Browsing by Subject "peaked"

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Identification Of Outflows And Candidate Dual Active Galactic Nuclei In SDSS Quasars At Z=0.8-1.6
(2013-06) Barrows, R. Scott; Lacy, Claud H. Sandberg; Kennefick, Julia; Comerford, Julia M.; Kennefick, Daniel; Berrier, Joel C.; Comerford, Julia M.
We present a sample of 131 quasars from the Sloan Digital Sky Survey at redshifts 0.8 < z < 1.6 with double peaks in either of the high-ionization narrow emission lines [Ne V]lambda 3426 or [Ne III]lambda 3869. These sources were selected with the intention of identifying high-redshift analogs of the z < 0.8 active galactic nuclei (AGNs) with double-peaked [O III]lambda 5007 lines, which might represent AGN outflows or dual AGNs. Lines of high ionization potential are believed to originate in the inner, highly photoionized portion of the narrow line region, and we exploit this assumption to investigate the possible kinematic origins of the double-peaked lines. For comparison, we measure the [Ne V]lambda 3426 and [Ne III]lambda 3869 double peaks in low-redshift (z < 0.8) [O III]-selected sources. We find that [Ne V]lambda 3426 and [Ne III]lambda 3869 show a correlation between line splitting and line width similar to that of [O III]lambda 5007 in other studies, and the velocity splittings are correlated with the quasar Eddington ratio. These results suggest an outflow origin for at least a subset of the double peaks, allowing us to study the high-ionization gas kinematics around quasars. However, we find that a non-negligible fraction of our sample show no evidence for an ionization stratification. For these sources, the outflow scenario is less compelling, leaving the dual AGN scenario as a viable possibility. Finally, we find that our sample shows an anti-correlation between the velocity-offset ratio and luminosity ratio of the components, which is a potential dynamical argument for the presence of dual AGNs. Therefore, this study serves as a first attempt at extending the selection of candidate dual AGNs to higher redshifts.
The Ultraviolet-Bright, Slowly Declining Transient PS1-11Af As A Partial Tidal Disruption Event
(2014-01) Chornock, Ryan; Berger, E.; Gezari, S.; Zauderer, B. A.; Rest, A.; Chomiuk, L.; Kamble, A.; Soderberg, Alicia M.; Czekala, I.; Dittmann, J.; Drout, M.; Foley, Ryan J.; Fong, W.; Huber, M. E.; Kirshner, Robert P.; Lawrence, A.; Lunnan, R.; Marion, G. H.; Narayan, G.; Riess, Adam G.; Roth, K. C.; Sanders, N. E.; Scolnic, D.; Smartt, S. J.; Smith, K.; Stubbs, C. W.; Tonry, J. L.; Burgett, W. S.; Chambers, K. C.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Magnier, E. A.; Martin, D. C.; Neill, J. D.; Price, P. A.; Wainscoat, R.; Marion, G. H.
We present the Pan-STARRS1 discovery of the long-lived and blue transient PS1-11af, which was also detected by Galaxy Evolution Explorer with coordinated observations in the near-ultraviolet (NUV) band. PS1-11af is associated with the nucleus of an early type galaxy at redshift z = 0.4046 that exhibits no evidence for star formation or active galactic nucleus activity. Four epochs of spectroscopy reveal a pair of transient broad absorption features in the UV on otherwise featureless spectra. Despite the superficial similarity of these features to P-Cygni absorptions of supernovae (SNe), we conclude that PS1-11af is not consistent with the properties of known types of SNe. Blackbody fits to the spectral energy distribution are inconsistent with the cooling, expanding ejecta of a SN, and the velocities of the absorption features are too high to represent material in homologous expansion near a SN photosphere. However, the constant blue colors and slow evolution of the luminosity are similar to previous optically selected tidal disruption events (TDEs). The shape of the optical light curve is consistent with models for TDEs, but the minimum accreted mass necessary to power the observed luminosity is only similar to 0.002 M-circle dot, which points to a partial disruption model. A full disruption model predicts higher bolometric luminosities, which would require most of the radiation to be emitted in a separate component at high energies where we lack observations. In addition, the observed temperature is lower than that predicted by pure accretion disk models for TDEs and requires reprocessing to a constant, lower temperature. Three deep non-detections in the radio with the Very Large Array over the first two years after the event set strict limits on the production of any relativistic outflow comparable to Swift J1644+57, even if off-axis.