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Massive Stars in the UV Spectra of Galaxies Claus Leitherer (STScI)

Massive Stars in the UV Spectra of Galaxies Claus Leitherer (STScI). Morton & Spitzer (1965). Average spectra of 16 local SF galaxies ( STIS ) vs. 811 LBGs ( LRIS ) Schwartz et al. (2006). Outline. Galaxy Properties Stellar Population Neutral and Ionized Gas Lyman- α Lyman continuum.

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Massive Stars in the UV Spectra of Galaxies Claus Leitherer (STScI)

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  1. Massive Stars in the UV Spectra of GalaxiesClaus Leitherer (STScI) Claus Leitherer: UV Spectra of Galaxies

  2. Morton & Spitzer (1965) Claus Leitherer: UV Spectra of Galaxies

  3. Claus Leitherer: UV Spectra of Galaxies

  4. Average spectra of 16 local SF galaxies (STIS) vs. 811 LBGs (LRIS) • Schwartz et al. (2006) Claus Leitherer: UV Spectra of Galaxies

  5. Outline • Galaxy Properties • Stellar Population • Neutral and Ionized Gas • Lyman-α • Lyman continuum Claus Leitherer: UV Spectra of Galaxies

  6. Galaxy Properties • UV-bright local star-forming galaxies are of late Hubble type, include Irr, BCDs, SB,….. • Stellar masses of order 108 – 109 M • Absolute magnitudes MB in the range –16 to –19 • Oxygen abundances from 1/20 Z to Z Claus Leitherer: UV Spectra of Galaxies

  7. Gil de Paz et al. (2007): GALEX FUV+NUV composite vs. SDSS image of NGC 5253 Claus Leitherer: UV Spectra of Galaxies

  8. Goldader et al. (2002) • VV 114 (d = 83 Mpc; log L = 11.7) • Interacting pair • UV vs. IR view Claus Leitherer: UV Spectra of Galaxies

  9. Stellar Population • Satellite UV is sensitive to stars with masses of ~10 M and above • Continuum: late-O/early-B • Spectral lines: O stars of all types • Most prominent lines: O VI 1035, N V 1240, Si IV 1400, C IV 1550 Claus Leitherer: UV Spectra of Galaxies

  10. Chandar et al. (2004) • UV line profiles suggest universal Salpeter IMF • N V: 77 eV; C IV: 49 eV; Si IV: 33 eV • Confirmed independently by modeling of optical emission lines (González Delgado et al. 2002) Claus Leitherer: UV Spectra of Galaxies

  11. Beware of selection effects! • HST slit sizes are small (0.2ʺ for STIS) • Massive stars form in clusters Claus Leitherer: UV Spectra of Galaxies

  12. Chandar et al. (2005) • Compare cluster and inter-cluster spectra • Inter-cluster spectra are softer • IMF or age? • Field population due to dissolving clusters Claus Leitherer: UV Spectra of Galaxies

  13. Direct comparison with high-z galaxies may be misleading → need large- or multi-aperture spectroscopy Claus Leitherer: UV Spectra of Galaxies

  14. Neutral and Ionized Gas • UV spectral region displays plethora of interstellar lines • Spectral region below 1200 Å in particular is dominated by IS lines • Well-suited for observations with FUSE because of wavelength coverage and spectral resolution (R ≈ 20,000) Claus Leitherer: UV Spectra of Galaxies

  15. Grimes et al. (2008): FUSE survey of local starburst galaxies Claus Leitherer: UV Spectra of Galaxies

  16. Grimes et al. (2008) • FUSE UV profiles of selected IS lines • All lines are blue-shifted and asymmetric • Outflows with velocities of order ~102 km s–1 • Galactic superwinds Claus Leitherer: UV Spectra of Galaxies

  17. LIR + LUV = SFR; LK = Mass • Outflow velocity shows trend with SFR/Mass • Outflows expected to be more signifcant at high z • Pollution of the IGM and leakage of radiation Claus Leitherer: UV Spectra of Galaxies

  18. Lyman-α • Leitherer (2007) • Predicted Ly-α strength for a standard population • W(Ly-α) ≈ 102 Å • Almost never observed in the local universe Claus Leitherer: UV Spectra of Galaxies

  19. Spectroscopy can cover only a small solid angle of the Lyman-α emission • HST/ACS Lyman-α imaging survey of local SF galaxies (PI: D. Kunth) • Haro 11: MB = ̶ 20.5; log O/H = 7.9 • Local analog of a Lyman-break galaxy Claus Leitherer: UV Spectra of Galaxies

  20. Östlin et al. (2007) • Fields: 20’’  20’’ or 8 kpc  8 kpc • Small W(Ly-α) in the center • Large W(Ly-α) where flux levels are small • Correlates with velocity field but not with E(B-V) • 2.7% Ly-α escapes Claus Leitherer: UV Spectra of Galaxies

  21. Deharveng et al. (2008) • GALEX survey of Ly-α emitters at z ≈ 0.3 • Equivalent width distribution consistent with observation at high z • Ly-α/UV luminosity function suggests increase of Ly-α escape with redshift Claus Leitherer: UV Spectra of Galaxies

  22. Lyman Continuum • Leitherer et al. (1999) • ~10% of the total luminosity emitted as ionizing radiation • Observationally verified via recombination lines • Leakage? Claus Leitherer: UV Spectra of Galaxies

  23. Grimes et al. (2008): FUSE survey; 9 galaxies have sufficiently high z to permit Lyman continuum observations Claus Leitherer: UV Spectra of Galaxies

  24. Bergvall et al. (2006): detection of Lyman continuum in Haro 11 using the same data; 5 – 10% escape fraction Claus Leitherer: UV Spectra of Galaxies

  25. Alternatively: use opacity of interstellar lines as proxy for H I opacity • C II 1036 • Upper limits of a few % for escape fraction • Local galaxies are opaque • Reionization? Claus Leitherer: UV Spectra of Galaxies

  26. Main Points • Restframe UV spectra of local and distant star-forming galaxies are superficially similar but suggest rather significant differences • Beware of selection effects introduced by aperture sizes • Mechanical energy input by newly formed stars is significant and increases with redshift • Growing importance of galactic winds, escape of Ly-α, and Lyman continuum leakage Claus Leitherer: UV Spectra of Galaxies

  27. UV spectroscopy with HST during C17 and later Claus Leitherer: UV Spectra of Galaxies

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