Near‐Infrared Spectroscopy of High‐Redshift Active Galactic Nuclei. I. A Metallicity–Accretion Rate Relationship

Abstract

We present new near-infrared spectroscopic measurements of the H region for a sample of 29 luminous high-redshift quasars. We have measured the width of H in those sources and added archival H width measurements to create a sample of 92 active galactic nuclei (AGNs) for which H width and rest-frame UV measurements of N v k1240 and C iv k1549 emission lines are available. Our sample spans 6 orders of magnitude in luminosity and includes 31 radio-loud AGNs. It also includes 10 narrow-line Seyfert 1 galaxies and one broad absorption line quasar. We find that metallicity, indicated by the N v/C iv line ratio, is primarily correlated with accretion rate, which is a function of luminosity and H line width. This may imply an intimate relation between starbursts, responsible for the metal enrichment of the nuclear gas, and AGN fueling, represented by the accretion rate. The correlation of metallicity with luminosity, or black hole (BH) mass, is weaker in contrast to recent results that were based on measurements of the width of C iv. We argue that using C iv as a proxy to H in estimating M BH might be problematic and lead to spurious BH mass and accretion rate estimates in individual sources. We discuss the potential implications of our new result in the framework of the starburst-AGN connection and theories of BH growth.

Sub-millimeter detectedz ~ 2 radio-quiet QSOs

“…Compared to the submm detected z ∼ 2 galaxies with broad Hα or broad Hβ from Alexander et al (2008), our sample QSOs all have higher Hα luminosities, but show a considerable overlap in Hα line widths. In continuum luminosity and FWHM Hα , our sample QSOs are very similar to the QSO sample studied by Shemmer et al (2004), but typically an order of magnitude more luminous in the continuum than the QSO sample of .…”

“…Quantities for the latter two samples were recalculated using the scaling relations and cosmology used in this work, and smaller symbols are used for QSOs with redshifts >2.5. The thin and thick arrows show the typical shift of the Shemmer et al (2004) and (Table 3) due to the slightly higher than usual luminosity of L 5100 compared to L Hα (Fig. 5).…”

“…We use the primary QSO samples of Shemmer et al (2004), and Alexander et al (2008) to compare and contrast the properties of our QSO sample. Shemmer et al (2004) present the results of new rest-frame optical spectra of a sample of 29 high-redshift (typically z ∼ 2.3) luminous (L ≥ 10 46 erg s −1 ) QSOs and present the results of new rest-frame optical spectroscopy of 15 luminous QSOs at z ∼ 2.3−3.4.…”

“…Shemmer et al (2004) present the results of new rest-frame optical spectra of a sample of 29 high-redshift (typically z ∼ 2.3) luminous (L ≥ 10 46 erg s −1 ) QSOs and present the results of new rest-frame optical spectroscopy of 15 luminous QSOs at z ∼ 2.3−3.4. Alexander et al (2008) present a sample of z ∼ 2 sub-millimeter detected galaxies (SMGs) which exhibit broad Hα or broad Hβ emission.…”

The low-metallicity QSO HE 2158 − 0107: a massive galaxy growing by accretion of nearly pristine gas from its environment?

“…The metallicities in the BLR were found to be supersolar, reaching 10 Z in some cases, and to be correlated with the AGN luminosity, accretion rate, and BH mass (e.g. Hamann & Ferland 1993;Shemmer et al 2004;Warner et al 2004;Nagao et al 2006;Matsuoka et al 2011), with almost no redshift evolution. This is usually interpreted in Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC) and on observations collected at the European Organisation for Astronomical Reasearch in the Southern Hemisphere, Chile (program 070.B-0418).…”