Stellar mass fraction and quasar accretion disk size in SDSS J1004+4112 from photometric follow-up

Forés-Toribio, R.; Muñoz, J. A.; Fian, C.; Jiménez-Vicente, J.; Mediavilla, E.
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The gravitational lens SDSS J1004+4112 was the first discovered system where a background quasar is lensed by a galaxy cluster instead of a single galaxy. We use the 14.5-year r-band light curves together with the recently measured time delay of the fourth brightest quasar image (Munõz et al. (2022)) and the mass model from Forés-Toribio et al. (2022) to study the microlensing effect in this system. We constrain the quasar accretion disk size to light-days at 2407Å in the restframe which is compatible with most previous estimates. We also infer the fraction of mass in stars at the positions of the quasar images: $${α _A} = 0.058_{ - 0.032}^{ + 0.024},{α _B} = 0.048_{ - 0.014}^{ + 0.032},{α _C} = 0.018_{ - 0.018}^{ + 0.015}$$ and $${α _D} = 0.008_{ - 0.008}^{ + 0.033}$$ . The stellar fraction estimates are reasonable for intracluster medium although the stellar fractions at images A and B are slightly larger, suggesting the presence of a near undetected galaxy.