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Valerie de Lapparent

Publications and source records attributed to Valerie de Lapparent.

11 recordsLinked to original sources
arXiv2007

A 12um ISOCAM Survey of the ESO-Sculptor Field: Data Reduction and Analysis

We present a detailed reduction of a mid-infrared 12um (LW10 filter) ISOCAM open time observation performed on the ESO-Sculptor Survey field (Arnouts et al. 1997). A complete catalogue of 142 sources (120 galaxies and 22 stars), detected with high significance (equivalent to 5sigma), is presented above an integrated flux density of 0.24mJy. Star/galaxy separation is performed by a detailed study of colour-colour diagrams. The catalogue is complete to 1mJy and below this flux density the incompleteness is corrected using two independent methods. The first method uses stars and the second uses optical counterparts of the ISOCAM galaxies; these methods yield consistent results. We also apply an empirical flux density calibration using stars in the field. For each star, the 12um flux density is derived by fitting optical colours from a multi-band chi^2 to stellar templates (BaSel-2.0) and using empirical optical-IR colour-colour relations. This article is a companion analysis to Rocca-Volmerange 2007 et al. where the 12um faint galaxy counts are presented and analysed by galaxy type with the evolutionary code PEGASE.3.

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arXiv2004

The ESO-Sculptor Survey: Evolution of late-type galaxies at redshifts 0.1-0.5

[ABRIDGED] Using the Gaussian+Schechter composite luminosity functions measured from the ESO-Sculptor Survey (de Lapparent et al. 2003), we obtain evidence for evolution in the late spectral class containing late-type Spiral (Sc+Sd) and dwarf Irregular (dI) galaxies. This evolution is detected as an increase of the Sc+Sd+dI galaxy density which can be modeled as either n(z)~1+3(z-0.15) or n(z) ~ (1+z)^2 using the currently favored cosmological parameters Omega_m=0.3 and Omega_Lambda=0.7, with an uncertainty in both evolution rates of order of unity. For Omega_m=1.0 and Omega_Lambda=0.0, the linear and power-law evolution rates are 4 and 2.5 resp. Both models yield a good match to the ESS BVRc redshift distributions to 21-22 mag and to the number-counts to 23-23.5 mag, which probe the galaxy distribution to redshifts z~0.5 and z~1.0 resp. This analysis illustrates how Gaussian+Schechter composite luminosity functions provide more robust constraints on the evolution rate than pure Schechter functions. The detected density evolution indicates that mergers could play a significant role in the evolution of late-type Spiral and dwarf Irregular galaxies. However, the ESO-Sculptor density increase with redshift could also be caused by a ~1 mag brightening of the Sc+Sd+dI galaxies at z~0.5 and a ~1.5-2.0 mag brightening at z~1, which is compatible with the expected passive brightening of Sc galaxies at these redshifts. Distinguishing between luminosity and density evolution is a major difficulty as these produce the same effect on the redshift and magnitude distributions. The detected evolution rate of the ESO-Sculptor Sc+Sd+dI galaxies is nevertheless among the range of measured values from the other existing analyses, whether they provide evidence for density or luminosity evolution.

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arXiv2003

Critical analysis of the luminosity functions per galaxy type measured from redshift surveys

[ABRIDGED] I perform a detailed comparison of the shape of the optical luminosity functions as a function of galaxy class and filter, which have been obtained from redshift surveys with an effective depth ranging from z~0.01 to z~0.6. This analysis is based on the M* and alpha Schechter parameters. I provide complete tables of all the existing measurements, converted into the UBVRcIc Johnson-Cousins system wherever necessary. By using as reference the intrinsic luminosity functions per morphological type measured from local galaxy concentrations (Jerjen et al 1997), I establish that the variations in the luminosity functions from survey to survey and among the galaxy classes are related to the criteria for galaxy classification used in the surveys, as these determine the amount of mixing of the morphological types within a given class. When using a spectral classification with inaccurate spectrophotometric calibrations, the luminosity functions are biased by type contamination with a smooth variation from type to type poorly related to the intrinsic luminosity functions per morphological type. In the case of multi-fiber spectroscopy, galaxy classification based on rest-frame colors might then provide better estimates of the intrinsic luminosity functions. All the existing surveys fail to measure the Gaussian luminosity functions for Spiral galaxies. Most surveys based on visual morphological classification also have their E/S0 luminosity functions contaminated at the faint end, except for analyses based on either multi-slit spectroscopy or medium-filter spectrophotometry combined with CCD photometry. These contamination effects are presumably due to dwarf galaxies. Measuring reliable intrinsic luminosity functions will thus require a more coherent approach in separating the giant and dwarf galaxy types.

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arXiv2003

The ESO-Sculptor Survey: Luminosity functions of galaxies per spectral type at redshifts 0.1-0.5

[ABRIDGED] We present the first statistical analysis of the complete ESO-Sculptor redshift survey (ESS). The flux-calibrated sample of 617 galaxy spectra with R_c<20.5 is separated into 3 spectral classes (early, intermediate, and late). We report in detail on the spectral classification, the polynomial K-corrections, and all sources of corresponding random and systematic errors. The derived luminosity functions (LF) in the Johnson-Cousins B and Rc bands are in agreement with the results from the comparable CNOC2 survey (Lin et al. 1999), whereas the ESS provides the first estimates of LFs per spectral type in the Johnson V band. A renewed interpretation of the galaxy LFs from a redshift survey are obtained by fitting the ESS LFs with composite functions based on the local LFs per morphological type (Sandage, Binggeli & Tammann 1985; Jerjen & Tammann 1997). As good or better fits than with pure Schechter functions are obtained using: for the early-type LF, a two-wing Gaussian; for the intermediate-type LF, the sum of a Gaussian modeling the Spiral galaxies and a steep Schechter function (alpha=-1.5) representing the dwarf elliptical galaxies; for the late-type LF, a similar composite function with a flat or weaker slope (-0.8 0.1 which separates the giant and dwarf galaxy populations.

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arXiv2002

Classification and redshift estimation by principal component analysis

We show that the first 10 eigencomponents of the Karhunen-Loève expansion or Principal Component Analysis (PCA) provide a robust classification scheme for the identification of stars, galaxies and quasi-stellar objects from multi-band photometry. To quantify the efficiency of the method, realistic simulations are performed which match the planned Large Zenith Telescope survey. This survey is expected to provide spectral energy distributions with a resolution $R\simeq40$ for $\sim10^6$ galaxies to $R\le23$ ($z\sim 1$), $\sim 10^4$ QSOs, and $\sim 10^5$ stars. We calculate that for a median signal-to-noise ratio of 6, 98% of stars, 100% of galaxies and 93% of QSOs are correctly classified. These values increase to 100% of stars, 100% of galaxies and 100% of QSOs at a median signal-to-noise ratio of 10. The 10-component PCA also allows measurement of redshifts with an accuracy of $σ_\mathrm{Res.}\la0.05$ for galaxies with $z\la0.7$, and to $σ_\mathrm{Res.}\la0.2$ for QSOs with $z\ga2$, at a median signal-to-noise ratio of 6. At a median signal-to-noise ratio 20, $σ_\mathrm{Res.}\la0.02$ for galaxies with $z\la1$ and for QSOs with $z\ga2.5$ (note that for a median $S/N$ ratio of 20, the bluest/reddest objects will have a signal-to-noise ratio of $\la 2$ in their reddest/bluest filters). This redshift accuracy is inherent to the $R\simeq40$ resolution provided by the set of medium-band filters used by the Large Zenith Telescope survey. It provides an accuracy improvement of nearly an order of magnitude over the photometric redshifts obtained from broad-band $BVRI$ photometry.

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arXiv2001

The different Clustering of red and blue galaxies: a robust signal from w(theta)

A sample of ~20,000 galaxies covering 0.76 deg2 were observed with the CFHT-UH8K up to V<23.5 and I<22.5. The angular correlation analysis of the red selected sample (V-I>1.4) shows a stronger amplitude than the blue selected sample at all cutoff magnitudes. This effect could be explained either by luminosity selection effects or by a true color segregation in which red objects are preferably found in denser regions. If the latter is true, and assuming that red galaxies are dominated by an older population of stars, this measurement supports the idea that galaxies evolve faster in the harsh environment of dense clusters than in the field, at fiducial redshifts of z~0.5.

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arXiv2001

The Large Zenith Telescope Survey: a deep survey using a 6-m liquid mirror telescope

The Large Zenith Telescope Survey whose construction is almost completed (first light expected in spring 2002) near Vancouver (Canada) is designed to observed a total strip of ~17' x 120 deg in 40 medium-band filters spanning 4000-10000 A. It will gather the spectrophotometric energy distributions of ca. \~10^6 galaxies to redshifts z~1, with redshift accuracy sigma_z=0.01 at s/n=10, sigma_z=0.04 at s/n=3, ca. 10^5 stars, and a large sample of QSOs, variable stars, and transient objects of the solar system. The survey is optimized for studying of the evolution of both the luminosity function and the clustering of galaxies to a redshift z~1. It will also provide a complete and homogeneous sample of stars at various galactic latitudes useful for studying galactic structure, and it will be a good instrument for the monitoring of variable objects.

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arXiv2000

The 2-point angular correlation function of 20,000 galaxies to V<23.5 and I<22

The UH8K wide field camera of the CFHT was used to image 0.68 deg^2 of sky. From these images, ~20,000 galaxies were detected to completeness magnitudes V<23.5 and I<22.5. The angular correlation function of these galaxies is well represented by the parameterization omega(theta) = A_W*theta^-delta. The slope delta=-0.8 shows no significant variation over the range of magnitude. The amplitude A_W decreases with increasing magnitude in a way that is most compatible with a Lambda-CDM model (Omega_0 = 0.2, Lambda=0.8) with a hierarchical clustering evolution parameter epsilon>0. We infer a best-fit spatial correlation length of r_00= 5.85+/-0.5 h^-1 Mpc at z=0. The peak redshift of the survey (I<22.5) is estimated to be z_peak~0.58, using the blue-evolving luminosity function from the CFRS and the flat Lambda cosmology, and r_0(z_peak)=3.5+/-0.5 h^-1 Mpc. We also detect a significant difference in clustering amplitude for the red and blue galaxies, quantitatively measured by correlation lengths of r_00=5.3+/-0.5 h^-1 Mpc and r_00=1.9+/-0.9 h^-1 Mpc respectively, at z=0.

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arXiv1999

The Large Zenith Telescope: Redshifts and Physical Parameters of Faint Objects from a Principal Component Analysis

The future Large Zenith Telescope Survey will provide a catalog of spectrophotometric energy distributions (40 filters) of ~10^6 objects. In this paper, we shows that the principal component analysis is efficient to separate stars, galaxies and QSOs. Realistic simulations are performed to assess quantitatively the efficiency of the method. Redshifts can be evaluated to sigmaz~0.02 for z<0.5 and sigmaz~0.05 for 0.5<z<1.5.

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arXiv1997

The ESO-Sculptor Survey: Spectral classification of galaxies with z < 0.5

Using the ESO-Sculptor galaxy redshift survey data (ESS), we have extensively tested the Principal Components Analysis (PCA) method to perform the spectral classification of galaxies with $z \la$ 0.5. This method allows us to classify all galaxies in an ordered and continuous spectral sequence, which is strongly correlated with the morphological type. The PCA allows to quantify the systematic physical properties of the galaxies in the sample, like the different stellar contributions to the observed light as well as the stellar formation history. We also examine the influence of the emission lines, and the signal-to-noise ratio of the data. This analysis shows that the emission lines play a significant role in the spectral classification, by tracing the activity and abnormal spectral features of the observed sample. The PCA also provides a powerful tool to filter the noise which is carried by the ESS spectra. By comparison of the ESS PCA spectral sequence with that for a selected sample of Kennicutt galaxies (Kennicutt 1992a), we find that the ESS sample contains 26% of E/S0, 71% of Sabc and 3% of Sm/Irr. The type fractions for the ESS show no significant changes in the redshift interval $z \sim 0.1-0.5$, and are comparable to those found in other galaxy surveys at intermediate redshift. The PCA can be used independently from any set of synthetic templates, providing a completely objective and unsupervised method to classify spectra. We compare the classification of the ESS sample given by the PCA, with a $χ^2$ test between the ESS sample and galaxy templates from Kennicutt (Kennicutt 1992a), and obtain results in good agreement. The PCA results are also in agreement with the visual morphological classification carried out for the 35 brightest galaxies in the survey.

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