Black Hole Growth to z = 2 - I: Improved Virial Methods for Measuring M_BH and L/L_Edd

By B. Trakhtenbrot, H. Netzer. 2012

217 citations recorded by the source corpus.

We analyze several large samples of AGN in order to establish the best tools required to study the evolution of black hole mass (M_BH) and normalized accretion rate (L/L_Edd). The data include spectra from the SDSS, 2QZ and 2SLAQ surveys at z<2, and a compilation of smaller samples with 0<z<5. We critically evaluate the usage of the MgII(2798A) and CIV(1549A) lines, and adjacent continuum bands, as estimators of M_BH and L/L_Edd, by focusing on sources where one of these lines is observed together with Hbeta. We present a new, luminosity-dependent bolometric correction for the monochromatic luminosity at 3000A, L_3000, which is lower by a factor of 1.75 than those used in previous studies. We also re-calibrate the use of L_3000 as an indicator for the size of the broad emission line region (R_BLR) and find that R_BLR is proportional to L_3000^0.62. We find that FWHM(MgII)\simeqFWHM(Hb) for all sources with FWHM(MgII)<6000 km/s. Beyond this FWHM, the MgII line width seems to saturate. The spectral region of the MgII line can thus be used to reproduce Hb-based estimates of M_BH and L/L_Edd, with negligible systematic differences and a scatter of 0.3 dex. The width of the CIV line, on the other hand, shows no correlation with either that of the Hb or the MgII lines and we could not identify the reason for this discrepancy. The scatter of M_BH(CIV), relative to M_BH(Hb) is of almost 0.5 dex. Moreover, 46% of the sources have FWHM(CIV)<FWHM(Hb), in contrast with the basic premise of the virial method, which predicts FWHM(CIV)/FWHM(Hbeta)~1.9. Thus, the CIV line cannot be used to obtain precise estimates of M_BH. We conclude by presenting the observed evolution of M_BH and L/L_Edd with cosmic epoch. The steep rise of L/L_Edd with redshift up to z~1 flattens towards the expected maximal value of L/L_Edd~1, with lower-M_BH sources showing higher values of L/L_Edd at all redshifts. [Abridged]

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/51e27b36b2061608c7dd17883432f7fed7276da9

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In Astronomy and Astrophysics

1. D. M. Alexander
2. R. Hickox
3. P. Hopkins
4. L. Hernquist
5. W. N. Brandt
6. Mara Salvato
7. A. Koekemoer
8. H. Netzer

In Instrumentation

1. D. M. Alexander
2. R. Hickox
3. Mara Salvato
4. A. Koekemoer
5. D. Sanders
6. J. Silverman
7. M. Malkan
8. T. Treu

Citations in the corpus

• The dust covering factor in active galactic nuclei (2016, background): “However, the correction factors adopted by different authors differ significantly (e.g. Shen et al. 2011; Trakhtenbrot & Netzer 2012; Runnoe et al. 2012; Krawczyk et al. 2013).”
• BAT AGN Spectroscopic Survey. I. Spectral Measurements, Derived Quantities, and AGN Demographics (2017, methodology): “For sources with broad Hβ we used the same prescription used in Trakhtenbrot & Netzer (2012), which uses the continuum and line emission parameters for virial estimates of MBH: MBH (Hβ )= 1.05×108 ( L5100 1046 ergs−1 )0.65 [FWHM(Hβ ) 103 kms−1 ]2 M , (2) where L5100 is the the monochromatic…”
• Active galactic nuclei: what’s in a name? (2017, background): “Generally speaking the types of AGN discussed herein have masses of 106–1010 M and accretion rates (in terms of L/LEdd) of 0.01–1 (Greene and Ho 2007; Vestergaard et al. 2008; Shen and Kelly 2012; Trakhtenbrot and Netzer 2012).”
• The Mass Relations between Supermassive Black Holes and Their Host Galaxies at 1 < z < 2 with HST-WFC3 (2019, background): “…(or MgII) line that may have unknown systematics, such as a nongravitational component of the gas dynamics of the broad-line region (BLR), when compared to local samples with masses based on broad Balmer lines(i.e., Hα and Hβ; Baskin & Laor 2005; Trakhtenbrot & Netzer 2012; Schulze et al. 2018).”
• The first ultraviolet quasar-stacked spectrum at z ≃ 2.4 from WFC3 (2015, result): “The latter is in agreement with previous results that have found BH mass values from C IV systematically higher, once calibrated with virial mass estimators based on the Mg II (e.g. Shen et al. 2008; Park et al. 2013, but see also Trakhtenbrot & Netzer 2012).”