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

TL;DR

This study compares simulated galaxy properties with SDSS observations by applying observational techniques to simulations, providing scaling relations to enable unbiased, consistent comparisons and assess galaxy formation models.

Contribution

It introduces scaling relations to correct simulation data for observational biases, improving the comparison between hydrodynamical simulations and SDSS galaxy observations.

Findings

Simulated galaxies appear older and less metal-rich than SDSS galaxies.

Scaling relations show high correlation for most properties, except ages and metallicities.

Proper bias correction is crucial for evaluating galaxy formation models.

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 galaxy mean stellar ages and gas oxygen metallicities. Our simulated galaxies are photometrically similar to galaxies in the blue cloud/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.