Do the Most Massive Black Holes at z = 2 Grow via Major Mergers?

M. Mechtley, K. Jahnke, R. A. Windhorst, R. Andrae, M. Cisternas, S. H. Cohen, T. Hewlett, A. M. Koekemoer, M. Schramm, A. Schulze, J. D. Silverman, C. Villforth, A. van der Wel, L. Wisotzki

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Abstract

The most frequently proposed model for the origin of quasars holds that the high accretion rates seen in luminous active galactic nuclei (AGN) are primarily triggered during major mergers between gas-rich galaxies. While plausible for decades, this model has only begun to be tested with statistical rigor in the past few years. Here, we report on a Hubble Space Telescope study to test this hypothesis for z = 2 quasars with high supermassive black hole masses ( ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn1.gif] $M_BH=10^9--10^10M_odot $ ), which dominate cosmic black hole growth at this redshift. We compare Wide Field Camera 3 ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn2.gif] $F160W$ (rest-frame V -band) imaging of 19 point source-subtracted quasar hosts to a matched sample of 84 inactive galaxies, testing whether the quasar hosts have greater evidence for strong gravitational interactions. Using an expert ranking procedure, we find that the quasar hosts are uniformly distributed within the merger sequence of inactive galaxies, with no preference for quasars in high-distortion hosts. Using a merger/non-merger cutoff approach, we recover distortion fractions of ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn3.gif] $f_m,qso=0.39pm 0.11$ for quasar hosts and ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn4.gif] $f_m,gal=0.30pm 0.05$ for inactive galaxies (distribution modes, 68% confidence intervals), with both measurements subjected to the same observational conditions and limitations. The slight enhancement in distorted fraction for quasar hosts over inactive galaxies is not significant, with a probability that the quasar fraction is higher ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn5.gif] $P(f_m,qsogt f_m,gal)=0.78$ ( ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn6.gif] $0.78sigma $ ), in line with results for lower mass and lower z AGN. We find no evidence that major mergers are the primary triggering mechanism for the massive quasars that dominate accretion at the peak of cosmic quasar activity.
Original languageEnglish
Pages (from-to)156
Number of pages1
JournalAstrophysical Journal
Volume830
Issue number2
Publication statusPublished - 19 Oct 2016

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merger
quasars
galaxies
accretion
active galactic nuclei
confidence interval
ranking
point source
extremely high frequencies
Hubble Space Telescope
point sources
gas
confidence
cut-off
cameras
intervals
augmentation

Cite this

Mechtley, M., Jahnke, K., Windhorst, R. A., Andrae, R., Cisternas, M., Cohen, S. H., ... Wisotzki, L. (2016). Do the Most Massive Black Holes at z = 2 Grow via Major Mergers? Astrophysical Journal, 830(2), 156.

Do the Most Massive Black Holes at z = 2 Grow via Major Mergers? / Mechtley, M.; Jahnke, K.; Windhorst, R. A.; Andrae, R.; Cisternas, M.; Cohen, S. H.; Hewlett, T.; Koekemoer, A. M.; Schramm, M.; Schulze, A.; Silverman, J. D.; Villforth, C.; Wel, A. van der; Wisotzki, L.

In: Astrophysical Journal, Vol. 830, No. 2, 19.10.2016, p. 156.

Research output: Contribution to journalArticle

Mechtley, M, Jahnke, K, Windhorst, RA, Andrae, R, Cisternas, M, Cohen, SH, Hewlett, T, Koekemoer, AM, Schramm, M, Schulze, A, Silverman, JD, Villforth, C, Wel, AVD & Wisotzki, L 2016, 'Do the Most Massive Black Holes at z = 2 Grow via Major Mergers?', Astrophysical Journal, vol. 830, no. 2, pp. 156.
Mechtley M, Jahnke K, Windhorst RA, Andrae R, Cisternas M, Cohen SH et al. Do the Most Massive Black Holes at z = 2 Grow via Major Mergers? Astrophysical Journal. 2016 Oct 19;830(2):156.
Mechtley, M. ; Jahnke, K. ; Windhorst, R. A. ; Andrae, R. ; Cisternas, M. ; Cohen, S. H. ; Hewlett, T. ; Koekemoer, A. M. ; Schramm, M. ; Schulze, A. ; Silverman, J. D. ; Villforth, C. ; Wel, A. van der ; Wisotzki, L. / Do the Most Massive Black Holes at z = 2 Grow via Major Mergers?. In: Astrophysical Journal. 2016 ; Vol. 830, No. 2. pp. 156.
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abstract = "The most frequently proposed model for the origin of quasars holds that the high accretion rates seen in luminous active galactic nuclei (AGN) are primarily triggered during major mergers between gas-rich galaxies. While plausible for decades, this model has only begun to be tested with statistical rigor in the past few years. Here, we report on a Hubble Space Telescope study to test this hypothesis for z = 2 quasars with high supermassive black hole masses ( ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn1.gif] $M_BH=10^9--10^10M_odot $ ), which dominate cosmic black hole growth at this redshift. We compare Wide Field Camera 3 ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn2.gif] $F160W$ (rest-frame V -band) imaging of 19 point source-subtracted quasar hosts to a matched sample of 84 inactive galaxies, testing whether the quasar hosts have greater evidence for strong gravitational interactions. Using an expert ranking procedure, we find that the quasar hosts are uniformly distributed within the merger sequence of inactive galaxies, with no preference for quasars in high-distortion hosts. Using a merger/non-merger cutoff approach, we recover distortion fractions of ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn3.gif] $f_m,qso=0.39pm 0.11$ for quasar hosts and ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn4.gif] $f_m,gal=0.30pm 0.05$ for inactive galaxies (distribution modes, 68{\%} confidence intervals), with both measurements subjected to the same observational conditions and limitations. The slight enhancement in distorted fraction for quasar hosts over inactive galaxies is not significant, with a probability that the quasar fraction is higher ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn5.gif] $P(f_m,qsogt f_m,gal)=0.78$ ( ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn6.gif] $0.78sigma $ ), in line with results for lower mass and lower z AGN. We find no evidence that major mergers are the primary triggering mechanism for the massive quasars that dominate accretion at the peak of cosmic quasar activity.",
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AU - Cisternas, M.

AU - Cohen, S. H.

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N2 - The most frequently proposed model for the origin of quasars holds that the high accretion rates seen in luminous active galactic nuclei (AGN) are primarily triggered during major mergers between gas-rich galaxies. While plausible for decades, this model has only begun to be tested with statistical rigor in the past few years. Here, we report on a Hubble Space Telescope study to test this hypothesis for z = 2 quasars with high supermassive black hole masses ( ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn1.gif] $M_BH=10^9--10^10M_odot $ ), which dominate cosmic black hole growth at this redshift. We compare Wide Field Camera 3 ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn2.gif] $F160W$ (rest-frame V -band) imaging of 19 point source-subtracted quasar hosts to a matched sample of 84 inactive galaxies, testing whether the quasar hosts have greater evidence for strong gravitational interactions. Using an expert ranking procedure, we find that the quasar hosts are uniformly distributed within the merger sequence of inactive galaxies, with no preference for quasars in high-distortion hosts. Using a merger/non-merger cutoff approach, we recover distortion fractions of ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn3.gif] $f_m,qso=0.39pm 0.11$ for quasar hosts and ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn4.gif] $f_m,gal=0.30pm 0.05$ for inactive galaxies (distribution modes, 68% confidence intervals), with both measurements subjected to the same observational conditions and limitations. The slight enhancement in distorted fraction for quasar hosts over inactive galaxies is not significant, with a probability that the quasar fraction is higher ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn5.gif] $P(f_m,qsogt f_m,gal)=0.78$ ( ##IMG## [http://ej.iop.org/images/0004-637X/830/2/156/apjaa36f1ieqn6.gif] $0.78sigma $ ), in line with results for lower mass and lower z AGN. We find no evidence that major mergers are the primary triggering mechanism for the massive quasars that dominate accretion at the peak of cosmic quasar activity.

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