About Research CV Outreach Links


I am a Zwicky prize postdoctoral fellow at the Department of Physics, ETH Zurich.
Before this, I was a Benoziyo prize postdoctoral fellow at the Benoziyo Center for Astrophysics, Weizmann Institute of Science. I graduated my PhD studies at the Department of Astronomy and Astrophysics at Tel-Aviv University, where I worked with Prof. Hagai Netzer.

My research focuses on the formation and evolution of the most massive black holes in the universe, and how these processes are linked to the galaxies that host the black holes. The main theme of my work is the observed cosmic history of mass assembly onto these "Supermassive Black Holes", as probed by measurements of the basic properties of the Black Hole and of their host galaxies - such as masses, growth rates, and energy outputs, extending to early cosmic epochs. Other projects aim at improving our understanding of the physics of accretion onto supermassive black holes. All these efforts are pursued by using a wide variety of data - including large optical spectroscopic surveys, detailed near-IR spectroscopy, far-IR imaging and sub-millimeter interferometry - obtained with some of the most advanced telescopes and instruments available.

At the ETH Zurich I'm working closely with members of the "Observational Cosmology", the "Extragalactic Astrophysics", and the "Galaxy and Black Hole Astrophysics" research groups.

Besides research, I'm trying to stay active in scientific public outreach, through the
Tel-Aviv University Astronomy Club ("TAU Astroclub"). Activities include lectures by renowned scientists, sidewalk observations and "open days" in the Wise Observatory.

[ post-observing-run beer, Hawaii, Feb. 2014 ]

My full CV (pdf)
My publications on ADS or arXiv

Department of Physics,
ETH Zurich,
Wolfgang-Pauli-Strasse 27 / HIT J12.2,
Zurich CH-8093,

Phone: +41-44-6324213
Fax: +41-44-6331238

benny.trakhtenbrot @ phys.ethz.ch


  • The Evolving Relations Between Supermassive Black Holes and Their Host Galaxies

    ALMA reveals the role of galaxy mergers for the fast growth of high-redshift SMBHs and host galaxies:

    Using the innovative Atacama Large Millimeter/submillimeter Array (ALMA), we identified interacting, star-forming galaxies accompaning half of the fast-growing z~4.8 SMBH hosts. The spectral data provided by ALMA indicate that these are "major mergers", but also suggest rotation-dominated gas kinematics in some systems (Trakhtenbrot et al. 2017a).

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

    A Keck-based study of a z~3.3 X-ray selected AGN revealed a SMBH with a mass of one tenth of the normal, star-forming host galaxy (Trakhtenbrot et al., Science, 2015).

    Check out the associated press release!

    Extreme star formation in the host galaxies of the fast-growing SMBHs at z~4.8:

    A follow-up study of the z~4.8 sample of fast-growing black holes, with the Herschel Space Telescope detected very high star formation rates in ~25% of the sources, as well as a "stacked signal" in the remaining 75% (Mor et al. 2012, Netzer et al. 2014).

    The evolution of MBH/Mhost to z~2:

  • The evolving mass function of galaxies and the luminosity function of quasars are used to support a strong evolution of MBH/Mhost~(1+z)2 (Caplar, Lilly & Trakhtenbrot 2015).

  • A combination of the "SF sequence" in galaxies and the BH-host relations are used to suggest a strong evolution in MBH/Mhost (Trakhtenbrot & Netzer 2010).

  • The BAT AGN Spectroscopic Survey (BASS):
      A Complete Census of Supermassive Black Hole Activity in the Local Universe

    BASS is an international collaboration that aims to provide a complete census of the brightest and most powerful SMBHs in the local universe. BASS obtains emission line measurements, black hole masses, and high-quality X-ray observations for a large sample (~1000) of AGN, selected in the hard X-rays (>10 keV) with the BAT instrument on the Swift space observatory.
    As a co-founder and a core-team member of BASS, I contributed extensively to optical spectral analysis, and particularly black hole mass and accretion rate measurements, as well as to general project oversight.

    Some of our published BASS studies include:

  • Showing that radiation pressure and the Eddington ratio dominate the degree of obscuration towards accreting SMBHs (Ricci, Trakhtenbrot et al., Nature, 2017). Read the press release!

  • Finding very limited evidence for a link between the shape of the X-ray SED and the Eddington ratio, contrary to earlier works (Trakhtenbrot et al. 2017c).

  • The first public data release of BASS is now available - find more at:   https://share.phys.ethz.ch/~blackhole/BASS/data.html

  • Black Hole Spins, Accretion Disks, and Radiative Efficiencies in High-Redshift Active Black Holes

    Using insights from accretion disk theory to constrain the accretion process and BH physics in luminous AGN, at z~1-6:

  • The observed first generation of SMBHs, at z~6-7, can be explained with thin, radiatively-efficient accretion disks (Trakhtenbrot, Volonteri & Natarajan 2017b).

  • The most massive active BHs at z~1.5-3.5 have high spins and radiative efficiencies (Trakhtenbrot 2015).

  • Slim accretion disks and high BH spins are common among luminous, SDSS-selected AGNs (Netzer & Trakhtenbrot 2014).

  • Evolution of Black Hole Mass and Accretion Rate

    Measuring MBH and growth rates at high redshifts, using NIR spectroscopy:

  • Faint black holes in the COSMOS field, at z~3.3 - observed with Keck: constraints on the earliest epoch of black hole growth (Trakhtenbrot et al. 2016).
  • The z~4.8 sample - observed with the VLT and Gemini-N: establishing the epoch of fastest growth for the most massive black holes (Trakhtenbrot et al. 2011).
  • The extended z~2.4 & 3.4 samples - observed with Gemini-S: ``mature'' black holes, reaching 10 billion solar masses (Netzer et al. 2007).

  • Evolution of black hole mass, accretion rate and metalicity in large quasar surveys:
  • Improving the "virial" methods for measuring MBH and L/LEdd, and tracing SMBH evolution to z~2 (Trakhtenbrot & Netzer 2012).
  • Analysis of ~10,000 spectra of unobscured accreting black holes from the SDSS (Netzer & Trakhtenbrot 2007).

  • Testing the Physics of Accretion Flows and Gas Dynamics Near Black Holes

    Measuring the emission from accretion disks and gas clouds around SMBHs, for a legacy sample - observed with the VLT/X-Shooter:

  • Measuring accretion flow properties and black hole spin (Capellupo et al. 2016).
  • Testing "virial" methods for measuring black hole masses (Mejia-Restrepo, Trakhtenbrot et al. 2016).
  • The X-Shooter sample: overview and accretion disk physics at z~1.5 (Capellupo et al. 2015).

  • Gas and Dust in Active Galactic Nuclei

    Hot, pure-graphite dust clouds around AGN:
    Matching the WISE and SDSS catalogs of type-I AGN enables to test several trends involving the covering factor of the clouds (Mor & Trakhtenbrot 2011).

    A View of the Narrow Line Region in the infrared:
    An archival Spitzer study to test the relations between the emission and dynamics of the NLR and basic AGN properties (Dasyra et al. 2011).

    Testing the High Accretion Rate Hypothesis in Weak Line Quasars:
    A pilot study of 2 z~3.5 WLQs with Gemini-N (Shemmer et al. 2010).


    TAU Astronomy Club


  • Institute for Astronomy, ETH Zurich
  • Observational Cosmology research group
  • Galaxy and Black Hole Astrophysics research group
  • Extragalactic Astrophysics research group

  • Benoziyo Center for Astrophysics, Weizmann Institute of Science
  • Experimental Astrophysics research group, Weizmann Institute of Science
  • Department of Astrophysics, Tel Aviv University

    This webpage was designed with the kind help of Keren Sharon and Or Graur.
    Images courtesy of NASA, SDSS, AURA, ESO, and Kyuseok Oh.