Group items tagged

Hezaveh et al simulate ALMA cycle 1 (ie 0.16" resolution) observations of Herschel/SPT sub mm lensed galaxies, and claim that the magnification is high enough, and the sources likely to be complex enough, to enable the detection of at least one DM subhalo of mass 10^8 or greater *in every system*

"We extrapolate a dark matter (DM) density in the solar neighborhood of 0+-1 mM_sun pc^-3, and all the current models of a spherical DM halo are excluded at a confidence level higher than 4sigma."

Deason et al have an improved measurement of density and velocities of blue horizontal branch stars in the MW halo: here they fit dynamical models an infer a halo of about 1e12 Msun (as before) and quite a high concentration (cvir~20). Since concentration reflects age, this is consistent with the picture in which the MW has been undisturbed for a long time.

Combining galaxy distribution / clustering measurements with weak lensing shear measurements is a hot topic at the moment and this is the latest attempt to use both to reconstruct the COSMOS density field.

An explanation of the anomalously low measurement of the local dark matter density that we discussed a few weeks ago?

The first detection of a filament.

Very nice. I'm a little surprised that it's the first detection - I swear some people working on this a few years ago. But maybe their detection wasn't significant enough. At least, they didn't get a Nature paper out of it!

Purcell and Zentner on why the "Too Big To Fail" problem might be a storm in a teacup: "We propose that the large variation in subhalo populations among different host halos can explain the dearth of large, dense subhalos orbiting the Milky Way without any making any adjustments to the host halo mass or accounting for baryonic feedback processes."

Using N-body simulation, the authors showed that velocity-dependent self-interacting dark matter gives the inner circular velocity profiles of the most massive subhalos that are compatible with the data of the brightest Milky Way dSphs.

Boylan-Kolchin et al identify a new problem with CDM at sub-galactic scales: the Aquarius simulated MW galaxy halos have subhalos that are about 5 times more massive than the actual dwarf satellites we see. Are we underestimating the MW satellites' masses somehow? Or is their something wrong with the simulations? Or both? Anyway, as Phil B said: add it to the list of things to investigate about CDM :-)

The observational counterpart? http://arxiv.org/abs/1111.2611

Interesting: Strigari & Wechsler prefer to state the problem as the sims predicting 25-75 times as many subhalos at the Fornax mass scale as are observed in the MW system - and in the paper you posted they look at thousands of MW analogs in the SDSS survey and find that the MW is not atypical. This strengthens MBK's conclusion, that there is a problem with CDM - although note that S&W put the emphasis on galaxy formation not being well understood at this mass scale. They imagine that there really are all those dark Fornaxes out there! Pretty cool - now, if we could just see them somehow...

There's been quite a bit of discussion about this issue this summer, it came up at the Bologna dark matter meeting as well as the Aosta strong lensing workshop. Basically, in strong lens systems we infer *more* subhalos/satellites than CDM predicts for massive lens galaxies (the satellites cause "millilensing", where the quasar/radio source image fluxes are affected by the small amounts of additional magnification and demagnification). One suggested resolution to this problem is to include all the subhalos along the line of sight - Metcalf (2008) claimed this was the answer, and now Dan Dan Xu has tested this claim using the Millenium Simulation, and various assumptions for the satellite subhalo density profile.