COS-Halos Galaxy Halo with H 2

1. COS-Halos Galaxy Halo with H2 Ethan Kruse Harvard College STScI Summer Program

2. COS-Halos Program • Use background quasars (z<1) to probe halos of galaxies at a range of impact parameters (10-150 kpc) • 39 Sightlines to survey the properties of the halos • Metallicity • Ionization

3. Separation: 20” =74kpc The Field • Galaxy A : • [O/H] ~ 0.16 • SFR ~ 0.3 M yr -1 • Absorbers: • z = 0.24784 • z = 0.24752 QSO z = 0.471 Bz = 0.2478 A z = 0.2468 Keck: LRIS spectra

4. Sub-DLA: log N(HI) = 19.653 Ly α Ly β Ly δ Ly ε

5. H2 Presence

6. H2 Curve of Growth log N(H2) = 16.89 N(H2)/N(HI) = -2.763

7. Two Components Ionized – Favor Left Component Neutral – Favor Right Component

8. Ionization Correction

9. Sembach et al. 2001: Comparison log N(H2) = 16.89 N(H2)/N(H ) = -3.1 log N(H2) = 16.89 N(H2)/N(HI) = -2.8 log N(H2) = 16.80 N(H2)/N(HI) = -3.1 log N(H2) = 16.80 N(H2)/N(H ) = -3.1 J=0 N = 16.24 1 N = 16.64 2 N = 15.20 3 N = 14.80 J=0 N = 16.24 1 N = 16.63 2 N = 16.15 3 N = 15.54

10. Summary • Found two clouds ~74 kpc from a pair of merging galaxies • One cloud has a strong H2 presence, yet 50% of the H is ionized • Sightline shows strong similarities with a cloud in the Magellanic Stream • Low metallicity indicates it is likely not related to the possible merger

11. Thank you for the opportunity and help to • Jason Tumlinson • Chris Thom • STScI Summer Program

14. Cloudy Modeling • GOAL: Determine the ionization fraction and H I column for each component • We do not have definite ratios to match to models (e.g. NII/NI or SiIII/SiII), only limiting cases due to saturation and blending • 1200 total models over ranges of N(HI), ionization parameters, and cloud density • Throw out results over 10kpc in diameter

15. N Constraint

16. Sembach et al. 2001: Comparison

17. T = 241 K T = 133 K

18. HI Solution: log N(HI) = 19.65

19. Total Metallicity

20. H2 Excitation