“Observations” of simulated dwarf galaxies

Abstract

Context. Apparent deviations between properties of dwarf galaxies from observations and simulations are known to exist, such as the “Missing Dwarfs” problem, the too-big-to-fail problem, and the cusp-core problem, to name a few. Recent studies have shown that these issues can at least be partially resolved by taking into account the systematic differences between simulations and observations. Aims. This work aims to investigate and address any systematic differences affecting the comparison of simulations with observations. Methods. To this aim, we analyzed a set of 24 realistically simulated Models of Realistic dwarfs In Action (MoRIA) dwarf galaxies in an observationally motivated way. We first constructed “observed” color-magnitude diagrams (CMDs) of the simulated dwarf galaxies in the typically used V- and I-bands. Then we used the synthetic CMD-fitting method to recover their star-formation histories (SFHs) from their observed CMDs. These solved SFHs were then directly compared to the true SFHs from the simulation star-particle data, mainly in terms of the star-formation rate (SFR) and the age-metallicity relation (AMR). We also applied a dust extinction prescription to the simulation data to produce observed CMDs affected by dust in the star-forming regions. Since future facilities, such as the James Webb Space Telescope and the European Extremely Large Telescope, will focus on the (near)-infrared rather than the optical, we also constructed and analyzed CMDs consisting of the I- and H- bands. Results. We find a very good agreement between the recovered and the true SFHs of all the simulated dwarf galaxies in our sample, from the synthetic CMD analysis of their V − I versus I as well as the I − H versus H CMDs. Dust leads to an underestimation of the SFR during the last few hundred million years, with the strength and duration of the effect dependent on the dust content. Overall, our analysis indicates that quantities like SFR and AMR derived from the photometric observations of galaxies are directly comparable to their simulated counterparts, thus eliminating any systematic bias in the comparison of simulations and observations.

Star Formation Histories from SEDs and CMDs Agree: Evidence for Synchronized Star Formation in Local Volume Dwarf Galaxies over the Past 3 Gyr

“…When one SFH is slowly varying and smooth, while the other is binned and fluctuates significantly, it can be unclear which case more closely matches the "truth." This makes it crucial for methods to be compared against a ground truth model, as in Rathi et al (2020), where SPH N-body simulations were used to create mock CMDs, allowing for a side by side comparison of SFHs from the CMD method with the input SFHs. Nevertheless, our comparison of these two methods through the metrics introduced in this paper has illuminated robust areas of agreement as well as a few systematics that generate differences between the CMD and SED methods.…”

“…While mostly concordant, the metrics used here have illuminated some fundamental disagreements between the two methods that imply methodological biases in the Dense Basis approach when applied to these low-redshift dwarf galaxies. A symmetrical investigation of the systematics for SFHs determined from CMDs is beyond the scope of this paper but was recently undertaken by Rathi et al (2020). We also looked for systematic disagreements between the Dense Basis results from the observed photometry and those from the mock photometry produced by assuming the CMD SFHs, but nothing significant was found, implying that the CMDs and SEDs reveal consistent information about the ANGST galaxy histories.…”