Browsing by Subject "emission-lines"

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A Candidate Dual Active Galactic Nucleus At Z=1.175
(2012-01) Barrows, R. Scott; Stern, Daniel; Madsen, Kristin; Harrison, Fiona; Assef, Roberto J.; Comerford, Julia M.; Cushing, Michael C.; Fassnacht, Christopher D.; Gonzalez, Anthony H.; Griffith, Roger; Hickox, Ryan; Kirkpatrick, J. Davy; Lagattuta, David J.; Comerford, Julia M.
The X-ray source CXOXBJ142607.6+353351 (CXOJ1426+35), which was identified in a 172 ks Chandra image in the Bootes field, shows double-peaked rest-frame optical/UV emission lines, separated by 0.''69 (5.5 kpc) in the spatial dimension and by 690 km s(-1) in the velocity dimension. The high excitation lines and emission line ratios indicate both systems are ionized by an active galactic nucleus (AGN) continuum, and the double-peaked profile resembles that of candidate dual AGNs. At a redshift of z = 1.175, this source is the highest redshift candidate dual AGN yet identified. However, many sources have similar emission line profiles for which other interpretations are favored. We have analyzed the substantial archival data available in this field as well as acquired near-infrared (NIR) adaptive optics (AO) imaging and NIR slit spectroscopy. The X-ray spectrum is hard, implying a column density of several 10(23) cm(-2). Though heavily obscured, the source is also one of the brightest in the field, with an absorption-corrected 2-10 keV luminosity of similar to 10(45) erg s(-1). Outflows driven by an accretion disk may produce the double-peaked lines if the central engine accretes near the Eddington limit. However, we may be seeing the narrow line regions of two AGNs following a galactic merger. While the AO image reveals only a single source, a second AGN would easily be obscured by the significant extinction inferred from the X-ray data. Understanding the physical processes producing the complex emission line profiles seen in CXOJ1426+35 and related sources is important for interpreting the growing population of dual AGN candidates.
High-Resolution H-Band Spectroscopy Of Be Stars With SDSS-III/Apogee. I. New Be Stars, Line Identifications, And Line Profiles
(2015-01) Chojnowski, S. Drew; Whelan, David G.; Wisniewski, John P.; Majewski, Steven R.; Hall, Matthew; Shetrone, Matthew; Beaton, Rachael; Burton, Adam; Damke, Guillermo; Eikenberry, Steve; Hasselquist, Sten; Holtzman, Jon A.; Meszaros, Szabolcs; Nidever, David; Schneider, Donald P.; Wilson, John; Zasowski, Gail; Bizyaev, Dmitry; Brewington, Howard; Brinkmann, J.; Ebelke, Garrett; Frinchaboy, Peter M.; Kinemuchi, Karen; Malanushenko, Elena; Malanushenko, Viktor; Marchante, Moses; Oravetz, Daniel; Pan, Kaike K.; Simmons, Audrey; Shetrone, Matthew D.
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has amassed the largest ever collection of multi-epoch, high-resolution (R similar to 22, 500), H-band spectra for B-type emission line (Be) stars. These stars were targeted by APOGEE as telluric standard stars and subsequently identified via visual inspection as Be stars based on H I Brackett series emission or shell absorption in addition to otherwise smooth continua and occasionally non-hydrogen emission features. The 128/238 APOGEE Be stars for which emission had never previously been reported serve to increase the total number of known Be stars by similar to 6%. Because the H band is relatively unexplored compared to other wavelength regimes, we focus here on identification of the H-band lines and analysis of the emission peak velocity separations (Delta v(p)) and emission peak intensity ratios (V/R) of the usually double-peaked H I and nonhydrogen emission lines. H I Br11 emission is found to preferentially form in the circumstellar disks at an average distance of similar to 2.2 stellar radii. Increasing Delta v(p) toward the weaker Br12-Br20 lines suggests these lines are formed interior to Br11. By contrast, the observed IR Fe II emission lines present evidence of having significantly larger formation radii; distinctive phase lags between IR Fe II and H I Brackett emission lines further supports that these species arise from different radii in Be disks. Several emission lines have been identified for the first time including C I 16895, a prominent feature in the spectra for almost a fifth of the sample and, as inferred from relatively large Delta v(p) compared to the Br11-Br20, a tracer of the inner regions of Be disks. Emission lines at 15760 angstrom and 16781 angstrom remain unidentified, but usually appear along with and always have similar line profile morphology to Fe II 16878. Unlike the typical metallic lines observed for Be stars in the optical, the H-band metallic lines, such as Fe II 16878, never exhibit any evidence of shell absorption, even when the H I lines are clearly shell-dominated. The first known example of a quasi-triple-peaked Br11 line profile is reported for HD 253659, one of several stars exhibiting intra- and/or extraspecies V/R and radial velocity variation within individual spectra. Br11 profiles are presented for all discussed stars, as are full APOGEE spectra for a portion of the sample.
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.
Kiloparsec-Scale Spatial Offsets In Double-Peaked Narrow-Line Active Galactic Nuclei. I. Markers For Selection Of Compelling Dual Active Galactic Nucleus Candidates
(2012-07) Comerford, Julia M.; Gerke, Brian F.; Stern, Daniel; Cooper, Michael C.; Weiner, Benjamin J.; Newman, Jeffrey A.; Madsen, Kristin; Barrows, R. Scott; Comerford, Julia M.
Merger-remnant galaxies with kiloparsec (kpc) scale separation dual active galactic nuclei (AGNs) should be widespread as a consequence of galaxy mergers and triggered gas accretion onto supermassive black holes, yet very few dual AGNs have been observed. Galaxies with double-peaked narrow AGN emission lines in the Sloan Digital Sky Survey (SDSS) are plausible dual AGN candidates, but their double-peaked profiles could also be the result of gas kinematics or AGN-driven outflows and jets on small or large scales. To help distinguish between these scenarios, we have obtained spatial profiles of the AGN emission via follow-up long-slit spectroscopy of 81 double-peaked narrow-line AGNs in SDSS at 0.03 <= z <= 0.36 using Lick, Palomar, and MMT Observatories. We find that all 81 systems exhibit double AGN emission components with similar to kpc projected spatial separations on the sky (0.2 h(70)(-1) kpc < Delta x < 5.5 h(70)(-1) kpc; median Delta x = 1.1 h(70)(-1) kpc), which suggests that they are produced by kiloparsec-scale dual AGNs or kiloparsec-scale outflows, jets, or rotating gaseous disks. Further, the objects split into two subpopulations based on the spatial extent of the double emission components and the correlation between projected spatial separations and line-of-sight velocity separations. These results suggest that the subsample (58(-6)(+5)%) of the objects with spatially compact emission components may be preferentially produced by dual AGNs, while the subsample (42(-5)(+6)%) with spatially extended emission components may be preferentially produced by AGN outflows. We also find that for 32(-6)(+8)% of the sample the two AGN emission components are preferentially aligned with the host galaxy major axis, as expected for dual AGNs orbiting in the host galaxy potential. Our results both narrow the list of possible physical mechanisms producing the double AGN components, and suggest several observational criteria for selecting the most promising dual AGN candidates from the full sample of double-peaked narrow-line AGNs. Using these criteria, we determine the 17 most compelling dual AGN candidates in our sample.
Near-Infrared Broad-Line Profiles In Low-Redshift QSOs
(1992-08) Thompson, Keith L.; Thompson, Keith L.
We present near-infrared and optical spectrophotometry of six low-redshift QSOs. The integrated Pa-alpha/H-alpha-ratios cluster near the value 0.1, with one exception having a larger ratio consistent with other evidence of reddening. At least two of the Pa-alpha/H-alpha-profile ratios decrease with observed velocity. We discuss some implications for the dynamics of the broad-line region and this ratio's usefulness as a reddening indicator. We also present a spectrum of the He I-lambda-10830, Pa-lambda-blend of 1226 + 023. The He I/H-alpha-profile ratio shows marginal evidence for decreasing with observed velocity, which is consistent with the interpretation for the Pa-alpha/H-alpha-profile ratios.