[Paper Review] The Star Formation History of the Local Group

E. K. Grebel|arXiv (Cornell University)|May 14, 2000

Astronomy and Astrophysical Research4 references3 citations

TL;DR

This paper synthesizes the star formation histories (SFHs) of Local Group galaxies, emphasizing that galaxy mass and environmental effects—such as ram pressure and tidal stripping—are primary drivers of SFH diversity. It proposes that low-mass dwarf irregulars (dIrrs) likely evolve into dwarf spheroidals (dSphs) through environmental processing, supported by observed trends in metallicity, morphology, and star formation episodes.

ABSTRACT

The star formation histories of Local Group galaxies are summarized. The three large spirals are discussed individually, whereas the discussion of the Local Group dwarfs concentrates on differences and commonalities. While Local Group galaxies exhibit an amazing diversity in their star formation and enrichment histories even within the same morphological type, they share a number of common global properties. Major determining factors for their evolution are galaxy mass and environmental effects such as ram pressure and tidal stripping. It seems likely that low-mass dwarf irregular galaxies evolve into dwarf spheroidals.

Motivation & Objective

• To synthesize and compare the star formation histories of Local Group galaxies, particularly focusing on dwarfs.
• To investigate the role of galaxy mass and environmental factors—such as ram pressure and tidal stripping—in shaping SFHs.
• To evaluate the hypothesis that low-mass dIrrs evolve into dSphs through environmental processing.
• To examine the origin of radial population gradients and episodic star formation in dwarf galaxies.
• To address unresolved issues such as the fate of gas in dSphs and the missing satellite problem.

Proposed method

• Compilation and analysis of observed star formation histories from deep photometric surveys of Local Group galaxies.
• Use of morphological classification (dIrr, dE, dSph) to group galaxies and compare their integrated properties.
• Application of scaling relations between absolute magnitude, metallicity, and central surface brightness to infer evolutionary trends.
• Comparison of star formation episodes with galactocentric distance to test environmental effects.
• Incorporation of simulations suggesting that orbital interactions can drive episodic star formation with gaps of a few Gyr.
• Use of kinematic and structural data (e.g., H I detection limits, mass-to-light ratios) to infer gas content and mass loss.

Experimental results

Research questions

• RQ1 What are the dominant factors shaping the star formation histories of Local Group dwarf galaxies?
• RQ2 To what extent do galaxy mass and environmental effects like ram pressure and tidal stripping influence SFHs?
• RQ3 Is there evidence that dwarf irregulars evolve into dwarf spheroidals through environmental processing?
• RQ4 Why do some dSphs, like Tucana, remain isolated and predominantly old despite proximity to massive hosts?
• RQ5 What is the fate of the interstellar gas in dSphs, and how does this relate to their low H I content?

Key findings

• Galaxy mass and environmental effects such as ram pressure and tidal stripping are the primary determinants of star formation history in Local Group galaxies.
• Low-mass dwarf irregulars (dIrrs) show ongoing or episodic star formation, while dSphs are dominated by old and intermediate-age populations with no current star formation.
• Dwarf spheroidals (dSphs) have high mass-to-light ratios and lack detectable H I, suggesting significant mass loss or gas removal.
• The presence of intermediate-age populations increases with Galactocentric distance in Milky Way dSphs, supporting environmental disruption as a driver of SFH evolution.
• Star formation in Carina shows episodic episodes without clear enrichment, suggesting possible accretion or metal loss.
• The observed trends in metallicity, surface brightness, and magnitude across dwarf types support a continuous evolutionary sequence from dIrrs to dSphs.