JSI Dwarf Galaxy Conference (Day 3)

Annapolis, Maryland

Joe Silk, “DM Annihilations as a Probe of CDM Substructure”

  • Proposing to use the Sun as a WIMP detector above 4 GeV (less massive ones are evaporated).
  • If WIMPs are low-mass (5-10 GeV) and trapped, they will lower the central temperature of the Sun.
  • Energetic neutrinos from WIMPs trapped in the Sun?  Detectable by AMANDA or IceCube?
  • Sommerfeld effect: boosting due to DM bound states (see this paper)
  • WMAP “haze” was seen in Fermi data, coming out of the halo center (Su+ 2010).
Al Kogut, “CMB Probes of DM and Structure Formation”
  • PIXIE (Primordial Inflation Explorer): Measures CMB linear polarization from the inflationary epoch (tensor-to-scalar ratio << 10^-3)
  • Data will constraint a number of topics: Inflation/GUT physics, recombination, first stars/galaxies, reionization
  • CMB scattering and polarization during reionization: determines electron density versus redshift.
  • y distortion gives electron pressure: combine to get n(z) and temperature.  Can determine the nature of the first luminous objects.
Jana Grcevich, “Finding Missing Satellites in Neutral Hydrogen”
  • Searching for new dwarf galaxies outside of the SDSS search area.  Found over 2000 HI clouds!
  • In those clouds, they have to filter out the known HVCs.  Found 35 dwarf galaxy candidates from the GALFA-HI survey.
Marla Geha, “MW’s Ultra-Faint Galaxies”
  • Also will present new work on the absence of quenched field dwarfs.
  • SDSS studies cut off above the field dwarf scale below M_V = -18 or M* ~ 10^9 Msun.  The problem with SDSS public release data is that 20-40% of the faint dwarfs are shredded pieces of larger galaxies.  They have re-reduced the data and are going to produce a public dataset of these dwarfs.
  • There are 8-10k dwarf galaxies in SDSS below the spectroscopic limit (M_V > -17.5).
  • They are extending the work of Wetzel+ (2011) to M* = 10^8 Msun.  They find that almost all field dwarfs are forming stars!
  • They see an environment effect within 1 Mpc with more dwarfs being quenched.
  • There is still a surface brightness limit for all dwarf and ultra-faint galaxies and GCs.
  • Tollerud+ (2011) M31 satellites are similar to MW galaxies in terms of size, luminosity, and mass.
  • Tollerud+ (2008) Correcting for sensitivity limits and incomplete coverage, we would expect 100-600 dwarf galaxies in the MW halo.
  • Bradford+ (2011) Pal 13 GC had some evidence for DM.  r_eff = 10 pc, M_V = -3. But they re-analyzed the velocity dispersion and found contributes from unresolved binaries.  Once this was corrected for, then it agrees with an object without DM.
  • Segue 3 (Belokurov+ 2010): D = 16 kpc, M_v = -0.4 (120 Lsun!).  Within a 1/2-light radius, velocity dispersion is 1.2 ± 2.0 km/s.  CMD is consistent with a single stellar population.
  • Segue 1 (Simon+ 2010): 71 members within 2 r_eff.  Velocity dispersion of 3.7 ± 1 km/s.  M/L ~ few thousand.  Much different than Segue 3.
  • Internal metallicity spread in Segue 1: Simon+ (2010), Norris+ (2010).  Internal spread of -1.5 dex with an average of [Fe/H] = -2.5.
  • There is a clear mass(i.e. M_V)-metallicity trend in the galaxies, but not GCs.
  • There are always a big spread (~ dex) in metallicity for all dSphs and uFds.
  • uFds still show an [alpha/Fe] = +0.3 overabundance in [Fe/H] = -3 stars, which indicates early star formation.
David Sand, “The Structure and SFH of the New MW Satellites”
  • Ultimate goal: connecting the observations with simulations.
  • New dwarfs (Ursa Major I, II) could be the cores of disrupted larger galaxies.
  • What drives the SFH of satellite galaxies?  All of the nearby dwarfs don’t show SF within the last 10 Gyr, but the more distant (d > 90 kpc) ones show an extended SFH with about 10% of their stars forming in these later times.
  • New dwarfs (Sand+ 2009,2010,2011): Her, Leo IV, Leo V, Pisces II, CVn II.
  • Uses Max-likelihood technique to measure the parameterized structure of the dwarfs.
  • Fits the CMD to obtain the star formation history.  A minimization routine is used to find the linear combination of the individual SF episodes.
  • There are some hints that there was a minor SF episode 2 Gyr ago in Leo IV.
  • All of the new dwarfs are metal-poor, [Fe/H] < -2 and are dominated by old stellar populations (>10 Gyr).
  • Leo V and CVn II have some evidence for tidal stripping.  They are outliers in the [Fe/H] vs. luminosity relation (see Kirby+ 2011).
  • The new dwarfs have the same ellipticity distribution as the “classical” dSphs (Sand+ 2011).

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