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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?

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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

  • 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


Galaxy formation is largely driven by the unseen...

MSO, Oct 09


Geha, Simon+ 08


Recent discovery of ultra-faint dwarfs

(UFDs)


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


  • "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)


Smooth vs. Clumped


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 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


Ŝ = <SFR density> ~ 10-4 M yr-1 kpc-2

SF timescale

Timescale

~ N★ / Ŝ π rc2

~ 1 Gyr


Ultra low-mass galaxy


MDM = 107 M

L00

L01


MDM = 106.5 M

L00

L01


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


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


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...


Einasto vs. Burkert (isothermal)


Wireless Access

  • Turn on wireless

    Select usyd-guest

    Open web browser to get wireless web page

  • username: mbiadconf

  • password: aShzWVPW


Are there gas-rich 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


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