 | | Office:
Cahill 346 Calendar | |
Extragalactic Observational Astronomer
Main areas of
research:
Early assembly and evolution of galaxies
Detection and study of very high redshift supernovae
Press
releases:
The
most distant supernovae
LBG-2377
Check this out (I think I recognize
#1)!
Top 10 Most Important Supernovae
(for the original site - click here)
Here is a brief description of some of the projects that
have been keeping me busy:
Detection of z > 2 Type IIn supernovae
- I developed a
technique to detect z > 2 Type IIn supernovae (SNe
IIn) in deep wide-field optical surveys (Cooke 2008). Previously, Type II supernovae, such as
SNe IIn, had not been detected beyond
z ~ 0.7. Detection of z ~ 2 SNe IIn will have
a large impact on areas such as the high-redshift supernova
rate, the feedback processes that affect galaxy formation,
and the enrichment of the interstellar and intergalactic
medium. Moreover, high-redshift SNe IIn detections will
directly measure the high-mass end of the stellar initial
mass function - a long sought-after measurement - and search
for evolution. I began my search for z ~ 2 SNe IIn
using the Canada-France-Hawaii Telescope Legacy Survey
(CFHTLS) Deep fields (Cooke
et al. 2009a). To date, I have detected and
spectroscopically confirmed five z ~ 2 SNe IIn and
hope to find about 30 candidates in total. This technique
should enable SN IIn detections to z ~ 6 with
upcoming deeper surveys and their spectroscopic confirmation
and study using the next generation 30 meter class
telescopes. With such distant detections, we would be
observing some of the very first stars! At z > 2,
optical surveys observe the redshifted rest-frame far
ultraviolet (UV). Because little data exists of SNe IIn FUV
continuum and bright emission lines, I have a Hubble
Space Telescope program to observe the UV of a sample of
low- to intermediate-redshift SNe IIn.
Lyman break
galaxy interactions at z ~ 3 - I am leading several
related projects that study the observed and predicted
behavior of close and interacting Lyman break galaxies
(LBGs) at z ~ 3. These projects use our deep Keck
imaging and spectroscopic surveys (see below) and an
analysis of a high resolution hybrid numerical/analytical
cosmological simulation. I use conventionally acquired
surveys to study interacting z ~ 3 LBGs from
serendipious spectroscopic galaxy pairs and investigate
their spectroscopic properties with respect to their
distribution (Cooke et al. 2010). This provides insight on the
physical changes in morphology and triggered star formation
that LBGs encounter from interactions. In addition, these
analyses will help to constrain other LBG rest-frame UV
properties and the LBG merger rate. The discovery of the
luminous LBG-2377 (image on right) has provided key
information in this work.
(Cooke et al. 2008).
Broadband
selection of Lyman break galaxy spectral types and Lyman
alpha emitters - Complementary to the above work, I
developed a technique to pre-select LBGs with desired
spectroscopic properties
using broadband imaging alone (Cooke
2009). In addition, this technique efficiently selects
Lyman alpha emitting galaxies (LAEs) which previously were
only detectable through narrow-band and blind spectroscopic
surveys. In this work, I show that LAEs are a natural
extension of the LBG population and hint at a bimodality in
the LBG population. By using this technique, the
correlation functions of each population can be measured to
high precision.
High redshift
Lyman break galaxies and QSO absorption-line
systems
- I have conducted two large, deep imaging and spectroscopic
surveys for high redshift (2.5 < z < 5) LBGs and QSO
absorption line systems, primarily the damped Lyman alpha
systems (DLAs). These surveys exploited the sensitivity and
field-of-view of the Keck LRIS and DEIMOS, Palomar COSMIC,
CTIO MOSAIC, MMT MegaCam, and Subaru SuprimeCam instruments
(Cooke
et al. 2005, 2010 in prep.). A primary goal of these
surveys is to measure the 3-D spatial distribution of LBGs
at z ~ 3 and z ~ 4 and the cross-correlation
of LBGs with DLAs. Measurement of these relationships help
to determine fundamental properties of these systems such as
galaxy bias, mass, and luminosity and their evolution. I
made the first measurement of the mass of z~3 DLAs (Cooke et al. 2006a, 2006b) and am working on
improving that measurement with the z ~ 4 survey. In
addition to DLAs, I am investigating MgII absorption-line
systems. We have a program that first selects galaxies in a
volume-limited survey and then searches for absorbers in QSO
sightlines (Barton & Cooke 2009). This "reverse approach"
minimizes many biases inherent to traditional surveys and
helps to better understand absorber characteristics as they
relate to galaxy properties, such as color and
environment.
Building
galaxies through minor mergers - Lambda Cold Dark
Matter (LCDM) cosmology predicts that the majority of mass
accreted by galaxies since z ~ 1 is by ~10:1 mass
mergers (minor mergers). In addition, the minor merger rate
evolves more rapidly than the major merger rate of nearly
equal mass galaxies over cosmic time. I am conducting a
survey of galaxies with faint (minor) companions at
intermediate redshift (0 < z < 0.9) to test LCDM
minor merger rate predictions. Using LRIS on Keck, I have
obtained moderate signal-to-noise spectroscopy of ~500 close
galaxy pairs in 11 deep fields imaged with the MiniMo camera
on the WIYN telescope. Because these ground-based images
have complementary Hubble Space Telescope (HST)
high-resolution imaging, I hope to quantify subtle
properties such as triggered star formation and
morphological signatures of the interacting close galaxy
pairs. I plan to apply these results to the high redshift
observations. Click here to access the ADS link displaying a list of
articles describing some of my work.
THE LATEST: Recently,
I used the LRIS and DEIMOS instruments on the Keck telescopes
to obtain deep spectroscopy of the first three SNe IIn
candidates in the CFHTLS Deep fields. I found them to have
redshifts z = 0.81, z = 2.01, and z = 2.36.
Click
here for the press release. We now have five confirmed
supernovae between z = 2.013 - 2.364. These are the
highest redshift supernova spectra ever! Each z ~ 2
supernova shows emission lines, with a few having strong Lyman
alpha emission (a hydrogen atomic transition). The light from
the z ~ 2 supernovae has traveled over 10 billion years
to reach Earth and, because of the expansion of the universe,
the remnants from those explosions are now about 18 billion
light years away. Overall, these data demonstrate the power
of this technique and the ability to detect, confirm, and
study supernovae at redshifts higher than previously thought
possible with existing facilities. Look for more high-redshift
SNe IIn detections to come this year!
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Welcome to my office
A false color (negative) image of
interacting Lyman break galaxies
(termed LBG-2377) comprise the brightest LBG at
z ~ 3 known to date (Cooke et al. 2008). These
"embryo" galaxies show evidence that they are merging and
provide information on the physical properties and formation
processes of galaxies about 11.4 billion years ago, when the
universe was only 15% its current age.
| LBGs, like those above, are visible because
they are undergoing a burst of star formation. One cause of
this burst may be the merging of galaxies, as is the case for
the much closer galaxies NGC 4038 and NGC 4039 (image to the
right) known as the Antennae Galaxies. |
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The search for z ~ 2 Type IIn
supernovae in the Deep component of the CFHTLS has
spectroscopically confirmed five to date, with more to
come.
The images directly to the right illustrate the
method used to find 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 type IIn supernova. The frames consist
of an entire year's worth of images stacked together to better
reveal these faint objects.
Below the three images is
the 2004 image with the constant light from the galaxies
subtracted away, revealing the supernova.
The five
confirmed supernovae lay between
z = 2.013 - 2.364. These are the highest redshift
supernovae of any type! With these discoveries, we are
witnessing light from explosions that happened nearly 11 billion
years ago. Such detections are crucial in understanding early
stellar and galaxy formation processes.
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The Hubble Space Telescope
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