Daniela Calzetti talks with
ScienceWatch.com and answers a few questions about
this month's Fast Moving Front in the field of Space
Science. The author has also sent along images of
Article: Star formation in NGC 5194 (M51a): The
panchromatic view from GALEX to Spitzer
D, et al.
Journal: ASTROPHYS J, 633 (2): 871-893 Part 1 NOV 10
Addresses: Space Telescope Sci Inst, 3700 San Martin Dr,
Baltimore, MD 21218 USA.
Space Telescope Sci Inst, Baltimore, MD 21218 USA.
Univ Arizona, Steward Observ, Tucson, AZ 85721 USA.
(addresses have been truncated)
Why do you think your paper is
This is a hard question to answer. The paper combines
two aspects. The first aspect is that the galaxy pair
M51, and in particular the large spiral M51a (also
known as the Whirlpool galaxy or NGC5194), have been
extensively studied by astronomers at virtually any
wavelength. NGC5194 is a nearby (by extragalactic
scales), almost face-on, grand-design spiral galaxy
with intense and extended star formation going on from
its center all along the spiral arms. The galaxy has
been used as testing ground for theories of spiral
formation, as well as studies of star formation, and
represents a sort of benchmark for comparisons with
galaxies at higher redshifts, in the distant and
not-so-distant past of the Universe.
The second aspect is the approach our paper took in
investigating this galaxy, which was a synthesis of
data at a range of wavelengths, from the ultraviolet to
the far-infrared. The novelty consisted in using
infrared data from the recently launched Spitzer Space
Telescope (~mid-2003) together with the ultraviolet
data of the relatively new GALEX space telescope, which
had been launched a few months before Spitzer.
Spitzer is providing the infrared view of astronomical
objects at unprecedented high angular resolution, thus
enabling for the first time a detailed view of galaxies
at wavelengths where the dust dominates the emission.
For the first time, Spitzer is enabling a view of
dust-emitting regions of galaxies on scales small
enough that the different stellar populations which
heat that dust can also be located and identified. This
is enabling the field of extragalactic astronomy to
finally attempt to identify the nature of the different
components of interstellar dust.
In our paper, we used the GALEX data to trace the young
stellar populations. We combined the Spitzer data with
the GALEX data because the two sets of data have
comparable angular resolutions, which made for an
"apple-to-apple" type of comparison. It is possible
that the combination of a famous galaxy with the new
type of data (Spitzer and GALEX) has attracted some
attention from the community and contributed to the
current impact of the paper.
Does it describe a new discovery,
methodology, or synthesis of knowledge?
I believe the best way to describe the paper is
"synthesis of knowledge," although there is also a
small component of "new methodology" as well. With
respect to the latter, in the paper we investigate a
new tool for measuring how fast galaxies form new
Would you summarize the significance
of your paper in layman’s terms?
One of the important results from the paper has been
the derivation of a new tool for measuring how rapidly
galaxies form new stars. This tool exploits the
(already known) fact that young stars heat the dust
that surrounds them to relatively high temperatures; we
proved that this dust emits radiation preferentially in
a specific infrared window. The tool, which has been
calibrated on a nearby galaxy, is potentially useful
for measuring the rate at which distant galaxies form
stars, and thus can offer an additional venue for
investigating galaxy evolution.
How did you become involved in this
research and were any particular problems
encountered along the way?
"One of the
the paper has
derivation of a
new tool for
The paper is part of a large collaboration called SINGS
(Spitzer Infrared Nearby Galaxies Survey), which
started in 2000. The paper itself is the result of the
efforts of many on the SINGS team.
My interest for the topic of star formation and the
interaction between stars and the dust that surrounds
them in galaxies dates back to the early stages of my
career, about 15 years ago. My interest in the topic
happened almost by chance: at the time I was working on
some ultraviolet spectra of nearby galaxies from the
International Ultraviolet Explorer (IUE), and my
collaborators and I noticed that there was a systematic
behavior of the spectra, which depended on how much
dust the galaxies contained. This was something we
considered important to pursue, since dust "robs" a
galaxy of its ultraviolet light; this means you cannot
probe the galaxy’s star formation with sufficient
clarity at those wavelengths, unless you can find a way
to "control" the effects of dust.
Where do you see your research
leading in the future?
Understanding how the different components of a
galaxy—stars, gas, and dust evolve through time
and interact with each other is fundamental for
unraveling how galaxies have evolved through cosmic
ages. Despite the many advances over the years, we
still have many questions left to answer. I believe
this quest will push me to investigate the full
electromagnetic spectrum from galaxies, from the
ultraviolet to the millimeter and radio wavelengths,
using both space facilities (including upcoming ones
like the Herschel Space Telescope and future ones like
the JWST) and ground-based telescopes.
Do you foresee any social or
political implications for your research?
I don’t foresee any impact at the social or
political level for the type of research I conduct.
Daniela Calzetti, Ph.D.
Department of Astronomy
University of Massachusetts at Amherst
Amherst, MA, USA