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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Lehmer, B.D., Brandt, W.N., Alexander, D.M., Bell, E.F., Hornschemeier, A.E., McIntosh, D.H., Bauer, F.E., Gilli, R., Mainieri, V., Schneider, D.P., Silverman, J.D., Steffen, A.T., Tozzi, P. & Wolf, C. (2008). Tracing the mass-dependent star formation history of late-type galaxies using X-ray emission results from the Chandra Deep Fields. The astrophysical journal 681(2): 1163-1182.

Author(s) from Durham


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 (LX/LB) and the X-ray-to-stellar mass mean ratio (LX/M*) for galaxy populations selected by LB and M*, respectively. When analyzing galaxy samples selected via SFR, we find that the mean X-ray-to-SFR ratio (LX/SFR) is consistent with being constant over the entire redshift range for galaxies with SFR = 1-100 Msolar yr-1, 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 LX/LB at z~3 is similar to its value at z=1.4.