## Wednesday, 25 June 2008

### It's the same!

From arXiv:0806.3278

Title:
Correlations between MIR, FIR, H$\alpha$, and FUV Luminosities for SWIRE galaxies

The figure shows the correlation between observed H-alpha + 24 micro (y-axis, left-hand panel) and H-alpha + 8 micro (y-axis, right-hand panel) luminosities with the extinction-corrected H-alpha luminosities (x-axis) for star-forming galaxies selected from the Spitzer-SWIRE fields.

Filled circles: Normal galaxies
Open circles: Dwarf galaxies
Lines: Best nonlinear (solid) and linear (dotted) fit

## Friday, 6 June 2008

### SXDF SMGs & BzKs

from Takagi et al., http://arxiv.org/abs/0806.0888

The authors attempt to investigate whether submillimeter galaxies can be
identified by simple color cuts. The answer is: probably not, with the
resolution of current submm instruments.

### Spectroscopic Confirmation Of An Extreme Starburst At Redshift 4.547

Capak et al., http://arxiv.org/abs/0806.0657

This is a set of images of an extreme object at z=4.5 in the COSMOS survey.  It is the most distant mm source not associated with an optically bright quasar. The rest-frame UV and Lya imaging (the first five panels on the left) show emission near the lower left of the panes, although no emission is detected in the B-band because it falls blueward of the Lyman break. At longer wavelengths, the emission shifts to the upper left; the panel on  the far right shows radio contours.

The estimated star formation rate is 1000-4000 Msun/yr, based on several indicators. The authors argue against significant AGN activity -- which would mean this SFR could be a severe overestimate -- because there is no xray detection and because an optical spectrum shows no hint of an AGN.  But, as the authors note, an AGN could lie outside the optical slit.  In fact I think this a fairly likely explanation since the authors placed the slit on the center of the UV emission (lower left), whereas an AGN would be expected to be associated with the longer wavelengths (upper right), which is where the most of the stellar mass and radio activity is.

### Evidence for a Stellar-Dominated UV Background and Against a Decline of Cosmic Star Formation Beyond z~3

From Faucher-Giguere et al (http://arxiv.org/abs/0806.0372). The authors use the Lyman-alpha forest opacity to estimate the photoionizing background at 2 < z < 4.2. After subtracting the contribution from AGNs, they suggest that stellar sources are dominant (and thus may be responsible for reionization). Perhaps more remarkably, they determine a cosmic star formation rate that is flat, at odds with the well accepted Hopkins and Beacom (2006) curve.