Richard Ellis

Astronomy 249-17, Caltech

Pasadena CA 91125

Overview of Research:

I am working primarily in observational cosmology addressing issues related to the nature of the world model, the origin and evolution of galaxies, the growth of large scale structure and the nature and distribution of dark matter. My recent focus is on addressing the origin of the earliest galaxies and understanding their role in cosmic reionisation.I am enthusiastic about the use of new instruments and observational opportunities when they further the progress that can be made in these areas.

Recent Outreach Activities:

  • Watch the Golden Webinar on Cosmic Dawn organised by the Pontifical Catholic University in Santiago, Chile
  • Read the interview on Searching for the First Stars sponsored by the Kavli Foundation
  • Watch the two supernova cosmology teams present reminiscences and anecdotes at Stockholm University as part of the 2011 Nobel Prize in Physics celebrations (mp4 format)
  • Read the Scientific Background on the Accelerating Universe awarded the 2011 Nobel Physics Prize in part to the Supernova Cosmology Project (led by Saul Perlmutter )
  • Listen to an interview on BBC Radio Wales on how I became an astronomer (light entertainment only!)
  • Scientific Publications:

    Check my scientific output on Google Scholar

    Past and Present Students:

    Check my proud list of successful graduate students!

    Personal Details:

    Curriculum Vitae (MS Word)

    Publication List (PDF)

    Research Programs:

    My current interests fall under 4 main headings:
  • Gravitational lensing: I have been interested in the role that gravitational lensing can play in cosmology and galaxy formation studies since the late 1980's. I remain hopeful that during my scientific career we can launch an imaging satellite (such as Euclid) capable of tracing the growth of structure from the time-dependent clustering of dark matter seen from weak lensing signals. On small scales I have used strong lensing to separate dark and baryonic matter distributions in clusters to understand how baryons influence the dark matter profile. Strong lensing also enlarges the apparent sizes of background galaxies and I have used this phenomenon to locate distant galaxies and study their internal properties such as their abundance gradients and velocity fields.

  • Distant Supernovae: I took part in one of the earliest successful studies to locate and characterize cosmologically-distant Type Ia supernovae and later joined the Supernova Cosmology Project . The resulting "accelerating Universe", recently awarded the 2011 Nobel Prize in Physics, is a bewildering result which has motivated a number of more ambitious ongoing and future supernovae surveys. I put most of my effort into examining the validity of using Type Ia SNe for future studies. My research included examining the environmental dependence of supernova properties as well as the question of possible spectral evolution such as might arise from changes in the progenitor composition. This work was undertaken with spectrographs on Keck and HST.

  • Large Scale Structure: I have been an enthusiastic promoter of multi-object spectroscopy since the 1980's, working with colleagues to develop early robotic positioners for the former Anglo-Australian Telescope and several multi-slit spectrographs. This work culminated in the 2 degree Field Galaxy Redshift Survey which demonstrated the presence of a baryonic acoustic peak in the large scale distribution of nearby galaxies whose precise measurement at various epochs is a very powerful cosmological probe. I am working with an international team to build the Prime Focus Spectrograph for the Subaru 8m Telescope. When constructed this instrument will undertake a survey of millions of faint galaxies to directly map the cosmic expansion history since a redshift 2 as well as probe the stellar halo of our Galaxy and M31. Read the detailed science case for this remarkable instrument. I also recently led a ESO Working Group that would take the next logical step towards a 10-12 meter class telescope with a 5 square degree field. Read the Working Group Report that describes the remarkable science potential of such an instrument as well as the White Paper submitted to Astro2020 .

  • Galaxy Formation and Evolution: I have been interested in studying the properties of distant galaxies since I was a postdoc in the late 1970's. I use the combination of HST images, Spitzer photometry, ground-based K-band imaging and, most of all, Keck/VLT spectroscopy to better understand the origin of the wide diversity of galaxy morphologies. Key questions I am working on include the mass-dependent assembly of galaxies over the redshift range 0 to 7, tracing cosmic reionization through deep Hubble imaging and statistical measures of line emission in distant galaxies. Read about the Hubble Ultra Deep Field 2012 program to study galaxies deep in the reionization epoch. Closer to home I also study the onset of ordered rotation and surprisingly compact nature in distant spiral and elliptical galaxies respectively. I am a recent convert to the phenomenal advances being made in these areas through the use of adaptive optics.
  • Recent Review Articles and Talks:

  • `Gravitational Lensing: Einstein's Unfinished Symphony' (Invited Review: United Nations `Year of Light' Series, Contemporary Physics)
  • `Cosmic Dawn: Studies of the Earliest Galaxies and their Role in Cosmic Reionization' (Invited Review: 26th Solvay Conference, Brussels October 2014)
  • Formation & Growth of Galaxies in the Young Universe (Conference Summary, Obergurgl April 2014)
  • `A Century of Redshift Surveys' (Invited Talk: Origins of the Expanding Universe)
  • `The Global Impact of ESO' (Invited Review), ESO's 50th Anniversary, Garching 2012
  • `First Light and the Faintest Dwarfs' (Conference Summary), KITP, Santa Barbara 2012
  • `New Horizons at High Redshift' (Conference Summary), Cambridge 2011
  • `Gravitational Lensing: Einstein's Unfinished Symphony' (popular talk)
  • `Cosmic Dawn: The Search for the First Galaxies' (popular talk)
  • `Early Star-Forming Galaxies and the Reionisation of the Universe' (review published in Nature November 4th 2010)
  • `The Origin of Galaxies' (Conference Summary (ppt), Obergurgl, Austria Dec 2009)
  • `The UKIRT Success Story' (opening talk at `UKIRT at 30' (doc), Edinburgh Sep 2009)
  • `Gravitational Lensing: An Unique Probe of Dark Matter and Dark Energy' (invited popular review to celebrate 350 years of Royal Society (doc), Aug 2009)
  • `The Quest for Giant Telescopes: Four Centuries of Challenge and Scientific Discovery' (Keynote Talk (ppt) at 2009 APS Meeting Denver, May 2009
  • `Scientific Opportunities for 30 Meter Class Optical Telescopes' (invited talk (doc) at New Visions 400, Beijing 2008)
  • `Panoramic Views of Galaxy Formation and Evolution' (Conference Summary (pdf), Hayama, Japan, Dec 2007)
  • Observations of the High Redshift Universe in `First Light' (Saas-Fee Lectures (pdf), Apr 2007)
  • Latest Refereed Papers (2024 submissions)

  • Spatially Resolved Galactic Winds at Cosmic Noon: Outflow Kinematics and Mass Loading in a Lensed Star-forming Galaxy at z=1.87
  • Latest Refereed Papers (2023 submissions)

  • CIII] 1909 emission as an alternative to Lyalpha in the reionization era: the dependence of CIII] and Lyalpha at 3~z~4 from the VANDELS survey
  • The galaxy UV luminosity function at z=11 from a suite of public JWST ERS, ERO and Cycle-1 programs
  • Deciphering Lyman-alpha Emission Deep into the Epoch of Reionisation
  • Spectroscopy of CASSOWARY gravitationally-lensed galaxies in SDSS: characterisation of an extremely bright reionization-era analog at z=1.42
  • A NOEMA molecular line scan of the Hubble Deep Field North: Improved constraints on the CO luminosity functions and cosmic density of molecular gas
  • Photometric IGM tomography with Subaru/HSC: the large scale structure of Lya emitters and IGM transmission in the COSMOS field at z=5
  • Current Committees

  • Scientific Advisory Committee Kavli Institute for Astronomy and Astrophysics, Beijing
  • Scientific Advisory Committee ORIGINS Cluster, Munich
  • Royal Society Research Professorships Panel
  • Editorial Board Contemporary Physics
  • Caltech Teaching

  • Ay 123 Structure and Evolution of Stars
  • Ay 211 Extragalactic Astronomy
  • Ay 124 Structure and Dynamics of Galaxies
  • Page maintained by Richard Ellis

    Last modified: 16th January 2023