2005-05-31

cosmic-ray cluster, galaxocentric distances

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.

2005-05-30

binomial uncertainties

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.

2005-05-29

infall regions

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.

2005-05-27

2005-05-25

ACS image combination, LRG clustering

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.

2005-05-24

ACS distortions, environments

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.

2005-05-23

galaxy environments

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.

2005-05-20

post-starburst galaxy environments

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.

2005-05-19

comments

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!

2005-05-18

post-starburst galaxies, moving object

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.

2005-05-17

mosaicing, LRG–LRG mergers

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.

2005-05-16

mosaicing, HST, source detection

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.

2005-05-15

post-starburst triggers

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?

2005-05-12

groups, environments

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:

  • get the multiplicity distribution right
  • get the velocity dispersions right
  • get the angular sizes right
This is particularly interesting because many investigators at the present day tune up to get the last two things right and then write papers about the multiplicity and mass functions. So, as long as he can get the word out, he has a pretty important result. And its not a negative result, because he does have a catalog that gets the multiplicity function right.

2005-05-11

GCN, Willman data, tidal trigger

I made SDSS imaging mosaics and finding charts for Eisenstein's GCN Circular on GRB 050509b.

I finished checking all the Willman astrometry and it is all completely fine, to my eye. I noticed some "data features" that made me suspect the cross-talk calculation (again!).

I worked out the steps involved in the small project Morad suggested, of looking at close neighbor separations as a function of A/K for the post-starburst galaxies, to see if they are plausibly tidally triggered.

2005-05-10

astrometry

I found and fixed a bug in the KPNO Mosaic astrometry code (mosaic_wcs in the astrometry.net codebase). I re-ran the Willman data and I started the hand-inspection of the astrometry in cases marked by the code as possible problems. All inspected so far are fine, although robust object detection of relevant objects (not stars, since the USNO-B1.0 is dominated by galaxies!) remains an issue.

Chris Stubbs gave a very nice talk at MIT on the use of astrophysics in testing fundamental physics; in particular he discussed the issue of absolute radiometry in the supernovae projects, an issue I sometimes get upset about.

2005-05-09

Willman data, GRBs

With cross-talk understood, I re-made the KPNO Mosaic zero, dark, and flats, and I re-flattened the Willman data.

My description of the cross-talk is now posted here.

I discussed the making of automated GCN circulars for GRBs in the SDSS footprint with Eisenstein and Strauss.

2005-05-08

yet more cross-talk

I figured out that the fastest and most robust estimate of the cross-talk would come from not the entire chip but from a high-variance small sub-image of the cross-talking chip, and that the fit I do should not be to all pixels in the image section, but only to pixels that are simultaneously extreme-valued in the cross-talking chip and non-extreme-valued in the cross-listening chip. This is now what the code fits. Tomorrow the job is to figure out which chip-chip pairs have significantly non-zero cross-talk amplitudes and modify mosaic_mrdfits() so that it can make use of that output.

2005-05-06

cross-talk

Fixed bugs in yesterday's code; left it running and will have answers tomorrow.

2005-05-05

cross-talk

I wrote (slow) code to determine (empirically) the cross-talk between CCD redouts in the KPNO Mosaic data we have of Willman's UMa Dwarf. It is mosaic_crosstalk.pro in astrometry/pro/morad/mosaic.

2005-05-04

cosmic ray cluster, LRG pairs, jackknife errors

I estimated specific star formation rates for the galaxies in the sky near the center of Farrar's putative cosmic ray cluster. We find no excess of star formation in that direction.

Morad and I discussed Richard Cool's (Arizona) testing of the SDSS photometry of close LRG–LRG pairs.

Morad and I figured out the following, tentatively: In what Eisenstein calls "jackknife" (I disagree, but that is a subject to discuss on Hogg's Universe, not here), you use your one data set to make N measurements of a quantity Q, for each of which you leave out (ie, do not use) a different 1/N part of your data. You take the root-variance of these N measurements about the mean, and multiply by sqrt(N-1) to estimate the uncertainty on your full-up measurement.

2005-05-03

K+A asymptotics, Tegmark

Whew. I finally got the K+A asymptotic passive evolution code written. The function hogg_kplusa_evolution() in eplusa returns the expected, long-term, observed-frame evolution in the SDSS r band as a function of redshift and A/K. This now lets us trim the sample of all K+A galaxies to just those that would make it into the SDSS Main Sample even at t [goes to] infinity.

Tegmark gave an off-the-cuff colloquium at MIT about the current state and future prospects for precision cosmology. He opined that if the dark matter has no non-gravitational interactions, if the dark energy is a cosmological constant, and if inflation produces no features in the power spectrum and no tensor modes and no non-gaussianities, it could be a boring future for us indeed. But he also predicted that it would not be so. Apparently there are no inflation models so "vanilla" (although the dark matter and dark energy can be so vanilla).

2005-05-02

astrometry polemic, environments

I worked on the introduction to what will be the first of the papers about the astrometry engine. The introduction (and even the abstract) of that first paper has to lay out the whole program and its justification.

After discussion with Morad about the possibility of showing (empirically) that K+A galaxies are triggered by interactions (ie, very small-scale environments), I worked out the skeleton of a project that shows that they are not preferentially in the infall regions of clusters, and furthermore that the infall regions show no interesting features at all (if they don't; I think they don't). This is all part of the general project of figuring out exactly what is related to environment; it is pretty subtle.