523 research outputs found
N-band Imaging of Seyfert Nuclei and the MIR-X-ray correlation
We present new mid-infrared (N-band) images of a sample of eight nearby
Seyfert galaxies. In all of our targets, we detect a central unresolved source,
which in some cases has been identified for the first time. In particular, we
have detected the mid-infrared emission from the active nucleus of NGC 4945,
which previously remained undetected at any wavelength but hard X-rays. We also
detect circumnuclear extended emission in the Circinus galaxy along its major
axis, and find marginal evidence for extended circumnuclear emission in NGC
3281.
The high spatial resolution (1.7") of our data allows us to separate the flux
of the nuclear point sources from the extended circumnuclear starburst (if
present). We complement our sample with literature data for a number of
non-active starburst galaxies, and relate the nuclear N-band flux to published
hard (2-10 kev) X-ray fluxes. We find tight and well-separated correlations
between nuclear N-band flux and X-ray flux for both Seyfert and starburst
nuclei which span over 3 orders of magnitude in luminosity. We demonstrate that
these correlations can be used as a powerful classification tool for galactic
nuclei.
For example, we find strong evidence against NGC 1808 currently harbouring an
active Seyfert nucleus based on its position in the mid-infrared-X-ray diagram.
On the other hand, we confirm that NGC 4945 is in fact a Seyfert 2 galaxy.Comment: 31 pages, incl. 4 figures, uses AASTex. Replaced with accepted
version after minor modifications. To appear in Ap
What is limiting near-infrared astrometry in the Galactic Center?
We systematically investigate the error sources for high-precision astrometry
from adaptive optics based near-infrared imaging data. We focus on the
application in the crowded stellar field in the Galactic Center. We show that
at the level of <=100 micro-arcseconds a number of effects are limiting the
accuracy. Most important are the imperfectly subtracted seeing halos of
neighboring stars, residual image distortions and unrecognized confusion of the
target source with fainter sources in the background. Further contributors to
the error budget are the uncertainty in estimating the point spread function,
the signal-to-noise ratio induced statistical uncertainty, coordinate
transformation errors, the chromaticity of refraction in Earth's atmosphere,
the post adaptive optics differential tilt jitter and anisoplanatism. For stars
as bright as mK=14, residual image distortions limit the astrometry, for
fainter stars the limitation is set by the seeing halos of the surrounding
stars. In order to improve the astrometry substantially at the current
generation of telescopes, an adaptive optics system with high performance and
weak seeing halos over a relatively small field (r<=3") is suited best.
Furthermore, techniques to estimate or reconstruct the seeing halo could be
promising.Comment: accepted by MNRAS, 13 pages, 14 figure
Infrared to millimetre photometry of ultra-luminous IR galaxies: new evidence favouring a 3-stage dust model
Infrared to millimetre spectral energy distributions have been obtained for
41 bright ultra-luminous infrared galaxies. The observations were carried out
with ISOPHOT between 10 and 200 micron and supplemented for 16 sources with
SCUBA at 450 and 850 micron and with SEST at 1.3 mm. In addition, seven sources
were observed at 1.2 and 2.2 m with the 2.2 m telescope on Calar Alto.
These new SEDs represent the most complete set of infrared photometric
templates obtained so far on ULIRGs in the local universe.Comment: 23 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
Evidence for Warped Disks of Young Stars in the Galactic Center
The central parsec around the super-massive black hole in the Galactic Center
hosts more than 100 young and massive stars. Outside the central cusp (R~1")
the majority of these O and Wolf-Rayet (WR) stars reside in a main clockwise
system, plus a second, less prominent disk or streamer system at large angles
with respect to the main system. Here we present the results from new
observations of the Galactic Center with the AO-assisted near-infrared imager
NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include
the detection of 27 new reliably measured WR/O stars in the central 12" and
improved measurements of 63 previously detected stars, with proper motion
uncertainties reduced by a factor of four compared to our earlier work. We
develop a detailed statistical analysis of their orbital properties and
orientations. Half of the WR/O stars are compatible with being members of a
clockwise rotating system. The rotation axis of this system shows a strong
transition as a function of the projected distance from SgrA*. The main
clockwise system either is either a strongly warped single disk with a
thickness of about 10 degrees, or consists of a series of streamers with
significant radial variation in their orbital planes. 11 out of 61 clockwise
moving stars have an angular separation of more than 30 degrees from the
clockwise system. The mean eccentricity of the clockwise system is 0.36+/-0.06.
The distribution of the counter-clockwise WR/O star is not isotropic at the 98%
confidence level. It is compatible with a coherent structure such as stellar
filaments, streams, small clusters or possibly a disk in a dissolving state.
The observed disk warp and the steep surface density distribution favor in situ
star formation in gaseous accretion disks as the origin of the young stars.Comment: ApJ in pres
Evidence for X-ray synchrotron emission from simultaneous mid-IR to X-ray observations of a strong Sgr A* flare
This paper reports measurements of Sgr A* made with NACO in L' -band (3.80
um), Ks-band (2.12 um) and H-band (1.66 um) and with VISIR in N-band (11.88 um)
at the ESO VLT, as well as with XMM-Newton at X-ray (2-10 keV) wavelengths. On
4 April, 2007, a very bright flare was observed from Sgr A* simultaneously at
L'-band and X-ray wavelengths. No emission was detected using VISIR. The
resulting SED has a blue slope (beta > 0 for nuL_nu ~ nu^beta, consistent with
nuL_nu ~ nu^0.4) between 12 micron and 3.8 micron.
For the first time our high quality data allow a detailed comparison of
infrared and X-ray light curves with a resolution of a few minutes. The IR and
X-ray flares are simultaneous to within 3 minutes. However the IR flare lasts
significantly longer than the X-ray flare (both before and after the X-ray
peak) and prominent substructures in the 3.8 micron light curve are clearly not
seen in the X-ray data. From the shortest timescale variations in the L'-band
lightcurve we find that the flaring region must be no more than 1.2 R_S in
size.
The high X-ray to infrared flux ratio, blue nuL_nu slope MIR to L' -band, and
the soft nuL_nu spectral index of the X-ray flare together place strong
constraints on possible flare emission mechanisms. We find that it is
quantitatively difficult to explain this bright X-ray flare with inverse
Compton processes. A synchrotron emission scenario from an electron
distribution with a cooling break is a more viable scenario.Comment: ApJ, 49 pages, 9 figure
Nuclear mid-infrared properties of nearby low-luminosity AGN
We present ground-based high-spatial resolution mid-infrared (MIR)
observations of 20 nearby low-luminosity AGN (LLAGN) with VLT/VISIR and the
preliminary analysis of a new sample of 10 low-luminosity Seyferts observed
with Gemini/Michelle. LLAGN are of great interest because these objects are the
most common among active galaxies, especially in the nearby universe. Studying
them in great detail makes it possible to investigate the AGN evolution over
cosmic timescale. Indeed, many LLAGN likely represent the final stage of an
AGN's lifetime. We show that even at low luminosities and accretion rates
nuclear unresolved MIR emission is present in most objects. Compared to lower
spatial resolution Spitzer/IRS spectra, the high-resolution MIR photometry
exhibits significantly lower fluxes and different PAH emission feature
properties in many cases. By using scaled Spitzer/IRS spectra of typical
starburst galaxies, we show that the star formation contribution to the 12
micron emission is minor in the central parsecs of most LLAGN. Therefore, the
observed MIR emission in the VISIR and Michelle data is most likely emitted by
the AGN itself, which, for higher luminosity AGN, is interpreted as thermal
emission from a dusty torus. Furthermore, the 12 micron emission of the LLAGN
is strongly correlated with the absorption corrected 2-10 keV luminosity and
the MIR--X-ray correlation found previously for AGN is extended to a range from
10^40 to 10^45 erg/s. This correlation is independent of the object type, and
in particular the low-luminosity Seyferts observed with Michelle fall exactly
on the power-law fit valid for brighter AGN. In addition, no dependency of the
MIR--X-ray ratio on the accretion rate is found. These results are consistent
with the unification model being applicable even in the probed low-luminosity
regime.Comment: to appear in the proceedings of AHAR 2011: The Central Kiloparsec in
Galactic Nucle
Simultaneous NIR/sub-mm observation of flare emission from SgrA*
We report on a successful, simultaneous observation and modeling of the
sub-millimeter to near-infrared flare emission of the Sgr A* counterpart
associated with the super-massive black hole at the Galactic center. Our
modeling is based on simultaneous observations that have been carried out on 03
June, 2008 using the NACO adaptive optics (AO) instrument at the ESO VLT and
the LABOCA bolometer at the APEX telescope. Inspection and modeling of the
light curves show that the sub-mm follows the NIR emission with a delay of
1.5+/-0.5 hours. We explain the flare emission delay by an adiabatic expansion
of the source components.Comment: 12 pages, 9 figures, 3 tables, in press with A&
Digitalisierte Beratung zur effizienteren Selbstoptimierung: Kritische Anmerkungen zu digitalen Formaten arbeitsbezogener Beratung aus einer Gouvernementalitätsperspektive
"Digital(isiert)e" Beratung verspricht neben Innovation auch Flexibilität, Ubiquität, Globalität, Geschwindigkeit und Legitimität durch evidenzbasierte Wirksamkeit. Für eine sozialwissenschaftlich fundierte arbeitsweltliche Beratung wie Coaching und Supervision ist danach zu fragen, welches Menschen- und Weltbild sich hinter der Digitalisierung verbirgt und welche Anliegen sie transportiert. Dazu wird mit den Theorien Michel Foucaults der gegenwärtige Diskurs auf Steuerungslogiken und Machtverhältnisse hin kritisch analysiert. Dabei zeigt sich, dass die Digitalisierung das "Zeitalter der Gouvernementalität" (Foucault) festigt: Humanistisch geprägte Werte und Ziele wie Reflexion, Anerkennung und Selbsterkenntnis treten in den Hintergrund, während die Nutzbarmachung und Optimierung des Selbst sowie des Beratungsprozesses wichtiger werden: Beratung will und muss effizienzgetrieben ihre Wirksamkeit evidenzbasiert legitimieren, und Digitalisierung erleichtert dies
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