Person:

Caldwell, Nelson

We explore the connection between different classes of active galactic nuclei (AGNs) and the evolution of their host galaxies, by deriving host galaxy properties, clustering, and Eddington ratios of AGNs selected in the radio, Xray, and infrared (IR) wavebands. We study a sample of 585 AGNs at 0.25 <z< 0.8 using redshifts from the AGN and Galaxy Evolution Survey (AGES). We select AGNs with observations in the radio at 1.4 GHz from the Westerbork Synthesis Radio Telescope, X-rays from the Chandra XBootes Survey, and mid-IR from ¨ the Spitzer IRAC Shallow Survey. The radio, X-ray, and IR AGN samples show only modest overlap, indicating that to the flux limits of the survey, they represent largely distinct classes of AGNs. We derive host galaxy colors and luminosities, as well as Eddington ratios, for obscured or optically faint AGNs. We also measure the two-point cross-correlation between AGNs and galaxies on scales of 0.3–10 h−1 Mpc, and derive typical dark matter halo masses. We find that: (1) radio AGNs are mainly found in luminous red sequence galaxies, are strongly clustered (with Mhalo ∼ 3 × 1013 h−1 M), and have very low Eddington ratios λ 10−3; (2) X-ray-selected AGNs are preferentially found in galaxies that lie in the “green valley” of color–magnitude space and are clustered similar to the typical AGES galaxies (Mhalo ∼ 1013 h−1 M), with 10−3 λ 1; (3) IR AGNs reside in slightly bluer, slightly less luminous galaxies than X-ray AGNs, are weakly clustered (Mhalo 1012h−1 M), and have λ > 10−2. We interpret these results in terms of a simple model of AGN and galaxy evolution, whereby a “quasar” phase and the growth of the stellar bulge occurs when a galaxy’s dark matter halo reaches a critical mass between ∼ 1012 and 1013 M. After this event, star formation ceases and AGN accretion shifts from radiatively efficient (optical- and IR-bright) to radiatively inefficient (optically faint, radio-bright) modes. Ke

We present 432 low-dispersion optical spectra of 32 Type Ia supernovae (SNe Ia) that also have well-calibrated light curves. The coverage ranges from 6 epochs to 36 epochs of spectroscopy. Most of the data were obtained with the 1.5 m Tillinghast telescope at the F. L. Whipple Observatory with typical wavelength coverage of 3700-7400 Å and a resolution of ~7 Å. The earliest spectra are 13 days before B-band maximum; two-thirds of the SNe were observed before maximum brightness. Coverage for some SNe continues almost to the nebular phase. The consistency of the method of observation and the technique of reduction makes this an ideal data set for studying the spectroscopic diversity of SNe Ia.