[Paper Review] Evolution of Stars and Gas in Galaxies

B. M. Tinsley|arXiv (Cornell University)|Mar 3, 2022

Stellar, planetary, and galactic studies64 citations

TL;DR

A comprehensive review of how stellar populations, chemical evolution, and photometric properties interrelate in galaxies, with emphasis on the IMF, star formation history, and environmental/dynamical effects.

ABSTRACT

Essentially everything of astronomical interest is either part of a galaxy, or from a galaxy, or otherwise relevant to the origin or evolution of galaxies. Diverse examples are that the isotropic composition of meteorites provides clues to the history of star formation billions of years ago, and cosmological tests for the deceleration of the Universe are strongly affected by changes in the luminosities of galaxies during the lookback time sampled. The aim of this article is to review some of the vital connections that galaxy evolution makes among many astronomical phenomena.

Motivation & Objective

• Explain how stellar populations trace the formation and evolution of galaxies across morphological types.
• Summarize chemical evolution processes in galaxies, including nucleosynthesis and gas flows.
• Describe how photometric properties of galaxies evolve with star formation history and stellar evolution.
• Discuss the role of dynamics, environment, and galaxy interactions in shaping chemical and photometric evolution.

Proposed method

• Define and discuss the initial mass function (IMF) and star formation rate (SFR) with formal notation: n(m) dm = phi(m) psi(t) dm dt and normalizations.
• Present and interpret the IMF in the Solar neighborhood, including constant and time-varying SFR scenarios.
• Provide analytical IMF approximations as piecewise power laws with slopes corresponding to -x in m^-(1+x) (e.g., the four segments in Eq. 2.9).
• Relate present-day stellar mass distribution n(m) to past and present SFRs via integral relations (e.g., Eq. 2.4–2.7).
• Discuss observational constraints on IMF from star counts, luminosity functions, and mass-to-light ratios.
• Outline how metallicity, gas flows, and star formation history influence chemical and photometric evolution.

Experimental results

Research questions

• RQ1 How do stellar populations and their evolution drive the observable photometric properties of galaxies across Hubble types?
• RQ2 What is the form of the IMF in the Solar neighborhood and how does it relate to past and present star formation rates?
• RQ3 How do chemical enrichment and gas flows shape the metallicity distributions in galaxies and within galactic radii?
• RQ4 To what extent is the IMF universal versus environment- or time-dependent across galaxies?
• RQ5 How do dynamical processes and environmental interactions influence the chemical and photometric evolution of galaxies?

Key findings

• Galaxies show a broad correlation between morphology, stellar populations, and ISM content, with older, redder populations in early-type systems and ongoing star formation in late-type systems.
• Chemical abundances in galaxies decrease outward from centers, and average metallicities tend to increase with galaxy luminosity.
• The IMF in the Solar neighborhood is not well described by a single power law; it is better represented by piecewise segments with increasing slope at higher masses.
• For masses 0.4–50 Msun, the present-day SFR in the Solar neighborhood is about 3.0 Msun pc^-2 Gyr^-1, given a specific IMF normalization.
• Present-day mass distribution n(m) and the IMF can be constrained using star counts, lifetimes, and SFR history, via relations like n(m) = ∫ φ(m) ψ(t) dt and its simplifications under constant or slowly varying SFR.
• Halo versus disk stellar populations show different metallicities and formation histories, with halo stars generally more metal-poor and older.