THE QUENCHING TIMESCALE AND QUENCHING RATE OF GALAXIES
- CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026 (China)
- Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506 (United States)
The average star formation rate (SFR) in galaxies has been declining since the redshift of 2. A fraction of galaxies quench and become quiescent. We constrain two key properties of the quenching process: the quenching timescale and the quenching rate among galaxies. We achieve this by analyzing the galaxy number density profile in NUV- u color space and the distribution in NUV- u versus u - i color–color diagram with a simple toy-model framework. We focus on galaxies in three mass bins between 10{sup 10} and 10{sup 10.6} M {sub ⊙}. In the NUV- u versus u - i color–color diagram, the red u - i galaxies exhibit a different slope from the slope traced by the star-forming galaxies. This angled distribution and the number density profile of galaxies in NUV- u space strongly suggest that the decline of the SFR in galaxies has to accelerate before they turn quiescent. We model this color–color distribution with a two-phase exponential decline star formation history. The models with an e-folding time in the second phase (the quenching phase) of 0.5 Gyr best fit the data. We further use the NUV- u number density profile to constrain the quenching rate among star-forming galaxies as a function of mass. Adopting an e-folding time of 0.5 Gyr in the second phase (or the quenching phase), we found the quenching rate to be 19%/Gyr, 25%/Gyr and 33%/Gyr for the three mass bins. These are upper limits of the quenching rate as the transition zone could also be populated by rejuvenated red-sequence galaxies.
- OSTI ID:
- 22667193
- Journal Information:
- Astrophysical Journal, Vol. 832, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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