A Numerical Investigation of the Impact of Inclinations on the Estimates of Photometric and Dynamical Properties of Galaxies
We exploit N-body simulations (GalactICS, Illustris, NIHAO) to study the impact of inclination on the estimates on various photometric and spectroscopic quantities of galaxies such as sizes, surface brightnesses, stellar masses, velocities, and dynamical masses. With the help of radiative transfer codes, we create mock images of galaxies to study the variation in sizes and various structural parameters as a function of inclination. We also generate observed rotation curves for Illustris and NIHAO galaxies to derive dynamical masses after correcting the rotation curves for inclinations. We find that in the dust-free (transparent) case, sizes derived for edge-on and face-on orientations diff er on average by 10% (6%) for the half-light (isophotal) radii of massive galaxies. However, for the same galaxies, the relative change in stellar masses due to inclination is insignificant, as expected for transparent systems. We compare our simulated size and mass measurements against the observed size-mass relation of CALIFA galaxies and conclude that inclination effects can contribute up to 20% of its slope. The inferred slope of the simulated size-mass relation remains in agreement with the observed relation within calculated errors. After correcting rotation curves of galaxies for basic projection effects, we also find the maximum circular velocity for Illustris galaxies varies by as much as 17%. Moreover, the velocity-stellar mass relation of Illustris galaxies is a poor match to observations (Ouellette et al. 2017). These discrepancies are attributed to numerical resolution issues and inadequate feedback prescriptions in Illustris. To circumvent these issues, we use NIHAO zoom-in simulations given their adequate and robust sub-grid physics implementation and find better agreements with observations. The future extension of this study will involve high-resolution zoom-in simulation that account for dust attenuation in a clumpy medium. With dust in the mix, projected galaxy sizes are expected to change significantly.
URI for this recordhttp://hdl.handle.net/1974/24839
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