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An over-massive black hole in a typical star-forming galaxy, 2 billion years after the Big Bang

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Science  10 Jul 2015:
Vol. 349, Issue 6244, pp. 168-171
DOI: 10.1126/science.aaa4506
  • Fig. 1 The observed Keck/MOSFIRE spectrum and best-fit model for the Hβ emission complex of CID–947.

    The data are modeled with a linear continuum (dotted), a broadened iron template (dot-dashed), and a combination of broad and narrow Gaussians (dashed), which correspond to the Hβ and [O III] emission lines (see section S1.2 in the supplementary materials for details regarding the spectral modeling). The broad component of Hβ has a full width at half maximum of FWHM(Hβ) = 11330 km s−1, which results in MBH = 6.9 × 109 M and MBH/M = 1/8. The red dashed line illustrates an alternative scenario, in which the SMBH mass derived from the Hβ line width would result in MBH/M = 1/100 [i.e., FWHM(Hβ) = 3218 km s−1], clearly at odds with the data. The spike at λrest ≃ 4640 Å is due to a sky feature. The bottom panel shows the residuals of the best-fit model.

  • Fig. 2 A comparison of CID–947 with a compilation of observed MBH and M estimates in the local universe

    [adapted from (4), assuming the tabulated bulge-to-total fractions]. CID–947 (red star) has a very high BH-to-stellar mass ratio of MBH/M ≃ 1/10. The asymmetric error bars shown on MBH and M represent measurement-related uncertainties, while the symmetric ones demonstrate systematic uncertainties of 0.3 dex (on MBH) and 0.1 dex (on M). The masses inferred for subsequent growth scenarios are highlighted as empty red stars. The CID–947 system is expected to evolve only mildly in MBH (perhaps to ∼1010 M), but M should grow to at least 2 × 1011 M, and possibly to as much as ∼7 × 1011 M, by z = 0. The local galaxies NGC 1277 and M87, which could be considered as descendants of systems like CID–947, are highlighted as filled symbols [(25) and (27), respectively]. Some studies suggest these galaxies to have somewhat higher MBH, and therefore relatively high mass ratios, of MBH/M = 1/7 and 1/127, respectively (24, 28).

  • Fig. 3 The observed cosmic evolution of the BH-to-stellar mass ratio, MBH/M, and its extrapolation beyond z ∼ 2.

    CID–947 (red star) has MBH/M = 1/8 at z ≃ 3.3, which is higher by a factor of at least ∼50 than the typical value in local, inactive galaxies (at most, MBH/M ∼ 1/500; dotted line). The error bars shown for CID–947 represent only the measurement-related uncertainties, propagating the uncertainties on MBH and on M. The different data points at z < 2 represent typical (median) values for several samples with MBH/M estimates, with uncertainties representing the scatter within each sample [filled symbols, open circles, and open triangles represent samples from (7), (29), and (6), respectively; adapted from (7)]. Even compared to the extrapolation of the evolutionary trend supported by these lower-redshift data, MBH/M ∼ (z + 1)2 [dashed line, scaled as in (30)], CID–947 has a significantly higher MBH/M.

Supplementary Materials

  • An over-massive black hole in a typical star-forming galaxy, 2 billion years after the Big Bang

    Benny Trakhtenbrot, C. Megan Urry, Francesca Civano, David J. Rosario, Martin Elvis, Kevin Schawinski, Hyewon Suh, Angela Bongiorno, Brooke D. Simmons

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

    Download Supplement
    • Data, Methods, and Supplementary Text S1 to S4
    • Figs. S1 to S4
    • Table S1

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