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What are the smallest galaxies?

This work by Joss Bland-Hawthorn at the University of Sydney presents a comprehensive investigation into the smallest galaxies, particularly ultra-faint dwarfs (UFDs). Collaborators R. Sutherland and T. Karlsson contribute to the dialogue surrounding dark matter (DM) halos and supernovae impacts on galaxy formation. The research examines gas retention in low-mass structures, addressing their origins and evolutionary processes. With new simulations and data, the study seeks to understand how UFDs interact with baryons and the role of DM in their survival amidst cosmic events.

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What are the smallest galaxies?

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  1. What are the smallest galaxies? Joss Bland-Hawthorn University of Sydney Missing Baryons Women's College 2009 Collaborators: R. Sutherland, T. Karlsson

  2. Building blocks of the Galaxy • Ultra faint dwarfs – just what are these? • Fyris simulations of supernovae in Einasto DM halos • Ultra low-mass galaxies – are these the same thing? • "the smallest DM halo that can retain cold gas in the event of a single SN explosion" • (JBH, Sutherland & Karlsson 2010) Outline

  3. Galaxy formation is largely driven by the unseen... MSO, Oct 09

  4. Geha, Simon+ 08

  5. Recent discovery of ultra-faint dwarfs (UFDs)

  6. Baryons swept out by single SN for MDM < 3×107 M

  7. "the smallest DM halo that can retain cold gas in the event of a single SN explosion" Ultra low-mass galaxy no gravity coldest clouds ~50 K, ~102 cm-3 Fractal medium (Kolmogorov)

  8. Smooth vs. Clumped

  9. PPM Riemann solver High order Gudonov scheme Refined not dynamic mesh Split-sweep; shock capturing Asplund (2005) metals except... [Fe/H] = -4.0 Fyris 3D hydrodynamics (Sutherland 2010) • Liska-Wendroff (2003) tests on • instability growth, shock capturing... C: 1.5× O: 5× Mg, Si, Ca: 2.5× H2, dust turned off • 3 level nested simulations: • L00: 12 rc • L01: 4 rc • L02: << rc Sutherland & Dopita (2003)

  10. Ultra low-mass galaxy These models were chosen to resemble UFDs, i.e. very low fb We have begun to consider higher fb models where the core baryons modify the potential – self gravity must be included

  11. Ŝ = <SFR density> ~ 10-4 M yr-1 kpc-2 SF timescale Timescale ~ N★ / Ŝ π rc2 ~ 1 Gyr

  12. Ultra low-mass galaxy

  13. MDM = 107 M L00 L01

  14. MDM = 106.5 M L00 L01

  15. Lowest mass ~ 106 M: Gas retention post SN at t=200,000 yrs is ~5% Fall back gives ~15% Off centred SN retains ~30% More gas retained if fb increased 107 M 106 M

  16. Turbulence timescale ~ 20-40 Myr Stars forming in bursts every ~ 100 Myr Kinematics σ ≈ 4 km s-1 is at low end of UFD range, σ ≈ 3-8 km s-1

  17. Number of stars, N★~ 300-3000 Core size, rc ~ 30-50 pc Dispersion, σ★ ~ 4 km s-1 Radial profile ~ Plummer or faster Non-detectability of HI But are ultra low-mass galaxies truly consistent with UFDs... See Torgny Karlsson's talk this afternoon. Summary so far...

  18. Einasto vs. Burkert (isothermal)

  19. Wireless Access • Turn on wireless Select usyd-guest Open web browser to get wireless web page • username: mbiadconf • password: aShzWVPW

  20. Are there gas-rich UFDs?

  21. Survival of baryons in UFDs How do UFDs receive and then retain their baryons? Are they stripped cores of larger ancient systems? binding energy of DM halo

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