Star formation and mass assembly at the highest redshifts

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics


The latest telescopes and instruments enable us to see galaxies at incredible distances. The motivation for searching for these distant objects is to look back through time - light left these galaxies many thousands of millions of years ago. We can trace the evolution of our Universe from the earliest structures to galaxies today. We have developed techniques using the Hubble Space Telescope and the largest telescopes on the ground to discover the most distant objects yet: these are about 12 thousand million years away - so light has been travelling more than twice the Earth's age to reach us. We can confirm the distance to these objects by analysing the spectrum of their light (spreading out with wavelength), and looking for the characteristic emission line fingerprints of atoms such as hydrogen. At great distances, the wavelengths will be stretched to longer (redder) wavelengths through the expansion of the Universe - we are interested in redshifts greater than one, where the Universe has more than doubled in size since the photons left our target galaxies. We can go beyond selecting candidate high-redshift galaxies in sensitive images and confirming their distance with spectroscopy; we can determine the rate at which stars are being born by measuring the amount of light emitted in the ultra violet by young, massive, short-lived stars. We can also study the brightness over a range of wavelengths to estimate the total number of stars and their average age. Finally, we can `weigh' these distant galaxies by studying the speed at which the stars and gas within these galaxies orbit the centre - the greater the mass of a galaxy, the higher the spread in speeds (measured by the spread in wavelength of the emission and absorption lines in the spectrum). The total mass of a galaxy comprises both the stars and gas, and the mysterious `dark matter'. How the stellar mass of a galaxy is related to the total mass, and how this evolves over the history of the Universe, are important unanswered questions in galaxy formation.


10 25 50
Description We were among the first to analyse data from the near-infrared images taken with the new WFC3 camera on Hubble Space Telescope of the Hubble Deep Field, the most sensitive picture of the Universe (Bunker et al. 2010) and identified several galaxies at high redshift, when the Universe was only 5 per cent of its current age. Our work confirmed the previous result when we were the first to publish the original Hubble Deep Field: the rate at which stars are forming at these early times is surprisingly low. We undertook spectroscopy from the large telescopes on the ground in Hawaii (Subaru) and Chile (VLT and Gemini), and discovered that Lyman alpha (an emission line of hydrogen which is powered by the UV light from young massive stars) is rare in many of these galaxies (Caruana et al. 2012, 2014; Bunker et al. 2013), probably because the space between the galaxies is filled with a large amount of neutral gas at these early times which can absorb this line emission.
Exploitation Route We have published lists of candidate high redshift galaxies which are appropriate for spectroscopic follow-up with the James Webb Space Telescope (Andrew Bunker is on the European Space Agency science team for the Near-InfraRed Spectrograph).
Sectors Education

Description We published locations of potential high redshift galaxies in Monthly Notices of the Royal Astronomical Society, and these have been used as targets for spectroscopic follow-up by our own group and others, and the luminosity functions derived from our analysis has been used to determine the contribution of star-forming galaxies to the reionization of the Universe.
First Year Of Impact 2009
Description Astrophysics and Planetary Science at Oxford (STFC Consolidated Grant)
Amount £3,672,785 (GBP)
Funding ID ST/K00106X/1 
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 01/2013 
End 03/2016
Description STFC Rolling Grant ("Astrophysics at Oxford: 2010-2015")
Amount £2,486,342 (GBP)
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 04/2010 
End 03/2013
Description EarLy unIverse Exploration with nIRspec (ELIXIR) 
Organisation Paris Institute of Astrophysics
Country France 
Sector Academic/University 
PI Contribution The Oxford network node has been analysing data from Hubble Space Telescope deep imaging fields (including those from the new WFC3 infrared camera) to determine observing strategies for JWST, and also to provide an initial target list for spectroscopy with NIRSpec on JWST.
Collaborator Contribution This is an EU FP7 network associated with the NIRSpec instrument on the James Webb Space Telescope. The Instrument Science Team comprises: Stephane Charlot (IAP, Paris - lead network); Andrew Bunker (Oxford); Marijn Franx (Leiden); Santiago Arribas (Madrid); Roberto Maiolino (Rome); Hans-Walter Rix (MPIA Heidelberg) and Peter Jakobsen (ESA), with out industrial partner (Astrium, Germany). We are responsible for the NIRSpec near-infrared spectrograph, which is being built and tested, and we will execute a 900-hour GTO programme to investigate galaxies at high redshift. The EU FP7 ELIXIR Network is intended to plan the science for this large programme.
Impact The Network funds several PhD students and Early Stage Researchers at the nodes across Europe, including two graduate students at Oxford (Joseph Caruana and Silvio Lorenzoni). These researchers have participated in many of the papers from our group, and Lorenzoni has a first-author paper accepted.
Start Year 2008
Description Galaxies in the Reionization Epoch 
Organisation California Institute of Technology
Department Caltech Astronomy
Country United States 
Sector Academic/University 
PI Contribution Oxford has been responsible for reducing the Hubble Space Telescope images and identifying potential high-redshift candidates through colour selection.
Collaborator Contribution Oxford has lead this project, in collaboration with Prof Richard Ellis at Caltech, using archival Hubble Space Telescope images with WFC3 to identify Lyman-break galaxies at z=7 and beyond. Caltech has mainly been involved in the spectroscopic follow-up.
Impact Five refereed accepted papers so far (Bunker et al. 2010; Wilkins et al. 2010; Lorenzoni et al. 2011; Wilkins et al. 2011, Wilkins et al. 2012). A press release in December 2009, resulting in extensive coverage. Several invited talks at conferences.
Start Year 2009
Description James Webb Space Telescope - European Space Agency Instrument Science Team for Near Infrared Spectrograph 
Organisation ESA - ESTEC
Country Netherlands 
Sector Public 
PI Contribution I am one of 7 members of the European Space Agency Instrument Science Team for Near Infrared Spectrograph on the James Webb Space Telescope. We have overseen the design and construction, and have been allocated 900 hours of Guaranteed Time Observations after launch in 2018. We plan a survey to chart galaxy evolution over much of cosmic time.
Collaborator Contribution The other appointed members of the Instrument Science Team are Hans-Walter Rix (MPIA Heidelberg), Roberto Maiolino (Cambridge), Santiago Arribas (Madrid), Stephane Charlot (IAP Paris), Marijn Franx (Leiden) and Pierre Ferruit (ESA-ESTAC and instrument scientist). We are all collaborating on a large survey on high redshift galaxies for the guaranteed time observations.
Impact The guaranteed time observations will commence after launch in 2018.
Description The WFC3 Spectroscopic Parallel (WISP) Survey 
Organisation University of California, Los Angeles (UCLA)
Department Physics and Astronomy
Country United States 
Sector Academic/University 
PI Contribution Oxford is responsible for studying the star formation rates of these galaxies from their H-alpha line luminosities, and for constructing the line luminosity function at redshifts around one.
Collaborator Contribution The WISP collaboration, based at UCLA and also the Spitzer Science Center (in Caltech) and with collaborators elsewhere in the USA and Germany, is responsible for reducing the Hubble Space Telescope slitless grism spectroscopy to search for emission line objects at high redshift. Most of this reduction and cataloging occurs in Los Angeles.
Impact One refereed paper on the initial work - Atek et al. (2010) - and several more in preparation. Various presentations by the team at American Astronomical Society meetings.
Start Year 2008
Description Oxford Astrophysics Public Outreach 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Type Of Presentation Keynote/Invited Speaker
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Oxford astrophysics organizes evening talks for the public, followed by observing through our teaching telescope (weather permitting!). There are several other activities in addition to the main talk and observing. Postdoc Stephen Wilkins has been active in developing these public outreach activities (including "Astrophysics Top Trumps" card games). Andrew Bunker has also been involved in these evenings, giving the main talk on 13 April 2011.

The public outreach evening always spark much interest and discussion - typical attendance is about 40 people, and we distribute feedback forms, the results of which indicate a high level of satisfaction.
Year(s) Of Engagement Activity 2009,2010,2011,2012,2013
Description Press release on the first Hubble WFC3 Deep Infrared Images 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact We issued a press release on our work on 8 December 2009 entitled "Reinvigorated Hubble Space Telescope Reveals Most Distant Galaxies Yet".

Our press release results in extensive coverage in the scientific media and the international press including:
Nature Blog hubble_revisits_distant_haunt.html

BBC News (online)

We also appeared in The Times (print version)
Year(s) Of Engagement Activity 2009
Description Search for a Star live astronomy show 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact We were able to give several shows to a diverse audience. Although we had difficulty in securing free venues around the country outside of the Edinburgh Fringe Festival, we were able to put on a number of shows at university venues and museums.
Co-investigator Sophia Khan was an invited participant in the Natural History Museum Science Uncovered 2012 event. A number of other shows included university venues, such as Physics Outreach graduate students at Imperial College.

Extensive interest from a number of organizations, including the BBC (who then spoke with co-investigator Sophia Khan about popular science broadcasting possibilities).
Year(s) Of Engagement Activity 2011,2012