Jeff Cooke

ARC Future Fellow - Centre for Astrophysics & Supercomputing
Swinburne University of Technology, PO Box 218, Mail number H30, Hawthorn, VIC 3122 Australia
office: +61 3 9214 5392 -- fax: +61 3 9214 8797 -- email:

AR 315

Detection of z > 2 supernovae

I pioneered a technique to detect supernovae in very high redshift (z > 2) Lyman break galaxies by exploiting the exceptional properties of type IIn supernovae (Cooke 2008). Our detections are probing 10 - 12 billion years into the past and only 1 - 3 billion years after the Big Bang.

Most type IIn supernova are the deaths of very massive stars (likely to be 30-80 times the mass of the Sun). These stars burn their fuel vigorously and experience mass-loss episodes where a large amount of their outer envelope of material is blown into space in a supernova-like eruption. This material then cools and forms a dense shell, or "cocoon", of gas at a large radius around the star (termed circumstellar material). The star finishes out its life and dies as a core-collapse supernova. When it explodes, the supernova crashes into the previously expelled circumstellar material and lights it up. This results in a spectacularly luminous event that is very luminous at ultraviolet wavelengths. The excited dense circumstellar material also emits extremely luminous narrow emission lines that remain bright for several years.

The ultraviolet light emitted by high redshift supernovae travels billions of years on its journey to Earth and stretches as a result of cosmological redshift as the Universe expands during that time. The stretched ultraviolet light then appears as optical light by the time it reaches Earth and can be detected using sensitive optical instruments mounted on ground-based telescopes, like the LRIS instrument on Keck.

Previously, core-collapse supernovae had not been detected beyond z ~ 0.7 (about 7 billion years ago). Detections at z ~ 2 (about 10 billion years ago), and greater, enable the measurement of the high-redshift supernova rate during the epoch of peak star formation in the universe. In addition, they provide a new avenue to explore the feedback processes that affect galaxy formation and the enrichment of the interstellar medium and intergalactic medium. Furthermore, the supernovae can be used as bright beacons to study their local environment, their host galaxy's environment, and the intervening material in the line-of-sight in a means similar to absorption systems in the line of sight to quasars and gamma ray bursts. Finally, high-redshift type IIn supernova detections offer the tantalizing possibility to measure the high-redshift stellar initial mass function directly for the first time.

I obtained deep spectroscopy of the first 12 z > 2 supernovae in the Canada-France-Hawaii Telescope Legacy Survey Deep fields (z = 1.9 - 3.3) using the LRIS and DEIMOS instruments on the Keck telescopes. The first two are presented in (Cooke et al. 2009) and the light curve for one is shown in the figure below. Nine of the high-redshift supernovae show ultraviolet emission lines intrinsic to type IIn supernovae resulting from circumstellar interaction, with a few having strong Lyman alpha emission (Cooke et al. 2013 in prep.).

Light curve for a type IIn supernova at z = 2.013. This redshift means the event occurred more than 10 billion years ago. The x-axis (days) is the Modified Julian Date , showing the days numbered from July 2005 through February 2006. The y-axis is the apparent magnitude of the supernova.

My technique and these data demonstrate the ability to detect, confirm, and study supernovae at redshifts much higher than previously thought possible, and not until the next decade with the advent of the next generation of large-aperture telescopes such as the Thirty Meter Telescope, the Giant Magellan Telescope, the European Extremely Large Telescope, and The James Webb Space Telescope. This research has opened the door to exploring the early Universe during a very formative time for galaxies and when the first generation of stars existed.

Click here to access the ADS link displaying a list of articles describing this work and other research of mine.



Artist's conception of a type IIn supernova

The search for z ~ 2 type IIn supernovae in the CFHTLS has spectroscopically confirmed 10 to date. The images directly to the right illustrate the first step in finding these distant objects. Each frame shows the same tiny section of a large one-square-degree image over three consecutive years and is centered on a z ~ 2 galaxy that was discovered to host a supernova. The frames consist of an entire year's worth of images stacked together to better reveal these faint objects.

The fourth image is the 2004 `subtraction' image with the constant light from the galaxies subtracted away, revealing the supernova. Deep spectroscopy with the Keck telescopes is used to confirm their redshifts (z = 1.9 - 2.4) and study their late-time emissin.
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The Hubble Space Telescope

The Milky Way can be seen, as well as two of our closest companion galaxies, the Large and Small Magellenic Clouds, in this long-exposure image of the 4 meter telescope at the CTIO located in the Southern Hemisphere (Chile).
  Astronomy 110
Physics 20A  
  Physics 7D
Curriculum Vitae
  Astro Grad Seminar
Centre for Astrophysics & Supercomputing
  Caltech Astronomy Department
Center for Cosmology
UC Irvine
  Center for Astrophysics and Space Sciences
UC San Diego
W. M. Keck Observatory  
  Palomar Observatory