stars, disruption, photometric redshifts

Today began with a meeting about GALEX, where Steven Mohammed (Columbia) showed that there is great metallicity information in the overlap of GALEX and Gaia, and we discovered that something must be seriously wrong with the astrometry in our re-calibration of the data.

Andy Casey (Cambridge) organized a phone meeting in which a bunch of us discussed possible scientific exploitation of the data in the ESO HARPS archive, which contains thousands of stars, each of which has tens to thousands of epochs, each of which is signal-to-noise of hundred-ish, and resolution of 100,000. Incredibly huge amounts of data. Huge. Casey asked each of us to describe low-hanging fruit, and take on short-term tasks. One thing we might do is re-factor the archive into something more directly useful to investigators.

Sjoert Van Velzen (JHU) gave the astrophysics seminar about tidal disruption events. He has a great set of results, starting from search and discovery, going through theory and models, and continuing on to multi-wavelength follow-up. The most intriguing result is that the TDEs are amazingly over-represented in post-starburst (E+A) galaxies (which I used to work on). It is hard to imagine any origin for TDEs that would so strongly concentrate them into these environments. It makes me wonder whether the things they are seeing aren't TDEs at all?

After the seminar, Boris Leistedt (NYU) posted to the arXiv our new paper on photometric redshifts. The idea is that we use what we know about Doppler Shift and bandpasses and calibration of photometry, but let the galaxy SEDs themselves be inferred, latent variables. This combines the best properties of machine-learning methods (that is, flexibility, non-parametrics) with the best properties of template-based methods (that is, regularization to physically realizable models, a generative model, and interpretability). It seems to work very well!

class2008, day two

This morning concentrated on understanding galaxies in large surveys. Among a set of interesting talks about galaxy classification, Boris Haeussler gave a nice talk in which he put the standard 2-d galaxy fitting codes through their paces, and found some very interesting things, including underestimated errors—even when he puts in fake data for which the fitting codes are not making approximations! Vivienne Wild spoke about a robust PCA and its use in understanding rare populations such as post-starbursts and their role in galaxy continuity. Two of my favorite topics in one talk! The PCA adjustment is very smart although somewhat ad-hoc (not described in terms of probabilistic inference). The post-starburst work is even better; it confirms our results that suggest that post-starbursts are key in the evolution of stellar mass from the blue to red sequences. Many other good contributions too numerous to mention, with a lot of people working on optimal extraction of information from spectra; very encouraging for the future of spectroscopy.

post-starbursts in GALEX, writing

Continued writing on the faint-motion paper. It is funny how much there is left to do when a project is done!

Wu began working on the GALEX properties of post-starburst galaxies: They aren't detected at the MIS depth. That is good, because star-forming galaxies are detected. So a GALEX selection is likely to work, at some level. The question is, how good will it be? We would like to have a GALEX-based selection of the post-starburst galaxies so we can perform emission-line studies without worrying about the fact that the post-starbursts are selected on the basis of emission lines. Fortuitously, Christy Tremonti (Arizona) showed up at the MPIA today for a month, so she may be able to help out.

null hypothesis

Wu and I are back onto looking at the processes that lead to post-starburst galaxies, this time with Frank van den Bosch and Anna Pasquali here at MPIA. The first step was to create comparison samples to make null hypotheses; because the catalog we are using has redshift and flux dependencies, we built comparison samples to be exactly matched in redshift and brightness (stellar mass). Wu finished that today.