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Joint Scientific Opportunities with the Giant Magellan Telescope and the Atacama Large Millimeter Array 1. Introduction 1.1 The Next Generation Radio Astronomy Observatory: The Atacama Large Millimeter Array (ALMA) is a state-of-the-art high-frequency radio astronomy facility under construction in the high Atacama desert in northern Chile. The effort is a joint program between the US, via the National Science Foundation and the National Radio Astronomy Observatory and Europe, via the European Southern Observatory. The array is scheduled to begin limited Figure 1. The ALMA dishes as they will science operations in 2007-8 and should enter full appear after completion at Chajnator in operations with 64 or more dishes in 2012. The telescope the Atacama desert of northern Chile. will operate in the millimeter and sub-millimeter wavelength regimes and will be the world’s most powerful probe of molecular chemistry and interstellar matter in both the Milky Way and in distant galaxies. Details of the ALMA project and its scientific mission can be found at www.alma.nrao.edu. 1.2 A Giant Segmented Mirror Telescope for Ground-based Optical Astronomy in the New Millennium: The Giant Magellan Telescope (GMT) is a 25-m class telescope to be constructed in central or northern Chile. The project is lead by a consortium of universities and private research institutions. The telescope is composed of seven primary mirror segments, each of which is 8.4m in diameter. The collecting area of the telescope is equivalent to a filled aperture 21.4m in diameter and the angular resolving power is equivalent to that of a filled aperture 24.5m in diameter. The details of the GMT project and the GMT science case can be found at www.gmto.org. The GMT and ALMA science missions span a broad Fig 2. The GMT range of topics, from cosmology and galaxy formation to studies of star formation and the energetics of the interstellar medium. In this brief report we examine areas in which there is strong synergy between the capabilities of the GMT and ALMA in addressing many of the forefront scientific frontiers in astronomy and GMT astrophysics in the coming decade. The large ALMA millimeter array was a top priority of the 1990 GMT decadal survey of Figure 3. Comparisions between the astronomy and angular resolving power of ALMA, the astrophysics, while a VLA, the GMT, and other optical-IR giant segmented optical instruments. The GMT will work in the telescope is the top diffraction-limit in the IR, and will use priority for ground-based partial ground-layer correction in the astronomy in the most visible. recent decadal survey. These two facilities Figure 4: The ALMA represent the crown jewels of radio and ground-based optical astronomy in and GMT sites in Chile. the coming decade. The southern hemisphere location of the GMT ensures that it will sample the same region of the sky as ALMA. The two facilities will probe similar physical scales: the GMT, operating at the diffraction-limit, has a resolution of 10mas at 1micron, while ALMA will achieve 10mas resolution at its highest operating frequencies. ALMA is currently under construction in the north of Chile. Site selection for the GMT is in progress and work will begin on the site in mid 2006. The candidate sites include three possible locations near Cerro Las Campanas, and a number of sites to the north. 2. Galaxies and Cosmology with the ALMA & the GMT 2.1 Surveys of Distant Star-forming Galaxies: ALMA will have unprecedented power to probe the early universe and star formation in galaxies. Working in the sub-mm continuum ALMA will be able to detect star forming galaxies to essentially any distance, the negative k-correction in the sub-mm ensures that starburst galaxies have approximately equal brightness over a very broad span of redshift. Figure 5. The HDF as imaged with SCUBA and the Small fields will be surveyed to extreme depths Hubble Space Telescope. ALMA will have greater in both the sub-mm continuum and in the lines sensitivity than SCUBA and higher angular of various species. The most sensitive sub-mm resolution that HST, allowing it to detected lower bolometer arrays on single-dish telescopes luminosity objects at high redshift. The GMT will today (e.g. SCUBA; Hughes et al. 2001) can have the sensitivity needed for redshift detect extreme starbursts to quite high redshifts determinations and detailed structural and dynamical (e.g. z ~ 3; Smail et al. 2001). Confusion, a studies on angular scales of 10-20mas. significant limiting factor in current surveys, will not be significant for deep surveys with ALMA. Most of the faint sub-mm sources detected in current surveys are extremely faint in the visible and spectroscopy of these systems pushes the current generation of optical telescopes to their limits (see e.g. Chapman et al. 2003). The GMT will allow optical/near-IR imaging and spectroscopy of the fainter and more distant star forming galaxies detected by ALMA. Modest area surveys with ALMA can be followed up with the wide-field multi-slit spectrograph on the GMT, while very deep, targeted observations are well matched to the GMT diffraction-limited AO modes. GMT spectroscopy of deep ALMA sub-mm surveys will resolve the full redshift distribution of the sub-mm population and address the issue of star formation at very high redshifts. Spectroscopy with the current generation of large telescopes is limited to targets brighter than R(Vega) < 24.5. The GMT multi-object spectrograph should reach to R ~ 26 in several hour exposures, while spectroscopy of point sources in the diffraction-limited regime could reach as faint as K(Vega) ~ 23-24. Deep K-band images at the diffraction limit will reveal the distribution of stellar mass within galaxies, while line and continuum images with ALMA will show active sites of star formation and giant molecular clouds. The two instruments working in coordination can provide a more complete picture of galaxy formation and evolution that either can working alone. Bringing the James Webb Space Telescope (JWST) into the mix will make for an extremely powerful Figure 6. Simulated ALMA (left) and optical probe of early star and galaxy formation from the images of a lensing cluster. Most of the sub- visible through sub-mm wavelengths. Joint science mm sources are star forming background opportunities between the GMT and JWST are galaxies. Joint studies with the GMT and discussed in a separate document. ALMA will allow us to probe both the very faint background population and small-scale 2.2 Distant Galaxy Clusters: ALMA will have the structure in the dark matter distribution within ability to probe the structure of distant galaxy clusters the cluster potential well. on small scales using the Sunyeav-Zeldovich effect. Deep blind S-Z surveys from dedicated S-Z telescopes will yield catalogs of hundreds of potential high redshift clusters, all of which will require some optical follow-up observations to determine their redshifts, optical richness and stellar content. These distant clusters provide an ideal laboratory for studies of stellar and chemical evolution in galaxies and the GMT provides the required capability to explore clusters beyond the reach of current facilities. ALMA will probe mass concentrations on scales of ~ 15” to 2’ within clusters via high spatial resolution S-Z studies with sensitivity in the micro-Kelvin range. Kinematic studies of the constituent galaxies with the GMT multi-object spectrometer in conjunction with these deep S-Z observations will allow one to develop a detailed picture of the dynamic state of individual rich clusters. Observations of large samples of clusters, particularly over a wide range in redshift will reveal the processes by which clusters are assembled, perhaps via the mergers of smaller groups. The GMT will be the telescope of choice for studies of these rare objects. The required fields of view are modest and the GMT optical and near-IR imaging spectrographs will be very powerful instruments for this work. The dedicated S-Z survey instruments are being deployed in the Antarctic and thus a southern hemishere (and the further south the better) ELT are required for spectroscopic follow-up of the most distant clusters. 3. Star and Planet Formation Several of the GMT’s unique capabilities in the study of exoplanets and sub-stellar mass objects are outlined in the GMT science case. These include direct imaging in the near-IR with coronographs and adaptive objects, imaging and spectroscopy in the mid-IR using nulling interferometry, and detailed studies of the low mass end of the IMF in crowded regions using adaptive optics in the near- and mid-IR. 3.1 The Sub-Stellar IMF: ALMA and the GMT bring powerful tools to bear on the problem of observing the formation of stars and planets from dense molecular clouds. The GMT will detect low mass stars and substellar objects via thermal radiation from dust grains in the near and mid-IR. The great sensitivity of the GMT and its high angular resolution in the laser tomography AO mode will allow it to probe highly enshrouded protostars and protoplanets in nearby star forming complexes. While near-IR and mid-IR observations provide a window with greatly reduced extinction, ALMA, operating in the mm and sub-mm regions of the spectrum can penetrate even the densest protostellar cores. Jupiter mass protoplanets with ages of a few million years will be detectable to distances of a few hundred pc with ALMA in reasonable integration times. The GMT and ALMA, by observing in different regions of the spectrum, sample a wide range of temperatures and densities and thus allow for more complete studies of star and planet forming regions in the southern sky.

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