1. 8/18/2010 Claus Leitherer: Young Stellar Populations 1 Young Stellar Populations in the Ultraviolet Claus Leitherer (STScI)

2. 8/18/2010 Claus Leitherer: Young Stellar Populations 2 o M83: Chandar et al. (2010)

3. 8/18/2010 Claus Leitherer: Young Stellar Populations 3 Topics o New UV Models for Young Populations o Probing the nearby and distant galaxies with UV Lines o Open Issues

4. 8/18/2010 Claus Leitherer: Young Stellar Populations 4 New UV Models for Young Populations o Goal: model UV spectra of nearby and distant young populations o Stellar initial mass function (IMF) and SF history o Stellar evolution models (conversion of mass into luminosity and introduction of the time-scale) o Spectral libraries (empirical and theoretical) o 2 nd order parameters (reddening, geometry)

5. 8/18/2010 Claus Leitherer: Young Stellar Populations 5 Modeling wind and photospheric lines with WM-Basic: Leitherer et al. (2010a) o Non-LTE, spherically extended, blanketed radiation- hydrodynamics code for hot stars o Pauldrach et al. (2001) o Accounts for wind instabilities and resulting shocks for modeling the wind lines o All Starburst99 UV spectra are now fully theoretical o Allows models for any Z,  /Fe, etc. o Wind lines of NV 1240, SiIV 1400, CIV 1550 trace stars with M > 30 M sol  IMF

6. 8/18/2010 Claus Leitherer: Young Stellar Populations 6 Probing Galaxies with UV Lines o Modeling the UV spectra of different classes of objects over a range of distances and spatial scales o Distances: ~2 Mpc to z  3 o Individual star clusters and galaxy disks o Sizes of ~1 pc to >kpc o Super-solar to extreme sub-solar Z

7. 8/18/2010 Claus Leitherer: Young Stellar Populations 7 o Shapley et al. (2003): composite of ~1000 LBGs o Integrated over galaxy disk o Z  0.4 Z sol o Stellar vs. interstellar lines o IMF very close to Kroupa/Salpeter Modeling rest-frame UV spectra of Lyman-break galaxies

8. 8/18/2010 Claus Leitherer: Young Stellar Populations 8 o Space-UV observations o D = 2 – 50 Mpc o ~ tens of pc coverage o A few…..many clusters and SF regions in aperture o Composite of all FOS+GHRS spectra in the HST archive (Leitherer et al. 2010b) UV spectra of local galaxies observed with HUT/ FUSE/HST

9. 8/18/2010 Claus Leitherer: Young Stellar Populations 9 o Fit to FOS+GHRS template: standard Kroupa/Salpeter IMF

10. Nuclear Star Clusters in M83 (Wofford et al. 2010) 8/18/2010 Claus Leitherer: Young Stellar Populations 10 1 2 14 4 5 6 7 8 9 12 11 13 3 10 9 7 4 14 1 5 2 3 10 12 6 11 13 8 1” : 20 pc OPTICAL HST/WFC3 FUV HST/STIS

11. M83: Ages from UV Spectra 8/18/2010 Claus Leitherer: Young Stellar Populations 11

12. M83: Ages from Photometry o Chandar et al. (2010) & the WFC3 SOC o Age-reddening degeneracy o Breaking the degeneracy with H  8/18/2010 Claus Leitherer: Young Stellar Populations 12

13. M83: Results 8/18/2010 Claus Leitherer: Young Stellar Populations 13 o ages – masses – reddening o Spectroscopic and photometric ages agree within 20% if H  is used o Oldest clusters are the most massive (selection effect in spectroscopy) o Few clusters with ages over ~100 Myr (photometry)

14. 8/18/2010 Claus Leitherer: Young Stellar Populations 14 Outliers and Open Issues o Wolf-Rayet stars (some – but not all – are the evolved end product of massive stars) o Missing ingredients in stellar evolution

15. 8/18/2010 Claus Leitherer: Young Stellar Populations 15 o NGC 3125-1: Wolf-Rayet cluster in a BCD o Strongest He II 1640 emission known in a local SF galaxy o IMF biased towards massive stars? o Overly strong He II 1640 also observed in LBGs

16. 8/18/2010 Claus Leitherer: Young Stellar Populations 16 o Erb et al. (2010) o restframe UV spectrum of BX418 o Young, metal-poor galaxy at z = 2.3 o He II 1640!

17. 8/18/2010 Claus Leitherer: Young Stellar Populations 17 o Effects of Rotation :  modifies hydrostatic structure  induces mixing  affects mass loss o Consequences:  larger convective core  higher luminosity  lower surface opacity  higher effective temperature o Affects the mass-luminosity relation of a population o Related effect: mass transfer in Close Binaries

18. 8/18/2010 Claus Leitherer: Young Stellar Populations 18 Take-Away Points o Stellar UV lines offer the most direct probe of massive stars in integrated galaxy spectra o Stellar atmosphere/wind models are sufficiently mature to provide spectra for galaxies at low and high redshift o On average, SF galaxies follow a Kroupa/Salpeter IMF o Stellar evolution models are the weak link (rotation, binaries) and require significant future effort