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Ultra-faint dwarfs as fossils of the First Galaxies

Ultra-faint dwarfs as fossils of the First Galaxies. Mia S. Bovill Advisor: Massimo Ricotti University of Maryland. Outline. Properties of Fossil Galaxies Missing Dwarfs Evolving Fossils to z = 0. Feedback. For halos with T VIR < 10 4 K, H 2 serves as the primary coolant.

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Ultra-faint dwarfs as fossils of the First Galaxies

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  1. Ultra-faint dwarfs as fossils of the First Galaxies Mia S. Bovill Advisor: Massimo Ricotti University of Maryland

  2. Outline • Properties of Fossil Galaxies • Missing Dwarfs • Evolving Fossils to z = 0

  3. Feedback • For halos with TVIR < 104 K, H2 serves as the primary coolant. • Negative Feedback • H2 is dissociated by non-ionizing UV radiation from Pop III stars. • Only M > 108 M can shield enough H2 to form stars (ie. Haiman et al, 2000). • Halos below 108 M will be dark. • Positive Feedback • Ionizing UV radiation facilitates formation of H2, lowering the mass threshold for star formation (ie. Whalen et al (2007)). • When relevant physics is included, stars form in halos of only 105 M (Ricotti et al (2002a,b) (R02a,b)).

  4. ** fossils Sloan Dwarf Observations

  5. ** fossils M31 Dwarf Observations

  6. R02a,b predictions. Willman I Known survivors Known polluted fossils SDSS limits Known true fossils New ultra-faint dwarfs Fossil Properties I ~ Ultra-faint dwarfs are detected to Sloan limits. Ricotti & Gnedin (2005), Bovill et al. (2007, in prep)

  7. M31 Milky Way R02a,b predictions. Known survivors Known polluted fossils Known true fossils Willman I New ultra-faint dwarfs M31 Milky Way Willman I Fossil Properties II ~ Without fossils, predicted Lv and rc values for given Ic are significantly above new observations. ~ M31 dwarf properties are consistent with predictions and known Milky Way fossils. Ricotti & Gnedin (2005), Bovill et al. (2007, in prep)

  8. R02a,b predictions. Known survivors Known polluted fossils Known true fossils New ultra-faint dwarfs Fossil Properties III ~ Observed and predicted values trace mass to edge of stellar distribution. ~ Ricotti & Gnedin (2005) predicted existence of high M/L fossil population. Ricotti & Gnedin (2005), Bovill et al. (2007, in prep)

  9. R02a,b predictions. Known survivors Known polluted fossils Known true fossils New ultra-faint dwarfs Fossil Properties IV ~ Z vs. Lv scatter for ultra-faint dwarfs agrees with fossil predictions. ~ Scatter in Z due to: - pollution from nearby halos - multiple bursts of star formation (ie. Stinson et al (2007)) ~ Where are dwarfs with Z < -2.4 - selection effects - physical effects Ricotti & Gnedin (2005), Bovill et al. (2007, in prep)

  10. Evolving Fossils to z = 0 • Fossil properties at z = 0 are simply related to their properties at reionization. • R02a,b results can be evolved to z=0 • Statistical comparison for a “Milky Way” (Gnedin & Kravtsov, 2006) • Direct N-body evolution for a “Local Volume” (Bovill & Ricotti, in prep)

  11. Observation Completeness Correction • We assume satellites are in an isotropic distribution around their hosts and the new dwarfs are a representative sample. • SDSS covers 1/4 of the sky. • Recent surveys covered ~ 1/4 of the sky around M31 • We multiply the numbers of new dwarfs by 4 for both galaxies to account for observational bias.

  12. Luminosity Function ~ For d < 100 kpc observations and theory agree ~ For d > 100 kpc SDSS cannot detect MV < -5 (LV < 8 x 103 L) (Koposov et al (2007)) ~ WMAP III parameters may lower the number of halos at large distances from their hosts. Gnedin & Kravtsov (2006) Bovill et al, in prep

  13. Radial Distribution ~ L > 105 L shows good agreement out to 1 Mpc ~ L > 103 L matches well for d < 250 kpc, the discrepancy for d > 250 kpc can be partially explained by observational bias. Gnedin & Kravtsov (2006), Bovill et al., in prep 250 kpc SDSS limit for HB (Simon & Geha, 2007)

  14. Need for primordial dwarfs • Simulations predict ~40 halos with vcirc > 20 kms-1 (Kravtsov et al (2004), Diemand et al (2007a,b)). • Milky Way now has: • 16 previously known satellites • 11 ultra-faint Sloan Dwarfs • ~ 30 undiscovered dwarfs above SDSS detection limits • If primordial fossils are included, ~100 halos are within L > 103 L within 300 kpc of the Milky Way (Gnedin & Kravtsov, 2006).

  15. Evolving Fossils to z = 0 • Fossil properties at z = 0 are simply related to their properties at zreion. • R02a,b results can be evolved to z=0 • Statistical comparison for single “Milky Way” (Gnedin & Kravtsov, 2006) • Direct N-body evolution for a “Local Volume” (Bovill & Ricotti, in prep) • Adding large scale modes, create a 103 Mpc3 volume from 1 Mpc3 R02a,b results. • Embed in a 503 Mpc3 low resolution centered on a filament. • Run from z ~10 to z = 0.

  16. z = 0 Luminosity Function ~ MHOST ~ 2 x 1011 M ~ Approximately 1/5 the dwarfs expected for the Milky Way ~ Number of dwarfs with d < 1 Mpc results agree with Gnedin & Kravtsov (2006) red = M < 109 M

  17. z = 0 Radial Distribution ~ MHOST ~ 2 x 1011 M ~ L > 105 LSUN new results agree with Gnedin & Kravtsov (2006) at 300 kpc. ~ Increase for d > 300 kpc due to our host galaxy not being isolated. red = M < 109 M

  18. Summary • Properties of the new Sloan and M31 dwarfs agree well with predictions for primordial galaxies • Within SDSS limits, the missing satellite problem is almost solved. • Tidal formation alone cannot produce enough dwarfs to account for the SDSS additions.

  19. Initial Conditions Start Point - Ricotti et al (2002a,b) 1 Mpc3 HD simulation including the effects of radiative transfer run to z = 8.3. ~ A HD run to z=0 is not computationally possible. ~ We turn HD halos into N-body particles and create a larger volume. ~ Density fluctuations on > 1 Mpc scales are then added.

  20. The First Galaxies At high z, the majority of the universe’s mass was contained in halos < 108 M. Approximately 10% of these early dwarfs will survive untouched to z = 0. CITATION??

  21. DR6 Predictions • SDSS DR6 (Citation) will include M31 • And XI - XVI have similar properties to previously known Milky Way dwarfs • From SDSS limits and current predictions we estimate 12 new dwarfs between 100 and 300 kpc of M31 are detectable by SDSS

  22. Survivors (M > 109 M) * star formation started after reionization * mostly dIrr, some dE LMC M32 Polluted fossils (M ~ 106 - 108/9 M) * significant star formation after reionization * tidal effects from host cause additional bursts * dSph and dE Pegasus True fossils (M ~ 106 - 108/9 M) * < 30% of stars formed after reionization * never accreted gas from the IGM * mostly dSph Cetus What is a Fossil*? *defined by Ricotti & Gnedin (2005)

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