LRG merger rate, K+A morphologies

I worked out an estimate of the merger rate for LRGs from Morad's correlation function result. It is one LRG-like merger for every LRG every 30 Gyr at the mean redshift of the LRG sample, z~1/3.

I commented on the appearances of the top 30 or so K+A-nuclei galaxies in Blanton's lowz sample. Many of them have evidence of recent (last few dynamical times) merger activity. Many do not, of course, but I think it will be much more common than in control samples (to-do).


integral field spectroscopy

Morad and I discussed integral field spectroscopy (IFU) of post-starburst galaxies with Burles and Adam Bolton. It looks like the post-starburst galaxies are perfectly matched to the instrumentation, so there is a great pilot project to propose this year.


bulges from disks

Today I outlined the arguments, pro and con, relating to the idea (very old now; I also found some old references on the subject) that bulges form through the mergers of disks. I read an old paper by Barnes that showed the results of a simulation in which two disks merge to form something that looked like an old bulge, and the bizarre thing is that the bulge so created had a higher central density than either of the two original disks. This goes against common sense, and against the principle that a merger heats the remnant relative to the inputs (the entire motivation for the study in the first place: disks cold, bulges hot). I will email Barnes in the morning for an explanation. I wonder what the current state of the art is.


close pairs, future surveys

I read and commented on (in my annotated bibliography) Carlberg et al. on close pairs, and prepared myself for a long flight to Kona (on which I will prepare my talk and work on my review) by printing out and downloading to my laptop many papers. I found, to my frustration, that many of the papers I am interested in are published in long-dead conference proceedings; Toomre is particularly guilty of publishing unique results this way. Don't publish in unrefereed, obscure, or one-off book locations! Duh!

I discussed with Glennys Farrar my (and NYU's) involvement in future observational projects.


interacting K+As

Morad noticed that the post-starburst galaxy images up at today's research page (named "SDSS_J01*.jpg") comprise a close pair, from which we can derive a timescale. I also noticed that this galaxy (below) is the highest luminosity galaxy in Blanton's "lowz" sample with a K+A nucleus. Nice interaction! (The circle has a radius of 100 h-1 kpc.)

In both of these cases, it is plausible that we will be able to estimate a timescale that is good to a factor of a few; the first with the crossing time, the second with the dynamical time times the number of visible loops. Email from Scott Tremaine a few days ago was pessimistic in the latter case.


Hipparcos paper

The only thing I accomplished today was a small fraction of the work needed to get our Hipparcos paper ready for resubmission. Not a good day!


post-starburst images

I started making some large-angle jpgs of low-redshift post-starburst galaxies (really just post-starburst nuclei, since the SDSS fibers are small); the first few can be viewed at today's research page. The circles are spaced at intervals of 100 h-1 kpc at the Blanton-inferred distance to the object.

So far (randomly) only dwarf galaxies have images; more images are being made as we blog.


dynamical times

Today I got no research done at all. This behavior is deprecated.

After I spoke at MIT CSR Science Lunch, Burles noted that if (a) the K+A events are triggered by mergers or interactions, and if (b) morphological merger evidence lasts for N dynamical times, where N is relatively independent of dynamical time, then (1) some significant fraction of K+As should show morphological evidence of interactions (duh!), and (2) the fraction should be a linear function of dynamical time, which can be estimated (at least crudely) from the SDSS data themselves. Smart idea, lets do it.


astrometry interface, K+A event rate

I gave Chris Wu his starter project on the astrometry user interface to introduce him to the group and our astronomical way of life (and to move the astrometry project forward, of course).

I worked out a very simple approach to the K+A galaxy modeling project (in which we use the statistics of K+A (post-starburst) galaxies to infer an event rate and starburst size distribution). The simplifying idea is to model not the space density of events, but to model the probability per unit time that any individual galaxy undergoes an event of a particular (fractional) size. With some simplifying assumptions, the project becomes very straightforward to implement and interpret. And Quintero has already done a lot of the heavy lifting on this one.


rules, student projects, astrometry

The most important rule for this research diary blog is that I must post every single work day (unless I am traveling or have no internet connection), and that I cannot count purely administrative work (eg, committees, letters of recommendation, grant administration) or purely teaching work (eg, class prep, lecture note writing). Indeed, if I have done no research that day, I must admit it up-front.

While I did nearly no research today, Blanton and I did work out a possible revised project for Ilya, and Sam, Blanton, and I worked out a trial project for Chris Wu.

Morad and I started the process of trimming the huge USNO-B1.0 catalog down to a useable size for the first astrometry demonstration project, which will be to solve all SDSS fields. I updated the astrometry WWW page to include milestone descriptions, and started work on the annotated bibliography.


Kona, Shectman

I outlined my talk for the Kona meeting by email to the group, and started it in Keynote (tm). The challenge is to present the primary result of Blanton et al. in an understandable way in a few minutes.

I discussed the future of optical detectors with Steve Shectman, who is visiting from OCIW.


RC3 atlas, brightness for astrometry

All I did today was announce to the SDSS Collaboration the completion of my atlas of SDSS images of a diameter-selected subsample of the RC3. I got lots of response from the Collaboration, but this does not qualify as a resarch accomplishment, so today was a failure.

I noticed this disturbed early-type galaxy, possibly revealing a recent-past accretion event:

Sam and I spent a bit of time discussing the use of magnitude/brightness information in the vapor-ware astrometry engine. We concluded that, for the demonstration project at least, it makes sense to make stellar patterns out of stars of similar brightness, where "similar" clearly involves some free parameters.

I spent last Thursday and Friday (2005-02-10 and 11) visiting McGill.


Spitzer, steady-state clustering

Morad and I "finished" the Spitzer proposals, although they will probably need to be resubmitted a few times as we (read: Blanton) find typos and improve the language and the specificity of the goals. My problem is: If you knew what you were going to do with the data, you wouldn't have to ask for it. I have trouble being specific in proposals.

Morad and I discussed his small-scale galaxy–galaxy clustering result in terms of a simple model: Imagine the clustering is "created" by a steady inflow of galaxies. Then the number density n(R) as a function of radius R should be related to the flow rate dR/dt. Two thoughts: (1) You can then reverse engineer the flow rate from the number density, or (2) You can use the intuition that the flow rate ought to increase with decreasing radius to argue that n(R) cannot be "steeper" (more centrally concentrated) than R–2. Morad is finding something steeper than this! One possibility: The flow rate into the system is not steady, but is in fact decreasing with time. This could steepen it, in principle. But it is certainly strange, especially at small scales where dynamical friction ought to dominate.


Spitzer, bowtie, CLASS/JVAS

Morad and I slaved away on Spitzer proposals, and Blanton and I argued over email about the expected flux of a r=16 mag dwarf galaxy (for the proposals). Eventually Morad and I decided that its minimum possible flux would be about 0.07 mJy at 10 microns, if it has a very blue spectrum and absolutely no hot dust or PAH emission. Most dwarfs ought to be substantially brighter.

Morad reminded me that one of the principal reasons to observe K+A galaxies with Spitzer is to rule out the possibility that they appear K+A only because the O and B stars are enshrouded in dust. This dust problem is not likely to be important, but it needs to be ruled out.

For sanity, I made some pretty pictures; check out this "bowtie" bulge-dominated galaxy with a dust lane. A merger remnant?

I discussed by email with Chris Fassnacht the possibility of doing a correlation function of flat-spectrum radio sources, inspired by an argument of mine that they could be used to accurately measure the merger rate (subject to many provisos). Unfortunately, it appears that nobody on CLASS/JVAS is interested, and I certainly don't have time. Any takers?


Spitzer proposals, Raleigh-Jeans tail

Today was all Spitzer proposals, one with Morad on post-starburst galaxies (because Spitzer can tell us if the starburst really did use all of the available fuel), and one with Blanton on low-luminosity galaxies (because we showed that low-luminosity galaxies are PAH-deficient, and no-one knows why).

I was reminded of the terrible "dwarf" terminology of astronomy; one of many classifications in astronomy that is either over-determined or under-determined, depending on who you ask, and for which the multiple determining factors are weighted differently by different investigators. Sounds like an issue for Hogg's Universe.

In the process of estimating Spitzer observing times, I was reminded that it is trivial to derive the Raleigh-Jeans blackbody approximation by dimensional analysis and the realization that, since it is the classical limit, h cannot appear in the formula.


at Texas Tech, public talks

Spent the last two days in Lubbock TX at Texas Tech. Gave the Physics Colloquium there and then a public talk. My public talk had several deficiencies: (1) it did not have any video of structure formation and galaxy merging, (2) it did not get across just how "empty" and transparent galaxies are, and (3) it did not get across the two somewhat contradictory ideas that (a) dark matter is hypothetical, but at the same time, (b) our evidence for it is very strong.


RC3 errors, Spitzer, dust lane

In inspecting the outputs of my automated RC3 atlas-making code, I have found many errors in the RC3 (or at least in our VAGC copy of it). This is perhaps not surprising, but I think we need to create and publish (on arXiv?) a corrected version. Unfortunately, I am only motivated to fix those parts that overlap the SDSS.

Morad and I discussed Spitzer proposals; we have outlined one to look at the star-formation fuel left in post-starburst galaxies.

I found this post-starburst galaxy (the small companion inside the bigger galaxy), that is associated with a galaxy with a minor-axis dust lane. Toomre tells me that minor-axis dust lanes are a sign of recent merging.


converting names to sky positions

I had a frustratingly unproductive day today. My only tangible accomplishment was to make a non-robust "name" to "RA,Dec" converter in IDL that makes use of wget and grep. It's available on today's research page, and in Princeton CVS module idlutils.