Presentation on theme: "Seeing the Skies with PAndA’s Eyes: Galactic Archaeology in our own backyard Geraint F. Lewis Sydney Institute for Astronomy The University of Sydney."— Presentation transcript:
Seeing the Skies with PAndA’s Eyes: Galactic Archaeology in our own backyard Geraint F. Lewis Sydney Institute for Astronomy The University of Sydney
Collaborators Mike Irwin (Cambridge) Rodrigo Ibata (Strasbourg) Annette Ferguson (Edinburgh) Scott Chapman (Cambridge) Nial Tanvir (Leicester) Alan McConnachie (DAO) Nicolas Martin (Heidelberg) Avon Huxor (Bristol) +Postdocs and Students
Cosmological Predictions The Spaghetti Survey: http://smaug.astr.cwru.edu/heather/spag.html
Cosmological Predictions Cosmological models predict that the Milky Way should be surrounded by the tidal debris of ongoing and ancient accretion events. However, the expected surface brightness of tidal features is very low (~31 mags/sq arc) and hence below photographic detection in integrated light. So we need CCD surveys of large areas to identify individual stars and examine the spatial (and kinematic) properties to identify streams.
In the Milky Way The Sagittarius Stream (2Mass; Majewski et al (2003))
Andromeda & Triangulum (M31 & M33) M31 is a grand design spiral very similar to the MW, located at 780kpc. M33 has a mass ~1/10 th that of the MW, located at a distance of 860kpc. Separated on the sky by ~15 degrees on the sky (physical separation of 230kpc) and M33 may be a bound satellite of M31, although it appears to be very undisturbed.
The Andromeda Train Wreck! This is the final result of the INT survey, with metal-poor being coloured blue, and metal-rich red. Features: The Andromeda Stream G1-Clump NGC205 Loop Northern Spur Eastern/Western Shelf Edge-brightened Shell There is significant colour variations through the outer edge of the disk (interpreted as metallicity differences), but it appears that the Eastern & Western Shelf and Andromeda Stream are related (Ferguson et al 2002).
CFHT/MegaCam Survey MegaCam is 36 CCDs covering ~1 sq deg. 25 fields per year (2003-2007) covering ~89 sq degs. Targeted the South (away from GP). Each field got to g~i~25, giving ~3 mag of the RGB at M31. Results published in Ibata et al 2007 (monster paper).
CFHT/MegaCam Survey Girardi et al. (2004) isochrones at the distance of M31 [Fe/H] = –3.0 [Fe/H] = –2.3 [Fe/H] = –1.7 [Fe/H] = –1.3 [Fe/H] = –0.7 [Fe/H] = –0.4 [Fe/H] = +0.0 [Fe/H] = +0.2 + matched filter to give lower weight to contaminated regions of the CMD
M31/M33 Stellar Halo? We can consider the stellar density as a function of radius (shown above for two metallicity cuts). This contains the substructures seen in the maps (accounting for the bumps and wiggles), but clearly the stellar halo of M31 is extended to the edge of our survey (~150kpc), and in fact overlaps with an extended stellar halo of M33!
Metallicity Structure The stream-like structures appear to possess differing metallicities, with D being metal-poor, while B and C are more metal-rich. The material between B & C is also seen to be metal-rich. This makes the interpretation of the streams as being the result of a single event trouble-some.
PAndAS (Pan-Andromeda Archaeological Survey) PI McConnachie (DAO) CFHT large program (total of 226 hours) 350 sq degrees of the haloes of M31 & M33. To g~25.5 and i~24.5, giving a couple of mags of the RGB.
Where next? Still digesting the first PAndAS data compilation (with several papers due soon) Key questions include; Can we reproduce the Andromeda Stream and other features? Are these streams related? Can we understand the structure of M33? What are the properties of dwarfs and faint fuzzies in the halo of M31? How do these compare to models of galaxy formation? …. and many more Summary Over the last decade we have been building a panoramic view of our nearest neighbours, and in the next few years PAndAS will provide the first complete picture of their halos. The results so far are spectacular. This is being accompanied with kinematic studies with Keck and Gemini to paint a more accurate picture of ongoing galactic evolution in our own backyard.