128 research outputs found
European ALMA operations: the interaction with and support to the users
The Atacama Large Millimetre/submillimetre Array (ALMA) is one of the largest
and most complicated observatories ever built. Constructing and operating an
observatory at high altitude (5000m) in a cost effective and safe manner, with
minimal effect on the environment creates interesting challenges. Since the
array will have to adapt quickly to prevailing weather conditions, ALMA will be
operated exclusively in service mode. By the time of full science operations,
the fundamental ALMA data product shall be calibrated, deconvolved data cubes
and images, but raw data and data reduction software will be made available to
users as well. User support is provided by the ALMA Regional Centres (ARCs)
located in Europe, North America and Japan. These ARCs constitute the interface
between the user community and the ALMA observatory in Chile. For European
users the European ARC is being set up as a cluster of nodes located throughout
Europe, with the main centre at the ESO Headquarters in Garching. The main
centre serves as the access portal and in synergy with the distributed network
of ARC nodes, the main aim of the ARC is to optimize the ALMA science output
and to fully exploit this unique and powerful facility. The aim of this article
is to introduce the process of proposing for observing time, subsequent
execution of the observations, obtaining and processing of the data in the ALMA
epoch. The complete end-to-end process of the ALMA data flow from the proposal
submission to the data delivery is described.Comment: 7 pages, three figure
The correct estimate of the probability of false detection of the matched filter in the detection of weak signals. II. (Further results with application to a set of ALMA and ATCA data)
The matched filter (MF) is one of the most popular and reliable techniques to
the detect signals of known structure and amplitude smaller than the level of
the contaminating noise. Under the assumption of stationary Gaussian noise, MF
maximizes the probability of detection subject to a constant probability of
false detection or false alarm (PFA). This property relies upon a priori
knowledge of the position of the searched signals, which is usually not
available. Recently, it has been shown that when applied in its standard form,
MF may severely underestimate the PFA. As a consequence the statistical
significance of features that belong to noise is overestimated and the
resulting detections are actually spurious. For this reason, an alternative
method of computing the PFA has been proposed that is based on the probability
density function (PDF) of the peaks of an isotropic Gaussian random field. In
this paper we further develop this method. In particular, we discuss the
statistical meaning of the PFA and show that, although useful as a preliminary
step in a detection procedure, it is not able to quantify the actual
reliability of a specific detection. For this reason, a new quantity is
introduced called the specific probability of false alarm (SPFA), which is able
to carry out this computation. We show how this method works in targeted
simulations and apply it to a few interferometric maps taken with the Atacama
Large Millimeter/submillimeter Array (ALMA) and the Australia Telescope Compact
Array (ATCA). We select a few potential new point sources and assign an
accurate detection reliability to these sources.Comment: 28 pages, 20 figures, Astronomy & Astrophysics, Minor changes and
some typos correcte
Type 1 AGN and their Link to ULIRGS
Increasing observational evidence supports a picture for a close link among
AGN phenomenum, star-formation processes and galaxy formation. Since the
physical phenomena related to the onset of both AGN and star formation are very
likely characterized by a strong far infrared (FIR) emission it becomes
mandatory to investigate the FIR energy domain. However, because of their
faintness in the FIR energy range, very little is known about the FIR
properties of type 1 AGN, and type 2 AGN, which are supposed to be missed in
classical searches, still lack definition and samples. Our aim is to
investigate the FIR properties of optically selected type 1 AGN, compare them
to Ultraluminous Infrared Galaxies (ULIRGs) and derive some general
characteristics of the population. Expectations for future surveys are also
presented.Comment: 6 pages, in "Issues in unifications of AGNs" Marciana Marina, May
2001; eds. R. Maiolino, A. Marconi and N. Naga
How many active galaxies and QSOs will future Space Missions detect?
Averaged spectral energy distributions (SEDs) of active and starburst
galaxies from the 12 micron sample in the Local Universe and Quasars, from an
optically selected sample at a mean redshift =0.7, are built from
optical/near-IR/far-IR (IRAS & ISO) photometric observations. These SEDs are
then used to predict at various redshifts the number of Seyfert type 1 and type
2, starburst, normal galaxies, and quasars, that will be detected by future
Space Missions dedicated to far-infrared and submillimeter astronomy, like
SIRTF and Herschel. These predictions are then compared with the expected
capabilities and detection limits of future deep far-IR surveys. Possible ways
to identify AGN candidates on far-IR colour-colour plots for follow-up
observations are then explored.Comment: accepted in Ap
Matched filter in the low-number count Poisson noise regime: an efficient and effective implementation
The matched filter (MF) is widely used to detect signals hidden within the
noise. If the noise is Gaussian, its performances are well-known and
describable in an elegant analytical form. The treatment of non-Gaussian noises
is often cumbersome as in most cases there is no analytical framework. This is
true also for Poisson noise which, especially in the low-number count regime,
presents the additional difficulty to be discrete. For this reason in the past
methods have been proposed based on heuristic or semi-heuristic arguments.
Recently, an analytical form of the MF has been introduced but the computation
of the probability of false detection or false alarm (PFA) is based on
numerical simulations. To overcome this inefficient and time consuming approach
we propose here an effective method to compute the PFA based on the saddle
point approximation (SA). We provide the theoretical framework and support our
findings by means of numerical simulations. We discuss also the limitations of
the MF in practical applications.Comment: 5 pages, 9 figures , accepted for publication in A&
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