Status Report

NASA Hubble Space Telescope Daily Report #3912

By SpaceRef Editor
July 28, 2005
Filed under , ,

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science


PERIOD COVERED: UT July 28, 2005 (DOY 209)


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.


Near-UV Snapshot Survey of Low Luminosity AGNs

Low-luminosity active galactic nuclei {LLAGNs} comprise ~30% of all
bright galaxies {B<12.5} 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.


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


Significant Spacecraft Anomalies: (The following are preliminary
reports of potential non-nominal performance that will be

HSTARS: (None)



              SCHEDULED     SUCCESSFUL 
 FGS Gsacq        08            08 
 FGS Reacq        11            11 
 FHST Update      12            12 


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