CfA OIR Division Lunch Talks
Wednesday, September 25, 2013, 11:00 am, Building A Classroom
> > > *Two* 30-minute talks; Note change of venue < < <

Galaxy Zoo: Observing Secular Evolution Through Bars
Edmond Cheung (UCSC)

In this talk, I use the Galaxy Zoo 2 dataset to study the behavior of bars in disk galaxies as a function of specific star formation rate (SSFR), and inner galactic structure, i.e., the prominence of the bulge as parameterized by Sérsic index and central surface stellar mass density. Our sample consists of 13,295 disk galaxies, with an overall bar fraction of 23.6 ± 0.4%, of which 1,154 barred galaxies also have bar length measurements. These samples are the largest ever used to study the role of bars in disk galaxy evolution. I find that the likelihood of a galaxy hosting a bar is anti-correlated with SSFR, regardless of stellar mass or bulge prominence. I find that the trends of bar likelihood with bulge prominence are bimodal with SSFR, i.e., in star-forming galaxies, bulges are more prominent in galaxies more likely to host bars, while in quiescent disk galaxies, bars are less frequent where there are prominent bulges. Our observations of bar length reveal a complex picture. In star-forming disks, longer bars are found where the bulges are more prominent, while in quiescent disks there is a maximum in the average bar length as a function of bulge prominence. I interpret these observations using state-of-the-art simulations of bar evolution which include live halos and the effects of gas and star formation. I suggest our observed trends of bar likelihood with SSFR are driven by the gas fraction of the disks; a factor demonstrated to significantly retard both bar formation and evolution in models. I interpret the bimodal relationship between bulge prominence and bar properties as due to the complicated effects of classical bulges and central mass concentrations on bar evolution, and also to the growth of disky pseudobulges by bar evolution. These results represent empirical evidence for secular evolution driven by bars in disk galaxies. This work suggests that bars are not stagnant structures within disk galaxies, but are a critical evolutionary driver of their host galaxies in the local universe (z < 1).

The link between the cosmic near-IR and X-ray backgrounds:
Signatures of the first black holes?
Kari Helgason (UMD)

The first galaxies and miniquasars will remain largely inaccessible to future telescopes, but may be detectable via their contribution to the Cosmic near-Infrared Background (CIB) anisotropies. A significant extragalactic clustering signal from an unresolved population is now well established by CIB fluctuation measurements. I will review the current status of the field, focusing on a recent discovery of a cross-correlation signal between the CIB fluctuations and the unresolved Cosmic X-ray Background. I present a population study of all galaxies and AGN and predict their contributions to the CIB and CXB including the mutual cross-correlation signal. I discuss the signal's potential for probing the early Universe in several upcoming CIB measurements, including LIBRAE, an ESA selected science program dedicated to CIB fluctuation exploration with the Euclid telescope.