CO lines in high redshift galaxies: perspective for future mm instruments

Nearly 10 high redshift (z>2) starburst galaxies have recently been detected in the CO lines, revealing the early presence in the universe of objects with large amounts of already-enriched molecular gas. The latter has sufficient density to be excited in the high-level rotational CO lines, which yield more flux, making easier high-redshift detections; however the effect is not as strong as for the sub-millimeter and far-infrared dust continuum emission. With the help of simple galaxy models, based on these first detections, we estimate the flux in all CO lines expected for such starbursting objects at various redshifts. We discuss the detection perspectives with the future millimeter instruments.Comment: 11 pages, 11 figures, accepted in A &

Mass - concentration relation and weak lensing peak counts

The statistics of peaks in weak lensing convergence maps is a promising tool to investigate both the properties of dark matter haloes and constrain the cosmological parameters. We study how the number of detectable peaks and its scaling with redshift depend upon the cluster dark matter halo profiles and use peak statistics to constrain the parameters of the mass - concentration (MC) relation. We investigate which constraints the Euclid mission can set on the MC coefficients also taking into account degeneracies with the cosmological parameters. To this end, we first estimate the number of peaks and its redshift distribution for different MC relations. We find that the steeper the mass dependence and the larger the normalisation, the higher is the number of detectable clusters, with the total number of peaks changing up to $40\%$ depending on the MC relation. We then perform a Fisher matrix forecast of the errors on the MC relation parameters as well as cosmological parameters. We find that peak number counts detected by Euclid can determine the normalization $A_v$, the mass $B_v$ and redshift $C_v$ slopes and intrinsic scatter $\sigma_v$ of the MC relation to an unprecedented accuracy being $\sigma(A_v)/A_v = 1\%$, $\sigma(B_v)/B_v = 4\%$, $\sigma(C_v)/C_v = 9\%$, $\sigma(\sigma_v)/\sigma_v = 1\%$ if all cosmological parameters are assumed to be known. Should we relax this severe assumption, constraints are degraded, but remarkably good results can be restored setting only some of the parameters or combining peak counts with Planck data. This precision can give insight on competing scenarios of structure formation and evolution and on the role of baryons in cluster assembling. Alternatively, for a fixed MC relation, future peaks counts can perform as well as current BAO and SNeIa when combined with Planck.Comment: 14 pages, 8 figures, accepted for publication on Astronomy & Astrophysic

Searching for galaxy clusters using the aperture mass statistics in 50 VLT fields

Application of the aperture mass (Map-) statistics provides a weak lensing method for the detection of cluster-sized dark matter halos. We present a new aperture filter function and maximise the effectiveness of the Map-statistics to detect cluster-sized halos using analytical models. We then use weak lensing mock catalogues generated from ray-tracing through N-body simulations, to analyse the effect of image treatment on the expected number density of halos. Using the Map-statistics, the aperture radius is typically several arcminutes, hence the aperture often lies partly outside a data field, consequently the signal-to-noise ratio of a halo detection decreases. We study these border effects analytically and by using mock catalogues. We find that the expected number density of halos decreases by a factor of two if the size of a field is comparable to the diameter of the aperture used. We finally report on the results of a weak lensing cluster search applying the Map-statistics to 50 randomly selected fields which were observed with FORS1 at the VLT. Altogether the 50 VLT fields cover an area of 0.64 square degrees. The I-band images were taken under excellent seeing conditions (average seeing 0.6 arcsec.) which results in a high number density of galaxies used for the weak lensing analysis (26/sq.arcmin). In five of the VLT fields, we detect a significant Map-signal which coincides with an overdensity of the light distribution. These detections are thus excellent candidates for shear-selected clusters.Comment: 23 pages, 5 tables, 24 figures, published in A&A, Sect. 3.5 and 7 are changed or altered; Fig. 11 is change

The power spectrum of systematics in cosmic shear tomography and the bias on cosmological parameters

Cosmic shear tomography has emerged as one of the most promising tools to both investigate the nature of dark energy and discriminate between General Relativity and modified gravity theories. In order to successfully achieve these goals, systematics in shear measurements have to be taken into account; their impact on the weak lensing power spectrum has to be carefully investigated in order to estimate the bias induced on the inferred cosmological parameters. To this end, we develop here an efficient tool to compute the power spectrum of systematics by propagating, in a realistic way, shear measurement, source properties and survey setup uncertainties. Starting from analytical results for unweighted moments and general assumptions on the relation between measured and actual shear, we derive analytical expressions for the multiplicative and additive bias, showing how these terms depend not only on the shape measurement errors, but also on the properties of the source galaxies (namely, size, magnitude and spectral energy distribution). We are then able to compute the amplitude of the systematics power spectrum and its scaling with redshift, while we propose a multigaussian expansion to model in a non-parametric way its angular scale dependence. Our method allows to self-consistently propagate the systematics uncertainties to the finally observed shear power spectrum, thus allowing us to quantify the departures from the actual spectrum. We show that even a modest level of systematics can induce non-negligible deviations, thus leading to a significant bias on the recovered cosmological parameters.Comment: 19 pages, 5 tables, 4 figure

Calibration of colour gradient bias in shear measurement using HST/CANDELS data

Accurate shape measurements are essential to infer cosmological parameters from large area weak gravitational lensing studies. The compact diffraction-limited point-spread function (PSF) in space-based observations is greatly beneficial, but its chromaticity for a broad band observation can lead to new subtle effects that could hitherto be ignored: the PSF of a galaxy is no longer uniquely defined and spatial variations in the colours of galaxies result in biases in the inferred lensing signal. Taking Euclid as a reference, we show that this colourgradient bias (CG bias) can be quantified with high accuracy using available multi-colour Hubble Space Telescope (HST) data. In particular we study how noise in the HST observations might impact such measurements and find this to be negligible. We determine the CG bias using HST observations in the F606W and F814W filters and observe a correlation with the colour, in line with expectations, whereas the dependence with redshift is weak. The biases for individual galaxies are generally well below 1%, which may be reduced further using morphological information from the Euclid data. Our results demonstrate that CG bias should not be ignored, but it is possible to determine its amplitude with sufficient precision, so that it will not significantly bias the weak lensing measurements using Euclid data

Cosmic shear surveys

Gravitational weak shear produced by large-scale structures of the universe induces a correlated ellipticity distribution of distant galaxies. The amplitude and evolution with angular scale of the signal depend on cosmological models and can be inverted in order to constrain the power spectrum and the cosmological parameters. We present our recent analysis of 50 uncorrelated VLT fields and the very first constrains on ($\Omega_m,\sigma_8$) and the nature of primordial fluctuations based on the join analysis of present-day cosmic shear surveys.Comment: Latex, 7 pages. To appear in the ESO Proceedings ``Deep Fields'', Garching Oct 9-12, 200

Jointly fitting weak lensing, x-ray, and Sunyaev-Zel'dovich data to constrain scalar-tensor theories with clusters of galaxies

Degenerate higher-order scalar-tensor (DHOST) theories are considered the most general class of scalar-tensor theories with an additional scalar field. DHOST theories modify the laws of gravity even at galaxy clusters scale hence affecting the weak lensing, x-ray, and Sunyaev-Zel'dovich observables. We derive the theoretical expression for the lensing convergence κ and the pressure profile P of clusters in the framework of DHOST theories and quantify how much they deviate from their general relativity counterparts. We argue that combined measurements of κ, P, and of the electron number density ne can constrain both the cluster parameters and some effective parameters of the DHOST theory. We carry on a Fisher matrix forecasts analysis to investigate whether this is indeed the case considering different scenarios for the spatial resolution and errors on the measured quantities

Molecular signals from primordial clouds at high redshift

The possibility to detect cosmological signals from the post-recombination Universe is one of the main aims of modern cosmology. In a previous paper we emphasized the role that elastic resonant scattering through LiH molecules can have in dumping primary CBR anisotropies and raising secondary signals. Here we extend our analysis to all the evolutionary stages of a primordial cloud, starting with the linear phase, through the turn-around and to the non linear collapse. We have done calculations for proto-clouds in a CDM scenario and, more generally, for a set of clouds with various masses and various turn-around redshifts, in this case without referring to any particular structure formation scenario. We found that the first phase of collapse, for $t/t_{free-fall}=0.05\div 0.2$ is the best one for simultaneous detection of the first two LiH rotational lines. The observational frequency falls between 30 and 250 GHz and the line width ${\Delta \nu\over \nu}$ is between $10^{-5}$ and $10^{-4}$. As far as we know this is the most favourable process to detect primordial clouds before they start star formation processes.Comment: 26 pages, uuencoded compressed postscript, 7 figures included. Accepted for publication in Ap.

A 380 GHz SIS receiver using Nb/AlO(x)/Nb junctions for a radioastronomical balloon-borne experiment: PRONAOS

The superheterodyne detection technique used for the spectrometer instrument of the PRONAOS project will provide a very high spectral resolution (delta nu/nu = 10(exp -6)). The most critical components are those located at the front-end of the receiver: their contribution dominates the total noise of the receiver. Therefore, it is important to perform accurate studies for specific components, such as mixers and multipliers working in the submillimeter wave range. Difficulties in generating enough local oscillator (LO) power at high frequencies make SIS mixers very desirable for operation above 300 GHz. The low LO power requirements and the low noise temperature of these mixers are the primary reason for building an SIS receiver. This paper reports the successful fabrication of small (less than or equal to 1 sq micron) Nb/Al-O(x)/Nb junctions and arrays with excellent I-V characteristics and very good reliability, resulting in a low noise receiver performance measured in the 368/380 GHz frequency range