19 research outputs found
A diversity of dusty AGN tori: Data release for the VLTI/MIDI AGN Large Program and first results for 23 galaxies
The AGN-heated dust distribution (the "torus") is increasingly recognized not
only as the absorber required in unifying models, but as a tracer for the
reservoir that feeds the nuclear Super-Massive Black Hole. Yet, even its most
basic structural properties (such as its extent, geometry and elongation) are
unknown for all but a few archetypal objects. Since most AGNs are unresolved in
the mid-infrared, we utilize the MID-infrared interferometric Instrument (MIDI)
at the Very Large Telescope Interferometer (VLTI) that is sensitive to
structures as small as a few milli-arcseconds (mas). We present here an
extensive amount of new interferometric observations from the MIDI AGN Large
Program (2009 - 2011) and add data from the archive to give a complete view of
the existing MIDI observations of AGNs. Additionally, we have obtained
high-quality mid-infrared spectra from VLT/VISIR. We present correlated and
total flux spectra for 23 AGNs and derive flux and size estimates at 12 micron
using simple axisymmetric geometrical models. Perhaps the most surprising
result is the relatively high level of unresolved flux and its large scatter:
The median "point source fraction" is 70 % for type 1 and 47 % for type 2 AGNs
meaning that a large part of the flux is concentrated on scales smaller than
about 5 mas (0.1 - 10 pc). Among sources observed with similar spatial
resolution, it varies from 20 % - 100 %. For 18 of the sources, two nuclear
components can be distinguished in the radial fits. While these models provide
good fits to all but the brightest sources, significant elongations are
detected in eight sources. The half-light radii of the fainter sources are
smaller than expected from the size ~ L^0.5 scaling of the bright sources and
show a large scatter, especially when compared to the relatively tight
size--luminosity relation in the near-infrared.Comment: A&A in press; 93 pages, 63 figures, 39 tables; data available only
via CD
Adaptive Optics: Observations and Prospects for Studies of Active Galactic Nuclei
These lectures take a look at how observations with adaptive optics (AO) are
beginning to influence our understanding of active galactic nuclei (AGN). By
focussing on a few specific topics, the aim is to highlight the different ways
in which enhanced spatial resolution from AO can aid the scientific analysis of
AGN data. After presenting some background about how AO works, I will describe
a few recent observations made with AO of QSO host galaxies, the Galactic
Center, and nearby AGN, and show how they have contributed to our knowledge of
these enigmatic objects.Comment: Accepted for NewAR in proceedings of "Active Galactic Nuclei at the
highest angular resolution: theory and observations", 2007 summer school,
Torun, Poland. A version with high resolution colour figures is available
from http://www.mpe.mpg.de/~davies/Davies_AGN_AO.pd
Roadmap on holography
From its inception holography has proven an extremely productive and attractive area of research. While specific technical applications give rise to 'hot topics', and three-dimensional (3D) visualisation comes in and out of fashion, the core principals involved continue to lead to exciting innovations in a wide range of areas. We humbly submit that it is impossible, in any journal document of this type, to fully reflect current and potential activity; however, our valiant contributors have produced a series of documents that go no small way to neatly capture progress across a wide range of core activities. As editors we have attempted to spread our net wide in order to illustrate the breadth of international activity. In relation to this we believe we have been at least partially successful.This work was supported by Ministerio de EconomĂa, Industria y Competitividad (Spain) under projects FIS2017-82919-R (MINECO/AEI/FEDER, UE) and FIS2015-66570-P (MINECO/FEDER), and by Generalitat Valenciana (Spain) under project PROMETEO II/2015/015
A Kinetic Isotope Effect and Isotope Exchange Study of the Nonenzymatic and the Equine Serum Butyrylcholinesterase-Catalyzed Thioester Hydrolysis
Formylthiocholine
(FTC) was synthesized and found to be a substrate
for nonenzymatic and butyrylcholinesterase (BChE)-catalyzed hydrolysis.
Solvent (D<sub>2</sub>O) and secondary formyl-H kinetic isotope effects
(KIEs) were measured by an NMR spectroscopic method. The solvent (D<sub>2</sub>O) KIEs are <sup>D<sub>2</sub>O</sup><i>k</i> =
0.20 in 200 mM HCl, <sup>D<sub>2</sub>O</sup><i>k</i> =
0.81 in 50 mM HCl, and <sup>D<sub>2</sub>O</sup><i>k</i> = 4.2 in pure water. The formyl-H KIEs are <sup>D</sup><i>k</i> = 0.80 in 200 mM HCl, <sup>D</sup><i>k</i> = 0.77 in 50
mM HCl, <sup>D</sup><i>k</i> = 0.75 in pure water, <sup>D</sup><i>k</i> = 0.88 in 50 mM NaOH, and <sup>D</sup>(<i>V</i>/<i>K</i>) = 0.89 in the BChE-catalyzed hydrolysis
in MES buffer at pH 6.8. Positional isotope exchange experiments showed
no detectable exchange of <sup>18</sup>O into the carbonyl oxygen
of FTC or the product, formate, under any of the above conditions.
Solvent nucleophile-O KIEs were determined to be <sup>18</sup><i>k</i> = 0.9917 under neutral conditions, <sup>18</sup><i>k</i> = 1.0290 (water nucleophile) or <sup>18</sup><i>k</i> = 0.989 (hydroxide nucleophile) under alkaline conditions, and <sup>18</sup>(<i>V</i>/<i>K</i>) = 0.9925 for BChE
catalysis. The acidic, neutral, and BChE-catalyzed reactions are explained
in terms of a stepwise mechanism with tetrahedral intermediates. Evidence
for a change to a direct displacement mechanism under alkaline conditions
is presented