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Daniela Calzetti talks with 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 their work.
Article: Star formation in NGC 5194 (M51a): The panchromatic view from GALEX to Spitzer
Authors: Calzetti, D, et al.
Journal: ASTROPHYS J, 633 (2): 871-893 Part 1 NOV 10 2005
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 highly cited?

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.

Figure 1: +enlarge
Click figure to enlarge and read description.

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 stars.

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?

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.
Associate Professor
Department of Astronomy
University of Massachusetts at Amherst
Amherst, MA, USA

2008 : March 2008 - Fast Moving Fronts : Daniela Calzetti