This week on HST

HST Programs: May 29 - June 4, 2017

Selected highlights

GO 14114: A Wide-Field WFC3 Imaging Survey in the COSMOS Field

The full COSMOS field

Hubble has made significant contributions in many science areas, but galaxy formation, assembly and evolution is a topic that has been transformed by the series of deep fields obtained over the past 20 years. The largest area survey to date was conducted in Cycles 12 & 13,when the Advanced Camera for Surveys was used to obtain single filter (F814) images of 2 square degrees in 640 orbits. The resultant dataset, the COSMOS survey, has been surveyed subsequently from both ground and space, with data spanning all wavelengths from X-ray through optical and infrared to the sub-millimetre and millimetre regimes. The HST data are important in providing data with exquisite angular resolution, as well as depth, providing important morphological information on galaxies in the field. Multi-wavelength data at the same resolution can provide important information on star formation history and evolution, and the spatial distribution of dust. Additional HST observations have been obtained for subsets of the field (eg the CANDELs field), but the large areal span has made full coverage overly expensive. That is, until a new observing technique was devised for HST that enables observations of multiple distinct fields in a single orbit. In standard the observing scenario, HST moves to a field, then acquries a guidestar to ensure acurate pointing and stability during the observation; each guide star acquisition takes 4-5 minutes, and HST is generally restricted to 2 pointings at most. In the new mode, HST makes the initial guide-star acquisition, but then offsets to new fields. The telescope drifts without a guide star, but this can be dealt with for near-infrared wavelength imaging; the HST detectors use multiple non-destructive reads, and the telescope drifts by a very limited amount in the time between reads. The net result is that it is possible to cover the COSMOS fields with H-band observations in 57 orbits, adding high angular resolution near-infrared data to compleemnt the ACS I-band data.

GO 14645: The stellar origins of supernovae

A recent supernova in M100

Supernovae mark the (spectacular) evolutionary endpoint for a subset of stellar systems. Standard models predict that Type II supernovae originate from relatively massive stars, while Type Ia arise from interactions between close binaries that include a compact (WD, neutron star) component. There are, however, still some questions over whether we fully understand the range of possible progenitors.The present program focuses on probing the progenitors of nearby supernovae. 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. Over the past 25 years, Hubble has acquired images of numerous galaxies, and some of the newly discovered supernovae fall within those galaxies. The research team associated with this project will scour those data for evidence of a point-source that matches the astrometric position of the supernova derived from ground-based data. Should such a candidate be detected, Hubble observations are triggered to refine the supernova position and obtain a more definitive match with a optential progenitor in the pre-supernova hubble image. The present observation targets the type IIb supernova SN2017EIN, discovered in NGC 3938 on May 25 2017.

GO 14772: Observing gas in Cosmic Web filaments to constrain simulations of cosmic structure formation

Cosmological simulations of structure in the WHIM

Only a small fraction of the baryons in the Universe, perhaps 10%, are thought to reside in visible matter in galaxies. About 30% of the total likely contributes to the ionised gas detected in Lyman-alpha absorption studies. The remainder is generally believed to reside in the WHIM - the Warm-Hot Intergalactic Medium. This material is generally expected to form highly filamentary structures, some of which collapse and condense to for galaxies in the early Universe. Such structures can only be detected through the effect that they have on the light emitted by background sources. As the light passes through the filament, absorption occurs at specific wavelengths that depend on the composition and ionisation of the component materials. The present program focuses on 10-Mpc long filamentary structure that has been identified by mapping the distribution of galaxies in the (relatively) local universe (the measured velocities correspond to a redshift, z~0.01). The present program is using the Cosmic Origins Spectrograph to obtain observations of QSOs and/or AGN, providing a detailed map of the density and ionisation structure.

GO 14811: The Grand Finale : probing the origin of Saturn's aurorae with HST observations simultaneous to Cassini polar measurements

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. Saturn passed through its equinox in August 2009, and in the succeeding years the north pole has tilted more and more towards the Sun. As a consequence, we now have an excellent view of the polar regions. Moreover, the Cassini probe has moved into a polar orbit, that takes it regularly across the auroral regiosn. The present program is using STIS to obtain time-tagged FUV images during those passages, enabling a direct comparison of the large-scale structure with in situ measurements by the Cassini spacecraft.