Browsing by Subject "digital-sky-survey"

Now showing 1 - 16 of 16

Adaptive Optics Imaging Of Quasi-Stellar Objects With Double-Peaked Narrow Lines: Are They Dual Active Galactic Nuclei?
(2011-09) Rosario, D. J.; McGurk, R. C.; Max, C. E.; Shields, Gregory A.; Smith, K. L.; Ammons, S. M.; Shields, Gregory A.; Smith, K. L.
Active galaxies hosting two accreting and merging supermassive black holes (SMBHs)-dual active galactic nuclei (AGNs)-are predicted by many current and popular models of black-hole-galaxy co-evolution. We present here the results of a program that has identified a set of probable dual AGN candidates based on near-infrared laser guide star adaptive optics imaging with the Keck II telescope. These candidates are selected from a complete sample of radio-quiet quasi-stellar objects (QSOs) drawn from the Sloan Digital Sky Survey (SDSS), which show double-peaked narrow AGN emission lines. Of the 12 AGNs imaged, we find 6 with double galaxy structure, of which four are in galaxy mergers. We measure the ionization of the two velocity components in the narrow AGN lines to test the hypothesis that both velocity components come from an active nucleus. The combination of a well-defined parent sample and high-quality imaging allows us to place constraints on the fraction of SDSS QSOs that host dual accreting black holes separated on kiloparsec scales: similar to 0.3%-0.65%. We derive from this fraction the time spent in a QSO phase during a typical merger and find a value that is much lower than estimates that arise from QSO space densities and galaxy merger statistics. We discuss possible reasons for this difference. Finally, we compare the SMBH mass distributions of single and dual AGNs and find little difference between the two within the limited statistics of our program, hinting that most SMBH growth happens in the later stages of a merger process.
AGN Host Galaxies At Redshift Z Approximate To 0.7: Peculiar Or Not?
(2013-01) Bohm, A.; Wisotzki, L.; Bell, E. F.; Jahnke, K.; Wolf, C.; Bacon, D.; Barden, M.; Gray, M. E.; Hoeppe, G.; Jogee, S.; McIntosh, D. H.; Peng, C. Y.; Robaina, A. R.; Balogh, M.; Barazza, F. D.; Caldwell, J. A. R.; Heymans, C.; Haussler, B.; van Kampen, E.; Lane, K.; Meisenheimer, K.; Sanchez, S. F.; Taylor, A. N.; Zheng, X.; Caldwell, J. A. R.
Aims. We perform a quantitative morphological comparison between the hosts of active galactic nuclei (AGN) and quiescent galaxies at intermediate redshifts (z approximate to 0.7). The imaging data are taken from the large HST/ACS mosaics of the GEMS and STAGES surveys. Our main aim is to test whether nuclear activity at this cosmic epoch is triggered by major mergers. Methods. Using images of quiescent galaxies and stars, we created synthetic AGN images to investigate the impact of an optical nucleus on the morphological analysis of AGN hosts. Galaxy morphologies are parameterized using the asymmetry index A, the concentration index C, the Gini coefficient G, and the M-20 index. A sample of similar to 200 synthetic AGN was matched to 21 real AGN in terms of redshift, host brightness, and host-to-nucleus ratio to ensure a reliable comparison between active and quiescent galaxies. Results. The optical nuclei strongly affect the morphological parameters of the underlying host galaxy. Taking these effects into account, we find that the morphologies of the AGN hosts are clearly distinct from galaxies undergoing violent gravitational interactions. Indeed, the host galaxy distributions in morphological descriptor space are more similar to undisturbed galaxies than to major mergers. Conclusions. Intermediate-luminosity (L-X less than or similar to 10(44) erg/s) AGN hosts at z approximate to 0.7 show morphologies similar to the general population of massive galaxies with significant bulges at the same redshifts. If major mergers are the driver of nuclear activity at this epoch, the signatures of gravitational interactions fade rapidly before the optical AGN phase starts, making them undetectable on single-orbit HST images, at least with usual morphological descriptors. This could be investigated in future synthetic observations created from numerical simulations of galaxy-galaxy interactions.
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.
The Century Survey Galactic Halo Project. III. A Complete 4300 Deg(2) Survey Of Blue Horizontal Branch Stars In The Metal-Weak Thick Disk And Inner Halo
(2008-02) Brown, Warren R.; Beers, Timothy C.; Wilhelm, Ronald; Prieto, Carlos Allende; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J.; Prieto, Carlos Allende
We present a complete spectroscopic survey of 2414 2MASS-selected blue horizontal branch ( BHB) candidates selected over 4300 deg(2) of the sky. We identify 655 BHB stars in this non-kinematically selected sample. We calculate the luminosity function of field BHB stars, and find evidence for very few hot BHB stars in the field. The BHB stars located at a distance from the Galactic plane | Z| < 4 kpc trace what is clearly a metal-weak thick disk population, with a mean metallicity of [Fe/H]=-1.7, a rotation velocity gradient of dv(rot)/d|Z|=-28 +/- 3.4 km s(-1) in the region |Z| < 6 kpc, and a density scale height of h(Z) = 1.26 +/- 0.1 kpc. The BHB stars located at 5 < | Z| < 9 kpc are a predominantly inner-halo population, with a mean metallicity of [ Fe/ H] = - 2.0 and a mean Galactic rotation of - 4 +/- 31 km s(-1). We infer the density of halo and thick disk BHB stars is 104 +/- 37 kpc(-3) near the Sun, and the relative normalization of halo to thick-disk BHB stars is 4 +/- 1% near the Sun.
Chandra Observations of A 1.9 Kpc Separation Double X-Ray Source in A Candidate Dual Active Galactic Nucleus Galaxy At Z=0.16
(2011-08) Comerford, Julia M.; Pooley, David; Gerke, Brian F.; Madejski, Greg M.; Comerford, Julia M.; Pooley, David
We report Chandra observations of a double X-ray source in the z = 0.1569 galaxy SDSS J171544.05+600835.7. The galaxy was initially identified as a dual active galactic nucleus (AGN) candidate based on the double-peaked [O III] lambda 5007 emission lines, with a line-of-sight velocity separation of 350 km s(-1), in its Sloan Digital Sky Survey spectrum. We used the Kast Spectrograph at Lick Observatory to obtain two long-slit spectra of the galaxy at two different position angles, which reveal that the two Type 2 AGN emission components have not only a velocity offset, but also a projected spatial offset of 1.9 h(70)(-1) kpc on the sky. Chandra/ACIS observations of two X-ray sources with the same spatial offset and orientation as the optical emission suggest that the galaxy most likely contains Compton-thick dual AGNs, although the observations could also be explained by AGN jets. Deeper X-ray observations that reveal Fe K lines, if present, would distinguish between the two scenarios. The observations of a double X-ray source in SDSS J171544.05+600835.7 are a proof of concept for a new, systematic detection method that selects promising dual AGN candidates from ground-based spectroscopy that exhibits both velocity and spatial offsets in the AGN emission features.
Comment On The Black Hole Recoil Candidate Quasar SDSS J092712.65+294344.0
(2009-05) Shields, Gregory A.; Bonning, E. W.; Salviander, Sarah; Shields, Gregory A.; Bonning, E. W.; Salviander, Sarah
The Sloan Digital Sky Survey (SDSS) quasar J092712.65+294344.0 has been proposed as a candidate for a supermassive black hole (similar to 10(8.8) M(circle dot)) ejected at high speed from the host galactic nucleus by gravitational radiation recoil, or alternatively for a supermassive black hole binary. This is based on a blueshift of 2650 km s(-1) of the broad emission lines ("b-system") relative to the narrow emission lines ("r-system") presumed to reflect the galaxy velocity. New observations with the Hobby-Eberly Telescope (HET) confirm the essential features of the spectrum. We note a third redshift system, characterized by weak, narrow emission lines of [O III] and [O II] at an intermediate velocity 900 km s(-1) redward of the broad-line velocity ("i-system"). A composite spectrum of SDSS QSOs similar to J0927+2943 illustrates the feasibility of detecting the calcium K absorption line in spectra of sufficient quality. The i-system may represent the QSO host galaxy or a companion. Photoionization requires the black hole to be similar to 3 kpc from the r-system emitting gas, implying that we are observing the system only 10(6) yr after the recoil event and contributing to the low probability of observing such a system. The HET observations give an upper limit of 10 km s(-1) per year on the rate of change of the velocity difference between the r- and b-systems, constraining the orbital phase in the binary model. These considerations and the presence of a cluster of galaxies apparently containing J0927+2943 favor the idea that this system represents a superposition of two active galactic nuclei.
Empirical Determination Of Convection Parameters In White Dwarfs. I. Whole Earth Telescope Observations Of EC14012-1446
(2012-06) Provencal, J. L.; Montgomery, Michael H.; Kanaan, A.; Thompson, Susan E.; Dalessio, J.; Shipman, H. L.; Childers, D.; Clemens, J. Christopher; Rosen, R.; Henrique, P.; Bischoff-Kim, Agnes; Strickland, W.; Chandler, Dean; Walter, B.; Watson, T. K.; Castanheira, B.; Wang, S.; Handler, G.; Wood, M.; Vennes, S.; Nemeth, P.; Kepler, S. O.; Reed, M.; Nitta, Atsuko; Kleinman, S. J.; Brown, T.; Kim, S. L.; Sullivan, D.; Chen, W. P.; Yang, M.; Shih, C. Y.; Jiang, X. J.; Sergeev, A. V.; Maksim, A.; Janulis, R.; Baliyan, K. S.; Vats, H. O.; Zola, S.; Baran, A.; Winiarski, M.; Ogloza, W.; Paparo, M.; Bognar, Z.; Papics, P.; Kilkenny, D.; Sefako, R.; Buckley, D.; Loaring, N.; Kniazev, A.; Silvotti, R.; Galleti, S.; Nagel, T.; Vauclair, G.; Dolez, N.; Fremy, J. R.; Perez, J.; Almenara, J. M.; Fraga, L.; Montgomery, Michael H.; Wang, S.
We report on an analysis of 308.3 hr of high-speed photometry targeting the pulsating DA white dwarf EC14012-1446. The data were acquired with the Whole Earth Telescope during the 2008 international observing run XCOV26. The Fourier transform of the light curve contains 19 independent frequencies and numerous combination frequencies. The dominant peaks are 1633.907, 1887.404, and 2504.897 mu Hz. Our analysis of the combination amplitudes reveals that the parent frequencies are consistent with modes of spherical degree l = 1. The combination amplitudes also provide m identifications for the largest amplitude parent frequencies. Our seismology analysis, which includes 2004-2007 archival data, confirms these identifications, provides constraints on additional frequencies, and finds an average period spacing of 41 s. Building on this foundation, we present nonlinear fits to high signal-to-noise light curves from the SOAR 4.1 m, McDonald 2.1 m, and KPNO 2 m telescopes. The fits indicate a time-averaged convective response timescale of tau(0) = 99.4 +/- 17 s, a temperature exponent N = 85 +/- 6.2, and an inclination angle of theta(i) = 32 degrees.9 +/- 3 degrees.2. We present our current empirical map of the convective response timescale across the DA instability strip.
The First Hyper-Luminous Infrared Galaxy Discovered By WISE
(2012-08) Eisenhardt, Peter R. M.; Wu, Jingwen; Tsai, Chao-wei; Assef, Roberto; Benford, Dominic; Blain, Andrew; Bridge, Carrie; Condon, J. J.; Cushing, Michael C.; Cutri, Roc; Evans, Neal J.; Gelino, Chris; Griffith, Roger L.; Grillmair, Carl J.; Jarrett, Tom; Lonsdale, Carol J.; Masci, Frank J.; Mason, Brian S.; Petty, Sara; Sayers, Jack; Stanford, S. A.; Stern, Daniel; Wright, Edward L.; Yan, Lin; Evans, Neal J.
We report the discovery by the Wide-field Infrared Survey Explorer (WISE) of the z = 2.452 source WISE J181417.29+341224.9, the first hyperluminous source found in the WISE survey. WISE 1814+3412 is also the prototype for an all-sky sample of similar to 1000 extremely luminous "W1W2-dropouts" (sources faint or undetected by WISE at 3.4 and 4.6 mu m and well detected at 12 or 22 mu m). The WISE data and a 350 mu m detection give a minimum bolometric luminosity of 3.7 x 10(13) L-circle dot, with similar to 10(14) L-circle dot plausible. Follow-up images reveal four nearby sources: a QSO and two Lyman break galaxies (LBGs) at z = 2.45, and an M dwarf star. The brighter LBG dominates the bolometric emission. Gravitational lensing is unlikely given the source locations and their different spectra and colors. The dominant LBG spectrum indicates a star formation rate similar to 300 M-circle dot yr(-1), accounting for less than or similar to 10% of the bolometric luminosity. Strong 22 mu m emission relative to 350 mu m implies that warm dust contributes significantly to the luminosity, while cooler dust normally associated with starbursts is constrained by an upper limit at 1.1 mm. Radio emission is similar to 10 times above the far-infrared/radio correlation, indicating an active galactic nucleus (AGN) is present. An obscured AGN combined with starburst and evolved stellar components can account for the observations. If the black hole mass follows the local M-BH-bulge mass relation, the implied Eddington ratio is greater than or similar to 4. WISE 1814+3412 may be a heavily obscured object where the peak AGN activity occurred prior to the peak era of star formation.
The First Mid-Infrared Spectra Of Cool White Dwarfs
(2008-05) Kilic, Mukremin; Kowalski, Piotr M.; Mullally, Fergal; Reach, William T.; von Hippel, Ted; von Hippel, Ted
We present the first mid-infrared spectra of two cool white dwarfs obtained with the Spitzer Space Telescope. We also present 3: 5-8 mu m photometry for 19 cool white dwarfs with 5000 K <= T-eff <= 9000 K. We perform a detailed model atmosphere analysis of these white dwarfs by fitting their UBVRIJHK and Spitzer photometry with state-of-the-art model atmospheres, and demonstrate that the optical and infrared spectral energy distributions of cool white dwarfs are well reproduced by our grid of models. Our mid-infrared photometry and 7.5-14.5 mu m spectrum of WD0018-267 are consistent with a T-eff 5720 K, pure hydrogen white dwarf model atmosphere. On the other hand, LHS 1126 remains peculiar, with significant mid-infrared flux deficits in all IRAC bands and a featureless spectrum in the 5.2-7.5 mu m range. Even though this deficit is attributed to collision-induced absorption ( CIA) due to molecular hydrogen, the shape of the deficit cannot be explained with current CIA opacity calculations. The infrared portion of the LHS 1126 spectral energy distribution is best fit with a power-law index of -1.99, identical to a Rayleigh-Jeans spectrum. This argues that the deficit may be due to an unrecognized graylike opacity source in the infrared.
The HETDEX Pilot Survey. III. The Low Metallicities Of High-Redshift Ly Alpha Galaxies
(2011-03) Finkelstein, Steven L.; Hill, Gary J.; Gebhardt, Karl; Adams, Joshua; Blanc, Guillermo A.; Papovich, Casey; Ciardullo, Robin; Drory, Niv; Gawiser, Eric; Gronwall, Caryl; Schneider, Donald P.; Tran, Kim-Vy; Hill, Gary J.; Gebhardt, Karl; Adams, Joshua; Blanc, Guillermo A.|
We present the results of Keck/NIRSPEC spectroscopic observations of three Ly alpha emitting galaxies (LAEs) at z similar to 2.3 discovered with the HETDEX pilot survey. We detect H alpha, [OIII], and H beta emission from two galaxies at z = 2.29 and 2.49, designated HPS194 and HPS256, respectively, representing the first detection of multiple rest-frame optical emission lines in galaxies at high redshift selected on the basis of their Ly alpha emission. We find that the redshifts of the Ly alpha emission from these galaxies are offset redward of the systemic redshifts (derived from the H alpha and [OIII] emission) by Delta v = 162 +/- 37 (photometric) +/- 42 (systematic) km s(-1) for HPS194 and Delta v = 36 +/- 35 +/- 18 km s-1 for HPS256. An interpretation for HPS194 is that a large-scale outflow may be occurring in its interstellar medium. This outflow is likely powered by star-formation activity, as examining emission line ratios implies that neither LAE hosts an active galactic nucleus. Using the upper limits on the [N II] emission, we place meaningful constraints on the gas-phase metallicities in these two LAEs of Z < 0.17 and < 0.28 Z(circle dot) (1 sigma). Measuring the stellar masses of these objects via spectral energy distribution (SED) fitting (similar to 10(10) and 6 x 10(8) M-circle dot, respectively), we study the nature of LAEs in a mass-metallicity plane. At least one of these two LAEs appears to be more metal poor than continuum-selected star-forming galaxies at the same redshift and stellar mass, implying that objects exhibiting Ly alpha emission may be systematically less chemically enriched than the general galaxy population. We use the SEDs of these two galaxies to show that neglecting the contribution of the measured emission line fluxes when fitting stellar population models to the observed photometry can result in overestimates of the population age by orders of magnitude and the stellar mass by a factor of similar to 2. This effect is particularly important at z greater than or similar to 7, where similarly strong emission lines may masquerade in the photometry as a 4000 angstrom break.
Identification Of Faint Chandra X-Ray Sources In The Core-Collapsed Globular Cluster NGC 6397: Evidence For A Bimodal Cataclysmic Variable Population
(2010-10) Cohn, Haldan N.; Lugger, Phyllis M.; Couch, Sean M.; Anderson, Jay; Cool, Adrienne M.; van den Berg, Maureen; Bogdanov, Slavko; Heinke, Craig O.; Grindlay, Jonathan E.; Couch, Sean M.
We have searched for optical identifications for 79 Chandra X-ray sources that lie within the half-mass radius of the nearby, core-collapsed globular cluster NGC 6397, using deep Hubble Space Telescope Advanced Camera for Surveys Wide Field Channel imaging in H alpha, R, and B. Photometry of these images allows us to classify candidate counterparts based on color-magnitude diagram location. In addition to recovering nine previously detected cataclysmic variables (CVs), we have identified six additional faint CV candidates, a total of 42 active binaries (ABs), two millisecond pulsars, one candidate active galactic nucleus, and one candidate interacting galaxy pair. Of the 79 sources, 69 have a plausible optical counterpart. The 15 likely and possible CVs in NGC 6397 mostly fall into two groups: a brighter group of six for which the optical emission is dominated by contributions from the secondary and accretion disk and a fainter group of seven for which the white dwarf dominates the optical emission. There are two possible transitional objects that lie between these groups. The faintest CVs likely lie near the minimum of the CV period distribution, where an accumulation is expected. The spatial distribution of the brighter CVs is much more centrally concentrated than those of the fainter CVs and the ABs. This may represent the result of an evolutionary process in which CVs are produced by dynamical interactions, such as exchange reactions, near the cluster center and are scattered to larger orbital radii, over their lifetimes, as they age and become fainter.
LBQS 0103-2753: A Binary Quasar In A Major Merger
(2012-01) Shields, Gregory A.; Rosario, D. J.; Junkkarinen, V.; Chapman, S. C.; Bonning, E. W.; Chiba, T.; Shields, Gregory A.
We present Hubble Space Telescope (HST) and United Kingdom Infrared Telescope spectra and images of the 2 kpc (0.'' 3) binary quasar LBQS 0103-2753 (z = 0.858). The HST images (V and I bands) show tidal features demonstrating that this system is a major galaxy merger in progress. A two-color composite image brings out knots of star formation along the tidal arc and elsewhere. The infrared spectrum shows that both objects are at the same redshift and that the discrepant redshift of C IV in component A is not representative of the true systemic redshift of this component. LBQS 0103-2753 is one of the most closely spaced binary QSOs known and is one of the relatively few dual active galactic nuclei showing confirmed broad emission lines from both components. While statistical studies of binary QSOs suggest that simultaneous fueling of both black holes during a merger may be relatively rare, LBQS 0103-2753 demonstrates that such fueling can occur at high luminosity at a late stage in the merger at nuclear spacing of only a few kpc, without severe obscuration of the nuclei.
Spatially Resolved Spectroscopy of SDSS J0952+2552: A Confirmed Dual Active Galactic Nucleus
(2011-09) McGurk, R. C.; Max, C. E.; Rosario, D. J.; Shields, G. A.; Smith, K. L.; Wright, S. A.; Shields, G. A.; Smith, K. L.
Most massive galaxies contain supermassive black holes (SMBHs) in their cores. When galaxies merge, gas is driven to nuclear regions and can accrete onto the central black hole. Thus, one expects to see dual active galactic nuclei (AGNs) in a fraction of galaxy mergers. Candidates for galaxies containing dual AGNs have been identified by the presence of double-peaked narrow [O III] emission lines and by high spatial resolution images of close galaxy pairs. Spatially resolved spectroscopy is needed to confirm these galaxy pairs as systems with spatially separated double SMBHs. With the Keck 2 Laser Guide Star Adaptive Optics system and the OH Suppressing InfraRed Imaging Spectrograph near-infrared integral field spectrograph, we obtained spatially resolved spectra for SDSS J09527.62+255257.2, a radio-quiet quasar shown by previous imaging to consist of a galaxy and its close (1.'' 0) companion. We find that the main galaxy is a Type 1 AGN with both broad and narrow AGN emission lines in its spectrum, while the companion galaxy is a Type 2 AGN with narrow emission lines only. The two AGNs are separated by 4.8 kpc, and their redshifts correspond to those of the double peaks of the [O I] emission line seen in the Sloan Digital Sky Survey spectrum. Line diagnostics indicate that both components of the double emission lines are due to AGN photoionization. These results confirm that J0952+2552 contains two spatially separated AGNs. As one of the few confirmed dual AGNs at an intermediate separation of < 10 kpc, this system offers a unique opportunity to study galaxy mergers and their effect on black hole growth.
Type 2 Active Galactic Nuclei With Double-Peaked O III Lines. II. Single AGNs With Complex Narrow-Line Region Kinematics Are More Common Than Binary AGNs
(2011-07) Shen, Yue; Liu, Xin; Greene, Jenny E.; Strauss, Michael A.; Greene, Jenny E.
Approximately 1% of low-redshift (z less than or similar to 0.3) optically selected type 2 active galactic nuclei (AGNs) show a doublepeaked [O III] narrow emission line profile in their spatially integrated spectra. Such features are usually interpreted as either due to kinematics, such as biconical outflows and/or disk rotation of the narrow line region (NLR) around single black holes, or due to the relative motion of two distinct NLRs in a merging pair of AGNs. Here, we report follow-up near-infrared (NIR) imaging and optical slit spectroscopy of 31 double-peaked [O III] type 2 AGNs drawn from the Sloan Digital Sky Survey (SDSS) parent sample presented in Liu et al. The NIR imaging traces the old stellar population in each galaxy, while the optical slit spectroscopy traces the NLR gas. These data reveal a mixture of origins for the double-peaked feature. Roughly 10% of our objects are best explained by binary AGNs at (projected) kpc-scale separations, where two stellar components with spatially coincident NLRs are seen. similar to 50% of our objects have [O III] emission offset by a few kpc, corresponding to the two velocity components seen in the SDSS spectra, but there are no spatially coincident double stellar components seen in the NIR imaging. For those objects with sufficiently high-quality slit spectra, we see velocity and/or velocity dispersion gradients in [O III] emission, suggestive of the kinematic signatures of a single NLR. The remaining similar to 40% of our objects are ambiguous and will need higher spatial resolution observations to distinguish between the two scenarios. Our observations therefore favor the kinematics scenario with a single AGN for the majority of these double-peaked [O III] type 2 AGNs. We emphasize the importance of combining imaging and slit spectroscopy in identifying kpc-scale binary AGNs, i.e., in no cases does one of these alone allow an unambiguous identification. We estimate that similar to 0.5%-2.5% of the z less than or similar to 0.3 type 2 AGNs are kpc-scale binary AGNs of comparable luminosities, with a relative orbital velocity greater than or similar to 150 km s(-1).
Visitors from the Halo: 11 Gyr Old White Dwarfs in the Solar Neighborhood
(2010-05) Kilic, Mukremin; Munn, Jeffrey A.; Williams, Kurtis A.; Kowalski, P. M.; von Hippel, Ted; Harris, Hugh C.; Jeffery, Elizabeth J.; DeGennaro, Steven; Brown, Warren R.; McLeod, B.; Williams, Kurtis A.
We report the discovery of three nearby old halo white dwarf (WD) candidates in the Sloan Digital Sky Survey (SDSS), including two stars in a common proper motion binary system. These candidates are selected from our 2800 deg(2) proper motion survey on the Bok and U. S. Naval Observatory Flagstaff Station 1.3 m telescopes, and they display proper motions of 0.'' 4-0 ''.5 yr(-1). Follow-up MMT spectroscopy and near-infrared photometry demonstrate that all three objects are hydrogen-dominated atmosphere WDs with T(eff) approximate to 3700-4100 K. For average mass WDs, these temperature estimates correspond to cooling ages of 9-10 Gyr, distances of 70-80 pc, and tangential velocities of 140-200 km s(-1). Based on the UVW space velocities, we conclude that they most likely belong to the halo. Furthermore, the combined main-sequence and WD cooling ages are 10-11 Gyr. Along with SDSS J1102+4113, they are the oldest field WDs currently known. These three stars represent only a small fraction of the halo WD candidates in our proper motion survey, and they demonstrate that deep imaging surveys like the Pan-STARRS and Large Synoptic Survey Telescope should find many old thick disk and halo WDs that can be used to constrain the age of the Galactic thick disk and halo.
The White Dwarf Population In NGC 1039 (M34) And The White Dwarf Initial-Final Mass Relation
(2008-06) Rubin, Kate H. R.; Williams, Kurtis A.; Bolte, M.; Koester, Detlev; Williams, Kurtis A.
We present the first detailed photometric and spectroscopic study of the white dwarfs (WDs) in the field of the similar to 225 Myr old (log tau(cl) = 8.35) open cluster NGC 1039 (M34) as part of the ongoing Lick-Arizona White Dwarf Survey. Using wide-field UBV imaging, we photometrically select 44 WD candidates in this field. We spectroscopically identify 19 of these objects as WDs; 17 are hydrogen-atmosphere DA WDs, one is a helium-atmosphere DB WD, and one is a cool DC WD that exhibits no detectable absorption lines. We find an effective temperature (T(eff)) and surface gravity (log g) for each DA WD by fitting Balmer-line profiles from model atmospheres to the observed spectra. WD evolutionary models are then invoked to derive masses and cooling times for each DA WD. Of the 17 DAs, five are at the approximate distance modulus of the cluster. Another WD with a distance modulus 0.45 mag brighter than that of the cluster could be a double-degenerate binary cluster member, but is more likely to be a field WD. We place the five single cluster member WDs in the empirical initial-final mass relation and find that three of them lie very close to the previously derived linear relation; two have WD masses significantly below the relation. These outliers may have experienced some sort of enhanced mass loss or binary evolution; however, it is quite possible that these WDs are simply interlopers from the field WD population. Eight of the 17 DA WDs show significant Ca II K absorption; comparison of the absorption strength with the WD distances suggests that the absorption is interstellar, though this cannot be confirmed with the current data.