HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT      # 4526

PERIOD COVERED: UT January 014, 2008 (DOY 014)

OBSERVATIONS SCHEDULED

SIGNIFICANT EVENTS: (None)

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.

NIC1/NIC2/NIC3 8794

NICMOS Post-SAA calibration - CR Persistence Part 5

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 DARKs. 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

images. Each observation will need its own CRMAP, as different SAA

passages leave different imprints on the NICMOS detectors.

NIC3 11195

Morphologies of the Most Extreme High-Redshift Mid-IR-luminous Galaxies

II: The `Bump' Sources

The formative phase of some of the most massive galaxies may be

extremely luminous, characterized by intense star- and AGN-formation.

Till now, few such galaxies have been unambiguously identified at high

redshift, and thus far we have been restricted to studying the

low-redshift ultraluminous infrared galaxies as possible analogs. We

have recently discovered a sample of objects which may indeed represent

this early phase in galaxy formation, and are undertaking an extensive

multiwavelength study of this population. These objects are optically

extremely faint {R>26} but nevertheless bright at mid-infrared

wavelengths {F[24um] > 0.5 mJy}. Mid-infrared spectroscopy with

Spitzer/IRS reveals that they have redshifts z~2, implying luminosities

~1E13 Lsun. Their mid-IR SEDs fall into two broad, perhaps overlapping,

categories. Sources with brighter F[24um] exhibit power-law SEDs and SiO

absorption features in their mid-IR spectra characteristic of AGN,

whereas those with fainter F[24um] show a "bump" characteristic of the

redshifted 1.6um peak from a stellar population, and PAH emission

characteristic of starformation. We have begun obtaining HST images of

the brighter sources in Cycle 15 to obtain identifications and determine

kpc-scale morphologies for these galaxies. Here, we aim to target the

second class {the "bump" sources} with the goal of determining if these

constitute morphologically different objects, or simply a "low-AGN"

state of the brighter class. The proposed observations will help us

determine whether these objects are merging systems, massive obscured

starbursts {with obscuration on kpc scales!} or very reddened {locally

obscured} AGN hosted by intrinsically low-luminosity galaxies.

WFPC2 10890

Morphologies of the Most Extreme High-Redshift Mid-IR-Luminous Galaxies

The formative phase of the most massive galaxies may be extremely

luminous, characterized by intense star- and AGN-formation. Till now,

few such galaxies have been unambiguously identified at high redshift,

restricting us to the study of low-redshift ultraluminous infrared

galaxies as possible analogs. We have recently discovered a sample of

objects which may indeed represent this early phase in galaxy formation,

and are undertaking an extensive multiwavelength study of this

population. These objects are bright at mid-IR wavelengths

{F[24um]>0.8mJy}, but deep ground based imaging suggests extremely faint

{and in some cases extended} optical counterparts {R~24-27}. Deep K-band

images show barely resolved galaxies. Mid-infrared spectroscopy with

Spitzer/IRS reveals that they have redshifts z ~ 2-2.5, suggesting

bolometric luminosities ~10^{13-14}Lsun! We propose to obtain deep ACS

F814W and NIC2 F160W images of these sources and their environs in order

to determine kpc-scale morphologies and surface photometry for these

galaxies. The proposed observations will help us determine whether these

extreme objects are merging systems, massive obscured starbursts {with

obscuration on kpc scales!} or very reddened {locally obscured} AGN

hosted by intrinsically low-luminosity galaxies.

WFPC2 11327

Red leaks

The aim of this program is to measure the red leaks in the 8 WFPC2 UV???

filters (F122M, F300W, F255W, F218W, F185W, F170W, F160BW, F122M). We

will use red crossing filters to isolate and directly measure the leaks.

No observations of this kind have ever been performed with WFPC2 to

check the red leaks in the UV filters, most of them being extensively

used by GO/GTO programs. A previous calibration program has only imaged

spectrophotometric standard stars with UV filters (no filter crossing)

thus the red leak is hard to measure using this data. The throughput

curves for some of the UV filters (F300W, F255W, F218W, F185W) in

synphot have incomplete information, some of them have gaps in the

measurements as wide as 3000A.

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               09                09                  

FGS REacq               05                05                  

OBAD with Maneuver 28                28               

SIGNIFICANT EVENTS: (None)