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Fig. 5.


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Left: CO(1–0) line luminosity versus infrared luminosity integrated over 8−1000 μm for our sample of unobscured QSOs, coloured as a function of offset from the MS. The CO(1–0) luminosities have been calculated using r21 = 0.86 (Kirkpatrick et al. 2019), and LIR has been corrected for AGN contamination. For comparison, we have plotted the low–redshift Palomar–Green QSOs from Shangguan et al. (2020b), high–redshift obscured (filled grey circles) and unobscured (open grey circles) QSOs from the compilation presented in Perna et al. (2018), a sample of high–redshift SMGs (black stars) and z = 1 − 3 SFGs from ASPECS (Boogaard et al. 2020, blue crosses). Where necessary, all quantities have been corrected for magnification. The black solid and dashed lines show the relation expected for main sequence and starburst galaxies at 0 < z < 3 from Sargent et al. (2014), respectively. Similar to other samples of QSOs at both low and high redshift, most of the z ∼ 1.5 QSOs lie below the relation for main sequence galaxies. Right: ratio of LIR/, used as a probe for star formation efficiency, versus redshift. The vertical line on the right shows the mean error of the comparison samples. Our targets show a large scatter, with a median LIR/ = 350 ± 170 L K km s−1 pc2. For comparison, high–redshift QSOs have a ratio of LIR/, and SMGs show LIR/.

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