A numerical twist on the observational spin parameter, $lambda_R$. (arXiv:1811.06148v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Harborne_K/0/1/0/all/0/1">K.E. Harborne</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Power_C/0/1/0/all/0/1">C. Power</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Robotham_A/0/1/0/all/0/1">A.S.G. Robotham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cortese_L/0/1/0/all/0/1">L. Cortese</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Taranu_D/0/1/0/all/0/1">D.S. Taranu</a>
A primary goal of integral field spectroscopic (IFS) surveys is to provide a
statistical census of galaxies classified by their internal kinematics. As a
result, the observational spin parameter, $lambda_R$, has become one of the
most popular methods of quantifying the relative importance of velocity
dispersion and rotation in supporting a galaxy’s inner structure. The goal of
this paper is to examine the relationship between the observationally deduced
$lambda_R$ and one of the most commonly used theoretical spin parameters in
the literature, the Bullock et al. (2001) $lambda’$. Using a set of $N$-body
realisations of galaxies from which we construct mock IFS observations, we
measure $lambda_R$ as an observer would, incorporating the effects of beam
smearing and seeing conditions. Assuming parameters typical of current IFS
surveys, we confirm that there are strong positive correlations between
$lambda_R$ and measurement radius, and strong negative correlations between
$lambda_R$ and size of the PSF, for late-type galaxies; these biases can be
reduced using a recently proposed empirical correction. Once observational
biases are corrected for, we find that $lambda_R$ provides a good
approximation to $sim sqrt{3}/2 ; lambda'(rm R_{rm eff})$, where
$lambda’$ is evaluated for the galactic stellar component within 1 R$_{rm
eff}$.
A primary goal of integral field spectroscopic (IFS) surveys is to provide a
statistical census of galaxies classified by their internal kinematics. As a
result, the observational spin parameter, $lambda_R$, has become one of the
most popular methods of quantifying the relative importance of velocity
dispersion and rotation in supporting a galaxy’s inner structure. The goal of
this paper is to examine the relationship between the observationally deduced
$lambda_R$ and one of the most commonly used theoretical spin parameters in
the literature, the Bullock et al. (2001) $lambda’$. Using a set of $N$-body
realisations of galaxies from which we construct mock IFS observations, we
measure $lambda_R$ as an observer would, incorporating the effects of beam
smearing and seeing conditions. Assuming parameters typical of current IFS
surveys, we confirm that there are strong positive correlations between
$lambda_R$ and measurement radius, and strong negative correlations between
$lambda_R$ and size of the PSF, for late-type galaxies; these biases can be
reduced using a recently proposed empirical correction. Once observational
biases are corrected for, we find that $lambda_R$ provides a good
approximation to $sim sqrt{3}/2 ; lambda'(rm R_{rm eff})$, where
$lambda’$ is evaluated for the galactic stellar component within 1 R$_{rm
eff}$.
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