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Office:
Cahill 346
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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!
Top Ten Supernovae
Here's a brief description of some of the projects that
have been keeping me busy:
Detection of z > 2 Type IIn
supernovae I have developed a technique to
detect z > 2 Type IIn supernovae (SNe IIn) in
wide-field optical surveys complete to m_R ~ 27.
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
supernova rate at high redshift, the supernovae contribution
to feedback processes that affect galaxy formation, and the
enrichment of metals in the interstellar and intergalactic
medium. Moreover, high-redshift SNe IIn detections will
directly measure the high-mass end of the universal stellar
initial mass function and search for evidence of evolution.
I began my search for z ~ 2.0 SNe IIn using the
Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) Deep
fields that consists of four deep fields imaged over five
years. I have detected four z ~ 2 candidates in two
fields over the two years analyzed so far, and I am
continuing this analysis on the rest of the survey. I hope
to find about 30 candidates in total. This method should
enable detections to z ~ 6 with upcoming deeper
surveys. 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 (FUV). Because little data exists of SNe IIn
FUV continuum and bright emission lines, I have a Hubble
Space Telescope program to observe the FUV 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 state-of-the-art high
resolution hybrid numerical/analytical cosmological
simulation. I use conventional LBG surveys to study
interacting z ~ 3 from serendipious spectroscopic
galaxy pairs and investigate the spectroscopic properties of
LBGs with respect to their distribution. 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 a wealth of information toward this analysis.
Press Release of LBG-2377.
High redshift
Lyman break galaxies and QSO absorption-line
systems I have conducted large imaging and spectroscopic
surveys for high redshift (2.5 < z < 5) Lyman break
galaxies (LBGs) and QSO absorption line systems, primarily
the damped Lyman alpha systems (DLAs), using LRIS and DEIMOS
on Keck, COSMOS on Palomar, MOSAIC on CTIO, MegaCam on the
MMT, and SuprimeCam on the Subaru telescope. One immediate
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.
Building
galaxies through minor mergers
LCDM 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 over 400 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. These are the highest redshift SNe
IIn to date and two are the highest redshift supernovae of
any type! I was even able to faintly detect the emission
lines emitted by the supernovae. 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 and confirm very
high redshift SNe IIn. Look for more high-redshift SNe IIn
detections to come this Fall and next Spring!
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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 uncovered
four candidates after analyzing 1/5th of the data so far. The
first three have been confirmed using deep Keck spectroscopy
with the fourth to be acquired in July. The images directly to
the right illustrate the method used to find these distant
objects in the deep images. Each frame is the same tiny section
of a large one-square-degree deep image. They are centered on
a z ~ 2 galaxy that was discovered to host a type IIn
supernova in the year 2004. Each frame is an entire year's
worth of images, with three consecutive years shown. Below
these three images is an image where the constant light from the
galaxies is subtracted away, revealing the supernova. The three
confirmed supernovae lay at z = 0.81, z = 2.01,
and z = 2.36. These are the highest redshift Type IIn
supernovae and the latter two are the highest redshift
supernovae of any type! With these discoveries, we are
witnessing light from explosions that happened as much as 11
billion years ago. Such detections are crucial in understanding
stellar and galaxy formation processes.
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The Hubble Space Telescope
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