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Chemo-Dynamical Structure of ETG Halos

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Chemo-dynamical Structure of ETG Halos Jacob Arnold UC Santa Cruz 2012 Jean Brodie Avishai Dekel Aaron Romanowsky Joel Primack Duncan Forbes Daniel Ceverino Loren Hoffman Dylan Tweed Chris Moody Andi Burkert Duncan Forbes Inside-Out / Two-Phase Galaxy Formation z = 2 z = 0 • ETG half-light radius grows by a factor of a few between z = 2 and today. e.g., Daddi+2005, van Dokkum+2008, ... VL1: Diemand, Kuhlen, Madau Image: Daddi+2005 Growth of Stellar Halos Halo Observables: metallicity ? substructure 1st Phase angular momentum … 2nd : Accretion Phase! aka “the trash pile”" Observations:! Present day galaxies have more extended stellar halos than z=2 galaxies. Theory:! A significant fraction of this material is accreted. Bezanson+2009 after Oser+2010 Angular Momentum at < 1 Re = specific angular momentum with 1 Re Atlas3D NGC 3377 3:1 Merger ? Fast Slow Bois+2011 Emsellem+2004 Emsellem+2011 •! 86 % of sampled ETGs are “fast rotators” with well-aligned photometric/kinematic axes •! Consistent with being oblate axisymmetric major-merger remnants The Bigger Picture 1st Phase 2nd : Accretion Phase! •! Most of what we know about L* ETG kinematics is restricted to either < 1 Re, or along the major/minor-axes. •! These data are telling us more about the 1st phase of growth (and very recent events) •! To study the 2nd accretionary phase, we need to extend our kinematic studies to the halo SKiMS (Stellar Kinematics from Multiple Slits) 16 ‘ •! We use the wide-field capabilities of the Sky Slits Keck/DEIMOS spectrograph to obtain 5 ‘ 5 stellar spectra at 3 – 5 Re. SKiMS Sky Slits •! Multiple pointings achieve sparse, but well sampled two-dimensional coverage of a galaxy. •! Extract line-of-sight-velocity distributions from the NIR CaT absorption features •! Kinematic measurements (V,σ,h3,h4) provide clues to the internal dynamical structure and assembly history The Big Picture Revealed NGC 3377! Fast rotation at < 1 Re Slow rotation at > 2 Re R / Re 4 110 [km/s] 3:1 Merger Y / Re 2 2 0 eff 0 0 R -2 −2 −110 −4 -4 -2 0 2 4 −6 −4 −20 2 4 6 X / Re Reff Loren Hoffman The Big Picture Revealed V " # " −110/110 40/150 h3" h4" 2 0 -2 −0.15/0.15 −0.15/0.15 -4 -2 0 2 4 X/ R e Wide-Field Kinematics for 17 ETGs kpc −20 −10 0 10 20 10 0 kpc −10 NGC 821 NGC 1023 NGC 1400 NGC 1407 NGC 2768 NGC 2974 NGC 3115 NGC 3377 NGC 4278 NGC 4365 NGC 4473 NGC 4486 10 0 kpc −10 NGC 4494 NGC 4526 NGC 4649 NGC 5846 NGC 7457 −20 −10 0 10 20 kpc Stellar kinematics on 3 – 5 Re for a representative sample of galaxies. Morphology ranges from small S0s to massive BCGs Velocity Maps 2 e 0 Y/R -2 -2 0 2 X/Re SAURON/Atlas3DSKiMS Angular momentum of the stellar halo after Proctor+2009 Stellar angular momentum within Classic results depend on the adopted spatial scale. 1 Re is a poor predictor of stellar angular momentum at 3 Re. Next Steps: Restrict study to ~ edge-on galaxies for simplicity Obtain kinematics at even larger radius Getting to 6 – 10 Re ~1 Re : SAURON IFU + Long-slit 3 – 5 Re : DEIMOS SKiMS 6 –10 Re : Globular Clusters & Planetary Nebulae SLUGGS.ucolick.org Literature Data: Halliday et al. 2001 Emsellem et al. 2004 Peng et al. 2004 Noordermeer et al. 2008 Coccato et al. 2009 Proctor et al. 2009 Woodley et al. 2010 Arnold et al. 2011 Pota et al. 2012 Christina Blom Examples Scale:" 1 Re" 3 Re" 7 Re" 4 4 2 2 eff 0 0 R −2 -2 −4 -4 -6−6 -4−4 -2−20 0 2 44 6 Reff X / Re Fast rotator designation only 4 applies to inner bulge. 2 0 -2 -4 -6 -4 -2 0 2 4 6 X / Re Coccato+2009, Emsellem+2004, Proctor+2009,Arnold+2011 Two-Zone Kinematics 4 4 NGC 2768 NGC 1023 NGC 3115 2 2 e eff 0 eff 0 R R Y / R / Y −2 −2 −4 −4 4 −6 −4 −20 2 4 6 4 −6 −4 −20 2 4 6 R eff NGC 3377 R eff NGC 4564 2 2 e eff 0 eff 0 R R Y / R / Y −2 −2 NGC 821 1 −4 −4 −6 −4 −20 2 4 6 −6 −4 −20 2 4 6 Reff Reff X / Re X / Re 0 -1 Edge-on Sample -2-10 1 2 • All show aligned but declining rotation X / Re • Size of inner “fast rotator” is variable Major-Mergers (3:1 – 10:1) ? Sample of 8 near to edge-on galaxies Representative major-merger remnants All show an outer decline in v/σ All show rising to flat v/σ profiles Bournaud et al. 2005 Bendo & Barnes 2000 Creon et al. 2001 Loren Hoffman The generic major-merger prediction is for flat or rising v/σ profiles resulting from residual progenitor disk spin and the conversion of orbital into internal angular momentum (Hernquist 1992, Bendo & Barnes 2000, Cretton et al. 2001, etc.) 1:1 Mergers? Simulated 1:1 major-merger Hoffman+2010 5 Decoupled inner/outer components through low-angular-momentum, gas-rich, 1:1 major-mergers. +1.0 [kpc] 0 Y +0.5 Frequently accompanied-5 by KDCs or kinematic twists. 0.0 V/σ e NGC 4365 5 -0.5 [kpc] 0 Y -1.0 -5 -10-5005510 -10 -5 10 X [kpc] X [kpc] Explains a few specific examples, but probably not the general phenomenon of falling V/σ Two-zone Kinematics 4 Cosmological Simulations Daniel Ceverino, Avishai Dekel 2 eff In-situ, inner, rotating bulge the result of an R 0 unstable disk (VDI) fed by cold flows. −2 −4 Numerous accretion events help build the slowly rotating outer spheroid −6 −4 −202 46 Vitvitska+2002, Abadi+06 R eff 1.0 e 1st Phase σ 0.5 V / 2nd : Accretion Phase! 0 Two-phase formation naturally produces two-zone kinematics. Chemical Structure of ETG Halos Searle & Zinn 1978 Key result: halo built via accretion exhibits a flattened metallicity gradient Wide-field imaging/spectroscopy is now Harris 2001 revealing this behavior in ETGs. (Harris 2009, Alves-Brito+2009, Strader+2011, Coccato+2010, Arnold+2011) Flat GC metallicity gradient beyond ~7 Re NGC 1407: Forbes et al. 2011 Summary Major-MergerMajor-Merger ObservationsObservations CosmologicalCosmological +1.0 3 +0.5 e 0 0.0 V/σe Y/R -0.5 -3 -1.0 -6 -3 0 3 6 -6 -3 0 3 6 -6 -3 0 3 6 X/Re X/Re X/Re Two-Zone Kinematics: Our sample of 8 edge-on galaxies all exhibit slowly rotating halos ( > 2 – 5 Re ) Two-phase assembly produces this kinematic structure via the accretion and subsequent disruption of infalling satellites. Our comparisons with simulated galaxies highlight the importance of including a cosmological accretion history in simulating realistic ETGs Major-merger: Burkert, Cosmological: Dekel+ .
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