Monday, December 31, 2012

2012 Recap

Another year gone. This one seemed to have flown by particularly fast (thanks to the arrival of Marten James Talles). Science results were not thin on the ground though. First paper from the NHEMESES survey (2012a), awarded more Herschel time for this survey, two nice results on dust lanes in edge-on galaxies (2012b and nearly submitted). 2012ab accepted in the same week that Marten arrived. That was a good week.

Oh and the final thesis paper was accepted by Astronomische Nachrichten. No more frankenpaper!

The HI Quantified Morphology series is ticking along nicely. One more accepted in 2012, one more submitted. There may be one more in the Hopper but that remains to be seen. A QM paper for the S4G is in the works too. For more HI results I'll have to wait for the WALLABY and WNSHS surveys.

LADUMA still ticking along. It's a "potje" project. Keep lumping coals on the fire under the kettle and some substantial time later, something good will come of it.

I got to go observing with the WHT on La Palma! Small occulting galaxies. The Occulting galaxy catalog by Bill Keel was finally published which makes follow-up much easier. IFU observations, Hubble proposals etc etc. That project is looking brighter.

Yes 2012 looked pretty good. And the Hopper for 2013 publications is pretty full. Hopefully this will all translate into an astro-job someplace.

Sunday, December 9, 2012

La Palma Night 2

Last night started with a leisurely tutorial in ACAM use since it was so cloudy & all (could see Sirius...briefly...) and then it cleared up. Some. I started with the highest priority objects. Observing is mostly that. Strategize, plan, prioritize, accurately tell the telescope what to do.
In that way it reminds me of flight school. None of the particular tasks in the cockpit were that difficult. Each of them can be done easily. By a trained monkey. But you have to do *all* of them. In order. At the right time. Efficiently. And that is very much the case with observing as well.

Tonight is a good night. Clear, everything is working great (knock on wood) and I racked in the other Priority 1 objects (well most of them) in short order. Time to doubt my strategy. Should I expose longer? Are two filters enough? With three I can make RGB images. Always good...

And I messes up slightly, I queued a pair too early (meaning we observed it not when it was at its highest point in the sky but still climbing. Rectifying that now.
There is some high cloud coming in so I will slot my cirrus special: an extra exposure in each filter to make sure we get enough photons.

In the meantime, I have not been idle. The raw data from last night has been converted into B/W images (bias subtraction, flatfielding and stacking, nothing more fancy). It reacquainted me with IRAF and its quirks some...


Saturday, December 8, 2012

La Palma night 1

As part of the occulting galaxies project with Bill Keel, we've been asking for follow-up time on various mid-sized telescopes (3 to 4m mirror, a 2m will do in a pinch). The idea is to improve on the depth of the SDSS images these were so nicely identified in by the GalaxyZoo volunteers.

So this week I have a run of 5 dark (!) nights on the William Herschel Telescope on La Palma.
Flew in yesterday, crashed, met fun other astronomers, went up to the telescope, sat in on the ongoing night of observations, looked at the coming cloud cover (blerg is the official term I believe) and
crashed again.

Tonight is the first night of real observing for my run, even if that means I may be staring at clouds the whole time. Plan B is to finish plots and write-up for a bunch of papers to I will keep busy.

Wednesday, December 5, 2012

The Andromeda Project


Thanks to the efforts of Bill Keel, I get to participate in the Andromeda Project, the latest in a series of astronomy citizen science efforts in which we-as-a-species find and classify objects on the sky.
It all started with the Galaxy ZOO project (currently in its 4th incarnation) which helped me and Bill find occulting galaxy pairs (more on that here).
This initial success hammered home for me the power of crowd source science, especially for astronomy.

And now we have

http://www.andromedaproject.org/

a new effort to find and size star clusters in our nearest neighbour galaxy, M31 aka Andromeda.
Thanks to the PHAT survey, there will be HST images for about 1/3 of that galaxy but to find
all the little clumps of stars, we will need a lot of eyeballs-on-data.

What can I contribute? Well back in the Pleistocene (ahem halcyon days of my PhD) I studied the number of background galaxies through foreground disks. I used that number to estimate the
dust content of the foreground spiral galaxy. But in this project. misclassification of a background object may well be the greatest contaminant to a clean cluster catalog. So the volunteers will be looking for these as well. Bill and me will be using these little galaxies to study the dust in M31.
I may have a go at using their number but the most interesting use will be to take a background galaxy (preferably an elliptical) and see if a dust structure from M31 is visible highlighted against the backdrop of the background galaxy.

During my PhD, I never thought there would be ever enough data on M31 to do any of this and then Julianne Dalcanton got the PHAT program approved. Super-excited to see several interests combine here: Hubble, citizen science, background galaxies, star clusters and dust.

So sign up! Help classify star clusters! Or keep playing Angry Birds...I know what I will do...

Wednesday, November 28, 2012

Lame Duck Comparison

I am an expert in the Sextractor software. It's a great tool. Not perfect (the coding could be cleaner, better annotated etc etc) but a veriable swiss army knife of a piece of software. So people use it as a yardstick to compare their own code to. However, this often happens in cases where it has already been clearly stated that SE won't work too well (crowded fields for example).

So a paper like this one annoys me slightly:

http://arxiv.org/abs/1211.5805

Probabilistic Catalogs for Crowded Stellar Fields

We introduce a probabilistic (Bayesian) method for producing catalogs from images of crowded stellar fields. The method is capable of inferring the number of sources (N) in the image and can also handle the challenges introduced by overlapping sources. The luminosity function of the stars can also be inferred even when the precise luminosity of each star is uncertain. This is in contrast with standard techniques which produce a single catalog, potentially underestimating the uncertainties in any study of the stellar population and discarding information about sources at or below the detection limit. The method is implemented using advanced Markov Chain Monte Carlo (MCMC) techniques including Reversible Jump and Nested Sampling. The computational feasibility of the method is demonstrated on simulated data where the luminosity function of the stars is a broken power-law. The parameters of the luminosity function can be recovered with moderate uncertainties. We compare the results obtained from our method with those obtained from the SExtractor software and find that the latter significantly underestimates the number of stars in the image and leads to incorrect inferences about the luminosity function of the stars.
The issues I have with this paper are twofold. First, the comparison is in crowded fields, an area that every piece of SE documentation (including my own) states is not what to use SE for.
And the actual comparison is extemely weak. They only tweak the detection threshold, which is only one of the relevant parameters here. The other are the level of deblending that could be tweaked and the number of deblending thresholds. I bet I can retrieve quite a few more than 30% of the stars with just SE.

So the whole paper now comes down to making their own (computationally heavy) approach look good. The SE catalog is a straw man. Of course I have not been asked to referee it so they're probably fine.


Monday, November 26, 2012

IMF

I crashed the Initial Mass Function workshop at the Lorentz Center, organized by Scott Trager.
Very nice atmosphere. Excellent discussion. Too many open questions on this topic.
The IMF has been on my "need to learn more about" list for a while. We're off to a good start.
Some of my tweets from today:

Opening the hood on how to get from cluster function to stellar one good definition of a can of worms (8)

Problem in M/L in high-mass, high-metallicity environments factor 10 worse. (7)

"All problems in extragalactic astrophysics can be solved by a suitable choice of the IMF" - Dave (6)

Many claims of different IMFs in extra-galactic systems, every whichaway (5)

Bastian: claims of bottom-heavy IMF never refuted, just ignored (4)

Bastian gave props to two (ex)ESA fellows: Nate Leigh & Morten Andersen (3)

Early types with high metallicity is where IMF gets weird (2)

Nate Bastian says IMF uniform in Galaxy according to MW SF community (1)

Sunday, November 25, 2012

ResearchGate

Just signed up for researchgate.net and it is an interesting experiment. The Astronomy side of things is still a little too light. And I cannot for the life of me figure out what their RG score means. Probably another metric to stress about. Meanwhile, hardly anyone I work with or whose work I follow is on it yet. Then again, maybe too early to tell for this new thing.


Friday, November 23, 2012

Skinning the pigs

Several papers are in the final stages. Almost ready to go to journal, almost ready to show to coautors. The colloquialism for that is that "one has skinned the pig except the ear". They are so close to done it's maddening. Today I finished the Zoo paper on dust lanes and it's off to co-authors. Last of the quantified morphology papers is pretty much ready to go to MNRAS. Next up are the S4G morphology paper wrap-up and submission, the Milky Way in M-dwarfs paper and then there is the paper on VIMOS observations of the occulting galaxy pair.

Good thing I gave the last of the talks for this year, the Internal Colloquium at ESTEC. Chatted about HI morphology to everyone interested in galaxies at ESA.

Wednesday, September 5, 2012

The Last Thesis Paper

A thesis is often a few papers bound together. Mine made it through the committee partly because it was made of 5 accepted articles and two successful HST proposals.

The thing is...often you end up with a chapter here or there or some follow-up idea that you'd really like to do...you know...sometime.
I had a few and as a result there were three more papers that were based in part on ideas I first mentioned in the thesis. I can't say that I had already forseen that it would be really interesting to compare the results from the number of background galaxies to the dust surface densities from spectral energy distribution model fits. We had to wait for Herschel to be launched first.

But a large part of the original science question was to compare the spiral disk opacity to the column density of neutral hydrogen gas. I finally did that. Not the radial profile, the actual surface density derived from a THINGS map. This kind of stuff is only possible if the HI survey is public. In this sense the THINGS survey has been the game-changer. No more, would a grad student have to beg the fits file off 20 different authors...or read in the radial profile from crappy gifs.
Data is online. Go play.

So the last idea using the thesis data points is done: http://arxiv.org/abs/1209.0306 We get a high dust-to-gas ratio. Most likely an upper limit if I am being honest but certainly a point worth making. SED models tend to underestimate the dust surface density in spirals unless it's the Draine et al model. I have made my point. It is the bookend for all the thesis work and we're done.

right?

unless I want to count the number of galaxies seen through M101 and M81...

just for fun...


Friday, August 31, 2012

They'll make a spectroscopist out of me yet

Putting together one of three (at least) proposals for WHT observations on La Palma. Already had some success obtaining Dutch time (going observing in December, woop!) but this time round, I'm aiming for some much more riskier idea that Torsten had and we are now developing.
And it involved that ol familiar: the WHT/ISIS spectrograph. I have not worked with that kind of data since my master's thesis. It looks like this particular instrument and setup will just nicely fit the bill.

Now to convince a casual onlooker that I know a thing or two about spectra and AGNs.

Thursday, August 30, 2012

Memory Leak

I suspect something has been updated in my python installation (possibly by yours truly) but a pice of code I've been relying on has started memory leaking like I have HD to spare.
Optemizing this python code had been on my "well someday" list anyway so here goes. Python code is nearly never optimized. If you wanted it to run superfast, you don't code in python. You code in python because it takes an afternoon of your time. If the runtime is then till the next day, who cares?

It better run a little more efficient. I need to run a local Galaxy Catalog through it. Time to optimize this puppy.

Wednesday, August 29, 2012

Saggitarius Again

For a while I had been struggling with a strange overdensity of M-dwarfs in the BoRG survey. It felt as a strange coincidence or a fault in the identification process. Thanks to Bob Benjamin, I finally got a positive ID on what could be causing the overdensity: the Saggitarius stream. Even the distances of the bulk of M-dwarfs in that particular field fit nicely with the typical distance to Saggitarius dwarf: 20-25 kpc.

To me this revealed a big gap in our knowledge of the Milky Way. Suppose you are a extragalactic astronomer and find some odd over-density of point sources. Before you write the paper on some z~8 cluster, you need to check there is no stellar stream surrounding the MW of any kind in the vicinity. But a decent map collating all the known streams, arms, satellites and globular clusters and their tidal features etc does not exist yet. My solution: email Bob but there has to be a better one.

Monday, July 23, 2012

The Shiny has landed

Fish has donated his iPhone to the good cause (yours truly). I am having a blast. Now I need to find apps and stuff.

Glee.

Research done today was only pimping my XUV disk paper to D. Thilker. Awesome! Now we will go and check his whole 2012 catalog with the morphological parameters. Spiff new collaborations.

Sunday, July 22, 2012

White Paper

Started thinking about writing a white paper for a specific mission. How do they get published? Do they count for the h-index? Probably not. How gauche is it to pimp own work?
Some of this might be trivial since it will be mostly based on various friend's work anyway.

So what are the ground rules for white paper? And how much time does one spend on one anyway? First time for everything.

Friday, July 20, 2012

pdf's in latex madness

Every time I plan to "quickly" do something, I end up fighting half a day with some weird error message. This time it was to put H12c on astro-ph (see your listing monday!) and to keep under the 15Mb total file size limit, I had to switch from .eps to pdf for the figures. This should all work but for the longest time it would not even compile. Here is what I found for the MNRAS template using tetex on the mac. It works. I may switch to pdfs as my figure format completely.


\documentclass[useAMS,usenatbib]{mn2e}
\usepackage{url}
\usepackage{stmaryrd}
\usepackage[pdftex]{graphicx}

\usepackage[draft]{hyperref}
it is the last two commands that really do it. Suddenly you can use width options in the \includegraphics etc. And we're well under 15Mb for the final figure. Grand. Took all morning.

In other news. Working on my own supersecret PHAT project. Matching postage stamps may be a bit of a challenge.

Wednesday, July 18, 2012

Stellar Stream

Talked to my fellow RFs about what the hell I do all day in that office. One of them being the stellar stream around a nearby galaxy. Nice result. I could convince them of most of my arguments. Now I will go forth and annoy theoreticians with them.

Also had a moment of linguistic debate over twitter whether or not "a generation of Astronomers" is plural or not. It is not.

Also, submitted H12c to astro-ph in the wee hours. A shade too many figures. harumph. Waiting for the moderators to give it a pass.

Monday, July 16, 2012

PHAT, GHOSTS and the last PhD paper

PHAT
Lots of emails from PHAT people on using their data for cool idea[TM]. Got told to use the public data. hmmkay. And they finally convinced me that the ZOO project on the clusters does not need an artificial galaxy test. I think they suspected I wanted to use the background galaxies as an extinction probe. Not for me anymore thank you.

GHOSTS
commented on a nice GHOSTS paper. Got a little worried about the observational strategy (can't be helped now...) but otherwise it is a solid result.

Every astronomer I know is still working on their "last" PhD paper. No exception here. It was going to be a quick comparison back in 2008... Meanwhile Astronomische Nachrichten has nearly accepted it. Motivating myself to finally put a bolt through the Frankenpaper. Cool to round out the trio of European journals though.

Then it's on to NHEMESES poster making and posting the XUV disk results on astro-ph. I need more hours in the day.


Sunday, July 15, 2012

QR codes

The new hip thing on posters at scientific conferences are QR codes on the poster so interested parties can go to the supporting website (or blog!) nice and quickly via their smartphone. I still feel that a mugshot is a better use of poster real estate. That serves the personal-science-ad nature of poster much better right? At SPIE I saw exactly no one use the QR codes.

But I put both on my latest poster. Of course...

Challenge Accepted!

Matt Kenworthy (aka Fish...) has been toying with the idea to blog about research. The rules follow David Hogg's research blog ; post at least 3-5x a week about astronomical research that I'm working on. Fish is doing it. So...Challenge Accepted!

And let's see what we get...