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Old galaxies in the young Universe
A Cimatti1, E Daddi, A Renzini
1INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125, Firenze, Italy. cimatti@arcetri.astro.it
Nature
|July 9, 2004
Summary
Massive spheroidal galaxies, crucial to the local Universe, formed much earlier than expected. This study identifies distant, fully assembled massive galaxies, challenging current models of galaxy evolution.
Area of Science:
- Astronomy and Astrophysics
- Cosmology
- Galaxy Formation and Evolution
Background:
- Massive spheroidal galaxies comprise over half of local Universe stars, featuring old stellar populations and minimal star formation.
- Current models suggest these galaxies form late via hierarchical merging, but their formation timeline and early appearance remain unclear.
Purpose of the Study:
- To investigate the formation timeline of massive spheroidal galaxies.
- To determine if their early appearance is due to evolutionary effects or observational limitations.
Main Methods:
- Spectroscopic analysis to confirm galaxy properties.
- Morphological identification to assess galaxy structure.
- Observation of galaxies at high redshift (1.6 < z < 1.9).
Main Results:
- Identification of four old, fully assembled, massive (10^11 solar masses) spheroidal galaxies.
- These galaxies were found at a redshift (z ~ 1.6-1.9) when the Universe was only about one-quarter of its present age.
- This represents the most distant detection of such massive, mature galaxies to date.
Conclusions:
- Massive early-type galaxies assembled much faster in the early Universe than predicted by theoretical simulations.
- The findings challenge existing models of hierarchical galaxy formation.
- Suggests a more rapid evolutionary pathway for massive galaxy formation in the early cosmos.
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