238 research outputs found
Aspects of Supermassive Black Hole Growth in Nearby Active Galactic Nuclei
Super-massive black holes (SBHs) have long been identified as the engines of active galactic nuclei (AGNs) and are now considered to play a key role in galaxy evolution. In this dissertation I present results from two observational studies conducted on nearby AGNs with the aim of furthering our understanding of SBH growth and their interplay with the host galaxies.
The first study is an observational search for SBHs spatially offset from the center of their host galaxies. Such offsets can be considered signatures of gravitational recoil following the coalescence of an SBH binary system (formed in the aftermath of a galaxy merger) due to emission of gravitational waves. The study is based on a photometric analysis of fourteen nearby elliptical galaxies observed with the Hubble Space Telescope. I find that parsec-scale offsets are common. However, while these are individually consistent with residual gravitational recoil oscillations, there is a high probability that larger offsets than those actually observed should have been found in the sample as a whole. There are a number of possible explanations for this result: the galaxy merger rate may be lower than current estimates; SBH-binaries may reach the merger stage with a configuration which minimizes recoil velocities; or the SBH oscillations are more quickly damped than predicted.
In the second study I use integral field spectroscopy obtained with the Gemini South telescope to investigate the kinematics of the circum-nuclear ionized gas in two active galaxies: NGC 1386, a Seyfert 2, and NGC 1365, a Seyfert 1. The goal of the study is to investigate outflows in low-luminosity AGNs, and the mechanisms channeling gas (the SBH fuel) from the inner kiloparsec down to a few tens of parsecs from the SBH. I find that the dominant kinematic components can be explained as a combination of rotation in the large-scale galactic disk and compact outflows along the axis of the AGN âradiation coneâ. However, in the case of NGC 1386, there is also compelling evidence for an equatorial outflow, which provides a new clue to the physical processes operating in AGNs
On Burst Error Correction and Storage Security of Noisy Data
Secure storage of noisy data for authentication purposes usually involves the
use of error correcting codes. We propose a new model scenario involving burst
errors and present for that several constructions.Comment: to be presented at MTNS 201
Hypercompact stellar clusters: morphological renditions and spectro-photometric models
Numerical relativity predicts that the coalescence of a black hole-binary
causes the newly formed black hole to recoil, and evidence for such recoils has
been found in the gravitational waves observed during the merger of
stellar-mass black holes. Recoiling (super)massive black holes are expected to
reside in hypercompact stellar clusters (HCSCs). Simulations of galaxy assembly
predict that hundreds of HCSCs should be present in the halo of a Milky
Way-type galaxy, and a fraction of those around the Milky Way should have
magnitudes within the sensitivity limit of existing surveys. However, recoiling
black holes and their HCSCs are still waiting to be securely identified. With
the goal of enabling searches through recent and forthcoming databases, we
improve over existing literature to produce realistic renditions of HCSCs bound
to black holes with a mass of 10 M. Including the effects of a
population of blue stragglers, we simulate their appearance in Pan-STARRS and
in forthcoming images. We also derive broad-band spectra and the
corresponding multi-wavelength colours, finding that the great majority of the
simulated HCSCs fall on the colour-colour loci defined by stars and galaxies,
with their spectra resembling those of giant K-type stars. We discuss the
clusters properties, search strategies, and possible interlopers.Comment: Accepted for publication on MNRAS, 17 pages, 7 figure
Gas inflows towards the nucleus of NGC1358
We use optical spectra from the inner 1.8 2.5kpc of the Seyfert
2 galaxy NGC1358, obtained with the GMOS integral field spectrograph on the
Gemini South telescope at a spatial resolution of 165pc, to assess
the feeding and feedback processes in this nearby active galaxy. Five gaseous
kinematical components are observed in the emission line profiles. One of the
components is present in the entire field-of-view and we interpret it as due to
gas rotating in the disk of the galaxy. Three of the remaining components we
interpret as associated to active galactic nucleus (AGN) feedback: a compact
unresolved outflow in the inner 1 arcsec and two gas clouds observed at
opposite sides of the nucleus, which we propose have been ejected in a previous
AGN burst. The disk component velocity field is strongly disturbed by a large
scale bar. The subtraction of a velocity model combining both rotation and bar
flows reveals three kinematic nuclear spiral arms: two in inflow and one in
outflow. We estimate the mass inflow rate in the inner 180pc obtaining
1.5 Myr, about 160
times larger than the accretion rate necessary to power this AGN.Comment: 12 pages, 11 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society. arXiv admin note: text overlap with
arXiv:1701.0086
Feeding and Feedback in the Inner Kiloparsec of the Active Galaxy NGC2110
We present two-dimensional gaseous kinematics of the inner 1.1 x 1.6kpc^2 of
the Seyfert 2 galaxy NGC2110, from optical spectra obtained with the GMOS
integral field spectrograph on the Gemini South telescope at a spatial
resolution of 100pc. Gas emission is observed over the whole field-of-view,
with complex - and frequently double - emission-line profiles. We have
identified four components in the emitting gas, according to their velocity
dispersion (sigma), which we refer to as: (1) warm gas disk (sigma =
100-220km/s); (2) cold gas disk (sigma = 60-90km/s); (3) nuclear component
(sigma = 220-600km/s); and (4) northern cloud (sigma = 60-80km/s). Both the
cold and warm disk components are dominated by rotation and have similar gas
densities, but the cold gas disk has lower velocity dispersions and reaches
higher rotation velocities. We attribute the warm gas disk to a thick gas layer
which encompasses the cold disk as observed in some edge-on spiral galaxies.
After subtraction of a rotation model from the cold disk velocity field, we
observe excess blueshifts of 50km/s in the far side of the galaxy as well as
similar excess redshifts in the near side. These residuals can be interpreted
as due to nuclear inflow in the cold gas, with an estimated ionized gas mass
inflow rate of 2.2 x 10^(-2)Msun/yr. We have also subtracted a rotating model
from the warm disk velocity field and found excess blueshifts of 100km/s to the
SW of the nucleus and excess redshifts of 40km/s to the NE, which we attribute
to gas disturbed by an interaction with a nuclear spherical outflow. This
nuclear outflow is the origin of the nuclear component observed within the
inner 300pc and it has a mass outflow rate of 0.9Msun/yr. In a region between
1" and 4" north of the nucleus we find a new low sigma component of ionized gas
which we attribute to a high latitude cloud photoionized by the nuclear source.Comment: 17 pages, 13 figures, 1 table; accepted for publication in MNRA
CONSOLE Project - Deliverable 2.5 - "EIP-AGRI abstract on current experience and existing initiatives on collective, result-based and value chain solutions for AECPG provision"
To improve the provision of agri-environmental-climate public goods (AECPGs) from agriculture and forestry, new solutions, such as result-based payments or collective implementation, and new strategies along the value chain might help. The analysis of ca. 120 case studies in and outside EU showed that many real-life cases of implementation combine different contract types. Collective implementation can be a precondition for environmental effectiveness, particularly if AECPGs are addressed that can be hardly improved by measures on single plots, (e.g. water quality). Result-based contracts can target specific AECPGs and increase engagement of land-managers due to flexible management choices. Some recommendations for contract design and implementation are distilled: 1.) Targeting contracts to specific regions addresses regional criticalities and enhances the farmersâ and forestersâ interest and understanding of measures. 2.) Involving land-managers in target-setting and measure development leads to higher compatibility with their businesses and can create win-win situations. 3.) Involving control authorities in the design of indicators in result-based schemes can guarantee integrability into RDPs. 4.) Fostering bottom-up approaches and involving regional key actors as coordinating units enhances commitment and motivation in collective approaches. 5.) Guaranteeing good levels of equity and fairness enhances acceptance particularly in value-chain based solutions. It becomes clear that result-based and collective solutions donât fit in each context situation, as they often demand high levels of knowledge and collaborative skills. Value chain approaches are often only suited if consumersâ awareness is high
The complex gas kinematics in the nucleus of the Seyfert 2 galaxy NGC 1386: rotation, outflows and inflows
We present optical integral field spectroscopy of the circum-nuclear gas of
the Seyfert 2 galaxy NGC 1386. The data cover the central 7 (530 680 pc) at a spatial resolution of 0.9"
(68 pc), and the spectral range 5700-7000 \AA\ at a resolution of 66 km
s. The line emission is dominated by a bright central component, with
two lobes extending 3 north and south of the
nucleus. We identify three main kinematic components. The first has low
velocity dispersion ( 90 km s), extends over the
whole field-of-view, and has a velocity field consistent with gas rotating in
the galaxy disk. We interpret the lobes as resulting from photoionization of
disk gas in regions where the AGN radiation cones intercept the disk. The
second has higher velocity dispersion ( 200 km s)
and is observed in the inner 150 pc around the continuum peak. This component
is double peaked, with redshifted and blueshifted components separated by
500 km s. Together with previous HST imaging, these features
suggest the presence of a bipolar outflow for which we estimate a mass outflow
rate of 0.1 M yr. The third
component is revealed by velocity residuals associated with enhanced velocity
dispersion and suggests that outflow and/or rotation is occurring approximately
in the equatorial plane of the torus. A second system of velocity residuals may
indicate the presence of streaming motions along dusty spirals in the disk.Comment: 24 pages, 16 figures, 3 tables, interesting results, accepted for
publication in Ap
Associations of Vascular Risk Factors and APOE Genotype With Perivascular Spaces Among CommunityâDwelling Older Adults
n/
Inferring urban social networks from publicly available data
The emergence of social networks and the definition of suitable generative
models for synthetic yet realistic social graphs are widely studied problems in
the literature. By not being tied to any real data, random graph models cannot
capture all the subtleties of real networks and are inadequate for many
practical contexts -- including areas of research, such as computational
epidemiology, which are recently high on the agenda. At the same time, the
so-called contact networks describe interactions, rather than relationships,
and are strongly dependent on the application and on the size and quality of
the sample data used to infer them. To fill the gap between these two
approaches, we present a data-driven model for urban social networks,
implemented and released as open source software. Given a territory of
interest, and only based on widely available aggregated demographic and
social-mixing data, we construct an age-stratified and geo-referenced synthetic
population whose individuals are connected by "strong ties" of two types:
intra-household (e.g., kinship) or friendship. While household links are
entirely data-driven, we propose a parametric probabilistic model for
friendship, based on the assumption that distances and age differences play a
role, and that not all individuals are equally sociable. The demographic and
geographic factors governing the structure of the obtained network, under
different configurations, are thoroughly studied through extensive simulations
focused on three Italian cities of different size
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