Evolution of galaxies with episodic star formation at 0.2 < z < 1.0 in COSMOS

Masaru Kajisawa

Using the COSMOS intermediate-band data set taken with Suprime-Cam, we investigated galaxies with episodic star formation at 0.2 < z < 1.0. We constructed the pseudo rest-frame UBV-bands two-color diagram, m_3400-m_4200 vs. m_4200-m_5400 for galaxies with Mv < -20 at 0.2 < z_phot < 1.0, and measured color offsets from a sequence of the continuous star formation models to search for galaxies with episodic star formation, namely, old population + recent bursty star formation or post-starburst galaxies. We found that the dispersion of the color offsets increases with redshift, which suggests that the fraction of galaxies with episodic star formation decreases with time from z~0.9 to z~0.3. At z>0.6, fainter galaxies tend to have the higher fraction of these galaxies. We also classified galaxies into “old + bursty star formation”, “post-starburst”, “continuous star formation”, and “passive evolution” on the two-color diagram, and investigated the physical properties of these populations. We performed the stacking analysis with optical spectra from zCOSMOS survey, and confirmed that the stacked spectra show the characteristic features for each population such as strong Balmer absorption lines, large equivalent widths of emission lines, and so on.