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Wijnholds S.J.,Netherlands Institute for Research in Astronomy ASTRON | Van Der Tol S.,Leiden University | Nijboer R.,Netherlands Institute for Research in Astronomy ASTRON | Van Der Veen A.-J.,Technical University of Delft
IEEE Signal Processing Magazine | Year: 2010

Instruments for radio astronomical observations have come a long way. While the first telescopes were based on very large dishes and two-antenna interferometers, current Instruments consist of dozens of steerable dishes, whereas future instruments will be even larger distributed sensor arrays with a hierarchy of phased array elements. For such arrays to provide meaningful output (images), accurate calibration is of critical importance. Calibration must solve for the unknown antenna gains and phases as well as the unknown atmospheric and ionospheric disturbances. Future telescopes will have a large number of elements and a large field of view (FOV). In this case, the parameters are strongly direction-dependent, resulting in a large number of unknown parameters, even if appropriately constrained physical or phenomenological descriptions are used. This makes calibration a daunting parameter-estimation task. © 2006 IEEE.


Young L.M.,New Mexico Institute of Mining and Technology | Bureau M.,University of Oxford | Davis T.A.,University of Oxford | Combes F.,Paris Observatory | And 25 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We have carried out a survey for CO J= 1-0 and J= 2-1 emission in the 260 early-type galaxies of the volume-limited ATLAS3D sample, with the goal of connecting their star formation and assembly histories to their cold gas content. This is the largest volume-limited CO survey of its kind and is the first to include many Virgo cluster members. Sample members are dynamically hot galaxies with a median stellar mass ∼3 × 1010 M⊙; they are selected by their morphology rather than colour, and the bulk of them lie on the red sequence. The overall CO detection rate is 56/259 = 0.22 ± 0.03, with no dependence on the K luminosity and only a modest dependence on the dynamical mass. There are a dozen CO detections among the Virgo cluster members; statistical analysis of their H2 mass distributions and their dynamical status within the cluster shows that the cluster's influence on their molecular masses is subtle at best, even though (unlike spirals) they seem to be virialized within the cluster. We suggest that the cluster members have retained their molecular gas through several Gyr residences in the cluster. There are also a few extremely CO-rich early-type galaxies with H2 masses ≳109 M⊙ and these are in low-density environments. We do find a significant trend between the molecular content and stellar specific angular momentum. The galaxies of low angular momentum also have low CO detection rates, suggesting that their formation processes were more effective at destroying the molecular gas or preventing its re-accretion. We speculate on the implications of these data for the formation of various subclasses of early-type galaxies. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

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