Bulge formation through disc instability

I. Stellar discs

¹ Université Paris XI, 91405 Orsay, France
² Observatoire de Paris/LERMA, PSL University, 61 av. de l’Observatoire, 75014 Paris, France
e-mail: andrea.cattaneo@obspm.fr
³ Institut d’Astrophysique de Paris, CNRS, 98bis Boulevard Arago, 75014 Paris, France
⁴ CEA/IRFU/SAp, 91191 Gif-sur-Yvette Cedex, France
⁵ Université de Cergy-Pontoise, 33 Boulevard du Port, 95011 Cergy, France
⁶ Observatório Nacional do Rio de Janeiro (ON), Rua Gal. José Cristino, 77, Sāo Cristóvão, 20921-400 Rio de Janeiro, RJ, Brazil
⁷ Observatoire de Paris/GEPI, PSL University, 61 av. de l’Observatoire, 75014 Paris, France

Received: 2 August 2019
Accepted: 27 September 2020

Abstract

We use simulations to study the growth of a pseudobulge in an isolated thin exponential stellar disc embedded in a static spherical halo. We observe a transition from later to earlier morphological types and an increase in bar prominence for higher disc-to-halo mass ratios, for lower disc-to-halo size ratios, and for lower halo concentrations. We compute bulge-to-total stellar mass ratios B/T by fitting a two-component Sérsic-exponential surface-density distribution. The final B/T is strongly related to the disc’s fractional contribution f_d to the total gravitational acceleration at the optical radius. The formula B/T = 0.5 f_d^1.8 fits the simulations to an accuracy of 30%, is consistent with observational measurements of B/T and f_d as a function of luminosity, and reproduces the observed relation between B/T and stellar mass when incorporated into the GALICS 2.0 semi-analytic model of galaxy formation.