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DAILY REPORT #3912
HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science
DAILY REPORT #3912 PERIOD COVERED: UT July 28, 2005 (DOY 209) OBSERVATIONS SCHEDULED ACS/HRC 10435 Merger-Induced Populations in Early-Type Galaxy Cores Hierarchical formation models predict that early-type galaxies are built up over an extended period from mergers of smaller systems, a process which should leave long- lived signatures in their light profiles and stellar population colors. Merger events should have continued up to relatively recent times {the last 1-5 Gyr}, and many ellipticals and S0 bulges should therefore show evidence of multiple, discrete, intermediate-age populations. Although there is substantial observational support for a dissipational merger origin for some early-type galaxies, most do not exhibit the expected anomalies in either their light profiles or color distributions. However, existing searches {mainly in the V and I bands} have not probed very deeply. Here we propose high resolution, broad-band, near-ultraviolet {2500-3400 A} imaging of the cores of bright early-type galaxies. This is the most sensitive probe available for the detection of spatially-segregated, multiple population components with ages in the range 1-5 Gyr. Our sample consists of dust- and AGN-free systems with both normal and mildly anomalous central light profiles. There is very little existing information on the near-UV structure of early-type galaxies, and our program would effectively explore new terrain. ACS/HRC/NIC3 10182 Towards a Comprehensive Understanding of Type Ia Supernovae: The Necessity of UV Observations Type Ia supernovae {SNe Ia} are very important to many diverse areas of astrophysics, from the chemical evolution of galaxies to observational cosmology which led to the discovery of dark energy and the accelerating Universe. However, the utility of SNe Ia as cosmological probes depends on the degree of our understanding of SN Ia physics, and various systematic effects such as cosmic chemical evolution. At present, the progenitors of SNe Ia and the exact explosion mechanisms are still poorly understood, as are evolutionary effects on SN Ia peak luminosities. Since early-time UV spectra and light curves of nearby SNe Ia can directly address these questions, we propose an approach consisting of two observational components: {1} Detailed studies of two very bright, young, nearby SNe Ia with HST UV spectroscopy at 13 epochs within the first 1.5 months after discovery; and {2} studies of correlations with luminosity for five somewhat more distant Hubble-flow SNe Ia, for which relative luminosities can be determined with precision, using 8 epochs of HST UV spectroscopy and/or broad-band imaging. The HST data, along with extensive ground-based optical to near-IR observations, will be analyzed with state-of-the-art models to probe SN Ia explosion physics and constrain the nature of the progenitors. The results will form the basis for the next phase of precision cosmology measurements using SNe Ia, allowing us to more fully capitalize on the substantial past {and future} investments of time made with HST in observations of high-redshift SNe Ia. ACS/HRC/WFC 10548 Near-UV Snapshot Survey of Low Luminosity AGNs Low-luminosity active galactic nuclei {LLAGNs} comprise ~30% of all bright galaxies {B12.5} and are the most common type of AGN. These include low-luminosity Seyfert galaxies, LINERs, and transition-type objects {TOs, also called weak-[OI] LINERs}. What powers them is still at the forefront of AGN research. To unveil the nature of the central source we propose a near-UV snapshot survey of 50 nearby LLAGNs using ACS/HRC and the filter {F330W}, a configuration which is optimal to detect faint star forming regions around their nuclei. These images will complement optical and near-IR images available in the HST archive, providing a panchromatic atlas of the inner regions of these galaxies, which will be used to study their nuclear stellar population. Our main goals are to: 1} Investigate the presence of nuclear unresolved sources that can be attributed to an AGN; 2} Determine the frequency of nuclear and circumnuclear stellar clusters, and whether they are more common in Transition Objects {TOs} than in LINERs; 3} Characterize the sizes, colors, luminosities, masses and ages of these clusters; 4} Derive the luminosity function of star clusters and study their evaporation over time in the vicinity of AGNs. Finally, the results of this project will be combined with those of a previous similar one for Seyfert galaxies in order to compare the nature of the nuclear sources and investigate if there could be an evolution from Seyferts to TOs and LINERs. By adding UV images to the existing optical and near-IR ones, this project will also create an extremely valuable database for astronomers with a broad range of scientific interests. ACS/WFC 10412 The host galaxies of dust-reddened quasars We have used the 2MASS near-infrared and FIRST radio surveys, together with the Palomar Observatory Sky Survey plates to select a sample of dust-reddened, radio- intermediate quasars. We wish to use ACS to study the host galaxies of these quasars. The dust reddening of the quasars makes it possible to study the hosts at rest-frame optical-UV wavelengths much more easily than the hosts of normal quasars of similar bolometric luminosity. Our study will compare the hosts of our dust-reddened quasars to those of normal quasars from the HST archive to test the hypothesis that dust-reddened quasars are young objects, whose hosts still show morphological evidence of recent merger events which triggered the quasar. ACS/WFC 10587 Measuring the Mass Dependence of Early-Type Galaxy Structure We propose two-color ACS-WFC Snapshot observations of a sample of 118 candidate early-type gravitational lens galaxies. Our lens-candidate sample is selected to yield {in combination with earlier results} an approximately uniform final distribution of 40 early- type strong lenses across a wide range of masses, with velocity dispersions {a dynamical proxy for mass} ranging from 125 to 300 km/s. The proposed program will deliver the first significant sample of low-mass gravitational lenses. All of our candidates have known lens and source redshifts from Sloan Digital Sky Survey data, and all are bright enough to permit detailed photometric and stellar-dynamical observation. We will constrain the luminous and dark-matter mass profiles of confirmed lenses using lensed- image geometry and lens-galaxy structural/photometric measurements from HST imaging in combination with dynamical measurements from spatially resolved ground- based follow-up spectroscopy. Hence we will determine, in unprecedented detail, the dependence of early-type galaxy mass structure and mass-to-light ratio upon galaxy mass. These results will allow us to directly test theoretical predictions for halo concentration and star-formation efficiency as a function of mass and for the existence of a cuspy inner dark-matter component, and will illuminate the structural explanation behind the fundamental plane of early-type galaxies. The lens-candidate selection and confirmation strategy that we propose has been proven successful for high-mass galaxies by our Cycle 13 Snapshot program {10174}. The program that we propose here will produce a complementary and unprecedented lens sample spanning a wide range of lens-galaxy masses. ACS/WFC 10624 Solving the Mystery of the Short-Hard Gamma-Ray Bursts Eight years after the afterglow detections that revolutionized studies of the long-soft gamma-ray bursts, not even one afterglow of a short-hard GRB has been seen, and the nature of these events has become one of the most important problems in GRB research. The Swift satellite, expected to be in full operation throughout Cycle 14, will report few-arcsecond localizations for short-hard bursts in minutes, enabling prompt, deep optical afterglow searches for the first time. Discovery and observation of the first short-hard optical afterglows will answer most of the critical questions about these events: What are their distances and energies? Do they occur in distant galaxies, and if so, in which regions of those galaxies? Are they the result of collimated or quasi- spherical explosions? In combination with an extensive rapid-response ground-based campaign, we propose to make the critical high-sensitivity HST TOO observations that will allow us to answer these questions. If theorists are correct in attributing the short- hard bursts to binary neutron star coalescence events, then they will serve as signposts to the primary targeted source population for ground-based gravitational-wave detectors, and short-hard burst studies will have a vital role to play in guiding those observations. ACS/WFC/WFPC2 10499 Life Before the Fall: Morphological Evolution of Galaxies in Groups Prior to Cluster Assembly at z=0.37 We propose to obtain a deep ACS/WFC mosaic of a protocluster comprised of 4 distinct galaxy groups that are gravitationally bound to each other at z=0.37. The galaxy groups have a total combined mass comparable to the Coma cluster and already have twice as many absorption line galaxies as the field. The SG1120 complex thus provides an unprecedented opportunity for determining whether "pre-processing" in the group environment is responsible for the bulk of observed diffences between galaxies in nearby clusters and those in the field. High resolution imaging with HST is needed to morphologically classify the group members and measure their structural parameters. By combining the early-type fraction and morphology-density relation in SG1120 with results from our wide-field spectroscopic survey, we will test whether spectral and morphological transformation timescales are decoupled on group scales and isolate the environmental mechanisms responsible for such evolution. We will also measure the Fundamental Plane and M/L ratios of the early-type members to constrain their formation epoch and how their stellar populations have evolved. Observations of the multiple galaxy groups in SG1120 provide a unique dataset to the community and will aid our understanding of how galaxies evolve in the still poorly studied group regime. FLIGHT OPERATIONS SUMMARY: Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) HSTARS: (None) COMPLETED OPS REQUEST: (None) COMPLETED OPS NOTES: (None) SCHEDULED SUCCESSFUL FGS Gsacq 08 08 FGS Reacq 11 11 FHST Update 12 12 SIGNIFICANT EVENTS: (None) |
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