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Young Stellar Populations in the Ultraviolet Claus Leitherer (STScI)

Young Stellar Populations in the Ultraviolet Claus Leitherer (STScI). M83: Chandar et al. (2010). Topics. New UV Models for Young Populations Probing the nearby and distant galaxies with UV Lines Open Issues. New UV Models for Young Populations.

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Young Stellar Populations in the Ultraviolet Claus Leitherer (STScI)

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  1. Young Stellar Populations in the UltravioletClaus Leitherer (STScI) Claus Leitherer: Young Stellar Populations

  2. M83: Chandar et al. (2010) Claus Leitherer: Young Stellar Populations

  3. Topics • New UV Models for Young Populations • Probing the nearby and distant galaxies with UV Lines • Open Issues Claus Leitherer: Young Stellar Populations

  4. New UV Models for Young Populations • Goal: model UV spectra of nearby and distant young populations • Stellar initial mass function (IMF) and SF history • Stellar evolution models (conversion of mass into luminosity and introduction of the time-scale) • Spectral libraries (empirical and theoretical) • 2nd order parameters (reddening, geometry) Claus Leitherer: Young Stellar Populations

  5. Modeling wind and photospheric lines with WM-Basic: Leitherer et al. (2010a) • Non-LTE, spherically extended, blanketed radiation-hydrodynamics code for hot stars • Pauldrach et al. (2001) • Accounts for wind instabilities and resulting shocks for modeling the wind lines • All Starburst99 UV spectra are now fully theoretical • Allows models for any Z, /Fe, etc. • Wind lines of NV 1240, SiIV 1400, CIV 1550 trace stars with M > 30 Msol  IMF Claus Leitherer: Young Stellar Populations

  6. Probing Galaxies with UV Lines • Modeling the UV spectra of different classes of objects over a range of distances and spatial scales • Distances: ~2 Mpc to z  3 • Individual star clusters and galaxy disks • Sizes of ~1 pc to >kpc • Super-solar to extreme sub-solar Z Claus Leitherer: Young Stellar Populations

  7. Modeling rest-frame UV spectra of Lyman-break galaxies • Shapley et al. (2003): composite of ~1000 LBGs • Integrated over galaxy disk • Z 0.4 Zsol • Stellar vs. interstellar lines • IMF very close to Kroupa/Salpeter Claus Leitherer: Young Stellar Populations

  8. UV spectra of local galaxies observed with HUT/ FUSE/HST • Space-UV observations • D = 2 – 50 Mpc • ~ tens of pc coverage • A few…..many clusters and SF regions in aperture • Composite of all FOS+GHRS spectra in the HST archive (Leitherer et al. 2010b) Claus Leitherer: Young Stellar Populations

  9. Fit to FOS+GHRS template: standard Kroupa/Salpeter IMF Claus Leitherer: Young Stellar Populations

  10. 1” : 20 pc 1 1 3 2 2 3 4 4 5 5 8 6 8 7 6 9 7 10 9 10 12 12 13 13 14 14 11 11 OPTICAL HST/WFC3 FUV HST/STIS Nuclear Star Clusters in M83 (Wofford et al. 2010) Claus Leitherer: Young Stellar Populations

  11. M83: Ages from UV Spectra Claus Leitherer: Young Stellar Populations

  12. M83: Ages from Photometry • Chandar et al. (2010) & the WFC3 SOC • Age-reddening degeneracy • Breaking the degeneracy with H Claus Leitherer: Young Stellar Populations

  13. M83: Results • ages – masses – reddening • Spectroscopic and photometric ages agree within 20% if H is used • Oldest clusters are the most massive (selection effect in spectroscopy) • Few clusters with ages over ~100 Myr(photometry) Claus Leitherer: Young Stellar Populations

  14. Outliers and Open Issues • Wolf-Rayet stars (some – but not all – are the evolved end product of massive stars) • Missing ingredients in stellar evolution Claus Leitherer: Young Stellar Populations

  15. NGC 3125-1: Wolf-Rayet cluster in a BCD • Strongest He II 1640 emission known in a local SF galaxy • IMF biased towards massive stars? • Overly strong He II 1640 also observed in LBGs Claus Leitherer: Young Stellar Populations

  16. Erb et al. (2010) • restframe UV spectrum of BX418 • Young, metal-poor galaxy at z = 2.3 • He II 1640! Claus Leitherer: Young Stellar Populations

  17. Effects of Rotation: • modifies hydrostatic structure • induces mixing • affects mass loss • Consequences: • larger convective core  higher luminosity • lower surface opacity  higher effective temperature • Affects the mass-luminosity relationof a population • Related effect: mass transfer in Close Binaries Claus Leitherer: Young Stellar Populations

  18. Take-Away Points • Stellar UV lines offer the most direct probe of massive stars in integrated galaxy spectra • Stellar atmosphere/wind models are sufficiently mature to provide spectra for galaxies at low and high redshift • On average, SF galaxies follow a Kroupa/Salpeter IMF • Stellar evolution models are the weak link (rotation, binaries) and require significant future effort Claus Leitherer: Young Stellar Populations

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