CEA Bolometer Arrays: the First Year in Space

The CEA/LETI and CEA/SAp started the development of far-infrared filled bolometer arrays for space applications over a decade ago. The unique design of these detectors makes possible the assembling of large focal planes comprising thousands of bolometers running at 300 mK with very low power dissipation. Ten arrays of 16x16 pixels were thoroughly tested on the ground, and integrated in the Herschel/PACS instrument before launch in May 2009. These detectors have been successfully commissioned and are now operating in their nominal environment at the second Lagrangian point of the Earth-Sun system. In this paper we briefly explain the functioning of CEA bolometer arrays, and we present the properties of the detectors focusing on their noise characteristics, the effect of cosmic rays on the signal, the repeatability of the measurements, and the stability of the system

Influence of Projection in Cluster Cosmology Studies

Projection tends to skew the mass-observable relation of galaxy clusters by creating a small fraction of severely blended systems, those for which the measured observable property of a cluster is strongly boosted relative to the value of its primary host halo. We examine the bias in cosmological parameter estimates caused by incorrectly assuming a Gaussian (projection-free) mass-observable relation when the true relation is non-Gaussian due to projection. We introduce a mixture model for projection and explore Fisher forecasts for a survey of 5000 sq. deg. to z=1.1 and an equivalent mass threshold of 10^13.7 h^-1 solar masses. Using a blended fraction motivated by optical cluster finding applied to the Millennium Simulation and applying Planck and otherwise weak priors, we find that the biases in Omega_DE and w are significant, being factors of 2.8 and 2.4, respectively, times previous forecast uncertainties. Incorporating eight new degrees of freedom to describe cluster selection with projection increases the forecast uncertainty in Omega_DE and w by similar factors. Knowledge of these additional parameters at the 5% level limits degradation in dark energy constraints to <10% relative to projection-free forecasts. We discuss strategies for using simulations and complementary observations to characterize the fraction of blended clusters and their mass selection properties.Comment: 11 pages, 4 figures to be submitted to phys. rev.

Evidence of triggered star formation in G327.3-0.6. Dust-continuum mapping of an infrared dark cloud with P-ArT\'eMiS

Aims. Expanding HII regions and propagating shocks are common in the environment of young high-mass star-forming complexes. They can compress a pre-existing molecular cloud and trigger the formation of dense cores. We investigate whether these phenomena can explain the formation of high-mass protostars within an infrared dark cloud located at the position of G327.3-0.6 in the Galactic plane, in between two large infrared bubbles and two HII regions. Methods: The region of G327.3-0.6 was imaged at 450 ? m with the CEA P-ArT\'eMiS bolometer array on the Atacama Pathfinder EXperiment telescope in Chile. APEX/LABOCA and APEX-2A, and Spitzer/IRAC and MIPS archives data were used in this study. Results: Ten massive cores were detected in the P-ArT\'eMiS image, embedded within the infrared dark cloud seen in absorption at both 8 and 24 ?m. Their luminosities and masses indicate that they form high-mass stars. The kinematical study of the region suggests that the infrared bubbles expand toward the infrared dark cloud. Conclusions: Under the influence of expanding bubbles, star formation occurs in the infrared dark areas at the border of HII regions and infrared bubbles.Comment: 4 page

Mid-Infrared Emission Features in the ISM: Feature-to-Feature Flux Ratios

Using a limited, but representative sample of sources in the ISM of our Galaxy with published spectra from the Infrared Space Observatory, we analyze flux ratios between the major mid-IR emission features (EFs) centered around 6.2, 7.7, 8.6 and 11.3 microns, respectively. In a flux ratio-to-flux ratio plot of EF(6.2)/EF(7.7) as a function of EF(11.3)/EF(7.7), the sample sources form roughly a $\Lambda$-shaped locus which appear to trace, on an overall basis, the hardness of a local heating radiation field. But some driving parameters other than the radiation field may also be required for a full interpretation of this trend. On the other hand, the flux ratio of EF(8.6)/EF(7.7) shows little variation over the sample sources, except for two HII regions which have much higher values for this ratio due to an ``EF(8.6\um) anomaly,'' a phenomenon clearly associated with environments of an intense far-UV radiation field. If further confirmed on a larger database, these trends should provide crucial information on how the EF carriers collectively respond to a changing environment.Comment: 16 pages, 1 figure, 1 table; accepted for publication in ApJ Letter

DUNE: The Dark Universe Explorer

Understanding the nature of Dark Matter and Dark Energy is one of the most pressing issues in cosmology and fundamental physics. The purpose of the DUNE (Dark UNiverse Explorer) mission is to study these two cosmological components with high precision, using a space-based weak lensing survey as its primary science driver. Weak lensing provides a measure of the distribution of dark matter in the universe and of the impact of dark energy on the growth of structures. DUNE will also include a complementary supernovae survey to measure the expansion history of the universe, thus giving independent additional constraints on dark energy. The baseline concept consists of a 1.2m telescope with a 0.5 square degree optical CCD camera. It is designed to be fast with reduced risks and costs, and to take advantage of the synergy between ground-based and space observations. Stringent requirements for weak lensing systematics were shown to be achievable with the baseline concept. This will allow DUNE to place strong constraints on cosmological parameters, including the equation of state parameter of the dark energy and its evolution from redshift 0 to 1. DUNE is the subject of an ongoing study led by the French Space Agency (CNES), and is being proposed for ESA's Cosmic Vision programme

Very weak lensing in the CFHTLS Wide: Cosmology from cosmic shear in the linear regime

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 sigma_8 with the matter density Omega_m. Spanning 57 square degrees to i'_AB = 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. We find sigma_8(Omega_m/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 LCDM cosmology. This allows for the first time to constrain cosmology using only cosmic shear measurements in the linear regime. Using only angular scales theta> 85 arcmin, we find sigma_8(Omega_m/0.25)_lin^0.53 = 0.837+-0.084, which agree with the results from our full analysis. Combining our results with data from WMAP3, we find Omega_m=0.248+-0.019 and sigma_8 = 0.771+-0.029.Comment: 23 pages, 16 figures (A&A accepted

Emission Features and Source Counts of Galaxies in Mid-Infrared

In this work we incorporate the newest ISO results on the mid-infrared spectral-energy-distributions (MIR SEDs) of galaxies into models for the number counts and redshift distributions of MIR surveys. A three-component model, with empirically determined MIR SED templates of (1) a cirrus/PDR component (2) a starburst component and (3) an AGN component, is developed for infrared (3--120\micron) SEDs of galaxies. The model includes a complete IRAS 25\micron selected sample of 1406 local galaxies ($z \leq 0.1$; Shupe et al. 1998a). Results based on these 1406 spectra show that the MIR emission features cause significant effects on the redshift dependence of the K-corrections for fluxes in the WIRE 25\micron band and ISOCAM 15\micron band. This in turn will affect deep counts and redshift distributions in these two bands, as shown by the predictions of two evolution models (a luminosity evolution model with $L\propto (1+z)^3$ and a density evolution model with $\rho\propto (1+z)^4$). The dips-and-bumps on curves of MIR number counts, caused by the emission features, should be useful indicators of evolution mode. The strong emission features at $\sim 6$--8\micron will help the detections of relatively high redshift ($z\sim 2$) galaxies in MIR surveys. On the other hand, determinations of the evolutionary rate based on the slope of source counts, and studies on the large scale structures using the redshift distribution of MIR sources, will have to treat the effects of the MIR emission features carefully. We have also estimated a 15\micron local luminosity function from the predicted 15\micron fluxes of the 1406 galaxies using the bivariate (15\micron vs. 25\micron luminosities) method. This luminosity function will improve our understanding of the ISOCAM 15\micron surveys.Comment: 24 pages, 14 EPS figures. Accepted by Ap

Accurate photometric redshifts for the CFHT Legacy Survey calibrated using the VIMOS VLT Deep Survey

We present photometric redshifts for an uniquely large and deep sample of 522286 objects with i'_{AB}<25 in the Canada-France Legacy Survey ``Deep Survey'' fields, which cover a total effective area of 3.2 deg^2. We use 3241 spectroscopic redshifts with 0<z<5 from the VIMOS VLT Deep Survey as a calibration to derive these photometric redshifts. We devise a robust calibration method which removes systematic trends in the photometric redshifts and significantly reduces the fraction of catastrophic errors. We use our unique spectroscopic sample to present a detailed assessment of the robustness of the photometric redshift sample. For a sample selected at i'_{AB}<24, we reach a redshift accuracy of \sigma_{\Delta z/(1+z)}=0.037 with \eta=3.7% of catastrophic error. The reliability of our photometric redshifts is lower for fainter objects: we find \sigma_{\Delta z/(1+z)}=0.029, 0.043 and \eta=1.7%, 5.4% for samples selected at i'_{AB}=17.5-22.5 and 22.5-24 respectively. We find that the photometric redshifts of starburst galaxies in our sample are less reliable: although these galaxies represent only 18% of the spectroscopic sample they are responsible for 54% of the catastrophic errors. We find an excellent agreement between the photometric and the VVDS spectroscopic redshift distributions at i'_{AB}<24. Finally, we compare the redshift distributions of i' selected galaxies on the four CFHTLS deep fields, showing that cosmic variance is already present on fields of 0.8 deg^2.Comment: 19 pages, 17 figures, submitted to A&A. The photometric redshifts described in this paper will be made publicly available from 1st may 2006 at http://terapix.iap.fr and http://cencosw.oamp.fr