About Research CV Outreach Links


Welcome!

I am a Senior Lecturer [equivalent to Assistant Prof.] at the Department of Astrophysics, Tel Aviv University.
Before this, I was a Zwicky prize postdoctoral fellow at the Department of Physics, ETH Zurich, and (briefly) a Benoziyo prize postdoctoral fellow at the Benoziyo Center for Astrophysics, Weizmann Institute of Science. I graduated my PhD studies at Tel-Aviv University, working with Prof. Hagai Netzer.

My research focuses on the formation and growth of the most massive black holes in the universe, and how these processes are linked to the galaxies in which these black holes reside. 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 holes themselves and of their host galaxies: their masses, growth rates, energy outputs, and large-scale environments. Other projects deal with the physics of accretion onto supermassive black holes, including the ways in which they switch "on" or "off". All these efforts are pursued by using a wide variety of data: large spectroscopic surveys, detailed near-IR spectroscopy, far-IR imaging and sub-millimeter interferometry - obtained with some of the most advanced ground- and space-based facilities available.

Besides research, I'm trying to stay active in scientific public outreach, through the
Tel-Aviv University Astronomy Club ("TAU Astroclub"), and Astronomy on Tap events in Tel Aviv.


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


My full CV (pdf)
My publications on ADS or arXiv
My profile on ORCID or Google Scholar

Address
School of Physics and Astronomy,
Tel Aviv University,
Tel Aviv 69978, Israel

Office: Kaplun 114

Phone: +972-3-6406108
E-Mail: benny @ astro.tau.ac.il




Research Themes and Highlights


  • New Types of Flares from Accreting Supermassive Black Holes
  • The BAT AGN Spectroscopic Survey (BASS)
  • The Evolving Relations Between Supermassive Black Holes and Their Host Galaxies
  • Evolution of Black Hole Mass and Accretion Rate
  • Black Hole Spins, Accretion Flows, and Radiative Efficiencies in (High-Redshift) Active Black Holes
  • Circumnuclear Gas and Dust in Active Galactic Nuclei


    New Types of Flares from Accreting Supermassive Black Holes

    Using responsive spectroscopic and multi-wavelength follow-up observations to study sudden changes in the accretion flows and gas distribution around supermassive black holes, including:

  • A new class of UV-bright flares from accreting supermassive black holes, characterized by broad Bowen fluorescence emission features -- robustly linked, for the first time, with high-velocity gas in the vicinity of the accreting SMBH (Trakhtenbrot et al., Nature Astronomy, 2019a). Read the press release!

  • An AGN caught "changing "look" on a timescale of months: this is the first case where the lag between the change in continuum and in broad line emission of a "changing-look" AGN has been temporally resolved (Trakhtenbrot et al. 2019b).


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




    BASS is an international collaboration that aims to provide a complete census of the most powerful accreting SMBHs in the local universe. Starting with a complete sample of over 1000 AGN, selected in the ultra-hard X-rays (>10 keV; with Swift/BAT), the BASS team collects and analyzes data from across the electromagnetic spectrum, through large allocations of observing time on a wide variety of advanced observatories (including VLT, Palomar, Keck, NuSTAR, Chandra, VLA, ALMA).
    We provide the community with reliable measuremetns of spectral distributions and features, black hole masses and accretion rates, host properties, and other related physical components (e.g., circumnuclear gas, radio jets).
    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.


    The BASS team has published over 18 papers, including:

  • 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!

  • Identifying a population of close separation (<1 kpc), obscured dual nuclei in the hearts of some powerful active galactic nuclei, using Keck/AO imaging (Koss et al., Nature, 2018).

  • 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 (DR1) is already available, and DR2 is planned for late 2020. Find out more at:  http://www.bass-survey.com/data.html


  • 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 gas-rich, star-forming galaxies accompaning (and interacting with) about one third of fast-growing SMBHs, at z~4.8. The spectral data provided by ALMA indicate that these are "major interactions", but also suggest rotation-dominated gas kinematics in some systems (Trakhtenbrot et al. 2017a, Nguyen et al. 2020).


    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 fast-growing SMBHs at z~4.8:

    A follow-up study of a sample of z~4.8 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:

  • No significant evolution of relations between black hole mass and galaxy total stellar mass up to z~2.5, in the COSMOS field (Suh et al. 2020)

  • 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, 2018).

  • 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).


  • 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).


  • Black Hole Spins, Accretion Flows, 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:

  • Large extragalactic surveys may be missing powerful SMBHs accreting at super-Eddington rates (Pognan, Trakhtenbrot, et al. 2020).

  • 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).

  • Measuring the emission from accretion disks and gas clouds around SMBHs, for a legacy sample of z~1.5 AGN - 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).


  • Circumnuclear 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).



  • Outreach



    Tel-Aviv University Astronomy Club
    Organizing lectures by renowned scientists, sidewalk observations,
    and "open days" at the Wise Observatory.



    Astronomy on Tap Tel Aviv
    Short open talks about the universe, over beer, in the city center.


    Links

  • Department of Astrophysics, Tel Aviv University
  • School of Physics and Astronomy, Tel Aviv University

  • Department of Physics, ETH Zurich
  • Institute for Particle Physics and Astrophysics, ETH Zurich
  • Benoziyo Center for Astrophysics, Weizmann Institute of Science
  • Experimental Astrophysics research group, Weizmann Institute of Science




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