Thursday, April 12, 2007

Simulations for Intracluster Light

I worked on simulating the ICL for our pipeline. This is just creating fake sersic profiles ala the measurements of Gonzales et al., so it should be straightforward. I found, however, that as with many things in astronomy I spent all my time just trying to figure out the units and conventions. There is the usual -2.5log crap for the surface brightness limits, but also the notation for Sersic profiles makes no sense. I wasted a lot of time thinking r_e really was the effective radius when people actually mean the half light radius.

In figuring all this out, I wrote pure IDL code for converting r0->r50 (roots of the incomplete gamma function) and making images of Sersic profiles. The images don't properly integrate over the pixels on small scales for large n, small r_e (in pixels) but they are fine for these purposes. I faked it by putting in a core.

28 mags/arcsec^2 = 6.3e-3 nmgy/arcsec^2

mags/arcsec^2 = worst unit ever


Reina said...

Good to know that i'm not the only one spending time converting units... To deduce whether the reported luminosities in the MaxBCG catalog contained h's or not, I converted a couple of SDSS AB magnitudes to solar luminosities (with simple k-correction). I think they use h=1.0, so there's a factor of 2 hidden in there.

Also good to know that i'm not the only one reading this blog. :)

-"student at Princeton"

P.S. See you at Wunch.

Erin Sheldon said...

I feel like magnitudes and other astronomical units are to science like inches and english units are to engineering.

P.S. yes, they use h=1

bk said...

Thanks for pointing us here, Erin.
Yeah, we used h=1.

If you don't mind talking about it here, what are you simulating ICL for? Are you measuring this in maxBCG or something?


Erin Sheldon said...

yes, we have a pipeline for measuring the ICL and we have run it on a set of simulations and the maxbcg cluster sample. The measurement was pretty straightforward, we had all the tools nearly in place already here at NYU. Now we need to figure out how to interpret it.

bk said...

Cool. Is this a stacking exercise, or can you acutally measure something with reasonable S/N in individual clusters? If you can, it would obviously be a potentially powerful lever arm on cluster mass proxies, given the fraction of total light contained in the ICL. I suspect there would be strong redshift dependencies though.

Erin Sheldon said...

It looks like we can detect it in some individual clusters but I can't say much more than that. My feeling is the stacking will be more useful, but Anne and Dennis think the opposite.