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Globular Cluster - Dwarf Galaxy Connection W1: a case study in our neighborhood

Globular Cluster - Dwarf Galaxy Connection W1: a case study in our neighborhood. 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)

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Globular Cluster - Dwarf Galaxy Connection W1: a case study in our neighborhood

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  1. Globular Cluster - Dwarf Galaxy ConnectionW1: a case study in our neighborhood 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) Beth Willman Ann Arbor, Aug 27 2007

  2. 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 < rhalf < 40 pc • -4 < MV < -2 mag • These values are very uncertain but their status as outliers is robust BooII SEGUE I W1 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

  3. Willman 1 D ~ 35 kpc Rhalf~ 1.9’; 20 pc MV ~ -2.5 mag Boo II Bootes II D ~ 50 kpc Rhalf~ 2.4’, 35 pc MV ~ -3.3 mag Willman et al 2006, Walsh et al, in prep

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

  5. Willman 1 D ~ 35 kpc Rhalf~ 1.9’, 20 pc MV ~ -2.5 mag Boo II Bootes II D ~ 50 kpc Rhalf~ 2.4’, 35 pc MV ~ -3.3 mag Willman et al 2006, Walsh et al, in prep; see also Martin et al 2007

  6. 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

  7. 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?

  8. W1: Evidence for Age Spread? • 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 Figure from Piotto et al 2007

  9. DEIMOS survey of W1 • Nov 2005, March 2007 - 4 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-1 • 111 stars with total velocity errors < 15 km sec-1. Median ~ 4 km sec-1 See also Martin et al 2007 In collaboration with Marla Geha, Jay Strader, & Connie Rockosi

  10. DEIMOS survey of W1 • Nov 2005, March 2007. 4 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-1 • 111 stars with total velocity errors < 15 km sec-1. Median ~ 4 km sec-1 In collaboration with Marla Geha, Jay Strader, & Connie Rockosi

  11. In collaboration with Marla Geha, Jay Strader, & Connie Rockosi

  12. In collaboration with Marla Geha, Jay Strader, & Connie Rockosi

  13. Vsys ~ -12 km sec-1 ~ 45 member stars -25 < v < 0.5 km sec-1 In collaboration with Marla Geha, Jay Strader, & Connie Rockosi

  14. [Fe/H] distribution of W1 stars [Fe/H] = -2.66 + 0.42[Ca - 0.64(VHB - V)] Use Rutledge, Hesser & Stetson (1997) for CaT EW to [Fe/H]. Use VHB = 0.88. In collaboration with Marla Geha, Jay Strader, & Connie Rockosi

  15. [Fe/H] distribution of W1 stars [Fe/H] = -1.54 +/- 0.45, using ML technique including [Fe/H] errors (median = 0.26) In collaboration with Marla Geha, Jay Strader, & Connie Rockosi

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

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

  18. Velocity dispersion of W1 * This is not a dispersion profile * • ~ 3 - 4 km sec-1 Before accounting for binaries Using Geha code based on maxilmum likelihood method in Walker et al 2006

  19. Velocity dispersion of W1 • ~ 3 - 4 km sec-1 Before accounting for binaries Using Geha code based on maxilmum likelihood method in Walker et al 2006

  20. Mass of W1 object M/L =  (9/2G) ( 02/ S0 rhalf )(Richstone & Tremaine 1986) or M = 167rc02(Illingworth 1976) For 0~ 2.5 - 3 km sec-1: M ~ 2d5 Msun 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

  21. 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

  22. 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 108 Msun). DM not obviously necessary, but do need a much higher mass to get [Fe/H] spread

  23. … 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?

  24. The End

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

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

  27. Vsys ~ -12 km sec-1 In collaboration with Marla Geha, Jay Stader, & Connie Rockosi

  28. M5 M15 M13

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

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