Date: August 31st 2010

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Daily Report #5168 - 1 messages, 1 author http://groups google com/group/sci astro hubble/t/de0ca6232323b98d?hl=en
Daily Report #5169 - 1 messages, 1 author http://groups google com/group/sci astro hubble/t/11d4df8f799191a4?hl=en
Daily Report #5170 - 1 messages, 1 author http://groups google com/group/sci astro hubble/t/e126c396a9973957?hl=en

============================================================================== TOPIC: Daily Report #5168

http://groups google com/group/sci astro hubble/t/de0ca6232323b98d?hl=en

== 1 of 1 == Date: Thurs, Aug 26 2010 5:24Ã‚Â am From: "Cooper, Joe"

HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science

DAILY REPORT #5168

PERIOD COVERED: 5am August 25 - 5am August 26, 2010 (DOY 237/09:00z-238/09:00z)

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:

18887-0 - Install COS CS FSW 4 11 @ 237/1542z

COMPLETED OPS NOTES: (None)

                    SCHEDULED  SUCCESSFUL

FGS GSAcq 05 05 FGS REAcq 10 10 OBAD with Maneuver 05 05

SIGNIFICANT EVENTS:

COS FSW 4 11 was successfully installed and verified by the FSW team at 237/15:42

OBSERVATIONS SCHEDULED:

ACS/WFC 11996

CCD Daily Monitor (Part 3)

This program comprises basic tests for measuring the read noise and dark current of the ACS WFC and for tracking the growth of hot pixels The recorded frames are used to create bias and dark reference images for science data reduction and calibration This program will be executed four days per week (Mon, Wed, Fri, Sun) for the duration of Cycle 17 To facilitate scheduling, this program is split into three proposals This proposal covers 308 orbits (19 25 weeks) from 21 June 2010 to 1 November 2010

STIS/CCD 11845

CCD Dark Monitor Part 2

Monitor the darks for the STIS CCD

STIS/CCD 11847

CCD Bias Monitor-Part 2

Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1, and 1x1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns

WFC3/ACS/UVIS 11613

GHOSTS: Stellar Outskirts of Massive Spiral Galaxies

We propose to continue our highly successful GHOSTS HST survey of the resolved stellar populations of nearby, massive disk galaxies using SNAPs These observations provide star counts and color-magnitude diagrams 2-3 magnitudes below the tip of the Red Giant Branch of the outer disk and halo of each galaxy We will measure the metallicity distribution functions and stellar density profiles from star counts down to very low average surface brightnesses, equivalent to ~32 V-mag per square arcsec

This proposal will substantially improve our unique sampling of galaxy outskirts Our targets cover a range in galaxy mass, luminosity, inclination, and morphology As a function of these galaxy properties, this survey provides: - the most extensive, systematic measurement of radial light profiles and axial ratios of the diffuse stellar halos and outer disks of spiral galaxies; - a comprehensive analysis of halo metallicity distributions as function of galaxy type and position within the galaxy; - an unprecedented study of the stellar metallicity and age distribution in the outer disk regions where the disk truncations occur; - the first comparative study of globular clusters and their field stellar populations

We will use these fossil records of the galaxy assembly process to test halo formation models within the hierarchical galaxy formation scheme

WFC3/IR 11694

Mapping the Interaction Between High-Redshift Galaxies and the Intergalactic Environment

With the commissioning of the high-throughput large-area camera WFC3/IR, it is possible for the first time to undertake an efficient survey of the rest-frame optical morphologies of galaxies at the peak epoch of star formation in the universe We therefore propose deep WFC3/IR imaging of over 320 spectroscopically confirmed galaxies between redshift 1 6 < z < 3 4 in well-studied fields which lie along the line of sight to bright background QSOs The spectra of these bright QSOs probe the IGM in the vicinity of each of the foreground galaxies along the line of sight, providing detailed information on the physical state of the gas at large galactocentric radii In combination with our densely sampled UV/IR spectroscopy, stellar population models, and kinematic data in these fields, WFC3/IR imaging data will permit us to construct a comprehensive picture of the structure, dynamics, and star formation properties of a large population of galaxies in the early universe and their effect upon their cosmological environment

WFC3/IR 11708

Determining the Sub-stellar IMF in the Most Massive Young Milky Way Cluster, Westerlund 1

Despite over 50 years of active research, a key question in galactic astronomy remains unanswered: is the initial mass function (IMF) of stars and sub-stellar objects universal, or does it depend on initial conditions? The answer has profound consequences for the evolution of galaxies as well as a predictive theory of star formation Work to date suggests that certain environments (high densities, e g Elmegreen 2004; low metallicity, e g Larson 2005) should produce a top-heavy IMF, and there are hints from unresolved star-bursts that this might be the case Yet, there is no clear evidence for an IMF that differs from that characterizing the Galactic field stars in a resolved stellar population down to one solar mass Westerlund 1 is the most massive young star cluster known in the Milky Way With an estimated mass of 5x10^4 Msun, an age of 3-5 Myr, and located at a distance of 3-4 kpc, it presents a unique opportunity to test whether the IMF in such a cluster deviates from the norm well down into the brown dwarf regime We propose WFC3 near-IR imaging to probe the IMF down to 40 Jupiter masses The data will enable use to: 1) provide a stringent test of the universality of the IMF under conditions approximating those of star-bursts; 2) search for primordial or dynamic mass segregation in the clusters; and 3) assess whether the cluster is likely to remain bound (as a massive open cluster) or disperse into the field We will obtain images in the F125W, F160W, and F139M filters The F139M filter covers a strong water absorption feature and the color F125W/F139M is a powerful temperature diagnostic in the range 2800-4000 K This information will enable us to: a) confirm membership for low mass stars suspected on the basis of their position in the color-magnitude diagram; b) place the members in the HR diagram; and c) estimate the masses and ages of cluster members for low-mass stars and sub-stellar objects This new capability offered with the WFC3 (through a novel combination of filter complement, high spatial resolution, and large field of view) will enable us to make a fundamental test of whether the IMF is universal on a unique resolved stellar population, as well as assess the clusters structure, dynamics, and ultimate fate

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 11928

WFC3/IR Low-Frequency Flat and Geometric Distortion

Multiple observations of globular cluster Omega Cen at multiple infrared wavelengths of IR detector will be used to derive filter dependency of low-frequency sensitivity (L_flat fields) across of IR detector and its time variation Additionally, the same data will be also used to derive filter-dependant geometric distortion of the detector and its time-dependency

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 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 3x3 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

============================================================================== TOPIC: Daily Report #5169

http://groups google com/group/sci astro hubble/t/11d4df8f799191a4?hl=en

== 1 of 1 == Date: Fri, Aug 27 2010 7:35Ã‚Â am From: "Cooper, Joe"

HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science

DAILY REPORT #5169

PERIOD COVERED: 5am August 26 - 5am August 27, 2010 (DOY 238/09:00z-239/09:00z)

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 03 03 FGS REAcq 12 12 OBAD with Maneuver 03 03

SIGNIFICANT EVENTS: (None)

OBSERVATIONS SCHEDULED:

STIS/CCD 11845

CCD Dark Monitor Part 2

Monitor the darks for the STIS CCD

STIS/CCD 11847

CCD Bias Monitor-Part 2

Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1, and 1x1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns

WFC3/IR 11708

Determining the Sub-stellar IMF in the Most Massive Young Milky Way Cluster, Westerlund 1

WFC3/UV 11638

Illuminating the HI Structure of a Proto-cluster Region at z=2 84

We propose very deep intermediate-band Lyman alpha imaging in the field of a newly-discovered proto-cluster region surrounding the extremely luminous QSO HS1549+19 at z=2 844 The large structure, initially discovered in a spectroscopic survey of galaxies in fields surrounding the brightest QSOs at z=2 5-2 8, represents an ideal laboratory for studying the response of the intergalactic medium to a source of ionizing photons that exceeds the UV background by factors

Within a single pointing of WFC3-UVIS there are already more than 45 known Lyman alpha emitters, most of which are already spectroscopically confirmed, and at least 3 of which are giant ?Lyman alpha blobs'' Many of the objects have properties similar to those expected from the process of fluorescence, in which Lyman alpha emission is induced by the UV radiation field of the QSO in any HI gas that dense enough to remain partially self-shielded Fortuitously, the F467M filter (Stromgren "b") in WFC3-UVIS is a perfect match to Lyman alpha at z=2 844 In combination with an equally deep broad-band continuum image, the observations will allow the construction of a Lyman alpha map tracing dense gas throughout the inner parts of a proto-cluster region at sub-kpc resolution The ability to measure the spatial sub-structure and surface brightness distribution of Lya emission, relative to known protocluster galaxies and AGN, will illuminate the "cosmic web'' in a dense region caught in a violent stage of formation

WFC3/UVIS 11905

WFC3 UVIS CCD Daily Monitor

============================================================================== TOPIC: Daily Report #5170

http://groups google com/group/sci astro hubble/t/e126c396a9973957?hl=en

== 1 of 1 == Date: Mon, Aug 30 2010 10:18Ã‚Â am From: "Cooper, Joe"

HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science

DAILY REPORT #5170

PERIOD COVERED: 5am August 27 - 5am August 30, 2010 (DOY 239/09:00z-242/09:00z)

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

12365 - GSAcq(1,2,1) at 240/23:21:19z took 2 attempts to acquire Fine Lock

Observations possibly affected: WFC3 204 Proposal ID#11908, WFC3 205-206 & ACS 44-47 Proposal ID#11613, STIS 45 Proposal ID#11845, STIS 46-47 Proposal ID#11847

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES:

2066-0 - Update CCS SOI after COS FSW 4 11 installation @ 241/2345z 2061-0 - HST486/NSSC-1 SOI Configuration -- PRD 7 3 (closed) @ 241/2359z 2067-0 - COS EEPROM & Exec SOIs out of synch between install & active (closed) @ 242/0001z

                   SCHEDULED SUCCESSFUL

FGS GSAcq 19 19 FGS REAcq 28 28 OBAD with Maneuver 16 16

SIGNIFICANT EVENTS:

Flash Report: COS FSW 4 11 installation complete

COS successfully transition down to boot and back-up to Operate (COS CS FSW 4 11 was active at 242/02:50z)

OBSERVATIONS SCHEDULED:

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

COS/NUV 12042

COS-GTO: Pluto

We seek to measure Pluto's albedo below 2100, to better constrain surface composition COS observations will provide a substantial improvement in the S/N of Pluto spectra from <1800 to 2100 Accumulation of past HST/FOS spectra yields extremely low S/N below 2000 (S/N of only 1-3 in 100 bins; Krasnopolsky 2001) We expect to achieve S/N=5 at 1950 with 10 binning In addition to spectrally broad albedo measurements, these observations could reveal line or molecular band emission, such as C I 1931 or CO 1993

ACS/WFC 11996

CCD Daily Monitor (Part 3)

WFC3/IR/S/C 11929

IR Dark Current Monitor

WFC3/UV 11922

UVIS Fringing

Multiple pointing observations of the globular cluster Omega Centauri (NGC 5139) in the narrow band filters F656N and F953N will be used to verify the fringing model developed during various tests (TV3) and its impact on photometric accuracy By measuring the relative changes in brightness of a star at different positions on the detector, we will determine the local variations induced by the fringing pattern

WFC3/UVIS 11908

Cycle 17: UVIS Bowtie Monitor

WFC3/UVIS 11905

WFC3 UVIS CCD Daily Monitor

STIS/CCD 11847

CCD Bias Monitor-Part 2

Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1, and 1x1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns

STIS/CCD 11845

CCD Dark Monitor Part 2

Monitor the darks for the STIS CCD

WFC3/IR 11738

SPIDERWEBS AND FLIES: OBSERVING MASSIVE GALAXY FORMATION IN ACTION

Distant luminous radio galaxies are among the brightest known galaxies in the early Universe, pinpoint likely progenitors of dominant cluster galaxies and are unique laboratories for studying massive galaxy formation Spectacular images with the ACS and NICMOS of one such object, the "Spiderweb Galaxy" at z = 2 2, show in exquisite detail, hierarchical merging occurring 11 Gyr ago By imaging 3 additional Spiderweb-like galaxies we wish to study this potentially crucial phase of massive galaxy evolution, when hierarchical merging, galaxy downsizing and AGN feedback are all likely to be occurring Properties of the complete sample of Spiderweb galaxies will be used to (i) constrain models for the formation and evolution of the most massive galaxies that dominate rich clusters and (ii) investigate the nature of chain and tadpole galaxies, a fundamental but poorly understood constituent of the early Universe

We shall image rest-frame UV and optical continuum emission from 3 radio galaxies with 2 4 < z < 3 8 that appear clumpy and large in shallow WFPC/PC observations The new observations will typically reach ~2 magnitudes fainter over 20-40 times larger area than previously Photometric and morphological parameters will be measured for satellite galaxies ("flies") in the clumpy massive hosts and for galaxies in ~ 1 5 Mpc x 1 5 Mpc regions of surrounding protoclusters Locations, sizes, elongations, clumpiness, masses, and star formation rates of the merging satellite and protocluster galaxies will be compared with new state of the art simulations Combination of ACS and WFC3 images will help disentangle the properties of the young and old populations

Specific goals include: (i) investigating star formation histories of the satellite galaxies and the extended emission, (ii) studying "downsizing" and merging scenarios and (iii) measuring the statistics of linear galaxies and relating them to models for the formation of massive galaxies and to the properties of the important but enigmatic class of chain/tadpole galaxies in the HUDF

STIS/CCD/MA1 11737

The Distance Dependence of the Interstellar N/O Abundance Ratio: A Gould Belt Influence?

The degree of elemental abundance homogeneity in the interstellar medium is a function of the enrichment and mixing processes that govern galactic chemical evolution Observations of young stars and the interstellar gas within ~500 pc of the Sun have revealed a local ISM that is so well-mixed it is having an impact on ideas regarding the formation of extrasolar planets However, the situation just beyond the local ISM is not so clear Sensitive UV absorption line measurements have recently revealed a pattern of inhomogeneities in the interstellar O, N, and Kr gas-phase abundances at distances of ~500 pc and beyond that appear nucleosynthetic in origin rather than due to dust depletion In particular, based on a sample of 13 sightlines, Knauth et al (2006) have found that the nearby stars (d < 500 pc) exhibit a mean interstellar N/O abundance ratio that is significantly higher (0 18 dex) than that toward the more distant stars Interestingly, all of their sightlines lie in the sky vicinity of the Gould Belt of OB associations, molecular clouds, and diffuse gas encircling the Sun at a distance of ~400 pc Is it possible that mixing processes have not yet smoothed out the recent ISM enrichment by massive stars in the young Belt region? By measuring the interstellar N/O ratios in a strategic new sample of sightlines with STIS, we propose to test the apparent N/O homogeneity inside the Gould Belt and determine if the apparent decline in the N/O ratio with distance is robust and associated with the Belt region

ACS/WFC3 11734

The Hosts of High Redshift Gamma-Ray Bursts

Gamma-ray bursts are the most luminous explosive events known, acting as beacons to the high redshift universe Long duration GRBs have their origin in the collapse of massive stars and thus select star forming galaxies across a wide range of redshift Due to their bright afterglows we can study the details of GRB host galaxies via absorption spectroscopy, providing redshifts, column densities and metallicities for galaxies far too faint to be accessible directly with current technology We have already obtained deep ground based observations for many hosts and here propose ACS/WFC3 and WFC3 observations of the fields of bursts at z>3 which are undetected in deep ground based images These observations will study the hosts in emission, providing luminosities and morphologies and will enable the construction of a sample of high-z galaxies with more detailed physical properties than has ever been possible before

WFC3/IR 11708

Determining the Sub-stellar IMF in the Most Massive Young Milky Way Cluster, Westerlund 1

WFC3/IR 11694

Mapping the Interaction Between High-Redshift Galaxies and the Intergalactic Environment

WFC3/UV/IR 11664

The WFC3 Galactic Bulge Treasury Program: Populations, Formation History, and Planets

Exploiting the full power of the Wide Field Camera 3 (WFC3), we propose deep panchromatic imaging of four fields in the Galactic bulge These data will enable a sensitive dissection of its stellar populations, using a new set of reddening-free photometric indices we have constructed from broad-band filters across UV, optical, and near-IR wavelengths These indices will provide accurate temperatures and metallicities for hundreds of thousands of individual bulge stars Proper motions of these stars derived from multi-epoch observations will allow separation of pure bulge samples from foreground disk contamination Our catalogs of proper motions and panchromatic photometry will support a wide range of bulge studies

Using these photometric and astrometric tools, we will reconstruct the detailed star-formation history as a function of position within the bulge, and thus differentiate between rapid- and extended-formation scenarios We will also measure the dependence of the stellar mass function on metallicity, revealing how the characteristic mass of star formation varies with chemistry Our sample of bulge stars with accurate metallicities will include 12 candidate hosts of extrasolar planets Planet frequency is correlated with metallicity in the solar neighborhood; our measurements will extend this knowledge to a remote environment with a very distinct chemistry

Our proposal also includes observations of six well-studied globular and open star clusters; these observations will serve to calibrate our photometric indices, provide empirical population templates, and transform the theoretical isochrone libraries into the WFC3 filter system Besides enabling our own program, these products will provide powerful new tools for a host of other stellar-population investigations with HST/WFC3 We will deliver all of the products from this Treasury Program to the community in a timely fashion

WFC3/UVIS 11630

Monitoring Active Atmospheres on Uranus and Neptune

We propose Snapshot observations of Uranus and Neptune to monitor changes in their atmospheres on time scales of weeks and months, as we have been doing for the past seven years Previous Hubble Space Telescope observations (including previous Snapshot programs 8634, 10170, 10534, and 11156), together with near-IR images obtained using adaptive optics on the Keck Telescope, reveal both planets to be dynamic worlds which change on time scales ranging from hours to (terrestrial) years Uranus equinox occurred in December 2007, and the northern hemisphere is becoming fully visible for the first time since the early 1960s HST observations during the past several years (Hammel et al 2005, Icarus 175, 284 and references therein) have revealed strongly wavelength-dependent latitudinal structure, the presence of numerous visible-wavelength cloud features in the northern hemisphere, at least one very long-lived discrete cloud in the southern hemisphere, and in 2006 the first clearly defined dark spot seen on Uranus Long term ground-based observations (Lockwood and Jerzekiewicz, 2006, Icarus 180, 442; Hammel and Lockwood 2007, Icarus 186, 291) reveal seasonal brightness changes that seem to demand the appearance of a bright northern polar cap within the next few years Recent HST and Keck observations of Neptune (Sromovsky et al 2003, Icarus 163, 256 and references therein) show a general increase in activity at south temperate latitudes until 2004, when Neptune returned to a rather Voyager-like appearance with discrete bright spots rather than active latitude bands Further Snapshot observations of these two dynamic planets will elucidate the nature of long-term changes in their zonal atmospheric bands and clarify the processes of formation, evolution, and dissipation of discrete albedo features

STIS/CCD/MA1/MA2 11616

The Disks, Accretion, and Outflows (DAO) of T Tau Stars

Classical T Tauri stars undergo magnetospheric accretion, power outflows, and possess the physical and chemical conditions in their disks to give rise to planet formation Existing high resolution FUV spectra verify that this spectral region offers unique diagnostics of these processes, which have the potential to significantly advance our understanding of the interaction of a star and its accretion disk To date the limited results are intriguing, with dramatic differences in kinematic structure in lines ranging from C IV to H2 among the few stars that have been observed We propose to use HST/COS to survey the disks, outflows, and accretion (the DAO) of 26 CTTS and 6 WTTS in the FUV at high spectral resolution A survey of this size is essential to establish how properties of accretion shocks, winds and disk irradiation depend on disk accretion rate Specifically, our goals are to (1) measure the radiation from and understand the physical properties of the gas very near the accretion shock as a function of accretion rate using emission line profiles of hot lines (C IV, Si IV, N V, and He II); (2) measure the opacity, velocity, and temperature at the base of the outflow to constrain outflow models using wind absorption features; and (3) characterize the radiation incident on disks and protoplanetary atmospheres using H2 line and continuum emission and reconstructed bright Ly-alpha line emission

WFC3/ACS/UVIS 11613

GHOSTS: Stellar Outskirts of Massive Spiral Galaxies

We will use these fossil records of the galaxy assembly process to test halo formation models within the hierarchical galaxy formation scheme

ACS/WFC3 11604

The Nuclear Structure of OH Megamaser Galaxies

We propose a snapshot survey of a complete sample of 80 OH megamaser galaxies Each galaxy will be imaged with the ACS/WFC through F814W and a linear ramp filter (FR656N or FR716N or FR782N or FR853N) allowing us to study both the spheroid and the gas morphology in Halpha + [N II] We will use the 9% ramps FR647M (5370-7570 angstroms) centered at 7000 angstroms and FR914M (7570-10, 719 angstroms) 8000 angstroms for continuum subtraction for the high and low z objects respectively OH megamaser galaxies (OHMG) form an important class of ultraluminous IR-galaxies (ULIRGs) whose maser lines emit QSO-like luminosities ULIRGs in general are associated with recent mergers but it is often unclear whether their power output is dominated by starbursts or a hidden QSO because of the high absorbing columns which hide their nuclei even at X-ray wavelengths In contrast, OHMG exhibit strong evidence for the presence of an energetically important and recently triggered active nucleus In particular it is clear that much of the gas must have already collapsed to form a nuclear disk which may be the progenitor of a circum-nuclear torus, a key element of the unified scheme of AGN A great advantage of studying OHMG systems over the general ULIRG population, is that the circum-nuclear disks are effectively "fixed" at an inner, edge on, orientation, eliminating varying inclination as a nuisance parameter We will use the HST observations in conjunction with existing maser and spectroscopic data to construct a detailed picture of the circum-nuclear regions of a hitherto relatively neglected class of galaxy that may hold the key to understanding the relationship between galaxy mergers, nuclear star- formation, and the growth of massive black holes and the triggering of nuclear activity

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