44 research outputs found
A direct image of the obscuring disk surrounding an active galactic nucleus
Active galactic nuclei (AGN) are generally accepted to be powered by the
release of gravitational energy in a compact accretion disk surrounding a
massive black hole. Such disks are also necessary to collimate powerful radio
jets seen in some AGN. The unifying classification schemes for AGN further
propose that differences in their appearance can be attributed to the opacity
of the accreting material, which may obstruct our view of the central region of
some systems. The popular model for the obscuring medium is a parsec-scale disk
of dense molecular gas, although evidence for such disks has been mostly
indirect, as their angular size is much smaller than the resolution of
conventional telescopes. Here we report the first direct images of a pc-scale
disk of ionised gas within the nucleus of NGC 1068, the archetype of obscured
AGN. The disk is viewed nearly edge-on, and individual clouds within the
ionised disk are opaque to high-energy radiation, consistent with the unifying
classification scheme. In projection, the disk and AGN axes align, from which
we infer that the ionised gas disk traces the outer regions of the long-sought
inner accretion disk.Comment: 14 pages, LaTeX, PSfig, to appear in Nature. also available at
http://hethp.mpe-garching.mpg.de/Preprint
Counter-rotation and High-velocity Outflow in the Parsec-scale Molecular Torus of NGC 1068
We present 1.4 pc resolution observations of 256 GHz nuclear radio continuum
and HCN () in the molecular torus of NGC 1068. The integrated radio
continuum emission has a flat spectrum consistent with free-free emission and
resolves into an X-shaped structure resembling an edge-brightened bicone. HCN
is detected in absorption against the continuum, and the absorption spectrum
shows a pronounced blue wing that suggests a high-velocity molecular outflow
with speeds reaching 450 km/s. Analysis of the off-nucleus emission line
kinematics and morphology reveals two nested, rotating disk components. The
inner disk, inside pc, has kinematics consistent with the nearly
edge-on, geometrically thin water megamaser disk in Keplerian rotation around a
central mass of 1.66\times 10^7\,\mbox{M}_\odot. The outer disk, which
extends to ~pc radius, counter-rotates relative to the inner disk. The
rotation curve of the outer disk is consistent with rotation around the same
central mass as the megamaser disk but in the opposite sense. The morphology of
the molecular gas is asymmetric around the nuclear continuum source. We
speculate that the outer disk formed from more recently introduced molecular
gas falling out of the host galaxy or from a captured dwarf satellite galaxy.
In NGC 1068, we find direct evidence that the molecular torus consists of
counter-rotating and misaligned disks on parsec scales.ERC grant 695671 'QUENCH
HIGH-VELOCITY BIPOLAR MOLECULAR EMISSION from AN AGN TORUS
We have detected in ALMA observations CO J = 6 - 5 emission from the nucleus
of the Seyfert galaxy NGC 1068. The low-velocity (up to +/- 70 km/s relative to
systemic) CO emission resolves into a 12x7 pc structure, roughly aligned with
the nuclear radio source. Higher-velocity emission (up to +/- 400 km/s) is
consistent with a bipolar outflow in a direction nearly perpendicular (roughly
80 degrees) to the nuclear disk. The position-velocity diagram shows that in
addition to the outflow, the velocity field may also contain rotation about the
disk axis. These observations provide compelling evidence in support of the
disk-wind scenario for the AGN obscuring torus.FONDECYT (Grant ID: 3140436), Science and Technology Facilities CouncilThis is the author accepted manuscript. The final version is available from Institute of Physics Publishing via http://dx.doi.org/10.3847/2041-8205/829/1/L
Investigation of the obscuring circumnuclear torus in the active galaxy Mrk231
Here we report on observations of powerful hydroxyl (OH) line emissions that
trace the obscuring material within the circumnuclear environment of the galaxy
Markarian 231. The hydroxyl (mega)-maser emission shows the characteristics of
a rotating, dusty, molecular torus (or thick disk) located between 30 and 100
pc from the central engine. We now have a clear view of the physical
conditions, the kinematics and the spatial structure of this material on
intermediate size scales, confirming the main tenets of unification models.Comment: 10 pages, including 3 Figures, published in Nature Vol 421 2003; the
published pdf--file and higher quality images are available at
http://www.astro.rug.nl/~hrkloeck/np/pubmrk231.htm
Scholarly publishing depends on peer reviewers
The peer-review crisis is posing a risk to the scholarly peer-reviewed journal system. Journals have to ask many potential peer reviewers to obtain a minimum acceptable number of peers accepting reviewing a manuscript. Several solutions have been suggested to overcome this shortage. From reimbursing for the job, to eliminating pre- publication reviews, one cannot predict which is more dangerous for the future of scholarly publishing. And, why not acknowledging their contribution to the final version of the article published? PubMed created two categories of contributors: authors [AU] and collaborators [IR]. Why not a third category for the peer-reviewer
Teaching: Natural or Cultural?
In this chapter I argue that teaching, as we now understand the term, is historically and cross-culturally very rare. It appears to be unnecessary to transmit culture or to socialize children. Children are, on the other hand, primed by evolution to be avid observers, imitators, players and helpers—roles that reveal the profoundly autonomous and self-directed nature of culture acquisition (Lancy in press a). And yet, teaching is ubiquitous throughout the modern world—at least among the middle to upper class segment of the population. This ubiquity has led numerous scholars to argue for the universality and uniqueness of teaching as a characteristically human behavior. The theme of this chapter is that this proposition is unsustainable. Teaching is largely a result of recent cultural changes and the emergence of modern economies, not evolution
25th Annual Computational Neuroscience Meeting: CNS-2016
Abstracts of the 25th Annual Computational Neuroscience
Meeting: CNS-2016
Seogwipo City, Jeju-do, South Korea. 2–7 July 201
Molecular gas distribution and dynamics in the luminous merger NGC 6240
We present the results of our subarcsecond resolution interferometric observations of the 1.3 mm CO J = 2-->1 line in the luminous merger NGC 6240. Roughly half of the CO flux is contained in a rotating and highly turbulent thick disk centered between the two radio and near-infrared nuclei. In this disk the molecular gas has velocity widths which reach FWZP line widths of up to 1000 km s(-1). The mass of this gas concentration makes up between 30%-70% of the dynamical mass in this region. NGC 6240 may be in an earlier merging stage than typical ULIRGs such as Arp 220. We compare these results from NGC 6240 with those of other luminous, gas-rich interacting galaxies and mergers
Imagining union: European cultural identity in the pre-federal future perfect
Water masers are found in dense molecular clouds closely associated with supermassive black holes at the centres of active galaxies. On the basis of the understanding of the local water-maser luminosity function, it was expected that masers at intermediate and high redshifts would be extremely rare. However, galaxies at redshifts z>2 might be quite different from those found locally, not least because of more frequent mergers and interaction events. Here we use gravitational lensing to search for masers at higher redshifts than would otherwise be possible, and find a water maser at redshift 2.64 in the dust- and gas-rich, gravitationally lensed type-1 quasar MGJ0414+0534 (refs 6-13). The isotropic luminosity is 10,000 (, solar luminosity), which is twice that of the most powerful local water maser and half that of the most distant maser previously known. Using the locally determined luminosity function, the probability of finding a maser this luminous associated with any single active galaxy is 10-6. The fact that we see such a maser in the first galaxy we observe must mean that the volume densities and luminosities of masers are higher at redshift 2.64
A "clear" view of the nucleus:the Megamaser perspective
Extragalactic emission from the hydroxyl and the water molecule was first detected in the early eighties, revealing a new class of maser emission with unexpected isotropic luminosities of many magnitudes higher than their galactic counterparts. Galaxies that harbor this so-called Megamaser emission show enhanced core activity in the form of a nuclear starburst or an active-galactic-nucleus. The exceptional maser properties together with the nuclear activity indicate that the line radiation originates in the circumnuclear environment close to the central engine. The environment for producing maser emission in our Galaxy fulfills some unique requirements that will be compared with those of the extra-galactic Megamaser emission. Using very-long-baseline-interferometry, the observational data show that the radio and the molecular line emission structure reveal a rather more complex picture of the circumnuclear environment where the masers occur. At such scale-sizes the individual Megamaser galaxies display diverse maser- and nuclear properties, which all contribute to the understanding of the molecular environment in active nuclei.</p