Are Galactic Winds Shaping the Properties of Dwarf Galaxies? Konstantinos Tassis The University of Chicago Andrey Kravtsov University of Chicago Nick GnedinFermilab, U.Chicago

GLCW8, June 2007Konstantinos Tassis Observations of Dwarfs Correlations between … –stellar mass and metallicity –stellar mass and circular velocity –stellar mass and surface brightness Local Group Dekel & Woo (2003 ) SDSS galaxies Tremonti et al (2004) Nearby dwarfs Lee et al. (2006) Local Group Dekel & Woo (2003) McGaugh (2005) Local Group Dekel & Woo (2003) SDSS Kauffmann et al. (2003)

GLCW8, June 2007Konstantinos Tassis Interpretation Traditionally: SN feedback, effect greater in lower-mass objects (e.g. Larson 1974; Dekel & Silk 1986; ) This work: paradigm shift SF inefficiency greater in lower-mass objects Our approach to the problem: Can correlations be reproduced without feedback? Does feedback make a difference in these correlations? Use simulations and interpret results with a semi analytic model

GLCW8, June 2007Konstantinos Tassis Four Simulations Code : ART (N-body + Eulerian Gas Dynamics) Size : 6 h -1 Mpc box Max. Resolution: ~ 60 pc

GLCW8, June 2007Konstantinos Tassis Four Simulations Code : ART (N-body + Eulerian Gas Dynamics) Size : 6 h -1 Mpc box Max. Resolution: ~ 60 pc SF recipe: Density Threshold n SF = 50 cm -3 Constant Efficiency, SN feedback Energy + Metals Equilibrium Cooling SN feedback metals only Equilibrium Cooling SN feedback Energy + Metals Radiative Transfer SN feedback Delayed Energy + Metals Radiative Transfer

GLCW8, June 2007Konstantinos Tassis Semi-Analytic Model: Main Physical Effects Gas accretion  total galaxy mass No gas or metal outflows Gas in protogalaxies forms exponential disk radial extent depends on: –virial radius ( depends on mass ), –angular momentum (mean of distribution found in sims), –cooling efficiency ( depends on mass ) Star formation follows the Kennicutt-Schmidt law with a density threshold Metal Production

GLCW8, June 2007Konstantinos Tassis Stellar Mass vs. Gas Mass Higher masses: power-law correlation, slope set by Kennicutt-Schmidt law Lower masses: not enough cooling  “puffy” disks  gas density lower  SF inefficient Feed EqCool NoFeed EqCool Feed RT

GLCW8, June 2007Konstantinos Tassis Mass - Metallicity Relation Feed EqCool NoFeed EqCool Feed RT SDSS galaxies Tremonti et al (2004)

GLCW8, June 2007Konstantinos Tassis Tully - Fisher Relation Feed / EqCool NoFeed/EqCool Feed / RT No break! contrary to what one would expect if SN feedback was expelling baryons + M * = f(M gas ) McGaugh (2005)

GLCW8, June 2007Konstantinos Tassis Conclusions Correlations between observables in dwarf galaxies reproduced in cosmological simulations even without feedback Correlations established at high z as a result of increasingly inefficient star formation in lower-mass systems: Lower masses: not enough cooling  “puffy” disks  gas density lower  SF inefficient Correlations insensitive to presence of feedback, details of cooling Simulation results well reproduced by semi-analytic model with no outflows, accounting for inflow, formation of exponential gas disk, star formation obeying Kennicutt-Schmidt law with threshold For more results, other correlations between observables (surface brightness, mass-to-light ratio, effective yield) : astro-ph/