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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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what are the smallest galaxies

What are the smallest galaxies?

Joss Bland-Hawthorn

University of Sydney

Missing Baryons

Women's College 2009

Collaborators: R. Sutherland, T. Karlsson

outline

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

ultra low mass galaxy

"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)

fyris 3d hydrodynamics sutherland 2010

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)

ultra low mass galaxy15

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

slide20

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

kinematics

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

summary so far

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...

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Wireless Access
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Open web browser to get wireless web page

  • username: mbiadconf
  • password: aShzWVPW
survival of baryons in ufds
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