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We use deep Chandra imaging to measure the distribution of X-ray luminosities (LX) for of star-forming galaxies as a function of stellar mass and redshift, using a Bayesian to push below the nominal X-ray detection limits. Our luminosity distributions all narrow peaks at LX ! 1042 erg s−1 that we associate with star formation, as opposed to that are traced by a broad tail to higher LX. Tracking the luminosity of these peaks as function of stellar mass reveals an ‘X-ray main sequence’ with a constant slope ≈0. 63 ± 0. 03 over 8. 5 ! logM∗/M⊙ ! 11. 5 and 0. 1 ! z ! 4, with a normalization that increases redshift as (1 + z) 3. 79 ± 0. 12. We also compare the peak X-ray luminosities with UV-to-IR of star formation rates (SFRs) to calibrate the scaling between LX and SFR. We find LX ∝ SFR0. 83 × (1 + z) 1. 3, where the redshift evolution and non-linearity likely reflect in high-mass X-ray binary populations of star-forming galaxies. Using galaxies with broader range of SFR, we also constrain a stellar-mass-dependent contribution to LX, likely to low-mass X-ray binaries. Using this calibration, we convert our X-ray main sequence SFRs and measure a star-forming main sequence with a constant slope ≈0. 76 ± 0. 06 and normalization that evolves with redshift as (1 + z) 2. 95 ± 0. 33. Based on the X-ray emission, is no evidence for a break in the main sequence at high stellar masses, although we rule out a turnover given the uncertainties in the scaling of LX to SFR.
Aird et al. (Thu,) studied this question.