MCMC code

I wrote and tested a general IDL implementation of Markov Chain Monte Carlo. It is checked into idlutils.


smooth image subtraction

Phil and I got the Bolton and Burles smooth-image fits working on all the LRGs, and fixed all download and data problems. We made b/w and color JPEGs of all LRGs and their residuals away from the smooth models, and a WWW page for browsing them. We discussed the short-term to-do list and the requirements for publication. Not bad for a 10-hour day starting at 06:00.


HST cutouts, smooth fits to LRGs

We cut out small postage stamps on all HST images (downloaded so far) of LRGs. Downloading continues as we blog. We got Burles's and Bolton's bspline image fitting code up and running (though we found a small bug).

I tried not to become enraged about the fact that ACS WCS header information is not correct!. It is our bound duty to fix this as soon as astrometry.net is off the ground.

Anatoly Spitkovsky gave a great talk on pulsar emission using force-free electrodynamics; he opined that full 3d time-dependent simulations would soon be possible.


HST/ACS imaging of LRGs

Phil and I got the HST data understood and staging at STScI, and downloading from the staging area. We started on the work of finding the LRG locations in the images and making cutouts for subtraction and inspection.


HST archive

Oh my goodness the HST Archive search, access, and retrieval tools are very bad if you want data on thousands of pointings! Phil and I beat our heads against this all day. But we do have all the datasets in which we are interested identified and tomorrow we hope to get them all downloaded.

What's wrong with the following numerology? HST takes an average of about 60 Mb of data per orbit, and orbits every 90 mins for 20 years. That's 1 Gb per day, or a lifetime total of about 7 Tb. We can spin this all at NYU, and give the community better (faster, more survey-oriented) access tools to boot.

Ted Baltz gave a wonderfully comprehensive talk about direct detection of dark matter.


HST archive

Phil and I found all HST/ACS pointings near all public SDSS LRGs. There aren't very many! Discussed lensing with much of Roger's group.


lensing and cosmology

Discussed many possible lensing and cosmology projects—with Phil Marshall, Roger Blandford, Marusa Bradac, Ted Baltz—for my week at SLAC. The goal is to do something in one week, preferably something interesting. Extreme coding may be involved.


Willman 2

I thought about the observing plan for our KPNO run. That's about it!


K+A asymptotics

I realized that in order to estimate the K+A event rate (or event probability), I need to select the K+As based on their asymptotic (t goes to infinity) expected properties, not their current properties. I figured out how to do this (sort-of) empirically.


cosmic ray cluster, astrometry, LSR

I looked at the AGN and star-forming galaxies in the field of Glennys Farrar's cosmic ray source candidate.

Morad, Sam, and I discussed the rejection of false positives for the astrometry engine, among other things.

I finished the LSR paper!


K+A rate density

I wrote (and typeset) the equations for the inference of the K+A rate density calculation for my disk–disk merger review.


Tyson, x-ray K+As

I discussed new large survey data with Tony Tyson, but did little else today.

In other news, Adrienne Juett wrote a Chandra proposal to observe some K+As, inspired partly by my talk at UVa yesterday!



I got the LSR paper slightly closer to re-submission. It is still not done.


LSR, Ursa Major, Barnes

I worked on getting the local standard of rest (LSR) paper ready for resubmission. It is not done yet.

I looked at the instrument manual and prepared some questions to answer in preparation for the April KPNO 4m Mosaic run to observe the new Ursa Major dwarf galaxy.

I digested Barnes' email and added his 1988 paper to my accretion bibliography. I had to type the abstract in by hand because NASA ADS has gramatically re-written abstracts. How insane is that?


astrometry, mergers

Sam, Morad and I got everything together to do the first full-blown test on pattern matching SDSS raw data fields (using SDSS-software stellar x,y positions).

I wrote to Barnes about disk-disk mergers, and started to review the literature on alpha-enhancement, to see if I can make quantitative claims about the size of needed alpha-enhancing starbursts.


color images

Nelson Caldwell (at the CfA) and I discussed making pretty three-color images from astronomical data, reminding me of some far-out ideas we had that go beyond our current, good, but simple system. In particular, because the brightest parts of the image make a saturated color map in our system, it can be that the brightest astronomical sources contain none of the brightest output image pixels. There are some good ideas floating around for maintaining the color information but still brightening the brightest pixels. Unfortunately, I can't see how to do it without adding new free parameters.


bulges from disks

I outlined a radically de-scoped review paper that addresses only the question of whether bulge-dominated galaxies might be formed by the mergers of disks. The minimum scope is to critically discuss the chemical abundance arguments and the central density arguments, and then to perform the updated rate analysis similar to but more reliable than that of Quintero et al. I reminded myself that I never emailed Barnes as I had planned to do in my previous post of this same title.


Willman 2

I read and commented on the nascent Willman 2 paper. Is it in Ursa Minor or Ursa Major? And does it have any emission in other bands, eg, 21 cm or 60 um?


Kona: what did I learn?

I learned that

  • doing the cluster mass function is very very hard, for many reasons, not the least of which is that clusters do not have well-defined masses, radii, and velocity dispersions, etc;
  • there are lots of quanitative measures of cluster merging (eg, offsets of x-ray from mass centers or bow shocks visible in the x-ray), though no-one seems to be using them to check halo–halo merger rate predictions;
  • weak and strong lensing are super-promising for blind cluster searches, not in particular because they do a good job, but because there is hope that the selection and statistics can be understood (it's the uncertainty on the uncertainty that matters);
  • there is pretty strong evidence that the low-mass end of the "red sequence" is evolving strongly since redshift of unity;
  • both the theorists and the observers believe that the stellar component of the intracluster light (ICL) must consist of stars stripped off of (or "harassed out of") cluster galaxies (I think this can be falsified immediately);
  • there is some evidence for evolution in the cD galaxies at the centers of clusters; they might not exist at all at redshifts significantly larger than a half; and
  • Morad has serious competition and needs to get that xi(r) done immediately.

On the ICL point, my argument is that cluster galaxies are not tidally limited (by which I mean they do not have significant numbers of stars near their tidal radii). Of course if the ICL is blown out when the galaxies smash right into the cD, I would be wrong; but is that plausible?

On the cD galaxy point, if this is true, then the cD properties as a function of redshift ought to be an integral of the close pair fraction; can Morad and I test this? I think so.