Wednesday 10th Oct 2012

GOODS-Herschel: radio-excess signature of hidden AGN activity in distant star-forming galaxies

A. Del Moro, D. M. Alexander, J. R. Mullaney, E. Daddi, M. Pannella, F. E. Bauer, A. Pope, M. Dickinson, D. Elbaz, P. D. Barthel, M. A. Garrett, W. N. Brandt, V. Charmandaris, R. R. Chary, K. Dasyra, R. Gilli, R. C. Hickox, H. S. Hwang, R. J. Ivison, S. Juneau, E. Le Floc’h, B. Luo, G. E. Morrison, E. Rovilos, M. T. Sargent, Y. Q. Xue

We present here a new spectral energy distribution (SED) fitting approach that we adopt to select radio-excess sources amongst distant star-forming galaxies in the GOODS-Herschel (North) field and to reveal the presence of hidden, highly obscured AGN. Through extensive SED analysis of 458 galaxies with radio 1.4 GHz and mid-IR 24 um detections using some of the deepest Chandra X-ray, Spitzer and Herschel infrared, and VLA radio data available to date, we have robustly identified a sample of 51 radio-excess AGN (~1300 deg^-2) out to redshift z~3. These radio-excess AGN have a significantly lower far-IR/radio ratio (q<1.68) than the typical relation observed for star-forming galaxies (q~2.2). We find that ~45% of these radio-excess sources have a dominant AGN component in the mid-IR band, while for the remainders the excess radio emission is the only indicator of AGN activity. The fraction of radio-excess AGN increases with X-ray luminosity reaching ~60% at Lx~10^44-10^45 erg/s, making these sources an important part of the total AGN population. However, almost half (24/51) of these radio-excess AGN are not detected in the deep Chandra X-ray data, suggesting that some of these sources might be heavily obscured. We also find that the specific star formation rates (sSFRs) of the radio-excess AGN are on average lower that those observed for X-ray selected AGN hosts, indicating that our sources are forming stars more slowly than typical AGN hosts, and possibly their star formation is progressively quenching.


Clustering of Far-Infrared Galaxies in the AKARI All-Sky Survey

A. Pollo (1,2,3), T. T. Takeuchi (4), T. L. Suzuki (4), S. Oyabu (4) (1 Center for Theoretical Physics of the Polish Academy of Sciences, 2 Astronomical Observatory of the Jagiellonian University, 3 The Andrzej Soltan Institute for Nuclear Studies, 4 Division of Particle and Astrophysical Science, Nagoya University)

We present the first measurement of the angular two-point correlation function for AKARI 90-$\mu$m point sources, detected outside of the Milky Way plane and other regions characterized by high Galactic extinction, and categorized as extragalactic sources according to our far-infrared-color based criterion (Pollo et al. 2010). This is the first measurement of the large-scale angular clustering of galaxies selected in the far-infrared after IRAS measurements. Although a full description of clustering properties of these galaxies will be obtained by more detailed studies, using either spatial correlation function, or better information about properties and at least photometric redshifts of these galaxies, the angular correlation function remains the first diagnostics to establish the clustering properties of the catalog and observed galaxy population. We find a non-zero clustering signal in both hemispheres extending up to $\sim 40$ degrees, without any significant fluctuations at larger scales. The observed correlation function is well fitted by a power law function. The notable differences between a northern and southern hemisphere are found, which can be probably attributed to the photometry problems and point out to a necessity of performing a better calibration in the data from southern hemisphere

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