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Alyson Brooks Fairchild Postdoctoral Fellow in Theoretical Astrophysics Caltech

The Interplay Between Gas Accretion and Feedback in the Formation of Galactic Disks. Alyson Brooks Fairchild Postdoctoral Fellow in Theoretical Astrophysics Caltech In collaboration with the University of Washington’s N-body Shop ™ makers of quality galaxies.

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Alyson Brooks Fairchild Postdoctoral Fellow in Theoretical Astrophysics Caltech

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  1. The Interplay Between Gas Accretion and Feedback in the Formation of Galactic Disks Alyson Brooks Fairchild Postdoctoral Fellow in Theoretical Astrophysics Caltech In collaboration with the University of Washington’s N-body Shop™ makers of quality galaxies

  2. What is the effect of cold flow gas accretion on the growth of galaxy disks?

  3. How Do Galaxies Get Their Gas? Cold Disk Infalling Cold Gas Dark Matter Halo + Hot Gas Dark Matter Halo + Hot Gas e.g., Peebles (1969), Rees & Ostriker (1977), Silk (1977), Binney (1977), White & Rees (1978), Fall & Efstathiou (1980), Somerville & Primack (1999)

  4. Standard • Not all gas is shock heated! • Fraction of shocked gas is a strong function of galaxy mass • Cold flow gas accretion due to both: • Mass threshold for stable shock • Even after shock develops, there can be cold gas accretion at high z in dense filaments Case 1 This is already in the SAMs. This is not. Case 2 Keres et al. (2005), Dekel & Birnboim (2006), Ocvirk et al. (2008)

  5. 3.4x1010 M 1.3x1011 M 1.1x1012 M 3.3x1012 M Gas Accretion Rates at the Virial Radius Brooks et al. (2009)

  6. Gas Accretion Rates Disk Star Formation Rates 3.4x1010 M 1.3x1011 M 1.1x1012 M 3.3x1012 M Brooks et al. (2009)

  7. z = 1 Historic Problem : Disk Growth After z=1, dramatic change in scale lengths since z=1 3.4x1010 M 1.3x1011 M Massive Disks at z=1: Vogt et al. (1996); Roche et al. (1998); Lilly et al. (1998); Simard et al. (1999); Labbe et al. (2003); Ravindranath et al. (2004); Ferguson et al. (2004); Trujillo & Aguerri (2004); Barden et al. (2005); Sargent et al. (2007); Melbourne et al. (2007); Kanwar et al. (2008); Forster-Shreiber et al. (2006); Shapiro et al. (2008); Genzel et al. (2008); Stark et al (2008); Wright et al. (2008); Law et al. (2009) 1.1x1012 M 3.3x1012 M

  8. A case study: The Formation of a Large Galaxy Disk in a Low z Major Merger

  9. NO GAS Mergers destroy or thicken disks e.g., Toth & Ostriker 1992, Kazantzidis et al. 2007, Bullock et al. 2008, Purcell et al. 2008 Therefore, disk galaxies must grow rather quiescently CDM  mergers Mergers or Smooth Gas Accretion?

  10. NO GAS ACCRETION NO GAS Mergers destroy or thicken disks Or do they? Baugh et al. 1996, Steinmetz & Navarro 2002, Robertson et al. 2006, Hopkins et al. 2008, Robertson & Bullock 2008 Not if the disks are gas rich (fgas > 50%) e.g., Toth & Ostriker 1992, Kazantzidis et al. 2007, Bullock et al. 2008, Purcell et al. 2008 Therefore, disk galaxies must grow rather quiescently CDM  mergers Mergers or Smooth Gas Accretion?

  11. The Formation of a Milky Way-Mass Galaxy to z=0 30 kpc on a side Green = gas Blue/Red = age/metallicity weighted stars

  12. The Role of Cold Flows Disk growth prior to z=1 due to cold flows Brooks et al. (2009), Governato et al. (2009) Keres et al. (2008), Ocvirk et al. (2008), Agertz et al. (2009), Dekel et al. (2009), Bournaud & Elmegreen (2009)

  13. What is the effect of feedback on the growth of galaxy disks?

  14. 5 10 Age of Universe (Gyr) The Role of Feedback Develop a gas reservoir, yet fgas never > 25% Bulge SFR (M/yr) Brooks et al. (2009), Governato et al. (2009)

  15. SFR increases by ~2-3x in mergersonly 5 10 Age of Universe (Gyr) The Role of Feedback Bulge SFR (M/yr) Jogee et al. (2008), Stewart et al. (2008), di Matteo et al. (2008), Hopkins et al. (2008), Cox et al. (2008), Daddi et al. (2007), Bell et al. (2005), Bergvall et al. (2003), Georgakakis et al. (2000)

  16. Disk Regrowth Young stellar disk, formed after last major merger (z < 0.8); 30% of z=0 disk mass (but dominates the light) ~30 % due to cold gas accreted prior to lmm; ~35% due to cold gas accreted after lmm; ~30% due to hot gas accretion Old stellar disk, formed prior to last major merger (z > 0.8); 70% of z=0 stellar disk mass Brightness not to scale!

  17. Disk Regrowth B/Di = 1.1 B/DM* = 1.2 M*disk = 2.07x1010 M B/Di = 0.49 B/DM* = 0.87 M*disk = 3.24x1010 M Sunrise: Jonsson (2006) www.ucolick.org/~patrik/sunrise/

  18. Conclusions • Although mergers are expected to be common in CDM, this is not at odds • with the existence of disks. • Cold gas accretion leads to the building of disks at higher z than predicted • by standard models • Feedback regulates SFR in galaxies, building a gas reservoir and limiting • gas consumption in mergers • New disk grows due to a) subsequent gas accretion, b) remaining gas from existing reservoir, c) cooling of hot gas from the galaxy halo • Do not require fgas > 50% to rebuild disks, due to subsequent gas accretion and cooling from hot halo

  19. High density threshold high efficiency. The Effects of Feedback Notall feedback is created equal

  20. Disks rotate too fast at a given luminosity Mass (dark and luminous) is too concentrated Log Vrot Disks are too small at a given rotation speed MI The Effects of Feedback: The CDM Angular Momentum Problem catastrophe! Navarro & Steinmetz (2000)

  21. The Effects of Feedback: The Tully-Fisher Relation baryonic Tully-Fisher relation (magnitudes from Sunrise) HI W20/2 velocity widths = Vmax Governato et al. (2009), Geha et al. (2006)

  22. A G E of S T E L L A R P O P The Effects of Feedback: “Downsizing” More Massive Galaxies Have older Stellar Populations MacArthur, Courteau & Bell (2004)

  23. 12+log(O/H) Stellar Mass (M) 12+log(O/H) Stellar Mass (M) The Effects of Feedback: The Mass-Metallicity Relationship Brooks et al. (2007)Tremonti et al. (2004)Erb et al. (2006)

  24. Feedback and resolution combine to yield simulated galaxies that match observed galaxy relations both at high z and at z=0 (Only some of these galaxies are simulated. Can you tell which?) Image by C. Brook, using Sunrise, courtesy P. Jonsson.

  25. Steps to Rapid Disk Regrowth • Cold gas accretion leads to the building of disks at higher z than predicted by standard models • Feedback regulates SFR in galaxies, building a gas reservoir and limiting gas consumption in mergers • Existing disk is thickened in merger events • New disk grows due to a) subsequent gas accretion, b) remaining gas from existing reservoir, c) cooling of hot gas from the galaxy halo

  26. Hot vs Cold 3.4x1010 1.3x1011 1.1x1012 3.3x1012 Galaxy Mass (M) Low mass High mass Gas Accretion at the Virial Radius “clumpy” accretion gas (from other halos) unshocked, smoothly accreted gas shocked, smoothly accreted gas Brooks et al. (2009)

  27. Disk Growth Historic Problem : Disk Growth After z=1 Heating gas shifts SF to z < 1, as models predict 1.1x1012 M 3.3x1012 M Models also predict dramatic change in scale lengths since z=1 Brooks et al. (2009)

  28. Hot vs Cold hot dense Keres et al. (2005)

  29. Disk Growth 3.4x1010 M 1.3x1011 M 3.3x1012 M 1.1x1012 M Historic Problem : Disk Growth After z=1 Mo et al. (1998); Mao et al. (1998); van den Bosch (1998); Somerville et al. (2008)

  30. Hot vs Cold No shock yet Unshocked gas in filaments Shock exists Definitions exclude “clumpy” accretion gas: gas that ever belonged to another galaxy halo

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