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, x—y 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.

nothing

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.

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.