4 years in the making...SNIa and their host extinction properties

Back in South Africa (a postdoc, a kid, two moves, a continent, and a lifetime ago) I worked with a summer student, Adam Reynolds, on the possibility of using the SDSS-III data to use Supernovea Type Ia (SNIa) as probes of the ISM. The idea worked in principle on the --then public-- SDSS-III data but to be really convincing, we'd need their final data-release.
This was a few years in the making but finally arrived in 2014 (huzzah!). I dug out Adam's report and converted it to a small paper (script everything folks...). My interest is of course the distribution of extinction values, could not give a fig about SNIa...

The results are interesting. SNIa effectively "see" a dust screen (inclination dependence is cos(i), nothing more fancy) and their distribution is roughly exponential. The latter is weird, based on everything I've seen (PHAT survey results, occulting galaxy pairs), one would expect a log-normal one. I suspect that is what it really is but right now an exponential is used in SNIa measurements.

The gist of the current paper is Host Galaxy Inclination Matters!

So constructing the next version of SNIa cosmology, should start by taking disk inclination into account as the first host observable to be included. My second guess is host mass. But that is the second paper (already submitted...)

After that, one would need to redo the lightcurves with different extinction priors. To provide the templates for that, I got my STARSMOG HST SNAP program. The ultimate goal is here to reduce the errors in SNIa to below 1%. That'll keep them competitive as a cosmological tool.

That'll keep me busy. All that from a side-interest...

you can find the paper here:

SNIa Host Galaxy Properties and the Dust Extinction Distribution

Supernovae Type Ia display a complex relation with their host galaxies. An important prior to the fit of the supernovae's lightcurve is the distribution of host galaxy extinction values that can be encountered. The SDSS-SN project has published light curve fits using both MLCS2k2 and SALT2. We use the former fits extinction parameter (AV) to map this distribution of extinction values.
We explore the dependence of this distribution on four observables; the inclination of the host galaxy disk, radial position of the supernova, redshift of the supernova and host, and the level of star-formation in the host galaxy. The distribution of AV values encountered by supernovae is typically characterised by: N0 e−AV/τ, with τ= 0.4 or 0.33.
We find that the inclination correction using an infinitely thin disk for the SNIa is sufficient, resulting in similar exponential AV distributions for high- and low-inclination disks. The AV distribution also depends on the radial position in the disk, consistent with previous results on the transparency of spiral disks. The distribution of AV values narrows with increased star-formation, possibly due to the destruction or dispersion of the dusty ISM by stellar winds prior to the ignition of the supernova.
In future supernova searches, certainly the inclination of the host galaxy disk, should be considered in the construction of the \av \ prior with τ=0.4/cos(i) as the most likely prior in each individual host galaxy's case.

ESO proposals in with time to spare

...and with time to spare I mean 7 min...

three went in. GAMA groups proposal was in first. occulting group one next. Then a KMOS high-redshift one last.

egads. working so close to a deadline is not my thing.

Fair use of Hubble Images

Hubble images, especially those pretty ones made available through the Hubble Heritage (link), are free to use by everyone. Sometimes by some kind-of-fringy people or plain astrologers. I have seen some professional astronomers lose their cool as their image got sued for a Astrology ad for example.

My attitude is: "Hey, the public paid for these images and everyone in that public gets to use them. Any and all of them. That's fair use."

So imagine my surprise when I got an email regarding my occulting galaxy image (the wallpaper of this blog etc etc) by an author of an alternative galaxy evolution model.

Here is the excerpt he sent me that talked about the overlapping pair:

Case Study of 2MASX J00482185-2507365.    You are on your own, Lil’ Doggy.

In the next illustration the secondarily formed nucleus is considerably smaller than the primary body.  A case of mitosis?  If it is, then a fragment or the tail end of a bar nucleus was dislocated and forcefully and speedily flung for some distance from the galaxy’s center.  It lodged there above the ‘mother’ galaxy, where it has begun to construct its own galaxy of stars.  So small, but it seems to have retained a preference for the bar shape. [Any suggested names for this ‘newbie’ galaxy?]  

  Image of 2MASX J00482185-2507365. Credit  NASA, ESA, and The Hubble Heritage Team STScI, AURA, B. Holwerda, Space Telescope Science Institute, J. Dalcanton U. of Washington

            Before reaching its present location this ‘offspring’ galaxy was a clump of heavy black holes. Perhaps less than 10% of the original nucleus, it still weighed as much as several hundred thousand Suns, perhaps millions.  As it soared through the inner most galaxy and partially through the spiral rings it caused some minor alteration of the star orbits in those areas, which is apparent in the image, minor effects because of its great speed.  Run-away stars and black holes have been well documented.  These are the losers of a gravity contest between two or more big boss bodies.  So, this junior galaxy quickly got to where it wanted to be, then slowed enough to start its own family of stars.  Again, runaways are slowed by the capture of dark matter and increasing weight.  Its present site is ideal for capturing inflowing dark matter.  (Dark matter is instrumental in star formation.)

[Someone want to calculate how long it took to reach the present location?] 

(It is asserted here that the Milky Way nucleus is preparing for a similar event.  See The Case of the Twisted Ring at the Center of the Milky Way, July 20, 2011.)

[Reminder:  Scientists state that no such action is possible because the nucleus is just one oversized black hole that never breaks up or decomposes.  (Except for some vague exceptions.)]

One of the characteristics that distinguish Mitosis from the more common merger of galaxies is the absence of gravitational or pressure waves.  The two entities do not interfere with each other.  Reasons given elsewhere.  

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I will not even pretend I understand the logic but I am flattered that someone got inspired by the picture I helped create (props really go to JD and the Hubble Heritage team) and I appreciate being told about its use. 

HST Cycle-22 Results

So after battling insomnia thanks to the Giant Unspecified Anxiety that I am apparently sensitive to from time to time, I got the results for the Cycle 22 HST proposals early. I had put in three as PI and was invited to a bunch more. The results were in. Two successful ones as PI and two as co-I. A bumper crop year!

The halo of M101 is going to be studied in detail with WFC3 adn ACS with the GHOSTS team and 150 occulting galaxy pairs are going to be the target for a SNAP project. V. cool. Especially the last one is a personal validation after several years in second quartile.

The other two (co-I) are z=9-10 galaxy surveys. One over the CANDELS field and one using the BoRG strategy. Very complementary. v. cool. And fits nice with my latest paper on z=9-10 galaxy sizes and my ongoing project to identify cool Milky Way.

So much SCIENCE!

Definitely a win. Bring me all the bagels and muffins in the land.

The kids playhouse lessons of project management

I have spent a few days spread over thelast months trying to build a swanky play house for the kids. The house itself has been met with approval by its customers, indicating i did a decent enough job.

Coupleof things that happened while building:

- small injury. Handeling wood and tools make scrapes etc inevitable.
- delay due to weather.
- goingback to the hardware store for that thing that I forgot.
- a thing that took longer.
- something that the instructional video made look trivial but wasn’t.
- back to the store for two more planks.
- it took longer.
- late stage suggestions for improvements.

Doesn’t this all sound familiar? With theexception of the more trips to the hardware store than originally anticipated, pretty much all of these are artifacts of astronomy projects. Such things pop up with every project. I have done two projects with woodworking around the house and immediately i can tell you there is a HUGE difference in the documentation. Vague instructions demand lots of improvisation and take much longer (playhoise) and detailed cut list makes it go very quick and smooth (work bench).
additional trips are inevitable but with a clear plan can be cut down significantly.

Small injury amd delay are inevitable. Weather will happen.

But it feels like we have to delude ourselves some every time in order to get started. If the first thought for a project would be “definitely going to need some bandaids during this”, we’d never get started. Same in astronomy I wager.

Is there a part-time phd?

In Europe there are no or hardly any part-time PhDs in astronomy. There used to people that would be on the dole until they finished the PhD. Strickter funding and other rules put mostly an end to that.

Of course there is a PhD comic on the topic.

Not so in the USA where not only do the students pay for the classes but it strongly depends on year-to-year funding. So many people do a phd on the side. Next to a full time job.

So how to set that up? The research part of a phd is a lot harder to do part time. It’s deep work. Hard to get back into after distractions. The kind you do while concentrating on a topic for a long time.
I may now have one or two people who will do a phd with me over many years. Does anyone have experience with the part time PhD student? And how to help them over the finish line?

No idea yet.

Students! Here for SCIENCE! And summer.

This year I am the LEAPS program coordinator together with the ruthlessly organized Catherine Walsh. We work well together. Logistically "interesting" problem, getting everyone from everywhere to Leiden and housed and set up etc. I am the local-Dutch-speaker-in-charge-of-yelling-at-people.
Most have arrived now and are getting started (getting bikes for example). Some final details regarding the four outings to be sorted out.

Funny how exhausting and time-consuming this program is. Fun too.

Excuse me while I call a man about a missing toilet seat. Ah science.