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little things in context a note on the unknown

little things in context a note on the unknown. Gerry Gilmore IoA Cambridge Dynamics 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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little things in context a note on the unknown

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  1. little things in contexta note on the unknown Gerry Gilmore IoA Cambridge Dynamics with Mark Wilkinson, Rosie Wyse, Jan Kleyna, Andreas Koch, Wyn Evans, Eva Grebel Discovery work with Vasily Belokurov, Dan Zucker, Sergey Koposov, et al Globular cluster properties with Dougal Mackey, Becky Elson ApJ 663 948 2007 (july10), arXiv 0706.2687

  2. The smallest galaxies are the places one must see thenature of dark matter, & galaxy formation astrophysics Inner DM mass density depends on the type(s) of DM Dwarf galaxy mass function depends on DM type Figs: Ostriker & Steinhardt 2003

  3. Challenges for small-scale DM • On large [>Mpc] scales LCDM is an astonishingly good description of data, but n~-1 (and maybe w=-1….) so not much physics made clear: lots still to learn… • On galaxy scales there is an opportunity to learn some physics: everything should happen late. But. • 0: big old galaxies, big old disks, SFR peaks z>1, • 1: the MWG has a thick disk, just one of them, and it is old. This seems common. • 2: massive old pure-thin-disk galaxies exist. None should • 3: Sgr proves late minor merging happens, but is clearly a rare event • 4 the substructure problem – where are the bodies? • 5 the feedback problem: what is it • 6 the early enrichment problem: what did it? When?

  4. Where are the bodies? No debris in inner MWG NB: the pre-enrichment problem has become more extreme: no very metal poor stars are found in dSph or GC Smc Lmc dIrr 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

  5. 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

  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. Why? Dark Matter? dSph Phase spacedensity (~ ρ/σ3) ~ 1/(σ2 rh)

  7. From Walcher etal 2006 apj 649 692

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

  9. 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

  10. 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

  11. 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 < 30pc 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 ~

  12. What are we really measuring with simple, non-DF, 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

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

  14. Derived mass density profiles: Jeans’ equation with assumed isotropic velocity dispersion: All consistent with cores(similar results from other analyses) 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.

  15. 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:

  16. 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

  17. 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

  18. 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 The information in the Mateo plot is the same as in the size and mass profile relations

  19. 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…

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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 • 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

  25. Properties of Dark-Matter dominated dSph galaxies:

  26. 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

  27. 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.

  28. 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

  29. 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 ~ ~ ~

  30. Walker etal arxiv:0708.0010

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

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

  33. 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

  34. Derived 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) Ignores surface- brightness discrepancies etc. Grey curve: power- law ‘fit’ to data Slope 1.1

  35. 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?

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

  37. 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

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

  39. 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

  40. 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)

  41. 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

  42. 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…

  43. 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.

  44. 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

  45. 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

  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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