1. Linking Galaxies’ Gas Content to their Metallicity Gradients Sean Moran Johns Hopkins University & The GASS Team

2. GASS: The GALEX Arecibo SDSS Survey Catinella et al. 2010 Key Selection: A UNIFORM distribution in stellar mass 0.025 10 1000 Galaxies with HI probed to M HI /M * <3% Sampling both sides of the red/blue divide!

3. The GASS Team JHU: Sean Moran Tim Heckman MPA: Guinevere Kauffmann Barbara Catinella Jing Wang Silvia Fabello MPE: Amelie Saintonge Javier Gracia Carpio Linda Tacconi Columbia: David Schiminovich (PI) Cameron Hummels Jenna Lemonias Ronin Wu Cornell: Martha Haynes Riccardo Giovanelli Arizona: Romeel Dave Plus many more!

4. Molecular Gas, too! Saintonge et al. 2010 IRAM 30m program to observe 300 GASS galaxies -CO J=1  0 observations as tracer of H 2 -Detected to a limit of M H2 /M * <3% -Plus a new COS program to probe halo gas!

5. MMT & APO Spectroscopy 250 longslit spectra maximizing overlap with COLD GASS – Split between 6.5m MMT and 3.5m Apache Point Slit aligned with galaxy major axis to yield: – Resolved measures of SFR, stellar population age (D4000), gas-phase and stellar metallicity – Galaxy kinematics (rotation curves, velocity dispersions, dynamical masses)

6. Moran et al. 2010 Radial cuts along major axis Adaptive binning on ~kpc scales Detect SF to R90 in most Continuum subtracted, line fluxes measured following SDSS method Gas phase metallicities calculated on: -Pettini & Pagel (2004) O3N2 index -Tremonti et al. (2004) system

7. What do we learn from gas-phase metallicity gradients? At any point, set by balance between processes that enrich gas: – Star formation (SNe) – mixing/metal transport And processes that dilute or remove metals: – Galactic winds, outflows – New accretion or transport of pristine gas How balance varies with radius depends on how galaxies grow (Inside-out? Outside-in?)

8. Metallicity Gradients Zaritsky et al. 1994

9. Metallicity Gradients Moustakas et al 2010 SINGS Galaxies Small numbers Very local, heterogeneous samples Small numbers Very local, heterogeneous samples

10. GASS: Uniform, Mass-limited Sample Measured metallicities for 1500 spatial locations w/ SF across 150 galaxies As representative as the GASS main sample

11. GASS Metallicities Pettini & Pagel (2004) O3N2 indicator

12. GASS Metallicities Mostly flat! Pettini & Pagel (2004) O3N2 indicator

13. GASS Metallicities Mostly flat! Tremonti et al (2004) method

14. Sings galaxies w/ gradients

15. SINGS points in our mass range Gradient slopes as function of Mass

16. GASS Metallicities Steep drops! ~12 galaxies w/ very big drops similar to UGC8802 ~10% of sample All have high HI content (>30%) UGC8802 hypothesis: infall of new gas driving disk buildup

17. Moran et al. 2011 UGC8802 High HI (f HI ~1) No companions Rapid star formation in relatively unenriched gas

18. UGC8802 toy model

19. Radial profiles for individual big-drop galaxies Less Enriched Younger Flat SFR DensityFaster Buildup

20. UGC8802 toy model: Valid for all? But is this new gas accretion?

21. Outer Metallicity Drop  High HI Correlation is *stronger* than that of any other global quantity vs metallicity (R>R90) A measuring stick for new gas infall? Or size of halo reservoir?

22. A Local Mass-Metallicity Relation Stellar mass density Specific SFR Do galaxies with these signs of accretion merge smoothly into the population of “normal galaxies”?

23. A Local Mass-Metallicity Relation Stellar mass density Specific SFR Tremonti et al. 2004

24. A Local Mass-Metallicity Relation Stellar mass density Specific SFR Tremonti et al. 2004 Centers of low-mass SDSS galaxies slightly offset: Metal escape into IGM?

25. Conclusions GASS galaxies exhibit largely flat metallicity gradients (but M * dependant!) ~10% show sharp drops at/near R90 Outer drop correlates most strongly with total HI content Seems to indicate metal dilution by new accretion Outer metallicity depends on stellar mass density and SFR

26. Big metal-drop galaxies

27. MMT & APO Spectroscopy Obtain 300 longslit spectra maximizing overlap with COLD GASS – Over 250 in hand, split between 6.5m MMT and 3.5m Apache Point, ~kpc spatial sampling Slit aligned with galaxy major axis to yield: – Resolved measures of SFR, stellar population age (D4000), gas-phase and stellar metallicity – Galaxy kinematics (rotation curves, velocity dispersions, dynamical masses) – Existing SDSS spectra inadequate!

28. A Local Mass-Metallicity Relation Stellar mass density Specific SFR Mannucci et al 2010

29. GASS Metallicities Also: Werk et al 2011, 2010 Long flat gradients in individual galaxies Moustakas et al 2010