The SIRTF wide-area infrared extragalactic survey (SWIRE) - exploring the dark side of galaxy evolution
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SWIRE infrared↗
Engineering topics
Franceschini, A.
Publications and source records attributed to Franceschini, A..
Small-scale fluctuations and angular correlations of the X-ray background in the HEAO 1 A-2 energy band - Constraints on clustering of X-ray sources
HEAO 1 A-2 all-sky survey data have been used to determine the amplitude of intensity fluctuations of the extragalactic 2-10 keV X-ray background (XRB) over an effective solid angle of 1.84 sq deg and their angular correlation function on angular scales of less than 3 deg. A good empirical fit to the data is obtained assuming that the integral counts in the A-2 band have a slope of 1.65 + 0.06 or - 0.07. Alternatively, the data may imply a significant clustering of extragalactic X-ray sources.
Martin-Mirones, J. M.↗
Constraints on large-scale clustering from the autocorrelation properties of the X-ray background
Expectations for the angular correlation function of intensity fluctuations of the extragalacitc 2-10 keV X-ray background are discussed in relation to the two-point spatial correlation functions, xi(r), of X-ray sources. A simple analytic formula for the amplitude of intensity correlations, Gamma(theta), holding in the low-redshift, small-separation approximation, is derived. The HEAO 1 A-2 upper limits on Gamma(theta) have been exploited to derive constraints on the local xi(r) functions of rich clusters of galaxies, of AGNs, and on the AGN-cluster cross-correlation, as well as on evolution of the correlation functions with cosmic time. X-ray data are found to be compatible with the Bahcall and Soneira estimates of xi(cluster-cluster) as well as with the results of recent studies of quasar clustering.
De Zotti, G.↗
On the relationship between optically selected and X-ray-selected active galactic nuclei
Available information on the optically selected active galactic nuclei (AGNs) (luminosity function, cosmological evolution, etc.), together with the knowledge of their X-ray to optical luminosity ratio, are used to predict the overall properties of X-ray-selected active galactic nuclei (number counts, evolution, luminosity and redshift distributions, etc.). The predicted properties are then compared with those observed. Similarly, predictions are carried out for the optical properties of the X-ray-selected AGN parent population. In the search for a possibility explanation for discrepancies, preliminary results are reported.
Franceschini, A.↗
On syntheses of the X-ray background with power-law sources
The conditions under which the combined emission from power-law sources can mimic the X-ray background (XRB) spectrum in the 3-50 keV range are considered in view of HEAO 1 A-2 experiment measurements, and it is confirmed that a good fit may be obtained. The required spectral properties of the component sources differ, however, from those observed for local active galactic nuclei. Constraints are deduced for both the low-luminosity extension and evolution of such local objects, and it is shown that any other class of sources contributing to the X-ray background must be characterized by an energy spectral index lower than about 0.4, which is the mean index of the XRB, and exhibit steeper spectra at higher energies.
De Zotti, G.↗
On syntheses of the X-ray background with power-law sources
The conditions under which the combined emission from power law sources can mimic the X-ray background (XRB) spectrum in the 3-50 keV range are considered in view of HEAO 1 A-2 experiment measurements, and it is confirmed that a good fit may be obtained. The required spectral properties of the component sources differ, however, from those observed for local active galactic nuclei. Constraints are deduced for both the low luminosity extension and evolution of such local objects, and it is shown that any other class of sources contributing to the X-ray background must be characterized by an energy spectral index lower than about 0.4, which is the mean index of the XRB, and exhibit sleeper spectra at higher energies.
Dezotti, G.↗