1. Alyson Brooks Fairchild Postdoctoral Fellow in Theoretical Astrophysics Caltech In collaboration with C. Brook (JHI), F. Governato (UW), L. Mayer (ETH, U Zurich), P. Madau (UCSC), and the University of Washington’s N-body Shop ™ makers of quality galaxies Modeling Realistic Dwarf Galaxies (and Stellar Halos)

2. The CDM Angular Momentum Problem Navarro & Steinmetz (2000) Disks are too small at a given rotation speed Disks rotate too fast at a given luminosity Mass (dark and luminous) is too concentrated Log V rot MIMI catastrophe!

3. Low resolution: disks heat and lose angular momentum to halo Rd=30% smaller Kaufmann et al. (2007) 20 kpc x10 19 atoms cm -2 N=1,000,000 100,000 30,000 Isolated (non-cosmological) galaxy simulation MW mass halo after 5 Gyr

4. “Zoom in” technique: high resolution halo surrounded by low resolution region 3 million particle simulation 1 million particles Computationally Efficient Cosmic Infall and Torques correctly included 6 Mpc100 Mpc Katz & White (1993)

5. No feedback Zavala et al. (2008) Scannapieco et al. (2008)

6. “Over-cooling” leads to loss of angular momentum similar to low resolution Maller & Dekel (2002)

7. Star Formation: reproduces the Kennicutt-Schmidt Law; each star particle a SSP with Kroupa IMF Energy from SNII deposited into the ISM as thermal energy based on McKee & Ostriker (1977) Radiative cooling disabled to describe adiabatic expansion phase of SNe (Sedov- Taylor phase); ~20Myr (blastwave model) Only Free Parameters: SN & Star Formation efficiencies Sub-grid physics & Blastwave Feedback Model Stinson et al. (2006), Governato et al. (2007) HI Map

8. Fully Cosmological, Parallel, N-body Tree Code, + smoothed particle hydrodynamics (SPH) -Star Formation Rate   1.5 -UV background radiation (Haardt & Madau 96) - Compton & radiative cooling -Low temperature cooling (<10 4 K, metal lines) -Supernovae feedback II & Ia (Stinson et al. 2006) - metal enrichment: H,He,O,Fe Stadel (2001) Wadsley et al. (2004)

9. The Formation of a Bulgeless Dwarf Galaxy M vir = 2x10 10 M  M * = 1.2x10 8 M  15 kpc on a side Green = gas Blue/Red = age/metallicity weighted stars

11. High threshold Low threshold “Resolving” Star Formation Regions Feedback becomes more efficient (more outflows per unit mass of stars formed) See also: Ceverino & Klypin (2008) Robertson & Kravtsov (2008) Tasker & Bryan (2008)

12. The effect of altering the SF density threshold Resolving Star Forming Complexes The effect of altering resolution Governato et al., 2009, Nature, 463, 203 arXiv: 0911.2237

13. At high z outflows remove low angular momentum gas at a rate 2-6 times SFR(t) Time J Accreted material Outflows Gas removal from the galaxy center Hot gas perpendicular to disk plane: 100km/sec Cold Gas in shells = 30 km/sec Outflows Remove Low Angular Momentum Gas See also: van den Bosch (2002), Maller & Dekel (2002), Bullock et al. (2001)

14. Angular Momentum of Stellar Disk vs DM halo van den Bosch et al. (2001) The Angular Momentum Distribution of baryons must be altered to match observed galaxies

15. Diffuse Star Formation “Observed” Surface Brightness Profile “Resolved” Star Formation Radius (kpc) 0123 4 5 6 7 18 20 22 24 Mag/arsec 2 0 1 23 4 Radius (kpc) 22 24 26 28 Mag/arsec 2 Governato et al., 2009, Nature, 463, 203, arXiv:0911.2237

16. HI W20/2 velocity widths = V max Geha et al. (2006) Brooks et al., in prep Governato et al. (2008, 2009) baryonic Tully-Fisher relation (magnitudes from Sunrise)

17. Size - Luminosity Relation Brooks et al., in prep. Data from Graham & Worley, 2008; van Zee 2000 Simulated Galaxies Observed Sample

18. Comparison to THINGS: the HI Nearby Galaxy Survey Rotation curve rises too slowly to match cuspy NFW profile Walter et al. (2008); Oh et al. (in prep)

19. Dark Matter with a Central Core Clumpy Gas transfers energy to DM DM expands as gas is rapidly removed e.g., Mashchenko et al. (2007, 2008); El-Zant et al. (2004); Navarro et al. (1996); Mo & Mao (2004); Tonini et al. (2006)

20. Belokurov et al.

21. Conclusions I Simulations are improving! (due to resolution and feedback) Bulgeless galaxies with shallow DM cores are compatible with CDM! Strong gas outflows can selectively remove low angular momentum gas (but force resolution < 100pc is required)

22. Alyson Brooks Fairchild Postdoctoral Fellow in Theoretical Astrophysics Caltech Primary collaborators: A. Zolotov (NYU), B. Willman (Haverford) Modeling Realistic Dwarf Galaxies (and Stellar Halos) Inner

23. Accreted Stellar Halos N-Body + SAM results of Bullock and Johnston; Cooper et al.: Stellar halos built through accretions alone. Need fully cosmological simulations wit baryons to examine if halo stars can be formed in the main galaxy. Cooper et al. (2010)

24. Observing the Simulations Zolotov et al. (2009)

25. Chemical Evolution + Mass – Metallicity – SFR Relation

26. Red: Stars formed in situ Black: Accreted stars Chemical Trends Zolotov et al. (2010) -3.0 -2.0 -1.0 0.0 [Fe/H] [O/Fe] [O/Fe] 0.4 0.0 0.4 0.0 New Stronger Feedback

27. Already observed? Nissen & Schuster (2010) 78 halo stars (kinematically selected)

28. Conclusions II Galaxies with quiescent merger histories may have inner halos dominated by stars formed in situ Outer halos always dominated by accreted stars Chemical trends may give a clue to the formation origin of individual stars