Rix, K+A asymptotics

Reviewed project status with Blanton, and—in the case of kcorrect—also with David Schiminovich and Hans-Walter Rix; did almost nothing else.

Hans-Walter gave another great talk; this time it was on the fossil record of the Milky Way's accretion history as it is recorded in phase space and the possible observational signatures.

I did look at the K+A asymptotic behaviors on the train, but got frustrated because we have the A spectrum from zero-redshift stars and the K spectrum from redshift 0.1 early-type galaxies, and so neither has complete wavelength coverage over gri bands! I will hack this weekend.


LSR, Rix

The LSR paper is resubmitted!

Hans-Walter Rix gave a nice talk at NYU about the evolution of galaxies since a redshift of unity. He showed that there is no direct evidence that the decline in the star formation rate is related to the decline in the interaction rate.


LSR again

I went through the second round of referee comments on the LSR paper. It should be ready tomorrow.


nothing, baryons

I did no research today, although I had pretty good reasons for the failure!

Daniel Eisenstein gave a great talk at MIT on the baryon acoustic feature in large-scale structure (the subject of a paper we wrote together). He noted that a spectrograph on an 8-m class telescope that can take a few thousand spectra in a couple square degrees at a time can measure the baryon acoustic feature at redshift three (or one) in about a hundred good nights.


double LRGs

Burles, Morad, Bolton, and I discussed a project (Lexi Moustakas's idea) to find double LRGs in the SDSS LRG spectra by finding spectra with non-gaussian absorption line profiles. The basic procedure should be:

  • Read in Schlegel's amplitudes for the Elodie spectral fits to the LRGs, along with his velocity dispersions, if all such exist in the spectro directory.
  • Construct the gaussian-smoothed, linearly combined Elodie spectrum for each LRG.
  • Difference the smoothed, combined Elodie spectra with others that have additional skewness and kurtosis (at fixed variance) to make "derivative" spectra that are derivatives with respect to skewness and kurtosis.
  • Make "residual" spectra that are the differences between the LRG spectra and their gaussian-smoothed Elodie models.
  • Compare the residual spectral with the derivative spectra and plot the "amplitudes" of the derivatives for all residual spectral vs each other and the velocity variances.
  • Inspect outliers, which may or may not be double-LRGs (or other oddities).

We also discussed the reconstruction of full 2d (spatial) by 1d (spectral) spectral "cubes" from grism (or slitless) spectra taken at multiple position angles; we all concluded that it is possible. Burles had the good idea not to allow arbitrary spectra at every pixel, but to restrict spectra in each pixel to lie in some N-dimensional subspace of spectrum space.


linear fitting, passive evolution

On the plane I figured out the correct, xy symmetric, minmal formalism for fitting a straight line to 2-d data not simply with errors in both dimensions, but with an arbitrary, different, 2×2 covariance matrix for each data point.

I semi-decided to punt on an empirical understanding of the passive evolution of post-starburst galaxies, and worked out a semi-theoretical method, which involves "photometering" the K and A spectra in the bandpasses we use. (I also re-discovered our nomenclature ambiguity between the amplitudes of the K and A spectra and the spectra themselves.)


galaxy environments, passive evolution

In what little time went to research today I fixed up some figures for Berlind's paper on galaxy environments.

I also began working out the median passive evolution behavior of post-starburst galaxies empirically, based on Quintero's K+A sample.



No research was accomplished today, from a combination of illness and Spitzer proposal evaluation.


tweaking astrometry

In what little time I devoted to original research today I tweaked the star-finding parameters for the hands-off KPNO Mosaic astrometry. We won't be able to do such tweaking for http://astrometry.net/; this problem could end up being important.


dark matter, astrometry

I attended a nice talk by Doug Finkbeiner about the possibility that excess flux in the WMAP CMB maps is due to dark-matter annihilation. It is a crazy hypothesis, but the next-best are that: (1) the black hole at the center of the Milky Way was orders of magnitude more powerful in gamma-rays 1 Myr ago, or (2) bulge stars have crazy chromospheric properties. Deep observations of nearby galaxies will be decisive.

I inspected (by eye) the hands-off astrometry output for the KPNO mosaic data and found several egregious faliures, such as this one. Clearly we need to be careful. For now we may just stop all fits at second order.


observing, astrometry

Morad and I continued to observe the Willman objects. We also started writing crude data reduction tools in IDL. They are checked into "astrometry/pro/morad/mosaic" for now.

In a long and painful session, we solved the hands-off (not blind, because it does use the telescope RA, Dec as a first guess) astrometry problem for the KPNO 4m Mosaic. Here's a QA plot from one chip in one image; squares show the locations of USNO stars; the fact that there are sources at the centers of the stars means that we have the astrometry correct.


KPNO Mosaic reductions

Morad and I broke down and started writing Mosaic data reduction code, including flattening, astrometry, and, soon, mosaicing code. We are continuing to get good data on Willman 1 and the Ursa Major dwarf.


Willman observing, ACS WCS

We got some good and some mediocre data for Beth last night; tonight is cloudy so we are working other things, particularly Morad's small-scale clustering paper.

Here is a comparison of an HST ACS image with the USNO stars in the field, after I have applied my WCS-fixing code. Note that many of the USNO "stars" are not stars at all:

(Image made with "astrometry/pro/hogg/hogg_acs_wcs.pro")


ACS WCS, observing for Willman

I got code working that fixes, roughly, the ACS image world coordinate system. It is ugly code, and it only does the shift part, but it seems to work.

Morad and I planned the observing run for Willman's Milky Way companion candidates; the run starts tonight.