About

Professor Anna-Christina Eilers is an observational astrophysicist leading the Cosmic Dawn Group at MIT. Her research focuses on the formation of the first galaxies, quasars, and supermassive black holes in the early universe, during an era known as the Cosmic Dawn. She is interested in the growth of the first supermassive black holes residing in the centers of luminous, distant galaxies called quasars, aiming to understand how black holes evolve from small stellar remnants to billion solar mass black holes within very short cosmic timescales. Eilers develops new methods to study the timescales of quasar activity and supermassive black hole growth phases, with the goal of understanding galaxy and black hole co-evolution, changes in accretion physics in the early universe, and the origins of these early massive black holes. Her approach combines multi-wavelength observations from telescopes around the world and in space, cosmological simulations, and machine learning models. She is heavily involved in programs utilizing NASA’s James Webb Space Telescope to probe deeper into the universe's distant past.

Research topics

• Physics
• Astrophysics
• Astronomy
• Optics

Selected publications

• Suppression of black-hole growth by strong outflows at redshifts 5.8–6.6

  Nature · 2022 · 73 citations

  • Physics
  • Astrophysics
  • Astronomy
  DOI

• Hydrogen reionization ends by <i>z</i> = 5.3: Lyman-α optical depth measured by the XQR-30 sample

  Monthly Notices of the Royal Astronomical Society · 2022 · 277 citations

  • Physics
  • Astrophysics
  • Astronomy

  ABSTRACT The presence of excess scatter in the Ly-α forest at z ∼ 5.5, together with the existence of sporadic extended opaque Gunn-Peterson troughs, has started to provide robust evidence for a late end of hydrogen reionization. However, low data quality and systematic uncertainties complicate the use of Ly-α transmission as a precision probe of reionization’s end stages. In this paper, we assemble a sample of 67 quasar sightlines at z &amp;gt; 5.5 with high signal-to-noise ratios of &amp;gt;10 per ≤15 km s−1 spectral pixel, relying largely on the new XQR-30 quasar sample. XQR-30 is a large program on VLT/X-Shooter which obtained deep (SNR &amp;gt; 20 per pixel) spectra of 30 quasars at z &amp;gt; 5.7. We carefully account for systematics in continuum reconstruction, instrumentation, and contamination by damped Ly-α systems. We present improved measurements of the mean Ly-α transmission over 4.9 &amp;lt; z &amp;lt; 6.1. Using all known systematics in a forward modelling analysis, we find excellent agreement between the observed Ly-α transmission distributions and the homogeneous-UVB simulations Sherwood and Nyx up to z ≤ 5.2 (&amp;lt;1σ), and mild tension (∼2.5σ) at z = 5.3. Homogeneous UVB models are ruled out by excess Ly-α transmission scatter at z ≥ 5.4 with high confidence (&amp;gt;3.5σ). Our results indicate that reionization-related fluctuations, whether in the UVB, residual neutral hydrogen fraction, and/or IGM temperature, persist in the intergalactic medium until at least z = 5.3 (t = 1.1 Gyr after the big bang). This is further evidence for a late end to reionization.

  DOI

• Probing Early Supermassive Black Hole Growth and Quasar Evolution with Near-infrared Spectroscopy of 37 Reionization-era Quasars at 6.3 &lt; z ≤ 7.64

  The Astrophysical Journal · 2021 · 159 citations

  • Astrophysics
  • Physics
  • Astronomy

  Abstract We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range 6.3 &lt; z ≤ 7.64, including 32 quasars at z &gt; 6.5, forming the largest quasar near-infrared spectral sample at this redshift. The spectra, taken with Keck, Gemini, VLT, and Magellan, allow investigations of central black hole mass and quasar rest-frame ultraviolet spectral properties. The black hole masses derived from the Mg ii emission lines are in the range (0.3–3.6) × 10 9 M ⊙ , which requires massive seed black holes with masses ≳10 3 –10 4 M ⊙ , assuming Eddington accretion since z = 30. The Eddington ratio distribution peaks at λ Edd ∼ 0.8 and has a mean of 1.08, suggesting high accretion rates for these quasars. The C iv –Mg ii emission-line velocity differences in our sample show an increase of C iv blueshift toward higher redshift, but the evolutionary trend observed from this sample is weaker than the previous results from smaller samples at similar redshift. The Fe ii /Mg ii flux ratios derived for these quasars up to z = 7.6, compared with previous measurements at different redshifts, do not show any evidence of strong redshift evolution, suggesting metal-enriched environments in these quasars. Using this quasar sample, we create a quasar composite spectrum for z &gt; 6.5 quasars and find no significant redshift evolution of quasar broad emission lines and continuum slope, except for a blueshift of the C iv line. Our sample yields a strong broad absorption line quasar fraction of ∼24%, higher than the fractions in lower-redshift quasar samples, although this could be affected by small sample statistics and selection effects.

  DOI

• A Luminous Quasar at Redshift 7.642

  The Astrophysical Journal Letters · 2021 · 354 citations

  • Physics
  • Astrophysics
  • Astronomy

  Distant quasars are unique tracers to study the formation of the earliest supermassive black holes (SMBHs) and the history of cosmic reionization. Despite extensive efforts, only two quasars have been found at z ≥7.5, due to a combination of their low spatial density and the high contamination rate in quasar selection. We report the discovery of a luminous quasar at z = 7.642, J0313-1806, the most distant quasar yet known. This quasar has a bolometric luminosity of 3.6 × 1013Le. Deep spectroscopic observations reveal a SMBH with a mass of (1.6 ± 0.4) × 109M⊙ in this quasar. The existence of such a massive SMBH just ∼670 million years after the big bang challenges significantly theoretical models of SMBH growth. In addition, the quasar spectrum exhibits strong broad absorption line (BAL) features in C IV and Si IV, with a maximum velocity close to 20% of the speed of light. The relativistic BAL features, combined with a strongly blueshifted C IV emission line, indicate that there is a strong active galactic nucleus (AGN)-driven outflow in this system. Atacama Large Millimeter/submillimeter Array observations detect the dust continuum and [C II] emission from the quasar host galaxy, yielding an accurate redshift of 7.6423 ± 0.0013 and suggesting that the quasar is hosted by an intensely star-forming galaxy, with a star formation rate of ∼200M⊙ yr-1 and a dust mass of ∼7 × 107M⊙. Follow-up observations of this reionizationera BAL quasar will provide a powerful probe of the effects of AGN feedback on the growth of the earliest massive galaxies.

  DOI

• A Significantly Neutral Intergalactic Medium Around the Luminous z = 7 Quasar J0252–0503

  The Astrophysical Journal · 2020 · 143 citations

  • Physics
  • Astrophysics
  • Optics

  Luminous z ≥ 7 quasars provide direct probes of the evolution of supermassive black holes (SMBHs) and the intergalactic medium (IGM) during the epoch of reionization (EoR). The Lyα damping wing absorption imprinted by neutral hydrogen in the IGM can be detected in a single EoR quasar spectrum, allowing the measurement of the IGM neutral fraction toward that line of sight. However, damping wing features have only been detected in two z &amp;gt; 7 quasars in previous studies. In this paper, we present new high-quality optical and near-infrared spectroscopy of the z = 7.00 quasar DES J025216.64-050331.8 obtained with Keck/Near-Infrared Echellette Spectrometer and Gemini/GMOS. By using the Mg ii single-epoch virial method, we find that it hosts a SMBH accreting at an Eddington ratio of λ Edd = 0.7 0.1, consistent with the values seen in other luminous z ∼ 7 quasars. Furthermore, the Lyα region of the spectrum exhibits a strong damping wing absorption feature. The lack of associated metal absorption in the quasar spectrum indicates that this absorption is imprinted by a neutral IGM. Using a state-of-the-art model developed by Davies et al., we measure a volume-averaged neutral hydrogen fraction at z = 7 of within 68% (95%) confidence intervals when marginalizing over quasar lifetimes of. This is the highest IGM neutral fraction yet measured using reionization-era quasar spectra.

  DOI

Frequent coauthors

• Joseph F. Hennawi

  97 shared

• Eduardo Bañados

  77 shared

• Frederick B. Davies

  76 shared

• Feige Wang

  72 shared

• Jinyi Yang

  University of Maryland, College Park

  71 shared

• Sarah E. I. Bosman

  70 shared

• Masafusa Onoue

  Kavli Institute for Theoretical Sciences

  64 shared

• Emanuele Paolo Farina

  60 shared

Awards & honors

• 2026 // Sloan Research Fellowship
• 2025-2027 // MIT “Committed to Caring” honoree
• 2025 // Ludwig Biermann Award, German Astronomical Society
• 2023 // Otto Haxel Prize for Physics
• 2020 // Otto Hahn Medal, Max Planck Society

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