167 research outputs found
The overmassive black hole in NGC 1277: new constraints from molecular gas kinematics
We report the detection of CO(1-0) emission from NGC 1277, a lenticular
galaxy in the Perseus Cluster. NGC 1277 has previously been proposed to host an
overmassive black hole (BH) compared to the galaxy bulge luminosity (mass),
based on stellar-kinematic measurements. The CO(1-0) emission, observed with
the IRAM Plateau de Bure Interferometer (PdBI) using both, a more compact
(2.9-arcsec resolution) and a more extended (1-arcsec resolution)
configuration, is likely to originate from the dust lane encompassing the
galaxy nucleus at a distance of 0.9 arcsec (~320 pc). The double-horned CO(1-0)
profile found at 2.9-arcsec resolution traces of
molecular gas, likely orbiting in the dust lane at $\sim 550\ \mathrm{km\
s^{-1}}\sim 2\times 10^{10}\
M_\odot\sim
1.7\times 10^{10}\ M_\odotM/L_V=6.3\sim 5\times 10^{9}\ M_\odotM/L_V=10$. While the molecular gas reservoir
may be associated with a low level of star formation activity, the extended
2.6-mm continuum emission is likely to originate from a weak AGN, possibly
characterized by an inverted radio-to-millimetre spectral energy distribution.
Literature radio and X-ray data indicate that the BH in NGC 1277 is also
overmassive with respect to the Fundamental Plane of BH activity.Comment: 15 pages, 13 figures; accepted for publication in MNRAS on 20 January
2016; updated version including minor changes and note added in proo
Two-Sample Testing for Event Impacts in Time Series
In many application domains, time series are monitored to detect extreme
events like technical faults, natural disasters, or disease outbreaks.
Unfortunately, it is often non-trivial to select both a time series that is
informative about events and a powerful detection algorithm: detection may fail
because the detection algorithm is not suitable, or because there is no shared
information between the time series and the events of interest. In this work,
we thus propose a non-parametric statistical test for shared information
between a time series and a series of observed events. Our test allows
identifying time series that carry information on event occurrences without
committing to a specific event detection methodology. In a nutshell, we test
for divergences of the value distributions of the time series at increasing
lags after event occurrences with a multiple two-sample testing approach. In
contrast to related tests, our approach is applicable for time series over
arbitrary domains, including multivariate numeric, strings or graphs. We
perform a large-scale simulation study to show that it outperforms or is on par
with related tests on our task for univariate time series. We also demonstrate
the real-world applicability of our approach on datasets from social media and
smart home environments.Comment: SIAM International Conference on Data Mining (SDM 2020) preprint,
source code and supplementary material is available at
https://github.com/diozaka/eites
The Nearby QSO Host I Zw 1: NIR Probing of Structural Properties and Stellar Populations
The likely merger process and the properties of the stellar populations in
the I Zw 1 host galaxy are analyzed on the basis of multi-wavelength
observations (with the ISAAC camera at the Very Large Telescope (VLT/UT1) of
the European Southern Observatory (ESO), Chile (Paranal), with the
interferometer of the Berkeley-Illinois-Maryland Association (BIMA), USA (Hat
Creek/California), and with the IRAM Plateau de Bure Interferometer (PdBI),
France) and N-body simulations. The data give a consistent picture of I Zw 1,
with properties between those of ultra-luminous infrared galaxies (ULIRGs) and
QSOs as displayed by transition objects in the evolutionary sequence of active
galaxies.Comment: 4 pages, 2 figures, to be published in "The Dense Interstellar Medium
in Galaxies", proceedings of the 4th Cologne-Bonn-Zermatt-Symposium held
September 22-26, 2003, in Zermatt, Switzerlan
Merger Dynamics and Stellar Populations in the Host Galaxies of the Quasi-Stellar Objects I Zw 1 and 3C 48
The thesis focuses on two case studies of the host galaxies of the quasi-stellar objects (QSOs) I Zw 1 and 3C 48. The studies are motivated by the hypothesis that ultra-luminous infrared galaxies (ULIRGs) might represent the early stage of QSO evolution (Sanders et al. 1988). According to this hypothesis, galaxy mergers and interactions trigger gas inflow which is followed by starburst activity and by the formation of an active nucleus. As likely transitionary objects between the ultra-luminous infrared stage and the QSO stage, I Zw 1 and 3C 48 are promising candidates to investigate the active nucleus, the starburst, and the merger properties as the essential links between all stages of the proposed evolutionary sequence. The case study of I Zw 1 has an observational focus and is based on near-infrared (NIR) imaging and spectroscopy, carried out with ISAAC (Infrared Spectrometer and Array Camera) at the Very Large Telescope of the European Southern Observatory (ESO) on Cerro Paranal in Chile. The two-armed spiral host galaxy of I Zw 1 shows two bright knots in the north and in the west of the optical disk region, respectively. Here, the new ISAAC spectra indicate that the northern object is a projected foreground star, as previously assumed but recently challenged. In the surroundings of the western source, the ISAAC J-band image displays tidal features. This gives further support for the scenario that I Zw 1 is presently in a minor merger process with this source. The new spectra and the NIR colors of the western source indicate an old stellar population. The host of I Zw 1 is analyzed in a one-dimensional structural decomposition into bulge, disk, and halo components, which results in mean J-band mass-to-light ratios. The latter indicate a young mean stellar population in the bulge component, while the disk ratios agree with those of normal spiral galaxies. Such a scenario of younger stellar populations in the central region of the I Zw 1 host is also plausible from a two-color analysis. The nuclear ISAAC spectrum of I Zw 1 basically confirms previous results, by showing hydrogen emission lines and indications of extremely blueshifted high-excitation lines. The case study of 3C 48 is the numerical focus of this thesis and based on simulations with multi-particle methods. The aim is to investigate the major merger scenario for 3C 48 by reproducing a 3C 48 model. Such a model is found for a certain projection angle during the inclined merger of two equal-mass spiral galaxies. It inspirits a new idea for the problem of the apparently missing second tidal tail in 3C 48. For the derived projection angle, this tidal tail is located in front of the main body of the modeled host galaxy and is likely to be missed in observations. In the model, both galaxy centers are still separated. This leaves room to interpret the known second luminosity peak, north-east of the QSO in 3C 48, as the center of the galaxy merging with 3C 48. A central gas accumulation and a complex system of gas lanes develop in the simulation with a non-gravitating gas component added. Both results qualitatively agree with the known distribution of molecular gas in 3C 48. The new results about I Zw 1 and 3C 48 complement the existing assumption that both are likely transitionary objects in the evolutionary sequence
Parameter Study of Star-Discs Encounters
Interactions between disc-surrounded stars might play a vital role in the
formation of planetary systems. Here a first parameter study of the effects of
encounters on low-mass discs is presented. The dependence of the mass and
angular momentum transport on the periastron distance, the relative mass of the
encountering stars and eccentricity of the encounter is investigated in detail.
This is done for prograde and retrograde coplanar encounters as well as
non-coplanar encounters. For distant coplanar encounters our simulation results
agree with the analytical approximation of the angular momentum loss by
Ostriker(1994). However, for close or high-mass encounters, significant
differences to this approximation are found. This is especially so in the case
of retrograde encounters, where the analytical result predict no angular
momentum loss regardless of the periastron distance whereas the simulations
find up to ~ 20% loss for close encounters. For the non-coplanar case a more
complex dependency on the inclination between orbital path and disc plane is
found than for distant encounters. For the coplanar prograde case new fitting
formulae for the mass and angular momentum loss are obtained, which cover the
whole range from grazing to distant encounters. In addition, the final disc
size and the mass exchange between discs is examined, demonstrating that for
equal mass stars in encounters as close as 1.5 the disc radius, the disc size
only is reduced by approximately 10%.Comment: 11 pages, 9 figure
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