Lensing papers submitted to ApJ

All three lensing papers have been submitted to ApJ. We now have eight papers out based on the MaxBCG cluster catalogs: the catalog papers (I,II), a cosmology analysis based on the number counts and selection function (III), a velocity dispersion paper (IV), a stacked X-ray luminosity paper (V) and three lensing papers (VI, VII, VIII). Soon, a ninth paper by Sarah Hansen on galaxy populations in the MaxBCG clusters will appear.

Lensing papers on astro-ph

The lensing papers were posted on astro-ph last week. Here are the links:

  Paper I:   Measurements        astro-ph 0709.1153
  Paper II:  Modeling/Inversions astro-ph 0709.1159
  Paper III: M/L                 astro-ph 0709.1162

There are still questions about calibration at the 10% level. We did the best we could with the data we had, I know that. But over the year since the initial measurements were made there have undoubtedly been improvements in our understanding of the photozs. But this is part of science; we have to publish sometime and we will incrementally improve our understanding as we go. Because this uncertainty comes in as a calibration, an overall amplitude, we can always re-calibrate the results in the future.

Erin

Collaborations

I've learned something extremely important about collaborations. It is something that people have often tried to tell me but I didn't have the experience to understand fully. Please note this is not a knock on any of my collaborators but simply a general observation:

You must set hard deadlines for the completion of papers.

I think at first this statement can seem either obvious or irrelevant to many people, but I'll explain why it is certainly not irrelevant.

First of all, it doesn't matter how good your work is if you don't communicate that work to the outside world efficiently. You won't be able to continue your good work because you won't be supported. And if you are in a collaboration your work depends on others, and you must consider others in order to produce efficiently.

This has been really hard for me to accept, because internally my motivation is to follow my interests, and that is it. This is true for most scientists I think, especially after they finish graduate school.

But when you join a collaboration most people are interested in lots projects but they themselves are the lead on at most one or two of those projects. But they have excellent ideas concerning all of the projects. This is where the fundamental problem arises: how do you get people to contribute work to your project on your timescale?

What usually happens is you think of a project and start working on it. You tell your collaborators about it. You think of all the most important issues right away and deal with them. Then you start thinking of not so obvious issues and work on them. Then the work starts to feel like it's ready to share with the larger community. You must do this in order to be supported. You write it up and send it off to collaborators. For the first time, your collaborators start to really think about the project, and they have many good ideas. Most of them you already thought of but there are some ideas you have yet to address. Addressing these new issues often requires work from you, but it often requires a fair amount of work from the individual collaborator because only they fully understand it. So you end up delaying publication for a while, sometimes a long while.

If only everyone involved knew from the beginning that the paper would be released on an exact day, with no possible delay, they would have been forced to think about the project from it's inception in order to contribute. They would have realized that some input was needed from them up front. They would have done this work while you were working. Most of these issues would have been dealt with by the time the first draft was written.

Collaborating is worth while because I learn so much by seeing other people's perspectives. And everyone has such varied skills that the work is always better for it. The theory is that a deadline is an impersonal rule that once established should help to keep the ideas and work flowing more naturally and efficiently.

Erin

M/L paper really close

I know I said it was close before, but unless something comes up it should be out in a couple of weeks. If things move fast it could come out with papers I and II, which should come out this week.

For those who want a preview: the M/L goes as M^0.33 within r200, the M/L reaches an asymptotic value on large scales (20Mpc) and when you multiply that number by the luminosity density you get 0.20 +/- 0.02. There is a factor of bias on that too, but we don't know what it is exactly other than it should be of order unity.

Erin

Brian May: Observing at La Palma?

I just found out that Brian May of Queen is finishing up his PhD in astrophysics this year. His thesis is on zodiacal dust and in fact he is observing at La Palma tonight (and last night)! I know this isn't my research, but its a good story.

Here are some entries from his blog.

Erin

M/L paper close

I have finished all the analysis and plots for the M/L paper. I just need to finish the writing. I think this paper might be ready to put an the archive at the same time as the other two MaxBCG lensing papers.

Erin

Anti-correlations

Made the discovery this week in aspen that certain types of galaxies are actually anti-correlated with MaxBCG clusters on certain scales. These are very luminous galaxies, and the cross-correlations are negative near the virial radius. Considering that more luminous galaxies tend to me more strongly clustered this was a bit of a surprise.

My guess is that this is due to the cluster finder. The cluster finder looks for groups of luminous red galaxies, ranks them by likelihood, and "percolates", meaning that smaller clusters are not allowed to live within r200 of larger clusters. Then if you choose a certain ngals200 this might cause a feature near r200 in the luminous galaxies. I'm checking simulations. I see that the feature is there for MaxBCG run on the sim, although the effect is weaker. Now I'm going to run on the halos and see if the feature persists.

Erin

Agreement

All the mass estimates for the clusters are now in basic agreement. The photoz fix brought up the lensing masses and they now agree with the dynamical and other masses. What I like is that we didn't try to make them agree, but bugs were found along the way that changed the answer; we would have fixed the bugs even if they lowered the masses.

Analysis on the ICL stuff is beginning in earnest now; Tim is looking at the outputs and I expect he will generate some science soon. If I get a chance I'll also look into it. I'm interested in getting the total optical light in the system for comparison with the total mass from lensing, both in the relative amount and relative distribution within the clusters.

Draft finished

Finished the near-final draft of the lensing paper. Now it's time to turn attention to running simulated data through the galaxy cross-correlation code for comparison with the clusters. I don't know yet what we will learn from this, but it is certain to be useful. I'm hoping to use the new computing cluster of our west coast friend which will kick some serious butt.

Cluster lensing finished

The final lensing measurements for the maxbcg clusters are finished. If there are any other issues that arise I will not address them in this paper. This is non-negotiable. For example the photozs are now fixed; other photoz methods may give different results. This just comes from choosing a method. I would not be surprised if we re-calibrated these results in the future as our knowledge of the source redshift distribution improves, but it won't happen before publication of these results.

The results after fixing the photoz bug have higher amplitude by about 15%.

I've finished making the new plots, now I'm re-working the text. This will take a little work because I need to write up how I have used our estimates of the photoz error distribution in the measurement itself rather than as a correction after the fact. This is the same formalism we used in the 2004 paper but now we actually have a good idea what the error distributions are.

Dave Johnston and I are still planning to release this paper and his analysis paper at the same time. I want this to happen before June.

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.

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

P.P.S.
mags/arcsec^2 = worst unit ever

Photozs

Rachel and a student at Princeton are working on a lensing project using the MaxBCG clusters. We did some comparisons and saw considerable disagreement between the recovered signals. It turns out that during the last iteration of the photozs a bug was introduced that made the colors look really wrong and the photozs too high. This was not in their estimator, but a difference in magnitude systems between training set and my catalog. It was just a confusion of conventions, but of course those can have disturbing consequences

By the way, does anyone read this blog besides my mom?

Erin

Finally 30Mpc + python cgi

The cluster-light cross correlations to 30Mpc finally finished. Now I have mass-to-light ratios over the whole range. I started looking at them and I'm seeing that in some cluster richness bins we may not be seeing the M/L asymptote. This is in the lower richness bins. At first this didn't make sense but maybe it is because the mis-centering is worse in those cases. It will be interesting to compare what we get when we try to model in these offsets.

Mulin and I also set up python CGI on the web server. This will be useful because writing these scripts in python is much easier and quicker than using php or perl. The server is old and decrepit, so we'll have to repeat all this when it is replaced in the next couple of weeks.

read_objmask

I wrote a code to read objmask info for SDSS objects from the fpatlas files. This came down to modifying the atlas reading code to get multiple objects and copy their objmask info into an output structure. I then linked this to IDL using the DLM mechanism.

I was motivated to do this because we are going to start working on intracluster light in the MaxBCG and Percolation clusters. This gives a first look at the area associated with each object in a frame, which we will need to mask out in order to measure just the ICL. We will probably use a different area once we decide on the best masking algorithm.

Erin

30 Mpc M/L

Today I started a bunch of jobs on the computubg cluster here "mafalda" here at NYU. These should take a few days to finish, and I'll run another set after that. These are the last of the jobs for calculating the light and number densities of galaxies around the MaxBCG clusters. I had these to 10Mpc but now I'll have them to 30Mpc along with the lensing masses, so I'll have M/L over that entire range. If things look good I'll start writing that paper in a week or so.

Erin

Change of plans

Sarah Hansen and I are going to combine our papers on MaxBCG cluster-galaxy cross correlations with Sarah as first author. I have written up the method, described the selection etc., and made a bunch of plots. Risa didn't like that there was so much overlap between the two papers. I think she is probably right. Sarah is going to merge the sections from my paper into hers.

Erin

Switching to svn

My CVS archive at UChicago is no longer available, so I talked to the sysadmin here at NYU and we set up an SVN repository for all the code. This is actually kind of important. SVN makes managing code across many different machines and many different developers simple, more simply than CVS. And I feel like I have a good shot at keeping it available for a long time here unlike at Chicago. It will be easier to move now if needed too.

The Aspen meeting is next week and the SDSS cluster folk are going to be there in nearly full force. The SZ cluster people will be there too so we may here some news from SZA.

Wanted Distractions

Decided to put aside the cluster correlations and work on accessing a database through the web using Python. Over the break I put my Mom's recipes into a database web applicatioin using python. I looked into doing something like that with a larger data set, it is as straighforward as it sounds. The only trick will be convincing the sysadmin that it is secure enough.

There has been an exchange in the cluster group about how to model the lensing signal. It has become clear that mis-centering of cluster sample relative to the mass could be a real interpretational issue. Any mis-centering is basically degenerate with the halo concentration. Eduardo Rozo and Dave Johnston have ideas on how to constrain the mis-centering outside of the lensing signal to break the degeneracy.

I think this centering issue could severely limit the usefullness of the M/L measurements on halo scales. We can only account for the mis-centering with modeling, but we don't want to assume a form for the light distribution, certainly not NFW. One of the points is to see how different the profiles are in mass and light. On the other hand, if we can constain the mis-centering outside of these measurements the very high S/N light measurements could be recovered non-parametrically.

Erin

Lot's of counting

I've been counting the galaxies around the MaxBCG clusters. I decided that while I was at it I might as well count the luminosity. And while I was at it, why just count the galaxies as a function of radius? Why not count them as a function of their other two basic observables, color and luminosity? So I now have this cube of counts as a function of radius, color (g-r) and luminosity, background subtracted and edge corrected. And the same for luminosity.

The original motivation for this was to measure mass-to-light ratios by comparing the excess luminosity to the excess mass from the lensing measurements. But I think this cube is going to yield a lot of science beyond that. I'm writing up the basic measurements and doing statistics like luminosity functions, blue fractions and such. Sarah Hansen is going to move along the lines of here 2005 paper with better S/N. Blanton and Hogg both have some good ideas which will either make it into my paper or separate papers.

Erin
P.S. I'm going to start posting regularly again. Seriously.