5,526 research outputs found
Fact: Many SCUBA galaxies harbour AGNs
Deep SCUBA surveys have uncovered a large population of ultra-luminous
galaxies at z>1. These sources are often assumed to be starburst galaxies, but
there is growing evidence that a substantial fraction host an AGN (i.e., an
accreting super-massive black hole). We present here possibly the strongest
evidence for this viewpoint to date: the combination of ultra-deep X-ray
observations (the 2 Ms Chandra Deep Field-North) and deep optical spectroscopic
data. We argue that upward of 38% of bright (f850um>=5mJy) SCUBA galaxies host
an AGN, a fraction of which are obscured QSOs (i.e., L_X>3x10^{44} erg/s).
However, using evidence from a variety of analyses, we argue that in almost all
cases the AGNs are not bolometrically important (i.e., <20%). Thus, star
formation appears to dominate their bolometric output. A substantial fraction
of bright SCUBA galaxies show evidence for binary AGN activity. Since these
systems appear to be interacting and merging at optical/near-IR wavelengths,
their super-massive black holes will eventually coalesce.Comment: Invited contribution - 10 pages, 4 figures, to appear in the
Proceedings of the ESO/USM/MPE Workshop on "Multiwavelength Mapping of Galaxy
Formation and Evolution", eds. R. Bender and A. Renzin
Tidal spin-up of stars in dense stellar cusps around massive black holes
We show that main-sequence stars in dense stellar cusps around massive black
holes are likely to rotate at a significant fraction of the centrifugal breakup
velocity due to spin-up by hyperbolic tidal encounters. We use realistic
stellar structure models to calculate analytically the tidal spin-up in soft
encounters, and extrapolate these results to close and penetrating collisions
using smoothed particle hydrodynamics simulations. We find that the spin-up
falls off only slowly with distance from the black hole because the increased
tidal coupling in slower collisions at larger distances compensates for the
decrease in the stellar density. We apply our results to the stars near the
massive black hole in the Galactic Center. Over their lifetime, ~1 Msol main
sequence stars in the inner 0.3 pc of the Galactic Center are spun-up on
average to ~10%--30% of the centrifugal breakup limit. Such rotation is ~20--60
times higher than is usual for such stars and may affect their subsequent
evolution and their observed properties.Comment: 25 pages, 7 figures. Submitted to Ap
Bipolar polaron pair recombination in P3HT/PCBM solar cells
The unique properties of organic semiconductors make them versatile base
materials for many applications ranging from light emitting diodes to
transistors. The low spin-orbit coupling typical for carbon-based materials and
the resulting long spin lifetimes give rise to a large influence of the
electron spin on charge transport which can be exploited in spintronic devices
or to improve solar cell efficiencies. Magnetic resonance techniques are
particularly helpful to elucidate the microscopic structure of paramagnetic
states in semiconductors as well as the transport processes they are involved
in. However, in organic devices the nature of the dominant spin-dependent
processes is still subject to considerable debate. Using multi-frequency pulsed
electrically detected magnetic resonance (pEDMR), we show that the
spin-dependent response of P3HT/PCBM solar cells at low temperatures is
governed by bipolar polaron pair recombination involving the positive and
negative polarons in P3HT and PCBM, respectively, thus excluding a unipolar
bipolaron formation as the main contribution to the spin-dependent charge
transfer in this temperature regime. Moreover the polaron-polaron coupling
strength and the recombination times of polaron pairs with parallel and
antiparallel spins are determined. Our results demonstrate that the pEDMR pulse
sequences recently developed for inorganic semiconductor devices can very
successfully be transferred to the study of spin and charge transport in
organic semiconductors, in particular when the different polarons can be
distinguished spectrally
Phenethylamine-derived new psychoactive substances 2C-E-FLY, 2C-EF-FLY, and 2C-T-7-FLY: Investigations on their metabolic fate including isoenzyme activities and their toxicological detectability in urine screenings
Psychoactive substances of the 2Câseries are phenethylamineâbased designer drugs that can induce psychostimulant and hallucinogenic effects. The soâcalled 2CâFLY series contains rigidified methoxy groups integrated in a 2,3,6,7âtetrahydrobenzo[1,2âb:4,5âb']difuran core. The aim of the presented work was to investigate the in vivo and in vitro metabolic fate including isoenzyme activities and toxicological detectability of the three new psychoactive substances (NPS) 2CâEâFLY, 2CâEFâFLY, and 2CâTâ7âFLY to allow clinical and forensic toxicologists the identification of these novel compounds. Rat urine, after oral administration, and pooled human liver S9 fraction (pS9) incubations were analyzed by liquid chromatographyâhighâresolution tandem mass spectrometry (LCâHRMS/MS). By performing activity screenings, the human isoenzymes involved were identified and toxicological detectability in rat urine investigated using standard urine screening approaches (SUSAs) based on gas chromatography (GC)âMS, LCâMSn, and LCâHRMS/MS. In total, 32 metabolites were tentatively identified. Main metabolic steps consisted of hydroxylation and Nâacetylation. Phase I metabolic reactions were catalyzed by CYP2D6, 3A4, and FMO3 and Nâacetylation by NAT1 and NAT2. Methoxyamine was used as a trapping agent for detection of the deaminated metabolite formed by MAOâA and B. Interindividual differences in the metabolism of the 2CâFLY drugs could be caused by polymorphisms of enzymes involved or drugâdrug interactions. All three SUSAs were shown to be suitable to detect an intake of these NPS but common metabolites of 2CâEâFLY and 2CâEFâFLY have to be considered during interpretation of analytical findings
The Resolved Near-Infrared Extragalactic Background
We present a current best estimate of the integrated near-infrared (NIR)
extragalactic background light (EBL) attributable to resolved galaxies in J, H,
and Ks. Our results in units of nW m-2 sr-1 are 11.7+5.6 -2.6 in J, 11.5+4.5
-1.5 in H and 10.0+2.8 -0.8 in Ks. We derive these new limits by combining our
deep wide-field NIR photometry from five widely separated fields with other
studies from the literature to create a galaxy counts sample that is highly
complete and has good counting statistics out to JHKs ~ 27-28. As part of this
effort we present new ultradeep Ks-band galaxy counts from 22 hours of
observations with the Multi Object Infrared Camera and Spectrograph (MOIRCS)
instrument on the Subaru Telescope. We use this MOIRCS Ks-band mosaic to
estimate the total missing flux from sources beyond our detection limits. Our
new limits to the NIR EBL are in basic agreement with, but 10 - 20% higher than
previous estimates, bringing them into better agreement with estimates of the
total NIR EBL (resolved + unresolved sources) obtained from TeV gamma-ray
opacity measurements and recent direct measurements of the total NIR EBL. We
examine field to field variations in our photometry to show that the integrated
light from galaxies is isotropic to within uncertainties, consistent with the
expected large-scale isotropy of the EBL. Our data also allow for a robust
estimate of the NIR light from Galactic stars, which we find to be 14.7 +/- 2.4
in J, 10.1 +/- 1.9 in H and 7.6 +/- 1.8 in Ks in units of nW m-2 sr-1.Comment: Accepted to Ap
High-redshift QSOs in the GOODS
The Great Observatories Origins Deep Survey provides significant constraints
on the space density of less luminous QSOs at high redshift, which is
particularly important to understand the interplay between the formation of
galaxies and super-massive black holes and to measure the QSO contribution to
the UV ionizing background. We present the results of a search for high-z QSOs,
identified in the two GOODS fields on the basis of deep imaging in the optical
(with HST) and X-ray (Chandra), and discuss the allowed space density of QSOs
in the early universe.Comment: Proceedings of 'Multiwavelength mapping of galaxy evolution'
conference held in Venice (Italy), October 2003, A. Renzini and R. Bender
(Eds.), 6 pages, 1 figur
An Extremely Deep Wide-Field Near-Infrared Survey: Bright Galaxy Counts and Local Large Scale Structure
We present a deep, wide-field near-infrared (NIR) survey over five widely
separated fields at high Galactic latitude covering a total of ~ 3 deg^2 in J,
H, and Ks. The deepest areas of the data (~ 0.25 deg^2) extend to a 5 sigma
limiting magnitude of JHKs > 24 in the AB magnitude system. Although depth and
area vary from field to field, the overall depth and large area of this dataset
make it one of the deepest wide-field NIR imaging surveys to date. This paper
discusses the observations, data reduction, and bright galaxy counts in these
fields. We compare the slope of the bright galaxy counts with the Two Micron
All Sky Survey (2MASS) and other counts from the literature and explore the
relationship between slope and supergalactic latitude. The slope near the
supergalactic equator is sub- Euclidean on average pointing to the possibility
of a decreasing average space density of galaxies by ~ 10-15% over scales of ~
250-350 Mpc. On the contrary, the slope at high supergalactic latitudes is
strongly super-Euclidean on average suggesting an increase in the space density
of galaxies as one moves from the voids just above and below the supergalactic
plane out to distances of ~ 250-350 Mpc. These results suggest that local large
scale structure could be responsible for large discrepancies in the measured
slope between different studies in the past. In addition, the local universe
away from the supergalactic plane appears to be underdense by ~ 25-100%
relative to the space densities of a few hundred megaparsecs distant. Subject
headings: cosmology: observations and large scale structure of
universe-galaxies: fundamental parameters (counts)-infrared: galaxiesComment: Accepted to ApJS, 18 Pages, 14 Figures, 8 Table
- âŠ