PAndAS - Globular Cluster Science ------------------------------------------------ Science Background ------------------------ The PAndAS project is a truly ambitious one which will image the nearest large galaxies to us - M31 and M33 - with unprecedented completeness. It will perform a survey of approximately 350 square degrees using MEGACAM at CFHT in 2 colours. The survey will extend out to a galactocentric radius of 150 kpc for M31 and 50 kpc for M33. The discovery space will include searching for new M31/M33 globular star clusters (GC) with the stated aim of finding all the clusters outside the inner regions of the galaxies down to an absolute magnitude of about 0. This will provide a significantly more complete sample than we currently have even in our own Galaxy. The primary science aim for the GC work is to probe the formation history of M31/M33 using these clusters and search for "streams" of them which could be related to major accretion events. An additional possible PAndAS topic involving GCs is the comparison of the properties of GCs with and without X-ray sources. This has been done before course, but (particularly for M31) generally by X-ray astronomers who don't know GCs that well. It will be a huge bonus to have a set of homogeneous optical properties for the M31 GCs, and with decent seeing it might well be possible to get reasonable estimates of sizes for most of them. The correlation with X-rays potentially yields information on black holes in these clusters or on their X-ray binary content. Time awarded ------------ PAndAS was the highest ranked of all the long term proposals considered by CFHT in 2008. It was awarded the full amount of time requested - namely 226 hours spread out over 3 years in the B semester in dark time at CFHT. The Collaboration ------------------------ PAndAS is an international collaboration of 25 astronomers from 7 institutions in Canada, 1 in France, 3 in the UK and 1 in Australia. The survey will be carried out using MEGACAM at CFHT, with the raw data being archived at the CADC. All subsequent data access will be through CADC. The size of the raw data set, the required compute power for pipeline reduction, the need to develop new reduction tools, the distributed nature of the collaboration and the planned involvement of CADC make this an ideal project within CANFAR. The size of the collaboration, and the scope of the project means that it is simply not feasible for processing to be carried out at any individual institution. A single, central processing and project management location is vital for the success of PAndAS to ensure consistency and ease of management. Members of the collaboration will need to examine the latest data products for quality assessment and be able to approve data products or issue requests for re-processing. These requests (and any changes to the processing steps) must be recorded for all members of the collaboration to examine. High Level Data Analysis Plans and Quality Control -------------------------------------------------- We have no real-time analysis requirements beyond the default quality assurance that takes place at the telescope and after running the Elixir pipeline. The Elixir pipeline will provide basic image processing, including first-pass photometric/astrometric calibration at the individual frame level. For all aspects of further data processing and management (e.g., image stacking, catalogue generation, morphological classification, and band-merging), we will use a variant of the VISTA Data Flow System. The optical pipeline processing component of the VDFS has been scientifically verified by successfully processing a range of wide field CCD mosaic imaging data, including our extant CFHT/MegaPrime surveys of M31. The processed data will be tagged with seeing measurements and other Data Quality Control information. We will further check seeing, limiting magnitudes and sky background level for consistency with legacy data quality requirements. If necessary fields failing these checks at a significant level will be reinserted into the observing programme and noted for report to CFHT staff. Data Analysis Plans Particular to Globular Clusters -------------------------------------------------- It is absolutely critical that a homogenous GC sample is produced using a well understood selection function (so we know precisely the level of completeness with respect to different GC parameters). Ideally, we'd like to come up with some selection strategy that selects surface brightness enhancements of differing spatial scales (i.e., the peak of the GC r_h distribution will almost certainly occur at ~ 3 pc, but it will also extend to lower, and potentially much higher, sizes). Beginning with the catalog of GC candidates (some of which can be immediately confirmed as GCs using existing radial velocity surveys), we will want to construct 1D surface brightness profiles for all candidate clusters (i.e., we need to measure intensity profiles along the major axis, ellipticity, and position angle). The 1D profiles can then be fitted with different types of models (i.e., King, Sersic and Wilson models, for starters) to obtain azimuthally-averaged structural parameters (i.e., r_c, c, rh, r_e, n, _e, etc) as well as total magnitudes, in both PAndAS bandpasses (and hence colours). We will also perform 2D fits of the GCs directly using GALFIT, KINGPHOT or ISHAPE. It will also be useful to compare the model-dependent parameters derived in this way with non-parametric estimates of the effective radii, total magnitude, effective surface brightness, etc. Depending on the brightness of the GCs, this can be done using a simple curve-of-growth type analysis. Ultimately, we aim to publish the definitive GC catalogs for this galaxy, tabulating all of the information given above. Since there are innumerable catalogs of the M31 GC system using different naming schemes, it would be helpful to cross-identify all of these GCs and introduce our own (hopefully final) naming scheme. Data Products -------------- The data will be available to the participating communities immediately, and to the world one year later. All primary data products will be in the form of FITS files, either multi-extension image or binary tables for the catalogues. These will be compliant with VO standards to expedite publishing the results. The following additional data products will be created and made available: (i) Stacked and/or mosaiced data for dithered observations of single targets; (ii) Statistical confidence maps for all image products; (iii) Derived object catalogues based on a standard set of object descriptors including astrometric and photometric measures, and morphological classification; (iv) DQC database including measurements of seeing, average stellar shape, aperture corrections, sky background and noise levels, limiting magnitudes; (v) Homogeneous band-merged catalogues from single pointings. Requested Support -------------- The GC group on the PAndAS project consists of 7 major investigators. Some support will be available from NSERC grants to the Canadians or other funding sources if international and some through CANFAR. For my particular work I am requesting 1/2 a postdoc per year over 2 years for a total support of ~$60k.