Browsing by Subject "mergers"
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Item 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.Item 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, DavidWe 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.Item Correlations Between Supermassive Black Holes, Velocity Dispersions, and Mass Deficits in Elliptical Galaxies with Cores(2009-02) Kormendy, John; Bender, Ralf; Kormendy, JohnHigh-dynamic-range surface photometry in a companion paper makes possible accurate measurement of the stellar light deficits L(def) and mass deficits M(def) associated with the cores of elliptical galaxies. We show that L(def) correlates with velocity dispersions sigma of the host galaxy bulge averaged outside the central region that may be affected by a supermassive black hole (BH). We confirm that L(def) correlates with BH mass M(center dot). Also, the fractional light deficit L(def)/L(*) correlates with M(center dot)/M(*), the ratio of BH mass to the galaxy stellar mass. All three correlations have scatter similar to or smaller than the scatter in the well-known correlation between M(center dot) and sigma. The new correlations are remarkable in view of the dichotomy between ellipticals with cores and those with central extra light. Core light deficit correlates closely with M(center dot) and sigma, but extra light does not. This supports the suggestion that extra light Es are made in wet mergers with starbursts whereas core Es are made in dry mergers. After dry mergers, cores are believed to be scoured by BH binaries that fling stars away as their orbits decay or by BHs that sink back to the center after recoiling from anisotropic gravitational radiation emitted when they merge. Direct evidence for these mechanisms has been elusive. We interpret the new correlations as the "smoking gun" that connects cores with BHs. Together, the M(center dot) - sigma and M(center dot) - L(def) correlations give us two independent ways to estimate BH masses in core Es.Item Demographics of Bulge Types Within 11 Mpc and Implications for Galaxy Evolution(2011-06) Fisher, David B.; Drory, Niv; Fisher, David B.We present an inventory of galaxy bulge types (elliptical galaxy, classical bulge, pseudobulge, and bulgeless galaxy) in a volume-limited sample within the local 11 Mpc sphere using Spitzer 3.6 mu m and Hubble Space Telescope data. We find that whether counting by number, star Formation rate, or stellar mass, the dominant galaxy type in the local universe has pure disk characteristics (either hosting a pseudobulge or being bulgeless). Galaxies that contain either a pseudobulge or no bulge combine to account for over 80% of the number of galaxies above a stellar mass of 10(9) M-circle dot. Classical bulges and elliptical galaxies account for similar to 1/4, and disks for similar to 3/4 of the stellar mass in the local 11 Mpc. About 2/3 of all star Formation in the local volume takes place in galaxies with pseudobulges. Looking at the fraction of galaxies with different bulge types as a function of stellarmass, we find that the frequency of classical bulges strongly increases with stellar mass, and comes to dominate above 10(10.5) M-circle dot. Galaxies with pseudobulges dominate at 10(9.5)-10(10.5) M-circle dot. Yet lower-mass galaxies are most likely to be bulgeless. If pseudobulges are not a product of mergers, then the frequency of pseudobulges in the local universe poses a challenge for galaxy evolution models.Item Double-Peaked Narrow-Line Active Galactic Nuclei. II. The Case Of Equal Peaks(2012-06) Smith, K. L.; Shields, Gregory A.; Salviander, Sarah; Stevens, A. C.; Rosario, D. J.; Smith, K. L.; Shields, Gregory A.; Salviander, Sarah; Stevens, A. C.Active galactic nuclei (AGNs) with double-peaked narrow lines (DPAGNs) may be caused by kiloparsec-scale binary AGNs, bipolar outflows, or rotating gaseous disks. We examine the class of DPAGNs in which the two narrow-line components have closely similar intensity as being especially likely to involve disks or jets. Two spectroscopic indicators support this likelihood. For DPAGNs from Smith et al., the "equal-peaked" objects (EPAGNs) have [Ne V]/[O III] ratios lower than for a control sample of non-double-peaked AGNs. This is unexpected for a pair of normal AGNs in a galactic merger, but may be consistent with [O III] emission from a rotating ring with relatively little gas at small radii. Also, [O III]/H beta ratios of the redshifted and blueshifted systems in the EPAGN are more similar to each other than in a control sample, suggestive of a single ionizing source and inconsistent with the binary interpretation.Item The Hot R Coronae Borealis Star DY Centauri is a Binary(2012-11) Rao, N. Kameswara; Lambert, David L.; Garcia-Hernandez, D. A.; Jeffery, C. Simon; Woolf, Vincent M.; McArthur, Barbara; Rao, N. Kameswara; Lambert, David L.; McArthur, BarbaraThe remarkable hot R Coronae Borealis (RCB) star DY Cen is revealed to be the first and only binary system to be found among the RCB stars and their likely relatives, including the extreme helium stars and the hydrogen-deficient carbon stars. Radial velocity determinations from 1982 to 2010 have shown that DY Cen is a single-lined spectroscopic binary in an eccentric orbit with a period of 39.67 days. It is also one of the hottest and most H-rich member of the class of RCB stars. The system may have evolved from a common envelope to its current form.Item Ionized Gas Kinematics At High Resolution. IV. Star Formation And A Rotating Core In The Medusa (NGC 4194)(2014-05) Beck, Sara C.; Lacy, John; Turner, Jean; Greathouse, Thomas K.; Neff, Susan; Lacy, JohnNGC 4194 is a post-merger starburst known as The Medusa for its striking tidal features. We present here a detailed study of the structure and kinematics of ionized gas in the central 0.65 kpc of the Medusa. The data include radio continuum maps with resolution up to 0."18 (35 pc) and a 12.8 mu m [Ne II] data cube with spectral resolution similar to 4 km s(-1): the first high-resolution, extinction-free observations of this remarkable object. The ionized gas has the kinematic signature of a core in solid-body rotation. The starburst has formed a complex of bright compact H II regions, probably excited by deeply embedded super star clusters, but none of these sources is a convincing candidate for a Galactic nucleus. The nuclei of the merger partners that created the Medusa have not yet been identified.Item 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.Item The L Proportional To Sigma(8) Correlation for Elliptical Galaxies With Cores: Relation With Black Hole Mass(2013-05) Kormendy, John; Bender, Ralf; Kormendy, JohnWe construct the Faber-Jackson correlation between velocity dispersion sigma and total galaxy luminosity L-V separately for elliptical galaxies with and without cores. The coreless ellipticals show the well-known, steep relationship d log sigma/d log L-V = 0.268 or L-V proportional to sigma(3.74). This corresponds to d log sigma/d log M = 0.203, where M is the stellar mass and we use M/L proportional to L-0.32. In contrast, the velocity dispersions of core ellipticals increase much more slowly with L-V and M: d log sigma/d log L-V = 0.120, L-V proportional to sigma(8.33), and d log sigma/d log M = 0.091. Dissipationless major galaxy mergers are expected to preserve sigma according to the simplest virial-theorem arguments. However, numerical simulations show that sigma increases slowly in dry major mergers, with d log sigma/d log M similar or equal to +0.15. In contrast, minor mergers cause sigma to decrease, with d log sigma/d log M similar or equal to -0.05. Thus, the observed relation argues for dry major mergers as the dominant growth mode of the most massive ellipticals. This is consistent with what we know about the Formation of cores. We know no viable way to explain galaxy cores except through dissipationless mergers of approximately equal-mass galaxies followed by core scouring by binary supermassive black holes. The observed, shallow sigma proportional to L-V(+ 0.12) relation for core ellipticals provides further evidence that they formed in dissipationless and predominantly major mergers. Also, it explains the observation that the correlation of supermassive black hole mass with velocity dispersion, M-circle proportional to sigma(4), "saturates" at high M-circle such that M-circle becomes almost independent of sigma.Item On The Binary Helium Star DY Centauri: Chemical Composition And Evolutionary State(2014-10) Pandey, Gajendra; Rao, N. Kameswara; Jeffery, C. Simon; Lambert, David L.; Lambert, David L.DY Cen has shown a steady fading of its visual light by about one magnitude in the last 40 yr, suggesting a secular increase in its effective temperature. We have conducted non-local thermodynamic equilibrium (LTE) and LTE abundance analyses to determine the star's effective temperature, surface gravity, and chemical composition using high-resolution spectra obtained over two decades. The derived stellar parameters for three epochs suggest that DY Cen has evolved at a constant luminosity and has become hotter by about 5000 K in 23 yr. We show that the derived abundances remain unchanged for the three epochs. The derived abundances of the key elements, including F and Ne, are as observed for the extreme helium stars resulting from a merger of a He white dwarf with a C-O white dwarf. Thus DY Cen by chemical composition appears to also be a product of a merger of two white dwarfs. This appearance seems to be at odds with the recent suggestion that DY Cen is a single-lined spectroscopic binary.Item A Petal Of The Sunflower: Photometry Of The Stellar Tidal Stream In The Halo Of Messier 63 (NGC 5055)(2011-11) Chonis, Taylor S.; Martinez-Delgado, David; Gabany, R. Jay; Majewski, Steven R.; Hill, Gary J.; Gralak, Ray; Trujillo, Ignacio; Hill, Gary J.We present deep surface photometry of a very faint, giant arc-loop feature in the halo of the nearby spiral galaxy NGC 5055 (M63) that is consistent with being a part of a stellar stream resulting from the disruption of a dwarf satellite galaxy. This faint feature was first detected in early photographic studies by van der Kruit; more recently, in the study of Martinez-Delgado and as presented in this work, from the loop has been realized to be the result of a recent minor merger through evidence obtained by wide-field, deep images taken with a telescope of only 0.16 m aperture. The stellar stream is clearly confirmed in additional deep images taken with the 0.5 m telescope of the BlackBird Remote Observatory and the 0.8 m telescope of the McDonald Observatory. This low surface brightness (mu(R) approximate to 26 mag arcsec(-2)) arc-like structure around the disk of the galaxy extends 14'0 (similar to 29 kpc projected) from its center, with a projected width of 1'6 (similar to 3.3 kpc). The stream's morphology is consistent with that of the visible part of a giant, >great-circle> type stellar stream originating from the recent accretion of a similar to 10(8) M-circle dot dwarf satellite in the last few Gyr. The progenitor satellite's current position and final fate are not conclusive from our data. The color of the stream's stars is consistent with dwarfs in the Local Group and is similar to the outer faint regions of M63's disk and stellar halo. From our photometric study, we detect other low surface brightness >plumes;> some of these may be extended spiral features related to the galaxy's complex spiral structure, and others may be tidal debris associated with the disruption of the galaxy's outer stellar disk as a result of the accretion event. We are able to differentiate between features related to the tidal stream and faint, blue extended features in the outskirts of the galaxy's disk previously detected by the Galaxy Evolution Explorer satellite. With its highly warped Hi gaseous disk (similar to 20 degrees), M63 represents one of the several examples of an isolated spiral galaxy with a warped disk showing recently discovered strong evidence of an ongoing minor merger.Item Toward Early-Warning Detection Of Gravitational Waves From Compact Binary Coalescence(2012-04) Cannon, Kipp; Cariou, Romain; Chapman, Adrian; Crispin-Ortuzar, Mireia; Fotopoulos, Nickolas; Frei, Melissa; Hanna, Chad; Kara, Erin; Keppel, Drew; Liao, Laura; Privitera, Stephen; Searle, Antony; Singer, Leo; Weinstein, Alan; Frei, MelissaRapid detection of compact binary coalescence (CBC) with a network of advanced gravitational-wave detectors will offer a unique opportunity for multi-messenger astronomy. Prompt detection alerts for the astronomical community might make it possible to observe the onset of electromagnetic emission from CBC. We demonstrate a computationally practical filtering strategy that could produce early-warning triggers before gravitational radiation from the final merger has arrived at the detectors.Item When No One's Looking, Merging Firms Manipulate Earnings(2017-04-04) Brooks, Steve