1,583 research outputs found
1.25 mm Observations of a Complete Sample of IRAS Galaxies: (II) Dust Properties
We present 1.25 mm continuum data for a southern galaxy sample selected from
the IRAS PSC and complete to S_60=2 Jy. Two thirds of the galaxies have been
detected and significant limits on the remaining objects have been set. We
find, on a statistical basis, indications that the dust emission in these
galaxies is somewhat more centrally concentrated than that of the optical
light, possibly tracing a higher metal content in the inner galactic regions.
This result also allows to estimate the aperture corrections to the millimetric
data. The latter, together with IRAS photometric data, have been used to
compare the broad-band FIR/mm spectra with a simple dust model. According to
their far-IR/mm spectrum, the sample galaxies show a dichothomy: almost half of
the objects, those displaying bright 25-60um fluxes ascribed to warm dust
residing in 'starburst' regions, are characterized by higher values of the
bolometric (optical + FIR) luminosity, of the dust-to-gas mass ratio, of the
dust optical depths and of the overall extinction. A complementary class of
objects dominated by cold dust ('cirrus') shows opposite trends. Because of the
favourable observational setup, selection wavelength and completeness, we
believe these data provide an exhaustive and unbiased view of dust properties
in spiral galaxies.Comment: 9 pg Latex file (using mn.sty) gzip'd tar'd file including 7 ps
figures and 3 tables. to appear in MNRA
An approach for the detection of point-sources in very high resolution microwave maps
This paper deals with the detection problem of extragalactic point-sources in
multi-frequency, microwave sky maps that will be obtainable in future cosmic
microwave background radiation (CMB) experiments with instruments capable of
very high spatial resolution. With spatial resolutions that can be of order of
0.1-1.0 arcsec or better, the extragalactic point-sources will appear isolated.
The same holds also for the compact structures due to the Sunyaev-Zeldovich
(SZ) effect (both thermal and kinetic). This situation is different from the
maps obtainable with instruments as WMAP or PLANCK where, because of the
smaller spatial resolution (approximately 5-30 arcmin), the point-sources and
the compact structures due to the SZ effect form a uniform noisy background
(the "confusion noise"). Hence, the point-source detection techniques developed
in the past are based on the assumption that all the emissions that contribute
to the microwave background can be modeled with homogeneous and isotropic
(often Gaussian) random fields and make use of the corresponding spatial
power-spectra. In the case of very high resolution observations such an
assumption cannot be adopted since it still holds only for the CMB. Here, we
propose an approach based on the assumption that the diffuse emissions that
contribute to the microwave background can be locally approximated by
two-dimensional low order polynomials. In particular, two sets of numerical
techniques are presented containing two different algorithms each. The
performance of the algorithms is tested with numerical experiments that mimic
the physical scenario expected for high Galactic latitude observations with the
Atacama Large Millimeter/Submillimeter Array (ALMA).Comment: Accepted for publication on "Astronomy & Astrophysics". arXiv admin
note: substantial text overlap with arXiv:1206.4536 Replaced version is the
accepted one and published in A&
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