epoch.net, huge galaxies

Barron and I spent the morning arguing about his project to automatically determine the date at which an image is taken, using only the information in the image pixels themselves. Most people (okay, not most people, but maybe most astronomers) laugh when you even suggest this, but it turns out that for typical historical plates, there often is enough information in the moving stars in the image to pinpoint the date to within years. It is straightforward to define a scalar to optimize; the optimum gives you the date. It is non-trivial to determine the uncertainty on that estimate of the date. By the end of the day, Barron had a promising estimate of the error bar. Time to write!

I spent the evening frantically preparing materials to talk about huge galaxies in the Sloan Digital Sky Survey at the collaboration meeting at Fermilab tomorrow. Thanks, Blanton!


USNO-B redux

Yesterday and today, Barron and I worked on responding to referee on the USNO-B paper. We resubmitted. It was a pleasure to update the paper according to constructive referee comments. The paper is improved.

Barron and I discussed several other blind astronomy image meta-data projects including: We have shown some success in determining the date at which an image was taken, using the USNO-B-tabulated proper motions of the stars in the image. We are writing that up. We believe we can also determine the bandpass of an image, using the brightness ranking of USNO-B stars of different colors.

In related news, Roweis, Yann LeCun (NYU), Barron, and I may start a new project to perform morphological classification of galaxies. Both of my readers will be stunned, because they know that I am adamantly against morphological classification! However, we have a very new idea, which is to build models of galaxies in three dimensions, and try to explain all galaxy image data with a small number of three-dimensional models plus Euler angles. That is, the project is to create a fundamentally three-dimensional generative model of all images of galaxies. That would be new, and not be subject to my usual wrath.


ADASS proceedings

I finished the ADASS proceedings today. I will post them to the web when I get a chance.


human-viewable images

Ryan Scranton (Google) was in town this morning, and he, Blanton, and I talked about how to make enormous amounts of high dynamic range imaging viewable by a human with a normal monitor. Think about viewing the whole terapixel SDSS dataset on a normal desktop monitor. This requires panning and zooming, of course. I think we all ended up agreeing that it also requires different stretches at different "zoom levels" in order for the imaging to be fully exploited. We hope to demo some ideas soon.

In the afternoon I worked on my ADASS proceedings and some proposals.


conference proceedings

I spent almost all of my research time today writing up my contribution to the proceedings of the ADASS meeting, in which I describe the why, what, and how of Astrometry.net.



Daniel Eisenstein (Arizona) was in for the day and we discussed SDSS-III, a project to follow the current phase of the Sloan Digital Sky Survey. NYU's main interest in SDSS-III is its project to measure the baryon acoustic feature at redshifts of 2/3 and 2.5 or so using luminous red galaxies and quasar absorption lines respectively. We are intending to contribute resources to the project in exchange for institutional participation and we will have some responsibility for the data analysis, data serving and sharing, archiving, and preservation. We spent most of our time working on what is needed for planning and budgeting, so it wasn't exactly a scientific morning. But that's research too, I guess!

In the afternoon I had a short but useful conversation with my colleague Scoccimarro about how best to measure the BAF given nonlinear evolution in the growth of structure at the scales of interest. He and Eisenstein disagree sharply on how to do this; I am confused because they are my two gurus on these subjects.



I spent a great day at the Institute for Advanced Study in Princeton. Peebles and I worked on our critical review of observations relating to CDM on galaxy scales in a borrowed office. We were interrupted by a great talk by Alice Shapley (Princeton) on gas-phase metallicities as a function of redshift, including all the complex differences between star-formation regions at high redshift and low. We were also interrupted by the inimitable Tuesday Lunch (now Bahcall Lunch) which continues in the traditional way. I spoke about Astrometry.net, which generated a surprising amount of questions given that most of the audience is concerned with much more theoretical matters.


USNO-B and 2MASS, embargoed correlations

Barron and I continued a multi-day conversation about how to use the 2MASS Catalog to verify and analyze our false negative rate on our work on removing spurious sources from the USNO-B Catalog. It is not trivial, because many of the spurious sources are very close to non-spurious sources, which often match at 2MASS entry.

Gruzinov, Berlind (visiting from Vanderbilt), and I spent some time discussing how to use statistical correlations to associate sources across very disparate bandpasses. I would say more, but the result in question is under embargo. I don't like it when the private journals and collaborations embargo results. Aren't we all scientists, living in a world of ideas? Who ever benefited from a scientific embargo? I bet it wasn't a scientist!


all talk

After a very thought-provoking Computer Science Colloquium about Ask.com, I had a lunch meeting with NYU's Rob Fergus in Computer Science, with whom I have significant research overlap. He and I discussed image combination and recognition of information in images, fields in which both of us currently work (with very different angles).

In the afternoon, Louie Strigari (Irvine) gave a nice astro seminar on using very small objects, and dark-matter properties on small scales, to test the fundamental properties of the dark sector. He argued that current data on the latter are not constraining, but that the dwarf galaxies are potentially very interesting.


spitzer spectroscopy, data analysis

Wu and I went up to Columbia to meet with Schiminovich and his group to discuss a possible spectroscopic observing proposal for the final cryogenic observing cycle of the Spitzer Space Telescope. The meeting was productive and we all have marching orders.

After my triumphant blog post yesterday, when I thought my research day was over, I went to a great talk by Bruce Knuteson (MIT) who spoke about extremely general data analysis plans for finding departures from the standard model in LEP and LHC data. It relates to a number of things we have been thinking about with astronomical data.


another referee report

The gods are smiling, because I got two friendly, constructive referee reports in the same week. When's the last time that happened? I spent time this morning working on the report on Masjedi et al; it is only 07:30 and I have already put in some solid research today!


fine astrometric calibration

Barron showed up today and we worked on getting the USNO-B paper ready for resubmission, after a very prompt (thanks, anonymous referee!) referee report from the AJ. We also discussed his system for determination of image dates, which involves precise astrometric calibration to a set of minutely different astrometric catalogs (each set to a different epoch), and decided that we should write it up now, with the thought that writing it up will focus the issues.

Mierle and I spent a few minutes discussing astrometric tweak at the end of our new, weekly Astrometry.net telecon; getting the output of Astrometry.net to be precise enough for use—unmodified—by scientific users is at the top of our priorities for the coming months. Mierle and I are convinced that a ransac-like approach will work, though neither of us has demonstrated this with functional code. Roweis and Lang are not convinced. Mierle put a bunch of tickets in our trac system to help get a ransac testbed working.


image dates, seminars

Barron demonstrated that he can determine approximately the date an image was taken, using the proper motions of the moving stars. His test was a real image of the Beehive cluster we found on the web. This is great: Not only can we calibrate the astrometry of your image based on the image pixels alone, we can also calibrate the clock! The precision is going to depend on the field size and the proper motion distribution that happens to exist in the field of view.

Group meeting was Blanton telling us what he learned in Spain about massive spectroscopy projects underway in the next few years. The Astro seminar was Alison Farmer (Harvard) describing a plasma-physics solution to some oddities about Saturn's rotation and radio emission.


libraries and astronomy

Had discussions this afternoon with NYU Libraries. We are looking into the possibility that the library could have a role in data archiving and preservation, even for astronomical data.


dimensions of space

Albion Lawrence (Brandeis) gave the high energy seminar on the meaning of the 10 dimensions of string theory. It seems that the true dimensionality is debatable, because it depends how you determine the dimensionality of spacetime, empirically. When dimensions are large or infinite it is easy, but small, finite, wrapped dimensions can appear as dimensions of spacetime or as extra particle states or as non-trivial topology in manifolds of lower dimensionality. Insane!


low-luminosity galaxies

After proposals, letters, and teaching, my only significant research today was reading and commenting on Wu's introduction for her paper on very low luminosity galaxies.


galaxies, linear algebra, and neutron star stuff

I barely put pen to paper—and when I did it was on merging galaxies—but a lot happened today. At group meeting, Zolotov spoke about her project to measure the properties of dark-matter halos using stellar tracers, either stellar tracers of the potential or of the configuration. Wu spoke about her project to look at the star-formation histories of galaxies as a function of their group environment. Both of these projects have a lot of different places to go.

The Computer Science Colloquium was by Ronen Basri (Weizmann), speaking about fast lookup of nearest neighbors in databases, but where the data objects are linear subspaces and the queries are points. His talk included some great example problems, but also some beautiful linear algebra. I spent some time after the talk thinking about the linear subspace issue; it is a great one. I don't think it has anything to do with Astrometry.net. After the talk I spoke with NYU CS's Yann LeCun and new faculty member Rob Fergus, both of whom have interests that partially overlap mine.

The Astro Seminar was by Bob Rutledge (McGill) and on the physical properties of neutron stars. By improving the modeling of their emission, he has greatly improved measurements of the mass–radius relation and can plausibly rule out some reasonable equations of state. If Constellation X never flies, Rutledge may have the last word on the subject!



I am not sure that prioritizing is a word, but I spent most of my research time today prioritizing the near-term activities of Astrometry.net. We need to get funding, and we need to have a clear research focus for those funding proposals. We need to interface with various viewer and archive and distributed computing systems. We need to work through a whole bunch of new data. And we need to facilitate new science and data discovery.


photon interactions with the dark sector

I attended a very nice seminar today by Aaron Chou (NYU) about his work on an experiment looking for oscillations between photons and dark particles like axions or equivalent. He has a null result, which rules out some experimental claims. I was interested in the work because it might be superseded by astronomical measurements of transparency, one of which I am in the process of making right now.


Planck, halo, tickets

Gorski (JPL) gave a nice talk on the Planck mission, drawing particular attention to comparisons with COBE and WMAP in design, survey strategy, and data analysis. He showed surprising evidence for anisotropy in the WMAP maps, although certainly did not advocate that our Universe is anisotropic! He has been working on high-end data analysis for the Planck mission with supercomputing facilities.

During the rest of the day, I generated a lot of tickets (bug reports) on the Astrometry.net management system related to funding (grrr) and our upcoming USNO-B clean data release. Lang and I spent a short phonecon with the VAMP team regarding meta data standards. I also discussed observational handles on the dark-matter component of the Milky Way with Zolotov.


rule violations, dark matter, magnetic fields

To violate my rules (see column at right), I will say that I spent Wednesday on teaching and administrivia, Thursday on an unplanned vacation, and the weekend and today on grants administration! I have almost forgotten what astrophysics is about!

On the other hand, on Friday I spent a beautiful day in Princeton, where there was a lovely memorial and reception in memory of Bodhan Paczynski, who I admired not just for his astrophysics contributions but for all sorts of reasons that don't count as research. I realized that Astrometry.net is nicely aligned with Paczynski's calls for opening up new observational capabilities, especially those that might lead to serendipitous discovery and time-domain astrophysics (lensing, supernovae, asteroids, etc.).

Before the memorial, Peebles and I spent a few hours arguing about ways to use the stellar and baryonic components of galaxies to infer the fundamental properties of the dark-matter concentrations in which they reside, as those fundamental properties are predicted by the CDM model. We spoke much and accomplished little, but it gave our writing on the subject a kick in the pants.

I also attended a Princeton gravity group talk by Battefeld (Princeton) on the possibility that primordial magnetic fields in galaxies arise from cosmic string interactions with cosmic plasma. Insane? You might think so, but in fact there are very few mechanisms out there that have a good shot of working to make the seeds that galactic dynamos could amplify to the observed levels at the present day.