SDSS IV MaNGA: Full spectroscopic bulge-disc decomposition of MaNGA
  early-type galaxies
  By applying spectroscopic decomposition methods to a sample of MaNGA
early-type galaxies, we separate out spatially and kinematically distinct
stellar populations, allowing us to explore the similarities and differences
between galaxy bulges and discs, and how they affect the global properties of
the galaxy. We find that the components have interesting variations in their
stellar populations, and display different kinematics. Bulges tend to be
consistently more metal rich than their disc counterparts, and while the ages
of both components are comparable, there is an interesting tail of younger,
more metal poor discs. Bulges and discs follow their own distinct kinematic
relationships, both on the plane of the stellar spin parameter, lambda_R, and
ellipticity, and in the relation between stellar mass and specific angular
momentum, j, with the location of the galaxy as a whole on these planes being
determined by how much bulge and disc it contains. As a check of the physical
significance of the kinematic decompositions, we also dynamically model the
individual galaxy components within the global potential of the galaxy. The
resulting components exhibit kinematic parameters consistent with those from
the spectroscopic decomposition, and though the dynamical modelling suffers
from some degeneracies, the bulges and discs display systematically different
intrinsic dynamical properties. This work demonstrates the value in considering
the individual components of galaxies rather than treating them as a single
entity, which neglects information that may be crucial in understanding where,
when and how galaxies evolve into the systems we see today.
