[Paper Review] The progenitor set of present-day early-type galaxies

Sugata Kaviraj, Julien Devriendt+3 more|arXiv (Cornell University)|Feb 15, 2006

Astronomy and Astrophysical Research3 citations

TL;DR

This study uses a semi-analytical galaxy formation model within the ΛCDM framework to quantify the progenitor set of present-day early-type galaxies, revealing that less than 50% of their stellar mass resides in early-type progenitors by z≈1, with significant progenitor bias due to missing spiral progenitors. It develops probabilistic color-luminosity criteria to identify likely spiral progenitors, showing that red, luminous spirals (MB < -21.5, B-V > 0.7) have 75–95% chance of becoming early-types, and finds the red sequence is a poor proxy for the true progenitor set at faint magnitudes.

ABSTRACT

We present a comprehensive theoretical study, within a fully realistic semi-analytical framework, of the photometric properties of early-type progenitors in the redshift range 00.7) spirals have ~75-95 percent chance of being a progenitor, while the corresponding probability for large blue spirals (M_B-21). Hence the red sequence is generally not a good proxy for the progenitor set of early-type galaxies.

Motivation & Objective

• To quantify the progenitor set of present-day early-type galaxies across redshifts 0 < z < 1, accounting for luminosity and environment.
• To address progenitor bias in high-redshift studies by identifying spiral galaxies that are likely progenitors of present-day early-types.
• To evaluate the reliability of the red sequence as a proxy for the true progenitor set of early-type galaxies.
• To develop probabilistic prescriptions for including spiral progenitors in high-redshift early-type galaxy evolution studies.

Proposed method

• Uses a fully realistic semi-analytical galaxy formation model within the ΛCDM paradigm to simulate mass assembly and morphological evolution.
• Tracks the formation history of early-type galaxies by identifying galaxies that evolve into present-day early-types via mergers and accretion.
• Compares photometric properties (luminosity, B-V and V-K colours) of spiral progenitors to the general spiral population to derive probabilistic selection criteria.
• Quantifies the fraction of stellar mass in early-type progenitors at z≈1, distinguishing between field and cluster environments.
• Maps the correspondence between the true progenitor set and the red sequence by comparing number and mass distributions in colour-magnitude space.
• Applies rest-frame magnitudes in the Johnson system to ensure consistent photometric comparisons across redshifts.

Experimental results

Research questions

• RQ1 What fraction of the stellar mass in present-day early-type galaxies was in early-type progenitors at z≈1, and how does this vary with luminosity and environment?
• RQ2 How do the photometric properties (luminosity and colour) of spiral galaxies at high redshift relate to their likelihood of becoming early-type galaxies?
• RQ3 To what extent does the red sequence accurately represent the true progenitor set of present-day early-type galaxies?
• RQ4 What is the role of morphological transformation timescales in dense environments compared to the field, and how does this affect progenitor completeness?
• RQ5 Can probabilistic criteria based on luminosity and optical colours reliably identify spiral galaxies that are likely progenitors of early-type galaxies?

Key findings

• Less than 50% of the stellar mass that ends up in present-day early-type galaxies is in early-type progenitors at z≈1 when averaged across all environments.
• In cluster environments, ~70% of early-type galaxies are already in place by z=1, compared to only ~30% in the field, due to faster morphological transformations.
• For large, red spirals (MB < -21.5, B-V > 0.7) at z≈0.5, the probability of being an early-type progenitor is 75–95%, while for blue spirals of similar luminosity it is 50–75%.
• The red sequence is a poor proxy for the true progenitor set at faint magnitudes (MV > -21), where the correspondence breaks down severely despite good agreement at the bright end (MV < -22).
• Spiral progenitors are typically bluer than early-type progenitors, so excluding them biases age-dating of the progenitor population toward older, redder estimates.
• The progenitor set doubles in mass between z≈1 and z=0, indicating that a significant fraction of mass assembles via non-early-type systems at high redshift.