Group items tagged

From N-body simulation, the authors find that concentration-mass relation displays a turnover for group scale dark matter haloes, for the case of WDM particles with masses of the order ~0.25 keV. This may be interpreted as a hint for top-down structure formation on small scales. Is there any reionization mechanism in this scenario?

1)Because the size of the simulated boxes were ten times smaller in previous studies. 2)Weak lensing at scale below ~1arcsec could work. Their results might be helpful for estimating non-linear power spectrum based on a certain halo model.

Cooool. Was Malin there this morning? This could be right up her street, with her flexion stuff! Also, weak lensing at < 1" sounds a bit like strong lensing to me - I'll read the paper in detail and see if there's anything we can already say from our (admittedly modest) SDSS samples. Thanks!

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."

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

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.

Axions are ultra-light particles that arise in string theory, and could make up some part of the dark matter in the universe. If so, what are the prospects for detecting their effects with galaxy surveys/CMB/weak lensing with future experiments? Come and ask the authors.

Pontzen and I were sitting there reckoning axions look a lot like hot dark matter - but I guess there must be some key difference at large angular scales to enable Dodi et al to distinguish between massive neutrinos and axions in a Planck+Euclid combo. Pretty cool :-)

Suyu et al combine strong gravitational lensing and stellar kinematics data for a spiral galaxy to measure the mass of both the disk and the dark matter halo. The constraints are very strong - they find an oblate, flattened halo, and get a disk stellar mass with small uncertainty (0.1dex); when they compare this with the stellar mass from the disk colours and K-band magnitude they find that stellar population models with Chabrier IMF work, and Salpeter does not - the opposite to the case of massive elliptical galaxies.

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!

A star with a mid-IR excess (circumstellar disk?) that vanishes in a 2-year interval.

Andy Lawrence suggests that the unaccounted for UV flux in AGN spectra could be coming from "clouds" of gas orbiting the black hole at ~10 Schwarzschild radii, and reflecting light as UV line emission which all gets blurred together to make a broad continuum due to the insane speeds involved.

I saw Andy yesterday at the Edinburgh sims workshop - he agreed that his clouds were probably shreds, but all that really matters is the filling factor and ionisation state, and the code he used to play around with it all is called "cloudy"... I told him we found the model pretty plausible (stuff comes off accretion disks and stays in orbit, absorbing and emitting, fine), his hope is that someone makes a more detailed model, checks his results and does some inference. That'll be Lance then...

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.