Assigned ID: 836
----- Attempting Submission 1 (Fri Feb 24 22:37:19 GMT 2012) ---------- Attempting Submission 1 (Tue Jul 10 03:36:54 GMT 2012) -----Origin of UCDs in the Coma ClusterWe propose to explore the nature and origin of ultra-compact dwarf galaxies through two passband imaging with the ACS/WFC of 6 fields in the Coma cluster core. This is part of an on-going ACS survey of the Coma cluster which was cut short by the ACS failure. The proposed 6 fields will provide contiguous coverage of the central core assuring legacy value of this treasury program while concurrently targeting regions expected to harbor large UCD populations where specific tests will help distinguish between different formation scenarios. Through the high spatial resolution of ACS we have successfully identified a population of UCDs in the Coma cluster, strongly concentrated around the central giants and along a narrow band through the core region. Based on the UCD properties, distribution, and similarities to the Coma cluster GC population in our current dataset, we find more evidence for UCDs originating as star clusters than as stripped nuclei from tidally disrupted dwarf ellipticals. However, other formation scenarios are not ruled out. The proposed observations fill in the principal axis of the core, targeting regions around 3 major galaxies, where we expect high concentrations of UCDs based on this previous work. With more complete coverage in the central core, we will establish whether GCs and UCDs maintain similar distributions and similarly higher densities around the 3 targeted galaxies, investigate previously noted color affiliations of UCDs with these host galaxies, and determine whether the number counts of UCDs are consistent with the bright tail of the GC luminosity function or the implied numbers of disrupted dwarfs with intracluster light measurements.We plan to observe 6 fields with ACS/WFC in both F814W and F475W as done previously for the Coma HST/ACS Treasury survey. These 6 fields extend the survey along the principal core axis and provide contiguous coverage in the core region. Additionally, these fields probe regions which are targeted specifically to help establish the origins of UCDs. This includes the region around the unusual galaxy IC 4051 which hosts a large GC population and which may host a large UCD population, and 4 fields immediately adjacent to NGC 4874 and NGC 4889 in order to investigate the extent of the large UCD populations bound to these central galaxies, their distribution, and especially any color trends.
Two filters are necessary for initial color selection of GC/UCDs and to study the color distribution of the GC/UCDs. We will use F814W and F475W as in the original survey and which proved to be a good discriminant for color selection. We will use the same observing strategy as implemented previously: 2 orbits per field, observing each field with 2 filters, and with a total 4 dithered exposures to be multidrizzle combined. Total exposure times previously were 1400s in F814W and 2677s in F475W, reaching a point source limit of I_C = 26.6. The total time per orbit pair for this cycle is 109s shorter. Thus total exposure times will be 1400s in F814W and 2568s in F475W. This provides the required depth and color information necessary for detections of GCs to M_I ~ -8.5 (90% completeness) and will allow identification of sources as UCDs down to M_I ~ -11 via measurement of effective radius in the ACS F814W images. Since M_I = -11 is often used as the cutoff between GC and UCDs, this depth is sufficient.
Orientations are specified to be +-15 deg for every 90 deg around the original survey orientation. Although it would be ideal to use an identical orientation as the original survey to assure no gaps in the coverage, we have relaxed this requirement in order to maximize schedulability while still assuring nearly complete survey coverage. The orientation for one target field, Coma2-0, is less restrictive, chosen only to ensure overlap with the unusual galaxy IC 4051. If it proves necessary to increase schedulability for any of these fields, the orientation requirements can be relaxed further. This may also be necessary in order to access good guide stars.UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE12false0.00.0falsefalsefalsefalseSUPPORTEDCLUSTER OF GALAXIESRICH CLUSTERJ2000J2000CLUSTER OF GALAXIESRICH CLUSTERJ2000J2000CLUSTER OF GALAXIESRICH CLUSTERJ2000J2000CLUSTER OF GALAXIESRICH CLUSTERJ2000J2000CLUSTER OF GALAXIESRICH CLUSTERJ2000J2000CLUSTER OF GALAXIESRICH CLUSTERJ2000J2000ACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF475WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF475WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF475WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF475WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF475WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF475WPOS-TARGDITHERDITHER23.011Across-the-gap dither plus hot pixel sub-ditherLINEfalsefalse0.2412285.28POS-TARGACS-WFC-DITHER-LINE22.32391true/data/opik/Dwarfs/observing/HST3/OP-cache/ComaUCDPhII-v01.xmlThe scheduling data was generated by CASM 20.2.CASM was run in Phase II mode.(Tic-Visit
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