2008ApJ...681.1163L

We report on the X-ray evolution over the last ~9 Gyr of cosmic history (i.e., since z=1.4) of late-type galaxy populations in the Chandra Deep Field-North and Extended Chandra Deep Field-South (CDF-N and E-CDF-S, respectively; jointly CDFs) survey fields. Our late-type galaxy sample consists of 2568 galaxies, which were identified using rest-frame optical colors and HST morphologies. We utilized X-ray stacking analyses to investigate the X-ray emission from these galaxies, emphasizing the contributions from normal galaxies that are not dominated by active galactic nuclei (AGNs). Over this redshift range, we find significant increases (factors of ~5-10) in the X-ray-to-optical mean luminosity ratio (L_X/L_B) and the X-ray-to-stellar mass mean ratio (L_X/M_*) for galaxy populations selected by L_B and M_*, respectively. When analyzing galaxy samples selected via SFR, we find that the mean X-ray-to-SFR ratio (L_X/SFR) is consistent with being constant over the entire redshift range for galaxies with SFR = 1-100 M_☉/yr, thus demonstrating that X-ray emission can be used as a robust indicator of star formation activity out to z~1.4. We find that the star formation activity (as traced by X-ray luminosity) per unit stellar mass in a given redshift bin increases with decreasing stellar mass over the redshift range z = 0.2-1, which is consistent with previous studies of how star formation activity depends on stellar mass. Finally, we extend our X-ray analyses to Lyman break galaxies at z∼3 and estimate that L_X/L_B at z∼3 is similar to its value at z=1.4.