9/7/04 Claus Leitherer: A Far-UV View 1

A Far-Ultraviolet View of Starburst Galaxies

Claus Leitherer (STScI)Claus Leitherer (STScI)

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Kinney et al. (1994): 1200 – 10,000 Å

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Leitherer et al. (2002): 900 – 1200 Å

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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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Heckman et al. (2001): NGC 1705 with FUSE

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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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Hoopes et al. (2004): H2 in starburst galaxies

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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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Deharveng et al. (2001): Mrk 54 with FUSE

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Malkan et al. (2003): 11 blue galaxies with STIS

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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%

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Steidel et al. (2001)

Haehnelt et al. (2001)