850LP filters) using ACS on HST with deep IRAC (3.6 to 8 micron) and MIPS (25 micron) imaging with Spitzer. These two fields have become among the most studied celestial regions. In addition to deep HST data at optical and near-infrared wavelengths (both fields have been covered by NICMOS), the fields have been covered at X-ray wavelengths by Chandra (obviously) and XMM-Newton, and ground-based imaging and spectroscopy using numerous telescopes, including the Kecks, Gemini, Surbaru and the ESO VLT. Part of the GOODS South field was covered by the WFC3 Early Release Science observations (see WFC3 ERS ), and both fields are also covered partially by one of the three Multi-Cycle Treasury programs allocated time in Cycle 18-20. Further observations were obtained in Cycle 17, using the G141 grism on the WFC3 IR camera to identify H-alpha+[N II] emission from galaxies at redshifts 0.7 < z < 1.5, and thereby set constraints on star formation at those redshifts. The present program builds on these multiple datasets by adding WFC3-UVIS imaging with the F275W and F336W. These data will cover the CANDELS sections of GOODs and sample far-UV radiation from galaxies at edshifts z > 0.5, tracing the evolution of the FUV luminosity through the peak epoch of star formation.

GO 14037: HST Frontier Fields - Observations of Abell S1063

The Frontier Fields cluster, Abell S1063

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. The present program builds on the highly successful CLASH program,which used 17-colour ACS/WFC3 images to map 25 galaxy clusters, tracing the mas profile and the dark matter distribution. in addition, the observations identified several lensed galaxies at redshifts that enter the JWST domaine, with the most distant object lying at a redshift z~11, within a few hundred million years of the Big Bang. The Frontier Fields program is a large-scale Director's Discretionary program that capitalises on the latter characteristic by targeting 6 strong-lensing galaxy clusters for very deep optical and near-infrared imaging. WFC3 and ACS will be used to observe the clusters, with simultaneous imaging obtained in parallel of a nearby "blank" field. Since the observations need to made at a specific orientation, they are being taken in two sets, ~6 months apart, alternating between detectors. Abell S1063 at z=0.348 is the fifth target. The first epoch of observation are currently being obtained, with the cluster imaged with ACS and WFC3-IR obtaining obtain optical data on the nearby blank field. The second epoch observations, in April-June 2016, switch cameras, with ACS on the cluster and WFC3-IR on the parallel field.

GO 14136: Search for material around Chiron

The location of the ring system surrounding the centaur, Chariklo

Ring systems are features of all of the gas giants in the Solar System. Saturn's rings are the most prominent, evident to Galileo even if he was unable to discern their nature; the Uranian rings were discovered through stellar occultation measurements in 1977; Neptune's ring system was revealed in a similar manner in the 1980s; and Jupiter's rings were identified by Voyager 1 in 1979. In each case, the rings are believed to be comprised of small particles of rock, ice and dust that are sustained through collisions and maintained in place by gravitational interactions with larger satellites. One other body is known to have a ring system - the asteroid, Chariklo. In contrast to the gas giants, Chariklo is a Centaur, a minor planet orbiting between Uranus and Saturn with a diameter of only ~230 km. Centaurs are believed to originate in the Kuiper belt and are in dynamically unstable orbits that may lead to ejection from the Solar System. Chiron is the original Centaur, discovered by Charles Kowal on the Palomar Schmidt, with a diameter of about 110 km. Chiron brightened significantly in 1988 and developed a coma in April 1989, suggesting the presence of extensive ice. In 2011, a stellar occultation revealed some photometric dips suggetive of the presence of a shel or ring. Chariklo showed similar characteristcis during an occultation of a background star in 2013. As noted, those observations have been interpreted as revealing the presence of two rings, ~7 and ~3 km wide and ~9 km apart. Those rings are hypothesised to include at least some water ice particles; previous spectroscopic observations had shown variable water-ice features, together with photometric variability, that could be explained if the rings were edge-on to earth at that epoch. Th existence of a ring system in such a small body is extremely unexpected, and the system is likely to have a dynamical lifetime of only a few million years. The present program targets Chiron and aims to image the potential ring system(s) directly through deep imaging with the UVIS camera on WFC3.

GO 14149: Continuing a Snapshot Survey of the Sites of Recent, Nearby Supernovae

A recent supernova in M100

Supernovae mark the (spectacular) evolutionary endpoint for a subset of stellar systems. Standard models predict that they originate from massive stars and (probably) close binaries with a compact (WD, neutron star) component, but there are still some questions remaining over whether we fully understand the range of possible progenitors. The last decade has seen the development of a number of large-scale programs, usually using moderate-sized telescopes, that are dedicated to monitoring (relatively nearby galaxies, searching for new supernovae. This program builds on observations taken in several previous cycles, and aims to obtain follow-up multi-waveband images of nearby galaxies, focusing on the sites of recent supernovae. The program concentrates on systems within 20 Mpc of the Milky Way. The observations are taken well after maximum, with the aim of using the unparalleled angular resolution of WFC3 to identify the fading remnant, search for evidence for light echoes,characterise the local stellar population and perhaps determine the nature of the likely progenitor.