Brice Ménard

Very weak lensing in the CFHTLS wide: cosmology from cosmic shear in the linear regime ,

Aims. We present an exploration of weak lensing by large-scale structure in the linear regime, using the third-year (T0003) CFHTLS Wide data release. Our results place tight constraints on the scaling of the amplitude of the matter power spectrum σ8 with the matter density Ωm. Methods. Spanning 57 square degrees to i � = 24.5 over three independent fields, the unprecedented contiguous area of this survey permits high signal-to-noise measurements of two-point shear statistics from 1 arcmin to 4 degrees. Understanding systematic errors in our analysis is vital in interpreting the results. We therefore demonstrate the percent-level accuracy of our method using STEP simulations, an E/B-mode decomposition of the data, and the star-galaxy cross correlation function. We also present a thorough analysis of the galaxy redshift distribution using redshift data from the CFHTLS T0003 Deep fields that probe the same spatial regions as the Wide fields. Results. We find σ8(Ωm/0.25) 0.64 = 0.785 ± 0.043 using the aperture-mass statistic for the full range of angular scales for an assumed flat cosmology, in excellent agreement with WMAP3 constraints. The largest physical scale probed by our analysis is 85 Mpc, assuming a mean redshift of lenses of 0.5 and a ΛCDM cosmology. This allows for the first time to constrain cosmology using only cosmic shear measurements in the linear regime. Using only angular scales θ> 85 arcmin, we find σ8(Ωm/0.25) 0.53 lin = 0.837 ± 0.084, which agree with the results from our full analysis. Combining our results with data from WMAP3, we find Ωm = 0.248 ± 0.019 and σ8 = 0.771 ± 0.029.

RADIATION PRESSURE FROM MASSIVE STAR CLUSTERS AS A LAUNCHING MECHANISM FOR SUPER-GALACTIC WINDS

Galactic outflows of cool (~104 K) gas are ubiquitous in local starburst galaxies and in most high-redshift galaxies. Hot gas from supernovae has long been suspected as the primary driver, but this mechanism suffers from its tendency to destroy the cool gas. We propose a modification of the supernova scenario that overcomes this difficulty. Star formation is observed to take place in clusters. We show that, for L galaxies, the radiation pressure from clusters with M cl 106 M ☉ is able to expel the surrounding gas at velocities in excess of the circular velocity vc of the disk galaxy. This cool gas travels above the galactic disk before supernovae erupt in the driving cluster. Once above the disk, the cool outflowing gas is exposed to radiation and hot gas outflows from the galactic disk, which in combination drive it to distances of ~50 kpc. Because the radiatively driven clouds grow in size as they travel, and because the hot gas is more dilute at large distance, the clouds are less subject to destruction. Therefore, unlike wind-driven clouds, radiatively driven clouds can give rise to the metal absorbers seen in quasar spectra. We identify these cluster-driven winds with large-scale galactic outflows. The maximum cluster mass in a galaxy is an increasing function of the galaxys gas surface density, so only starburst galaxies are able to drive cold outflows. We find the critical star formation rate for launching large-scale cool outflows to be , in good agreement with observations.

Measuring the galaxy-mass and galaxy-dust correlations through magnification and reddening

We present a simultaneous detection of gravitational magnification and dust reddening effects due to galactic haloes and large-scale structure. The measurement is based on correlating the brightness of ~85 000 quasars at z > 1 with the position of 24 million galaxies at z ~ 0.3 derived from the Sloan Digital Sky Survey and is used to constrain the galaxy-mass and galaxy-dust correlation functions up to cosmological scales. The presence of dust is detected from 20 kpc to several Mpc, and we find its projected density to follow: Σ dust ~ r -0.8 p , a distribution similar to mass. On large scales, its wavelength dependence is described by R v ≃ 4.9 ± 3.2, consistent with interstellar dust. This, in turn, implies a cosmic dust density of Ω dust ≃ 5 x 10 -6 , roughly half of which comes from dust in haloes of ~L* galaxies. We estimate the resulting opacity of the Universe for various evolutionary models and find 〈A v 〉 ~ 0.03 mag up to z = 0.5. We present magnification measurements, corrected for dust extinction, from which the galaxy-mass correlation function is inferred to give the mean surface mass density profile around galaxies Σ ~ 30 (θ/1 arcmin) -0.8 h M ⊙ pc -2 up to a radius of 10 Mpc, in agreement with gravitational shear estimates.

Lensing, reddening and extinction effects of Mg ii absorbers from z= 0.4 to 2

Using a sample of almost 7000 strong Mg II absorbers with W 0 > 1 A and 0.4 < z < 2.2 detected in the SDSS DR4 data set, we investigate the gravitational lensing and dust extinction effects they induce on background quasars. After carefully quantifying several selection biases, we isolate the reddening effects as a function of redshift and absorber rest equivalent width, W 0 . We find the amount of dust to increase with cosmic time as τ(z) α(1 I + z)- 1.1± 0.4, following the evolution of cosmic star density or integrated star formation rate. We measure the reddening effects over a factor of 30 in E(B - V) and we find that r α (W 0 ) 1.9+0.1 , providing us with an important scaling for theoretical modelling of metal absorbers. We also measure the dust-to-metal ratio and find it similar to that of the Milky Way. In contrast to previous studies, we do not detect any gravitational magnification by Mg II systems. We measure the upper limit μ < 1.10 and discuss the origin of the discrepancy. Finally, we estimate the fraction of absorbers missed due to extinction effects and show that it rises from 1 to 50 per cent in the range 1 < W 0 < 6 A. We parametrize this effect and provide a correction for recovering the intrinsic ∂N/bw 0 distribution.

Low-ionization Line Emission from a Starburst Galaxy: A New Probe of a Galactic-scale Outflow

We study the kinematically narrow, low-ionization line emission from a bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with Keck/LRIS. The spectrum reveals strong absorption in Mg II and Fe II resonance transitions with Doppler shifts of –200 to –300 km s-1, indicating a cool gas outflow. Emission in Mg II near and redward of systemic velocity, in concert with the observed absorption, yields a P-Cygni-like line profile similar to those observed in the Lyα transition in Lyman break galaxies. Further, the Mg II emission is spatially resolved and extends significantly beyond the emission from stars and H II regions within the galaxy. Assuming that the emission has a simple, symmetric surface brightness profile, we find that the gas extends to distances 7 kpc. We also detect several narrow Fe II* fine-structure lines in emission near the systemic velocity, arising from energy levels that are radiatively excited directly from the ground state. We suggest that the Mg II and Fe II* emission is generated by photon scattering in the observed outflow and emphasize that this emission is a generic prediction of outflows. These observations provide the first direct constraints on the minimum spatial extent and morphology of the wind from a distant galaxy. Estimates of these parameters are crucial for understanding the impact of outflows in driving galaxy evolution.

On the impact of intergalactic dust on cosmology with Type Ia supernovae

Supernova (SN) measurements have become a key ingredient in current determinations of cosmological parameters. These sources can however be used as standard candles only after correcting their apparent brightness for a number of effects. In this paper, we discuss some limitations imposed by the formalism currently used for such corrections and investigate the impact on cosmological constraints. We show that colour corrections are, in general, expected to be biased. In addition, colour excesses which do not add a significant scatter to the observed SN brightnesses affect the value of cosmological parameters but leave the slope of the colour-luminosity relation unchanged. We quantify these biases in the context of the redshift-dependent dust extinction suggested by the recent detection of intergalactic dust by Menard et al. Using a range of models for the opacity of the Universe as a function of redshift, we find that colour-magnitude-stretch scaling relations are virtually insensitive to the presence of cosmic dust while cosmological parameters such as Ω M and w are biased at the level of a few per cent, i.e. offsets comparable to the current statistical errors. Future surveys will be able to limit the impact of intergalactic extinction by observing at longer wavelengths. In addition, such data sets will provide direct detections of intergalactic dust by cross-correlating SN colours and the density of foreground galaxies, which can be used as a consistency check on the cosmic dust extinction correction. Alternatively, such biases could be avoided by correcting the colours of SNe on an object-by-object basis with accurate photometry.

Photometric redshifts: estimating their contamination and distribution using clustering information

We present a new technique to estimate the level of contamination between photometric redshift bins. If the true angular cross-correlation between redshift bins can be safely assumed to be zero, any measured cross-correlation is a result of contamination between the bins. We present the theory for an arbitrary number of redshift bins, and discuss in detail the case of two and three bins which can be easily solved analytically. We use mock catalogues constructed from the Millennium Simulation to test the method, showing that artificial contamination can be successfully recovered with our method. We find that degeneracies in the parameter space prohibit us from determining a unique solution for the contamination, though constraints are made which can be improved with larger data sets. We then apply the method to an observational galaxy survey: the deep component of the Canada-France-Hawaii Telescope Legacy Survey. We estimate the level of contamination between photometric redshift bins and demonstrate our ability to reconstruct both the true redshift distribution and the true average redshift of galaxies in each photometric bin.

On the connection between metal absorbers and quasar nebulae

We establish a simple model for the distribution of cool (~10^4 K) gas around L* galaxies using the properties of strong Mg II absorption line systems as observational constraints. Our analysis suggests that the halos of L* galaxies are filled with cool gas clouds having sizes of order 1 kpc and densities of ~10^−2 cm^−3. We then investigate the physical conditions of a similar ensemble of clouds situated around a central quasar. We show that the flux from the quasar gives rise to (1) extended narrow line emission on ~100 kpc scales and (2) an anisotropy in the properties of the absorbing gas arising from the geometry of the quasar radiation field. Provided that quasars reside in gaseous halos more massive than those of L* galaxies, our predictions agree with the results from detections of both narrow emission line nebulae and ~100 kpc Mg II-absorbing halos around quasars, suggesting a common origin for these phenomena. We discuss the implications of our results for understanding quasar absorption line systems, quasar environments at high redshifts, and the quasar unification scheme.

Incidence of Mg ii absorbers towards blazars and the GRB/QSO puzzle

In order to investigate the origin of the excess of strong Mg II systems towards GRB afterglows as compared to QSO sightlines, we have measured the incidence of Mg II absorbers towards a third class of objects: the blazars. This class includes the BL Lac object population for which a tentative excess of Mg II systems had already been reported. We observed with FORS1 at the ESO-VLT 42 blazars with an emission redshift 0.8 1.0 A) and weaker (0.3 < w r (2796) < 1.0 A) Mg II systems. The dependence on velocity separation with respect to the background blazars indicates, at the ∼1.5σ level, a potential excess for β ≡ v/c ∼ 0.1. We show that biases involving dust extinction or gravitational amplification are not likely to notably affect the incidence of Mg II systems towards blazars. Finally we discuss the physical conditions required for these absorbers to be gas entrained by the powerful blazar jets. More realistic numerical modelling of jet-ambient gas interaction is required to reach any firm conclusions as well as repeat observations at high spectral resolution of strong Mg II absorbers towards blazars in both high and low states.