Dwarf Spheroidals and Reionization: Is There a Link? Nick Gnedin

Co-starring: Massimo Ricotti (UMD)

Our backyard

Who Commands Dwarf Galaxies? Looks familiar? Reionization? Formation of LG? Just a fluke? Grebel 1998

Life of a Dwarf Galaxy “True fossil” “Polluted fossil” “Survivor” z ~ 6 reionization z ~ 3 Local Group forms z = 0 today Time

Observer’s view (Grebel 2005)

Resolving All Reionized @ z=9 Stopped @ z=8.3 Space 1 chimp Simulation Local Group @z=0 25 pc @z=8 900 M8 Mass

Fornax twins Born: 13,283,456,789 BCE Born: 2003 CE

Who Is Who? Survivors Polluted fossils Virtual dwarfs True fossils Real dwarfs Too bright & too large to be fossils

Star Formation

Metallicity

Kinematics

Metallicity Spread I

Metallicity Spread II

Dividing the Loot Survivors Luminosity True fossils Polluted fossils IC 10 IC 1613 IC 5152 LMC M32 NGC 55 NGC 147 NGC 185 NGC 205 NGC 3109 NGC 6822 Sextans A Sextans B SMC WLM Luminosity And I And II And III And V And VI Antlia Cetus Draco KKR 25 Phoenix Sculptor Sextans Tucana Ursa Minor Carina DDO 210 GR8 Fornax Leo A Leo I Leo II LGC 3 Pegasus Sagittarius True fossils Polluted fossils

Horizontal Branch Index Prediction “True fossils” (like And I and And II) are about 1.5 Gyr older than “survivors” (like WLM or NGC3109) $ Horizontal Branch Index can test this!

Lilliput Spheroidals? Const survival probability Best fit

Conclusions Virtual galaxies formed before reionization resemble lowest mass dwarf spheroidals in all observable properties – is it a coincidence? Possible tests: spatial distribution with the Local Group (need to relate z=0 and z>6) metallicity spread (but virtual dwarfs have it too) alpha-to-iron ratio (no signatures of SNIa in dSphs – Tsujimoto 2005) relative ages using the HB index (perhaps, the best method) existence of “lilliput spheroidals”. Sextans Ursa Major

The End