Dark Matter Candidates: Dark Matter Candidates: ParticlesParticles

WIMPs, particularly WIMPs, particularly LSPsLSPs: mass : mass >GeV>GeV.. NeutralinosNeutralinos: New parity associated with : New parity associated with

supersymmetry (a way for fermionssupersymmetry (a way for fermionsbosons).bosons). AxionsAxions: Invented to explain why weak force : Invented to explain why weak force

violates CP, but strong force does not.violates CP, but strong force does not. 1010-6-6<m<maxax<10<10-3-3eVeV: Upper limit from SN1987A : Upper limit from SN1987A

cooling; lower from BBN.cooling; lower from BBN. Currently neutralinos and axions are best Currently neutralinos and axions are best

candidates for dark matter; neither has been candidates for dark matter; neither has been detected or is predicted in Standard Model.detected or is predicted in Standard Model.

Dark Matter Dark Matter DetectionDetection

To detect, To detect, generally generally look for look for signatures signatures of Earth of Earth moving moving through through DM fluid DM fluid (seasonal).(seasonal).

Really Cold and Really Cold and Collisionless?Collisionless? 2 problems with CDM halos: Too 2 problems with CDM halos: Too

cuspy, too much substructure.cuspy, too much substructure. Dark matter not cold?Dark matter not cold? Self-interacting (Spergel & Stein-Self-interacting (Spergel & Stein-

hardt): Must avoid core collapse!hardt): Must avoid core collapse! Fuzzy: 10Fuzzy: 10-22-22eV Bose condensate.eV Bose condensate. Decaying: ~½ of DM decays into Decaying: ~½ of DM decays into

relativistic particles.relativistic particles. Disappearing: Goes into 5Disappearing: Goes into 5thth

dimension via brane.dimension via brane. Fluid: Scalar field with quartic Fluid: Scalar field with quartic

potential yields “pressure”.potential yields “pressure”. Probably forgotten some…Probably forgotten some…

Modified Newtonian Dynamics Modified Newtonian Dynamics (MOND)(MOND)

MOND proposes MOND proposes that on large that on large scales, scales, F=(GMa0)F=(GMa0)1/21/2/r./r.

Can fit RCs of Can fit RCs of galaxies galaxies extremely well.extremely well.

Can almost fit Can almost fit CMB: 3CMB: 3rdrd peak is peak is key.key.

Runs into trouble Runs into trouble in clusters and Ly-in clusters and Ly- forest. forest.

MOND+baryonic MOND+baryonic DM? Hmm…DM? Hmm…

Aguirre et al 2001

Bullet Cluster: Bullet Cluster: Dark Matter is Dark Matter is CollisionlessCollisionless

Interacting cluster Interacting cluster lensing+X-rays shows lensing+X-rays shows that mass doesn’t that mass doesn’t trace baryons.trace baryons.

Exactly as predicted Exactly as predicted by CDM: Dark matter by CDM: Dark matter passes thru, gas is passes thru, gas is shocked.shocked.

Difficult with baryonic Difficult with baryonic DM because high DM because high velocities would velocities would destroy cold, unseen destroy cold, unseen baryons.baryons.

Clowe et al 2006

Galaxy Galaxy MergersMergers

Orders of magnitudeOrders of magnitude

2x102x1012 12 MM galaxies colliding @ 300 galaxies colliding @ 300 km/s km/s 10 105353 J (~10 J (~108-98-9 SNe, ~binding energy). SNe, ~binding energy).

Power (assuming 1Gyr time): 10Power (assuming 1Gyr time): 1037 37 W (1 SN)W (1 SN) Stellar collisions VERY rare: Near center, Stellar collisions VERY rare: Near center,

~1000 stars/ly~1000 stars/ly22 collision prob ~ 10 collision prob ~ 10-11-11.. OTOH, ISM filling fraction is high, so OTOH, ISM filling fraction is high, so

molecular cloud collisions common, and molecular cloud collisions common, and highly supersonic (T~100K, v~300 km/s highly supersonic (T~100K, v~300 km/s MM~300). Coronal gas has T~10~300). Coronal gas has T~1066, so , so MM~1.~1.

Hence old stellar population reconfigures, Hence old stellar population reconfigures, but new stars may be formed via but new stars may be formed via collisionalcollisional processes.processes.

Early N-body Early N-body merger merger

simulationssimulations Holmberg 1941: 74 light Holmberg 1941: 74 light

bulbs and a lot of patience.bulbs and a lot of patience. Toomre & Toomre 1972: Toomre & Toomre 1972:

Mergers cause tidal features.Mergers cause tidal features. Barnes & Hernquist 1991: Barnes & Hernquist 1991:

Remnants look like ellipticals, Remnants look like ellipticals, with kinematic features.with kinematic features.

Holmberg 1941

Toomre & Toomre 1972

Mergers fuel Mergers fuel starbursts & starbursts & transform transform

morphologiesmorphologies Mihos & Hernquist 1996: Mihos & Hernquist 1996:

Included SF (Schmidt Included SF (Schmidt Law) in hydro sims.Law) in hydro sims.

Gas gets driven into Gas gets driven into central regions owing to central regions owing to dynamical instabilities, dynamical instabilities, fuels starburst.fuels starburst.

Remnant looks Remnant looks something like an something like an elliptical.elliptical.

Merger Trees & Semi-analytic Merger Trees & Semi-analytic modelsmodels

CDM is a “bottom-up” CDM is a “bottom-up” structure formation structure formation model.model.

Dark matter has no Dark matter has no known pressure; it known pressure; it collapses immediately collapses immediately into small units (size into small units (size unknown).unknown).

Units merge thru Units merge thru gravitational instability.gravitational instability.

Semi-analytic models Semi-analytic models (SAMs): Merger tree + (SAMs): Merger tree + MMW disks + heuristic MMW disks + heuristic algorithm for how algorithm for how mergers affect galaxies.mergers affect galaxies.

Wechsler et al 2001

Ellipticals: Nature vs. Ellipticals: Nature vs. NurtureNurture

Can ellipticals form Can ellipticals form mostly from low-spin mostly from low-spin halos?halos?

No! Not enough.No! Not enough. But not totally clear But not totally clear

that mergers alone that mergers alone can explain it either…can explain it either…

In simulations, gas In simulations, gas reaccretes, E’s reaccretes, E’s S’s! S’s!

Not only must merge Not only must merge spirals, but also spirals, but also prevent reaccretion.prevent reaccretion.

Spiral Galaxy FormationSpiral Galaxy Formation

Kinematics of merger Kinematics of merger remnantsremnants

Can mergers reproduce Can mergers reproduce E isophotes?E isophotes?

Large E’s boxy, small Large E’s boxy, small E’s disky (Davies et al E’s disky (Davies et al 83).83).

Naab etal: Put in Naab etal: Put in merger tree, try to merger tree, try to reproduce fraction of reproduce fraction of anisotropic (non-rot) E’s.anisotropic (non-rot) E’s.

Spiral-spiral mergers Spiral-spiral mergers alone can’t do it!alone can’t do it!

Need E-E/E-S mergers…Need E-E/E-S mergers… alsoalso needs gas supply needs gas supply

shut-off above some Mshut-off above some M**..

boxy disky

Rotation-supported

Pressure-supported

Naab, Kochfar, Burkert 06

Dry MergersDry Mergers If halos merge late, but stars If halos merge late, but stars

are old are old dry mergersdry mergers!! Do dry mergers preserve Do dry mergers preserve

tight E properties?tight E properties? Fundamental plane: Fundamental plane: RRaa I I-b-b.. Red sequence: Tilted!Red sequence: Tilted!

Clusters & Galaxy HarassmentClusters & Galaxy Harassment In clusters, In clusters, clcl »» galgal

Direct collisions rare!Direct collisions rare! But morphologies still But morphologies still

altered due to altered due to harassmentharassment: Tidal : Tidal disturbance from close disturbance from close passage.passage.

Can help explain why Can help explain why clusters have ~no spirals.clusters have ~no spirals.

Moore, Katz, Lake 1997

Spiral + Spiral = SpiralSpiral + Spiral = Spiral If initial systems is gas rich enough, then gas If initial systems is gas rich enough, then gas

flung to large radii can reaccrete into a flung to large radii can reaccrete into a spiral.spiral.

So gas fraction is another parameter in So gas fraction is another parameter in morphological transformations.morphological transformations.

To produce late-type galaxies today, need to To produce late-type galaxies today, need to prevent growth of bulge prevent growth of bulge AGN? AGN?

Robertson et al 2006

Mergers Mergers AGN? AGN? diMatteo, Springel, diMatteo, Springel,

Hernquist: Assume Hernquist: Assume some fraction of inflow some fraction of inflow at resolution limit (~100 at resolution limit (~100 pc) reaches central BH.pc) reaches central BH.

Add feedback energy, Add feedback energy, grow BH.grow BH.

Significantly suppresses Significantly suppresses post-merger SF.post-merger SF.

Get red sequence, MBH-Get red sequence, MBH-s relation, etc.s relation, etc.

Realistic? Realistic? Springel, di Matteo, Hernquist 2005