Why Warps ?… Accretion, Recycling, Stimulation ? NGC 3344 Sancisi 1976

Why Warps ?… Accretion, Recycling, Stimulation ? NGC 3344 Sancisi 1976

Warped disks… NGC 3344 Sky plane

Isolated, face-on, L*, Sc NGC 628 = M74 Kamphuis & Briggs 1992

NGC 628 = M74 Kamphuis & Briggs 1992 Ring Analysis Lopsided Lumpy

NGC 628 = M74 Kamphuis & Briggs 1992 Model Velocity Field Edge-on View

in flattened potential NGC 628 = M74 Kamphuis & Briggs 1992 Perpendicular to inner disk plane Perspective View Line of Nodes regresses in flattened potential !

Which ones ? Large Relatively isolated Kim, de Blok, Briggs

in flattened potential Times Scales: Orbital Times -> 1Gyr carries imprint/memory of formation/accretion Differential Precession (Differential Rotation) Angular momentum: “Corotation” ! Line of Nodes regresses in flattened potential

Mechanisms: “Primordial Rain” (Binney ~2000) from Random Directions… “Cold Mode Accretion” (Kereš et al. 2005, 2009) streams… Recirculation/re-accretion galaxy-galaxy interactions

“Cold” gas only Cold Mode of Gas Accretion Kereš et al. 2005, 2009 Simulation Cold Mode of Gas Accretion m_p ~106 M⊙, resolution ~500pc (at z=2) “Cold” gas only

Accretion rate vs Redshift Kereš et al. 2009 from Simulations Accretion rate vs Redshift Cold

NGC 1512 NGC 1510

Relatively small perturbers spray gas into orbits that remember NGC 1512 Relatively small perturbers spray gas into orbits that remember angular momentum of interaction… (doesn’t look like smooth warp)

Mechanisms: “Cold Mode Accretion” Recirculation/re-accretion M83 (Miller et al 2009) “Cold Mode Accretion” Recirculation/re-accretion … need to measure metalicity of gas… absorption lines against background AGN HII regions in faint star forming lumps