Theoretical Perspectives Amr El-Zant Canadian Institute for Theoretical Astrophysics

Paradigms Lost Peebles (1980) intro lists (as possible sources of structure formation) ** Magnetohydrodynamic - Thermal – Plasma Instabilities + host of others ** Dead stars etc as probable forms of the dominant dark matter

LCDM CDM: largely a consequence of clustering and BBN results. It is also simple to deduce its consequences Cosmological constant: Supernovae and CMB. But CMB is degenerate! Consistent with Einstein de Sitter and low Hubble constant…

Galaxy and Halo Biasing as Cosmological Constant Probe Evolution of Galaxy-sized halo density as a function of CDM overdensity in an Einstein de Sitter universe (Dekel & Lahav 1999) Z = 0 Z = 1

Cosmological Tools: CDM Direct simulations Halo Model (Bertschinger, Peacock and others) - assumes collapsed structures distributed according to linear theory – produces power spectrum well (at least at z=0). Peak Patch (Bond & Myers) - follows peaks in initial density field with Zeldovich approximation (Lagrangian linear theory) + and ellipsoidal collapse

Correlation functions and the sizes of Collapsed Structures Dark matter cold  `everything’ is made of collapsed objects: haloes Smaller structures collapse first  high z most galaxies in one halo while at low z, galaxies tend to share larger halo Scale and strength of transition changes with time Angle in deg

Feedback and cooling flow suppression Gas dynamics simulations: generally fail to form proper galaxies (e.g. Disks too small) Semi analytic models: relatively successful  need proper treatment of feedback Problem similar to that in cluster cooling flows. Many solutions proposed, e.g.: i) Heating by AGN ii) Conduction (Zakamska & Narayan) iii) Heating from substructure and galaxy motions (El-Zant, Kim & Kamionkowski)

Bars Probes of epoch when undisturbed cold disks are in place: In CDM  this happens relatively late at z < ~1 (Mo, Mao & White) Shapes of dark matter haloes around galaxies:  Unmodified CDM haloes unsuitable for hosting long lived bars: El-Zant & Shlosman; Berentzen, Shlosman & Jojee

Bars in Cosmological Haloes

Bars  AGN’s Bars known to drive gas to central ~ 1kpc Mechanism driving gas to very centre still in dispute Useful observational diagnostic: correlations between AGN and bars  AGN’s without bars may indicate other mechanisms: e.g., interactions or triaxial haloes (El-Zant, Begelman & Frank)