Friday, August 18, 2006

M. Wood-Vassey: The ESSENCE of dark energy

There are different approaches to measure w (Baryon accoustics, Galaxy clusters, Supernova Luminosity distances and an on-the-spot addition of weak lensing (was fun watching the speaker change his slide...). For supernova distancies the systematics have to be understood, and get the statistics right (finding the correct confidence limits on w).

M.W. then made some general remarks that were quite funny, and I also wholeheartedly agree on most of them.
Thoughts for observers: Design your experiment, design your analysis, test your analys, ignore the theorist, get a pet theorist.
Thoughts on theorists: Too many theories (quintessence as an example), far too many models (can fit anything)-> All M.W. wants is a well-motivated theory.

The ESSENCE survey is a 6year project on the CTIO in Chile. Data released immediately after reduction, using 2 filters. Getting SNe at z~0.7. They are cross-checking the results using the SNLS SALT. They get w=-0.88 (0.12), but it's still consistent with w=-1 (error margin only 68% confidence). Essence is using a similar approach as the the project I'm working on for subtracting images and detecting SNe.

P. Garnavich: What do host galaxies of Ia supernovae tell us

It's important to understand host galaxy properties of Ia SNe to beat down the systematic uncertainties in the SN photometry => better determination of cosmological parameters.

Ia SNe ar not good standard candles (vary by a factor of 10-30). Dust extinction laws has to be used to correct or dust in hosts. This uses the obserevd colours of the SNe. Measure the host galaxy properties to constrain this and other uncertainties: (i) Metallicity; (ii) Star formation history; (iii) Dust properties.

A strong division of Ia properties in different host morpholgies is known and confirmed with the current sample. Fast declining Ia's preferntially in spiral/SF galaxies (need more than morphology, spectra better than colours). Perhaps due to a brightness-metallicity relation? No clear trend found for decline rate vs host metallicity. Fast SNe found only(!) in hosts with very low SFR (more important than the metallicity). A correlation of SFR in galaxies and numbers of bright SNe how that brighter SNe are more common in galaxies with higher SFR. No clear change with redshift of this is detected (SNLS result).

There are many more high SFR galaxies in the field than as SN hosts, P.G. claim this is support for delay times of Ia's (or rather a second delay time "channel", having Ia SNe that are not related to the ongoing SF in the galaxies).

R. Ellis: New constraints on the comoving SFR in the redshift interval 6

A declining UV luminosity density at z>3 is found for dropout galaxies. Still a bit controversial, mostly due to big errors on the initial measurements at these high redshifts, but most people agree that it's real. Another interesting discovery is the luminosity-dependent evolution discovered in dropoout galaxies (cf. talks by R. Bouwens and I. Iwata).

An independent check: the accumulated stellar mass has to be produced. The found SFH's must be consistent with the assembled stellar mass. R.E. uses GOODs v-dropouts to estimate the stellar mass density at z~3-4. Part of the the sample have spectra, use these to calibrate the method (?, he went pretty quickly through those slides). They parametrize the SFH and compare with the found masses. The result is that there is too little SF going on to account for the stellar mass history. These stars could be formed in low-luminosity systems that occupy the faint end of the LF (and suffer from incompleteness).

A survey of lensed galaxies around a number of Abell cluster, have been able to deetct objects at very high z. Six objects have been found at z~10(!). The lensing is redshift dependent in the way that a specific region ("isophote") of the cluster is where objects of a certain redshift will fall. => bias against low-z galaxies. These galaxies might(?) have Lalpha emission, but is very faint in that case. They might contribute significantly to reionization.

D. Koo: CATS: Center for Adaptive optics Treasury Survey of distant galaxies, SNe and AGN

AO is very expensive, this survey is focused on observing the already well-studied fields (GOODs, GEMS, EGS).

AO for distant galaxies is valuable becasue: (i) Good match of psf cf HST; (ii) galaxy components have sub-kpc sizes ideal for AO (z~0.5-5);(iii)optical regime shifted to NIR. Why not use AO? Need AO stars, PSF is uncertain (problematic for SN detections?), low efficiency. Laser guide star is in use, this increases the possible area for doing AO.

Study merging galaxies (resolve components) and comparing to stellar synthesis models can give information on merging processes at high redshifts. Can find SNe at high redshifts inside galaxies at NIR wavelengths (one found at z=1.24), but need nearby PSF star and give precisions of ~0.1 mag (which to me suggests that they have problems with the photometry).

The second week

I just tried to convince a collegue, who will be here during the next week, to continue what I started. I've said it before: If you yourself are an astronomer at this meeting and are interested in blogging here, please drop me an email (thomas.marquart (at) and I'll add you to the list. The technical part is easy.

Not quite the end

I will post some more of the talks I've attended, there have been quite a few really nice talks during this week.

On a sidenote...
Arp220 optical image

Arp220 corrected for dust, slightly smoothed using a Voronoi beer algorithm

The end?

First of all, thanks to Jens, who also wrote some summaries during the last days and posted them below.

The poster session is over (I got some nice feedback from people), I have checked out and will soon meet the guy with whom I'll be staying over the week-end (with HC). This means the conference is over for me and I certainly enjoyed it.

During the week-end, I'll finally get to see Prague. There is a slight chance that I will attend some talks on Monday before I fly back to Sweden in the evening. If not, I will at least address some of the critics that I got for turning down the "planet issue" below.

It was fun to write this blog and it felt good that it at least got some attention. Thanks to all readers. At times it was more effort than I expected to simultaneously listen, get the major points and rephrase them in own words. I will have to read over all of it after a while to judge for myself if I succeeded or not.

R. Abraham: Morphology, the 6th road to downsizing

A very apt title, the topic of downsizing have been discussed in almost all of the talks in the galaxy session so far.

Five roads to downsizing:
- Massive red and dead galaxies
- Mass density evolution
- Mass-segregated SFH
- Abundant post starburst pop at z~1
- Evolutio of mass-metallicty relation

R.A. worry that this might be a "bandwagon" that everyone is jumping on. Galaxy evolution sweetspot is at z~1-2, highest derivative of mass assembly is at this time. Playing devil's advocate he finds that if the z~0 points of mass essembly is correct, 50 % of massive galaxies are from between z~1-2. But this might be a problem of large errors in the derivations.

Use ACS observations of galaxy morpholgies at z~1-2 to investigate how the mass in stars have changed from 2 to 0. When doing this you have to make sure you're going deep enough, that you have a sufficiently large area (should be larger than HDF) and to misapply the assymetry vs concentration diagram (S/N or completeness problems perhaps, not sure I got that, it could also be a question of which filters are used?).

How to measure morphology? R.A. thinks that concentration is not the best way to do this, rather use a more general statistic => Gini statistic/coefficient. This coefficient seems to be more robust than the concentration parameter. He finds that at z~1 about 70% of the stellar should exist in the early-type galaxies and that there is strong evolution in this fraction in z~1-2. Another conclusion is that mass density evolution of early types + assymetric early types is similar to the evolution of post-starbursts at z~3.

C. Popovich: The star formation and assembly of high redshift galaxies

Observational constraints regarding massive galaxy formation, (i) when did the stars form; (ii) when did massive galaxies arrive at their current configuration. Comparison to theoretical predictions. Massive galaxies at high redshift are found in the red sequence of colour-magnitude diagrams (COMBO-17).

Luminosity density evolution in the red-sequence galaxies is more or less constant (mild evolution), this shows that passive evolution is not the complete explanation. Looking at SFR for galaxies of different masses show that massive galaxies start to dominate the total SF at high redshifts (>~2).

Using Spitzer 24micron observations it's found that massive galaxies at high-z (~1.5-3) are in an IR-active phase of evolution. Looking at the specific SFR C.P. finds that at z~1.5-3 massive galaxies form stars as fast or faster than the cosmic average. At z<1 the galaxies have already formed their stars and the total SF is dominated by lower mass galaxies. (Cf. talks by many others, this seems to be accepted). Understanding of the role of AGN is also important to explain these observations.

Agreement between SFRs from X-ray, IR, submm, UV by a factor of 2. This is good because Spitzer 24 micron probes restframe mid-IR at z~2 => use this data to get SFRs for these galaxies. This show an increasing cosmic SFR out to z~2. These observations might not be in line with hierarchical models (De Lucia et al. 2006).

New blogger entering

My name is Jens Melinder and I'm a PhD student at Stockholm Observatory working on detections of supernovae at high redshifts. During the first week of the general assembly I've attended talks in the Galaxy evolution session (S235), in the Universe at redshifts>6 session (JD06) and the Supernova session (JD09), my blogs will be about my impressions of some of the talks and a short summary of the topic covered in them. Disclaimer: I make no claims to getting things right when writing the notes/summary, in many cases I might be totally wrong...

Friday's star formation

I missed some talks in the morning, but sleep is important, too. I came in time for the last three talks of S237 on "Triggered Star Formation in a Turbulent ISM" and all three were interesting.

C. Norman was talking about his theoretical work on disk simulations and what struck me a little was that people have enough confidence in the simulations being a good approximation for the real world, to do physics with "observations" on the simulated world and derive properties and laws from there. Of course, this is tempting since one has complete control over the simulation and can get much better "data" than in the real world. There are tons of arguments and tests that reassure and convince people that this really works and, indeed, why should a program that implements a well-understood physical process fail, except for (also well-understood) limitations like resolution and other approximations. But still, if one could observe it, one would not need simulated data, so since we cannot, there is also a lack in testing the simulations to the real world.

Using the density distribution function of the ISM (log-normal except at very low densities) and a scaling relation for the critical density where SF sets in, Norman showed an alternative to the Schmitt-law (also called Kennicutt-law) that has a more shallow slope and flattens out at high gas surface densities. The observed slope then has to be understood by a change in SF-efficiency, which offset the model with respect to each other. Since the observed correlation is very tight, this would mean that also SFE correlates tighly with gas density.

The next speaker, M. Krumholtz, started from simple arguments to understand why SF is so inefficient in the sense that the SFR would be 50 higher (both in the Milky-Way and in extreme cases like Arp220) if all the molecular clouds that are present would collapse and form stars. I cannot reproduce the whole line of argument now, but he also used the density distribution (depending on mass and virial parameter) in the turbulent medium and integrated over the region above the critical value to get SFRs which fell into the observed regime. This could be tested, if the census of molecular clouds in nearby galaxies would stretch to smaller masses, by simply comparing the predicted SFR as derived from the molecular gas content with the observed one.

The last talk and summary of this symposium was given by B. Elmegreen and he again stressed the importance of turbulence for SF, instead of the older picture of monolithic collapse of a molecular cloud.

In the afternoon, there will be a "poster session", which basically means that everyone who has a poster, stands by it to answer the questions of the people coming by. The problem is that, although not all have posters, many do and one has to find the balance to also look at the other posters and talk to the author, but that won't work if they just do the same thing. Surprisingly, it always works out somehow anyway and I am happy that they scheduled this also for S235 for which no poster session was planned initially.