Insights from Synthetic Star-forming Regions. I. Reliable Mock Observations from SPH Simulations

Abstract

Through synthetic observations of a hydrodynamical simulation of an evolving star-forming region, we assess how the choice of observational techniques affects the measurements of properties which trace star formation. Testing and calibrating observational measurements requires synthetic observations which are as realistic as possible. In this part of the paper series (Paper I), we explore different techniques for how to map the distributions of densities and temperatures from the particle-based simulations onto a Voronoi mesh suitable for radiative transfer and consequently explore their accuracy. We further test different ways to set up the radiative transfer in order to produce realistic synthetic observations. We give a detailed description of all methods and ultimately recommend techniques. We have found that the flux around 20 µm is strongly overestimated when blindly coupling the dust radiative transfer temperature with the hydrodynamical gas temperature. We find that when instead assuming a constant background dust temperature in addition to the radiative transfer heating, the recovered flux is consistent with actual observations. We present around 5800 realistic synthetic observations for Spitzer and Herschel bands, at different evolutionary time-steps, distances and orientations. In the upcoming papers of this series (Paper II, Paper III and Paper IV), we will test and calibrate measurements of the star-formation rate (SFR), gas mass and the star-formation efficiency (SFE) using our realistic synthetic observations.

Synthetic observations of star formation and the interstellar medium

“…They present about 6000 synthetic continuum observations at multiple wavelengths for models of different evolutionary stages, distances and orientations. These resulting synthetic observations are all freely available to the community (Koepferl et al, 2017a). In Koepferl et al (2017b) They used these synthetic observations to test mass estimates using the commonly-applied modified black-body fitting technique.…”

“…The resolution required to make robust synthetic observations of particular tracers is often unclear, and although there have been a few recent efforts to quantify it in particular cases (e.g. Seifried et al, 2017b;Koepferl et al, 2017a), much more work remains to be done on this.…”

Modelling of ionising feedback with Smoothed Particle Hydrodynamics and Monte Carlo Radiative Transfer on a Voronoi grid

“…This type of grid, however, has a known issue when large density gradients are present. The cells at the interface between low density and high density material become elongated and under-resolve the interface (Koepferl et al 2017).…”

“…In order to reconcile the particle-and grid-based descriptions of the diffuse medium we have employed the use of Voronoi grids, which have been successfully used by other authors for postprocessing SPH snapshots (e.g. Hubber et al 2016;Koepferl et al 2017). We test the scheme by successfully applying it to the wellstudied problem of spherical expansion of an H II region.…”

Fast and accurate Voronoi density gridding from Lagrangian hydrodynamics data

“…Some hydrodynamics codes are built explicitly around a moving Voronoi grid (Springel [2010], Duffell and MacFadyen [2011], Vandenbroucke and De Rijcke [2016]) for the above reasons. Others, such as Smoothed Particle Hydrodynamics (SPH) (Lucy [1977], Gingold and Monaghan [1977]), follow a particle representation, however their output is often post-processed with a radiative transfer code, requiring a density grid (Koepferl et al [2016], Clementel et al [2014], Hubber et al [2016]). Due to the fact that SPH particles follow the fluid motion and are thus potentially irregular, the density profile is typically reconstructed using an adaptive mesh refinement scheme (Kurosawa and Hillier [2001], Steinacker et al [2002], Harries et al [2004]) or, more recently, a Voronoi grid (Camps et al [2013]).…”