do protoplanetry disks make an important contribution to the NIR flux of star forming galaxies?

The most common (and best) way of deriving stellar masses from broadband SEDs is to fit the observed SED with synthetic stellar population models.  This method basically assumes that you can reliably decompose the observed SED into the contributions from stars of all ages, almost always with some simplifying assumption about the actual age distribution (viz. a parameterised star formation history and a stellar initial mass function).

Mentuch et al. have modelled a bunch of galaxies using standard stellar population models.  Their sample is drawn from the GDDS, and comprises 103 galaxies at z < 1 with strong detections in IRAC channel 4 (8 microns).  They have shown that the star forming galaxies in their sample show an excess in the NIR at 2--5 microns (upper panel of this Figure).  This Figure also shows that the excess can be very well described by inclusion of an additional component (lower panel), which they describe as 'a template PAH spectrum superposed on an 850 K greybody modified by lamba^-1 extinction'.  They argue that this additional component is most likely associated with emission from circumstellar protoplanetary disks (rather than instellar cirrus, reflection nebulae, or post AGB stars).

This is pretty cool, 'cause it potentially offers a means of probing the formation of planetary systems in high-redshift galaxies. (!!)

Galaxy Zoo Green Peas: Discovery of A Class of Compact Extremely Star-Forming Galaxies

Mmmmmm peas!!!!!

The next journal club to be presented on the 10th of August.

Check it out at;

http://arxiv.org/abs/0907.4155

Plot: Inhomogeneity in the Supernova Remnants as Natural Explanation of the PAMELA/ATIC Observations

PAMELA anomaly could have a simple answer.

Plot: Strong [CII] emission at high redsift

With the detection of the [CII] transition this increases the potential to use this transition to search and characterise high-z sources.

A Comparison of Galaxy Merger History Observations and Predictions from Semi-Analytic Models

 This paper (http://xxx.lanl.gov/abs/0904.2365) presents some interesting results from comparing predicted merger rates and fractions from the Millennium Simulation to observations of galaxy mergers out to z~3.   

Plot: Cluster Strong Lensing in Millennium Simulation

The Problem: How do secondary matter structures and stellar mass in galaxies along the line-of-sight affect strong cluster lensing?
What they do: Use ray-tracing through the Millennium simulation to probe this contribution.
Answer: There can be considerable increases to strong-lensing optical depth and cross-sections.

160309: Evidence for hierarchical, inside-out growth

The Problem: massive but really compact, high z, quiescent galaxies have been observed - but where are their descendants?

What they do: compare the densities of a sample of these high z galaxies to nearby elliptical galaxies;

compare growth evolution from three models  

Answer:  they may be the dense cores of nearby galaxies suggesting inside-out growth