Partial Covering of the Broad Emission Line Region by an Fe I-rich Intervening Weak Mg II Absorber
Four Mg II clouds (with Mg II 2796 equivalent width of 0.14Å) have been detected along the line of sight of quasar HE0001-2340 at z=0.4523. Three of these clouds display properties that are normal for Mg II absorbers; however, the fourth cloud is extremely unusual. It contains Fe I, which is not known to exist in other extragalactic absorbers, as well as Mn II, Ca I, and Ca II. Its Mg II absorption line profile is also indicative of partial covering of the quasar's broad emission line region, with a covering factor of 0.6, implying an extremely small cloud size. We explore Cloudy photoionization models for two possibilities: a cloud with a covering factor of 0.6, and one of 1.0 (full coverage). We conclude that the only way to produce the Fe I observed in the system is by using the model with partial coverage, and show that such models produce a small cloud size, as consistent with this theory. No other published absorption line system is known to partially cover the quasar, except for those covering a gravitational lens. We theorize that such small absorbers (0.01 pc< r <1 pc), with very low temperatures, high quantities of molecular hydrogen, and masses similar to that of the sun must be commonplace, and that they are observed so rarely merely because of the selection effect due to their size. Thousands of similar systems, containing similar bare molecular clouds, may be located in the outskirts of galaxies. This system was studied using resolution R=45,000 data UVES/VLT data from the ESO archive, and research was supported by the National Science Foundation under Grant AST-07138 and by the REU Supplement Program.