99 research outputs found
Implementation of PhotoZ under Astro-WISE - A photometric redshift code for large datasets
We describe the implementation of the PhotoZ code in the framework of the
Astro-WISE package and as part of the Photometric Classification Server of the
PanSTARRS pipeline. Both systems allow the automatic measurement of photometric
redshifts for the millions of objects being observed in the PanSTARRS project
or expected to be observed by future surveys like KIDS, DES or EUCLID.Comment: Accepted for publication in topical issue of Experimental Astronomy
on Astro-WISE information system, references update
How covariant is the galaxy luminosity function?
We investigate the error properties of certain galaxy luminosity function
(GLF) estimators. Using a cluster expansion of the density field, we show how,
for both volume and flux limited samples, the GLF estimates are covariant. The
covariance matrix can be decomposed into three pieces: a diagonal term arising
from Poisson noise; a sample variance term arising from large-scale structure
in the survey volume; an occupancy covariance term arising due to galaxies of
different luminosities inhabiting the same cluster. To evaluate the theory one
needs: the mass function and bias of clusters, and the conditional luminosity
function (CLF). We use a semi-analytic model (SAM) galaxy catalogue from the
Millennium run N-body simulation and the CLF of Yang et al. (2003) to explore
these effects. The GLF estimates from the SAM and the CLF qualitatively
reproduce results from the 2dFGRS. We also measure the luminosity dependence of
clustering in the SAM and find reasonable agreement with 2dFGRS results for
bright galaxies. However, for fainter galaxies, L<L*, the SAM overpredicts the
relative bias by ~10-20%. We use the SAM data to estimate the errors in the GLF
estimates for a volume limited survey of volume V~0.13 [Gpc/h]^3. We find that
different luminosity bins are highly correlated: for L<L* the correlation
coefficient is r>0.5. Our theory is in good agreement with these measurements.
These strong correlations can be attributed to sample variance. For a
flux-limited survey of similar volume, the estimates are only slightly less
correlated. We explore the importance of these effects for GLF model parameter
estimation. We show that neglecting to take into account the bin-to-bin
covariances can lead to significant systematic errors in best-fit parameters.Comment: 19 pages, 12 figures. Accepted for publication in MNRAS. Refs
updated; Fig 6 added; Figs 7 and 10 improve
Using the 1.6um Bump to Study Rest-frame NIR Selected Galaxies at Redshift 2
We explore the feasibility and limitations of using the 1.6um bump as a
photometric redshift indicator and selection technique and use it to study the
rest-frame H-band galaxy luminosity and stellar mass functions at redshift z~2.
We use publicly available Spitzer/IRAC images in the GOODS fields and find that
color selection in the IRAC bandpasses alone is comparable in completeness and
contamination to BzK selection. We find that the shape of the 1.6um bump is
robust, and photometric redshifts are not greatly affected by choice of model
parameters. Comparison with spectroscopic redshifts shows photometric redshifts
to be reliable. We create a rest-frame NIR selected catalog of galaxies at z~2
and construct a galaxy stellar mass function (SMF). Comparisons with other SMFs
at approximately the same redshift but determined using shorter wavelengths
show good agreement. This agreement suggests that selection at bluer
wavelengths does not miss a significant amount of stellar mass in passive
galaxies. Comparison with SMFs at other redshifts shows evidence for the
downsizing scenario of galaxy evolution. We conclude by pointing out the
potential for using the 1.6um technique to select high-redshift galaxies with
the JWST, whose lambda > 0.6 um coverage will not be well suited to selecting
galaxies using techniques that require imaging at shorter wavelengths.Comment: Accepted for publication in Ap
Galaxy Zoo: CANDELS barred discs and bar fractions
The formation of bars in disc galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in discs decreases from the local Universe to z ~ 1, and by z > 1 simulations predict that bar features in dynamically mature discs should be extremely rare. Here, we report the discovery of strong barred structures in massive disc galaxies at z ~ 1.5 in deep rest-frame optical images from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. From within a sample of 876 disc galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a subsample within the same region of the evolving galaxy luminosity function (brighter than L*), we find that the bar fraction across the redshift range 0.5 ≤ z ≤ 2 (fbar = 10.7+6.3 -3.5 per cent after correcting for incompleteness) does not significantly evolve.We discuss the implications of this discovery in the context of existing simulations and our current understanding of the way disc galaxies have evolved over the last 11 billion yearsPeer reviewedFinal Accepted Versio
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
A new method for classifying galaxy SEDs from multiwavelength photometry
We present a new method to classify the broad-band optical–near-infrared spectral energy distributions (SEDs) of galaxies using three shape parameters (super-colours) based on a principal component analysis of model SEDs. As well as providing a compact representation of the wide variety of SED shapes, the method allows for easy visualization of information loss and biases caused by the incomplete sampling of the rest-frame SED as a function of redshift. We apply the method to galaxies in the United Kingdom Infrared Telescope Infrared Deep Sky Survey Ultra Deep Survey with 0.9 11, declining steadily to 13 per cent at logM∗/M_ = 10. The properties and mass function of the poststarburst galaxies are consistent with a scenario in which gas-rich mergers contribute to the growth of the low- and intermediate-mass range of the red sequence
Host galaxy identification for supernova surveys
Host galaxy identification is a crucial step for modern supernova (SN) surveys such as the Dark Energy Survey (DES) and the Large Synoptic Survey Telescope (LSST), which will discover SNe by the thousands. Spectroscopic resources are limited, so in the absence of real-time SN spectra these surveys must rely on host galaxy spectra to obtain accurate redshifts for the Hubble diagram and to improve photometric classification of SNe. In addition, SN luminosities are known to correlate with host-galaxy properties. Therefore, reliable identification of host galaxies is essential for cosmology and SN science. We simulate SN events and their locations within their host galaxies to develop and test methods for matching SNe to their hosts. We use both real and simulated galaxy catalog data from the Advanced Camera for Surveys General Catalog and MICECATv2.0, respectively. We also incorporate "hostless" SNe residing in undetected faint hosts into our analysis, with an assumed hostless rate of 5%. Our fully automated algorithm is run on catalog data and matches SNe to their hosts with 91% accuracy. We find that including a machine learning component, run after the initial matching algorithm, improves the accuracy (purity) of the matching to 97% with a 2% cost in efficiency (true positive rate). Although the exact results are dependent on the details of the survey and the galaxy catalogs used, the method of identifying host galaxies we outline here can be applied to any transient survey
Roy Olivier, L'Afghanistan, Islam et modernité politique
Ilbert Robert. Roy Olivier, L'Afghanistan, Islam et modernité politique. In: Vingtième Siècle, revue d'histoire, n°9, janvier-mars 1986. pp. 132-133
Gresh Alain, Vidal Dominique, Les Cent Portes du Proche-Orient Soliman Lotfallah, Pour une histoire profane de la Palestine Picaudou Nadine, Le mouvement national palestinien. Genèse et structures Picaudou Nadine, La déchirure libanaise Auli Mohammed-Reza, Diplomatie islamique. Stratégie internationale du khomeynisme Burgat François, L'islamisme au Maghreb. La voix du Sud Berque Jacques, Mémoires des deux rives
Ilbert Robert. Gresh Alain, Vidal Dominique, Les Cent Portes du Proche-Orient Soliman Lotfallah, Pour une histoire profane de la Palestine Picaudou Nadine, Le mouvement national palestinien. Genèse et structures Picaudou Nadine, La déchirure libanaise Auli Mohammed-Reza, Diplomatie islamique. Stratégie internationale du khomeynisme Burgat François, L'islamisme au Maghreb. La voix du Sud Berque Jacques, Mémoires des deux rives. In: Vingtième Siècle, revue d'histoire, n°26, avril-juin 1990. Le football, sport du siècle. pp. 141-145
De Beyrouth à Alger : la fin d'un ordre urbain
From Beirut to Alger, the end of an urban order, Robert Ilbert.
Like Beirut, the inmost extreme example, the port-cities of the Ottoman Empire have gone little by little from the stage of dynamism and brilliance to that of dismantlement, when not chaos... Understanding such a process implies an analysis of the very specifie urban order which characterized them at the time of their apogee : they were cosmopolitan cities functioning almost like genuine city-states, organized around the power of their elites, the social and cultural weight of their communitarian System and of the relative autonomy of their municipal agencies. But the logic of the nation-states gained increasingly and broke their always precarious balance, pushing them into an apparently unending crisis.Ilbert Robert. De Beyrouth à Alger : la fin d'un ordre urbain. In: Vingtième Siècle, revue d'histoire, n°32, octobre-décembre 1991. La Méditerranée. Affrontements et dialogues. pp. 15-24
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