Metallicity: A Smoking Gun for Gas Flows in Mergers Lisa Kewley U. Hawaii Margaret Geller (SAO), Betsy Barton (UC Irvine)

Summary Motivation Metallicity diagnostics Luminosity-Metallicity Relation Central Star Formation Blue Bulges Merger Models Conclusions & Future Work

Motivation Effect of mergers on metallicity? unknown Predicted gas flows? elusive Fe Si Mg Chandra X-ray spectra : Metallicity map of the hot ISM of the Antennae, where red, green, and blue indicate emission by Fe, Si, and Mg, respectively. The continuum was subtracted by estimating the contribution of the overall best-fit two-component thermal bremsstrahlung model in the two bands at 1.4–1.65 and 2.05–3.50 keV, where no strong lines are observed. Pointlike sources were excluded, following Fabbiano et al. (2003b). The Fe-L image was adaptively smoothed to a significance between 3 and 5 σ, and the same scales were applied to the other line images. Fabbiano et al. (2004)

Galaxy Pairs Field Galaxies 502 galaxies from the CfA redshift catalog (v > 2300 km/s, Dv < 1035 km/s, DD < 77 h-1 Mpc) (Barton et al. 2000) Nuclear spectra for ~200 galaxies in pairs Field Galaxies 198 galaxies from the CfA redshift catalog full range in Hubble type & Magnitudes in CfA survey (Jansen et al. 2000) http://cfa-www.harvard.edu/~jansen/nfgs/nfgssample.html In normal spiral galaxies, nuclear spectra can be corrected (albeit with some uncertainty) for aperture effects, if we know what HUbble type and luminosity a galaxy has, so that we can correct for metallicity gradients. However with galaxy pairs, we may run into a further complication: dynamical effects of tidally-driven gas flows. In the following slides we investigate this effect.

Metallicity Diagnostics “R23” Kewley & Dopita (2002, ApJS, 142, 35) Also: Pagel (1979), McCall et al. (1985), ..., Skillman et al. (1989), McGaugh (1991),..., Zaritsky et al. (1994), Charlot (2001), ...

Galaxy Pairs Luminosity-metallicity Relation 1. shifts for close pairs Although a few studies of individual galaxies using integral field or HI velocity maps show evidence for gas flows in merging galaxies, the effect on the metallicity gradient, and hence on the nuclear metallicities of galaxy pairs is To investigate the effect of possible dynamical Kewley, Geller, & Barton (2005, AJ, 131, 2004)

Luminosity Effect? Need 1-2 Mag rise Kewley, Geller, & Barton wwide pairs close pairs Need 1-2 Mag rise Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations. NFGS cz < 2300 km/s Kewley, Geller, & Barton (2006, AJ, 131, 2004)

Luminosity Effect? No shift in upper bound : MB Negative shift in wwide pairs No shift in upper bound : MB Negative shift in right bound: metallicity close pairs Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations. NFGS cz < 2300 km/s Kewley, Geller, & Barton (2006, AJ, 131, 2004)

Luminosity Effect? R-Band Luminosity-metallicity Relation 1. still shifts for close pairs Although a few studies of individual galaxies using integral field or HI velocity maps show evidence for gas flows in merging galaxies, the effect on the metallicity gradient, and hence on the nuclear metallicities of galaxy pairs is To investigate the effect of possible dynamical Kewley, Geller, & Barton (2006, AJ, 131, 2004)

Galaxy Pairs metallicity effect? gas infall? Luminosity-metallicity Relation 1. shifts for close pairs metallicity effect? gas infall? Although a few studies of individual galaxies using integral field or HI velocity maps show evidence for gas flows in merging galaxies, the effect on the metallicity gradient, and hence on the nuclear metallicities of galaxy pairs is To investigate the effect of possible dynamical Kewley, Geller, & Barton (2006, AJ, 131, 2004)

Central Burst Strength, SR(t) Barton, Geller & Kenyon (2003): Stellar population synthesis models + colors + EWs assuming 2 populations (old & young) SR(t) = current fraction of R-band light from young burst

Central Burst Strength Barton, Geller & Kenyon (2003)

Galaxy Pairs Luminosity-metallicity Relation 1. shifts for close pairs 2. correlated with central burst strength Kewley, Geller, & Barton (2006, AJ, 131, 2004)

Galaxy Pairs Luminosity-metallicity Relation 1. shifts for close pairs 2. correlated with central burst strength Kewley, Geller, & Barton (2006, AJ, 131, 2004)

Blue Bulges (B-R) = (B-R)outer - (B-R)inner where Kannappan et al. (2003): “blue bulge parameter” (B-R) = (B-R)outer - (B-R)inner where (B-R)outer = (B-R) at 75% light radius (B-R)inner = (B-R) at 1/2 light radius

Galaxy Pairs Luminosity-metallicity Relation 1. shifts for close pairs Blue Bulges Luminosity-metallicity Relation 1. shifts for close pairs 2. correlated with central burst strength 3. correlated with blue bulges Kewley, Geller, & Barton (2006, AJ, 131, 2004)

Metallicity Gradient Keck LRIS Spectroscopy Kewley, Geller, & Barton (2005, AJ, submitted)

Metallicity Gradient Keck LRIS Spectroscopy See also: Li Hsin Chien’s Poster Kewley, Geller, & Barton (2005, AJ, submitted)

Merger Scenario Images Courtesy Chris Mihos Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations. Images Courtesy Chris Mihos

Galaxy Pairs Luminosity-metallicity Relation 1. shifts for close pairs 2. correlated with central burst strength 3. correlated with blue bulges Evidence for Gas Infall Kewley, Geller, & Barton (2006, AJ, 131, 2004)

Metallicity Gradients Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations.

Metallicity Gradients Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations. Kennicutt, Bresolin & Garnett (2003)

Merger Scenario . Iono et al. (2004): Simulations predict: 1. Gas inflow rate ~ 7 Mo/yr 2. Gas flows within 1st 100 Myr but before disk merger . Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations.

Merger Scenario . Iono et al. (2004): Simulations predict: 1. Gas inflow rate ~ 7 Mo/yr 2. Gas flow within 100 Myr but before disk merger . Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations.

Merger Scenario . Assuming: How much infalling gas is required? 1. Gas inflow rate ~ 7 Mo/yr 2. Normal Spiral Metallicity gradient . How much infalling gas is required? Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations.

Merger Scenario . Assuming: How much central dilution is required? 1. Gas inflow rate ~ 7 Mo/yr 2. Normal Spiral Metallicity gradient . How much central dilution is required? 50-60% Merger models predict: 60% infall Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations.

Merger Scenario . Assuming: . How long will it take to infall? 1. Gas inflow rate ~ 7 Mo/yr 2. Normal Spiral Metallicity gradient 3. Central Gas Mass 108 - 109 Mo ave v. high . . How long will it take to infall? Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations.

Merger Scenario . Assuming: . How long will it take to infall? 1. Gas inflow rate ~ 7 Mo/yr 2. Normal Spiral Metallicity gradient 3. Central Gas Mass 108 - 109 Mo . . How long will it take to infall? 9x106 - 9x107 years Merger models predict: within 1x108 years Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations.

New Theoretical Models Josefa Perez et al. (2006, astro-ph/0605131) Chemical evolution model (Scannappieco et al. 2005) L-CDM model (GADGET-2; Springel & Hernquist 2003) Lower mean central (O/H) in pairs from inflows + Smoothed particle hydrodynamic simulations such as the one shown here predict that the tidal forces induce gravitational torques which remove angular momentum from the gas. The gravitational potential of the galaxy also becomes distorted which then affects the motions of the gas. The gas rapidly accumulates into the spiral arms of the galaxy, forming shocked, dense filaments. In a dissipative medium, these filiments allow rapid streaming of the gas down the spiral arms and into the nuclear region. Simulations predict that gas infall occurs at an average rate of 7 solar masses per year after the initial close pass, and that the infall continues until 100 Myr. If we calculate the amount of infall and timescale required to dilute the nuclear metallicities by ~0.2 dex, we require an infall timescale of 9-90 Myr, consistent with the merger simulations.

Conclusions Close galaxy pairs have lower than field central metallicities “Smoking gun” for gas infall during merger? Central metallicity correlates with: central burst strength blue bulges Timescale consistent with current merger simulations

Future Directions Keck LRIS spectra of matched pair members Merger simulations of metallicity gradients

Starburst99-Mappings On-Line L. Kewley & C. Leitherer Available Now! Starburst99-Mappings On-Line L. Kewley & C. Leitherer Starburst99-Mappings Interface: http://www.stsci.edu/science/starburst99/ Mappings Interface: http://www.ifa.hawaii.edu/~kewley/Mappings Pre-run model grids Interactive web form to run models

Motivation Effect of mergers on metallicity is unknown Si Mg Chandra X-ray spectra : Metallicity map of the hot ISM of the Antennae, where red, green, and blue indicate emission by Fe, Si, and Mg, respectively. The continuum was subtracted by estimating the contribution of the overall best-fit two-component thermal bremsstrahlung model in the two bands at 1.4–1.65 and 2.05–3.50 keV, where no strong lines are observed. Pointlike sources were excluded, following Fabbiano et al. (2003b). The Fe-L image was adaptively smoothed to a significance between 3 and 5 σ, and the same scales were applied to the other line images. Fabbiano et al. (2004)

Metallicity Diagnostic Comparisons Kewley & Ellison (2005)

Metallicity: Strong lines vs Auroral Lines Garnett, Kennicutt, Bresolin

Classification Scheme

Galaxy Pairs Luminosity-metallicity Relation 1. shifts for close pairs 1’ Luminosity-metallicity Relation 1. shifts for close pairs 2. correlated with central burst strength 3. correlated with blue bulges Evidence for Gas Infall Kewley, Geller, & Barton (2005, AJ, submitted)

GOODS Survey: 0.3 < z< 1 Kobulnicky & Kewley (2004, ApJ, 617,240)

Metallicity - [NII]/Ha Pettini & Pagel (2004)

Metallicity Diagnostics 1. Theoretical - photoionization models e.g., McGaugh (1991), Kewley & Dopita (2002), Tremonti et al. (2004) 2. Empirical - fit to Te metallicities e.g., Pilyugin (2000), Pettini & Pagel (2004) Combination - fit to Te method + theoretical metallicities e.g., Denicolo, Terlevich & Terlevich (2002)

Metallicity - [OIII]/Hb,[NII]/Ha Pettini & Pagel (2004)

Metallicity Diagnostic Comparisons Kewley & Ellison (2005, in prep)

Metallicity: Strong lines vs Auroral Lines Garnett, Kennicutt, Bresolin

GOODS Survey: 0.3 < z< 1 Kobulnicky & Kewley (2004, ApJ, 617, 240)

Auroral Line Saturation Stasinska (2002,2005)