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How cold is Cold Dark Matter dSph galaxies as a probe

How cold is Cold Dark Matter dSph galaxies as a probe. Gerry Gilmore IoA Cambridge Dynamics, abundances with Mark Wilkinson, Rosie Wyse, Jan Kleyna, Andreas Koch, Wyn Evans, Eva Grebel Discovery work with Vasily Belokurov, Dan Zucker, Sergey Koposov, et al.

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How cold is Cold Dark Matter dSph galaxies as a probe

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  1. How cold is Cold Dark MatterdSph galaxies as a probe Gerry Gilmore IoA Cambridge Dynamics, abundances with Mark Wilkinson, Rosie Wyse, Jan Kleyna, Andreas Koch, Wyn Evans, Eva Grebel Discovery work with Vasily Belokurov, Dan Zucker, Sergey Koposov, et al ApJ 663 948 2007 (july10), arXiv 0706.2687 Also Wilman, Walker & Mateo, Kamaya, Grillmair, Simons & Geha

  2. The smallest galaxies are the places one must see thenature of dark matter, & galaxy formation astrophysics mssm has 120+ free parameters… lots to learn Inner DM mass density depends on the type(s) of DM Dwarf galaxy mass function depends on DM type Figs: Ostriker & Steinhardt 2003

  3. Satellite population problem: Fewer expected in LG? reaching the cooling limit? NB: predictions running out just where the data are today. Ishiyama etal 0708.1987. dashed line from Moore etal

  4. Real satellite luminosity function Koposov et al 07 arXiv:0706.2687 Open symbols: Volume-corrected satellite LF from DR5 Filled symbols: ‘all Local Group dSph’ Coloured curves: Semi-analytic theory (Benson et al 02, red Somerville 02, blue) --severe surface- brightness discrepancies Grey curve: power- law ‘fit’ to data Slope 1.1

  5. Sgr & Field of Streams (and dots)outer halo is lumpy: but is a tiny mass fraction Streams  accretion history Several new satellites  CDM test Two wraps? Halo DM shape Disk accretion? Warp? Belokurov et al (2006b) SDSS data, 19< r< 22, g-r < 0.4 colour-coded by mag (distance), blue (~10kpc), green, red (~30kpc) Sgr discovered 1994 Ibata, Gilmore, Irwin Nat 370

  6. Walcher et al 2005 Dotted line is virial theorem for stars, no DM • There is a discontinuity • in (stellar) phase-space • density between small • galaxies and star clusters. • Main difference is in • surface brightness • Why? • Dark Matter? • Size differences dSph Phase spacedensity (~ ρ/σ3) ~ 1/(σ2 rh)

  7. New systems extend overlap between galaxies and star clusters in luminosity Belokurov et al. 2006 Analyses of kinematic follow-up underway  ~103 L

  8. New photometric and kinematic studies of UCDs, nuclear clusters, etc  ALL the small things are purely stellar systems, M/L~1-4 Seth etal astro-ph 0609302 Virgo & Fornax UCDs have stellar M/L – Hilker etal, A&A 463 119 2007 MWG nuclear cluster has size ~5pc, mass 10^6Msun Schodel etal A+A 469 125 N5128 GC study by Rejkuba et al 2007 faint fluffies MWG GCs extend down to M~-2

  9. Slightly different perspective… (updated data) M31; MWG; Other Nuclear clusters, UCDs, M/L ~ 3 Pure stars Dark Matter haloes boundary Tidal tails dSph galaxies star clusters Gilmore, Wilkinson, Wyse et al 2007 ApJ 663 948

  10. Conclusion one: • Galaxy scaling relations work well, and indicate a systematic star-cluster vs small galaxy distinction in phase-space density • There is a well-established half-light size bi-modality • all systems with size < 40pc are purely stellar −16< Mv < 0 (!!) M/L ~ 3; e.g. UCDs, Hilker et al 07; Rejkuba et al 07 • all systems with size greater than ~120pc have a dark-matter halo • There are no known (virial equilibrium) galaxies with half-light radius r < 120pc • So now look at the dSph galaxies’ masses ~

  11. Note different scales: information at small and large r poor. Mateo, walker etal

  12. Derived mass density profiles: Jeans’ equation with assumed isotropic velocity dispersion: All consistent with cores(similar results from other analyses) Not conclusive yet. CDM predicts slope of -1.3 at 1% of virial radius and asymptotes to -1 (Diemand et al. 04) Need different technique at large radii, e.g. full velocity distribution function modelling.. And understand tides.

  13. Conclusion two: • High-quality kinematic data exist • Jeans’ analyses  prefers cored mass profiles • Mass-anisotropy degeneracy allows cusps • Substructure, dynamical friction  prefers cores • Equilibrium assumption is valid inside optical radius • More sophisticated DF analyses underway • Cores always preferred, but not always required • Central densities always similar and low • Consistent results from available DF analyses • Extending analysis to lower luminosity systems difficult due to small number of stars • Integrate mass profile to enclosed mass:

  14. 2007: extension of dynamic range [UMa, Boo, AndIX], new kinematic studies:Mateo plot improves. Mass enclosed within stellar extent ~ 4 x 107M Now a factor of 300+ in luminosity, 1000+ in M/L Scl – Walker etal If NFW assumed, virial masses are 100x larger, Draco is the most massive Satellite (8.109M) (old data) Globular star clusters, no DM

  15. Summary: • A minimum physical scale for galaxies, ~100pc, max size for star clusters ~30pc • Galaxy mass size scale somewhat larger (?) • Galaxy nuclei are just massive star clusters? • Cored mass profiles, with similar mean mass densities ~0.1M/pc3, ~5GeV/cc • Phase space densities fairly constant, maximum for galaxies (cf Walcher et al 2005) • An apparent characteristic (minimum) mass dark halo in all dSph, mass ~4 x 107M ??? • This is just a consistency check, not new info • dSph debris not yet found: cannot be (much of) the MWG halo, thick disk, or thin disk • How did everything get pre-enriched? context: substructure `issue’, old disks, one thick disk, too few dead bodies, old red gals…

  16. Consistency? • A minimum half-light size for galaxies, ~100pc •  mass scale similar, or a little larger • Probably cored mass profiles, with similar mean mass densities ~0.1M/pc3, ~5GeV/cc • An apparent characteristic (minimum) mass dark halo at dSph, • mass ~4 x 107M characteristic mass profile convolved with characteristic normalisation must imply characteristic mass  internal consistency only Minimum size natural with cored potential?

  17. Implications for Dark Matter: • Characteristic Density ~10GeV/c²/cm³ • If DM is very massive particles, they must be extremely dilute (Higgs ~100GeV) • Characteristic Scale above 100pc, several 107M • Cooling? power-spectrum scale break? • This would (perhaps!) naturally solve the substructure and cusp problems • Number counts low relative to CDM • lots of similar challenges on galaxy scales • Need to consider seriously non-C DM candidates

  18. Properties of Dark-Matter dominated dSph galaxies:

  19. Does the Mateo plot extend to the lowest luminosities? Data still limited, lowest surface brightness gals may have lowest sigma. Simon & Geha: these are central values

  20. Central velocity dispersion `masses’ are really dispersions, and are only just resolved by the RV errors eg Simon/Geha here, our outer Draco `cold’, etc. Independent confirmation is desirable

  21. No parameters are *VERY* accurate. CVnI (top) has σ=13.9 (Ibata 2006) or 8.1 (Simon +Geha, here), from the same instrument. LeoIV has σ=3.3+-1.7derived here – 2bins?

  22. Implications from Astrophysics: Can one plausibly build a dSph as observed without disturbing the DM? • Star formation histories and IMF are easily determined  survival history, energy input… • Chemical element distributions define gas flows, accretion/wind rates, • debris from destruction makes part of the field stellar halo: well-studied, must also be understood • Feedback processes are not free parameters

  23. What are we really measuring with simple, non-Distribution Function, analyses? • Dispersion profile close to flat, so sigma ~ cst, and range of sigma is small (data <2) • derivative term is (log) luminosity profile : light, NOT mass, and this is similar in scale for all the dSph (factor of few) • So the derived mass really is a measure of the radial extent of the data, and only a weak function of anything else. • Increase in M in Mateo plot is a measure of increase in data range

  24. Hernandez, Gilmore & Valls-Gabaud 2000 Carina dSph Leo I UMi dSph Atypical SFH Intermediate-age population dominates in typical dSph satellite galaxies – with very low average SFR over long periods (~5M/105yr), until recently

  25. Comparing globular cluster structures, abundances, orbits, ages and likely survival Implies ~5 [<Sgr-like] mergers in total, forming ~20% of the outer halo (Mackey & Gilmore MNRAS 355 504 2004) This is consistent with SDSS-observed halo lumpiness, and older (eg Unavane, GG, RW 1996 MN)age-metallicity limits Globular cluster view of halo accretion

  26. Constant mass scale of dSph? Based on central velocity dispersions only low M/L line corresponds to dark halo mass of 107M Mateo 98 ARAA dSph filled symbols

  27. 2007: extension of dynamic range [UMa, Boo, AndIX], new kinematic studies:Mateo plot improves. Mass enclosed within stellar extent ~ 4 x 107M (old data) Globular star clusters, no DM

  28. It isn’t only gas-poor galaxies: all small galaxies are similar Mass – to – light ratios for local dSph The star is LeoA, a gas-rich dwarf with recent star formation, the arrow shows how it will fade with age. The square is Phoenix. This is from Brown, Geller etal arXiv:0705.1093

  29. Dynamics: three regimes • Body of galaxy, out to break/r_lim recent vast increase in good data (Camb group, Ibata/Chapman/Martin at keck, Simon/geha at keck, Walker/mateo at Magellan/MMT, good agreement, real progress, now pushing limits of known systems • Outer limits: tidal tails, etc: data very limited, agreement only fair, rather open analyses, fair outcome: no strong effects in distant objects, Sgr a model for the nearby. • Cores: just starting now.

  30. Breaking the degeneracy – first steps Survival of cold subsystem in UMi dSph implies shallow mass density profile(Kleyna et al 03) • Dynamical friction limits on Fornax dSph Globular Clusters also favour cores to extend timescalesGoerdt etal 2006

  31. Main Focus: Dwarf Spheroidals • Low luminosity, low surface-brightness satellite galaxies, ‘classical’ L ~ 106L, V ~ 24 mag/sq • Extremely gas-poor • Apparently dark-matter dominated  ~ 10km/s, 10 < M/L < 100 • Metal-poor, mean stellar metallicity < –1.5 dex • All contain old stars; extended star-formation histories typical, intermediate-age stars dominate • Most common galaxy nearby • Crucial tests for CDM and other models ~ ~ ~

  32. Walker etal arxiv:0708.0010

  33. Omega Cen: Reijns etal A&A 445 503 Mass does not follow light Leo II: Koch etal

  34. Other lumps exists too, and are not understood at all. astro-ph/0701790

  35. CDM predicts many more satellite galaxies than observed, at all masses (Moore et al 1999)

  36. new large datasets of stellar line of sight kinematics, now covering spatial extent, & photometry for dSph satellite galaxies  new discoveries; SDSS mostly – original key project (also Willman et al 05; Grillmair 06; Grillmair & Dionatos 06; Sakamoto & Hasegawa 06; Jerjen 07..)  confirm and extend scaling relations  Dark matter properties G. Gilmore, M. Wilkinson, R.F.G.Wyse, J. Kleyna, A. Koch, N. Evans & E. Grebel 2007, ApJ v663 p948; astro-ph/0703308

  37. M31 and MWG GC size-lum, from Federici etal, 0706.2337, Stars From Mackey etal (M31), triangles: nuclei of Virgo dEs asterisk Virgo UCDs,

  38. Core properties: adding anisotropy Koch et al 07 AJ 134 566 ‘07 Fixed β Radially varying β Leo II Core and/or mild tangential anisotropy slightly favoured

  39. Mass – anisotropy degeneracy prevents robust cusp/core distinction, but core provides better fit (see also Wu 2007 astro-ph/0702233) • Break degeneracy by complementary information: • Ursa Minor has a cold subsystem, requiring shallow gradients for survival (Kleyna et al 2003 ApJL 588 L21) • Fornax globular clusters should have spiralled in through dynamical friction unless core (e.g. Goerdt et al 2006) • Simplicity argues that cores favoured for all? • New data and df-models underway to test (GG etal, VLT high-resolution core/cusp project)

  40. NFW fits require very high mass, and a very wide range of mass Draco = 8.10^9Msun and M/L=100,000 MWG vs M31 offset no simple mass-luminosity link astro-ph/0701780 Strigari etal (in prep) central mass fits – no simple rank

  41. Thick and thin disk element ratio data: The thick/thin distinction is evident. The thick disk occupies an empty part of the halo-dSph-Sgr plot, suggesting its parent was different again… This fig from A+A 465 271 Ramirez etal 2007 Sgr and the thick disk are 2 good `accretions’, But both seem unique…

  42. Thick disk Galaxy halo (green), dSph (blue), LMC (cyan), Sgr (red) and dIrr (yellow) element ratios The systematic difference is apparent (from Geisler, Wallerstein, etal 0708.0570) NB Sgr is *very* distinctive: it must be the first such event.

  43. CDM predicts many more satellite galaxies than observed, at all masses • `Solutions’: warm DM; self-interacting DM; star formation suppression by re-ionization; self-regulated star formation; very high M/L plus some other variant; predictions `wrong’, count different things; predictions host-dependent; …. • Conclude: • very many proposed solutions suggests there is still much to learn, both in models and data

  44. Satellite population depends on environment? Fewer expected in LG? NB: predictions running out just where the data are today. What should be believe from the simulations? Ishiyama etal 0708.1987. dashed line from Moore etal

  45. Where are the bodies? Little debris in inner MWG? Field halo Thick disk Thin disk dSph members NB: the pre-enrichment problem has become more extreme: no very metal poor stars are found in dSph or GC SMC LMC dIrr Sgr including thick disk (red) and thin disk (blue) stars: Chemically the local halo is much more similar to the thick disk (progenitor?) than anything else, but has very different orbital angular momentum. Sgr and its clusters are shown from Sbordone etal A+A 465 815 2007

  46. Very many attempts to model feedback on CDM structure…. • Some of our examples: • Read et al2006 MN 367 387, MN 366 429, 2005 MN 356 107…; Fellhauer etal in prep • Conclusion: DM halos certainly respond to tides and mass-loss, but secularly If various histories leave similar mass profiles, history cannot be dominant

  47. Stellar kinematic data across faces of dSph now quite extensive e.g. Gilmore et al 2007 MOND problem… dSph Seitzer 1983; van de Ven et al 06 Globular cluster M/LV ~ 2.5

  48. dSph: only one part of the challenge • Among the first systems to collapse, form stars • Star formation history and chemical enrichment are sensitive probes of stellar ‘feedback’, galactic winds, ram pressure stripping, re-ionization effects.. • BUT all seem pre-enriched • Most extreme (apparently) dark-matter dominated systems: trends contain constraints on its nature (Dekel & Silk 1986; Kormendy & Freeman 04; Zaritsky et al 06) • What are mass profiles within dSph? CDM predicts a cusp in central regions • Accessible through current observations • Luminosity and mass functions critical tests

  49. The MWG cdm challenge is not rare: large disk galaxies with no bulge are common, and are a very serious challenge for CDM. They should not exist. In fact large old disks are a REALLY big challenge… cf Kormendy & Kennicutt ARAA 2004 and arXiv:0708.2104 The small pseudo-bulge here is a disk bar.

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