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Decomposed Stellar Kinematics of Galaxy Bulges and Disks

Published onJun 01, 2020
Decomposed Stellar Kinematics of Galaxy Bulges and Disks

We investigate the stellar kinematics of the bulge and disk components in 826 galaxies with a wide range of morphological types from the Sydney-AAO Multi-object Integral-field spectroscopy (SAMI) Galaxy Survey. The spatially-resolved rotation velocity and velocity dispersion of bulge and disk components have been simultaneously estimated using the penalized pixel fitting (pPXF) method with photometrically defined weights for the two components. We introduce a new subroutine of pPXF for dealing with degeneracy in the solutions. We show that the total rotational velocity and velocity dispersions in each galaxy can be reconstructed using the kinematics and weights of the bulge and disk components. The agreement between the reconstructed and observed kinematics suggests the combination of two distinct components provides a consistent description of the kinematics of galaxies. We present Tully-Fisher and Faber-Jackson relations showing that the galaxy stellar mass scales with kinematics for both bulge and disk components of all galaxy types. We find a tight Faber-Jackson relation even for the disk component. We show that the bulge and disk components are kinematically distinct: (1) the two components show scaling relations with similar slopes, but dif- ferent intercepts; (2) the spin parameter indicates bulges are pressure-dominated systems and disks are supported by rotation; (3) the bulge and disk components have, respectively, low and high values in intrinsic ellipticity. Our findings suggest that the relative contributions of bulge and disk components explain, at least to first order, the complex kinematic behavior of galaxies according to galaxy type.

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