Browsing by Author "Stern, Daniel"

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    Open Access
    The Role of the Most Luminous Obscured AGNs in Galaxy Assembly at z similar to 2
    (2017) Farrah, Duncan; Petty, Sara; Blain, Andrew; Efstathiou, Andreas; Lacy, Mark; Stern, Daniel; Lake, Sean; Jarrett, Tom; Benford, Dominic; Tsai, Chao-Wei; Assef, Roberto; Moustakas, Leonidas
    We present Hubble Space Telescope WFC3 F160W imaging and infrared spectral energy distributions for 12 extremely luminous, obscured active galactic nuclei (AGNs) at 1.8 < z < 2.7. selected via "hot, dust-obscured" mid-infrared colors. Their infrared luminosities span (2-15) x 10(13) L-circle dot, making them among the most luminous objects in the universe at z similar to 2. In all cases, the infrared emission is consistent with arising at least for the. most part from AGN activity. The AGN fractional luminosities are higher than those in either submillimeter galaxies. or AGNs selected via other mid-infrared criteria. Adopting the G, M-20, and A morphological parameters, together with traditional classification boundaries, infers that three-quarters of the sample are mergers. Our sample does not, however, show any correlation between the considered morphological parameters and either infrared luminosity or AGN fractional luminosity. Moreover, the asymmetries and effective radii of our sample are distributed identically to those of massive galaxies at z similar to 2. We conclude that our sample is not preferentially associated with mergers, though a significant merger fraction is still plausible. Instead, we propose that our sample includes. examples of the massive galaxy population at z similar to 2 that harbor a briefly luminous, "flickering" AGN. and in which the G and M-20 values have been perturbed. due to either the AGN. and/or the earliest formation stages of a bulge in an inside-out manner. Furthermore, we find that the mass assembly of the central black holes in our sample leads the mass assembly of any bulge component. Finally, we speculate that our sample represents. a small fraction of the immediate antecedents of compact star-forming galaxies at z similar to 2.
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    Wise detections of known QSOs at redshifts greater than six
    (2013) Blain, Andrew W; Assef, Roberto; Stern, Daniel; Tsai, Chao-Wei; Eisenhardt, Peter; Bridge, Carrie; Benford, Dominic; Jarrett, Tom; Cutri, Roc; Petty, Sara; Wu, Jingwen; Wright, Edward L
    We present WISE All-Sky mid-infrared (IR) survey detections of 55% (17/31) of the known QSOs at z > 6 from a range of surveys: the SDSS, the CFHT-LS, FIRST, Spitzer, and UKIDSS. The WISE catalog thus provides a substantial increase in the quantity of IR data available for these sources: 17 are detected in the WISE W1 (3.4 mu m) band, 16 in W2 (4.6 mu m), 3 in W3 (12 mu m), and 0 in W4 (22 mu m). This is particularly important with Spitzer in its warm-mission phase and no faint follow-up capability at wavelengths longward of 5 mu m until the launch of James Webb Space Telescope (JWST). WISE thus provides a useful tool for understanding QSOs found in forthcoming large-area optical/IR sky surveys using PanSTARRS, SkyMapper, VISTA, DES, and LSST. The rest-UV properties of the WISE-detected and the WISE-non-detected samples differ: the detections have brighter i/z-band magnitudes and redder rest-UV colors. This suggests that a more aggressive hunt for very high redshift QSOs by combining WISE W1 and W2 data with red, observed optical colors could be effective at least for a subset of dusty candidate QSOs. Stacking the WISE images of the WISE-non-detected QSOs indicates that they are, on average, significantly fainter than the WISE-detected examples, and are thus not narrowly missing detection in the WISE catalog. The WISE catalog detection of three of our sample in the W3 band indicates that their mid-IR flux can be detected individually, although there is no stacked W3 detection of sources detected in W1 but not W3. Stacking analyses of WISE data for large active galactic nucleus samples will be a useful tool, and high-redshift QSOs of all types will be easy targets for JWST.
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    WISE J233237.05–505643.5: A DOUBLE-PEAKED, BROAD-LINED ACTIVE GALACTIC NUCLEUS WITH A SPIRAL-SHAPED RADIO MORPHOLOGY
    (2013) Tsai, Chao-Wei; Jarrett, T H; Stern, Daniel; Emonts, Bjorn; Barrows, R Scott; Assef, Roberto J; Norris, Ray P; Eisenhardt, Peter R M; Lonsdale, Carol; Blain, Andrew W; Benford, Dominic J; Wu, Jingwen; Stalder, Brian; Stubbs, Christopher W; High, F William; Li, K L; Kong, Albert K H
    We present radio continuum mapping, optical imaging and spectroscopy of the newly discovered double-peaked broad-lined AGN WISE J233237.05-505643.5 at redshift z = 0.3447. This source exhibits an FR-I and FR-II hybrid-morphology, characterized by bright core, jet, and Doppler-boosted lobe structures in ATCA continuum maps at 1.5, 5.6, and 9 GHz. Unlike most FR-II objects, W2332-5056 is hosted by a disk-like galaxy. The core has a projected 5" linear radio feature that is perpendicular to the curved primary jet, hinting at unusual and complex activity within the inner 25 kpc. The multi-epoch optical-near-IR photometric measurements indicate significant variability over a 3-20 year baseline from the AGN component. Gemini-South optical data shows an unusual double-peaked emission-line features: the centroids of the broad-lined components of H-alpha and H-beta are blueshifted with respect to the narrow lines and host galaxy by ~ 3800 km/s. We examine possible cases which involve single or double supermassive black holes in the system, and discuss required future investigations to disentangle the mystery nature of this system.