543 research outputs found
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
A Radio Galaxy at z=5.19
We report the discovery of the most distant known AGN, the radio galaxy TN
J0924-2201 at z = 5.19. The radio source was selected from a new sample of
ultra-steep spectrum (USS) sources, has an extreme radio spectral index
alpha_365MHz^1.4GHz = -1.63, and is identified at near-IR wavelengths with a
very faint, K = 21.3 +- 0.3 object. Spectroscopic observations show a single
emission line at lambda ~ 7530A, which we identify as Ly-alpha. The K-band
image, sampling rest frame U-band, shows a multi-component, radio-aligned
morphology, typical of lower-redshift radio galaxies. TN J0924-2201 extends the
near-IR Hubble, or K-z, relation for powerful radio galaxies to z > 5, and is
consistent with models of massive galaxies forming at even higher redshifts.Comment: 11 Pages, including 3 PostScript figures. Accepted for publication in
the Astrophysical Journal Letter
Computing Distances between Probabilistic Automata
We present relaxed notions of simulation and bisimulation on Probabilistic
Automata (PA), that allow some error epsilon. When epsilon is zero we retrieve
the usual notions of bisimulation and simulation on PAs. We give logical
characterisations of these notions by choosing suitable logics which differ
from the elementary ones, L with negation and L without negation, by the modal
operator. Using flow networks, we show how to compute the relations in PTIME.
This allows the definition of an efficiently computable non-discounted distance
between the states of a PA. A natural modification of this distance is
introduced, to obtain a discounted distance, which weakens the influence of
long term transitions. We compare our notions of distance to others previously
defined and illustrate our approach on various examples. We also show that our
distance is not expansive with respect to process algebra operators. Although L
without negation is a suitable logic to characterise epsilon-(bi)simulation on
deterministic PAs, it is not for general PAs; interestingly, we prove that it
does characterise weaker notions, called a priori epsilon-(bi)simulation, which
we prove to be NP-difficult to decide.Comment: In Proceedings QAPL 2011, arXiv:1107.074
Survival under conditions of variable food availability: Resource utilization and storage in the cold-water coral Lophelia pertusa
Cold‐water coral (CWC) reefs are hotspots of biodiversity and productivity in the deep sea, but their distribution is limited by the availability of food, which undergoes complex local and temporal variability. We studied the resource utilization, metabolism, and tissue storage of CWC Lophelia pertusa during an experimentally simulated 3‐day food pulse, of 13C15N‐enriched phytodetritus, followed by a 4‐week food deprivation. Oxygen consumption (0.145 μmol O2 [mmol organic carbon {OC}]−1 h−1), release of particulate organic matter (0.029 μmol particulate organic carbon [POC] [mmol OC]−1 h−1 and 0.005 μmol particulate organic nitrogen [mmol OC]−1 h−1), ammonium excretion (0.004 μmol NH4+ [mmol OC]−1 h−1), tissue C and N content, and fatty acid (FA) and amino acid composition did not change significantly during the experiment. Metabolization of the labeled phytodetritus, however, underwent distinct temporal dynamics. Initially, L. pertusa preferentially used phytodetritus‐derived C for respiration (2.2 ± 0.36 nmol C [mmol OC]−1 h−1) and mucus production (0.94 ± 0.52 nmol C [mmol OC]−1 h−1), but those tracer fluxes declined exponentially to <20% within 2 weeks after feeding and then remained stable, indicating that the remainder of the incorporated phytodetritus had entered a tissue pool with lower turnover. Analysis of 13C in individual FAs revealed a mismatch between the FAs incorporated from phytodetritus and the FA requirements of the coral. We suggest that feeding on other resources, such as lipid‐rich zooplankton, could fill this deficiency. A release of 10% of their total OC as respired C and POC during the 4‐week food deprivation underlines the importance of regular food pulses for CWC reefs.publishedVersio
The B3-Vla CSS sample. III: Evn & Merlin images at 18 cm
EVN and MERLIN observations at 18 cm are presented for 18 Compact
Steep--spectrum radio Sources (CSSs) from the B3-VLA CSS sample. These sources
were marginally resolved in previous VLA A-configuration observations at 4.9
and 8.4 GHz or had peculiar morphologies, two of them looking like core-jets.
The MERLIN images basically confirm the VLA structures at 8.4 GHz while the EVN
and/or the combined images reveal several additional details.Comment: 17 pages, many low resoltion figures, A&A accepted. A higher
resolution gzipped postscript file can be found at
http://www.ira.cnr.it/~ddallaca/h3443.ps.g
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