Globular Cluster - Dwarf Galaxy Connection W1: a case study in our neighborhood Ann Arbor, Aug Beth Willman W1 DEIMOS Observations M.Geha (HIA/Yale) C. Rockosi (UCSC) J. Strader (UCSC) W1 KPNO Observations M. Blanton (NYU) D. Hogg (NYU) D. Martinez-Delgado (IAC) Bootes II MMT/Megacam J. Harris (UA) H. Jerjen (ANU) D. Sand (UA) A. Seth (CfA) S. Walsh (ANU) D. Zaritsky (UA)

Dwarfs and clusters - a local investigation Three of the recently discovered Milky Way companions (Bootes II, SEGUE I, W1) inhabit an unusual region of size-luminosity space: 20 pc < r half < 40 pc -4 < M V < -2 mag These values are very uncertain but their status as outliers is robust New MW discoveries: Willman et al 2005a,b, Zucker et al 2006 a,b, Belokurov et al 2006,2007; Irwin et al 2007; Walsh, Jerjen & Willman 2007 W1 BooII SEGUE I

Willman et al 2006, Walsh et al, in prep Willman 1 D ~ 35 kpc R half ~ 1.9’; 20 pc M V ~ -2.5 mag Bootes II D ~ 50 kpc R half ~ 2.4’, 35 pc M V ~ -3.3 mag Boo II

Willman et al 2006; Geha et al in prep; Walsh et al, in prep Willman 1 D ~ 35 kpc R half ~ 1.9’, 20 pc M V ~ -2.5 mag Bootes II D ~ 50 kpc R half ~ 2.4’, 35 pc M V ~ -3.3 mag M92 [Fe/H] = -2.2 Boo II

Willman et al 2006, Walsh et al, in prep; see also Martin et al 2007 Willman 1 D ~ 35 kpc R half ~ 1.9’, 20 pc M V ~ -2.5 mag Bootes II D ~ 50 kpc R half ~ 2.4’, 35 pc M V ~ -3.3 mag Boo II

Dwarfs or clusters? traditionally classified by their size and luminosity recent discoveries underscore that this is an insufficient metric simple distance, age, [Fe/H] measurements don’t get us much farther New metrics for classification: Single burst of star formation? [Fe/H] spread? Need dark matter to explain kinematics? Dwarf - born in own dark matter halo Cluster - not born in dark matter halo New MW discoveries: Willman et al 2005a,b, Zucker et al 2006 a,b, Belokurov et al 2006,2007; Irwin et al 2007

W1: Evidence for Age Spread? At present, best guess is based on color spread near MSTO. Color spread is a bit larger than phot errors (see also Martin et al 2007). Additional information from careful CMD modelling? (Harris, Sand, Seth, Zaritsky; de Jong et al) What about complicating factors such as He abundance? Can we learn more by using Washington filters?

W1: Evidence for Age Spread? Figure from Piotto et al 2007 At present, best guess is based on color spread St 2007). Additional information from careful CMD modelling? (Harris, Sand, Seth, Zaritsky; de Jong et al) What about complicating factors such as He abundance? Can we learn more by using Washington filters? NGC 2808

DEIMOS survey of W1 Nov 2005, March masks: 2 2.5h and 2 1.5h total integration time Reduce with spec2D (Cooper et al in prep) Velocities and random errors derived with Geha technique Systematic errors set at 2.2 km sec stars with total velocity errors < 15 km sec -1. Median ~ 4 km sec -1 In collaboration with Marla Geha, Jay Strader, & Connie Rockosi See also Martin et al 2007

DEIMOS survey of W1 Nov 2005, March masks: 2 2.5h and 2 1.5h total integration time Reduce with spec2D (Cooper et al in prep) Velocities and random errors derived with Geha technique Systematic errors set at 2.2 km sec stars with total velocity errors < 15 km sec -1. Median ~ 4 km sec -1 In collaboration with Marla Geha, Jay Strader, & Connie Rockosi

V sys ~ -12 km sec -1 ~ 45 member stars -25 < v < 0.5 km sec -1

[Fe/H] distribution of W1 stars Use Rutledge, Hesser & Stetson (1997) for CaT EW to [Fe/H]. Use V HB = In collaboration with Marla Geha, Jay Strader, & Connie Rockosi [Fe/H] = [  Ca (V HB - V)]

[Fe/H] distribution of W1 stars In collaboration with Marla Geha, Jay Strader, & Connie Rockosi [Fe/H] = /- 0.45, using ML technique including [Fe/H] errors (median = 0.26)

Kinematic distribution of W1 stars In collaboration with Marla Geha, Jay Strader, & Connie Rockosi

Kinematic distribution of W1 stars In collaboration with Marla Geha, Jay Strader, & Connie Rockosi

Velocity dispersion of W1 Using Geha code based on maxilmum likelihood method in Walker et al 2006 * This is not a dispersion profile *  ~ km sec -1 Before accounting for binaries

Velocity dispersion of W1 Using Geha code based on maxilmum likelihood method in Walker et al 2006  ~ km sec -1 Before accounting for binaries

Mass of W1 object M/L =  (9/2  G) (  0 2 / S 0 r half ) (Richstone & Tremaine 1986) or M = 167r c  0 2 (Illingworth 1976) For  0 ~ km sec -1 : M ~ 2d5 M sun and M/L ~ 200 If M/L = 10 and MFL, then expect:  0 ~ 0.6 km sec -1 See work by Walker et al and Strigari et al for detailed kinematic modelling of new dwarfs in a CDM context

W1: Dwarf or Not? W1 appears: old, metal-poor, not a simple stellar population, to display a substantial [Fe/H] spread Although only 1d3 solar luminosities… Stellar population is more like that of a dwarf galaxy

W1: Dark or Not? Is W1 presently residing in a very massive dark matter halo? If so - what about apparent tidal features? If not - could it have been in the past?  is marginally inconsistent with zero; must have M/L > 30 to support even 1 km sec -1 in an MFL model … but what about possibility of inflated velocity from unbound stars? Is this an L. Mayer remnant? [Is this a Kuhn/Kroupa “dwarf”? … but wouldn’t expect stellar population spread] On kinematics alone - W1 is consistent with residing within a very massive dark matter halo (Strigari et al, few 10 8 M sun ). DM not obviously necessary, but do need a much higher mass to get [Fe/H] spread

… the bigger picture… What is definition of GC vs. dwarf? Can the metrics discussed here uniquely distinguish these two classes of objects? Are kinematics necessary? Are kinematics enough? Should we re-assess known GCs?

The End

In collaboration with Marla Geha, Jay Stader, & Connie Rockosi

[Fe/H] distribution of W1 stars In collaboration with Marla Geha, Jay Stader, & Connie Rockosi

V sys ~ -12 km sec -1

M5 M13 M15

So what’s the deal with the missing satellite problem? Image courtesy J. Diemand