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Summary
The formation rate of luminous galaxies remained constant from redshift 2 to 4, while luminous quasars declined significantly. Mergers of luminous galaxies likely trigger quasar activity, explaining this difference.
Area of Science:
- Cosmology
- Galaxy Evolution
- Astrophysics
Background:
- Recent observations indicate a constant formation rate for luminous galaxies (LBG) between redshift (z) 2 and 4.
- Luminous quasar abundance shows a significant drop (factor > 20) from z=2 to z=5.
- Discrepancies in the evolutionary paths of these objects require explanation within the observed redshift range (z=2-4).
Purpose of the Study:
- To reconcile the observed co-evolution of luminous galaxies and quasars.
- To investigate the role of galaxy mergers in triggering quasar activity.
- To predict the behavior of luminous galaxy formation rates at higher redshifts (z>4).
Main Methods:
- Comparative analysis of observational data for Lyman break galaxies (LBGs) and luminous quasars.
- Modeling quasar activity triggered by mergers of luminous LBGs.
- Extrapolation of merger scenario to higher redshifts to test consistency.
Main Results:
- A merger scenario, with quasar lifetimes of 10^7-10^8 years, naturally explains the observed difference in evolution between LBGs and quasars from z=2 to 4.
- The formation rate of luminous LBGs must decrease rapidly at z>4 for consistency with quasar abundance trends.
Conclusions:
- Quasar activity is likely triggered by the merger of luminous LBGs.
- The formation rate of luminous LBGs is predicted to decline sharply beyond z=4, following a specific exponential decay.
- This model provides a unified framework for understanding the evolution of both luminous galaxies and quasars in the early universe.