1,721,004 research outputs found
The cool side of Lyman alpha emitters
No full textWe extend a previous study of Lyman alpha emitters (LAEs) based on hydrodynamical cosmological simulations, by including two physical processes important for LAEs: (i) Lyα and continuum luminosities produced by cooling of collisionally excited HI in the galaxy and (ii) dust formation and evolution; we follow these processes on a galaxy-by-galaxy basis. HI cooling on average contributes 16-18 per cent of the Lyα radiation produced by stars, but this value can be much higher in low-mass LAEs and further increased if the HI is clumpy. The continuum luminosity is instead almost completely dominated by stellar sources. The dust content of galaxies scales with their stellar mass, Mdust ~ M0.7*, and stellar metallicity, Z*, such that Mdust ~ Z1.7*. As a result, the massive galaxies have Lyα escape fraction as low as fα = 0.1, with a LAE-averaged value decreasing with redshift: = (0.33, 0.23) at z = (5.7, 6.6). The ultraviolet (UV) continuum escape fraction shows the opposite trend with z, possibly resulting from clumpiness evolution. The model successfully reproduces the observed Lyα and UV luminosity functions at different redshifts and the Lyα equivalent width scatter to a large degree, although the observed distribution appears to be more more extended than the predicted one. We discuss possible reasons for such tension
Photometric and clustering properties of hydrodynamical galaxies in a cosmological volume: results at z= 0
No full textIn this work, we present results for the photometric and clustering properties of galaxies that arise in a Λ cold dark matter hydrodynamical simulation of the local Universe. The present-day distribution of matter was constructed to match the observed large-scale pattern of the IRAS 1.2-Jy galaxy survey. Our simulation follows the formation and evolution of galaxies in a cosmological sphere with a volume of ~1303h-3Mpc3 including supernova feedback, galactic winds, photoheating due to a uniform meta-galactic background and chemical enrichment of the gas and stellar populations. However, we do not consider active galactic nuclei. In the simulation, a total of ~20000 galaxies are formed above the resolution limit, and around 60 haloes are more massive than ~1014Msolar. Luminosities of the galaxies are calculated based on a stellar population synthesis model including the attenuation by dust, which is calculated from the cold gas left within the simulated galaxies. Environmental effects such as colour bimodality and differential clustering power of the hydrodynamical galaxies are qualitatively similar to observed trends. Nevertheless, the overcooling present in the simulations leads to too blue and overluminous brightest cluster galaxies (BCGs). To overcome this, we mimic the late-time suppression of star formation in massive haloes by ignoring recently formed stars with the aid of a simple post-processing recipe. In this way we find luminosity functions, both for field and for group/cluster galaxies, in better agreement with observations. Specifically, the BCGs then follow the observed luminosity-halo mass relation. However, in such a case, the colour bimodality is basically lost, pointing towards a more complex interplay of late suppression of star formation than what is given by the simple scheme adopted
Simulating the effect of active galactic nuclei feedback on the metal enrichment of galaxy clusters
No full text
Cosmology with the pairwise kinematic SZ effect: calibration and validation using hydrodynamical simulations
Full text linkWe study the potential of the kinematic Sunyaev-Zel'dovich (kSZ) effect as a probe for cosmology, focusing on the pairwise method. The main challenge is disentangling the cosmologically interesting mean pairwise velocity from the cluster optical depth and the associated uncertainties on the baryonic physics in clusters. Furthermore, the pairwise kSZ signal might be affected by internal cluster motions or correlations between velocity and optical depth. We investigate these effects using the Magneticum cosmological hydrodynamical simulations, one of the largest simulations of this kind performed to date. We produce thermal SZ and kSZ maps with an area of ≃ 1600 deg2, and the corresponding cluster catalogues with M500c ≳ 3 × 1013 h-1 M☉ and z ≲ 2. From these data sets, we calibrate a scaling relation between the average Compton-y parameter and optical depth. We show that this relation can be used to recover an accurate estimate of the mean pairwise velocity from the kSZ effect, and that this effect can be used as an important probe of cosmology. We discuss the impact of theoretical and observational systematic effects, and find that further work on feedback models is required to interpret future high-precision measurements of the kSZ effect
Evolution of the metal content of the intracluster medium with hydrodynamical simulations
No full textFitting covariance matrix models to simulations
Full text linkData analysis in cosmology requires reliable covariance matrices. Covariance
matrices derived from numerical simulations often require a very large number
of realizations to be accurate. When a theoretical model for the covariance
matrix exists, the parameters of the model can often be fit with many fewer
simulations. We write a likelihood-based method for performing such a fit. We
demonstrate how a model covariance matrix can be tested by examining the
appropriate distributions from simulations. We show that if model
covariance has amplitude freedom, the expectation value of second moment of
distribution with a wrong covariance matrix will always be larger than
one using the true covariance matrix. By combining these steps together, we
provide a way of producing reliable covariances without ever requiring running
a large number of simulations. We demonstrate our method on two examples.
First, we measure the two-point correlation function of halos from a large set
of mock halo catalogs. We build a model covariance with free
parameters, which we fit using our procedure. The resulting best-fit model
covariance obtained from just simulation realizations proves to be as
reliable as the numerical covariance matrix built from the full set. We
also test our method on a setup where the covariance matrix is large by
measuring the halo bispectrum for thousands of triangles for the same set of
mocks. We build a block diagonal model covariance with free parameters as
an improvement over the diagonal Gaussian covariance. Our model covariance
passes the test only partially in this case, signaling that the model
is insufficient even using free parameters, but significantly improves over the
Gaussian one.Comment: Accepted for publication in JCAP. 24 pages, 8 figure
Cosmological simulations of black hole growth: AGN luminosities and downsizing
No full textIn this study, we present a detailed, statistical analysis of black hole growth and the evolution of active galactic nuclei (AGN) using cosmological hydrodynamic simulations run down to z = 0. The simulations self-consistently follow radiative cooling, star formation, metal enrichment, black hole growth and associated feedback processes from both Type II/Ia supernovae and AGN. We consider two simulation runs, one with a large comoving volume of (500 Mpc)3 and one with a smaller volume of (68 Mpc)3 but with a factor of almost 20 higher mass resolution. We compare the predicted statistical properties of AGN with results from large observational surveys. Consistently with previous results, our simulations can widely match observed black hole properties of the local Universe. Furthermore, our simulations can successfully reproduce the evolution of the bolometric AGN luminosity function for both the low-luminosity and the high-luminosity end up to z = 3.0, only at z = 1.5-2.5, the low-luminosity end is overestimated by up to 1 dex. In addition, the smaller but higher resolution run is able to match the observational data of the low bolometric luminosity end at higher redshifts z = 3-4. We also perform a direct comparison with the observed soft and hard X-ray luminosity functions of AGN, including an empirical correction for a torus-level obscuration, and find a similarly good agreement. These results nicely demonstrate that the observed `antihierarchical' trend in the AGN number density evolution (i.e. the number densities of luminous AGN peak at higher redshifts than those of faint AGN) is self-consistently predicted by our simulations. Implications of this downsizing behaviour on active black holes, their masses and Eddington ratios are discussed. Overall, the downsizing behaviour in the AGN number density as a function of redshift can be mainly attributed to the evolution of the gas density in the resolved vicinity of a (massive) black hole (which is depleted with evolving time as a consequence of star formation and AGN feedback)
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