Revealing Elliptical Galaxy Halos

Duncan Forbes, Swinburne University

Collaborators

• Robert Proctor (Sao Paulo)• Alan Brito (Swinburne)• George Hau (Swinburne) • Lee Spitler (Swinburne) • Caroline Foster (Swinburne)• Christina Blom (Swinburne)• Jean Brodie (UCSC)• Aaron Romanowsky (UCSC)• Jacob Arnold (UCSC) • Jay Strader (Harvard)• Soeren Larsen (Utrecht)

Why study elliptical galaxy halos?

Also some kinematic signatures of galaxy formation only apparent at

large radii

Halo stellar populations and kinematics using Deimos on

Keckmultiplexing times 4 !

Metallicity Kinematics

Globular Clusters ~10 Reff

Foster et al. In prep~10 Reff

Romanowsky et al. 2009

Halo starlight ~3 Reff

Foster et al. 2009~3 Reff

Proctor et al. 2009

“Need outer halo kinematics” - Rix

Deimos spectra and fits to the galaxy halo light in the 3 Calcium Tripletregions

S/N

NGC 2768: Deimos as an IFUNGC 2768: Deimos as an IFU

Velocity map for NGC 2768Velocity map for NGC 2768

Sauron maps Reff = 64 arcsec

Radial Kinematics - NGC 821

Proctor,Forbes etal. 2009

NGC 821: a low DM galaxy?

N2768 and N821

Anisotropy (Binney) diagramAnisotropy (Binney) diagram

NGC 2768

Fast -> Faster

NGC 821Fast ->Slow

Metallicity gradients (<1Re) vs mass

Spolaor et al. 2009

Log sigma MB

NGC 2768: Metallicity to ~3 Re

Gal

axy

Hal

o M

ass

Globular Cluster System Mass

New Halo vs Globular Cluster Mass (linear)

Relation

Spitler & Forbes 2008

Globular Cluster FormationGC formation is directly

proportional to the host halo mass with little environmental trend0.007% of Halo Mass = (Globular Cluster System Mass)

Science progresses best when observations force us to alter our preconceptions.

Vera RubinTeacher and Coauthor

Conclusions• New method for measuring 2D halo starlight kinematics and stellar populations to large Re

•Fast/slow rotators may change with radius.•Outer gE halos may be very metal-poor, built by low mass progenitors?•Mass modelling – see talk by Romanowsky. •New method for obtaining halo masses (based on globular cluster system mass) – see poster by Spitler.