The physics of baryons and dark matter interactions


1. Radial DM Profiles

I would suggest also considering the question: can baryonic and DM slopes be separately constrained from observations of galaxy lenses alone? There are interesting papers claiming they can (Dye & Warren 2005) although opinions seem to differ on how unique the constraint is. One could also make the following argument: the SLACS lenses imply an overall mass slope of 2 with small dispersion (Koopmans et al. 2006). However, lenses with a measured time delay give small values of H0 (Kochanek 2002) or, doing it the other way round, if you assume a H0 of 72+/-8 you get a slope steeper than 2, 2 being ruled out at the 3-sigma confidence level (Dobke & King, astro-ph 0609293). There are five possibilities, the first two of which are dull:
(i) We are seeing a nearly-3-sigma event
(ii) Some of the errors are too small
(iii) H0 is <=60
(iv) The SLACS lenses are systematically closer to isothermal than others, perhaps by the selection of luminous lens galaxies
(v) The fact that mass slopes in time-delay lenses are calculated from the radii of the inner and outer lens images, whereas the SLACS slopes are from the einstein radius to reff, is telling us that there is a turnover in mass slope and we are seeing the transition from a dark matter to a baryonic slope (although this may end up the wrong way round)....
(Thanks to Leon for pointing out (v)!)

[Neal Jackson].

I think (i) and (ii) mostly explain. The result of Kochanek (2002) paper was from a small sample of lenses and did not include eg HE0435 which have a high H0 value (for isothermal). Dobke&King paper did underestimate the error baecause all the complexity of lenses including ellipticity/shear was ignored. Another possible explanation is the selection effect; lensed quasars may preferentially select concentrated (ie steep slope) galaxies that have larger lensing cross sectiosn...(I guess SLACS has quite different selection function from that of traditional quasar lenses) [Masamune Oguri]

a) Cusps?

b) Outer Behavior

c) Super-Massive BH's

2. Baryonic Physics

a) How Do Baryons's Settle?

b) How Do Baryons Affect the DM Distribution

c) Probing the mass function N(M); low mass end and high mass end