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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 l.jpg

What are the smallest galaxies?

Joss Bland-Hawthorn

University of Sydney

Missing Baryons

Women's College 2009

Collaborators: R. Sutherland, T. Karlsson


Outline l.jpg

  • 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


Slide3 l.jpg

Galaxy formation is largely driven by the unseen...

MSO, Oct 09


Slide4 l.jpg

Geha, Simon+ 08


Slide10 l.jpg

Recent discovery of ultra-faint dwarfs

(UFDs)


Baryons swept out by single sn for m dm 3 10 7 m l.jpg

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


Ultra low mass galaxy l.jpg

  • "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 l.jpg

Smooth vs. Clumped


Fyris 3d hydrodynamics sutherland 2010 l.jpg

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 l.jpg

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


Sf timescale l.jpg

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

SF timescale

Timescale

~ N★ / Ŝ π rc2

~ 1 Gyr


Ultra low mass galaxy17 l.jpg

Ultra low-mass galaxy


M dm 10 7 m l.jpg

MDM = 107 M

L00

L01


M dm 10 6 5 m l.jpg

MDM = 106.5 M

L00

L01


Slide20 l.jpg

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 l.jpg

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 l.jpg

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 l.jpg

Einasto vs. Burkert (isothermal)


Wireless access l.jpg

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 l.jpg

Are there gas-rich UFDs?


Survival of baryons in ufds l.jpg

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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