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Linking Galaxies’ Gas Content to their Metallicity Gradients

Linking Galaxies’ Gas Content to their Metallicity Gradients. Sean Moran Johns Hopkins University & The GASS Team. GASS: The GALEX Arecibo SDSS Survey. Sampling both sides of the red/blue divide!. Key Selection: A UNIFORM distribution in stellar mass 0.025 < z <0.05, Log(M * )>10

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Linking Galaxies’ Gas Content to their Metallicity Gradients

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

  2. GASS: The GALEX Arecibo SDSS Survey Sampling both sides of the red/blue divide! • Key Selection: A UNIFORM distribution in stellar mass • 0.025<z<0.05, Log(M*)>10 • 1000 Galaxies with HI probed to MHI/M*<3% Catinella et al. 2010

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

  4. Molecular Gas, too! • IRAM 30m program to observe 300 GASS galaxies • -CO J=10 observations as tracer of H2 • Detected to a limit of MH2/M*<3% • Plus a new COS program to probe halo gas! Saintonge et al. 2010

  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. Radial cuts along major axis • Adaptive binning on ~kpc scales • Detect SF to R90 in most Moran et al. 2010 • 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 radiusdepends on how galaxies grow (Inside-out? Outside-in?)

  8. Metallicity Gradients Zaritsky et al. 1994

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

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

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

  18. UGC8802 toy model

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

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

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

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

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

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

  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 Specific SFR Stellar mass density Mannucci et al 2010

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

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