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Browsing by Author "Fu, Hai"

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    About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Ly alpha blobs
    (Oxford University Press, 2016-07-28) Schirmer, Mischa; Malhotra, Sangeeta; Levenson, Nancy A.; Fu, Hai; Davies, Rebecca L.; Keel, William C.; Torrey, Paul; Bennert, Vardha N.; Pancoast, Anna; Turner, James E. H.; Arizona State University; Arizona State University-Tempe; University of Iowa; Australian National University; University of Alabama Tuscaloosa; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; Massachusetts Institute of Technology (MIT); California State University System; California Polytechnic State University San Luis Obispo
    We report the discovery of 14 Ly alpha blobs (LABs) at z similar to 0.3, existing at least 4-7 billion years later in the Universe than all other LABs known. Their optical diameters are 20-70 kpc, and GALEX data imply Ly alpha luminosities of (0.4-6.3) x 10(43) erg s(-1). Contrary to high-z LABs, they live in low-density areas. They are ionized by AGN, suggesting that cold accretion streams as a power source must deplete between z = 2 and 0.3. We also show that transient AGN naturally explain the ionization deficits observed in many LABs. Their Ly alpha and X-ray fluxes decorrelate below less than or similar to 10(6) years because of the delayed escape of resonantly scattering Ly alpha photons. High Ly alpha luminosities do not require currently powerful AGN, independent of obscuration. Chandra X-ray data reveal intrinsically weak AGN, confirming the luminous optical nebulae as impressive ionization echoes. For the first time, we also report mid-infrared thermal echoes from the dusty tori. We conclude that the AGN have faded by three to four orders of magnitude within the last 10(4-5) years, leaving fossil UV, optical and thermal radiation behind. The host galaxies belong to the group of previously discovered Green Bean galaxies (GBs). Gemini optical imaging reveals smooth spheres, mergers, spectacular outflows and ionization cones. Because of their proximity and high flux densities, GBs are perfect targets to study AGN feedback, mode switching and the Ly alpha escape. The fully calibrated, co-added optical FITS images are publicly available.
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    The nature of optical features in the inner region of the 3C 48 host galaxy
    (University of Chicago Press, 2007-04-10) Stockton, Alan; Canalizo, Gabriela; Fu, Hai; Keel, William; University of Hawaii System; University of California System; University of California Riverside; University of Alabama Tuscaloosa
    The well-known quasar 3C 48 is the most powerful compact steep-spectrum radio-loud QSO at low redshifts. It also has two unusual optical features within the radius of the radio jet (similar to 1"): (1) an anomalous, high-velocity narrow-line component, and (2) a bright continuum peak (3C 48A) similar to 1" northeast of the quasar. Both of these optical features have been conjectured to be related to the radio jet. We have obtained Gemini North GMOS integral field unit (IFU) spectroscopy of the central region around 3C 48. We use the unique features of the IFU data to remove unresolved emission at the position of the quasar. The resolved emission at the wavelength of the high-velocity component is peaked <= 0.25" north of the quasar, at the same position angle as the base of the radio jet. These observations appear to confirm that this high-velocity gas is connected with the radio jet. However, most of the emission comes from a region where the jet is still well collimated, rather than from the regions where the radio maps indicate strong disruption. We also present the results of HST STIS spectroscopy of 3C 48A. We show that 3C 48A is dominated by stars with a luminosity-weighted age of similar to 1: 4; 10(8) yr, substantially older than any reasonable estimate for the age of the radio source. Thus, 3C 48A almost certainly cannot be attributed to jet-induced star formation. The host galaxy of 3C 48 is clearly the result of a merger, and 3C 48A seems much more likely to be the distorted nucleus of the merging partner in which star formation was induced during the previous close passage.