885 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
Strategies for Imaging Faint Extended Sources in the Near-Infrared
Quantitative information about variations in the background at J and K' are
presented and used to develop guidelines for the acquisition and reduction of
ground-based images of faint extended sources in the near-infrared, especially
those which occupy a significant fraction of the field of view of a detector or
which are located in areas crowded with foreground or background sources.
Findings are based primarily upon data acquired over three photometric nights
with the 3.6x3.6 arcmin CFHT-IR array on the Canada-France-Hawaii Telescope
atop Mauna Kea. Although some results are specific to CFHT, overall conclusions
should be useful in guiding observing and reduction strategies of extended
objects elsewhere.Comment: Accepted for publication in PASP July 2004. 29 pages, including 2
tables and 9 figure
The 12 μm ISO-ESO-Sculptor and 24 μm Spitzer faint counts reveal a population of ULIRGs as dusty massive ellipticals: Evolution by types and cosmic star formation
Context. Multi-wavelength galaxy number counts provide clues to the nature of galaxy evolution. The interpretation per galaxy type of
the mid-IR faint counts obtained with ISO and Spitzer, consistent with the analysis of deep UV-optical-near IR galaxy counts, provide
new constraints on the dust and stellar emission. Discovering the nature of new populations, such as high redshift ultra-luminous
(≥10^(12) L_⊙) infrared galaxies (ULIRGs), is also crucial for understanding galaxy evolution at high redshifts.
Aims. We first present the faint galaxy counts at 12 μm from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) published in a
companion article (Seymour et al. 2007a, A&A, 475, 791). They go down to 0.31 mJy after corrections for incompleteness. We verify
the consistency with the existing ISO number counts at 15 μm. Then we analyse the 12 μm (ISO-ESS) and the 24 μm (Spitzer) faint
counts, to constrain the nature of ULIRGs, the cosmic star formation history and time scales for mass buildup.
Methods. We show that the “normal” scenarios in our evolutionary code PÉGASE, which had previously fitted the deep UV-opticalnear
IR counts, are unsuccessful at 12 μm and 24 μm. We thus propose a new ULIRG scenario adjusted to the observed cumulative
and differential 12 μm and 24 μm counts and based on observed 12 μm and 25 μm IRAS luminosity functions and evolutionary
optical/mid-IR colours from PÉGASE.
Results. We succeed in simultaneously modelling the typical excess observed at 12 μm, 15 μm (ISO), and 24 μm (Spitzer) in the
cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty galaxies
evolving as ellipticals, and interpreted as distant ULIRGs. These objects present similarities with the population of radio-galaxy hosts
at high redshift. No number density evolution is included in our models even if minor starbursts due to galaxy interactions remain
compatible with our results.
Conclusions. Higher spectral and spatial resolution in the mid-IR, together with submillimeter observations using the future Herschel
observatory, will be useful to confirm these results
The 12 μm ISO-ESO-Sculptor and 24 μm Spitzer faint counts reveal a population of ULIRGs as dusty massive ellipticals: Evolution by types and cosmic star formation
Context. Multi-wavelength galaxy number counts provide clues to the nature of galaxy evolution. The interpretation per galaxy type of
the mid-IR faint counts obtained with ISO and Spitzer, consistent with the analysis of deep UV-optical-near IR galaxy counts, provide
new constraints on the dust and stellar emission. Discovering the nature of new populations, such as high redshift ultra-luminous
(≥10^(12) L_⊙) infrared galaxies (ULIRGs), is also crucial for understanding galaxy evolution at high redshifts.
Aims. We first present the faint galaxy counts at 12 μm from the catalogue of the ISO-ESO-Sculptor Survey (ISO-ESS) published in a
companion article (Seymour et al. 2007a, A&A, 475, 791). They go down to 0.31 mJy after corrections for incompleteness. We verify
the consistency with the existing ISO number counts at 15 μm. Then we analyse the 12 μm (ISO-ESS) and the 24 μm (Spitzer) faint
counts, to constrain the nature of ULIRGs, the cosmic star formation history and time scales for mass buildup.
Methods. We show that the “normal” scenarios in our evolutionary code PÉGASE, which had previously fitted the deep UV-opticalnear
IR counts, are unsuccessful at 12 μm and 24 μm. We thus propose a new ULIRG scenario adjusted to the observed cumulative
and differential 12 μm and 24 μm counts and based on observed 12 μm and 25 μm IRAS luminosity functions and evolutionary
optical/mid-IR colours from PÉGASE.
Results. We succeed in simultaneously modelling the typical excess observed at 12 μm, 15 μm (ISO), and 24 μm (Spitzer) in the
cumulative and differential counts by only changing 9% of normal galaxies (1/3 of the ellipticals) into ultra-bright dusty galaxies
evolving as ellipticals, and interpreted as distant ULIRGs. These objects present similarities with the population of radio-galaxy hosts
at high redshift. No number density evolution is included in our models even if minor starbursts due to galaxy interactions remain
compatible with our results.
Conclusions. Higher spectral and spatial resolution in the mid-IR, together with submillimeter observations using the future Herschel
observatory, will be useful to confirm these results
SpecPro: An Interactive IDL Program for Viewing and Analyzing Astronomical Spectra
We present an interactive IDL program for viewing and analyzing astronomical
spectra in the context of modern imaging surveys. SpecPro's interactive design
lets the user simultaneously view spectroscopic, photometric, and imaging data,
allowing for rapid object classification and redshift determination. The
spectroscopic redshift can be determined with automated cross-correlation
against a variety of spectral templates or by overlaying common emission and
absorption features on the 1-D and 2-D spectra. Stamp images as well as the
spectral energy distribution (SED) of a source can be displayed with the
interface, with the positions of prominent photometric features indicated on
the SED plot. Results can be saved to file from within the interface. In this
paper we discuss key program features and provide an overview of the required
data formats.Comment: Accepted for publication in the Publications of the Astronomical
Society of the Pacific (PASP) journal. Website: specpro.caltech.ed
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