By any measure, Professor Wallace L. W. Sargent (known to colleagues and friends as “Wal”) was one of the most influential and consistently productive astronomers of the last 50 years; he authored or coauthored more than 320 refereed journal articles, which have received more than 25,000 citations. He never rested on past laurels—65 of his papers (with >5000 citations) have appeared since the year 2000. Wal remained active as a teacher and researcher until just weeks before the end of his life (he officially retired from the Caltech faculty on 2012 October 1). His impact on the field of astrophysics was remarkably broad as well as seminal; among many other awards, he was elected in 1981 as a Fellow of the Royal Society (U.K.) and as a member of the National Academy of Sciences in 2005, his first year of eligibility after becoming a naturalized U.S. citizen

Steidel, Charles C.

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Wallace L. W. Sargent (1935–2012)
Author(s): Charles C. Steidel
Source: Publications of the Astronomical Society of the Pacific, Vol. 125, No. 925 (March
2013), pp. 225-226
Published by: The University of Chicago Press on behalf of the Astronomical Society of the Pacific
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Obituary
Wallace L. W. Sargent (1935–2012)
CHARLES C. STEIDEL
California Institute of Technology, Cahill Center for Astronomy and Astrophysics MS 249-17,
1200 E. California Boulevard, Pasadena, CA 91125
Received 2013 January 10; accepted 2013 January 14; published 2013 February 12
By any measure, Professor Wallace L. W. Sargent (known to
colleagues and friends as “Wal”) was one of the most influential
and consistently productive astronomers of the last 50 years; he
authored or coauthored more than 320 refereed journal articles,
which have received more than 25,000 citations. He never rested
on past laurels—65 of his papers (with >5000 citations) have
appeared since the year 2000. Wal remained active as a teacher
and researcher until just weeks before the end of his life (he
officially retired from the Caltech faculty on 2012 October 1).
His impact on the field of astrophysics was remarkably broad as
well as seminal; among many other awards, he was elected in
1981 as a Fellow of the Royal Society (U.K.) and as a member
of the National Academy of Sciences in 2005, his first year of
eligibility after becoming a naturalized U.S. citizen.
Many who know Wal will also be aware that his personal
history was no less remarkable—he was born into a distinctly
working-class family (his father was a gardener and his mother a
house cleaner) in central Lincolnshire (UK) just before the start
of the second World War. To provide an idea as to how unlikely
his path has been, he was the very first student from the
Scunthorpe Technical High School to attend university of any
kind. Wal studied at the University of Manchester for both his
undergraduate degree (1956) and his PhD (1959). Upon receiv-
ing his PhD, Wal moved to California to become a Research
Fellow at Caltech, working with Jesse Greenstein. Aside from
2 years as a Senior Research Fellow at the Royal Greenwich
Observatory (a most important time in retrospect, since that
is where he met his wife and fellow astronomer Anneila; they
were married in 1964), Wal spent all of his 45 year career in
California, first as a junior faculty member in Physics at UC
San Diego (1964–1966), after which he moved to Caltech
(1966) where he spent the rest of his career on the faculty.
In 1981 he became the Ira S. Bowen Professor of Astronomy.
Perhaps the most impressive aspect of Wal Sargent’s contri-
butions to astrophysics is the range of subjects in which he made
fundamental contributions. Among them are the first measure-
ment of the primordial abundance of helium from observations
of metal-poor galaxies (with Leonard Searle), the first dynam-
ical evidence for the presence of super-massive black holes at
the centers of galaxies (with Peter Young), the measurement of
the mass of the Galaxy using the radial velocities of outer sa-
tellites (showing that it supported the developing view that the
mass distribution in galaxies is very extended and isotropic;
with F.D.A. Hartwick), the discovery that most nearby galaxies
harbor low-luminosity nuclear activity (with Alex Filippenko
and Luis Ho), and inferences concerning the mechanism gen-
erating the luminosity of quasars and Seyfert galaxies (e.g., with
Matt Malkan).
If there is an area of astrophysics in which Wal’s accomplish-
ments were greatest, it is the study of the diffuse intergalactic
medium and the chemical history of the universe—a field he
pioneered in the 1960s and of which he remained in the fore-
front through his entire career. Beginning soon after the discov-
ery of the cosmological nature of quasars, Wal took an
immediate interest in analyzing their spectra as a means to learn
about the distribution, physical state, and cosmic evolution of
diffuse gas comprising the general medium outside of galaxies.
Initially, the quality of the information was limited by the tech-
nology of the time, particularly the detectors—photographic
emulsions. Beginning in the early- to mid-1970s, Wal began
an extremely fruitful collaboration with Alec Boksenberg (then
at University College, London), who had developed a two-
dimensional photon counting detector system (called the IPCS)
which allowed for spectroscopy of relatively faint objects with
up to 20 times higher throughput than photography, along with
zero detector noise. The IPCS coupled with the Palomar
200-inch telescope made it possible to obtain quasar spectra
of unprecedented quality. This capability allowed Sargent,
Boksenberg, and colleagues to revolutionize the field over
the ensuing decade, with a spectacular series of papers that
not only presented exciting new data, but also introduced many
of the statistical techniques and scientific interpretation that
have remained the standard ever since. Wal’s 1980 paper (with
Peter Young, Alec Boksenberg, and David Tytler) on the inter-
galactic nature of the Lyman α forest firmly established that
these lines represented intergalactic neutral hydrogen using so-
phisticated statistical methods, many of which were new to as-
trophysics. It was a huge paper, both in terms of its influence,
and physically—it could have been 10 separate papers, given its
content. Subsequent papers established the first evidence for
cosmological evolution of the intergalactic medium, and evi-
dence connecting absorption systems containing detected heavy
elements with intervening galaxies (at redshifts that were then
far beyond where galaxies were being observed directly)
225
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, 125:225–226, 2013 March
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Through the mid 1980s to early 1990s, Sargent and colleagues
collected larger samples of QSO absorption line systems in or-
der to improve constraints on the evolutionary behavior of the
IGM over time, as well as to establish the connection with gal-
axies; these surveys were ambitious enough to remain relevant
some 15–20 years after publication.
During the years 1984–1993, Wal spent a huge portion of his
time on the development of the Keck Observatory as a co-chair
of the Keck Science Steering Committee, a group of scientists
that oversaw nearly every aspect of the project, from scientific
capabilities to the design of the support facilities. It is impossi-
ble to overstate the importance of this group, and of Wal’s lead-
ership of it, during the ∼10 year period between inception and
first light—they were largely responsible for the immediate sci-
entific success of Keck. The Keck telescope and HIRES spec-
trometer, both of which saw first light in 1993, opened up an
entirely new era in the study of the intergalactic medium, thanks
to the routine ability to obtain high resolution, high signal-to-
noise ratio spectra of a large numbers of quasars. The combi-
nation of the quantum leap in the information content of the
spectra, and concurrent advances in the theoretical understand-
ing of diffuse baryonic material (increasingly seen as a medium
which accurately traces the filaments of dark matter on all
scales), led to new insights into the chemistry and physical evo-
lution of the IGM. Sargent and colleagues led many, if not most,
of the developments on the observational side—measuring
abundances and abundance ratios in so-called “damped Lyman
α” systems, sites of large columns of neutral H believed to be
associated with distant galaxies along the line of sight, charac-
terization of the chemistry of the diffuse IGM far from galaxies,
and most recently, extending the IGM observations to the high-
est redshifts, close to the epoch (z > 6) when the medium is
believed to have been reionized by a combination of quasars
and young galaxies. These investigations helped open up
entirely new fields, such as the study of “Population III” stars,
which may have imprinted a “metallicity floor” on the entire
diffuse IGM, and theoretical study of the mechanisms for mov-
ing heavy elements from the sites of their creation into low-
density regions of the universe. The Lyman α forest has now
become a primary tool for cosmology because of its apparently-
faithful tracing of the dark matter distribution on scales where
other techniques break down.
Wal was justifiably proud of his cohort of graduate students
over the course of his career—there was a total of 18 students
according to Wal’s web page devoted to the subject, which he
introduced with the following: “All of my Ph.D. students are
listed below. Remarkably, like me, they almost all showed a re-
luctance to work for a living and instead found jobs in acade-
mia.” In addition to his personal achievements, his track record
with his graduate students was exceptional—most of the 18
went on to distinguished academic careers in a startling variety
of scientific areas. To name a few, along with their most recent
institutions and general areas of study: A. Filippenko (UC
Berkeley; supernovae and supernova cosmology), Edwin
Turner (Princeton; exoplanets), Patrick Osmer, Matthew
Malkan (respectively, Ohio State and UCLA; quasars and active
galaxies), John Huchra and Steve Kent (respectively, Harvard-
Smithsonian CfA, U. Chicago/Fermilab; stellar populations and
surveys of the local universe), John Kormendy (U. of Texas;
galaxy structure and dynamics), Robert O’Connell and Daniel
Kunth (respectively, U. of Virginia, Institut d’Astrophysique de
Paris; UV and X-ray astronomy), and Peter Young (Caltech,
deceased 1981), Rob Simcoe (MIT), and George Becker
(IoA Cambridge), all working on quasar absorption line studies
of the distant universe.
I confess that I am also a Sargent “product”—I was lucky en-
ough toworkwithWal at Caltech over the years 1984–1989, dur-
ing which time I was his only graduate student. Wal (with tongue
in cheek) always calledme “Team”—a name I am surewill sound
familiar to some of his other former students. Any conversation
we had could then be called a “Team meeting”, which Wal en-
joyed as an ironic tweak of groups that were actually large en-
ough to need such things. I remember my first meeting with Wal
(nearly 30 years ago) in his office in Robinson Hall, during the
first few weeks of the academic year—I was terrified and intimi-
dated and was not at all sure I had a right to be there. Quickly I
learned that I had nothing to fear—Wal turned out to be funny,
irreverent, and extremely interested in discussing many subjects
both within and outside of astronomy. Our conversations would
almost always end up on a topic other than my thesis—some of
Wal’s favorites were baseball, music, Manchester United, books,
and sumo wrestling. Wal had an uncanny ability to inject humor
into any situation that was in danger of becoming overly serious,
quite necessary for calming a neurotic young graduate student
such as myself. A favorite game of Wal’s was where he would
pretend to be ignorant of all American popular culture and askme
naive questions about it (since I was apparently his only direct
link to all things American, despite his decades spent in southern
California). Looking back on my formative years as a Caltech
graduate student, it is hard to recall ever receiving direct advice
from Wal, and yet somehow he profoundly influenced the way I
view science. In my personal view, the principal characteristics
that Wal passed on to his students are a taste for interesting prob-
lems, a healthy degree of skepticism and self-criticism, and an
attitude that celebrates the unexpected turns and tangents that of-
ten arise when one “looks to see what is out there.”
As a colleague,Wal has been just as important to me as he had
been as a mentor. Although we had not worked together directly
on science since I returned to Caltech 17 years ago, I realize how
much Iwould look forward toWal’s regular visits tomy office for
informal conversations and catching up on “gossip” (of which
Walwas a big fan). In all honesty, such times spent withWal have
been essential to my sanity and well-being. I am not quite sure
how I will copewithout our “Teammeetings.” I will missWal for
much more than his scientific accomplishments—he was a close
friend.
226 STEIDEL
2013 PASP, 125:225–226
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Wallace L. W. Sargent (1935–2012)

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Wallace L. W. Sargent (1935–2012)

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