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| Paper IPM / Astronomy / 16829 |
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Using the MEGAFLOW survey, which consists of a combination of MUSE and UVES observations of 22 quasar fields selected to contain strong MgâII absorbers, we measure the covering fractions of CâIV and MgâII as a function of impact parameter b using a novel Bayesian logistic regression method on unbinned data, appropriate for small samples. We also analyse how the CâIV and MgâII covering fractions evolve with redshift. In the MUSE data, we found 215 z=1â1.5 [OâII] emitters with fluxes >10â17 ergâsâ1âcmâ2 and within 250âkpc of quasar sight-lines. Over this redshift path z=1â1.5â , we have 19 (32) CâIV (MgâII) absorption systems with rest-frame equivalent width (REW) Wr> 0.05âÃ
associated with at least one [OâII] emitter. The covering fractions of zâ1.2 CâIV (MgâII) absorbers with mean Wrâ 0.7âÃ
(1.0âÃ
), exceeds 50 per cent within 23+62â16 (46+18â13â ) kpc. Together with published studies, our results suggest that the covering fraction of CâIV (MgâII) becomes larger (smaller) with time, respectively. For absorption systems that have CâIV but not MgâII, we find in 73 per cent of the cases no [OâII] counterpart. This may indicate that CâIV comes from the intergalactic medium (IGM), i.e. beyond 250âkpc, or that it is associated with lower mass or quiescent galaxies
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