I made thumbnail images of all the galaxies in the clusters in the field of Glennys Farrar's putative high-energy cosmic-ray cluster. To my eye, there is nothing obviously interesting or strange about the field.
I worked on the K+A environment figures and discussed them with Morad. We worked out a new figure to make, analogous to the clustocentric-distance figure, but with distances to nearby, luminous galaxies. We are pretty sure it will show an effect.
Blanton asked for error bars on yesterday's plot, so I calculated the uncertainties for binomial estimation, by taking two derivatives of the log likelihood for the "success" probability p given a sample of N trials in which there are M successes. (I used a flat prior on p.)
As expected (from the first derivative) I get that the maximum likelihood estimate of p is M/N, and (from the second derivative) I get that the (linearized) uncertainty on this is sqrt(pq/N), where q=1−p.
The clustocentric result of yesterday appears marginally significant.
I found a possible excess of post-starburst galaxies in the infall regions of large galaxy clusters. It appears significant. Code is hogg_kplusa_clustocentric in eplusa/pro and the plot (PostScript) is on today's research page.
I hacked together the simplest possible HST/ACS image combination code in IDL, building on the distortions code I wrote earlier in the week. It is not yet checked into the astrometry module. I made this image of one of Schechter's favorite lenses, 1RXS J113155.4-123155, using my new code and some public ACS data
I gave Morad comments on parts of his small-scale LRG-LRG clustering paper.
I modified Burles's ACS image processing script into a set of procedures (prefixed "hogg_acs" in astrometry/pro/hogg) that perform x,y to RA,Dec (and back) transformations for ACS "FLT" (ie, not distortion-corrected) images. This will plug into image combination code downstream, and might be a prototype implementation for future astrometry.net output.
Morad improved his K+A nearby neighbor figures. Oh wait, that only counts for Morad's research blog, not mine. D'oh! We did discuss the problem of making easy-to-read figures.
I discussed Quintero's clustocentric results and strategy with Quintero, Blanton, and Berlind on a phone call.
Morad kicked my butt on computing nearest-neighbor statistics for the K+A galaxies (and, indeed, everything in the VAGC), and he finds that there is evidence for tidal triggering of post-starburst galaxies. So the "environments of post-starburst galaxies" project has a positive result. Time to start writing! We still need to do the clustocentric distances, but the upshot of the Quintero call is that Quintero is making us the FITS file we need.
I worked on code to gather the environment measures we need for the paper on the environments of post-starburst galaxies. I found many bugs and fixed them. My "closest-comparable-neighbor" code is super-slow. Following up on Quintero's awesome plots, I gave hogg_scatterplot in idlutils ADQ-style shading functionality.
I only "did research" today if commenting on Richard Cool's (excellent) draft paper on the color-magnitude relation and commenting on Quintero's (beautiful) clustocentric figures counts as research!
We worked on getting Quintero's K+A galaxy catalog into archival form for other users.
I started work on the environmental properties of K+A galaxies by looking at the 1h-1 Mpc radius overdensity measurements. Indeed, they are much more like those of spirals than those of ellipticals, as we found in Quintero et al (linked above).
Morad and I found a moving object in the KPNO mosaic I made yesterday. It puzzled us for a while (because of its proper motion of about one arcmin per hour), but now I just think it is a high-inclination asteroid within an AU or so. If anyone tells us it is interesting, we will give the data to someone who will use them.
Kept banging my head against bugs in the KPNO Mosaic mosaicing code; I have something that works, but I am still not masking out enough pixels.
Discussed with Morad how his results fit in to the recent literature on the evolution of red-sequence galaxies, especially the nice paper by Bell et al. Strictly speaking, the Bell et al result constrains the addition of stellar mass to the red sequence, while Morad's result constrains the merging of galaxies within the red sequence, but clearly there is a relevance. We also realized that the evolution of the bright end of the LRG luminosity function with redshift constrains some combination of the fading of LRG stellar populations and the total merger activity.
Worked on the code to mosaic together the KPNO Mosaic data into huge images (and pretty pictures).
Discussed with Phil Marshall, Lexi Moustakas, Chris Fassnacht, et al. the issues involved in setting up our duplicate of the HST Archive, which will have special functionality for those who are doing survey science. Much of the discussion centered around what form of the data to store/serve. The raw bits—for the entire HST lifetime—add up to only 1.7 Tb or something in that ballpark. The reduced data are more than ten times larger (more numerous?). Phil posted the minutes here.
In the context of this discussion, we discussed briefly the issue of working on/with stacked images. Everyone is in more-or-less agreement that it is possible—in principle—to do all image measurements (including photometry, profile fitting, etc., but especially faint source detection) on the individual, unstacked frames; working on the stack can only be same or—more likely—worse. The problem is that in practice there are no good codes available. Perhaps this collaboration will create some.
In the short term, however, the project is science-oriented and just-in-time, in the extreme coding model, so we won't write any such code until we need it.
I tried the simplest possible implementation of Morad's idea for checking the hypothesis that K+A galaxies are tidally triggered. Its in hogg_kplusa_tidal.pro in the eplusa CVS module. I get a completely null result, but I don't trust it; it might be a bug.
I iterated the cross-talk calculation and Mosaic data reduction, but I won't be talking about that now, will I?
I spoke with Blanton about his argument that almost all relationships between galaxies and their environments can be explained as coming from the masses of the gravitationally bound objects ("groups" in my vocabulary, "haloes" in the new economy) in which they reside, and their locations within. Really his results are about multiplicity, not mass, but the punchline is mass.
The one exception is very small-scale clustering or close pairs. It appears that there is color-related substructure within groups. Not surprising, but very interesting. The challenge is to demonstrate it in a clear way.
Berlind and I reviewed the figures for Berlind's groups paper, which is beautiful. He shows that you cannot find groups with high completeness in a survey (eg, SDSS) and also simultaneously meet the following three criteria:
