Context. This paper is the fourth of a series evaluating the ASpiX cosmological method, based on X-ray diagrams, which are constructed from simple cluster observable quantities, namely: count rate ...(CR), hardness ratio (HR), core radius (rc), and redshift. Aims. Following extensive tests on analytical toy catalogues (Paper III), we present the results of a more realistic study over a 711 deg2 template-based maps derived from a cosmological simulation. Methods. Dark matter haloes from the Aardvark simulation have been ascribed luminosities, temperatures, and core radii, using local scaling relations and assuming self-similar evolution. The predicted X-ray sky-maps were converted into XMM event lists, using a detailed instrumental simulator. The XXL pipeline runs on the resulting sky images, produces an observed cluster catalogue over which the tests have been performed. This allowed us to investigate the relative power of various combinations of the CR, HR, rc, and redshift information. Two fitting methods were used: a traditional Markov chain Monte Carlo (MCMC) approach and a simple minimisation procedure (Amoeba) whose mean uncertainties are a posteriori evaluated by means of synthetic catalogues. The results were analysed and compared to the predictions from the Fisher analysis (FA). Results. For this particular catalogue realisation, assuming that the scaling relations are perfectly known, the CR-HR combination gives σ8 and Ωm at the 10% level, while CR-HR-rc-z improves this to ≤3%. Adding a second HR improves the results from the CR-HR1-rc combination, but to a lesser extent than when adding the redshift information. When all coefficients of the mass-temperature relation (M-T, including scatter) are also fitted, the cosmological parameters are constrained to within 5–10% and larger for the M-T coefficients (up to a factor of two for the scatter). The errors returned by the MCMC, those by Amoeba and the FA predictions are in most cases in excellent agreement and always within a factor of two. We also study the impact of the scatter of the mass-size relation (M-Rc) on the number of detected clusters: for the cluster typical sizes usually assumed, the larger the scatter, the lower the number of detected objects. Conclusions. The present study confirms and extends the trends outlined in our previous analyses, namely the power of X-ray observable diagrams to successfully and easily fit at the same time, the cosmological parameters, cluster physics, and the survey selection, by involving all detected clusters. The accuracy levels quoted should not be considered as definitive. A number of simplifying hypotheses were made for the testing purpose, but this should affect any method in the same way. The next publication will consider in greater detail the impact of cluster shapes (selection and measurements) and of cluster physics on the final error budget by means of hydrodynamical simulations.
Aims. A well characterised detection pipeline is an important ingredient for X-ray cluster surveys. Methods. We present the final development of the XXL Survey pipeline. The pipeline optimally uses ...X-ray information by combining many overlapping observations of a source when possible, both for its detection and its characterisation. It can robustly detect and characterise several types of X-ray sources: AGNs (point-like), galaxy clusters (extended), galaxy clusters contaminated by a central AGN, and pairs of AGNs close on the sky. We perform a thorough suite of validation tests via realistic simulations of XMM-Newton images and we introduce new selection criteria for various types of sources that will be detected by the survey. Results. We find that the use of overlapping observations allows new clusters to be securely identified that would be missed or less securely identified by using only one observation at a time. We also find that, with the new pipeline we can robustly identify clusters with a central AGN that would otherwise have been missed, and we can flag pairs of AGNs close on the sky that might have been mistaken for a cluster.
Context. Despite compelling theoretical arguments, the use of clusters as cosmological probes is, in practice, frequently questioned because of the many uncertainties surrounding cluster-mass ...estimates. Aims. Our aim is to develop a fully self-consistent cosmological approach of X-ray cluster surveys, exclusively based on observable quantities rather than masses. This procedure is justified given the possibility to directly derive the cluster properties via ab initio modelling, either analytically or by using hydrodynamical simulations. In this third paper, we evaluate the method on cluster toy-catalogues. Methods. We model the population of detected clusters in the count-rate – hardness-ratio – angular size – redshift space and compare the corresponding four-dimensional diagram with theoretical predictions. The best cosmology+physics parameter configuration is determined using a simple minimisation procedure; errors on the parameters are estimated by averaging the results from ten independent survey realisations. The method allows a simultaneous fit of the cosmological parameters of the cluster evolutionary physics and of the selection effects. Results. When using information from the X-ray survey alone plus redshifts, this approach is shown to be as accurate as the modelling of the mass function for the cosmological parameters and to perform better for the cluster physics, for a similar level of assumptions on the scaling relations. It enables the identification of degenerate combinations of parameter values. Conclusions. Given the considerably shorter computer times involved for running the minimisation procedure in the observed parameter space, this method appears to clearly outperform traditional mass-based approaches when X-ray survey data alone are available.
Context.
Despite compelling theoretical arguments, the use of clusters as cosmological probes is, in practice, frequently questioned because of the many uncertainties surrounding cluster-mass ...estimates.
Aims.
Our aim is to develop a fully self-consistent cosmological approach of X-ray cluster surveys, exclusively based on observable quantities rather than masses. This procedure is justified given the possibility to directly derive the cluster properties via ab initio modelling, either analytically or by using hydrodynamical simulations. In this third paper, we evaluate the method on cluster toy-catalogues.
Methods.
We model the population of detected clusters in the count-rate – hardness-ratio – angular size – redshift space and compare the corresponding four-dimensional diagram with theoretical predictions. The best cosmology+physics parameter configuration is determined using a simple minimisation procedure; errors on the parameters are estimated by averaging the results from ten independent survey realisations. The method allows a simultaneous fit of the cosmological parameters of the cluster evolutionary physics and of the selection effects.
Results.
When using information from the X-ray survey alone plus redshifts, this approach is shown to be as accurate as the modelling of the mass function for the cosmological parameters and to perform better for the cluster physics, for a similar level of assumptions on the scaling relations. It enables the identification of degenerate combinations of parameter values.
Conclusions.
Given the considerably shorter computer times involved for running the minimisation procedure in the observed parameter space, this method appears to clearly outperform traditional mass-based approaches when X-ray survey data alone are available.
The XXL Survey Faccioli, L.; Pacaud, F.; Sauvageot, J.-L. ...
Astronomy and astrophysics (Berlin),
12/2018, Letnik:
620
Journal Article
Recenzirano
Odprti dostop
Aims.
A well characterised detection pipeline is an important ingredient for X-ray cluster surveys.
Methods.
We present the final development of the XXL Survey pipeline. The pipeline optimally uses ...X-ray information by combining many overlapping observations of a source when possible, both for its detection and its characterisation. It can robustly detect and characterise several types of X-ray sources: AGNs (point-like), galaxy clusters (extended), galaxy clusters contaminated by a central AGN, and pairs of AGNs close on the sky. We perform a thorough suite of validation tests via realistic simulations of
XMM-Newton
images and we introduce new selection criteria for various types of sources that will be detected by the survey.
Results.
We find that the use of overlapping observations allows new clusters to be securely identified that would be missed or less securely identified by using only one observation at a time. We also find that, with the new pipeline we can robustly identify clusters with a central AGN that would otherwise have been missed, and we can flag pairs of AGNs close on the sky that might have been mistaken for a cluster.
In the Valotti et al. (2018) paper, Figs. 2, 3, and 10 were published at low resolution, resulting in images that are not easy to read. We provide higher-quality figures here in the downloadable pdf.
Context.
This paper is the fourth of a series evaluating the ASpiX cosmological method, based on X-ray diagrams, which are constructed from simple cluster observable quantities, namely: count rate ...(CR), hardness ratio (HR), core radius (
r
c
), and redshift.
Aims.
Following extensive tests on analytical toy catalogues (Paper III), we present the results of a more realistic study over a 711 deg
2
template-based maps derived from a cosmological simulation.
Methods.
Dark matter haloes from the Aardvark simulation have been ascribed luminosities, temperatures, and core radii, using local scaling relations and assuming self-similar evolution. The predicted X-ray sky-maps were converted into XMM event lists, using a detailed instrumental simulator. The XXL pipeline runs on the resulting sky images, produces an observed cluster catalogue over which the tests have been performed. This allowed us to investigate the relative power of various combinations of the CR, HR,
r
c
, and redshift information. Two fitting methods were used: a traditional Markov chain Monte Carlo (MCMC) approach and a simple minimisation procedure (Amoeba) whose mean uncertainties are a posteriori evaluated by means of synthetic catalogues. The results were analysed and compared to the predictions from the Fisher analysis (FA).
Results.
For this particular catalogue realisation, assuming that the scaling relations are perfectly known, the CR-HR combination gives
σ
8
and
Ω
m
at the 10% level, while CR-HR-
r
c
-z improves this to ≤3%. Adding a second HR improves the results from the CR-HR
1
-
r
c
combination, but to a lesser extent than when adding the redshift information. When all coefficients of the mass-temperature relation (M-T, including scatter) are also fitted, the cosmological parameters are constrained to within 5–10% and larger for the M-T coefficients (up to a factor of two for the scatter). The errors returned by the MCMC, those by Amoeba and the FA predictions are in most cases in excellent agreement and always within a factor of two. We also study the impact of the scatter of the mass-size relation (M-Rc) on the number of detected clusters: for the cluster typical sizes usually assumed, the larger the scatter, the lower the number of detected objects.
Conclusions.
The present study confirms and extends the trends outlined in our previous analyses, namely the power of X-ray observable diagrams to successfully and easily fit at the same time, the cosmological parameters, cluster physics, and the survey selection, by involving all detected clusters. The accuracy levels quoted should not be considered as definitive. A number of simplifying hypotheses were made for the testing purpose, but this should affect any method in the same way. The next publication will consider in greater detail the impact of cluster shapes (selection and measurements) and of cluster physics on the final error budget by means of hydrodynamical simulations.
PDF
