Various things are broken

So, things are working ...sortof.  And sortof not.  Item 1: I ran hpick and got a bunch of halos, but either hpick had a bug in it, or I introduced a bug when I attempted to print out only halos with >1000 particles, or the parent.find file is corrupt and missing halos.  Here is the evidence:

If you recall my plot from before, the pn simulation did not have gaps in the hids, so this seems to be wrong.  Unless halopick kept hn instead of new_hn, that is also possible, but I am pretty sure not.

Nonetheless, because I was in the mood to pretend to do science for a change I made a mass function plot, which will look much more sane after this issue gets sorted out.   Here it is:

And, for kicks and giggles, a velocity dispersion function too:

 

These will all improve once I figure out where the missing halos are.

ID catalogs are done

Just a quick post to say, I now have lists of all halos, their masses, and the line number that they start on.

Here is the complete _pe_ simulation, thinnned by a factor of 100:

Sorry about that green corner there.  And here is the complete _pn_ simulation, also thinned by 100.

I talked to mike about the weird hid gaps, he says that is okay, but given that pn doesn't have them, I am not sure whether to believe him or not.  Anyway.

Testing Latex

$\int_0^\infty x^2 dx = $


This is made possible by this person's blog entry.

Preliminary halo mass plot

For several weeks now, I have been working on generating a mass limited sample of halos.  None of the .find files are sorted by halo mass, the option are halo id, or particle id.   So I have modified haloproc.c to generate a list of halos as it processes them for velocity dispersions and other statistics.  This list contains the halo ID, the number of particles in that halo, and the startline in the .find file.  My plan is to sort this list, and threshold it, and generate individual halo files for all halos above the threshold.  I have already done the individual halo files for just the first 500 halos (and run a subhalo finder on each of them), but I think the subhalo velocity function statistics will not be valid unless we are using ALL halos in the sim above a given mass.  Here is a preliminary plot from the lcdm_pe simulation:

It shows a couple of things.  1) simply thresholding on halo id is terrible, because neighboring id numbers can vary by something like an order of magnitude in mass.  2) there seem to be certain halo id numbers that are just missing.  


Mike, you should tell me if this is what you were expecting to see. 

Incidentally, looking at this plot equivalent for one of the smaller simulations showed that there was a second population of very high mass halos, with very large halo id numbers, so that this relation wasn't even approximately monatonic.  Unfortunately I cannot find this plot, I wish I'd thrown it on the blog!! The same MIGHT be true in this simulation too, you'll note that there are only about 4 million halos plotted here, whereas this sim has something closer to 70 million.

I am unsure what caused haloproc.c to stop after 18 billion particles (possibly I simply didn't ask for quite enough time in my batch submission), but I am working on trying to restart it (not from the very beginning) so that we can get a completed halo list for this simulation.

When I have something better I will post again.

velocity dispersion function

mass versus subhalo velocity dispersion

The zeroth order question is the following:  If you observe the velocity dispersion of galaxies in a halo, how tightly does that correlate to the halo mass?  To answer this I've taken halos in the lcdm_pe simulation, and run subhalo finders on each of them.  Using the mean velocities of each of the subhalos in a halo, I've computed a velocity dispersion.  I have plotted this against the host halo mass.  Here is a plot, using all identified subhalos.

The top panel is the total velocity dispersion, and the bottom panel is the radial velocity dispersion, the quantity that can potentially be observed.   There is a noticeable correlation, with a lot of scatter.

Next, I thought it would be interesting to place mass thresholds on the subhalos used.  This is interesting because we believe that different morphological types of galaxies live in dark matter halos of different masses, e.g. big old red dead ellipticals can be expected to have a higher characteristic dark halo mass than young star-forming spirals.

Below is a sequence of subhalo thresholding, ranging from 1e10 to 1e12.  Note that the y axis on the 5e11 and 1e12 plots have been significantly expanded.

What we see is that as we go to larger subhalos, the velocity dispersion is a much less accurate tracer of host halo mass.  Assuming the brightest galaxies live in the largest subhalos, this means it's unlikely that choosing the brightest few galaxies to compute the velocity dispersion will yeild a result that correlates at all tightly with the mass.

Originally we were thinking of generating light cylinders and computing the velocity dispersion among all galaxies along the line of sight, but to me, the scatter for the bright guys looks large enough that there may not be a point.

Notes to own self:  Procedure for getting these plots:
1) modified tree19/apps/etc/haloproc.c to dump a separate file for every halo in the .find file of lcdm_pe simulation
2) ran isodensity subhalo finder tree16/vfind64/pos/vfind.x86_64-mpi on each halo from step 1
3) ran original tree19/apps/etc/haloproc.corei7 on the .find files from step 2
4) to get subhalo masses ran ~mswarren/tree16/apps/hmassr/hmassr.x86_64 to generate .halos files
5) code to make these plots lives in projects/velfunc/hproc/shvdvsmass

Halo Gallery: Corrected

The bug in Mike's halo files has been corrected, and these are the updated plots of the highest velocity particles in the halo, at early times.