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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 Globular cluster properties with Dougal Mackey, Becky Elson ApJ 663 948 2007 (july10), arXiv 0706.2687 The smallest galaxies are the places one must see the nature of dark matter, & galaxy formation astrophysics Dwarf galaxy mass function depends on DM type Inner DM mass density depends on the type(s) of DM Figs: Ostriker & Steinhardt 2003 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? 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 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 Dotted line is virial theorem for stars, no DM Walcher et al 2005 There is a discontinuity in (stellar) phase-space density between small galaxies and star clusters. dSph Why? Dark Matter? Phase space density (~ ρ/σ3) ~ 1/(σ2 rh) From Walcher etal 2006 apj 649 692 New systems extend overlap between galaxies and star clusters in luminosity Belokurov et al. 2006 Analyses of kinematic follow-up underway ~103 L New photometric and kinematic studies of UCDs, nuclear clusters, etc ALL the small things are purely stellar Seth etal astro-ph 0609302 systems, M/L~1-4 Virgo & Fornax UCDs have stellar M/L – Hilker etal, A&A 463 119 2007 N5128 GC study by Rejkuba et al 2007 MWG GCs extend down to M~-2 MWG nuclear cluster has size ~5pc, mass 10^6Msun Schodel etal A+A 469 125 faint fluffies Slightly different perspective… (updated data) M31; MWG; Other Nuclear clusters, UCDs, M/L ~ 3 Pure stars boundary Dark Matter haloes Tidal tails star clusters Gilmore, Wilkinson, Wyse et al 2007 dSph galaxies 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 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 Note different scales: information at small and large r poor. Mateo, walker etal 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. 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: 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 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) Globular star clusters, no DM (old data) 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 7 x 10 M 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 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 7 in all dSph, mass ~4 x 10 M ??? 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… 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 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 2007: extension of dynamic range [UMa, Boo, AndIX], new kinematic studies: Mateo plot improves. Mass enclosed within stellar extent ~ 4 x 107M Globular star clusters, no DM (old data) 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 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 Properties of Dark-Matter dominated dSph galaxies: 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 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. 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 timescales Goerdt etal 2006 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 Walker etal arxiv:0708.0010 Omega Cen: Reijns etal A&A 445 503 Mass does not follow light Leo II: Koch etal Other lumps exists too, and are not understood at all. astro-ph/0701790 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 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’ Grey curve: powerlaw ‘fit’ to data Slope 1.1 Coloured curves: Semi-analytic theory (Benson et al 02, red Somerville 02, blue) Ignores surfacebrightness discrepancies etc. 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+-1.7 derived here – 2bins? CDM predicts many more satellite galaxies than observed, at all masses (Moore et al 1999) 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 M31 and MWG GC size-lum, from Federici etal, 0706.2337, Stars From Mackey etal (M31), triangles: nuclei of Virgo dEs asterisk Virgo UCDs, 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 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) 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 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… 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. CDM predicts many more satellite galaxies than observed, at all masses `Solutions’: warm DM; self-interacting DM; star formation suppression by reionization; 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 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 Very many attempts to model feedback on CDM structure…. Some of our examples: Read et al 2006 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 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 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 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. Kormendy & Freeman 04 Disk galaxy scaling relations are wellestablished Do the dSph (green) fit? Yes, KF No, they tend to lie OFF the disk galaxy extrapolations.. Limits instead Sgr & Field of Streams (and dots) outer halo is lumpy: but is a tiny mass fraction Belokurov et al (2006b) Two wraps? Disk accretion? Warp? 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 Bulk of stellar halo is OLD, as is bulge: Did not form from typical satellites disrupted later than a redshift of 2 Unavane, Wyse & Gilmore 1996 Scatter plot of [Fe/H] vs B-V for local high-velocity halo stars (Carney): few stars bluer (younger) than old turnoffs (5Gyr, 10Gyr, 15Gyr Yale) Mass measurements: the early context • • • The ``standard’’ value for local DM at the Sun is 0.3GeV/c²/cm³, all in a `halo’ component (cf pdg.lbl.gov: Eidelman etal 2004) the original work, and origin of this value, is the first analysis to include a full 3-D gravitational potential, parametric modelling, and a direct determination of both the relevant density scale length and kinematic (pressure) gradients from data, allowing full DF modelling for the first time: Kuijken & Gilmore 1989 (MN 239 571, 605, 651), 1991 (ApJ 367 L9); Gilmore, Wyse & Kuijken (ARAA 27 555 1989): cf Bienayme etal 2006 A&A 446 933 for a recent study • Dark halos are `predicted’ down to sub-earth masses; but… • Neither the local disk, nor star clusters, nor spiral arms, nor GMC, nor the solar system, have associated DM: Given the absence of a very local enhancement, what is the smallest scale on which DM is concentrated? How can sub-halos in dSph galaxies with star formation over 10Gyr avoid collecting any baryons? From kinematics to dynamics: Jeans equations, simple and robust method Relates spatial distribution of stars and their velocity dispersion tensor to underlying mass profile Either (i) determine mass profile from projected dispersion profile, with assumed isotropy, and smooth functional fit to the light profile Or (ii) assume a parameterised mass model M(r) and velocity dispersion anisotropy β(r) and fit dispersion profile to find best forms of these (for fixed light profile) Full distribution function modelling, as opposed to velocity moments, also underway: needs very large data sets. Where available, DF and Jeans’ models agree. King models are not appropriate for dSph too few stars Main sequence luminosity functions of UMi dSph and of globular clusters are indistinguishable. normal stellar M/L HST star counts Wyse et al 2002 M92 M15 0.3M Massive-star IMF constrained by elemental abundances – also normal