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

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

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!

Molecular Gas, too! Saintonge et al 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!

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)

Moran et al 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

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?)

Metallicity Gradients Zaritsky et al. 1994

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

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

GASS Metallicities Pettini & Pagel (2004) O3N2 indicator

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

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

Sings galaxies w/ gradients

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

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

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

UGC8802 toy model

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

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

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?

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”?

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

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

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

Big metal-drop galaxies

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!

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

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