E. Rollinde

Pierre and Marie Curie University - Paris 6, Lutetia Parisorum, Île-de-France, France

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Publications (39)68.71 Total impact

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    ABSTRACT: We use, for the first time, the Detrend Fluctuation Analysis (DFA) to study the correlation properties of the transmitted flux fluctuations, in the Lyman-$\alpha$ (Ly$\alpha$) Forest along the lines of sight (LOS) to QSOs, at different space scales. We consider in our analysis the transmitted flux in the intergalactic medium over the redshift range 2 $\leq$ z $\leq$ 4.5 from a sample of 45 high-quality medium resolution (R $\sim$ 4300) quasar spectra obtained with Echelle Spectrograph and Imager (ESI) mounted on the Keck II 10-m telescope, and from a sample of 19 high-quality high resolution (R $\sim$ 50000) quasar spectra obtained with Ultra-Violet and Visible Echelle Spectrograh (UVES) mounted on the ESO KUEYEN 8.2 m telescope. The result of the DFA method applied to both datasets, shows that there exists a difference in the correlation properties between the short and long-range regimes: the slopes of the transmitted flux fluctuation function are different on small and large scales. The scaling exponents, $\alpha_{1}$ = 1.635$\pm$ 0.115 and $\alpha_{2}$ = 0.758$\pm$ 0.085 for the ESI/Keck sample and $\alpha_{1}$ = 1.763 $\pm 0.128$ and $\alpha_{2}$ = 0.798 $\pm 0.084$ for the UVES/VLT sample for the short and long range regime respectively. The transition between the two regims is observed at about $\sim 1.4 h^{-1} Mpc$ (comoving). The fact that $\alpha_{1}$ is always larger than $\alpha_{2}$ for each spectrum supports the common view that the Universe is smoother on large scales than on small scales. The non detection of considerable variations in the scaling exponents from LOS to LOS confirms that anisotropies cannot be ubiquitous, at least on these scales.
    10/2013;
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    ABSTRACT: The EAGLE and EVE Phase A studies for instruments for the European Extremely Large Telescope (E-ELT) originated from related top-level scientific questions, but employed different (yet complementary) methods to deliver the required observations. We re-examine the motivations for a multi-object spectrograph (MOS) on the E-ELT and present a unified set of requirements for a versatile instrument. Such a MOS would exploit the excellent spatial resolution in the near-infrared envisaged for EAGLE, combined with aspects of the spectral coverage and large multiplex of EVE. We briefly discuss the top-level systems which could satisfy these requirements in a single instrument at one of the Nasmyth foci of the E-ELT.
    07/2012;
  • apjs. 08/2011; 195:26.
  • apjs. 08/2011; 195:26.
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    ABSTRACT: The imprint of Baryonic Acoustic Oscillations (BAO) on the matter power spectrum can be constrained using the neutral hydrogen density in the intergalactic medium as a tracer of the matter density. One of the goals of the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) is to derive the Hubble expansion rate and the angular scale from the BAO signal in the IGM. To this aim, the Lyman-alpha forest of 10^5 quasars will be observed in the redshift range 2.2<z<3.5 and over 10,000 deg^2. We simulated the BOSS QSO survey to estimate the statistical accuracy on the BAO scale determination provided by such a large scale survey. In particular, we discuss the effect of the poorly constrained estimate of the unabsorbed intrinsic quasar spectrum. The volume of current N-body simulations being too small for such studies, we resorted to Gaussian random field (GRF) simulations. We validated the use of GRFs by comparing the output of GRF simulations with that of the Horizon N-body simulation with the same initial conditions. Realistic mock samples of QSO Lyman-\alpha forest were generated; their power spectrum was computed and fitted to obtain the BAO scale. The rms of the results for 100 different simulations provides an estimate of the statistical error expected from the BOSS survey. We confirm the results from Fisher matrix estimate. In the absence of error on the unabsorbed quasar spectrum, the BOSS quasar survey should measure the BAO scale with an error of the order of 2.3%, or the transverse and radial BAO scales separately with errors of the order of 6.8% and 3.9%, respectively. The significance of the BAO detection is assessed by an average \Delta\chi^2=17 but for individual realizations \Delta\chi^2 ranges from 2 t o 35. The error on the unabsorbed quasar spectrum increases the error on the BAO scale by 10 to 20% and results in a sub percent bias.
    Astronomy and Astrophysics 07/2011; · 5.08 Impact Factor
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    ABSTRACT: BigBOSS is a Stage IV ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the growth of structure with a wide-area galaxy and quasar redshift survey over 14,000 square degrees. It has been conditionally accepted by NOAO in response to a call for major new instrumentation and a high-impact science program for the 4-m Mayall telescope at Kitt Peak. The BigBOSS instrument is a robotically-actuated, fiber-fed spectrograph capable of taking 5000 simultaneous spectra over a wavelength range from 340 nm to 1060 nm, with a resolution R = 3000-4800. Using data from imaging surveys that are already underway, spectroscopic targets are selected that trace the underlying dark matter distribution. In particular, targets include luminous red galaxies (LRGs) up to z = 1.0, extending the BOSS LRG survey in both redshift and survey area. To probe the universe out to even higher redshift, BigBOSS will target bright [OII] emission line galaxies (ELGs) up to z = 1.7. In total, 20 million galaxy redshifts are obtained to measure the BAO feature, trace the matter power spectrum at smaller scales, and detect redshift space distortions. BigBOSS will provide additional constraints on early dark energy and on the curvature of the universe by measuring the Ly-alpha forest in the spectra of over 600,000 2.2 < z < 3.5 quasars. BigBOSS galaxy BAO measurements combined with an analysis of the broadband power, including the Ly-alpha forest in BigBOSS quasar spectra, achieves a FOM of 395 with Planck plus Stage III priors. This FOM is based on conservative assumptions for the analysis of broad band power (kmax = 0.15), and could grow to over 600 if current work allows us to push the analysis to higher wave numbers (kmax = 0.3). BigBOSS will also place constraints on theories of modified gravity and inflation, and will measure the sum of neutrino masses to 0.024 eV accuracy.
    06/2011;
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    ABSTRACT: From a Principal Component Analysis (PCA) of 78 z~3 high quality quasar spectra in the SDSS-DR7, we derive the principal components characterizing the QSO continuum over the full wavelength range available. The shape of the mean continuum, is similar to that measured at low-z (z~1), but the equivalent width of the emission lines are larger at low redshift. We calculate the correlation between fluxes at different wavelengths and find that the emission line fluxes in the red part of the spectrum are correlated with that in the blue part. We construct a projection matrix to predict the continuum in the Lyman-$\alpha$ forest from the red part of the spectrum. We apply this matrix to quasars in the SDSS-DR7 to derive the evolution with redshift of the mean flux in the Lyman-$\alpha$ forest due to the absorption by the intergalactic neutral hydrogen. A change in the evolution of the mean flux is apparent around z~3 in the sense of a steeper decrease of the mean flux at higher redshifts. The same evolution is found when the continuum is estimated from the extrapolation of a power-law continuum fitted in the red part of the quasar spectrum if a correction, derived from simple simulations, is applied. Our findings are consistent with previous determinations using high spectral resolution data. We provide the PCA eigenvectors over the wavelength range 1020-2000 \AA\ and the distribution of their weights that can be used to simulate QSO mock spectra.
    Astronomy and Astrophysics 04/2011; 530. · 5.08 Impact Factor
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    ABSTRACT: The first 10 Principal Components derived from a sub-sample of SDSS-DR7 QSO spectra are presented over the 1020-2000A wavelength range (in the restframe, xi.dat) and redwards to the Ly-alpha emission (1216-2000A in the restframe, zeta.dat). A projection matrix is also provided (proj.dat), allowing to fit a quasar continuum. (3 data files).
    VizieR Online Data Catalog. 04/2011;
  • E. Rollinde, E. Vangioni
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    ABSTRACT: A new cosmological model of LiBeB production in the first structures has been performed. This was motivated by observations of 6Li in halo Pop II stars that indicated a potentially high abundance of this isotope, about a thousand times higher than its predicted primordial value. Using a cosmological model for the cosmic ray-induced production of this isotope in the IGM allows us to explain the observed abundance at very low metallicity. Given this constraint on the 6Li, we also calculate the non-thermal evolution with redshift of D, Be, and B in the IGM, and the resulting extragalactic gamma-ray background. The computation is performed in the framework of hierarchical structure formation considering several star formation histories including specifically Pop III stars. We find that spallative D production is negligible and that a potentially detectable Be and B plateau is produced by these processes at the time of the formation of the Galaxy (z˜3).
    Memorie della Societa Astronomica Italiana. 01/2011;
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    ABSTRACT: Context. Baryonic acoustic oscillations (BAO) and their effects on the matter power spectrum can be studied using the Lyman-alpha absorption signature of the matter density field along quasar (QSO) lines of sight. A measurement sufficiently accurate to provide useful cosmological constraints requires the observation of ~105 quasars in the redshift range 2.2 < z < 3.5 over ~8000 deg2. Such a survey is planned by the Baryon Oscillation Spectroscopic Survey (BOSS) project of the Sloan Digital Sky Survey (SDSS-III). Aims: We assess one of the challenges for this project, that of building from five-band imaging data a list of targets that contains the largest number of quasars in the required redshift range. In practice, we perform a stellar rejection of more than two orders of magnitude with a selection efficiency for quasars better than 50% to magnitudes as bright as g ~ 22. Methods: To obtain an appropriate target list and estimate quasar redshifts, we develop artificial neural networks (ANNs) with a multilayer perceptron architecture. The input variables are photometric measurements, i.e., the object magnitudes and their errors in the five bands (ugriz) of the SDSS photometry. The ANN developed for target selection provides a continuous output variable between 0 for non-quasar point-like objects to 1 for quasars. A second ANN estimates the QSO redshift z using the photometric information. Results: For target selection, we achieve a non-quasar point-like object rejection of 99.6% and 98.5% for a quasar efficiency of, respectively, 50% and 85%, comparable to the performances of traditional methods. The photometric redshift precision is on the order of 0.1 over the region relevant to BAO studies. These statistical methods, developed in the context of the BOSS project, can easily be extended to any quasar selection and/or determination of their photometric redshift.
    Astronomy and Astrophysics 01/2010; · 5.08 Impact Factor
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    ABSTRACT: The Baryon Oscillation Spectroscopic Survey (BOSS) on the Sloan Telescope will make a 3-D map of neutral hydrogen gas using the Ly-alpha forest along lines of sight to 160,000 QSOs between redshifts of 2.2 and 3.5. The power spectrum of this map will make the first measurement of dark energy at z>2. The Ly-alpha forest spectra taken during BOSS commissioning in Fall 2009 already represent a two order-of-magnitude improvement over any dataset in the number of quasar pairs with separations < 100 Mpc/h. This data allows an unprecedented measurement of dimensional large-scale structure in the Lya forest. We present example spectra and data checks as well as early results.
    01/2010;
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    ABSTRACT: Baryonic Acoustic Oscillations (BAO) and their effects on the matter power spectrum can be studied by using the Lyman-alpha absorption signature of the matter density field along quasar (QSO) lines of sight. A measurement sufficiently accurate to provide useful cosmological constraints requires the observation of ~100000 quasars in the redshift range 2.2<z<3.5 over ~8000 deg2. Such a survey is planned by the Baryon Oscillation Spectroscopic Survey (BOSS) project of the Sloan Digital Sky Survey (SDSS-III).In practice, one needs a stellar rejection of more than two orders of magnitude with a selection efficiency for quasars better than 50% up to magnitudes as large as g ~ 22. To obtain an appropriate target list and estimate quasar redshifts, we have developed an Artificial Neural Networks (NN) with a multilayer perceptron architecture. The input variables are photometric measurements, i.e. the object magnitudes and their errors in the five bands (ugriz) of the SDSS photometry. For target selection, we achieve a non-quasar point-like object rejection of 99.6% and 98.5% for a quasar efficiency of, respectively, 50% and 85%. The photometric redshift precision is of the order of 0.1 over the region relevant for BAO studies. Comment: 7 pages, 7 figures, submitted to A&A
    10/2009;
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    ABSTRACT: Context: The runaway star HD 34078, initially selected to investigate small scale structure in a foreground diffuse cloud, has been shown to be surrounded by highly excited H2, the origin of which is unclear. Aims: We first search for an association between the foreground cloud and HD 34078. Second, we extend previous investigations of temporal absorption line variations (CH, CH^+, H2) in order to better characterize them and understand their relation to small-scale structure in the molecular gas. Methods: We have mapped the 12CO(2-1) emission at 12´´ resolution around HD 34078's position, using the 30 m IRAM antenna. The follow-up of CH and CH+ absorption lines has been extended over 5 more years: 26 visible spectra have been acquired since 2003 at high or intermediate resolution. In parallel, CH absorption towards the reddened star ζ Per has been monitored to check the instrumental stability and homogeneity of our measurements. Three more FUSE spectra have been obtained to search for N(H2) variations. Results: CO observations show a pronounced maximum near HD 34078's position, clearly indicating that the star and diffuse cloud are associated. The optical spectra confirm the reality of strong, rapid and correlated CH and CH+ fluctuations (up to 26% for N(CH^+) between 2007 and 2008). On the other hand, N(H2, J=0) has varied by less than 5% over 4 years, indicating the absence of marked density structure at scales below 100 AU. We also discard N(CH) variations towards ζ Per at scales less than 20 AU. Conclusions: Observational constraints from this work and from 24 μm dust emission appear to be consistent with H2 excitation but inconsistent with steady-state bow shock models and rather suggest that the shell of compressed gas surrounding HD 34078 or lying at the boundary of a small foreground clump is seen at an early stage of the interaction. The CH and CH+ time variations as well as their high abundances are likely due to chemical structure in the shocked gas layer located at the stellar wind/ambient cloud interface. Finally, the lack of variation in both N(H2, J=0) towards HD 34078 and N(CH) towards ζ Per suggests that quiescent molecular gas is not subject to pronounced small-scale structure. Based on observations made mainly at IRAM, Observatoire de Haute Provence (France), McDonald Observatory (USA) and with FUSE.
    Astronomy and Astrophysics 07/2009; 501(1):221-237. · 5.08 Impact Factor
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    ABSTRACT: We present 12CO(2-1) emission line observations of the region surrounding HD 34078, together with new optical and FUSE spectra of this runaway star. CO(2-1) emission peaks close to the star position and correlates well with IR thermal dust emission. Our follow-up of CH and CH+ optical absorption lines confirms the reality of marked time variations while FUSE spectra indicate no such changes for H2. These results are consistent with a picture in which all absorption lines in HD 34078's spectrum originate from material located close to the star, in a dense inhomogeneous shell formed at the stellar wind/ambient cloud interface where CH and CH+ are overabundant.
    FUTURE DIRECTIONS IN ULTRAVIOLET SPECTROSCOPY: A Conference Inspired by the Accomplishments of the Far Ultraviolet Spectroscopic Explorer Mission. AIP Conference Proceedings, Annapolis (Maryland); 05/2009
  • E. Rollinde, E. Vangioni
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    ABSTRACT: New observations from the Hubble ultra deep field suggest that the star formation rate at z>7 drops off faster than previously thought. Using the newly determined star formation rate for the normal mode of PopII/I stars we compute the Thomson optical depth. We also investigate the consequences of PopIII stars on the local metallicity distribution function of the Galactic halo and on the evolution of C, O abundances as a function of [Fe/H], with special emphasis on carbon-enhanced metal-poor stars (CEMPS). The metallicity distribution function shape is well reproduced at low redshift ([Fe/H]>~-4), in agreement with other studies. However, the Hamburg/ESO survey hints at a sharp decrease of the number of low-mass stars at very low iron abundance, which is not reproduced in models with only PopII/I stars. The presence of PopIII stars helps in reproducing this feature, leading to a prompt initial enrichment before the onset of PopII/I stars. Finally, we show that the nucleosynthetic yields of PopIII stars leads to abundance patterns in agreement with those observed in extremely metal-poor stars. This can be evidenced by the transition discriminant (a criterion for low-mass star formation taking into account the cooling due to C II and O I). In this simple approach for cosmic evolution, PopIII stars prove to be a compulsory ingredient, and extremely metal poor stars are found to be born at high redshift.
    05/2009;
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    ABSTRACT: The runaway star HD34078, initially selected to investigate small scale structure in a foreground diffuse cloud has been shown to be surrounded by highly excited H2. We first search for an association between the foreground cloud and HD34078. Second, we extend previous investigations of temporal absorption line variations (CH, CH+, H2) in order to better characterize them. We have mapped the CO(2-1) emission at 12 arcsec resolution around HD34078's position, using the 30 m IRAM antenna. The follow-up of CH and CH+ absorption lines has been extended over 5 more years. In parallel, CH absorption towards the reddened star Zeta Per have been monitored to check the homogeneity of our measurements. Three more FUSE spectra have been obtained to search for N(H2) variations. CO observations show a pronounced maximum near HD34078's position, clearly indicating that the star and diffuse cloud are associated. The optical spectra confirm the reality of strong, rapid and correlated CH and CH+ fluctuations. On the other hand, N(H2, J=0) has varied by less than 5 % over 4 years. We also discard N(CH) variations towards Zeta Per at scales less than 20 AU. Observational constraints from this work and from 24 micron dust emission appear to be consistent with H2 excitation but inconsistent with steady-state bow shock models and rather suggest that the shell of compressed gas surrounding HD34078, is seen at an early stage of the interaction. The CH and CH+ time variations as well as their large abundances are likely due to chemical structure in the shocked gas layer located at the stellar wind/ambient cloud interface. Finally, the lack of variations for both N(H2, J=0) towards HD34078 and N(CH) towards Zeta Per suggests that quiescent molecular gas is not subject to pronounced small-scale structure.
    03/2009;
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    ABSTRACT: New observations from the Hubble ultra deep field suggest that the star formation rate at z>7 drops off faster than previously thought. Using a newly determined star formation rate for the normal mode of Population II/I stars (PopII/I), including this new constraint, we compute the Thomson scattering optical depth and find a result that is marginally consistent with WMAP5 results. We also reconsider the role of Population III stars (PopIII) in light of cosmological and stellar evolution constraints. While this input may be needed for reionization, we show that it is essential in order to account for cosmic chemical evolution in the early Universe. We investigate the consequences of PopIII stars on the local metallicity distribution function of the Galactic halo (from the recent Hamburg/ESO survey of metal-poor stars) and on the evolution of abundances with metallicity (based on the ESO large program on very metal-poor stars), with special emphasis on carbon-enhanced metal-poor stars. Our most important results show that the nucleosynthetic yields of PopIII stars lead to abundance patterns in agreement with those observed in extremely metal-poor stars. In this chemical approach to cosmic evolution, PopIII stars prove to be a compulsory ingredient, and extremely metal-poor stars are inevitably born at high redshift. (Abridged) Comment: 11 pages, 7 figures, MNRAS in press
    Monthly Notices of the Royal Astronomical Society 06/2008; · 5.52 Impact Factor
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    ABSTRACT: We investigate how well the three-dimensional density field of neutral hydrogen in the intergalactic medium (IGM) can be reconstructed using the Lyman absorptions observed along lines-of-sight to quasars separated by arcmin distances in projection on the sky. We use cosmological hydrodynamical simulations to compare the topologies of different fields: dark matter, gas and neutral hydrogen optical depth and to investigate how well the topology of the IGM can be recovered from the Wiener interpolation method implemented by Pichon et al. The global statistical and topological properties of the recovered field are analysed quantitatively through the power spectrum, the probability distribution function (PDF), the Euler characteristics, its associated critical point counts and the filling factor of underdense regions. The local geometrical properties of the field are analysed using the local skeleton by defining the concept of interskeleton distance.As a consequence of the nearly lognormal nature of the density distribution at the scales under consideration, the tomography is best carried out on the logarithm of the density rather than the density itself. At scales larger than ∼1.4 〈dLOS〉, where 〈dLOS〉 is the mean separation between lines-of-sight, the reconstruction accurately recovers the topological features of the large-scale density distribution of the gas, in particular the filamentary structures: the interskeleton distance between the reconstruction and the exact solution is smaller than 〈dLOS〉. At scales larger than the intrinsic smoothing length of the inversion procedure, the power spectrum of the recovered H i density field matches well that of the original one and the low-order moments of the PDF are well recovered as well as the shape of the Euler characteristic. The integral errors on the PDF and the critical point counts are indeed small, less than 20 per cent for a mean line-of-sight separation smaller than ∼2.5 arcmin. The small deviations between the reconstruction and the exact solution mainly reflect departures from the lognormal behaviour that are ascribed to highly non-linear objects in overdense regions.
    Monthly Notices of the Royal Astronomical Society 04/2008; 386(1):211 - 229. · 5.52 Impact Factor
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    ABSTRACT: We investigate how well the 3D density field of neutral hydrogen in the Intergalactic Medium (IGM) can be reconstructed using the Lyman-alpha absorptions observed along lines of sight to quasars separated by arcmin distances in projection on the sky. We use cosmological hydrodynamical simulations to compare the topologies of different fields: dark matter, gas and neutral hydrogen optical depth and to investigate how well the topology of the IGM can be recovered from the Wiener interpolation method implemented by Pichon et al. (2001). The global statistical and topological properties of the recovered field are analyzed quantitatively through the power-spectrum, the probability distribution function (PDF), the Euler characteristics, its associated critical point counts and the filling factor of underdense regions. The local geometrical properties of the field are analysed using the local skeleton by defining the concept of inter-skeleton distance. At scales larger than ~1.4 , where is the mean separation between lines of sight, the reconstruction accurately recovers the topological features of the large scale density distribution of the gas, in particular the filamentary structures. At scales larger than the intrinsic smoothing length of the inversion procedure, the power spectrum of the recovered HI density field matches well that of the original one and the low order moments of the PDF are well recovered as well as the shape of the Euler characteristic. The integral errors on the PDF and the critical point counts are indeed small, less than 20% for ~2.5 arcmin. The small deviations between the reconstruction and the exact solution mainly reflect departures from the log-normal behaviour that are ascribed to highly non-linear objects in overdense regions.
    02/2008;
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    ABSTRACT: New observations from the Hubble ultra deep field suggest that the star for- mation rate at z > 7 drops off faster than previously thought. Using the newly determined star formation rate for the normal mode of PopII/I stars we compute the Thomson optical depth and find a result that is marginally consistent with WMAP5 results. We also reconsider the role of Popula- tion III stars in light of cosmological and stellar evolution constraints. We investigate the consequences of PopIII stars on the local metallicity distribu- tion function of the Galactic halo (from the recent Hamburg/ESO survey of metal-poor stars) and on the evolution of abundances with metallicity (based on the ESO large program on very metal-poor stars), with special emphasis on carbon-enhanced metal-poor stars. The metallicity distribution function shape is well reproduced at low redshift ((Fe/H)& −4), in agreement with
    01/2008;