Alan McConnachie

Mike Irwin, Annette Ferguson, Nial Tanvir, Rodrigo Ibata, Geraint Lewis, Scott Chapman, Avon Huxor

A Bird’s Eye View of M31 and its

Satellite Galaxies

IDM2004

The INT WFS of M31:

Ibata et al. 2001Ferguson et al. 2002

Irwin et al. 2004

Status as of July 2001(58 pointings)

Currently 165 pointings+ M33 (21 pointings) + total of 15 other dwarf galaxies

Blue RGB Red RGB12

5 kp

c

95 kpcFaintest features:

Faintest features have

Extent of the Stream:CFH12K Mosaic

McConnachie et al. 2003

Progress so far...

Ibata et al. 2004

radial velocities for ~15 000 stars in 34 distinct fields

concentrated on known substructure, general halo, and outer disk fields

RVs accurate to ~5km/s

McConnachie et al. 2004aKeck/DEIMOS radial velocity survey of M31

And VIIIIbata et al. 2004

First DIRECT measurement of the gravitational potential of a giant galaxy out to ~125 kpc:

Best fitting orbits:

Ibata et al. 2004

The Satellite Galaxies of Andromeda:

McConnachie et al. 2004b,c

Andromeda I & II

TRGB = 20.40 TRGB = 20.13

An M31 All-Sky View:(Aitoff equal-area projection)

An M31 All-Sky View:(Aitoff equal-area projection)

An M31 All-Sky View:

Preference for satellites to lie on near side of M31

The Line-of-Sight Probability Distribution Function

Why are the satellites lop-sided?

Why do they know about the Milky Way?

Are they tracing the underlying potential?

•Copious amounts of substructure: clue to formation history?

•First direct measure of dynamical mass of a galaxy over such a large distance range:

•Satellite distribution shows a strong anisotropy; tracers of underlying dark matter potential?

Summary: