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Register a new userTesting gravity on large scales. The skewness of the galaxy distribution at z~1
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We study the evolution of the low-order moments of the galaxy overdensity distribution over the redshift interval 0.7<z<1.5. We find that the variance and the normalized skewness evolve over this redshift interval in a way that is remarkably consistent with predictions of first- and second-order perturbation theory. This finding confirms the standard gravitational instability paradigm over nearly 9 Gyrs of cosmic time and demonstrates the importance of accounting for the non-linear component of galaxy biasing to avoid disagreement between theory and observations.
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We study the reduced skewness, $S_{3,g}equivbar{xi}_{3,g}/bar{xi}_{2,g}^2$ of galaxy distribution at $z=0.5$ in two families of modfied gravity models: the Hu-Sawicki $f(R)$-gravity and normal-branch of Dvali-Gabadadze-Porrati (nDGP) models. We use a set of mock galaxy catalogues specifally designed to match CMASS spectroscopic galaxy sample. For the first time we investigate the third reduced moment of such galaxy distributions both in the redshift space. Our analysis confirms that the signal previously indicated only for dark matter halo catalogues persists also in realistic mock galaxy samples. This result offers a possibility to extract a potential modified gravity signal in $S_3$ from spectroscopic galaxy data without a need for a very precise and self-consistent RSD models constructed for each and every modified gravity scenario separately. We show that the relative deviations from $Lambda$CDM~ $S_{3,g}$ of various modified gravity models can vary from $7$ down to $sim 2-3%$ effects. Albeit, the effect looks small, we show that for considered models it can foster a $2-3sigma$ falsification. Finally we argue that galaxy sample of a significantly higher number density should provide even stronger constraints by limiting shot-noise effects affecting the $S_{3,g}$ estimates at small comoving separations.
We investigate the possibility of testing Einsteins general theory of relativity (GR) and the standard cosmological model via the $E_{rm G}$ statistic using neutral hydrogen (HI) intensity mapping. We generalise the Fourier space estimator for $E_{rm G}$ to include HI as a biased tracer of matter and forecast statistical errors using HI clustering and lensing surveys that can be performed in the near future, in combination with ongoing and forthcoming optical galaxy and Cosmic Microwave Background (CMB) surveys. We find that fractional errors $< 1%$ in the $E_{rm G}$ measurement can be achieved in a number of cases and compare the ability of various survey combinations to differentiate between GR and specific modified gravity models. Measuring $E_{rm G}$ with intensity mapping and the Square Kilometre Array can provide exquisite tests of gravity at cosmological scales.
We report ALMA observations of the most massive (star forming) galaxy in the redshift range 3<z<4 within the whole GOODS-S field. We detect a large elongated structure of molecular gas around the massive primeval galaxy, traced by the CO(4-3) emission, and extended over 40 kpc. We infer a mass of the large gaseous structure of Mgas~2-6x10^11 Msun. About 60% of this mass is not directly associated with either the central galaxy or its two lower mass satellites. The CO extended structure is also detected in continuum thermal emission. The kinematics of the molecular gas shows the presence of different components, which cannot be ascribed to simple rotation. Furthermore, on even larger scales, we detect nine additional CO systems within a radius of 250 kpc from the massive galaxy and mostly distributed in the same direction as the CO elongated structure found in the central 40 kpc. The stacked images of these CO systems show detections in the thermal continuum and in the X-rays, suggesting that these systems are forming stars at a rate of 30-120 Msun/yr. We suggest that the extended gas structure, combined with its kinematic properties, and the gas rich star forming systems detected on larger scales, are tracing the inner and densest regions of large scale accreting streams, feeding the central massive galaxy. These results corroborate models of galaxy formation, in which accreting streams are clumpy and undergo some star formation (hence enriching the streams with metals) even before accreting onto the central galaxy.
Recently, a measurement of the pressure distribution experienced by the quarks inside the proton has found a strong repulsive (positive) pressure at distances up to 0.6 femtometers from its center and a (negative) confining pressure at larger distances. In this paper we show that this measurement puts significant constraints on modified theories of gravity in which the strength of the gravitational interaction on microscopic scales is enhanced with respect to general relativity. We consider the particular case of Eddington-inspired Born-Infeld gravity, showing that strong limits on $kappa$, the only additional parameter of the theory with respect to general relativity, may be derived from the quark pressure measurement ($|kappa| lsim 10^{-1} , {rm m^5 , kg^{-1} , s^{-2}}$). Furthermore, we show how these limits may be significantly improved with precise measurements of the first and second moments of the pressure distribution inside the proton.
The beyond-Horndeski gravity has recently been reformulated in the dark energy paradigm - which has been dubbed, Unified Dark Energy (UDE). The evolution equations for the given UDE appear to correspond to a non-conservative dark energy scenario, in which the total energy-momentum tensor is not conserved. We investigate both the background cosmology and, the large-scale imprint of the UDE by probing the angular power spectrum of galaxy number counts, on ultra-large scales; taking care to include the full relativistic corrections in the observed overdensity. The background evolution shows that only an effective mass smaller than the Planck mass is needed in the early universe in order for predictions in the given theory to match current observational constraints. We found that the effective mass-evolution-rate parameter, which drives the evolution of the UDE, acts to enhance the observed power spectrum and, hence, relativistic effects (on ultra-large scales) by enlarging the UDE sound horizon. Conversely, both the (beyond) Horndeski parameter and the kineticity act to diminish the observed power spectrum, by decreasing the UDE sound horizon. Our results show that, in a universe with UDE, a multi-tracer analysis will be needed to detect the relativistic effects in the large-scale structure. In the light of a multi-tracer analysis, the various relativistic effects hold the potential to distinguish different gravity models. Moreover, while the Doppler effect will remain significant at all epochs and, thus can not be ignored, the integrated Sachs-Wolfe, the time-delay and the potential (difference) effects, respectively, will only become significant at epochs near z=3 and beyond, and may be neglected at late epochs. In the same vein, the Doppler effect alone can serve as an effective cosmological probe for the large-scale structure or gravity models, in the angular power spectrum - at all z.
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