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Victor P. Debattista Secular Evolution in Disc Galaxies
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… into bulge+disc to test for secular evolution of classical bulges and how this affects the M BH - σ e relation … in the vertical direction to understand the thin/thick disc dichotomy in the Milky Way Deconstructing Galaxies…
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Classical vs Pseudo Bulges CLASSICAL BULGES: Mergers produce elliptical galaxies. In the early universe, disks formed around dwarf ellipticals. Predict: old stars, low rotation, short SF timescales, ellipsoidal morphology, de Vaucouleurs type profiles (Sersic index ~ 4) PSEUDO BULGES: Gas funnelled to the centre by disk processes, forming new stars and central mass concentration Predict: younger stars, high rotation, long SF timescales, disky or boxy morphology, exponential type profile (Sersic index ~ 1)
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Drory & Fisher 2007; Fisher & Drory 2008, 2010
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Schawinski+ 2012 Schawinski+ 2011 The Evolving View of AGN Hosts A sample of 140 X-ray selected AGN showed distortions (“mergers”) were no more likely to be ongoing than in a control sample Cisternas+ 2011
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Semi-analytic models suggest that AGN in discs dominate the AGN luminosity for low mass Hopkins+ 13
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The growth of a disk compresses a pre-existing (classical) bulge raising its velocity dispersion No disc 5x M b 10x M b 15x M b 20x M b Zero mass disc (for scale) 20x M b
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Fitting function following Wolf et al. 2010: The parameters ( ϒ,δ) account for the finite-thickness and assumption of fixed effective radius
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Data: Gadotti & Kauffmann 2009 Ellipticals Bulges R eff σ8σ8 EllipticalsBulges σ8σ8 Mass
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Data: Gadotti & Kauffmann 2009 Bulges Bulges uncompressed Ellipticals
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Exponential Disks? Boeker+ 2003 Dutton 2009
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D/B and Rd/Re correlate weakly with σ e. Neglecting this correlation, the M - σ e relation of SMBHs which start out on the relation but fail to grow with this disc is given by: log M = α – β log + β log σ e σ8σ8 R d /R eff D/B
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Gültekin+ 2009 Doubling σ requires that M grow by a factor of 16 Gadotti 09
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Ellipticals No offset between bulges now and ellipticals Bulges Expected offset if SMBHs do not grow while discs reform is δα = -0.2 dex Gültekin+ 2009 sample δα = 0.08
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Ellipticals Bulges Predicted initial dispersions Expected offset if SMBHs do not grow while discs reform is δα = -0.26 dex Beifiori+ 2009 sample Also no offset between bulges now and ellipticals δα = 0.11
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Barred Galaxies But Beifiori et al. 2012 find no offset between barred and unbarred galaxies Graham 08 Graham+ 11
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Bar driven angular momentum redistribution increases the disc mass at the centre, raising σ e and causing an offset for the SMBH Hartmann+ 14 All B+D simulations are models of the MW from Widrow+ 08
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Classical bulges δα = -0.19 ± 0.20 Hartmann+ 14 Pseudo bulges δα = -0.73 ± 0.09 Sample of McConnell & Ma 13 10 other galaxies with no reliable bulge classification
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Sellwood & Binney 2002 But negligible heating associated with the migration FullNear circular ∆L L Radius RR J R = ( p - ) L/ E = p L
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R form Roškar+ 08 Schoenrich & Binney 09ab Gilmore & Reid 1983
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Ro š kar+13 Predictions from Schönrich & Binney 12 Plotted for stars 5-6 Gyr old Solway+ 2012 Thick disk Thin disk Accretion: Abadi+03; thickening: Quinn+93; gas rich mergers: Brook+05; direct gas formation: Stinson+13; Bird+13; clump heating: Bournaud+07; resonant capture: Sridhar+96
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Migration can give rise to a thick disc with density, kinematic, metallicity and abundance patterns not inconsistent with the observed Loebman+ 11 Roškar+ 13 Ruchti+ 11
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Decreasing metallicity and v rot with height SDSS at Thin-Thick Transition z [pc] |z| [kpc] V Y [km/s] Photometric [Fe/H] [Fe/H] Data from SDSS Ivezic+ 08; Bond+ 10
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V y [km/s] [Fe/H] Age [Gyr] z [kpc] Age, velocity and metallicity all correlate with height above the mid-plane. But there is little correlation between velocity and metallicity, as found by SDSS
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Stars are born on circular orbits and hence have no correlation between V and [Fe/H]. Heating brings stars into the local volume creating a correlation. Migration shuffles [Fe/H] and erases the correlation Solar nbhd Loebman+ 11 [Fe/H] R [kpc]
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all youngold Geneva-Copenhagen Survey in mid- plane after selecting non- binary stars (Qualitatively similar results with Casagrande+ 11 ages) ΔV/Δ[Fe/H] = -0.5 ± 1.5 ΔV/Δ[Fe/H] = -1.9 ± 1.6 ΔV/Δ[Fe/H] = 22.1 ± 0.8 Loebman+ 11
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Bovy+ 2012abc Liu & van de Ven 2012 Sales+ 2009 Dierickx+ 10, Wilson+ 11
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Discs growing around pre-existing bulges compress them and raise their velocity dispersion. This implies SMBHs in classical bulges must grow on average by 50-80% to remain on the M BH - σ e relation. A comparison between the M BH - σ e relations of elliptical galaxies and classical bulges finds no offset. Bar evolution also compresses the bulge, and there is evidence that barred galaxies are offset from the M BH - σ e relation. The thick disc in the MW may have been substantially contaminated by migrated thin disc stars. A thin/thick disc dichotomy can easily arise as a result of migration. Some evidence for an unmigrated population can be recovered from the distribution of orbital eccentricities. Conclusions
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