Astronomical News The Experience of Two High School Students Doing Astronomical Research at ESO Lia Sartori1 could therefore learn a great deal about velocity profiles, etc). A few technicalities, Clara Pelloni1 activities at ESO: telescope design such as the working of telescopes, spec­ and construction, observation prepara­ trographs and CCDs were also needed. tion and realisation. At first, we felt a This study constituted the first part of our 1 Liceo Lugano 2, Savosa, Switzerland bit disorientated in this new world of sci­ project. The complete manuscript of entific researchers. But soon we got our project report is available (in Italian) on acquainted with many nice and helpful the web2. As a project for diploma work at the astronomers who showed us the various end of Swiss high school, long-slit kine- research activities at ESO. We could matic data for two giant elliptical gal- also discuss our diploma project and get Data reduction axies, observed with the FORS1 spec- some precious advice. During this full trograph at the ESO VLT, were reduced immersion in the scientific world, some­ The goal of our project was to fully by two students. The reduction of these thing completely new for us, the impres­ reduce long­slit spectra of two giant ellip­ data was our first research experience. sion was really positive and stimulating. tical galaxies, NGC 5018 and NGC 3706, The preparation and reduction of the At ESO, we found a nice and welcoming and to obtain the corresponding kine­ long-slit data is outlined. We also atmosphere: everybody was very help­ matic quantities: mean line­of­sight describe our impressions of this first ful and the interactions between astrono­ velocities, velocity dispersions and higher encounter with the scientific research mers seemed to us very friendly. The order moments of the velocity profile. world. desire to work one day in a research Figure 1 shows one of the target galaxies, institute such as ESO has been an extra NGC 5018. Spectra were obtained with motivation for us to start, with even the FORS1 spectrograph of the VLT in We are two Swiss students who started more enthusiasm, our university studies. 2000 and 2001. The light of elliptical gal­ work on the high school diploma two During the visit to Garching, we also axies is dominated by the emission from years ago. In Switzerland the diploma in ­ visited the outreach department where red giant stars with spectral types such cludes a research project that takes we were offered a lot of goodies: DVDs, as our calibration templates stars. Visible place during the last two years of high posters, caps, postcards, etc. absorption lines include the K, H lines school: the project can be done in any of of calcium, the Hβ, Hγ and Mgb lines (see the subjects taught in this kind of school. The visits to ESO helped immensely in Figure 2). These two galaxies had already Usually professors propose a list of achieving the goals of the diploma pro­ been observed (e.g., Carollo & Danziger, projects for the students to choose from. ject. Once the project was completed, 1994a,b and Carollo et al.,1995), but We decided to work in astronomy, one we participated in various regional and never with such a large telescope as the of the most fascinating fields of physics. national competitions. The most signifi­ VLT. With these data, we tried to confirm Our project, entitled “Spectroscopic cant one was the national competition and extend to larger radii previously analysis of elliptical galaxies”, has led us “Science and Youth” that took place in published data. For both galaxies there to a whole new experience and to meet Geneva at the end of April 20091: four is an indication of dark matter in the new people (including a few astrono­ days of project presentations and discus­ outer parts, so very extended kinematic mers), but most importantly, has brought sions with experts, other participants data (up to two to three effective radii, us to a mythical place in the astronomi­ and the public. Presenting our project to Reff) could improve the confidence on the cal world, namely the ESO observatories such a wide audience turned out to presence of a dark halo. Previous work at La Silla, Paranal and Chajnantor be challenging, since we had to adapt our has shown the importance of both (ALMA) in Chile, which are equipped with explanations to the various levels of increased radial extension and the calcu­ some of the world’s best telescopes. scientific expertise. But the Geneva com­ lation of higher order moments in quan­ petition was not only work: there was a tifying the amount of dark matter in ellipti­ During the entire project, we were guided lot of free time to get to know all the other cal galaxies. by our physics teacher, Nicolas Cretton, participants, who came from all over astronomer and ex­ESO fellow. Together Switzerland. It is notoriously difficult to measure dark with Hans­Walter Rix, he wrote the origi­ halos in elliptical galaxies, since one has nal ESO observing proposals (65.N­0285 to rely on absorption spectra, which are and 68.B­0590) on which our project Preparatory theoretical work very hard to obtain beyond one Reff due was based. During the entire work, we re ­ to the sharp drop in stellar luminosity and ceived a lot of help and advice from Piero Since the high school programme con­ because of the absence of an extended Rosati, an astronomer at ESO. When the tains little astronomy, before starting gas tracer, as in spiral galaxies. One spectra were all reduced, Eric Emsellem the data reduction work we had to learn alternative to stellar kinematics is to use from the Observatoire de Lyon (and now at a few necessary astronomical concepts: planetary nebulae that can be detected ESO) extracted the kinematical quantities stellar evolution (life cycle of stars, at large radii. The present study confirms for each axis of the galaxies. Hertzsprung–Russell diagram), galaxy and extends previously published kine­ structure and morphology, dark matter matic data such as those obtained by We visited ESO Headquarters in Garching in galaxies, long­slit spectroscopy (emis­ Carollo & Danziger (1994a,b) and Carollo twice during the summer of 2008 and sion lines, absorption lines, line­of­sight et al. (1995). It therefore constitutes an 46 The Messenger 141 – September 2010 $ Figure 2. The central major axis spectrum of NGC 5018 is shown from $ the FORS1 observations. The major absorption lines of calcium, hydro­ * '"@ gen and magnesium are indicated. 'β ,FA 'γ 6@UDKDMFSGÄ Figure 1. A Digital Sky Survey image of NGC 5018, for NGC 3706 they were 135 minutes was given to the sky subtraction, since with the position of the FORS1 long slit on the major for the major axis, 90 minutes for the we wanted to obtain reliable kinematic axis (green) shown and the circles of radii 1, 2 and intermediate (45­degree) axis and 225 data at large distances from the galaxy 3 Reff overlaid (pink). Asymmetric features beyond 2 Reff are probably the sign of a past merger in this minutes for the minor axis. centres. In this respect, the 408­arcsec­ galaxy. ond long FORS1 slit was very useful. We As the first step, we obtained the raw also reduced in the same manner spec­ improved basis for the dynamical model­ data (science and calibration frames) for tra of calibration template stars observed ling that is needed to study the amount the FORS1 programme from the ESO at the same telescope: as templates and distribution of dark matter in giant Archive. From there, a lot of effort and we used the following giant stars, indi­ elliptical galaxies; such modelling is how­ time went into understanding: 1) the cated with their respective spectral type: ever outside the scope of our diploma nature of the imaging and spectroscopic HR 4595 (K3III), HR 4790 (G3III), HR 4801 project. data and corresponding calibrations; (K5III), HR 4818 (K4III). 2) the methodology to remove instrumen­ With the GRIS­600B+12 grism and a tal signatures; and 3) the calibration pro­ 1.31 arcsecond­wide slit, we had an in ­ cedures to go from instrumental to physi­ Results: stellar kinematics of NGC 5108 strumental spectral resolution σinstr of cal units. For all these tasks, we were and NGC 3076 200 km s–1, similar to the galaxy velocity also introduced to IRAF 3, which we ran dispersion, which is just sufficient to on a Linux laptop as part of the ESO Sci­ To quantify the line­of­sight velocity distri­ obtain good kinematic measurements. soft package4. butions along the principal axis of the The wavelength resolution was 1.2 Å per galaxies, Eric Emsellem computed the pixel, which corresponds to 7.8 Å for All raw spectra were bias­subtracted, Gauss–Hermite moments with dedicated the CCD pixels and slit size we used. The flat­fielded, sky­subtracted and wave­ software (a C version of a penalised pixel­ total exposure times for NGC 5018 length­calibrated following the various fitting routine, described by Cappellari are 200 minutes for the major axis and steps described in Massey et al. (1992) & Emsellem, 2004): mean rotation veloc­ 150 minutes for the minor axis, whereas and Massey (1997). Particular attention ity, velocity dispersion sigma, and -&" 11D 11D l l l l ,@INQ ,HMNQ R JL l Figure 3. The stellar velocity, velocity 5 l dispersion, h and h profiles as func­ l 3 4 tions of distance from the galaxy cen­ tre (in arcseconds) are shown along R the major axis of NGC 5018, from top JL m to bottom respectively and for the major and minor axes (left and right).