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28 April 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT #3350

PERIOD COVERED: DOY 115-117

Part 2 of 5

ACS 9470

Deep Lyman alpha images of starburst galaxies

We propose a pilot study to obtain deep ACS Ly-alpha images of a
carefully selected sample of local starburst galaxies. Ly-alpha
imaging of such objects has become feasible with ACS. These
observations will bring unprecedented insight into the processes
regulating the luminosity of the cosmologically important Ly-alpha
line. Our targets cover the full range of observed Ly-alpha
properties. They have been chosen to investigate the effects of dust,
the starburst luminosity, and outflows within the ISM. The sample is
optimized for a most favorable trade-off between the relevant
parameter space and the minimum number of orbits. We can build on
this pilot study for a much larger follow-up survey in a later cycle.
Deep H Alpha and H Beta high-resolution images from the ground will
allow us to quantify the Ly-alpha emission {or its lack} and its
attenuation as a function of the local dust content. The H Alpha
emission at a given location will constrain the intrinsic intensity
of the expected Ly-alpha emission. A non-detection will allow us to
quantify the fraction of Ly-alpha photons destroyed within the
neutral gas, and to correlate this fraction with the properties of
the neutral gas and dust. Since Ly-alpha emitters are used to
identify and study galaxies at redshift 3-6, our study will document
the circumstances when a star--forming galaxy shows Ly-alpha
emission. This will be an important first step towards an empirical
calibration of the relation between Ly-alpha and the star--formation
rate.

ACS 9352

The Deceleration Test from Treasury Type Ia Supernovae at Redshifts
1.2 to 1.6


Type Ia supernovae {SNe Ia} provide the only direct evidence for an
accelerating universe, an extraordinary result that needs a rigorous
test. The case for cosmic acceleration rests on the observation that
SNe Ia at z ~ 0.5 are ~ 0.25 mag fainter than they would be in a
universe without acceleration. A powerful and straightforward way to
assess the reliability of the SN Ia measurement and the conceptual
framework of its interpretation is to look for cosmic deceleration at
z >= 1. This would be a clear signature of a mixed dark-matter and
dark-energy universe. Systematic errors in the SN Ia result
attributed to grey dust or cosmic evolution of the SN Ia peak
luminosity would not show this change of sign. We have demonstrated
proof of this concept with a single SN Ia, SN 1997ff at z = 1.7,
found and followed by HST. The results suggest an early epoch of
deceleration, but this is too important a conclusion to rest on just
one object. Here we propose to use HST for observations of six SNe Ia
in the range 1.2 <= z <= 1.6, that will be discovered as a byproduct
from proposed Treasury programs for high-latitude ACS surveys. Six
objects will provide a much firmer foundation for a conclusion that
touches on important questions of fundamental physics. 

ACS/WFC 9584

ACS Default {Archival} Pure Parallel Program II.

The Advanced Camera for Surveys (WFC) was used to test ACS pure
parallels.

ACS/WFC 9351

Determining Hubble's Constant from Observations of Cepheids in the
Host Galaxy of SN Ia 1994ae

We propose to determine the luminosity of the type Ia supernova {SN
Ia} 1994ae by observing Cepheids in the host spiral galaxy NGC 3370.
Modern CCD photometry has yielded an extremely tight Hubble diagram
for SNe Ia with a precisely determined intercept {i.e., Delta
H_0/H_0} 1 measurement of the true Hubble constant is still limited
by the calibration. The HST calibration of all but a few SNe Ia
observed to date is significantly compromised by the systematics of
photographic photometry and host galaxy extinction, as well as by the
photometric uncertainties associated with WFPC2. In contrast, SN
1994ae is one of the very best-observed SNe Ia with CCD photometry.
The exquisite B, V, R, and I light curves are well-sampled beginning
10 days before maximum brightness, and they indicate little
reddening. From our supernova photometry and the current provisional
SN Ia calibration we would find a distance of 30 +/- 2.1 Mpc, well
within the range where ACS can accurately observe Cepheid light
curves and distinguish Cepheids from nonvariable stars.

ACS/WFPC2 9481

Pure Parallel Near-UV Observations with WFPC2 within High-Latitude
ACS Survey Fields

In anticipation of the allocation of ACS high-latitude imaging
survey{s}, we request a modification of the default pure parallel
program for those WFPC2 parallels that fall within the ACS survey
field. Rather than duplicate the red bands which will be done much
better with ACS, we propose to observe in the near-ultraviolet F300W
filter. These data will enable study of the rest-frame ultraviolet
morphology of galaxies at 0 * Origin: SpaceBase(tm) Pt 1 -14.4- Van BC Canada 604-473-9358 (1:153/719.1)

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