Articles by Jens Melinder

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.

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).

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.

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).

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

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.

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 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).