1,204 research outputs found
Spatially Resolved Stellar Populations of Eight GOODS-South Active Galactic Nuclei at z ~ 1
We present a pilot study of the stellar populations of eight active galactic nucleus (AGN) hosts at z ~ 1 and compare with (1) lower redshift samples and (2) a sample of nonactive galaxies of similar redshift. We utilize K' images in the Great Observatories Origins Deep Survey South field obtained with the laser guide star adaptive optics system at Keck Observatory. We combine these K' data with B, V, i, and z imaging from the Advanced Camera for Surveys on Hubble Space Telescope to give multicolor photometry at a matched spatial resolution better than 100 mas in all bands. The hosts harbor AGNs as inferred from their high X-ray luminosities (LX > 10^42 erg s^–1) or mid-IR colors. We find a correlation between the presence of younger stellar populations and the strength of the AGN, as measured with [O III] line luminosity or X-ray (2-10 keV) luminosity. This finding is consistent with similar studies at lower redshift. Of the three Type II galaxies, two are disk galaxies and one is of irregular type, while in the Type I sample there are only one disk-like source and four sources with smooth, elliptical/spheroidal morphologies. In addition, the mid-IR spectral energy distributions of the strong Type II AGNs indicate that they are excited to Luminous InfraRed Galaxy (LIRG) status via galactic starbursting, while the strong Type I AGNs are excited to LIRG status via hot dust surrounding the central AGN. This supports the notion that the obscured nature of Type II AGNs at z ~ 1 is connected with global starbursting and that they may be extincted by kpc-scale dusty features that are by-products of this starbursting
Integrated Laboratory Demonstrations of Multi-Object Adaptive Optics on a Simulated 10-Meter Telescope at Visible Wavelengths
One important frontier for astronomical adaptive optics (AO) involves methods
such as Multi-Object AO and Multi-Conjugate AO that have the potential to give
a significantly larger field of view than conventional AO techniques. A second
key emphasis over the next decade will be to push astronomical AO to visible
wavelengths. We have conducted the first laboratory simulations of wide-field,
laser guide star adaptive optics at visible wavelengths on a 10-meter-class
telescope. These experiments, utilizing the UCO/Lick Observatory's Multi-Object
/ Laser Tomography Adaptive Optics (MOAO/LTAO) testbed, demonstrate new
techniques in wavefront sensing and control that are crucial to future on-sky
MOAO systems. We (1) test and confirm the feasibility of highly accurate
atmospheric tomography with laser guide stars, (2) demonstrate key innovations
allowing open-loop operation of Shack-Hartmann wavefront sensors (with errors
of ~30 nm) as will be needed for MOAO, and (3) build a complete error budget
model describing system performance. The AO system maintains a performance of
32.4% Strehl on-axis, with 24.5% and 22.6% at 10" and 15", respectively, at a
science wavelength of 710 nm (R-band) over the equivalent of 0.8 seconds of
simulation. The MOAO-corrected field of view is ~25 times larger in area than
that limited by anisoplanatism at R-band. Our error budget is composed of terms
verified through independent, empirical experiments. Error terms arising from
calibration inaccuracies and optical drift are comparable in magnitude to
traditional terms like fitting error and tomographic error. This makes a strong
case for implementing additional calibration facilities in future AO systems,
including accelerometers on powered optics, 3D turbulators, telescope and LGS
simulators, and external calibration ports for deformable mirrors.Comment: 29 pages, 11 figures, submitted to PAS
Fractional crystallization of high-K arc magmas: biotite- versus amphibole-dominated fractionation series in the Dariv Igneous Complex, Western Mongolia
Many studies have documented hydrous fractionation of calc-alkaline basalts producing tonalitic, granodioritic, and granitic melts, but the origin of more alkaline arc sequences dominated by high-K monzonitic suites has not been thoroughly investigated. This study presents results from a combined field, petrologic, and whole-rock geochemical study of a paleo-arc alkaline fractionation sequence from the Dariv Range of the Mongolian Altaids. The Dariv Igneous Complex of Western Mongolia is composed of a complete, moderately hydrous, alkaline fractionation sequence ranging from phlogopite-bearing ultramafic and mafic cumulates to quartz–monzonites to late-stage felsic (63–75 wt% SiO2) dikes. A volumetrically subordinate more hydrous, amphibole-dominated fractionation sequence is also present and comprises amphibole (±phlogopite) clinopyroxenites, gabbros, and diorites. We present 168 whole-rock analyses for the biotite- and amphibole-dominated series. First, we constrain the liquid line of descent (LLD) of a primitive, alkaline arc melt characterized by biotite as the dominant hydrous phase through a fractionation model that incorporates the stepwise subtraction of cumulates of a fixed composition. The modeled LLD reproduces the geochemical trends observed in the “liquid-like” intrusives of the biotite series (quartz–monzonites and felsic dikes) and follows the water-undersaturated albite–orthoclase cotectic (at 0.2–0.5 GPa). Second, as distinct biotite- and amphibole-dominated fractionation series are observed, we investigate the controls on high-temperature biotite versus amphibole crystallization from hydrous arc melts. Analysis of a compilation of hydrous experimental starting materials and high-Mg basalts saturated in biotite and/or amphibole suggests that the degree of K enrichment controls whether biotite will crystallize as an early high-T phase, whereas the degree of water saturation is the dominant control of amphibole crystallization. Therefore, if a melt has the appropriate major-element composition for early biotite and amphibole crystallization, as is true of the high-Mg basalts from the Dariv Igneous Complex, the relative proximity of these two phases to the liquidus depends on the H2O concentration in the melt. Third, we compare the modeled high-K LLD and whole-rock geochemistry of the Dariv Igneous Complex to the more common calc-alkaline trend. Biotite and K-feldspar fractionation in the alkaline arc series results in the moderation of K2O/Na2O values and LILE concentrations with increasing SiO2 as compared to the more common calc-alkaline series characterized by amphibole and plagioclase crystallization and strong increases in K2O/Na2O values. Lastly, we suggest that common calc-alkaline parental melts involve addition of a moderate pressure, sodic, fluid-dominated slab component while more alkaline primitive melts characterized by early biotite saturation involve the addition of a high-pressure potassic sediment melt
Near Infrared Activity Close to the Crab Pulsar Correlated with Giant Gamma-ray Flares
We describe activity observed in the near-infrared correlated with a giant gamma-ray flare in the Crab Pulsar. The Crab Pulsar has been observed by the Fermi and AGILE satellites to flare for a period of 3 to 7 days, once every 1-1.5 years, increasing in brightness by a factor of 3-10 between 100MeV and 1GeV. We used Keck NIRC2 laser guide star adaptive optics imaging to observe the Crab Pulsar and environs before and during the March 2013 flare. We discuss the evidence for the knot as the location of the flares, and the theoretical implications of these observations. Ongoing target-of-opportunity programs hope to confirm this correlation for future flares
Stellar and Gaseous Nuclear Disks Observed in Nearby (U)LIRGs
We present near-infrared integral field spectroscopy of the central
kiloparsec of 17 nearby luminous and ultra-luminous infrared galaxies
undergoing major mergers. These observations were taken with OSIRIS assisted by
the Keck I and II Adaptive Optics systems, providing spatial resolutions of a
few tens of parsecs. The resulting kinematic maps reveal gas disks in at least
16 out of 19 nuclei and stellar disks in 11 out of 11 nuclei observed in these
galaxy merger systems. In our late-stages mergers, these disks are young
(stellar ages Myr) and likely formed as gas disks which became unstable
to star formation during the merger. On average, these disks have effective
radii of a few hundred parsecs, masses between and ,
and between 1 and 5. These disks are similar to those created in
high-resolution hydrodynamical simulations of gas-rich galaxy mergers, and
favor short coalescence times for binary black holes. The few galaxies in our
sample in earlier stages of mergers have disks which are larger
( pc) and likely are remnants of the galactic disks that
have not yet been completely disrupted by the merger.Comment: accepted for publication in Ap
Following Black Hole Scaling Relations Through Gas-Rich Mergers
We present black hole mass measurements from kinematic modeling of
high-spatial resolution integral field spectroscopy of the inner regions of 9
nearby (ultra-)luminous infrared galaxies in a variety of merger stages. These
observations were taken with OSIRIS and laser guide star adaptive optics on the
Keck I and Keck II telescopes, and reveal gas and stellar kinematics inside the
spheres of influence of these supermassive black holes. We find that this
sample of black holes are overmassive ( M) compared to
the expected values based on black hole scaling relations, and suggest that the
major epoch of black hole growth occurs in early stages of a merger, as opposed
to during a final episode of quasar-mode feedback. The black hole masses
presented are the dynamical masses enclosed in 25pc, and could include
gas which is gravitationally bound to the black hole but has not yet lost
sufficient angular momentum to be accreted. If present, this gas could in
principle eventually fuel AGN feedback or be itself blown out from the system.Comment: accepted to Ap
Elliptical Galaxy in the Making: The Dual Active Galactic Nuclei and Metal-enriched Halo of Mrk 273
A systematic analysis of the X-ray emission from the nearby ultraluminous
infrared galaxy Mrk 273 was carried out by combining new 200 ksec Chandra data
with archived 44 ksec data. The active galactic nucleus (AGN) associated with
the Southwest nucleus is confirmed by the new data, and a secondary hard X-ray
(4-8 keV) point source is detected, coincident with the Northeast nucleus at a
projected distance of 0.75 kpc from the Southwest nucleus. The hard X-ray
spectrum of the Northeast nucleus is consistent with a heavily absorbed AGN,
making Mrk 273 another example of a dual AGN in a nearby galaxy merger.
Significant 1-3 keV emission is found along the ionization cones and outflowing
gas detected in a previous study. The data also map the giant X-ray nebula
south of the host galaxy with unprecedented detail. This nebula extends on a
scale of 40 kpc 40 kpc, and is not closely related to the
well-known tidal tail seen in the optical. The X-ray emission of the nebula is
best described by a single-temperature gas model, with a temperature of
7 million K and a super-solar /Fe ratio. Further analysis suggests that
the southern nebula has most likely been heated and enriched by multiple
galactic outflows generated by the AGN and/or circumnuclear starburst in the
past, on a time scale of 0.1 Gyr, similar to the merger event itself.Comment: 25 pages, 22 figures, 4 tables, accepted for publication in the
Astrophysical Journa
Shocked Gas in IRAS F17207-0014: ISM Collisions and Outflows
We combine optical and near-infrared AO-assisted integral field observations
of the merging ULIRG IRAS F17207-0014 from the Wide-Field Spectrograph (WiFeS)
and Keck/OSIRIS. The optical emission line ratios [N II]/H, [S
II]/H, and [O I]/H reveal a mixing sequence of shocks present
throughout the galaxy, with the strongest contributions coming from large radii
(up to 100% at 5 kpc in some directions), suggesting galactic-scale
winds. The near-infrared observations, which have approximately 30 times higher
spatial resolution, show that two sorts of shocks are present in the vicinity
of the merging nuclei: low-level shocks distributed throughout our
field-of-view evidenced by an H/Br line ratio of 0.6-4, and
strong collimated shocks with a high H/Br line ratio of
4-8, extending south from the two nuclear disks approximately 400 pc
(0.5 arcsec). Our data suggest that the diffuse shocks are caused by the
collision of the interstellar media associated with the two progenitor galaxies
and the strong shocks trace the base of a collimated outflow coming from the
nucleus of one of the two disks.Comment: accepted to MNRA
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