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Register a new userGalaxy Lookback Evolution Models -- a Comparison with Magneticum Cosmological Simulations and Observations
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We construct empirical models of star-forming galaxy evolution assuming that individual galaxies evolve along well-known scaling relations between stellar mass, gas mass and star formation rate following a simple description of chemical evolution. We test these models by a comparison with observations and with detailed Magneticum high resolution hydrodynamic cosmological simulations. Galaxy star formation rates, stellar masses, gas masses, ages, interstellar medium and stellar metallicities are compared. It is found that these simple lookback models capture many of the crucial aspects of galaxy evolution reasonably well. Their key assumption of a redshift dependent power law relationship between galaxy interstellar medium gas mass and stellar mass is in agreement with the outcome of the complex Magneticum simulations. Star formation rates decline towards lower redshift not because galaxies are running out of gas, but because the fraction of the cold ISM gas, which is capable of producing stars, becomes significantly smaller. Gas accretion rates in both model approaches are of the same order of magnitude. Metallicity in the Magneticum simulations increases with the ratio of stellar mass to gas mass as predicted by the lookback models. The mass metallicity relationships agree and the star formation rate dependence of these relationships is also reproduced. We conclude that these simple models provide a powerful tool for constraining and interpreting more complex models based on cosmological simulations and for population synthesis studies analyzing integrated spectra of stellar populations.
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We perform a set of non--radiative cosmological simulations of a preheated intracluster medium in which the entropy of the gas was uniformly boosted at high redshift. The results of these simulations are used first to test the current analytic techniques of preheating via entropy input in the smooth accretion limit. When the unmodified profile is taken directly from simulations, we find that this model is in excellent agreement with the results of our simulations. This suggests that preheated efficiently smoothes the accreted gas, and therefore a shift in the unmodified profile is a good approximation even with a realistic accretion history. When we examine the simulation results in detail, we do not find strong evidence for entropy amplification, at least for the high-redshift preheating model adopted here. In the second section of the paper, we compare the results of the preheating simulations to recent observations. We show -- in agreement with previous work -- that for a reasonable amount of preheating, a satisfactory match can be found to the mass-temperature and luminosity-temperature relations. However -- as noted by previous authors -- we find that the entropy profiles of the simulated groups are much too flat compared to observations. In particular, while rich clusters converge on the adiabatic self--similar scaling at large radius, no single value of the entropy input during preheating can simultaneously reproduce both the core and outer entropy levels. As a result, we confirm that the simple preheating scenario for galaxy cluster formation, in which entropy is injected universally at high redshift, is inconsistent with observations.
We present cosmological zoom-in hydro-dynamical simulations for the formation of disc galaxies, implementing dust evolution and dust promoted cooling of hot gas. We couple an improved version of our previous treatment of dust evolution, which adopts the two-size approximation to estimate the grain size distribution, with the MUPPI star formation and feedback sub-resolution model. Our dust evolution model follows carbon and silicate dust separately. To distinguish differences induced by the chaotic behaviour of simulations from those genuinely due to different simulation set-up, we run each model six times, after introducing tiny perturbations in the initial conditions. With this method, we discuss the role of various dust-related physical processes and the effect of a few possible approximations adopted in the literature. Metal depletion and dust cooling affect the evolution of the system, causing substantial variations in its stellar, gas and dust content. We discuss possible effects on the Spectral Energy Distribution of the significant variations of the size distribution and chemical composition of grains, as predicted by our simulations during the evolution of the galaxy. We compare dust surface density, dust-to-gas ratio and small-to-big grain mass ratio as a function of galaxy radius and gas metallicity predicted by our fiducial run with recent observational estimates for three disc galaxies of different masses. The general agreement is good, in particular taking into account that we have not adjusted our model for this purpose.
The evolution of the metal content of galaxies and its relations to other global properties [such as total stellar mass (M*), circular velocity, star formation rate (SFR), halo mass, etc.] provides important constraints on models of galaxy formation. Here we examine the evolution of metallicity scaling relations of simulated galaxies in the Galaxies-Intergalactic Medium Interaction Calculation suite of cosmological simulations. We make comparisons to observations of the correlation of gas-phase abundances with M* (the mass-metallicity relation, MZR), as well as with both M* and SFR or gas mass fraction (the so-called 3D fundamental metallicity relations, FMRs). The simulated galaxies follow the observed local MZR and FMRs over an order of magnitude in M*, but overpredict the metallicity of massive galaxies (log M* > 10.5), plausibly due to inefficient feedback in this regime. We discuss the origin of the MZR and FMRs in the context of galactic outflows and gas accretion. We examine the evolution of mass-metallicity relations defined using different elements that probe the three enrichment channels (SNII, SNIa, and AGB stars). Relations based on elements produced mainly by SNII evolve weakly, whereas those based on elements produced preferentially in SNIa/AGB exhibit stronger evolution, due to the longer timescales associated with these channels. Finally, we compare the relations of central and satellite galaxies, finding systematically higher metallicities for satellites, as observed. We show this is due to the removal of the metal poor gas reservoir that normally surrounds galaxies and acts to dilute their gas-phase metallicity (via cooling/accretion onto the disk), but is lost due to ram pressure stripping for satellites.
High-redshift Lyman-alpha blobs (LABs) are an enigmatic class of objects that have been the subject of numerous observational and theoretical investigations. It is of particular interest to determine the dominant power sources for the copious luminosity, as direct emission from HII regions, cooling gas, and fluorescence due to the presence of active galactic nuclei (AGN) can all contribute significantly. In this paper, we present the first theoretical model to consider all of these physical processes in an attempt to develop an evolutionary model for the origin of high-z LABs. This is achieved by combining a series of high-resolution cosmological zoom-in simulations with ionization and Lyman-alpha (Lya) radiative transfer models. We find that massive galaxies display a range of Lya luminosities and spatial extents (which strongly depend on the limiting surface brightness used) over the course of their lives, though regularly exhibit luminosities and sizes consistent with observed LABs. The model LABs are typically powered from a combination of recombination in star-forming galaxies, as well as cooling emission from gas associated with accretion. When AGN are included in the model, the fluorescence caused by AGN-driven ionization can be a significant contributor to the total Lya luminosity as well. We propose that the presence of an AGN may be predicted from the Gini coefficient of the blobs surface brightness. Within our modeled mass range, there are no obvious threshold physical properties that predict appearance of LABs, and only weak correlations of the luminosity with the physical properties of the host galaxy. This is because the emergent Lya luminosity from a system is a complex function of the gas temperature, ionization state, and Lya escape fraction.
Cosmological hydrodynamical simulations are rich tools to understand the build-up of stellar mass and angular momentum in galaxies, but require some level of calibration to observations. We compare predictions at $zsim0$ from the Eagle, Hydrangea, Horizon-AGN, and Magneticum simulations with integral field spectroscopic (IFS) data from the SAMI Galaxy Survey, ATLAS3D, CALIFA and MASSIVE surveys. The main goal of this work is to simultaneously compare structural, dynamical, and stellar population measurements in order to identify key areas of success and tension. We have taken great care to ensure that our simulated measurement methods match the observational methods as closely as possible. We find that the Eagle and Hydrangea simulations reproduce many galaxy relations but with some offsets at high stellar masses. There are moderate mismatches in $R_e$ (+), $epsilon$ (-), $sigma_e$ (-), and mean stellar age (+), where a plus sign indicates that quantities are too high on average, and minus sign too low. The Horizon-AGN simulations qualitatively reproduce several galaxy relations, but there are a number of properties where we find a quantitative offset to observations. Massive galaxies are better matched to observations than galaxies at low and intermediate masses. Overall, we find mismatches in $R_e$ (+), $epsilon$ (-), $sigma_e$ (-) and $(V/sigma)_e$ (-). Magneticum matches observations well: this is the only simulation where we find ellipticities typical for disk galaxies, but there are moderate differences in $sigma_e$ (-), $(V/sigma)_e$ (-) and mean stellar age (+). Our comparison between simulations and observational data has highlighted several areas for improvement, such as the need for improved modelling resulting in a better vertical disk structure, yet our results demonstrate the vast improvement of cosmological simulations in recent years.
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