Linking Galaxies’ Gas Content to their Metallicity Gradients
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Linking Galaxies’ Gas Content to their Metallicity Gradients Sean Moran Johns Hopkins University & The GASS Team
description
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 10 - PowerPoint PPT Presentation
Transcript of Linking Galaxies’ Gas Content to their Metallicity Gradients
Linking Galaxies’ Gas Content to their
Metallicity Gradients
Sean MoranJohns Hopkins University
& The GASS Team
GASS: The GALEX Arecibo SDSS Survey
Catinella et al. 2010
•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%
Sampling both sidesof the red/blue divide!
The GASS Team• JHU:
Sean MoranTim Heckman
• MPA: Guinevere KauffmannBarbara CatinellaJing WangSilvia Fabello
• MPE:Amelie SaintongeJavier Gracia Carpio
Linda Tacconi
• Columbia:David Schiminovich (PI)
Cameron HummelsJenna LemoniasRonin Wu
• Cornell:Martha HaynesRiccardo Giovanelli
• Arizona:Romeel Dave
Plus many more!
Molecular Gas, too!
Saintonge et al. 2010
•IRAM 30m program to observe 300 GASS galaxies-CO J=10 observations as tracer of H2
- Detected to a limit of MH2/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. 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
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?)
Metallicity Gradients
Zaritsky et al. 1994
Metallicity Gradients
Moustakas et al 2010SINGS Galaxies
•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. 2011
UGC8802•High HI (fHI~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 Density Faster 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>R
90)
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 densitySpecific SFR
Tremonti et al. 2004
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, 2010Long flat gradients inindividual galaxiesMoustakas et al 2010
