From the Milky Way to Andromeda: A PAndAS View of Galactic Halos

Brendan McMonigalSupervisor - Geraint F. Lewis

Sydney Institute for AstronomySchool of Physics, The University of Sydney

Original image: Stephen Rahn (Flikr)

Outline

• A PAndAS Introduction

• Mapping the contamination

• The Smooth Halo of M31

• A new MW Stream

Canada-France-Hawaii TelescopeCFHT – 3.6m on Hawaii

PAndAS(Pan-Andromeda Archaeological Survey)

MegaCam (~1 degree FOV)

Andromeda & Triangulum (M31 & M33)

M31 is a grand design spiral very similar to the MW, located at 780kpc.M33 has a mass ~1/10th 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.

Ibata et al (2014)

Martin et al (2013)

Martin et al (2013)

Original image: Stephen Rahn (Flikr)

Original image: Stephen Rahn (Flikr)

PAndAS Collaborators

PAndAS: The Pan-Andromeda Archaeological Survey

Alan McConnachieLead PI

Annette Ferguson

Rodrigo Ibata

Mike Irwin

Nicolas Martin

Scott Chapman Geraint Lewis

PAndAS Collaborators

Bullock & Johnston (2005) 300kpc

Expectations from Simulations

Full PAndAS CMD

Ibata et al (2014)

[Fe/H] = -1.91[Fe/H] = -1.29[Fe/H] = -0.71[Fe/H] = -0.20

PAndAS Contamination

Martin et al (2013)

α β γ

Before and...

Mar

tin e

t al (

2013

)

...After

Mar

tin e

t al (

2013

)

Source Identification

Mar

tin e

t al (

2013

)

Smoothed Density Significance η M31 Halo [Fe/H]

Dwarf [Fe/H] Log(N) Half light radius Detections

Significance Map

Martin et al (2013)

Known Dwarf

Known GC

Detections

Martin et al (2013)

Known Dwarf

Known GC

Algorithm Detection

A New Extended Cluster

Martin et al (2013)

The search for the smooth halo

Ibata et al (2014)

Metal Poor

Metal Poor-ish

Metal Rich

Metal Rich-ish

The search for the smooth halo

Ibata et al (2014)

Metal Poor

Metal Poor-ish

Metal Rich

Metal Rich-ish

Combined Map

Ibata et al (2014)

Residuals

Ibata et al (2014)

Metal Poor

Metal Poor-ish

Metal Rich

Metal Rich-ish

Profiling: Metal Poor

Ibata et al (2014)

Profiling: Metal Poor-ish

Ibata et al (2014)

Profiling: Metal Rich (and Rich-ish)

Ibata et al (2014)

Substructure in the Milky Way

Koposov et al (2012)SDSS-III

Substructure in the Milky Way

Martin et al. (2014)

Substructure in the Milky Way

Take home points…• PAndAS: We now have the most comprehensive view of a galaxy halo out to

150kpc (as well as to 50kpc in M33)

• Substructure: We see extensive substructure, consisting of streams and clumps, both in Andromeda and the MW.

• Dwarf Population: We’ve uncovered a large populations of dwarf galaxies, but still not as many as expected from cosmological predictions (modulo gas physics).

Still to come: Globular Clusters (Nick), 3D structure (Anthony)