Title: A combined photometric and kinematic recipe for evaluating the nature of bulges using the CALIFA sample,
Abstract: Understanding the nature of bulges in disc galaxies can provide important
insights into the formation and evolution of galaxies. For instance, the
presence of a classical bulge suggests a relatively violent history, in
contrast, the presence of simply an inner disc (also referred to as a
"pseudobulge") indicates the occurrence of secular evolution processes in the
main disc. However, we still lack criteria to effectively categorise bulges,
limiting our ability to study their impact on the evolution of the host
galaxies. Here we present a recipe to separate inner discs from classical
bulges by combining four different parameters from photometric and kinematic
analyses: The bulge Sérsic index $n_\mathrm{b}$, the concentration index
$C_{20,50}$, the Kormendy (1977) relation and the inner slope of the radial
velocity dispersion profile $\nabla\sigma$. With that recipe we provide a
detailed bulge classification for a sample of 45 galaxies from the
integral-field spectroscopic survey CALIFA. To aid in categorising bulges
within these galaxies, we perform 2D image decomposition to determine bulge
Sérsic index, bulge-to-total light ratio, surface brightness and effective
radius of the bulge and use growth curve analysis to derive a new concentration
index, $C_{20,50}$. We further extract the stellar kinematics from CALIFA data
cubes and analyse the radial velocity dispersion profile. The results of the
different approaches are in good agreement and allow a safe classification for
approximately $95\%$ of the galaxies. In particular, we show that our new
"inner" concentration index performs considerably better than the traditionally
used $C_{50,90}$ when yielding the nature of bulges. We also found that a
combined use of this index and the Kormendy (1977) relation gives a very robust
indication of the physical nature of the bulge.