Richard Ellis's Homepage

Richard Ellis

Astronomy 249-17, Caltech

Pasadena CA 91125

Position: Visiting Associate:
On September 1st 2015 I moved to a new position at University College London and my contact details are on my UCL web page
However the US communication details below are still functional
Secretary: (626)-395-4970
Fax: (626)-568-9352
Emails: rse@astro.caltech.edu; richard.ellis@ucl.ac.uk

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 since the late 1980's. I was a member of three independent teams that first detected cosmic shear, the weak lensing by large scale structure, in 2000. The subject has advanced enormously, culminating in the successful launch of Euclid) which aims to trace the growth of structure from the time-dependent clustering of dark matter. 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 magnifies and enlarges the apparent sizes of background sources and I have used this phenomenon to locate distant galaxies and study their internal properties such as their abundance gradients and velocity fields, as well as determine the faint end of the galaxy luminosity function at high redshift.

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 powerful cosmological probe. I have worked since 2006 with an international team to build the Prime Focus Spectrograph for the Subaru 8m Telescope. Now being commissioned this will undertake a survey of millions of faint galaxies to directly map the cosmic expansion history to beyond a redshift 2 as well as probe the stellar halo of our Galaxy and M31. Read the detailed science case for this remarkable instrument. In 2016 I also led a ESO Working Group that would take the next logical step towards a 12 meter telescope with a 3 square degree field. This has now become a major future project called the Wide Field Spectroscopic Telescope. Check out a recently completed Scientific White Paper.

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 have used 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 now on include the luminosity evolution and mass-dependent assembly of galaxies over the redshift range 7 to 15, tracing cosmic reionization through deep JWST imaging and spectroscopy. Closer to home I also study the onset of ordered rotation and surprisingly compact nature in distant spiral and elliptical galaxies respectively.