Browsing by Author "Willner, S. P."

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    Beyond Simple AGN Unification with Chandra-observed 3CRR Sources at 0.5 < z < 1
    (2021) Kuraszkiewicz, Joanna; Wilkes, Belinda J.; Atanas, Adam; Buchner, Johannes; McDowell, Jonathan C.; Willner, S. P.; Ashby, Matthew L. N.; Azadi, Mojegan; Barthel, Peter; Haas, Martin; Worrall, Diana M.; Birkinshaw, Mark; Antonucci, Robert; Chini, Rolf; Fazio, Giovanni G.; Lawrence, Charles; Ogle, Patrick
    Low-frequency radio selection finds radio-bright galaxies regardless of the amount of obscuration by gas and dust. We report Chandra observations of a complete 178 MHz-selected, and so orientation-unbiased, sample of 44 0.5 < z < 1 3CRR sources. The sample is comprised of quasars and narrow-line radio galaxies (NLRGs) with similar radio luminosities, and the radio structure serves as both an age and an orientation indicator. Consistent with unification, intrinsic obscuration (measured by N (H), X-ray hardness ratio, and X-ray luminosity) generally increases with inclination. However, the sample includes a population not seen in high-z 3CRR sources: NLRGs viewed at intermediate inclination angles with N (H) < 10(22) cm(-2). Multiwavelength analysis suggests that these objects have lower L/L (Edd) than typical NLRGs at similar orientation. Thus, both orientation and L/L (Edd) are important, and a "radiation-regulated unification" provides a better explanation of the sample's observed properties. In comparison with the 3CRR sample at 1 < z < 2, our lower-redshift sample shows a higher fraction of Compton-thin NLRGs (45% versus 29%) but a similar Compton-thick fraction (20%), implying a larger covering factor of Compton-thin material at intermediate viewing angles and thus a more "puffed-up" torus atmosphere. We posit that this is due to a range of L/L (Edd) extending to lower values in this sample. In contrast, at high redshifts, the narrower range and high L/L (Edd) values allowed orientation (and so simple unification) to dominate the sample's observed properties.
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    ON THE NATURE OF THE FIRST GALAXIES SELECTED AT 350 mu m
    (IOP PUBLISHING LTD, 2009) Khan, Sophia A.; Chanial, Pierre F.; Willner, S. P.; Pearson, Chris P.; Ashby, M. L. N.; Benford, Dominic J.; Clements, David L.; Dye, Simon; Farrah, Duncan; Fazio, G. G.; Huang, J. S.; Lebouteiller, V.; Le Floc'h, Emeric; Mainetti, Gabriele; Moseley, S. Harvey; Negrello, Mattia; Serjeant, Stephen; Shafer, Richard A.; Staguhn, Johannes; Sumner, Timothy J.; Vaccari, Mattia
    We present constraints on the nature of the first galaxies selected at 350 mu m. The sample includes galaxies discovered in the deepest blank-field survey at 350 mu m (in the Bootes Deep Field) and also later serendipitous detections in the Lockman Hole. In determining multiwavelength identifications, the 350 mu m position and map resolution of the second generation Submillimeter High Angular Resolution Camera are critical, especially in the cases where multiple radio sources exist and the 24 mu m counterparts are unresolved. Spectral energy distribution templates are fitted to identified counterparts, and the sample is found to comprise IR-luminous galaxies at 1 < z < 3 predominantly powered by star formation. The first spectrum of a 350 mu m selected galaxy provides an additional confirmation, showing prominent dust grain features typically associated with star-forming galaxies. Compared to submillimeter galaxies selected at 850 and 1100 mu m, galaxies selected at 350 mu m have a similar range of far-infrared color temperatures. However, no 350 mu m selected sources are reliably detected at 850 or 1100 mu m. Galaxies in our sample with redshifts 1 < z < 2 show a tight correlation between the far-and mid-infrared flux densities, but galaxies at higher redshifts show a large dispersion in their mid-to far-infrared colors. This implies a limit to which the mid-IR emission traces the far-IR emission in star-forming galaxies. The 350 mu m flux densities (15 < S(350) < 40 mJy) place these objects near the Herschel/SPIRE 350 mu m confusion threshold, with the lower limit on the star formation rate density suggesting the bulk of the 350 mu m contribution will come from less luminous infrared sources and normal galaxies. Therefore, the nature of the dominant source of the 350 mu m background-star-forming galaxies in the epoch of peak star formation in the universe-could be more effectively probed using ground-based instruments with their angular resolution and sensitivity offering significant advantages over space-based imaging.