6,079 research outputs found
Seismic and solar performance of historical city. Urban form-based multicriteria analysis
The understanding of the global performance of a historical city is a complex balance
of several specific issues and requires a multi-disciplinary approach to face with actual urban
phenomena and challenges, such as the seismic risk and energy efficiency, that are strongly
influenced by urban form. This paper focuses on the potential of urban metrics and typological
indicators for describing the seismic vulnerability and the solar radiation availability of distinct
urban textures, and the correlation between the two aspects. Comparative analysis at fabric scale
was conducted on the historical centre of Rieti (Latium, Italy), to underline the main seismic and
solar indicators. In the last decade, we witnessed the spreading of urban scale assessment and
analysis tools, but seldom using an integrated approach to face the complexity of the historical
city. Relying on morpho-typological indicators, the proposed method characterizes the fabrics in
terms of seismic vulnerability and solar availability through a multicriteria analysis. The analysis
reveals substantial differences between fabrics using three groups of indicators: Plan, Space and
Analysis-oriented. Each group describes different features of the urban fabrics that affect seismic
and solar performance and suggests improvement strategies. The purpose is to support
policymaker and designer in the urban renovation process
Circumnuclear HI disks in radio galaxies: The case of Cen A and B2 0258+35
New HI observations of the nearby radio-loud galaxies Centaurus A and B2
0258+35 show broad absorption (Delta_v=400km/s) against the unresolved nuclei.
Both sources belong to the cases where blue- and redshifted absorption is
observed at the same time. In previous Cen A observations only a relative
narrow range of redshifted absorption was detected. We show that the data
suggest in both cases the existence of a circumnuclear disk. For Cen A the
nuclear absorption might be the atomic counterpart of the molecular
circumnuclear disk that is seen in CO and H_2. Higher resolution observations
are now needed to locate the absorption and to further investigate the
structure and kinematics of the central region of the AGN and the way the AGN
are fueled.Comment: Talk given at "The Central Kiloparsec: Active Galactic Nuclei and
Their Hosts", Ierapetra, Crete, 4-6 June, 2008. To appear in Volume 79 of the
Memorie della Societa Astronomica Italiana. 4 pages, 2 figure
Is Centaurus A special? A neutral hydrogen perspective
Due to the proximity, the neutral hydrogen belonging to Centaurus A can be
observed at high resolution with good sensitivity. This allows to study the
morphology and kinematics in detail in order to understand the evolution of
this radio-loud source (e.g. merger history, AGN activity). At the same time,
it is important to compare the results to other sources of the same class (i.e.
early-type galaxies in general and radio galaxies in particular) to see how
Centaurus A fits into the global picture of early-type/radio galaxy evolution.
The amount of HI, the morphology of a warped disk with HI clouds surrounding
the disk and the regular kinematics of the inner part of the HI disk are not
unusual for early-type galaxies. The growing evidence that mergers are not
necessarily responsible for AGN activity fits with the observational result
that the recent merger event in Centaurus A is not connected to the current
phase of activity. Based on these results, we conclude that Centaurus A has
typical neutral hydrogen properties for an early-type and radio galaxy and it
can therefore - from an HI perspective - be seen as a typical example of its
class.Comment: submitted to PASA; 7 pages, 4 figure
Anomalous HI kinematics in Centaurus A: evidence for jet-induced star formation
We present new 21-cm HI observations performed with ATCA of the large HI
filament located about 15 kpc NE from the centre of Centaurus A and discovered
by Schiminovich et al.(1994). This HI cloud is situated (in projection) near
the radio jet of Centaurus A, as well as near a large filament of ionised gas
of high excitation and turbulent velocities and near regions with young stars.
The higher velocity and spatial resolution of the new data reveals that, apart
from the smooth velocity gradient corresponding to the overall rotation of the
cloud around Centaurus A, HI with anomalous velocities of about 100 km/s is
present at the southern tip of this cloud. This is interpreted as evidence for
an ongoing interaction between the radio jet and the HI cloud. Gas stripped
from the HI cloud gives rise to the large filament of ionised gas and the star
formation regions that are found downstream from the location of the
interaction. The implied flow velocities are very similar to the observed
anomalous HI velocities. Given the amount of HI with anomalous kinematics and
the current star formation rate, the efficiency of jet-induced star formation
is at most of the order of a percent.Comment: Accepted for publication in A&A, 7 pages, 4 figures. The full paper
with high resolution images can be downloaded from
http://www.astron.nl/~morganti/Papers/cena.paper.pd
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