Reconciling radio relic observations and simulations: The NVSS sample

The diffusive shock acceleration scenario is usually invoked to explain radio relics, although the detailed driving mechanism is still a matter of debate. Our aim is to constrain models for the origin of radio relics by comparing observed relic samples with simulated ones. Here we present a framework to homogeneously extract the whole sample of known radio relics from NVSS so that it can be used for comparison with cosmological simulations. In this way, we can better handle intrinsic biases in the analysis of the radio relic population. In addition, we show some properties of the resulting NVSS sample relics such as the correlation between relic shape and orientation with respect to the cluster. Also, we briefly discuss the typical relic surface brightness and its relation to projected cluster distance and relic angular sizes.Comment: 4 pages, 2 figures. Proceedings of "The many facets of extragalactic radio surveys: towards new scientific challenges" (EXTRA-RADSUR2015). 20-23 October 2015. Bologna, Ital

A model for molecular hydrogen-dependent star formation in simulations of galaxy evolution

Star formation, together with the associated chemical and energy feedback, is one of the most important processes in galaxy evolution. The star formation activity in galaxies defines and affects many of their fundamental properties, such as stellar mass, morphology and chemical enrichment levels. Simple models for star formation in cosmological hydrodynamical simulations have shown to be successful in reproducing the star formation rate (SFR) levels and shapes of different types of galaxies. However, with the advent of high-resolution simulations and more detailed observations, more sophisticated star formation models are needed; in particular, to better understand the relation between star formation and the amount of gas in the atomic and molecular phases. In this work, we apply a novel star formation model, recently developed to work in the context of hydrodynamical simulations, to the study of the SFR in Milky Way-mass galaxies. The new implementation describes the formation of molecular hydrogen from atomic material, considering also possible dependencies with the chemical abundance of the gas. This allows to implement various star formation models, where the SFR of a gas cloud is determined by the atomic and/or molecular gas phases, and to compare their predictions to recent observational results.Comment: 3 pages, 3 figures. To appear in the 64nd Bulletin of the Argentine Astronomical Societ

The Milky Way and Andromeda galaxies in a constrained hydrodynamical simulation: morphological evolution

We study the two main constituent galaxies of a constrained simulation of the Local Group as candidates for the Milky Way (MW) and Andromeda (M31). We focus on the formation of the stellar discs and its relation to the formation of the group as a rich system with two massive galaxies, and investigate the effects of mergers and accretion as drivers of morphological transformations. We use a state-of-the-art hydrodynamical code which includes star formation, feedback and chemical enrichment to carry out our study. We run two simulations, where we include or neglect the effects of radiation pressure from stars, to investigate the impact of this process on the morphologies and star formation rates of the simulated galaxies. We find that the simulated M31 and MW have different formation histories, even though both inhabit, at z=0, the same environment. These differences directly translate into and explain variations in their star formation rates, in-situ fractions and final morphologies. The M31 candidate has an active merger history, as a result of which its stellar disc is unable to survive unaffected until the present time. In contrast, the MW candidate has a smoother history with no major mergers at late times, and forms a disc that grows steadily; at z=0 the simulated MW has an extended, rotationally-supported disc which is dominant over the bulge. Our two feedback implementations predict similar evolution of the galaxies and their discs, although some variations are detected, the most important of which is the formation time of the discs: in the model with weaker/stronger feedback the discs form earlier/later. In summary, by comparing the formation histories of the two galaxies, we conclude that the particular merger/accretion history of a galaxy rather than its environment at the LG-scales is the main driver of the formation and subsequent growth or destruction of galaxy discs.Comment: 12 pages, 7 figures, accepted for publication in A&

The Effect of Environment on Milky Way-mass galaxies in a Constrained Simulation of the Local Group

In this letter we present, for the first time, a study of star formation rate, gas fraction and galaxy morphology of a constrained simulation of the Milky Way (MW) and Andromeda (M31) galaxies, compared to other MW-mass galaxies. By combining with unconstrained simulations we cover a sufficient volume to compare these galaxies environmental densities ranging from the field to that of the Local Group (LG). This is particularly relevant as it has been shown that, quite generally, galaxy properties depend intimately upon their environment, most prominently when galaxies in clusters are compared to those in the field. For galaxies in loose groups such as the LG, however, environmental effects have been less clear. We consider the galaxy's environmental density in spheres of 1200 kpc (comoving) and find that whilst environment does not appear to directly affect morphology, there is a positive trend with star formation rates. This enhancement in star formation occurs systematically for galaxies in higher density environments, regardless whether they are part of the LG or in filaments. Our simulations suggest that the richer environment at Mpc-scales may help replenish the star-forming gas, allowing higher specific star formation rates in galaxies such as the MW.Comment: 6 pages, 4 figures, accepted to ApJ

The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: single-probe measurements from CMASS anisotropic galaxy clustering

With the largest spectroscopic galaxy survey volume drawn from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), we can extract cosmological constraints from the measurements of redshift and geometric distortions at quasi-linear scales (e.g. above 50 $h^{-1}$Mpc). We analyze the broad-range shape of the monopole and quadrupole correlation functions of the BOSS Data Release 12 (DR12) CMASS galaxy sample, at the effective redshift $z=0.59$, to obtain constraints on the Hubble expansion rate $H(z)$, the angular-diameter distance $D_A(z)$, the normalized growth rate $f(z)\sigma_8(z)$, and the physical matter density $\Omega_mh^2$. We obtain robust measurements by including a polynomial as the model for the systematic errors, and find it works very well against the systematic effects, e.g., ones induced by stars and seeing. We provide accurate measurements $\{D_A(0.59)r_{s,fid}/r_s$ $\rm Mpc$, $H(0.59)r_s/r_{s,fid}$ $km s^{-1} Mpc^{-1}$, $f(0.59)\sigma_8(0.59)$, $\Omega_m h^2\}$ = $\{1427\pm26$, $97.3\pm3.3$, $0.488 \pm 0.060$, $0.135\pm0.016\}$, where $r_s$ is the comoving sound horizon at the drag epoch and $r_{s,fid}=147.66$ Mpc is the sound scale of the fiducial cosmology used in this study. The parameters which are not well constrained by our galaxy clustering analysis are marginalized over with wide flat priors. Since no priors from other data sets, e.g., cosmic microwave background (CMB), are adopted and no dark energy models are assumed, our results from BOSS CMASS galaxy clustering alone may be combined with other data sets, i.e., CMB, SNe, lensing or other galaxy clustering data to constrain the parameters of a given cosmological model. The uncertainty on the dark energy equation of state parameter, $w$, from CMB+CMASS is about 8 per cent. The uncertainty on the curvature fraction, $\Omega_k$, is 0.3 per cent. We do not find deviation from flat $\Lambda$CDM.Comment: 15 pages, 11 figures. The latest version matches and the accepted version by MNRAS. A bug in the first version has been identified and fixed in the new version. We have redone the analysis with newest data (BOSS DR12

The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Baryon Acoustic Oscillations in the Data Release 9 Spectroscopic Galaxy Sample

We present measurements of galaxy clustering from the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the Sloan Digital Sky Survey III (SDSS-III). These use the Data Release 9 (DR9) CMASS sample, which contains 264,283 massive galaxies covering 3275 square degrees with an effective redshift z=0.57 and redshift range 0.43 < z < 0.7. Assuming a concordance Lambda-CDM cosmological model, this sample covers an effective volume of 2.2 Gpc^3, and represents the largest sample of the Universe ever surveyed at this density, n = 3 x 10^-4 h^-3 Mpc^3. We measure the angle-averaged galaxy correlation function and power spectrum, including density-field reconstruction of the baryon acoustic oscillation (BAO) feature. The acoustic features are detected at a significance of 5\sigma in both the correlation function and power spectrum. Combining with the SDSS-II Luminous Red Galaxy Sample, the detection significance increases to 6.7\sigma. Fitting for the position of the acoustic features measures the distance to z=0.57 relative to the sound horizon DV /rs = 13.67 +/- 0.22 at z=0.57. Assuming a fiducial sound horizon of 153.19 Mpc, which matches cosmic microwave background constraints, this corresponds to a distance DV(z=0.57) = 2094 +/- 34 Mpc. At 1.7 per cent, this is the most precise distance constraint ever obtained from a galaxy survey. We place this result alongside previous BAO measurements in a cosmological distance ladder and find excellent agreement with the current supernova measurements. We use these distance measurements to constrain various cosmological models, finding continuing support for a flat Universe with a cosmological constant.Comment: 33 page