Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Iron Emission in z ~ 6 QSOs and its Possible Implications   We have obtained low-resolution near-infrared spectra of five SDSS QSOs at
5.3 < z < 6.3 using the NICMOS instrument of the Hubble Space Telescope. We
find evidence of emission in the Fe II complex centered near 2500 A (rest) in
all five objects. We estimate Fe II / Mg II 2800 A flux ratios comparable to
those measured in QSOs at lower redshifts, which indicate metallicities near or
above the solar level. We discuss the possible implications of this result
assuming the iron enrichment to have been produced mainly in Type Ia
supernovae.

35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
24
The categories of this paper are: dg-ga
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
26
The categories of this paper are: bayes-an
14
The categories of this paper are: math-ph