I am an astrophysicist, and a professor in the School of Earth and Space Exploration
at Arizona State University.
These pages provide a brief overview of some of my research.
The SESE web pages provide further information on ASU's
Astronomy and Astrophysics
and astronomy and astrophysics
graduate school in SESE.
Finding and Studying the First Galaxies
Most of my work in observational cosmology, galaxy formation, and
galaxy evolution is done in collaboration with
ASU Professor Sangeeta Malhotra.
Lyman Alpha Galaxies
The youngest galaxies in the early universe can tell us most
directly about the process and history of galaxy formation. These
young galaxies contain many young, hot stars, whose energetic
photons are expected to ionize their gas. The
ionized gas will then glow strongly in the Lyman alpha line (i.e.,
the 2-1 transition of neutral hydrogen). By searching for
strong sources of Lyman alpha emission, we have identified large
samples of star forming galaxies in the early universe. The
Large Area Lyman Alpha (LALA)
survey is a narrowband imaging program at redshifts z=4.5, 5.7, and 6.5
that has covered 106 cMpc3 and identified about
500 Lyman alpha galaxies. We have about 250 spectroscopic
confirmations from LALA and from related projects.
The Deep and Wide Narrowband (DAWN) survey is an ongoing forty-night
survey program using the NEWFIRM camera at the
4m Mayall telescope of the Kitt Peak National
Observatory. DAWN is observing five fields with a
narrow bandpass filter (1.06 micron central wavelength and 3.5nm bandpass).
These fields will range in narrowband integration times from 10 to over 50 hours, with one ultra-deep field (COSMOS), two deep fields (UDS and EGS),
and two medium-deep fields (CFHTLS-D4 and MACS0717).
DAWN will answer key open questions about the evolution of
Lyman alpha galaxy numbers in the epoch of reionization, and their potential
implications for determining reionization history. It will also
enable sensitive studies of faint star forming galaxies across a
wide range of cosmic time.
The Most Sensitive Spectroscopic Surveys
GRism ACS Program for Extragalactic Science
Evolution And Reionization Spectroscopically
FIGS: the Faint Infrared Grism Survey
These projects exploit the low background, high throughput, and unmatched
spatial resolution of the Hubble Space Telescope's slitless
spectroscopic modes to obtain some of the most sensitive spectra
ever. Core science includes studying the Lyman break galaxy
populations at redshifts z=4 to z=6.5; searching for both Lyman alpha
galaxies in this redshift range and other emission line galaxies closer
to home; studying older stellar populastions at intermediate redshifts;
and even studying the distribution of faint stars in our own Galaxy.
The Faint Infrared Grism Survey
is a new cycle 22 Treasury program on the Hubble Space Telescope,
led by ASU professor Sangeeta Malhotra.
FIGS will use the Hubble Space Telescope for an aggregate of
10 full days (160 orbits) to obtain the most sensitive continuum
spectra yet obtained at near infrared wavelengths, using
the Wide Field Camera 3- IR channel's G102 slitless grism.
Gamma Ray Burst Afterglows
Gamma ray bursts (or GRBs) are short-lived sources of high energy
photons that occur about once a day over the full sky. They may
last anywhere between 1000 seconds and 0.01 second. In that brief
time, they emit tremendous energy: 1051 to 1054
ergs. In 1993, Bohdan Paczynski and I predicted that observable
radio afterglows would follow GRBs after a lag of days. The first
such radio afterglow was observed in 1997, three months after the first
optical afterglow. Identification of these long wavelength
counterparts to GRBs opened the way for major progress in understanding
their nature, beginning with direct distance measurements to GRB
afterglows. Starting in 1997, I worked on devising tests
for collimation of gamma ray bursts. One of the tests I suggested
has been used to show that GRB energies are about 100 to 1000 times
smaller than one might naively guess. I have also been active in
observations of GRB afterglows, primarily at optical and near-infrared
I am an affiliate member of the science team for the Swift satellite,
which is the best GRB hunting mission to date.
Instruments and Missions
Wide field surveys in the far red and near-infrared wavelength
ranges are critically important for future progress in understanding
how galaxies formed and evolved in the early universe, and how they
ionized the hydrogen between the galaxies.
I am interested in instrumentation that will help perform
such surveys- through wide field imaging or slitless spectroscopy,
on the ground or in space.
Currently, I am a science team member for the Star Formation Camera
instrument on the Theia mission concept. I am also exploring
possibilities for wide-field, narrowband-capable near-infrared cameras
on a range of large ground based telescopes. I have a strong interest
in filter development for astronomical instruments, springing from
our extensive use of narrowband filters in Lyman alpha galaxy hunting.
I led three NSF proposals for an
The Infrared Widefield Imager (IWI),
which was to be a wide field (21 x 21 arcminute) near infrared (zYJH band)
capability for the Large Binocular Telescope. IWI would function
as an integral component of the existing Large Binocular Camera,
and would use JWST NIRCam heritage chips,
provided by Marcia Rieke and the NIRCam team at University
of Arizona. IWI has not been funded, though it remains a viable
instrument concept that would provide a better survey efficiency
in the Y, J, and H bands than any existing telescope + camera
combination in the near-IR.
I was also a science team member for the DESTINY Joint
Dark Energy Mission concept, one of only three funded by NASA for
development. DESTINY would use repeated, deep spectroscopic
observations of two patches of sky to identify and study distant type
Ia supernovae, and use their measured fluxes and redshifts to study the
nature of the dark energy that dominates the makeup of the present day
universe. It would also conduct a complimentary weak lensing
survey, thus studying the same phenomenon in two entirely independent
ways. See the
Teaching and Public Outreach
AST 111, Introduction to Solar System
Astronomy: fall 2008, spring 2009, fall 2011, fall 2013
AST 321, Introduction to Stellar and
Planetary Astrophysics: fall 2007, fall 2010, fall 2014
AST 322, Introduction to Galactic and Extragalactic
Astrophysics: Spring 2010, spring 2015
AST 522, Stellar Structure and Evolution: fall 2006
AST 532, Galaxies: spring 2011, spring 2014
AST 533, Cosmology: Spring 2006, spring 2008, fall 2009, spring 2012
Where I Work
Arizona State University is a large, state-supported university located in
Tempe, in the Phoenix metropolitan area. ASU astronomers have access
to the state-funded Arizona telescope system, which includes world
class telescopes in south-eastern Arizona (LBT, MMT) and in Chile
All ASU astronomers (faculty, postdocs, and gradudate students) can lead
proposals for observing time on any of these telescopes.
Astronomy at ASU resides in the School of Earth and Space Exploration, along
with planetary science, geology, and some engineering. We have a group
of about a dozen astronomy professors, and some 20-25 graduate students
in our astrophysis PhD program. We have an active research environment
with regular seminars, colloquia,
lunches, and coffee discussions. Our recent PhD graduates have gone
on to postdoctoral fellowships at UC Davis, Texas A+M, UC Riverside,
and NASA's Goddard Space Flight Center. Phoenix offers big-city amenities,
a warm climate, and great access to outdoor recreation... so if you're
considering graduate school in astronomy, please take a look at what we have
Some useful web links on my web resources page.