What are the smallest galaxies?. Joss Bland-Hawthorn University of Sydney Missing Baryons Women's College 2009. Collaborators: R. Sutherland, T. Karlsson. Building blocks of the Galaxy Ultra faint dwarfs – just what are these? Fyris simulations of supernovae in Einasto DM halos
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University of Sydney
Women's College 2009
Collaborators: R. Sutherland, T. Karlsson
coldest clouds ~50 K, ~102 cm-3
Fractal medium (Kolmogorov)
PPM Riemann solver of a single SN explosion"
High order Gudonov scheme
Refined not dynamic mesh
Split-sweep; shock capturing
Asplund (2005) metals except...
[Fe/H] = -4.0
Mg, Si, Ca: 2.5×
H2, dust turned off
Sutherland & Dopita (2003)
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
Ŝ of a single SN explosion" = <SFR density> ~ 10-4 M yr-1 kpc-2
~ N★ / Ŝ π rc2
~ 1 Gyr
Lowest mass ~ 10 of a single SN explosion"6 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
Turbulence timescale ~ 20-40 Myr of a single SN explosion"
Stars forming in bursts every ~ 100 Myr
σ ≈ 4 km s-1
is at low end of UFD range, σ ≈ 3-8 km s-1
Number of stars, N of a single SN explosion"★~ 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.
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How do UFDs receive and then retain their baryons?
Are they stripped cores of larger ancient systems?
binding energy of DM halo