Identifying the progenitor set of present-day early-type galaxies: a view from the standard model

TL;DR

This study uses a semi-analytical model within the LCDM framework to analyze the properties and evolution of progenitors of present-day early-type galaxies from redshift 0 to 1, highlighting environmental effects and progenitor bias.

Contribution

It introduces probabilistic prescriptions to include spiral progenitors in studies of early-type galaxy evolution, addressing progenitor bias within the standard cosmological model.

Findings

70% of early-types in clusters are in place by z=1

Less than 50% of the stellar mass in early-types at z=0 was in early-type progenitors at z=1

High-probability spiral progenitors can be identified based on luminosity and colour

Abstract

We present a comprehensive theoretical study, using a semi-analytical model within the standard LCDM framework, of the photometric properties of the progenitors of present-day early-type galaxies in the redshift range 0<z<1. We explore progenitors of all morphologies and study their characteristics as a function of the luminosity and local environment of the early-type remnant at z=0. In agreement with previous studies, we find that, while larger early-types are generally assembled later, their luminosity-weighted stellar ages are typically older. In dense cluster-like environments, 70% of early-type systems are `in place' by z=1 and evolve without interactions thereafter, while in the field the corresponding value is 30%. Averaging across all environments at z~1, less than 50% of the stellar mass which ends up in early-types today is actually in early-type progenitors at this redshift, in agreement with recent observational work. We develop probabilistic prescriptions which provide a means of including spiral (i.e. non early-type) progenitors at intermediate and high redshifts, based on their luminosity and optical colours. For example, we find that, at intermediate redshifts (z~0.5), large (M_V<-21.5), red (B-V>0.7) spirals have 75-95% chance of being an early-type progenitor, while the corresponding probability for large blue spirals (M_B<-21.5, B-V<0.7) is 50-75%. The prescriptions developed here can be used to address, from the perspective of the standard model, the issue of `progenitor bias', whereby the exclusion of late-type progenitors in observational studies can lead to inaccurate conclusions regarding the evolution of the early-type population over cosmic time. (abridged)