Red Versus Blue Disks in Triaxial Dark Matter Halos (wrt the Milky - - PowerPoint PPT Presentation
Red Versus Blue Disks in Triaxial Dark Matter Halos (wrt the Milky Way) Victor P. Debattista Debattista et al. 2008 Valluri et al. 2010 Valluri et al. 2012 Valluri et at. 2013 Debattista et al. 2013 Debattista et al. 2015 Earp et al. 2017
Debattista et al. 2008 Valluri et al. 2010 Valluri et al. 2012 Valluri et at. 2013 Debattista et al. 2013 Debattista et al. 2015 Earp et al. 2017
Butsky+ 16 5% RVir 12% RVir
Wang+ 08 <NR(θ)> is the number of pairs with angle of the central galaxy randomised Conclusion: red centrals are aligned with their halos (as traced by satellites), blue galaxies are more randomly orientated. (Profoundly important to understanding if we want to use weak lensing to measuring the equation of state of dark energy, e.g. Kirk+ 12.)
Based on the location and velocities of stars in the Sagittarius stream, MW halo is triaxial with c/a = 0.72 and b/a = 0.99 (pot). Nearly oblate with intermediate axis perpendicular to plane of disk
Law & Majewski 10
Also Martinez-Delgado+04; Johnston+05; Helmi 04; Deg & Widrow 13
Briggs 90
Transform the ORIENTATION of a vector into a 2D cylindrical polar plot, with tilt angle represented as radius angle in (x,y) plane from x-axis represented as cylindrical angle ϕ The angles (θi,ϕi) specifying the orientation of the annulus are plotted in cylindrical coordinates as
Debattista+ 15
DM only No gas
Controlled experiments A rigid disk placed inside a triaxial halo with its spin axis along the halo’s intermediate axis. The disk mass is grown from 0 to MW mass; in the process the shape of the halo
equilibrium kinematics and released.
Controlled experiments A series dark matter + adiabatic gas mergers producing a triaxial halo with gas angular momentum along the intermediate axis. At that point gas cooling and star formation are switched on. Disk is not able to form or persist in an intermediate axis orientation. What modelling step fails? Assumption that the MW disk in one of the global symmetry planes of the halo is broken
Debattista+ 15
Discs in short axis vs long axis orientations High mass disc + 2% satellite No gas
Tilt angle In the absence of gas, the only stable disk
minor axis of the halo
8 Gyr evo.
Mass evo. Torque from DM Stellar L evo. In the presence of cooling gas, the spin of the cooling gas determines the orientation
Simulations find that the angular momentum axis of the corona evolves with time (e.g. Roškar+ 10)
The evolution of gas angular momentum is driven by hydrodynamic forces, not by the torque from the triaxial halo The inner corona and cool disk gas are misaligned throughout
Roškar+ 10
The tilting rate of most of the MW- like galaxies in this cosmological volume are > 0.28° Gyr-1 = Gaia detection limit (Perryman+ 14)
Earp+ 17
Sample A: MW mass galaxies Subsample B: MW mass and no mergers or large interactions Drawn from a cosmological zoom simulation of a volume 25 × 25 × 25 Mpc3
Tilting does not appear to correlate strongly with distance to largest similar mass galaxy or to tilting rate
Earp+ 17
Sample A: MW mass galaxies Subsample B: MW mass and no mergers or large interactions
Hints that the tilting rate is larger as the sSFR increases but secondary effects too
Earp+ in progress
for the MW by Law & Majewski 2010) is NEVER stable.
perpendicular to the short axis. Satellites help discs reach this lowest- energy orientation.
stronger driver than the halo torques on the orientation of the disc. This delivery of gas is the driving mechanism for the difference between the intrinsic alignments of red versus blue galaxies. Direct tidal torques do not dominate the orientation of disks.
the stellar disk. It should therefore be tilting.
6.3 deg/Gyr. The Gaia detection limit is 0.28 deg/Gyr The tilting rate is correlated with misalignment between disk and coronal spins.