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Daily # 4202



 
 
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Old September 20th 06, 04:59 PM posted to sci.astro.hubble
Joe Cooper
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Default Daily # 4202

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 4202

PERIOD COVERED: UT September 19, 2006 (DOY 262)

OBSERVATIONS SCHEDULED

ACS/SBC 10872

Lyman Continuum Emission in Galaxies at z=1.2

Lyman continuum photons produced in massive starbursts may have played
a dominant role in the reionization of the Universe. Starbursts are
important contributors to the ionizing metagalactic background at
lower redshifts as well. However, their contribution to the background
depends upon the fraction of ionizing radiation that escapes from the
intrinsic opacity of galaxies below the Lyman limit. Current surveys
suggest escape fractions of a few percent, up to 10%, with very few
detections {as opposed to upper limits} having been reported. No
detections have been reported in the epochs between z=0.1 and z=2. We
propose to measure the fraction of escaping Lyman continuum radiation
from 15 luminous z~1.2 galaxies in the GOODS fields. Using the
tremendous sensitivity of the ACS Solar-blind Channel, we will reach
AB=30 mag., allowing us to detect an escape fraction of 1%. We will
correlate the amount of escaping radiation with the photometric and
morphological properties of the galaxies. A non-detection in all
sources would imply that QSOs provide the overwhelming majority of
ionizing radiation at z=1.3, and it would strongly indicate that the
properties of galaxies at higher redshift have to be significantly
different for galaxies to dominate reionization. The deep FUV images
will also be useful for extending the FUV study of other galaxies in
the GOODS fields.

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 10813

MgII Absorption Line Systems: Galaxy Halos or the Metal-Enriched IGM?

MgII QSO absorption lines detected in the spectra of background QSOs
were used over a decade ago to infer that all redshift z 0.2
galaxies have gaseous halos of radius ~ 60 kpc. The actual size of the
halo was believed to be proportional to the luminosity of the galaxy.
However, these conclusions are now much harder to understand in light
of the results from numerical simulations which show how gas evolves
in the universe. These models predict that gas and galaxies merely
share the same filamentary structures defined by dark matter. If these
models are correct, how are MgII systems and galaxies really related?
We can better understand the distribution of absorbing gas if we FIRST
select galaxies close to QSO sightlines and THEN search for MgII
absorption at the redshift of the intervening galaxies. This is the
antithesis of the original experiments which sought to find absorbing
galaxies based on known MgII systems. The frequency with which we
detect MgII lines from randomly selected galaxies should enable us to
better understand if absorption arises in the halos of individual
galaxies, or if MgII merely arises in the same IGM that galaxies
inhabit. We have used ground-based telescopes to indentify twenty z =
0.31-0.55 galaxies within 14-51 kpc of a g 20 QSO, and to search for
MgII absorption at the galaxies' redshifts. Surprisingly, we find that
only 50% of our QSOs show MgII absorption. In this proposal, we seek
multi-color ACS images of twelve of the fields to i} correlate the
incidence of MgII with galaxy morphology; ii} determine if absorption
{or lack thereof} is related to galaxy disks or halos; iii} search for
signs of galaxy interactions which may explain the large
cross-sections of MgII systems; and iv} look for faint interloping
galaxies closer to the line of sight than the one we identified. An
important component of the program is to observe each field in the
SDSS g-, r- and i-bands, to permit an estimate of the photometric
redshift of any objects which lie closer to the QSO sightline than the
identified galaxy, and which might actually be responsible for the
absorption.

NIC1/NIC2/NIC3 8793

NICMOS Post-SAA calibration - CR Persistence Part 4

A new procedure proposed to alleviate the CR-persistence problem of
NICMOS. Dark frames will be obtained immediately upon exiting the SAA
contour 23, and every time a NICMOS exposure is scheduled within 50
minutes of coming out of the SAA. The darks will be obtained in
parallel in all three NICMOS Cameras. The POST-SAA darks will be
non-standard reference files available to users with a USEAFTER
date/time mark. The keyword 'USEAFTER=date/time' will also be added to
the header of each POST-SAA DARK frame. The keyword must be populated
with the time, in addition to the date, because HST crosses the SAA ~8
times per day so each POST-SAA DARK will need to have the appropriate
time specified, for users to identify the ones they need. Both the raw
and processed images will be archived as POST-SAA DARKSs. Generally we
expect that all NICMOS science/calibration observations started within
50 minutes of leaving an SAA will need such maps to remove the CR
persistence from the science images. Each observation will need its
own CRMAP, as different SAA passages leave different imprints on the
NICMOS detectors.

WFPC2 10915

ACS Nearby Galaxy Survey

Existing HST observations of nearby galaxies comprise a sparse and
highly non-uniform archive, making comprehensive comparative studies
among galaxies essentially impossible. We propose to secure HST's
lasting impact on the study of nearby galaxies by undertaking a
systematic, complete, and carefully crafted imaging survey of ALL
galaxies in the Local Universe outside the Local Group. The resulting
images will allow unprecedented measurements of: {1} the star
formation history {SFH} of a 100 Mpc^3 volume of the Universe with a
time resolution of Delta[log{t}]=0.25; {2} correlations between
spatially resolved SFHs and environment; {3} the structure and
properties of thick disks and stellar halos; and {4} the color
distributions, sizes, and specific frequencies of globular and disk
clusters as a function of galaxy mass and environment. To reach these
goals, we will use a combination of wide-field tiling and pointed deep
imaging to obtain uniform data on all 72 galaxies within a
volume-limited sample extending to ~3.5 Mpc, with an extension to the
M81 group. For each galaxy, the wide-field imaging will cover out to
~1.5 times the optical radius and will reach photometric depths of at
least 2 magnitudes below the tip of the red giant branch throughout
the limits of the survey volume. One additional deep pointing per
galaxy will reach SNR~10 for red clump stars, sufficient to recover
the ancient SFH from the color-magnitude diagram. This proposal will
produce photometric information for ~100 million stars {comparable to
the number in the SDSS survey} and uniform multi-color images of half
a square degree of sky. The resulting archive will establish the
fundamental optical database for nearby galaxies, in preparation for
the shift of high-resolution imaging to the near-infrared.

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 06 06
FGS REacq 08 08
OBAD with Maneuver 30 30

SIGNIFICANT EVENTS: (None)

 




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