Title: A study of FeII/MgII flux ratio in quasars
Author(s): H.Sameshima, J.Maza, Y.Matsuoka, S.Oyabu, K.Kawara, Y.Yoshii, N.Asami, N.Ienaka, Y.Tsuzuki
Abstract:
According to current chemical enrichment scenarios, alpha-elements such as magnesium are produced predominantly in Type II Supernovae (SNe II), while iron is produced predominantly in SNe Ia. Because of the difference in lifetime of their progenitors, iron enrichment delays relative to alpha-elements by about 1 Gyr. If FeII/MgII, the relative strength of Fe II emission lines and the Mg II 2798 doublet, reflects the Fe/Mg abundance ratio, there will be a break in FeII/MgII at high redshift. Despite of much efforts made by many observational groups, there have been found no signs of such a break. FeII/MgII looks constant from low-redshift up to z=6.4 with large scatter. We present results of spectroscopy of six quasars at z=2 with the Gemini Multi-Object Spectrographs (GMOS) on Gemini-South Telescope. We measured FeII(UV)/MgII flux ratios of these quasars, and confirmed that they are systematically greater than those of z < 0.6 quasars. It is unclear whether this excess is caused by rich Fe abundance at z=2 over low-redshift or by non-abundance effects such as high gas density, strong radiation field, and high microturbulent velocity. In order to study non-abundance effects on FeII(UV)/MgII flux ratio, we measured FeII(UV)/MgII flux ratio of about 10,000 quasars selected from SDSS Quasar Catalog. We confirmed that FeII(UV)/MgII flux ratio correlates with FWHM (Full Width at Half Maximum) of MgII. This correlation is quite similar to those of found in so-called "Eigenvector 1" space. We suggest that a correction of these effects may decrease the scatter of FeII/MgII in high-redshift quasars and make it clear where the break is.