Physical properties of galaxies: towards a consistent comparison between hydrodynamical simulations and SDSS

Abstract

We study the effects of applying observational techniques to derive the properties of simulated galaxies, with the aim of making an unbiased comparison between observations and simulations. For our study, we used fifteen galaxies simulated in a cosmological context using three different feedback and chemical enrichment models, and compared their z = 0 properties with data from the Sloan Digital Sky Survey (SDSS). We show that the physical properties obtained directly from the simulations without post-processing can be very different to those obtained mimicking observational techniques. In order to provide simulators a way to reliably compare their galaxies with SDSS data, for each physical property that we studied -colours, magnitudes, gas and stellar metallicities, mean stellar ages and star formation rates -we give scaling relations that can be easily applied to the values extracted from the simulations; these scalings have in general a high correlation, except for the gas oxygen metallicities. Our simulated galaxies are photometrically similar to galaxies in the blue sequence/green valley, but in general they appear older, passive and with lower metal content compared to most of the spirals in SDSS. As a careful assessment of the agreement/disagreement with observations is the primary test of the baryonic physics implemented in hydrodynamical codes, our study shows that considering the observational biases in the derivation of the galaxies' properties is of fundamental importance to decide on the failure/success of a galaxy formation model.

First results from the IllustrisTNG simulations: the galaxy colour bimodality

“…For Z stars we include approximate corrections from Guidi et al (2016) for the difference between our luminosity weighted fiber-aperture technique and the spectral index fitting technique actually used in Gallazzi et al (2005) (dashed blue and orange lines). In green we show the TNG100-1 trend and its scatter derived by fitting mock SDSS spectra with matched noise and resolution characteristics (see footnote for details).…”

First results from the IllustrisTNG simulations: a tale of two elements – chemical evolution of magnesium and europium

“…between the observationally derived and simulated [Fe/H] values (e.g.,Guidi et al 2016,Figure 2ofNelson et al 2017).The right panel ofFigure 5showsa comparison of the galaxy wide [Mg/H] ratio as a function of stellar mass for quiescent galaxies. As with [Fe/H], simulated [Mg/Fe] values are calculated as the r-band luminosity-weighted [Mg/Fe] average for all stars in the galaxy using the Bruzual & Charlot (2003) models.…”

Horizon-AGN virtual observatory – 1. SED-fitting performance and forecasts for future imaging surveys

“…Beyond the impact of simplistic SFHs (like the τ-model defined in Bruzual A. 1983), metallicity or dust distribution (see also Guidi et al 2016), the performance of SED fitting is extremely sensitive to the choice of photometric filters, the depth of the survey, and flux measurements (see Bernardi et al 2013). Hydrodynamical simulations have already been widely used to test the impact of the photometry extraction, as they allow to work on -often high resolution-mock images of realistic galaxies.…”

“…However, most of the literature is based either on simple phenomenological prescriptions or semi-analytical models, or when the sample is based on hydrodynamical simulation, it consists in no more than a handful of galaxies (e.g. Guidi et al 2016). Hence we still lack a study relying on a sample that combines highly realistic baryon physics with a large cosmological volume (in order to minimize statistical uncertainties), capturing both galaxies' internal properties and environment.…”