Ultra-faint dwarfs as fossils of the First Galaxies

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Ultra-faint dwarfs as fossils of the First
Galaxies

• Mia S. Bovill
• Advisor Massimo Ricotti
• University of Maryland

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Outline

• Properties of Fossil Galaxies
• Missing Dwarfs
• Evolving Fossils to z 0

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Feedback

• For halos with TVIR lt 104 K, H2 serves as the
  primary coolant.
• Negative Feedback
• H2 is dissociated by non-ionizing UV radiation
  from Pop III stars.
• Only M gt 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)).

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Sloan Dwarf Observations
fossils
Dwarf Discovery Follow-up
Bootes I Belokurov et al (2006) Munoz et al (2006), Bailin Ford (2006), Martin et al (2007)
Bootes II Walsh et al (2007)
Canes Venatici I Zucker et al (2006a) Ibata et al (2006), Martin et al (2007), Simon Geha (2007)
Canes Venatici II Belokurov et al (2007) Simon Geha (2007)
Coma Berenics Belokurov et al (2007) Simon Geha (2007)
Hercules Belokurov et al (2007) Simon Geha (2007)
Leo IV Belokurov et al (2007) Simon Geha (2007)
Leo T Irwin et al (2007) Simon Geha (2007)
Ursa Major I Willman et al (2005) Kleyna et al (2005), Martin et al (2007), Simon Geha (2007)
Ursa Major II Zucker et al (2006b) Martin et al (2007), Simon Geha (2007)
Willman I Willman et al (2005) Martin et al (2007)
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M31 Dwarf Observations
fossils
Dwarf Discovery Follow-up
And XI Martin et al (2006)
And XII Martin et al (2006) Chapman et al (2007)
And XIII Martin et al (2006)
And XIV Majewski et al (2007)
And XV Ibata et al (2007)
And XVI Ibata et al (2007)
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Fossil Properties I
Ultra-faint dwarfs are detected to Sloan limits.
Ricotti Gnedin (2005), Bovill et al. (2007, in
prep)
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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)
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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)
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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 lt
-2.4 - selection effects -
physical effects
Ricotti Gnedin (2005), Bovill et al. (2007, in
prep)
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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 z0
• Statistical comparison for a Milky Way (Gnedin
  Kravtsov, 2006)
• Direct N-body evolution for a Local Volume
  (Bovill Ricotti, in prep)

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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.

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Luminosity Function
For d lt 100 kpc observations and theory agree
For d gt 100 kpc SDSS cannot detect MV lt -5
(LV lt 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
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Radial Distribution
L gt 105 L? shows good agreement out to 1 Mpc
L gt 103 L? matches well for d lt 250 kpc, the
discrepancy for d gt 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)
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Need for primordial dwarfs

• Simulations predict 40 halos with vcirc gt 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 gt 103 L? within 300 kpc of the Milky
  Way (Gnedin Kravtsov, 2006).

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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 z0
• 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.

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z 0 Luminosity Function
MHOST 2 x 1011 M? Approximately 1/5 the
dwarfs expected for the Milky Way Number of
dwarfs with d lt 1 Mpc results agree with Gnedin
Kravtsov (2006)
red M lt 109 M?
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z 0 Radial Distribution
MHOST 2 x 1011 M? L gt 105 LSUN new results
agree with Gnedin Kravtsov (2006) at 300 kpc.
Increase for d gt 300 kpc due to our host
galaxy not being isolated.
red M lt 109 M?
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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.

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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 z0 is not computationally
possible. We turn HD halos into N-body
particles and create a larger volume.
Density fluctuations on gt 1 Mpc scales are then
added.
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The First Galaxies
At high z, the majority of the universes mass
was contained in halos lt 108 M?. Approximately
10 of these early dwarfs will survive untouched
to z 0.
CITATION??
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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

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What is a Fossil?
defined by Ricotti Gnedin (2005)
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