23 research outputs found
Probabilistic positional association of catalogs of astrophysical sources: the Aspects code
We describe a probabilistic method of cross-identifying astrophysical sources
in two catalogs from their positions and positional uncertainties. The
probability that an object is associated with a source from the other catalog,
or that it has no counterpart, is derived under two exclusive assumptions:
first, the classical case of several-to-one associations, and then the more
realistic but more difficult problem of one-to-one associations.
In either case, the likelihood of observing the objects in the two catalogs
at their effective positions is computed and a maximum likelihood estimator of
the fraction of sources with a counterpart -- a quantity needed to compute the
probabilities of association -- is built. When the positional uncertainty in
one or both catalogs is unknown, this method may be used to estimate its
typical value and even to study its dependence on the size of objects. It may
also be applied when the true centers of a source and of its counterpart at
another wavelength do not coincide.
To compute the likelihood and association probabilities under the different
assumptions, we developed a Fortran 95 code called "Aspects" ([asp{\epsilon}],
"ASsociation PositionnellE/ProbabilistE de CaTalogues de Sources" in French);
its source files are made freely available. To test Aspects, all-sky mock
catalogs containing up to 10^5 objects were created, forcing either
several-to-one or one-to-one associations. The analysis of these simulations
confirms that, in both cases, the assumption with the highest likelihood is the
right one and that estimators of unknown parameters built for the appropriate
association model are reliable.Comment: One typo corrected and links added. One-column format (A&A official
version is in two-column format). 20 pages, 5 figures. Version 2 of code
Aspects available at http://www2.iap.fr/users/fioc/Aspects/ . Detailed
documentation and complements at arXiv:1404.4224. Numerical Recipes routines
not needed anymor
P\'egase.3: A code for modeling the UV-to-IR/submm spectral and chemical evolution of galaxies with dust
A code computing consistently the evolution of stars, gas and dust, as well
as the energy they radiate, is required to derive reliably the history of
galaxies by fitting synthetic SEDs to multiwavelength observations. The new
code P\'egase.3 described in this paper extends to the far-IR/submm the
UV-to-near-IR modeling provided by previous versions of P\'egase. It first
computes the properties of single stellar populations at various metallicities.
It then follows the evolution of the stellar light of a galaxy and the
abundances of the main metals in the ISM, assuming some scenario of mass
assembly and star formation. It simultaneously calculates the masses of the
various grain families, the optical depth of the galaxy and the attenuation of
the SED through the diffuse ISM in spiral and spheroidal galaxies, using grids
of radiative transfer precomputed with Monte Carlo simulations taking
scattering into account. The code determines the mean radiation field and the
temperature probability distribution of stochastically heated individual
grains. It then sums up their spectra to yield the overall emission by dust in
the diffuse ISM. The nebular emission of the galaxy is also computed, and a
simple modeling of the effects of dust on the SED of star-forming regions is
implemented. The main outputs are UV-to-submm SEDs of galaxies from their birth
up to 20 Gyr, colors, masses of galactic components, ISM abundances of metallic
elements and dust species, supernova rates. The temperatures and spectra of
individual grains are also available. The paper discusses several of these
outputs for a scenario representative of Milky Way-like spirals. P\'egase.3 is
fully documented and its Fortran 95 source files are public. The code should be
especially useful for cosmological simulations and to interpret future mid- and
far-IR data, whether obtained by JWST, LSST, Euclid or e-ELT.Comment: 15 pages. In press in A&A. Source files of the code available at
http://www.iap.fr/users/fioc/Pegase/Pegase.3/ (and
http://www.iap.fr/pegase/); documentation at arXiv:1902.0219