Research Interests

  • Quasar and Galaxy Evolution in the Early Universe
  • Formation and Growth of Supermassive Black Holes
  • The Intergalactic Medium during the Epoch of Reionization
  • Structure and Dynamics of the Milky Way
  • Machine Learning and Data-Driven Models
  • Image Credit: Christina Eilers

    Current Research Projects

    The Lifetime of Quasars

    Constraints on Quasar Lifetimes from Proximity Zone Measurements

    In the standard picture of black hole growth the rest mass energy of the accreted matter is divided between radiation and black hole growth, implying that the emission of quasar light is concurrent with the build-up of supermassive black holes. Therefore the lifetime of quasars - the time that galaxies shine as luminous quasars - is one of the most fundamental quantities for understanding black hole formation and quasar evolution, but yet it remains uncertain by several orders of magnitude. We developed a new method to constrain quasar lifetimes by measuring the sizes of their proximity zones observed in their rest-frame UV spectra, which is the region of enhanced transmitted flux around the quasar due to its own ionizing radiation. By analyzing a new data set of 34 medium resolution spectra at redshift 5.8 ≤ z ≤ 6.5 we identified a new population of quasars with very small proximity zones, indicating quasar lifetimes of less than 100,000 years. These objects pose a significant challenge to current black hole formation models, which require lifetimes of the order of the Hubble time to grow the observed supermassive black holes in the center of these quasars. For more information please have a look at our paper and at the press release.

    First Spectroscopic Study of a Young Quasar

    The presence of young quasars in the early Universe poses an interesting challenge for current models of the growth and formation of supermassive black holes. We conduct the first comprehensive spectroscopic study of the youngest quasar known, SDSS J1335+3533 at z=5.9012, whose lifetime we estimate to be less than 10,000 years. Deep optical and near-infrared spectra allow us to measure the mass of the central black hole, the Eddington ratio of its mass accretion rate, and its bolometric luminosity, which are consistent with properties of other co-eval quasar of similar luminosity. The only possible anomaly associated with youth are its weak emission lines, but larger samples are needed to shed light on a potential causal connection. We discuss the implications of short quasar lifetimes for various black hole growth scenarios, and argue that future observations of young quasars with JWST could distinguish between them. For details please have a look at our paper.

    Detecting and Characterizing Young Quasars with Multi-Wavelength Observations

    In a multi-wavelength survey of 13 quasars at 5.8 ≤ z ≤ 6.5, we find five objects with extremely small proximity zone sizes that may imply UV-luminous lifetimes of ≤ 100,000 years. We combine sub-mm observations from the Atacama Large Millimetre Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA), as well as deep optical and near-infrared spectra from medium-resolution spectrographs on the Very Large Telescope (VLT) and on the Keck telescopes, in order to identify and characterize new young quasars, which provide valuable clues about the accretion behavior of supermassive black holes in the early universe. We measure the quasars' systemic redshifts, black hole masses, Eddington ratios, emission line luminosities, and star formation rates of their host galaxies. Combined with previous results we estimate the fraction of young objects within the high-redshift quasar population at large to be between 5%-10%, which allows us to set new constraints on the lifetime of the quasar population at large. Details can be found in our paper.

    Here (15 min) and here (5 min) are recent talks about my work on quasar lifetimes and the growth of supermassive black holes.

    The Epoch of Reionization

    The Opacity of the Intergalactic Medium and its Implications for the Epoch of Reionization

    Determining when and how the epoch of reionization proceeded is one of the major goals of observational cosmology today. During this early evolutionary phase of our universe, the cosmic “dark ages” following recombination ended, and the intergalactic medium (IGM) transitioned from a neutral state into the ionized medium that we observe today due to the ultraviolet radiation of the first stars, galaxies and quasars. The details of the reionization process not only reflect the nature of these primordial objects, but also the formation of large scale structure and are therefore a subject of major interest. We present new measurements of the evolution of the mean opacity of the IGM within the Lyman-alpha forest between 4.8 ≲ z ≲ 6.3, which provides constraints about the timing of the reionization process as well as its morphology. More information can be found in our paper. The data set used for this project is publicly available.

    Anomaly in the IGM Opacity of the Lyman-beta Forest

    We present new measurements of the IGM opacity in the Lyman-alpha as well as the Lyman-beta forest along 19 quasar sightlines at high redshift, probing the end stages of the reionization process. Owing to its lower oscillator strength the Lyman-beta transition is sensitive to different gas temperatures and densities than Lyman-alpha, providing additional constraints on the ionization and thermal state of the IGM. A comparison of our measurements to different models of the post-reionization IGM, leads to two primary conclusions: First, we find that including the effects of spectral noise is key for a proper data to model comparison. Second, we find that models which come close to reproducing the distribution of Lyman-alpha effective optical depths nevertheless significantly underpredict the Lyman-beta opacity at the same spatial locations. Check out our paper for more informtaion.

    Dynamics of the Milky Way

    Spectrophotometric Distances to Luminous Red Giant Stars

    With contemporary infrared spectroscopic surveys like APOGEE, red-giant stars can be observed to distances and extinctions at which Gaia parallaxes are not highly informative. Here we employ a linear combination of APOGEE spectral pixel intensities and multi-band photometry from Gaia, 2MASS, and WISE to predict parallaxes spectrophotometrically, using a data-driven model for 45,000 red-giant branch stars that are more luminous than the red clump. We obtain distance estimates with 10% uncertainties out to heliocentric distances of 20 kpc, which enables us to make global maps of the Milky Way’s disk. For more information, please check out our paper. Our predicted spectrophotometric parallaxes are available here.

    The Circular Velocity Curve of the Milky Way out to 25 kpc

    The circular velocity of the Milky Way and in particular its value at the Sun's Galactocentric radius, provide important constraints on the mass distribution of our Galaxy and the local dark matter density. The latter is crucial for interpreting and analyzing any direct as well as indirect detection experiments of dark matter. Furthermore, the local circular velocity at the Sun's location plays an important role when placing the Milky Way in a cosmological context and asking for instance, whether it falls onto the Tully-Fisher relation. Assuming an axisymmetric gravitational potential of the Milky Way we measure its circular velocity by means of Jeans modeling out to a Galactocentric distance of 25 kpc with more than 23,000 luminous red giant stars as a tracer population. We find that the circular velocity curve is gently declining with a very shallow derivative. For more information, please have a look at our paper.

    Dynamical Spiral Perturbation in the Galactic Disk

    The mean Galactocentric radial velocities of luminous red giant stars within the mid-plane of the Milky Way reveal a spiral signature, which could plausibly reflect the response to a non-axisymmetric perturbation of the gravitational potential in the Galactic disk. We apply a simple steady-state toy model of a logarithmic spiral to interpret these observations, and find a good qualitative and quantitative match. Presuming that the amplitude of the gravitational potential perturbation is proportionate to that in the disk's surface mass density, we estimate the surface mass density amplitude. Combined with the local disk density, this implies a surface mass density contrast between the arm and inter-arm regions of approximately 10% at the solar radius, with an increase towards larger Galactocentric radii. Our model constrains the pitch angle of the dynamical spiral arms to be approximately 12°. For details, please have a look at our paper.

    Curriculum Vitae

    Positions

    since 2019: NASA Hubble Fellow at MIT

    Education

    2015-2019: Graduate Student at the Max-Planck Institute for Astronomy in Heidelberg
    2012-2015: Master of Science in Physics at the University of Heidelberg
    2008-2011: Bachelor of Science in Physics at the University of Göttingen

    Honours & Fellowships

    2020: IAU PhD Prize, International Astronomical Union
    2020: Otto Hahn Medal, Max Planck Society
    2020: Doctoral Thesis Award, German Astronomical Society
    2020: KlarText Prize, Prize for Science Communication, Klaus Tschira Foundation
    2020: Heraeus PhD Prize, University of Heidelberg
    2019: NASA Hubble Fellowship
    2019: Pappalardo Fellowship, Massachusetts Institute of Technology
    2016-2018: PhD Fellowship of the German National Academic Foundation
    2017: Ernst Patzer Award
    2016: Max Planck Fellow for the 66th Lindau Nobel Laureate Meeting
    2012-2015: Scholarship of the German National Academic Foundation

    Full CV.

    Image Credit: NASA/STScI

    Science Communication & Outreach

    During my PhD I worked as an Outreach Fellow at the "Haus der Astronomie" - Center for Astronomy Education and Outreach, where I showed groups of visitors our planetarium and the telescopes, guided them through the Max Planck Institute for Astronomy and the outreach center, and explained the astronomical research that is conducted in Heidelberg.

    I have recently been awarded the KlarText Prize, which is an award for science communication. A video and article about my work (in German) can be found here.

    I have written a couple of articles about the growth of black holes and a new map of the Milky Way for a German popular science magazine "Sterne und Weltraum".

    Image Credit: Ingo Knopf

    Contact

    MIT Kavli Institute for Astrophysics and Space Research
    Massachusetts Institute of Technology
    77 Massachusetts Avenue, 37-641
    Cambridge, MA 02139
    USA

    Email: eilers(at)mit.edu
    Phone: +1 (617) 253-7242