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. (!!)