Status Report

NASA Hubble Space Telescope Daily Report #4342

By SpaceRef Editor
April 17, 2007
Filed under , ,
NASA Hubble Space Telescope Daily Report #4342

Notice: For the foreseeable future, the daily reports may contain apparent discrepancies between some proposal descriptions and the listed instrument usage. This is due to the conversion of previously approved ACS WFC or HRC observations into WFPC2, or NICMOS observations subsequent to the loss of ACS CCD science capability in late January.


– Continuing to collect World Class Science

PERIOD COVERED: UT April 16, 2007 (DOY 106)


NIC2 10798

Dark Halos and Substructure from Arcs & Einstein Rings

The surface brightness distribution of extended gravitationally lensed arcs and Einstein rings contains super-resolved information about the lensed object, and, more excitingly, about the smooth and clumpy mass distribution of the lens galaxies. The source and lens information can non-parametrically be separated, resulting in a direct “gravitational image” of the inner mass-distribution of cosmologically-distant galaxies {Koopmans 2005; Koopmans et al. 2006 [astro-ph/0601628]}. With this goal in mind, we propose deep HST ACS-F555W/F814W and NICMOS-F160W WFC imaging of 20 new gravitational-lens systems with spatially resolved lensed sources, of the 35 new lens systems discovered by the Sloan Lens ACS Survey {Bolton et al. 2005} so far, 15 of which are being imaged in Cycle-14. Each system has been selected from the SDSS and confirmed in two time- efficient HST-ACS snapshot programs {cycle 13&14}. High-fidelity multi-color HST images are required {not delivered by the 420s snapshots} to isolate these lensed images {properly cleaned, dithered and extinction-corrected} from the lens galaxy surface brightness distribution, and apply our “gravitational maging” technique. Our sample of 35 early-type lens galaxies to date is by far the largest, still growing, and most uniformly selected. This minimizes selection biases and small-number statistics, compared to smaller, often serendipitously discovered, samples. Moreover, using the WFC provides information on the field around the lens, higher S/N and a better understood PSF, compared with the HRC, and one retains high spatial resolution through drizzling. The sample of galaxy mass distributions – determined through this method from the arcs and Einstein ring HST images – will be studied to: {i} measure the smooth mass distribution of the lens galaxies {dark and luminous mass are separated using the HST images and the stellar M/L values derived from a joint stellar-dynamical analysis of each system}; {ii} quantify statistically and individually the incidence of mass-substructure {with or without obvious luminous counter- parts such as dwarf galaxies}. Since dark-matter substructure could be more prevalent at higher redshift, both results provide a direct test of this prediction of the CDM hierarchical structure-formation model.

WFPC2 10809

The nature of “dry” mergers in the nearby Universe

Recent studies have shown that “dry” mergers of red, bulge-dominated galaxies at low redshift play an important role in shaping today’s most massive ellipticals. These mergers have been identified in extremely deep ground-based images of red sequence galaxies at z ~ 0.1. The ground-based images reach surface brightness limits of AB ~ 29, but lack the resolution to study the morphologies of the galaxies inside the effective radius. Here we propose to obtain ACS images of a representative sample of 40 of these red sequence galaxies: 15 ongoing dry mergers, 15 remnants, and 10 undisturbed objects. We will measure the isophote shapes and ellipticities of the galaxies, their dust content, morphological fine structure {shells and ripples}, AGN content, and their location on the Fundamental Plane. By comparing galaxies in different stages of the merging process we can constrain the amount of gas associated with these red mergers, the effect of active nuclei, and track structural changes. As two galaxies can be observed in a single orbit20 orbits are requested to observe the 40 galaxies.

WFPC2 10829

Secular Evolution at the End of the Hubble Sequence

The bulgeless disk galaxies at the end of the Hubble Sequence evolve at a glacial pace relative to their more violent, earlier-type cousins. The causes of their internal, or secular evolution are important because secular evolution represents the future fate of all galaxies in our accelerating Universe and is a key ingredient to understanding galaxy evolution in lower-density environments at present. The rate of secular evolution is largely determined by the stability of the cold ISM against collapse, star formation, and the buildup of a central bulge. Key diagnostics of the ISM’s stability are the presence of compact molecular clouds and narrow dust lanes. Surprisingly, edge-on, pure disk galaxies with circular velocities below 120 km/s do not appear to contain such dust lanes. We propose to obtain ACS/WFC F606W images of a well-selected sample of extremely late-type disk galaxies to measure the characteristic scale size of the cold ISM and determine if they possess the unstable, cold ISM necessary to drive secular evolution. Our sample has been carefully constructed to include disk galaxies above and below the critical circular velocity of 120 km/s where the dust properties of edge-on disks change so remarkably. We will then use surface brightness profiles to search for nuclear star clusters and pseudobulges, which are early indicators that secular evolution is at work, as well as measure the pitch angle of the dust lanes as a function of radius to estimate the central mass concentrations.

WFPC2 10886

The Sloan Lens ACS Survey: Towards 100 New Strong Lenses

As a continuation of the highly successful Sloan Lens ACS {SLACS} Survey for new strong gravitational lenses, we propose one orbit of ACS-WFC F814W imaging for each of 50 high-probability strong galaxy-galaxy lens candidates. These observations will confirm new lens systems and permit immediate and accurate photometry, shape measurement, and mass modeling of the lens galaxies. The lenses delivered by the SLACS Survey all show extended source structure, furnishing more constraints on the projected lens potential than lensed-quasar image positions. In addition, SLACS lenses have lens galaxies that are much brighter than their lensed sources, facilitating detailed photometric and dynamical observation of the former. When confirmed lenses from this proposal are combined with lenses discovered by SLACS in Cycles 13 and 14, we expect the final SLACS lens sample to number 80–100: an approximate doubling of the number of known galaxy-scale strong gravitational lenses and an order-of-magnitude increase in the number of optical Einstein rings. By virtue of its homogeneous selection and sheer size, the SLACS sample will allow an unprecedented exploration of the mass structure of the early-type galaxy population as a function of all other observable quantities. This new sample will be a valuable resource to the astronomical community by enabling qualitatively new strong lensing science, and as such we will waive all but a short {3-month} proprietary period on the observations.

WFPC2 11024


This calibration proposal is the Cycle 15 routine internal monitor for WFPC2, to be run weekly to monitor the health of the cameras. A variety of internal exposures are obtained in order to provide a monitor of the integrity of the CCD camera electronics in both bays {both gain 7 and gain 15 — to test stability of gains and bias levels}, a test for quantum efficiency in the CCDs, and a monitor for possible buildup of contaminants on the CCD windows. These also provide raw data for generating annual super-bias reference files for the calibration pipeline.

NIC1/NIC2/NIC3 8795

NICMOS Post-SAA calibration – CR Persistence Part 6

A new proceedure proposed to alleviate the CR-persistence problem of NICMOS. Dark frames will be obtained immediately upon exiting the SAA contour 23, and everytime 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.

WFPC2 10925

Imaging the Nearest Damped Lyman Alpha Absorbers

We propose to acquire broad-band and H-alpha imaging of three bright, very nearby host galaxies for damped Ly-alpha absorbers {DLAs}. Our targets are the only DLA hosts at z < 0.03 {i.e., spatial resolutions of < 1.2 kpc}. The purpose of these observations is to discover the detailed morphology and kinematics and thus the origins of the gas giving rise to DLAs. While ground-based spectroscopy of DLAs is used to infer indirectly the evolution of galaxy metallicity and thick disk kinematics out to z > 4, only with HST imaging of the very lowest redshift DLA galaxies can we discover these relationships directly. In conjunction with H I 21-cm VLA emission maps, broad-band and H-alpha images of these DLAs will allow us to determine: {1} the sites of active star formation in the host galaxies and their relationship to the QSO sightline, {2} the presence of stellar streams, supernova shells, or bipolar “superwind” outflows in DLA host galaxies, and {3} the detailed spiral structure of the host galaxies, which will allow us to use the lower resolution H I 21-cm emission line images to determine unambiguous DLA kinematics with respect to the host galaxy {i.e., is the DLA rotating with the disk?}. Thus, the high resolution imaging will allow us to correctly interpret the kinematics and metallicity information provided by the H I 21-cm VLA maps and HST UV spectroscopy to better inform the high-z results.

WFPC2 11023

WFPC2 CYCLE 15 Standard Darks – part 1

This dark calibration program obtains dark frames every week in order to provide data for the ongoing calibration of the CCD dark current rate, and to monitor and characterize the evolution of hot pixels. Over an extended period these data will also provide a monitor of radiation damage to the CCDs.

WFPC2 11079

Treasury Imaging of Star Forming Regions in the Local Group: Complementing the GALEX and NOAO Surveys

We propose to use WFPC2 to image the most interesting star-forming regions in the Local Group galaxies, to resolve their young stellar populations. We will use a set of filters including F170W, which is critical to detect and characterize the most massive stars, to whose hot temperatures colors at longer wavelengths are not sensitive. WFPC2’s field of view ideally matches the typical size of the star-forming regions, and its spatial resolution allows us to measure indvidual stars, given the proximity of these galaxies. The resulting H- R diagrams will enable studies of star-formation properties in these regions, which cover largely differing metallicities {a factor of 17, compared to the factor of 4 explored so far} and characteristics. The results will further our understanding of the star-formation process, of the interplay between massive stars and environment, the properties of dust, and will provide the key to interpret integrated measurements of star-formation indicators {UV, IR, Halpha} available for several hundreds more distant galaxies. Our recent deep surveys of these galaxies with GALEX {FUV, NUV} and ground-based imaging {UBVRI, Halpha, [OIII] and [SII]} provided the identification of the most relevant SF sites. In addition to our scientific analysis, we will provide catalogs of HST photometry in 6 bands, matched corollary ground-based data, and UV, Halpha and IR integrated measurements of the associations, for comparison of integrated star-formation indices to the resolved populations. We envisage an EPO component.


Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) HSTARS: (None)



                        SCHEDULED      SUCCESSFUL 
FGS GSacq               07                   07 
FGS REacq               06                   06 
OBAD with Maneuver      24                  24 


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