Download Joint Scientific Opportunities with the Giant Magellan Telescope and

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
science operations in 2007-8 and should enter full
Figure 1. The ALMA dishes as they will
operations with 64 or more dishes in 2012. The telescope
appear after completion at Chajnator in
will operate in the millimeter and sub-millimeter
the Atacama desert of northern Chile.
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
Fig 2. The GMT
science missions span a broad
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
ALMA
coming decade. The large
millimeter array was a top
GMT
priority of the 1990
decadal survey of
astronomy
and
Figure 3. Comparisions between the
astrophysics, while a
angular resolving power of ALMA, the
giant segmented optical
VLA, the GMT, and other optical-IR
telescope is the top
instruments. The GMT will work in the
priority for ground-based
diffraction-limit in the IR, and will use
astronomy in the most
partial ground-layer correction in the
recent decadal survey.
visible.
Figure 4: The ALMA
These two facilities
and GMT sites in Chile.
represent the crown jewels of radio and ground-based optical astronomy in
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.
Figure 6. Simulated ALMA (left) and optical
images of a lensing cluster. Most of the submm sources are star forming background
galaxies. Joint studies with the GMT and
ALMA will allow us to probe both the very
faint background population and small-scale
structure in the dark matter distribution within
the cluster potential well.
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
probe of early star and galaxy formation from the
visible through sub-mm wavelengths. Joint science
opportunities between the GMT and JWST are
discussed in a separate document.
2.2 Distant Galaxy Clusters: ALMA will have the
ability to probe the structure of distant galaxy clusters
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. The nearest star forming complexes in Orion and Ophiuchus area ideal
laboratories for panochromatic studies of star formation with the GMT and ALMA.
3.2 The Binary Fraction and Companion
Mass Ratio:
Figure 7. A protoplanetary disk with a tidal gap created
by a Jupiter-like planet at 7AU from its central star. The
simulated ALMA 350GHz image (right) clearly reveals
the presence of the gap in the disk. From the ALMA
science case.
One of the key science goals for the GMT
is focused on understanding the origin of
stellar masses and the role of binary star
formation in the determination of star and
planetary mass distributions. With its high
spatial resolution and sensitive mid-IR
spectroscopy the GMT can probe binary
mass fractions over a wider range of ages,
environments and separations than is
currently possible. Disk formation and
destruction is a key process in star
formation and the evolution of disks and
close binaries are intimately connected.
ALMA will have the sensitivity to measure disk emission from large samples of such stars to test whether
the diminution of flux is due to clearing of material by binary companions. ALMA will be able to resolve
the structure of disks in binary environments. The size and morphology of gaps will test the dynamical
theory, which is also fundamental to theories of planet formation. In addition, ALMA will measure directly
the masses of the circumstellar disks in young binary systems, constraining disk accretion physics and
reflecting on the planet formation rate in binary systems.
3.3 Debris Disks and Protoplanets.
The GMT is being designed with extreme adaptive optics and imaging of exoplanets as a high priority. Old
Jupiter class planets with small orbital semimajor axes will be detected in reflected light in the near-IR
while younger giant planets will be imaged at longer wavelengths and larger distances from their parent
stars. The youngest planetary sized objects are expected to be embedded in protoplanetary debris disks and
thus may not be discernable directly against disk emission. The existence of such planets can be inferred
indirectly from their clearing of regions of the disk. With the GMT high-resolution mid-IR spectroscopy of
debris disks can reveal double peaked line profiles characteristic of incomplete disks. This is described in
detail in the GSMT science case (http://www.aura-nio.noao.edu/book/ch2/2_4.html). ALMA will be able to
image disk gaps at large radii in material that is too cold to be detected at near- and mid-IR wavelengths.
An example simulation, from the ALMA science case, is shown in Figure 7. Together ALMA and the
GMT allow searches for young protoplanets over a wide range of ages, separations and contrast ratios. The
southern hemisphere offers and ideal location for such studies as many of the richest star forming
complexes pass overhead in Chile.
3.4 Star Formation. Star formation is a key part of galaxy formation and is intimately connected to the
process of planet formation. The physics of star formation remains poorly understood. The relevant region
of the spectrum for physical studies of protostars and molecular clouds stretches from cm wavelengths in
the radio to the near- and mid-IR. The mid-IR through mm regions of the spectrum are particularly critical
as they sample a wide range of molecular species and are sensitive to dust emission at temperatures from
10 to 100 K. ALMA will provide a vast new areas of empirical studies star formation, within the Milky
Way, the Magellenic Clouds and other nearby galaxies. The GMT can play an important role in
complementing mm and sub-mm studies with ALMA. The mid-IR high-resolution spectrograph on the
GMT will allow access to higher energy transitions from a variety of molecular species. The GMT mid-IR
imager, working in the diffraction-limited laser AO mode, will provide imaging and resolutions comparable
to those of ALMA and 2-3 times better than what can be achieved with present instruments.
4.0 Summary. In less than a decade ALMA will emerge as one of the forefront research facilities in the
world. It will open new windows on star formation, galaxy formation and fundamental astrophysics. The
Giant Magellan Telescope will come on line soon after the completion of ALMA and will likely be the
largest optical/IR telescope in existence at that time. Its excellent near- and mid-IR performance and
Chilean location made it ideally suited to complement the power of ALMA. Together the two facilities
enable a range of science that would not be possible with either facility alone. The likely deployment of the
James Web Space Telescope on roughly the same time frame rounds out the suite of next generation
optical-to-mm wave astronomical facilities.