Volume 562, February 2014
|Number of page(s)||10|
|Published online||04 February 2014|
Nicolaus Copernicus Astronomical Center, Bartycka 18,
2 Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
3 Astronomical Observatory of the Jagiellonian University, Orla 171, 30-244 Cracow, Poland
Received: 14 August 2013
Accepted: 4 November 2013
Context. The Mg II line is of extreme importance in intermediate redshift quasars since it allows us to measure the black hole mass in these sources and to use these sources as probes of the distribution of dark energy in the Universe, as a complementary tool to SN Ia.
Aims. Reliable use of Mg II requires a good understanding of all the systematic effects involved in the measurement of the line properties, including the contamination by Fe II UV emission.
Methods. We performed three spectroscopic observations of a quasar LBQS 2113-4538 (z = 0.956) with the SALT telescope, separated in time by several months and we analyze in detail the mean spectrum and the variability in the spectral shape.
Results. We show that even in our good-quality spectra the Mg II doublet is well fit by a single Lorentzian shape. We tested several models of the Fe II pseudo-continuum and showed that one of them well represents all the data. The amplitudes of both components vary in time, but the shapes do not change significantly. The measured line width of LBQS 2113-4538 identifies this object as a class A quasar. The upper limit of 3% for the contribution of the narrow line region (NLR) to Mg II may suggest that the separation of the broad line region and NLR disappears in this class of objects.
Key words: dark energy / quasars: emission lines / quasars: individual: LBQS 2113-4538
Based on observations made with the Southern African Large Telescope (SALT) under program 2012-1-POL-008 (PI: Czerny).
Fe II template shown in Fig. 8 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/562/A34
© ESO, 2014
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