EMIR addresses the core observing goals of a 10-m class telescope by providing multi-object near-IR spectroscopy of faint sources. Typical targets will be faint galaxies, low-mass stars, brown dwarfs, distant supernovae, stellar populations in resolved external galaxies, HII regions and objects in dust obscured regions: galactic nuclei, young stellar objects and edge-on galaxies. Some representative examples of scientific projects that are ideally suited for EMIR are:
Brown dwarfs have recently been unambiguously identified. The current data suggest that they may be a common constituent of open clusters and also abundant in the field. Surveys of brown dwarfs will allow to investigate the IMF at extremely low masses thus helping to understand the largely unknown processes of star formation at the faint end of the IMF. The most massive brown dwarfs are quite red, i.e., I-K > 3, and on the basis of evolutionary models, much redder colors are expected for intermediate- and low-mass brown dwarfs. This implies an easier detectability in the near-IR than at optical wavelengths. Typical spectral resolutions of 5000 are excellent in order to disentangle a number of molecular and atomic features. Due to the intrinsic low luminosities, large telescopes are needed.
Molecular clouds hold the key for the process of star-formation: we believe they are the cradle of normal stars. But molecular clouds are usually dense regions of high dust obscuration with a visual extinction of 5-20 magnitudes. Infrared imaging can be best used to penetrate through these heavily obscured regions and detect embedded objects such as T-Tauri stars. EMIR is ideal for a follow-up spectroscopic study of these objects.
Preliminary studies of the CO absorption band at 2.3 microns indicate a great sensitivity to both stellar effective temperature and gravity, making this feature a powerful tool to determine both the age of starburst galaxies and the stellar population properties of elliptical galaxies (i.e., metallicities, and giant-to-dwarf stellar ratios). A first step to use this feature is its empirical calibration as a function of the main stellar parameters using a proper stellar library (see Gorgas et al., 1998, in prep.). CO surveys of nearby giant ellipticals are currently being undertaken using 4m-class telescopes (e.g., Guzmán & Mobasher 1998). EMIR is the ideal instrument to extend these surveys to dwarf ellipticals in nearby clusters.
EMIR will have a major impact on the field of AGN and the environment of AGN . In the local universe, the fraction of AGN occurrence among galaxies (estimated to be as high as 35% according to ) can be extensively explored from mostly unextincted, high-S/N near-IR spectral features such as the coronal [Si IV] 11.962 mm and the broad Brγ emission lines. The content of young stars around the nuclei, relevant to the starburst- AGN connection, will be evaluated through observations of Brγ emission and the photospheric Si 11.59 microns and CO 2.3 microns absorption in nearby galaxies harbouring AGN . At high redshifts, a multi-object spectrograph like EMIR will most efficiently determine what fraction of the observed excess of red faint galaxies in the environments of QSO s (and Radio Galaxies) are cluster members and/or lensed objects. This not only will allow to determine the nature of the lower-z intervening galaxies in the line of sight of the QSO (DLA, Mg or C absorbers), but it can also be a powerful technique to study normal galaxies at the same cosmic age as that of the highest redshift QSO s. Finally, the search for classical rest-frame optical stellar features and scattered emission lines off-nucleus in the near-IR will solve the controversy about the nature of the high luminosities encountered in normal QSO hosts at high-z .
EMIR is ideal to undertake the spectroscopic follow-up of all-sky surveys. For instance, AXAF (Advanced X-ray Astrophysics Facility) is expected to detect QSO s and active galaxies 100 times fainter than the Einstein satellite did. IR spectroscopy of the most distant sources will be essential for resolving the question of the origin of the extragalactic X-ray background and to determine the relative contribution of QSO s, AGN and starburst galaxies. Similarly, ELAIS is expected to identify several thousand extra-galactic sources in the range 2.5-240 mm, including a high redshift population of objects most likely dominated by starburst and Seyfert galaxies which will require ground-based follow-up spectroscopy in the near-IR.
The evolution of clusters of galaxies remains poorly known beyond z=0.5. EMIR will allow observations of a large number of clusters to establish unambiguously cluster membership and study: