HUBBLE SPACE TELESCOPE - Continuing to collect World Class
Science
DAILY REPORT # 4551
PERIOD COVERED: UT February 20, 2008 (DOY 051)
OBSERVATIONS SCHEDULED
FGS 11211
An Astrometric Calibration of
Population II Distance Indicators
In 2002 HST produced a highly precise parallax for RR Lyrae. That
measurement resulted in an absolute magnitude, M{V}=
0.61+/-0.11, a
useful result, judged by the over ten refereed
citations each year
since. It is, however, unsatisfactory to have the
direct,
parallax-based, distance scale of Population II
variables based on a
single star. We propose, therefore, to obtain the
parallaxes of four
additional RR Lyrae stars
and two Population II Cepheids, or
stars. The Population II Cepheids
lie with the RR Lyrae stars on a
common K-band Period-Luminosity relation. Using these
parallaxes to
inform that relationship, we anticipate a zero-point
error of 0.04
magnitude. This result should greatly strengthen
confidence in the
Population II distance scale and increase our understanding of RR Lyrae
star and Pop II Cepheid astrophysics.
NIC1/NIC2/NIC3 8795
NICMOS Post-SAA calibration - CR Persistence Part 6
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 i
mages. Each observation will need its own CRMAP, as
different SAA
passages leave different imprints on the NICMOS
detectors.
NIC2 11219
Active Galactic Nuclei in nearby galaxies: a new view of
the origin of
the radio-loud radio-quiet dichotomy?
Using archival HST and Chandra observations of 34 nearby
early-type
galaxies {drawn from a complete radio selected sample}
we have found
evidence that the radio-loud/radio-quiet dichotomy is
directly connected
to the structure of the inner regions of their host
galaxies in the
following sense: [1] Radio-loud AGN are associated
with galaxies with
shallow cores in their light profiles [2] Radio-quiet
AGN are only
hosted by galaxies with steep cusps. Since the
brightness profile is
determined by the galaxy's evolution, through its
merger history, our
results suggest that the same process sets the AGN flavour. This
provides us with a novel tool to explore the
co-evolution of galaxies
and supermassive black
holes, and it opens a new path to understand the
origin of the radio-loud/radio-quiet AGN dichotomy.
Currently our
analysis is statistically incomplete as the brightness
profile is not
available for 82 of the 116 targets. Most galaxies
were not observed
with HST, while in some cases the study is obstructed
by the presence of
dust features. We here propose to perform an infrared
NICMOS snapshot
survey of these 82 galaxies. This will enable us to i} test the reality
of the dichotomic behaviour in a substantially larger sample; ii} extend
the comparison between radio-loud and radio-quiet AGN
to a larger range
of luminosities.
NIC3 11236
Did Rare, Large Escape-Fraction Galaxies Reionize the Universe?
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 that
the escape fraction is close to zero in most galaxies,
even among young
starbursts, but is large in 15-25% of them.
Non-uniform escape fractions
are expected as a result of violent events creating
clear paths in small
parts of galaxies. The number of galaxies observed
with high escape
fraction will result from the combination of the
intrinsic number with
clear lines of sight and their orientation with
respect to the observer.
We propose to measure the fraction of escaping Lyman continuum radiation
in a large sample (47) of z~0.7 starbursts in the
COSMOS field. These
compact UV-luminous galaxies are good analogs to high redshift LBGs.
Using the SBC/PR130L we can quickly (1-4 orbits) detect relative escape
fractions (f_LC/f_1500) of 25% or more. This will be
the first
measurement of the escape fraction in sources between
z=1 and the local
universe. We expect ~10 detections. Stacking will set
limits of <4% on
the relative escape fraction in the rest. We will correlate
the LC
detections with the properties of the galaxies. By
targeting z~0.7 in
COSMOS, we will have tremendous ancillary information on those sources.
A non-detection in all sources would be significant
(99% confidence).
This would imply that QSOs provide the overwhelming
majority of ionizing
radiation at z<1, requiring substantial evolution
in the processes within
Lyman break galaxies which allow large escape fractions at high
redshift.
WFPC2 11030
WFPC2 WF4 Temperature Reduction #3
In the fall of 2005, a serious anomaly was found in images
from the WF4
CCD in WFPC2. The WF4 CCD bias level appeared to have
become unstable,
resulting in sporadic images with either low or zero
bias level. The
severity and frequency of the problem was rapidly increasing,
making it
possible that WF4 would soon become unusable if no
work-around were
found. Examination of bias levels during periods with
frequent WFPC2
images showed low and zero bias episodes every 4 to 6
hours. This
periodicity is driven by cycling of the WFPC2
Replacement Heater, with
the bias anomalies occurring at the temperature peaks.
The other three
CCDs {PC1, WF2, and WF3} appear to be unaffected and
continue to operate
properly. Lowering the Replacement Heater temperature
set points by a
few degrees C effectively eliminates the WF4 anomaly.
On 9 January 2006,
the upper set point of the WFPC2 Replacement Heater
was reduced from
14.9C to 12.2C. On 20 February 2006, the upper set
point was reduced
from 12.2C to 11.3C, and the lower set point was reduced
from 10.9C to
10.0C. These changes restored the WF4 CCD bias level; however, the bias
level has begun to trend downwards again, mimicking
its behavior in late
2004 and early 2005. A third temperature reduction is
planned for March
2007. We will reduce the upper set point of the heater from 11.3C to
10.4C and the lower set point from 10.0C to 9.1C. The
observations
described in this proposal will test the performance
of WFPC2 before and
after this temperature reduction. Additional
temperature reductions may
be needed in the future, depending on the performance
of WF4. Orbits:
internal 26, external 1
WFPC2 11083
The Structure, Formation and Evolution of Galactic Cores
and Nuclei
A surprising result has emerged from the ACS Virgo Cluster
Survey
{ACSVCS}, a program to obtain ACS/WFC gz imaging for
a large, unbiased
sample of 100 early-type galaxies in the Virgo
Cluster. On subarcsecond
scales {i.e., <0.1"-1"}, the HST
brightness profiles vary systematically
from the brightest giants {which have nearly constant
surface brightness
cores} to the faintest dwarfs {which have compact
stellar nuclei}.
Remarkably, the fraction of galaxy mass contributed by the nuclei in the
faint galaxies is identical to that contributed by supermassive black
holes in the bright galaxies {0.2%}. These findings
strongly suggest
that a single mechanism is responsible for both types
of Central Massive
Object: most likely internally or externally modulated gas inflows that
feed central black holes or lead to the formation of
"nuclear star
clusters". Understanding the history of gas
accretion, star formation
and chemical enrichment on subarcsecond
scales has thus emerged as the
single most pressing question in the study of nearby
galactic nuclei,
either active or quiescent. We propose an ambitious
HST program {199
orbits} that constitutes the next, obvious step
forward:
high-resolution, ultraviolet {WFPC2/F255W} and
infrared {NIC1/F160W}
imaging for the complete ACSVCS sample. By
capitalizing on HST's unique
ability to provide high-resolution images with a sharp
and stable PSF at
UV and IR wavelengths, we will leverage the existing optical HST data to
obtain the most complete picture currently possible
for the history of
star formation and chemical enrichment on these small
scales. Equally
important, this program will lead to a significant
improvement in the
measured structural parameters and density
distributions for the stellar
nuclei and the underlying galaxies, and provide a
sensitive measure of
"frosting" by young stars in the galaxy
cores. By virtue of its superb
image quality and stable PSF, NICMOS is the sole
instrument capable of
the IR observations proposed here. In the case of the
WFPC2
observations, high-resolution UV imaging {<
0.1"} is a capability unique
to HST, yet one that could be lost at any time.
WFPC2 11130
AGNs with Intermediate-mass Black
Holes: Testing the Black Hole-Bulge
Paradigm, Part II
The recent progress in the study of central black holes in
galactic
nuclei has led to a general consensus that supermassive {10^6-10^9 solar
mass} black holes are closely connected with the
formation and
evolutionary history of large galaxies, especially
their bulge
component. Two outstanding issues, however, remain
unresolved. Can
central black holes form in the absence of a bulge?
And does the mass
function of central black holes extend below 10^6
solar masses?
Intermediate-mass black holes {<10^6 solar masses}, if they exist, may
offer important clues to the nature of the seeds of supermassive black
holes. Using the SDSS, our group has successfully
uncovered a new
population of AGNs with
intermediate-mass black holes that reside in
low-luminosity galaxies. However, very little is known
about the
detailed morphologies or structural parameters of the
host galaxies
themselves, including the crucial question of whether
they have bulges
or not. Surprisingly, the majority of the targets of
our Cycle 14 pilot
program have structural properties similar to dwarf
elliptical galaxies.
The statistics from this initial study, however, are really too sparse
to reach definitive conclusions on this important new
class of black
holes. We wish to extend this study to a larger
sample, by using the
Snapshot mode to obtain WFPC2 F814W images from a parent sample of 175
AGNs with intermediate- mass black holes selected
from our final SDSS
search. We are particularly keen to determine whether
the hosts contain
bulges, and if so, how the fundamental plane
properties of the host
depend on the mass of their central black holes. We
will also
investigate the environment of this unique class of AGNs.
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
11
11
FGS REacq
03
03
OBAD with Maneuver 28
28
SIGNIFICANT EVENTS: (None)
-
____________________________________________________________
Lynn F. Bassford
Hubble Space Telescope
CHAMP
CHAMP Flight Operations Team Manager
Lockheed Martin
NASA GSFC PH#: 301-286-2876
"The Hubble Space Telescope is
the astronomical observatory and key to unlocking the most cosmic mysteries of
the past, present and future." - 7/26/6