We investigate the possibility of constraining coupled dark energy (cDE) cosmologies using the three-point correlation function (3PCF). Making use of the CoDECS N-body simulations, we study the statistical properties of cold dark matter (CDM) haloes
for a variety of models, including a fiducial $Lambda$CDM scenario and five models in which dark energy (DE) and CDM mutually interact. We measure both the halo 3PCF, $zeta(theta)$, and the reduced 3PCF, $Q(theta)$, at different scales ($2<r,[$Mpch$]<40$) and redshifts ($0leq zleq2$). In all cDE models considered in this work, $Q(theta)$ appears flat at small scales (for all redshifts) and at low redshifts (for all scales), while it builds up the characteristic V-shape anisotropy at increasing redshifts and scales. With respect to the $Lambda $CDM predictions, cDE models show lower (higher) values of the halo 3PCF for perpendicular (elongated) configurations. The effect is also scale-dependent, with differences between $Lambda$CDM and cDE models that increase at large scales. We made use of these measurements to estimate the halo bias, that results in fair agreement with the one computed from the two-point correlation function (2PCF). The main advantage of using both the 2PCF and 3PCF is to break the bias$-sigma_{8}$ degeneracy. Moreover, we find that our bias estimates are approximately independent of the assumed strength of DE coupling. This study demonstrates the power of a higher-order clustering analysis in discriminating between alternative cosmological scenarios, for both present and forthcoming galaxy surveys, such as e.g. BOSS and Euclid.
We present the analysis of photometric, spectroscopic, and morphological properties for differently selected samples of passive galaxies up to z=1 extracted from the zCOSMOS-20k spectroscopic survey. This analysis intends to explore the dependence of
galaxy properties on the selection criterion adopted, study the degree of contamination due to star-forming outliers, and provide a comparison between different commonly used selection criteria. We extracted from the zCOSMOS-20k catalog six different samples of passive galaxies, based on morphology, optical colors, specific star-formation rate, a best fit to the observed spectral energy distribution, and a criterion that combines morphological, spectroscopic, and photometric information. The morphological sample has the higher percentage of contamination in colors, specific star formation rate and presence of emission lines, while the red & passive ETGs sample is the purest, with properties mostly compatible with no star formation activity; however, it is also the less economic criterion in terms of information used. The best performing among the other criteria are the red SED and the quiescent ones, providing a percentage of contamination only slightly higher than the red & passive ETGs criterion (on average of a factor of ~2) but with absolute values of the properties of contaminants still compatible with a red, passively evolving population. We also provided two revised definitions of early type galaxies based on restframe color-color and color-mass criteria, that better reproduce the observed bimodalities. The analysis of the number densities shows evidences of mass-assembly downsizing, with galaxies at 10.25<log(M/Msun)<10.75 increasing their number by a factor ~2-4 from z=0.6 to z=0.2, by a factor ~2-3 from z=1 to z=0.2 at 10.75<log(M/Msun)<11, and by only ~10-50% from z=1 to z=0.2 at 11<log(M/Msun)<11.5.
We present new improved constraints on the Hubble parameter H(z) in the redshift range 0.15 < z < 1.1, obtained from the differential spectroscopic evolution of early-type galaxies as a function of redshift. We extract a large sample of early-type ga
laxies (sim11000) from several spectroscopic surveys, spanning almost 8 billion years of cosmic lookback time (0.15 < z < 1.42). We select the most massive, red elliptical galaxies, passively evolving and without signature of ongoing star formation. Those galaxies can be used as standard cosmic chronometers, as firstly proposed by Jimenez & Loeb (2002), whose differential age evolution as a function of cosmic time directly probes H(z). We analyze the 4000 {AA} break (D4000) as a function of redshift, use stellar population synthesis models to theoretically calibrate the dependence of the differential age evolution on the differential D4000, and estimate the Hubble parameter taking into account both statistical and systematical errors. We provide 8 new measurements of H(z) (see Tab. 4), and determine its change in H(z) to a precision of 5-12% mapping homogeneously the redshift range up to z sim 1.1; for the first time, we place a constraint on H(z) at z eq 0 with a precision comparable with the one achieved for the Hubble constant (about 5-6% at z sim 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial to distinguish many different quintessence cosmologies. These measurements have been tested to best match a Lambda CDM model, clearly providing a statistically robust indication that the Universe is undergoing an accelerated expansion. This method shows the potentiality to open a new avenue in constrain a variety of alternative cosmologies, especially when future surveys (e.g. Euclid) will open the possibility to extend it up to z sim 2.
We present the analysis of the U-V rest-frame color distribution and some spectral features as a function of mass and environment for two sample of early-type galaxies up to z=1 extracted from the zCOSMOS spectroscopic survey. The first sample (red g
alaxies) is defined with a photometric classification, while the second (ETGs) by combining morphological, photometric, and spectroscopic properties to obtain a more reliable sample. We find that the color distribution of red galaxies is not strongly dependent on environment for all mass bins, with galaxies in overdense regions redder than galaxies in underdense regions with a difference of 0.027pm0.008 mag. The dependence on mass is far more significant, with average colors of massive galaxies redder by 0.093pm0.007 mag than low-mass galaxies throughout the entire redshift range. We study the color-mass relation, finding a mean slope 0.12pm0.005, while the color-environment relation is flatter, with a slope always smaller than 0.04. The spectral analysis that we perform on our ETGs sample is in good agreement with our photometric results: we find for D4000 a dependence on mass between high and low-mass galaxies, and a much weaker dependence on environment (respectively a difference of of 0.11pm0.02 and of 0.05pm0.02); for the equivalent width of H{delta}we measure a difference of 0.28pm0.08 {AA}across the same mass range and no significant dependence on environment.By analyzing the lookback time of early-type galaxies, we support the possibility of a downsizing scenario, in which massive galaxies with a stronger D4000 and an almost constant equivalent width of $Hdelta$ formed their mass at higher redshift than lower mass ones. We also conclude that the main driver of galaxy evolution is the galaxy mass, the environment playing a subdominant role.
