Rotation curves of mock EAGLE dwarf galaxies vs simulations

Abstract

The dark matter mass distribution within galaxies has been the subject of extensive studies, leading to the cusp/core problem as one of the main topics of discussion. Mock observations provide a way to bridge the gap between simulations and observations by understanding the source of this discrepancy. In this thesis, we create mock observations of the stellar component of dwarf galaxies from two runs of the EAGLE simulations with different star-formation gas density thresholds, a low threshold (LT) and a high threshold (HT). We use SimSpin to make the observations, and define the observing parameters as those from the MUSE instrument with a redshift of 0.2. The galaxies are observed both with and without atmospheric seeing conditions i.e. a point-spread-function (PSF) convolution of . The kinematics of these galaxies are obtained through GIST, which fits the spectrum of the integral field unit cube and recovers the velocity at each pixel. From the line-of-sight velocity map, we select a slit two pixels wide and recover the rotation curves, which we compare directly with the input EAGLE particle data using a slit of the same size. We find dissimilarities between the two as a result of the fitting routines, which are emphasized by the differences caused by the star formation gas density threshold on the structures of the galaxies. HT galaxies have less ordered rotation which leads to less pronounced absorption lines to be used for the spectrum fit and lower velocities, hence, we find larger discrepancies between the rotation curves at HT than at LT. We attempt different methods of processing one LT galaxy, such as removing the PSF convolution, reducing the signal-to-noise ratio, and changing the spectral template, but the discrepancies remain. In particular, we compare the maximum and the fiducial velocities for the mock observations using the radii from EAGLE and the input EAGLE data and find differences between the two as a result of the choice of radii. In general, the differences between the mocks and EAGLE are not seen across all galaxies, but rather in the sample as a whole. This study demonstrates how we can use instruments such as SimSpin to study the role of observational biases in the study of stellar kinematics.