The stellar mass Fundamental Plane: the virial relation and a very thin plane for slow rotators
Abstract
Earlytype galaxies  slow and fast rotating ellipticals (ESRs and EFRs) and S0s/lenticulars  define a Fundamental Plane (FP) in the space of halflight radius R_{e}, enclosed surface brightness I_{e}, and velocity dispersion σ_{e}. Since I_{e} and σ_{e} are distanceindependent measurements, the thickness of the FP is often expressed in terms of the accuracy with which I_{e} and σ_{e} can be used to estimate sizes R_{e}. We show that: (1) The thickness of the FP depends strongly on morphology. If the sample only includes ESRs, then the observed scatter in R_{e} is $\sim 16{{\ \rm per\ cent}}$ , of which only $\sim 9{{\ \rm per\ cent}}$ is intrinsic. Removing galaxies with M_{*} < 10^{11} M_{☉} further reduces the observed scatter to $\sim 13{{\ \rm per\ cent}}$ ( $\sim 4{{\ \rm per\ cent}}$ intrinsic). The observed scatter increases to $\sim 25{{\ \rm per\ cent}}$ usually quoted in the literature if EFRs and S0s are added. If the FP is defined using the eigenvectors of the covariance matrix of the observables, then the ESRs again define an exceptionally thin FP, with intrinsic scatter of only 5 per cent orthogonal to the plane. (2) The structure within the FP is most easily understood as arising from the fact that I_{e} and σ_{e} are nearly independent, whereas the R_{e}I_{e} and R_{e}σ_{e} correlations are nearly equal and opposite. (3) If the coefficients of the FP differ from those associated with the virial theorem the plane is said to be 'tilted'. If we multiply I_{e} by the global stellar masstolight ratio M_{*}/L and we account for nonhomology across the population by using Sérsic photometry, then the resulting stellar mass FP is less tilted. Accounting selfconsistently for M_{*}/L gradients will change the tilt. The tilt we currently see suggests that the efficiency of turning baryons into stars increases and/or the dark matter fraction decreases as stellar surface brightness increases.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 May 2020
 DOI:
 10.1093/mnras/staa1064
 arXiv:
 arXiv:2004.07847
 Bibcode:
 2020MNRAS.494.5148B
 Keywords:

 galaxies: elliptical and lenticular;
 cD;
 galaxies: fundamental parameters;
 galaxies: structure;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 13 pages, 9 figures, 3 tables, accepted for publication in MNRAS