Status Report

NASA Hubble Space Telescope Daily Report #5002

By SpaceRef Editor
December 31, 2009
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Continuing to Collect World Class Science

PERIOD COVERED: 5am December 29 – 5am December 30, 2009 (DOY 363/10:00z-364/10:00z)


COS/FUV 11895

FUV Detector Dark Monitor

The purpose of this proposal is to monitor the FUV detector dark rate by taking long science exposures without illuminating the detector. The detector dark rate and spatial distribution of counts will be compared to pre-launch and SMOV data in order to verify the nominal operation of the detector. Variations of count rate as a function of orbital position will be analyzed to find dependence of dark rate on proximity to the SAA. Dependence of dark rate as function of time will also be tracked.


The Stellar Halos of Dwarf Galaxies

The metal-poor stellar halo is the oldest extended structure in the Galaxy. Such halos are thought to form through hierarchical merging, and contain stars pulled from accreted subhalos. The diffuse stellar halo therefore stores information about the prop reties of the accreted galaxies (i.e., their orbits, stellar masses, and metallicities). It is therefore unsurprising that stellar halos have become a popular probe of the early epoch of galaxy formation.

Almost all current work on stellar halos has focused on massive galaxies, however. We propose to extend the work on stellar halos to much lower mass scales, by studying the halos of faint dwarf galaxies. By taking halo studies into the dwarf galaxy regime, we can probe exceptionally small mass scales for the accreted halos. At these mass scales the effects of reionization and supernova feedback have the largest impact on the galaxy population. Stellar halos of dwarf galaxies are therefore a sensitive probe of the key processes needed to resolve the lack of substructure observed at low masses.

We are requesting two far-field ACS pointings for the three closest isolated nearby dwarf irregular galaxies whose inner halos have already been mapped with the ACS Nearby Galaxy Survey Treasury. These outer fields will allow us to trace the halo out to roughly half the virial radius, further than any previous study. We will use the resulting distribution of halo stars (1) to unambiguously measure the structure of the stellar halo, with minimal contamination from the main galaxy; (2) to constrain the flattening of the stellar halo; (3) to measure the metallicity of halo stars as a function of radius; (4) to correlate any changes in halo profile with changes in metallicity. The resulting data will constrain models of halo accretion and the epoch of reionization.


Probing Warm-Hot Intergalactic Gas at 0.5 < z < 1.3 with a Blind Survey for O VI, Ne VIII, Mg X, and Si XII Absorption Systems Currently we can only account for half of the baryons (or less) expected to be found in the nearby universe based on D/H and CMB observations. This “missing baryons problem” is one of the highest-priority challenges in observational extragalatic astronomy. Cosmological simulations suggest that the baryons are hidden in low-density, shock-heated intergalactic gas in the log T = 5 – 7 range, but intensive UV and X-ray surveys using O VI, O VII, and O VIII absorption lines have not yet confirmed this prediction. We propose to use COS to carry out a sensitive survey for Ne VIII and Mg X absorption in the spectra of nine QSOs at z(QSO) > 0.89. For the three highest-redshift QSOs, we will also search for Si XII. This survey will provide more robust constraints on the quantity of baryons in warm-hot intergalactic gas at 0.5 < z < 1.3, and the data will provide rich constraints on the metal enrichment, physical conditions, and nature of a wide variety of QSO absorbers in addition to the warm-hot systems. By comparing the results to other surveys at lower redshifts (with STIS, FUSE, and from the COS GTO programs), the project will also enable the first study of how these absorbers evolve with redshift at z < 1. By combining the program with follow-up galaxy redshift surveys, we will also push the study of galaxy-absorber relationships to higher redshifts, with an emphasis on the distribution of the WHIM with respect to the large-scale matter distribution of the universe. S/C 12046 COS FUV DCE Memory Dump Whenever the FUV detector high voltage is on, count rate and current draw information is collected, monitored, and saved to DCE memory. Every 10 msec the detector samples the currents from the HV power supplies (HVIA, HVIB) and the AUX power supply (AUXI). The last 1000 samples are saved in memory, along with a histogram of the number of occurrences of each current value. In the case of a HV transient (known as a “crackle” on FUSE), where one of these currents exceeds a preset threshold for a persistence time, the HV will shut down, and the DCE memory will be dumped and examined as part of the recovery procedure. However, if the current exceeds the threshold for less than the persistence time (a “mini-crackle” in FUSE parlance), there is no way to know without dumping DCE memory. By dumping and examining the histograms regularly, we will be able to monitor any changes in the rate of “mini-crackles” and thus learn something about the state of the detector. STIS/CCD 11703 The Nature of the Black Hole in a NGC 4472 Globular Cluster and the Origin of Its Broad [OIII] Emission We propose to use STIS to obtain optical spectroscopy at high spatial resolution of the black hole-hosting globular cluster RZ2109 in the Virgo elliptical NGC 4472. This is motivated by our very recent discovery broad [OIII] 4959, 5007 emission with a width of several thousand km/s in this globular cluster. The STIS spectroscopy will enable us to determine if the very broad [OIII] emission is due to material driven at high velocity from the central accreting black hole across the globular cluster, or if the velocity widths are due to gravitational motions very close to the central black hole. In the former case, the [OIII] emission should extend over a few-tenths of an arcsecond and be spatially resolved by HST and STIS, while in the latter case, the emission lines will be unresolved. Distinguishing between these two possibilities will allow us to – 1) determine whether the black hole is of intermediate mass or a stellar mass, and thereby whether the black hole mass – sigma relation extends to globular cluster masses, 2) test models of black hole formation and evolution in dense stellar systems, and 3) address the nature of accretion in the high luminosity black-hole X-ray source, and constrain the feedback processes from luminous black holes into their surrounding medium in dense stellar systems. STIS/CCD 11844 CCD Dark Monitor Part 1 The purpose of this proposal is to monitor the darks for the STIS CCD. STIS/CCD 11846 CCD Bias Monitor-Part 1 The purpose of this proposal is to monitor the bias in the 1×1, 1×2, 2×1, and 2×2 bin settings at gain=1, and 1×1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns. STIS/CCD/FGS 11848 CCD Read Noise Monitor This proposal measures the read noise of all the amplifiers (A, B, C, D) on the STIS CCD using pairs of bias frames. Full-frame and binned observations are made in both Gain 1 and Gain 4, with binning factors of 1×1, 1×2, 2×1, and 2×2. All exposures are internals. Pairs of visits are scheduled monthly for the first four months and then bi-monthly after that. WFC3/ACS/UVIS 11803 Observing Cluster Assembly Around the Massive Cluster RXJ0152-13 We request ACS imaging for groups and filaments in the outskirts of two z=0.8 forming clusters of galaxies. These images will be combined with an unparalleled dataset of wide-field spectroscopy from Magellan, with ~2200 confirmed members (~3200 by the summer) of the superstructures surrounding the two clusters. We will estimate merger rates and determine the morphological composition of the galaxy populations within the infalling groups and filaments identified in our spectroscopic dataset. The HST data are critical to understand how the early-type galaxy fraction remains constant in cluster centers, while clusters double in mass through the steady accretion of lower mass groups. One possibility is that the galaxies in the filaments and infalling groups already have predominantly early-type morphologies, while another is that galaxies transform during, and possibly even in connection with, the process of infall. Our unique dataset of spectroscopic membership, when combined with the exquisite high-resolution imaging of ACS and WF3, will enable us to witness the accretion of galaxies unto massive clusters and how this process affects their properties. WFC3/IR 11696 Infrared Survey of Star Formation Across Cosmic Time We propose to use the unique power of WFC3 slitless spectroscopy to measure the evolution of cosmic star formation from the end of the reionization epoch at z>6 to the close of the galaxy-building era at z~0.3.Pure parallel observations with the grisms have proven to be efficient for identifying line emission from galaxies across a broad range of redshifts. The G102 grism on WFC3 was designed to extend this capability to search for Ly-alpha emission from the first galaxies. Using up to 250 orbits of pure parallel WFC3 spectroscopy, we will observe about 40 deep (4-5 orbit) fields with the combination of G102 and G141, and about 20 shallow (2-3 orbit) fields with G141 alone.

Our primary science goals at the highest redshifts are: (1) Detect Lya in ~100 galaxies with z>5.6 and measure the evolution of the Lya luminosity function, independent of of cosmic variance; 2) Determine the connection between emission line selected and continuum-break selected galaxies at these high redshifts, and 3) Search for the proposed signature of neutral hydrogen absorption at re-ionization. At intermediate redshifts we will (4) Detect more than 1000 galaxies in Halpha at 0.5< z<1.8 to measure the evolution of the extinction-corrected star formation density across the peak epoch of star formation. This is over an order-of-magnitude improvement in the current statistics, from the NICMOS Parallel grism survey. (5) Trace ``cosmic downsizing" from 0.5< z<2.2; and (6) Estimate the evolution in reddening and metallicty in star-forming galaxies and measure the evolution of the Seyfert population. For hundreds of spectra we will be able to measure one or even two line pair ratios -- in particular, the Balmer decrement and [OII]/[OIII] are sensitive to gas reddening and metallicity. As a bonus, the G102 grism offers the possibility of detecting Lya emission at z=7-8.8. To identify single-line Lya emitters, we will exploit the wide 0.8–1.9um wavelength coverage of the combined G102+G141 spectra. All [OII] and [OIII] interlopers detected in G102 will be reliably separated from true LAEs by the detection of at least one strong line in the G141 spectrum, without the need for any ancillary data. We waive all proprietary rights to our data and will make high-level data products available through the ST/ECF. WFC3/IR 11926 IR Zero Points We will measure and monitor the zeropoints through the IR filters using observations of the white dwarf standard stars, GD153, GD71 and GD191B2B and the solar analog standard star, P330E. Data will be taken monthly during Cycle 17. Observations of the star cluster, NGC 104, are made twice to check color transformations. We expect an accuracy of 2% in the wide filter zeropoints relative to the HST photometric system, and 5% in the medium- and narrow-band filters. WFC3/IR/S/C 11929 IR Dark Current Monitor Analyses of ground test data showed that dark current signals are more reliably removed from science data using darks taken with the same exposure sequences as the science data, than with a single dark current image scaled by desired exposure time. Therefore, dark current images must be collected using all sample sequences that will be used in science observations. These observations will be used to monitor changes in the dark current of the WFC3-IR channel on a day-to-day basis, and to build calibration dark current ramps for each of the sample sequences to be used by Gos in Cycle 17. For each sample sequence/array size combination, a median ramp will be created and delivered to the calibration database system (CDBS). WFC3/UVIS 11594 A WFC3 Grism Survey for Lyman Limit Absorption at z=2 We propose to conduct a spectroscopic survey of Lyman limit absorbers at redshifts 1.8 < z < 2.5, using WFC3 and the G280 grism. This proposal intends to complete an approved Cycle 15 SNAP program (10878), which was cut short due to the ACS failure. We have selected 64 quasars at 2.3 < z < 2.6 from the Sloan Digital Sky Survey Spectroscopic Quasar Sample, for which no BAL signature is found at the QSO redshift and no strong metal absorption lines are present at z > 2.3 along the lines of sight. The survey has three main

observational goals. First, we will determine the redshift frequency dn/dz of the LLS over the column density range 16.0 < log(NHI) < 20.3 cm^-2. Second, we will measure the column density frequency distribution f(N) for the partial Lyman limit systems (PLLS) over the column density range 16.0 < log(NHI) < 17.5 cm^-2. Third, we will identify those sightlines which could provide a measurement of the primordial D/H ratio. By carrying out this survey, we can also help place meaningful constraints on two key quantities of cosmological relevance. First, we will estimate the amount of metals in the LLS using the f(N), and ground based observations of metal line transitions. Second, by determining f(N) of the PLLS, we can constrain the amplitude of the ionizing UV background at z~2 to a greater precision. This survey is ideal for a snapshot observing program, because the on-object integration times are all well below 30 minutes, and follow-up observations from the ground require minimal telescope time due to the QSO sample being bright. WFC3/UVIS 11657 The Population of Compact Planetary Nebulae in the Galactic Disk We propose to secure narrow- and broad-band images of compact planetary nebulae (PNe) in the Galactic Disk to study the missing link of the early phases of post-AGB evolution. Ejected AGB envelopes become PNe when the gas is ionized. PNe expand, and, when large enough, can be studied in detail from the ground. In the interim, only the HST capabilities can resolve their size, morphology, and central stars. Our proposed observations will be the basis for a systematic study of the onset of morphology. Dust properties of the proposed targets will be available through approved Spitzer/IRS spectra, and so will the abundances of the alpha-elements. We will be able thus to explore the interconnection of morphology, dust grains, stellar evolution, and populations. The target selection is suitable to explore the nebular and stellar properties across the galactic disk, and to set constraints on the galactic evolutionary models through the analysis of metallicity and population gradients. WFC3/UVIS 11905 WFC3 UVIS CCD Daily Monitor The behavior of the WFC3 UVIS CCD will be monitored daily with a set of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K subarray biases are acquired at less frequent intervals throughout the cycle to support subarray science observations. The internals from this proposal, along with those from the anneal procedure (Proposal 11909), will be used to generate the necessary superbias and superdark reference files for the calibration pipeline (CDBS). WFC3/UVIS 11908 Cycle 17: UVIS Bowtie Monitor Ground testing revealed an intermittent hysteresis type effect in the UVIS detector (both CCDs) at the level of ~1%, lasting hours to days. Initially found via an unexpected bowtie-shaped feature in flatfield ratios, subsequent lab tests on similar e2v devices have since shown that it is also present as simply an overall offset across the entire CCD, i.e., a QE offset without any discernable pattern. These lab tests have further revealed that overexposing the detector to count levels several times full well fills the traps and effectively neutralizes the bowtie. Each visit in this proposal acquires a set of three 3×3 binned internal flatfields: the first unsaturated image will be used to detect any bowtie, the second, highly exposed image will neutralize the bowtie if it is present, and the final image will allow for verification that the bowtie is gone. WFC3/UVIS/IR 11700 Bright Galaxies at z>7.5 with a WFC3 Pure Parallel Survey

The epoch of reionization represents a special moment in the history of the Universe as it is during this era that the first galaxies and star clusters are formed. Reionization also profoundly affects the environment where subsequent generations of galaxies evolve. Our overarching goal is to test the hypothesis that galaxies are responsible for reionizing neutral hydrogen. To do so we propose to carry out a pure parallel WFC3 survey to constrain the bright end of the redshift z>7.5 galaxy luminosity function on a total area of 176 arcmin^2 of sky. Extrapolating the evolution of the luminosity function from z~6, we expect to detect about 20 Lyman Break Galaxies brighter than M_* at z~8 significantly improving the current sample of only a few galaxies known at these redshifts. Finding significantly fewer objects than predicted on the basis of extrapolation from z=6 would set strong limits to the brightness of M_*, highlighting a fast evolution of the luminosity function with the possible implication that galaxies alone cannot reionize the Universe. Our observations will find the best candidates for spectroscopic confirmation, that is bright z>7.5 objects, which would be missed by small area deeper surveys. The random pointing nature of the program is ideal to beat cosmic variance, especially severe for luminous massive galaxies, which are strongly clustered. In fact our survey geometry of 38 independent fields will constrain the luminosity function like a contiguous single field survey with two times more area at the same depth. Lyman Break Galaxies at z>7.5 down to m_AB=26.85 (5 sigma) in F125W will be selected as F098M dropouts, using three to five orbits visits that include a total of four filters (F606W, F098M, F125W, F160W) optimized to remove low-redshift interlopers and cool stars. Our data will be highly complementary to a deep field search for high-z galaxies aimed at probing the faint end of the luminosity function, allowing us to disentangle the degeneracy between faint end slope and M_* in a Schechter function fit of the luminosity function. We waive proprietary rights for the data. In addition, we commit to release the coordinates and properties of our z>7.5 candidates within one month from the acquisition of each field.


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

HSTARS: (None)



FGS GSAcq 7 7
FGS REAcq 8 8
OBAD with Maneuver 5 5


SpaceRef staff editor.