Sirio Belli

Clay Fellow

Center for Astrophysics
Harvard & Smithsonian


I study the physical properties of high-redshift galaxies, and I am particularly interested in understanding the quenching of star formation and the evolution of the first massive quiescent systems. My research is based on a combination of optical, near-infrared, and submillimeter observations from large ground-based facilities such as Keck, VLT, Magellan, and NOEMA.

I grew up in Italy, went to Caltech for graduate school, spent a few years as a postdoc at the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany, and then moved to the CfA as a Clay Fellow. You can download my full CV here.


By modelling deep absorption-line spectra of high-redshift quiescent galaxies it is possible to measure their star formation history and constrain the quenching timescale. Using a large sample of deep Keck spectra (which is now publicly available) I found that massive galaxies at z~2 can undergo either fast quenching or slow quenching, and these two channels are likely due to distinct physical processes. I have also studied the relation between stellar ages and sizes of early massive galaxies, finding that older galaxies tend to be smaller.

From deep, spatially unresolved spectra of high-redshift quiescent galaxies we can measure the stellar velocity dispersion, which is one of the most fundamental physical properties of galaxies. I have used these velocity dispersions to trace galaxies across cosmic time and also to show that on average quiescent galaxies were rotating much faster in the past compared to today.

The physical properties of the gas content of massive quiescent galaxies can help us understand the physics involved in the star formation quenching. By measuring the Halpha emission line in the KMOS-3D survey carried out at the VLT, I have found a rare population of quiescent galaxies with low-level star formation activity at z~1. I am currently working on a sample of deep LBT spectra targeting the Halpha emission in quiescent galaxies at intermediate redshift.

Observing molecular gas in quiescent galaxies at high redshift is observationally difficult, but is important to constrain models of galaxy quenching. Using deep observations with the NOEMA array, I studied the CO emission in three quiescent systems; these are among the first CO detections at z>1 for these type of galaxies.

I wrote the Flame pipeline to reduce near-infrared spectroscopic data taken with the LUCI spectrograph at the Large Binocular Telescope (LBT). Flame has a highly flexible architecture, which means that it can be easily adapted to reduce spectroscopic data taken with virtually any optical or near-infrared instrument. The pipeline is described in detail in this paper.


Below is a selection of peer-reviewed articles. In the ADS you can find a list of all my publications and a list of my first-author publications.
  1. Sirio Belli, Alessandra Contursi, Reinhard Genzel, et al. (2021)

    The Diverse Molecular Gas Content of Massive Galaxies Undergoing Quenching at z ∼ 1

    ApJ, in press

  2. Sirio Belli, Andrew B. Newman, and Richard S. Ellis (2019)

    MOSFIRE Spectroscopy of Quiescent Galaxies at 1.5 < z < 2.5. II. Star Formation Histories and Galaxy Quenching

  3. Sirio Belli, Alessandra Contursi, and Richard I. Davies (2018)

    Flame: a flexible data reduction pipeline for near-infrared and optical spectroscopy

  4. Andrew B. Newman, Sirio Belli, Richard S. Ellis, and Shannon G. Patel (2018)

    Resolving quiescent galaxies at z > 2: II. Direct measures of rotational support

  5. Sirio Belli, Reinhard Genzel, Natascha M. Förster Schreiber, et al. (2017)

    KMOS-3D reveals low-level star formation activity in massive quiescent galaxies at 0.7 < z < 2.7

  6. Sirio Belli, Andrew B. Newman, and Richard S. Ellis (2017)

    MOSFIRE spectroscopy of quiescent galaxies at 1.5 < z < 2.5. I. Evolution of structural and dynamical properties

  7. Sirio Belli, Andrew B. Newman, and Richard S. Ellis (2015)

    Stellar populations from spectroscopy of a large sample of quiescent galaxies at z > 1: measuring the contribution of progenitor bias to early size growth

  8. Andrew B. Newman, Sirio Belli, and Richard S. Ellis (2015)

    Discovery of a strongly lensed massive quiescent galaxy at z = 2.636: spatially resolved spectroscopy and indications of rotation

  9. Adi Zitrin, Ivo Labbé,
    Sirio Belli, et al. (2015)

    Lyman alpha emission from a luminous z = 8.68 galaxy: implications for galaxies as tracers of cosmic reionization

  10. Sirio Belli, Andrew B. Newman, Richard S. Ellis, and Nick P. Konidaris (2014)

    MOSFIRE absorption line spectroscopy of z > 2 quiescent galaxies: probing a period of rapid size growth

  11. Sirio Belli, Andrew B. Newman, and Richard S. Ellis(2014)

    Velocity dispersions and dynamical masses for a large sample of quiescent galaxies at z > 1: improved measures of the growth in mass and size

  12. Sirio Belli, Tucker Jones, Richard S. Ellis, and Johan Richard (2013)

    Testing the universality of the fundamental metallicity relation at high redshift using low-mass gravitationally lensed galaxies


sirio.belli [at]

Office P-323
Center for Astrophysics
Harvard & Smithsonian
60 Garden St.
Cambridge, MA 02138

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