This week on HST


HST Programs: June 30 - July 6, 2014

Program Number Principal Investigator Program Title
13291 Masao Hayashi, National Astronomical Observatory of Japan (NAOJ) Resolving internal structures of the progenitors of early-type galaxies in a vigorously forming cluster at z=2.5
13297 Giampaolo Piotto, Universita degli Studi di Padova The HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation
13305 Carolin Villforth, University of St. Andrews Do mergers matter? Testing AGN triggering mechanisms from Seyferts to Quasars
13330 Bradley M Peterson, The Ohio State University Mapping the AGN Broad Line Region by Reverberation
13332 Seth Redfield, Wesleyan University A SNAP Survey of the Local Interstellar Medium: New NUV Observations of Stars with Archived FUV Observations
13352 Matthew A. Malkan, University of California - Los Angeles WFC3 Infrared Spectroscopic Parallel Survey WISP: A Survey of Star Formation Across Cosmic Time
13360 Saurabh W. Jha, Rutgers the State University of New Jersey The Peculiar Type Ia Supernova 2012Z: A Massive Star Progenitor?
13366 Roelof S. de Jong, Leibniz-Institut fur Astrophysik Potsdam The vertical disk structure of spiral galaxies and the origin of their thick disks
13386 Steven A. Rodney, The Johns Hopkins University Frontier Field Supernova Search
13397 Luciana C. Bianchi, The Johns Hopkins University Understanding post-AGB Evolution: Snapshot UV spectroscopy of Hot White Dwarfs
13398 Christopher W. Churchill, New Mexico State University A Breakaway from Incremental Science: Full Characterization of the z<1 CGM and Testing Galaxy Evolution Theory
13412 Tim Schrabback, Universitat Bonn, Argelander Institute for Astronomy An ACS Snapshot Survey of the Most Massive Distant Galaxy Clusters in the South Pole Telescope Sunyaev-Zel'dovich Survey
13425 Hua Feng, Tsinghua University Multiwavelength Test For A Standard Accretion Disk Around An Intermediate Mass Black Hole Candidate
13444 Bart P. Wakker, University of Wisconsin - Madison Constraining the size of intergalactic clouds with QSO pairs
13445 Joshua S. Bloom, University of California - Berkeley Absolute Calibration of the Extragalactic Mira Period-Luminosity Relation
13448 Andrew J. Fox, Space Telescope Science Institute - ESA The Closest Galactic Wind: UV Properties of the Milky Way's Nuclear Outflow
13456 Michael McDonald, Massachusetts Institute of Technology Searching for 300, 000 Degree Gas in the Core of the Phoenix Cluster with HST-COS
13460 Sylvain Veilleux, University of Maryland The Remarkable Ultraviolet Spectrum of Mrk 231
13463 Kailash C. Sahu, Space Telescope Science Institute Detecting and Measuring the Masses of Isolated Black Holes and Neutron Stars through Astrometric Microlensing
13472 Wendy L. Freedman, Carnegie Institution of Washington The Hubble Constant to 1%? STAGE 4: Calibrating the RR Lyrae PL relation at H-Band using HST and Gaia Parallax Stars
13483 Goeran Oestlin, Stockholm University eLARS - extending the Lyman Alpha Reference Sample
13495 Jennifer Lotz, Space Telescope Science Institute HST Frontier Fields - Observations of Abell 2744
13513 Julia Comerford, University of Colorado at Boulder A Pilot Search for Spatially Offset AGN in Galaxy Merger Remnants
13515 Breanna Binder, University of Washington The Effect of Intermediate-Luminosity Transients on the X-ray Luminosity Functions of Spiral Disks

Selected highlights

GO 13297: The HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation


Hubble image of the metal-poor globular cluster, M15
Globular clusters are members of the Galactic halo population, representing remnants from the first extensive period of star formation in the Milky Way. As such, the properties of the 106 to 107 stellar constituents can provide crucial insight into the earliest stages of galaxy formation. Until recently, conventional wisdom was that these are simple systems, where all the stars formed in a single starburst and, as a consequence, have the same age and metallicity. One of the most surprising disoveries in recent years is the realisation that this simple picture no longer holds. Up until about 5 years ago, the only known counter-example to convention was the cluster Omega Centauri, which is significantly more massive than most clusters and has both a complex main sequence structure and a range of metallicities among the evolved stars. High precision photometric observations with HST has demonstrated that Omega Cen is far from unique, with multiple populations evident in numerous other clusters, including NGC 2808, NGC 1851, 47 Tuc and NGC 6752. Multiple populations have also been discerned in a number of clusters in the Magellanic clouds. Sustaining multiple bursts of star formation within these systems demands that they retain gas beyond the first star forming event, which appears to set a requirement that these clusters were significantly more massive during their epoch of formation; put another way, the current globulars may represent the remnant cores of dwarf galaxy-like systems. That, in turn, implies that the stars ejected from those systems make a significant contribution to the current galactic halo. One of the most effective means of identifying and studying multi-population clusters is combining high-precision photometry over a wide wavelength range, particularly extending to UV wavelengths. Sixty-five globular clusters already have R/I (F606W, F814W) Hubble imaging and photometry thanks to the Cycle 14 program, An ACS Survey of Galactic Globular Clusters (GO 10775). The present program aims to build on those data by adding UV/blue observations using the F275W, F336W and F438W filters on the WFC3-UVIS camera. The colorus derived from these filters enable characterisation of the C, N and O abundances of the component stellar populations in these systems.

GO 13330: Mapping the AGN Broad Line Region by Reverberation


Simulations of the appearance and velocity structure within an AGN disk (see
Active galaxies (AGNs) are generally luminous systems, characterised by the presence of strong nuclear emission lines of numerous species including H, He I, He II, and Fe, Ca, O, C and S over a range of ionisations. These features originate from gas clouds in the nuclear regions, with the energy supplied through accretion onto a central massive black hole. The high-temperature, rapidly-rotating gas clouds nearest the central engine are responsible for producing broad emission lines (hence, the "Broad Line Region"). The structure of the BLR can be discerned using a technique known as reverberation mapping: variations in the accretion rate lead to fluctuations in luminosity; those variations lead, in turn, to variations in the photoionisation of the BLR, and corresponding changes in spectral line strengths and velocities; monitoring those changes, and correlating them with the photometric variability of the central source, measures the light travel time from nucleus to BLR gas, and hence maps the size of the BLR. The present prorgam will use the Cosmic Origins Spectrograph to undertake systematic monitoring of the nuclear regions of the Seyfert I galaxy, NGC 5548. The first observations were taken on February 2nd 2014 and the program will run through July at a cadence of one orbit per day for 179 days.

GO 13366: The vertical disk structure of spiral galaxies and the origin of their thick disks



Ground-based imaging of the edge-on spiral, NGC 891
The stars in the Milky Way are generally grouped into stellar populations, building blocks that provide insight into the process of galaxy assembly. The traditional populations are the near-spherical, metal-poor Halo, representing the first significant burst of star formation; the Disk, whose constituents have higher metallicities, a flattened density distribution (which defines the Galactic Plane) and significant angular momentum, suggesting a formation history that includes collapse and dissipation; and the central Bulge, which, with a spheroidal distribution and broad metallicity range, may be something of an amalgam of disk and halo. The original models for the Disk envisaged a relatively simple population, with a continuous star formation history and an exponential density distribution, both radially and perpendicular to the Plane. However, in the mid-1980s, starcount analyses revealed more complexity in the vertical density distribution, with evidence for two components with scaleheights ~300 and 1000-1300 pc. The extended component is clearly old (>9 Gyrs in age). A variety of emchanisms have been proposed for its formation, dubbed the thick disk, including dynamical scattering within the early disk, formation in situ, or perturbations as the result of major or minor mergers. Ground and space-based observations show that other spiral galaxies possess a similar component. Clearly, the frequency of such systems and their age distribution offer clues to the merging history of the average spiral galaxy. The present program will use ACS and WFC3 to image three massive edge-on spirals at several locations perpendicular to the Plane, with the aim of resolving the underlying stellar populations and tracing the metallicity distribution and overall morphology of the extended disk components.

GO 13444: Constraining the size of intergalactic clouds with QSO pairs


Radio imaging of the Magellanic Stream and intergalactic clouds in the vicinity of the Milky Way (NRAO)
Galaxy formation, and the overall history of star formation within a galaxy, clearly demands the presence of gas. The detailed evolution therefore depends on how gas is accreted, recycled, circulated through the halo and, perhaps, ejected back into the intergalactic medium. Tracing that evolutionary history is difficult, since gas passes through many different phases, some of which are easier to detect than others. During accretion and, probably, subsequent recycling, the gas is expected to be reside predominantly at high temperatures. The most effective means of detecting such gas is through ultraviolet spectroscopy, where gas within nearby systems can be detected as absorption lines superimposed on the spectra of more distant objects, usually quasars. Such observations show the presence of extensive clouds of material in the intergalactic medium in the low redshift universe. The aim of the present program is to set constraints on the spatial size of these objects by using the Cosmic Origins Spectrograph to obtain spectra of QSOs lying at relatively small angular separation on the sky. These QSO pairs lie only 2 to 5 arcminutes apart, corresponding to linear separations of ~20-50 kpc. Matching the absorption spectra in these objects, and searching for lines that match, can therefore constrain the size of foreground IGM clouds.

Past weeks:
page by Neill Reid, updated 18/5/2014
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