The size--mass and other structural parameter (n,μz,Rz) relations for local bulges/spheroids from multicomponent decompositions

Dexter S. -H. Hon, Alister W. Graham, Nandini Sahu

Submitted on 4 September 2022


We analyse the bulge/spheroid size-(stellar mass), Re,SphM,Sph, relation and spheroid structural parameters for 202 local (predominantly 110 Mpc) galaxies spanning M3×1091012 M and 0.1Re,Sph32 kpc from multicomponent decomposition. The correlations between the spheroid S\'ersic index (nSph), central surface brightness (μ0,Sph), effective half-light radius (Re,Sph), absolute magnitude (MSph) and stellar mass (M,Sph) are explored. We also investigate the consequences of using different scale radii, Rz,Sph, encapsulating a different fraction (z, from 0 to 1) of the total luminosity. The correlation strengths for projected mass densities, Σz and Σz, vary significantly with the choice of z. Spheroid size (Rz,Sph) and mass (M,Sph) are strongly correlated for all light fractions z. We find: log(Re,Sph/kpc)=0.88log(M,Sph/M)9.15 with a small scatter of Δrms=0.24 dex. This result is discussed relative to the \textit{curved} size-mass relation for early-type galaxies due to their discs yielding larger galaxy radii at lower masses. Moreover, the slope of our spheroid size-mass relation is a factor of 3, steeper than reported bulge size-mass relations, and with bulge sizes at M,sph3×109 M which are 2 to 3 times smaller. Finally, we show that the local spheroids align well with quiescent galaxies at z1.25--2.25. In essence, local spheroids and high-z quiescent galaxies appear structurally similar, likely dictated by the virial theorem.


Comment: 19 pages, 15 figures, submitted to MNRAS

Subject: Astrophysics - Astrophysics of Galaxies