EVIDENCE FOR NON-EVOLVING Fe ii/Mg ii RATIOS IN RAPIDLY ACCRETING z ∼ 6 QSOs

By G. D. Rosa, R. Decarli, F. Walter, Xiaohui Fan, Linhua Jiang, J. Kurk, A. Pasquali, Hans-Walter Rix. 2011

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Quasars (QSOs) at the highest known redshift (z ∼ 6) are unique probes of the early growth of supermassive black holes (BHs). Until now, only the most luminous QSOs have been studied, often one object at a time. Here we present the most extensive consistent analysis to date of 4 < z < 6.5 QSOs with observed near-infrared spectra, combining three new z ∼ 6 objects from our ongoing Very Large Telescope–Infrared Spectrometer And Array Camera program with nineteen sources from the literature. The new sources extend the existing Sloan Digital Sky Survey (SDSS) sample toward the faint end of the QSO luminosity function. Using a maximum likelihood fitting routine optimized for our spectral decomposition, we estimate the BH mass (MBH), the Eddington ratio (defined as Lbol/LEdd), and the Fe ii/Mg ii line ratio, a proxy for the chemical abundance, to characterize both the central object and the broad-line region gas. The QSOs in our sample host BHs with masses of ∼109 M☉ that are accreting close to the Eddington luminosity, consistent with earlier results. We find that the distribution of observed Eddington ratios is significantly different than that of a luminosity-matched comparison sample of SDSS QSOs at lower redshift (0.35 < z < 2.25): the average 〈log (Lbol/LEdd)〉 = −0.37 (Lbol/LEdd ∼ 0.43) with a scatter of 0.20 dex for the z > 4 sample and the 〈log (Lbol/LEdd)〉 = −0.80 (Lbol/LEdd ∼ 0.16) with a scatter of 0.24 dex for the 0.35 < z < 2.25 sample. This implies that, at a given luminosity, the MBH at high-z is typically lower than the average MBH of the lower-redshift population, i.e., the z > 4 sources are accreting significantly faster than the lower-redshift ones. We show that the derived Fe ii/Mg ii ratios depend sensitively on the analysis performed: our self-consistent, homogeneous analysis significantly reduces the Fe ii/Mg ii scatter found in previous studies. The measured Fe ii/Mg ii line ratios show no sign of evolution with cosmic time in the redshift range 4 < z < 6.5. If the Fe ii/Mg ii line ratio is used as a secondary proxy of the Fe/Mg abundance ratio, this implies that the QSOs in our sample have undergone a major episode of Fe enrichment in the few 100 Myr preceding the cosmic age at which they are observed.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/127116dfb7b122127fc1b08e8fa60d8607d630b3

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Citations in the corpus

What drives the growth of black holes (2011, background): “However, these samples comprise only the most massive end of the BH distribution, and these quasars appear to be growing more rapidly than their lowerredshift counterparts (De Rosa et al., 2011) indicating that they are also biased to higher Eddington ratios.”
THE PAN-STARRS1 DISTANT z > 5.6 QUASAR SURVEY: MORE THAN 100 QUASARS WITHIN THE FIRST GYR OF THE UNIVERSE (2016, unknown): “…(21) Willott et al. (2009), (22) Carilli et al. (2010), (23) Wang et al. (2010), (24) Willott et al. (2010b), (25) Willott et al. (2010a), (26) De Rosa et al. (2011), (27) Mortlock et al. (2011), (28) Wang et al. (2011), (29) Zeimann et al. (2011), (30) Morganson et al. (2012), (31) Venemans et…”
An ALMA [C ii] Survey of 27 Quasars at z > 5.94 (2018, background): “Both the gas in the broad line region around the central black hole, and the interstellar medium (ISM) of their host galaxies, appear metal-enriched (e.g., Bertoldi et al. 2003a, 2003b; Walter et al. 2003; Beelen et al. 2006; De Rosa et al. 2011; Mortlock et al. 2011).”
The Illustris simulation: the evolving population of black holes across cosmic time (2014, background): “Whereas for quasars at z ∼ 6−7 (Willott et al. 2010; De Rosa et al. 2011) the range of luminosities probed is still relatively narrow, for z .”
SUBARU HIGH-z EXPLORATION OF LOW-LUMINOSITY QUASARS (SHELLQs). I. DISCOVERY OF 15 QUASARS AND BRIGHT GALAXIES AT 5.7 < z < 6.9 (2016, unknown): “The chemical enrichment, and thus the preceding star formation history, can be measured with strong metal emission lines arising from ionized gas around the quasar nuclei (e.g., Jiang et al. 2007; De Rosa et al. 2011, 2014).”
Black Hole Growth to z = 2 - I: Improved Virial Methods for Measuring M_BH and L/L_Edd (2012, background): “Thesesystems could have grown to be the most massive BHs known (MBH ∼ 1010M⊙) as early asz ∼ 4 (Willott et al. 2010; Kurk et al. 2007; De Rosa et al. 2011; Trakhtenbrot et al. 2011, hereafter T11).”
THE FINAL SDSS HIGH-REDSHIFT QUASAR SAMPLE OF 52 QUASARS AT z > 5.7 (2016, background): “13 Alfred P. Sloan Research Fellow. solar or supersolar metallicity, implying that vigorous star formation and element enrichment have occurred in their broad-line regions (e.g., Jiang et al. 2007; Juarez et al. 2009; De Rosa et al. 2011).”
DISCOVERY OF THREE z > 6.5 QUASARS IN THE VISTA KILO-DEGREE INFRARED GALAXY (VIKING) SURVEY (2013, background): “These black hole masses are very similar to those powering quasars at z ∼ 6 that were discovered in the SDSS main survey (e.g., Jiang et al. 2007; Kurk et al. 2007; De Rosa et al. 2011), but generally more massive than those of the z ∼ 6 quasars discovered in the CFHQS (Willott et al. 2010a).”
Physical Properties of 15 Quasars at z ≳ 6.5 (2017, methodology): “We show the quasars in our sample (red squares and, in case of upper limits, down-pointing triangles) and taken from the literature: De Rosa et al. 2011 (blue points) and z .”
BLACK HOLE MASS ESTIMATES AND EMISSION-LINE PROPERTIES OF A SAMPLE OF REDSHIFT z > 6.5 QUASARS (2013, methodology): “The slope coefficients are in agreement within 1σ with both the local slope estimated by De Rosa et al. (2011) and the global value obtained by Decarli et al. (2010).”
STAR FORMATION AND GAS KINEMATICS OF QUASAR HOST GALAXIES AT z ∼ 6: NEW INSIGHTS FROM ALMA (2013, background): “…et al. 2009, 2011; and the Panoramic Survey Telescope and Rapid Response System [Pan-STARRS], Morganson et al. 2012) with optical z-band magnitudes from 18.8 to 24.4 and inferred SMBH masses from 108 to a few 109 M (Kurk et al. 2007; Jiang et al. 2007; Willott et al. 2010; De Rosa et al. 2011).”