Surveys DOI: 10.18727/0722-6691/5128 4MOST Consortium Survey 9: One Thousand and One Magellanic Fields (1001MC) Maria-Rosa L. Cioni 1 et al., 2013). This has motivated many MAgellanic Stellar History (SMASH), and Jesper Storm 1 studies aimed at explaining the structure the Optical Gravitational Lensing Experi- Cameron P. M. Bell 1 and the star formation history of the ment (OGLE), were made possible by the Bertrand Lemasle 2 Large Magellanic Cloud (LMC), the Small development of wide-field cameras at Florian Niederhofer 1 Magellanic Cloud (SMC) and their tidal telescopes dedicated to survey observa- Joachim M. Bestenlehner 3 features, i.e., the Magellanic Bridge and tions for a large fraction of the available Dalal El Youssoufi 1 Stream. Furthermore, with the increased time. Sofia Feltzing 4 number of deep imaging observations Carlos González-Fernández 5 we have discovered potential satellite Next to this wealth of photometric obser- Eva K. Grebel 2 galaxies of the Magellanic Clouds and vations, which have yet to reach their full David Hobbs 4 new stellar streams possibly associated exploitation (also including data from the Mike Irwin 5 with tidal stripping events (for example, Gaia satellite), there is a pronounced lack Pascale Jablonka 6 Koposov et al., 2018). of spectroscopic observations across Andreas Koch2 the range of stellar populations and sub- Olivier Schnurr 1, 7 The Magellanic Clouds are the largest structures of the Magellanic Clouds. The Thomas Schmidt 1 and most massive satellite galaxies of largest samples of moderate resolution Matthias Steinmetz 1 the Milky Way. The LMC resembles a (at least R = 4000) spectra, suitable for spiral galaxy, with a rotating disc, an off- kinematics and metallicity measurements, centre bar, and a few spiral arms. Young, comprise about 9000 giant stars (for 1 Leibniz-Institut für Astrophysik Potsdam intermediate-age and old stars show example, Dobbie et al., 2014). Chemical (AIP), Germany different levels of substructures extending tagging, a powerful tool to discern the 2 Zentrum für Astronomie der Universität to large radii. The LMC hosts the most history of stellar populations, requires Heidelberg/Astronomisches Rechen- massive stars known today (for example, high-resolution (at least R = 20 000) spec- Institut, Germany Bestenlehner et al., 2014). The SMC is a tra and these only exist for about 4000 3 Physics and Astronomy, University of dwarf spheroidal galaxy, with a significant giant stars and 1300 early-type massive Sheffield, UK depth along the line of sight and a mor- stars, and for much smaller samples of 4 Lund Observatory, Lund University, phology shaped by tidal interactions (for other stellar types (for example, Nidever Sweden example, Niederhofer et al., 2018). The et al. 2019). Despite the major scientific 5 Institute of Astronomy, University of SMC formed half of its stellar mass prior advances of these programmes, where Cambridge, UK to an age of ~ 6 Gyr (for example, Rubele two thirds of the spectra refer to LMC 6 Laboratoire d’astrophysique, École et al., 2018). The Magellanic Bridge is stars and one third to SMC stars, they are Polytechnique Fédérale de Lausanne, the product of an LMC–SMC collision far from providing a comprehensive view Switzerland ~ 200 Myr ago; it is likely formed of SMC of a system where stars span the age 7 Cherenkov Telescope Array Observ atory, material and it contains both gas and range of the Universe and that is strongly Bologna, Italy stars. The origin of the Magellanic Stream, shaped by dynamical interactions. which is made of both LMC and SMC gas (for example, Richter et al., 2013), depends The One Thousand and One Magellanic on the orbital history of the Magellanic Specific scientific goals Fields (1001MC) survey aims to measure Clouds and their one-to-many interactions the kinematics and elemental abun- with the Milky Way and with each other. The 1001MC survey aims are as follows: dances of many different stellar popu- – To find and characterise kinematic and lations that sample the history of for- Large amounts of telescope time have chemical patterns within the Magellanic mation and interaction of the Magellanic been invested in imaging the Magellanic Clouds system. Clouds. The survey will collect spectra Cloud stars, studying their distribution, – To study links between kinematics and of about half a million stars with G < 19.5 and measuring their ages, distances, chemical patterns as well as their spa- magnitudes (Vega) distributed over an and motions. A major ESO programme, tial distribution across different stellar area of about 1000 square degrees and that will provide targets for spectroscopic populations. will provide an invaluable dataset for follow-up studies, is the VISTA survey – To establish how the star formation his- a wide range of scientific applications. of the Magellanic Clouds system (VMC 1), tory and the dynamical evolution of the aimed at deriving the spatially resolved system are related to these patterns. star formation history and three-dimen- – To study the metallicity-dependent Scientific context sional geometry of the system. The VMC physical and wind properties of massive is the most sensitive high-spatial-resolution stars and their evolutionary stages. During the last decade, our view of survey of the Magellanic Clouds in the – To quantify the metallicity dependence the Magellanic Clouds has changed sig- near-infrared to date. The VMC and other of key distance indicators. nificantly. These galaxies most likely contemporary surveys in the optical approached the Milky Way only a few Gyr domain, such as the SMC in Time: Evolu- A comprehensive study of the kinematics ago, rather than having orbited around it tion of a Prototype interacting late-type and chemistry of a large number of stars for a Hubble time (for example, Kallivayalil dwarf galaxy (STEP), the Survey of the at different evolutionary phases and with 54 The Messenger 175 – March 2019 a wide spatial distribution is needed to radial velocity variations (for example, solar to very metal-poor (Δ[Fe/H] > 2 dex), address these goals. Sana et al., 2013) and derive approxi- and uncertainties in the Fe abundance mate systemic velocities of variable stars of 0.2 dex or better are needed to distin- Line-of-sight (radial) velocities are one of using templates, for example in the case guish between different stellar popula- the fundamental components of motion of Cepheids, RR Lyrae stars, and long- tions. These can be derived from spectra to describe the internal kinematics of gal- period variables (for example, Nicholls et of individual stars, but for some faint axies from which the distribution of mass al., 2010). targets the spectra will be combined to is estimated. Radial velocities, together reach a minimum signal-to-noise ratio with proper motions, are necessary to The 1001MC survey data will also be (S/N) of 20 per Å within the spectral derive space velocities from which to used to quantify and map the dust regions above. We aim to reach similar infer orbital motions. The 1001MC survey absorption within the Magellanic Clouds accuracies in measuring the abundance will provide radial velocities that match using background galaxies. This is of other prominent elements. the accuracy of the tangential velocities achieved by comparing the rest-frame (proper motions) that are measured using spectra of galaxies with a reddening free A fraction of the 1001MC targets are astrometry from, for example, the VMC template where the adjustment of the variable stars, which means that they survey (Niederhofer et al., 2018) and continuum level will provide a measure change temperature across the pulsation Gaia. These are of the order of 2.5 km s –1 of the dust content along the line of sight cycle. To derive elemental abundances for an ensemble of stars (which corre- (for example, Dutra et al., 2001). Com- for Cepheids it is necessary to acquire sponds to 1% of the radial velocity of the pared to an ongoing study, based on the spectra before the temperature changes Magellanic Clouds and is a factor of 10 analysis of spectral energy distributions, significantly and therefore we plan to smaller than the internal motion), consid- spectra provide the redshifts of galaxies observe for 1 hour at any given epoch, erably improving our capability to spa- which are needed to scale the templates, this time being sufficient to reach the tially sample kinematical substructures reducing considerably the uncertainties required S/N. RR Lyrae stars, instead, are within the Magellanic Clouds. associated with a photometric determi- faint and for them we will focus on kine- nation. We estimate that with 120 galax- matics. However, we will explore the pos- The iron abundance [Fe/H] is usually ies per square degree we would obtain sibility of also measuring average Fe used as a proxy for the metallicity of stars. a dust map with a spatial resolution of abundances by combining, for example, Age and metallicity of red giant branch 0.143 square degrees, directly compara- stars with similar metallicities as esti- stars are, however, degenerate in the ble to that of current star formation history mated from the Fourier decomposition of colour-magnitude diagrams. More over, studies (for example, Rubele et al., 2018). their light-curves. the dependence on metallicity of key dis- tance indicators (for example, the peri- od-luminosity relations of Cepheids, the Science requirements Target selection and survey area luminosity of red clump stars) is still not well assessed. The 1001MC survey will The 1001MC survey aims to reach accu- The 1001MC survey will cover an area of derive the metallicity of different stellar racies of ± 2 km s –1 for the radial veloci- about 1000 square degrees (Figure 1). populations, provide a metallicity map of ties of individual stars. This accuracy is This area comprises targets that trace the system as a function of age, and lift designed to match the accuracy of the the extent of different stellar populations some of the degeneracies that affect proper motion obtained with other facili- and that describe substructures through- the tracers of stellar population parame- ties.