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
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.
Open web browser to get wireless web page
How do UFDs receive and then retain their baryons?
Are they stripped cores of larger ancient systems?
binding energy of DM halo