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A Far-Ultraviolet View of Starburst Galaxies
Claus Leitherer (STScI)Claus Leitherer (STScI)
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Outline
Stellar Populations
Dust Obscuration
Gas: Hot and Cold Phases
Gas: Lyman Continuum
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Stellar Populations
Far-UV lines: Age-IMF degeneracy
Far-UV continuum: Age-Reddening degeneracy
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Robert et al. (2003):
Synthetic far-UV spectrum of SSP
Strongest lines: O VI 1035; C III 1175
C III: radiative O VI: non-radiative O VI decoupled from
stellar parameters O VI constant with Teff
for Teff > 30,000 K
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Robert et al. (2003):
Trade between age and IMF
IMF slopes with = 3.3, 2.35, 1.5
C III varies, O VI is constant
Changing M affects L more than Teff
C III, a radiative wind line, scales with L
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Leitherer et al. (2002): Trade between age
and reddening HUT spectrum, synth.
line spectrum, synth. continuum
Age from Si IV+C IV Reddening from 1500
Å slope Use far-UV reddening
law Predict galaxy
spectrum down to Lyman limit
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Dust Obscuration
Reddening shortward of 1200 Å studied by Voyager, HUT, ORFEUS, and FUSE (+ sounding rockets)
Extragalactic studies: HUT: Leitherer et al. (2002) FUSE: Buat et al. (2002)
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Buat et al. (2002): 950 – 1175 Å reddening law is flatter
than Galactic law Extension of “Calzetti”
curve Agrees with model for
clumps + shell geometry
Most stars totally hidden; light comes from few stars with little attenuation
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Gas: Hot and Cold Phases
The spectral region 912 – 1200 Å includes includes transitions of the hottest (105 K) and coldest (102 K) gas
Coronal gas traced by O VIMolecular gas traced by
rotational/vibrational transitions of H2
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Detection of broad (100 km s–1), blueshifted (–77 km s–1) O VI
Formation in a blow-out from expanding superbubble
N(O VI) consistent with shock-heated gas cooling radiatively
Cooling rate << supernova heating rateRadiative losses are negligible and wind
continues to expand Implications for IGM enrichment
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Weak H2 absorption detected in two out of five starburst galaxies
Upper limit of total M(H2) 10 M
Therefore, most of the molecular gas is missed by the FUSE sightlines
Diffuse ISM has little H2, probably because of the destructive UV radiation
H2 located in dense clouds with covering factor < 1 clumpy ISM
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Gas: Lyman Continuum
Star-forming galaxies are the dominant contributor to the non-ionizing radiation field
Are starburst galaxies a significant component of the ionizing background?
Local tests: need far-UV observationsHigh-z galaxies: IGM radiative transfer
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Attempts to detect Lyman continuum radiation
Leitherer et al. (1995) HUT 4 galaxies; z 0 < 3 %
Hurwitz et al. (1997) HUT 4 galaxies; z 0 < 19%
Deharveng et al. (1997) H/UV LF in local universe < 1%
Deharveng et al. (2001) FUSE Mrk 54; z 0 < 5%
Giallongo et al. (2002) FORS2 z = 2.96, 3.32 < 16%
Fernández-Soto et al. (2003) WFPC2 HDF; 1.9 < z < 3.5 < 4%
Malkan et al. (2003) STIS 1.1 < z < 1.4 < 1%
Steidel et al. (2001) Keck 29 galaxies; z = 3.4 100%