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Notice Board IRIS (InfraRed Imaging Spectrograph)
Overview
PI: James Larkin (UCLA)
Co-PI: Anna Moore (Caltech)
Project Scientist: Shelley Wright (Dunlap Institute, University of Toronto)
Other Local Member: David Law (Dunlap Institute, University of Toronto)
IRIS is a first generation
near-infrared (0.85-2.5 μm) instrument being designed to
sample the diffraction limit of the Thirty Meter Telescope
(TMT). IRIS will include an integral field spectrograph
(R~4000) and imaging camera (17"x17"). Both the spectrograph
and imager will take advantage of the high spatial
resolution achieved with the Narrow-Field Infrared Adaptive
Optics System (NFIRAOS) at four spatial scales (0.004",
0.009", 0.025", 0.05"). IRIS will achieve an angular
resolution ten times better than images from the Hubble
Space Telescope, and will be the highest angular resolution
near-infrared instrument in the world.
Integral field Spectrograph
Imager
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Integral Field Spectrograph
Team Leads:
James Larkin(UCLA), Anna Moore(Caltech), Brian Bauman(UCSC)
The purpose of an integral
field spectrograph (IFS) is to acquire spectra over a
two-dimensional area of the sky, where for each spatial
location (or dissecting element) a spectrum is produced.
IRIS is designed with two spatial sampling techniques,
lenslet array and mirror slicer, to optimize the best
quality spectra with both high throughput and low wavefront
error. Both the lenslet array and slicer optics are fed into
a single spectrograph, and share similar optics (i.e., TMAs,
reimaging optics, gratings, filters, and detector). The
lenslet array is used for the finest spatial resolutions
(0.004", 0.009") and the mirror slicer is used for the
coarsest spatial resolutions (0.025", 0.05"). When
delivered, IRIS will have a fully packaged data reduction
pipeline for real-time reductions during observations and
final reductions for user astronomers.
Cartoon illustration
showing how a lenslet array (top) and slicer (bottom) samples
the plane of the sky and the locations of the spectra along
the 2D detector. The IRIS pipeline will then extract each
spectrum from the detector and generate a reduced cube (x, y,
wavelength).
Imager
Team Leads:Ryuji Suzuki (IfA), Masahiro Konishi (NAOJ), Tomonori Usuda (NAOJ)The near-infared (0.8 - 2.5 μm) imager will have a sp ati al sampling of 0.004" per pixel with a total field of view of 17.2" x 17.2". The optical design has been optimized to achieve the lowest wavefront error (~30 nm) in order to sample the high spatial resolutions achieved from the adaptive optics system, NFIRAOS. The leading science cases for the imager require a high level of astrometric precision (e.g., Galactic Center, star forming regions,). The imager is expected to achieve an astrometric absolute accuracy of 2-4 mas and relative accuracy of 30 μas. |
 Picture of
the latest Hawaii-2RG detector being tested at UCLA's
infrared laboratory. Both the IRIS imager and
spectrograph are being desiged to use the developing
Teledyne Hawaii-4RG detector, which should have
similar low readout and detector noise and high
quantum efficiencies to the Hawaii-2RG detector. |
On-Instrument Wavefront Sensors (OIWFS)
Team Leads:David Loop (HIA) and Anna Moore(Caltech)IRIS will house low-order wavefront sensors (WFS) that will be used by NFIRAOS to monitor tip-tilt, astigmatism, and focus. IRIS will have three WFSs, which will sample stars as faint as J = 22 mag over a 2 arcminute field-of-view (FOV). The WFSs must be deployable over the entire FOV to maximize sky coverage, and allow for optimum AO correction (the best correction is obtained when the WFSs are deployed symmetrically about the science target). The figure below shows the geometric configuration of the three tip-tilt guide arms and the locations of the IRIS imager and spectrograph. |
Geometric
configuration for the three wavefront sensor arms
that can be positioned over the entire 2 arcminute
field-of-view. The IRIS imager (red) is on-axis and
the integral field spectrograph (blue) is 18"
off-axis.
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Atmosphere Dispersion Corrector (ADC)
Team Lead:Drew Philips (UCSC)One of the challenges of generating an instrument with high angular resolutions (0.004") is compensating for the dispersion that occurs within Earth's atmosphere. In order to counter this effect IRIS will house an atmospheric dispersion corrector (ADC) in front of IRIS science's dewar. beIt will use real-time knowledge of atmospheric conditions (temperature, pressure, humidity) and optical elements to correct for dispersion over varying observing elevations. |
 Atmospheric dispersion that occurs for six different wavelengths over varying airmasses. IRIS's ADC will able to correct for these observed dispersions over the entire near-infared wavelength range (0.85 - 2.5 μm). |
IRIS Science
Team Lead:
Shelley Wright (UofT)
The combination of a large
collecting area and unprecedented angular resolution will
have a direct impact on a broad range of science programs
that span topics as diverse as the search for extrasolar
planets to studies of the first stars to illuminate the
Universe. The science team has generated a plethora of
astronomical topics that IRIS will be capable of exploring.
Summary of Science Cases
| First
Light: Identification and characterization
of first light galaxies and population III stars. Figure on the right is a simulation of a forming galaxy at z=12.5 and the expected hydrogen number density (Johnson, Greif, Bromm 2008). The dense gas (orange-white) just left of the center of the galaxy represents the formation of two Pop III stars. Overlaid on the figure is a 1"x3" field of view (3.6kpc x 10.8kpc), which is close to the FOV using IRIS's 0.025" slicer scale. |
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High-z
Galaxy Dynamics and Morphologies:
Studying galaxy formation and mass assembly over
cosmic time (1 < z <5). Using optical emission
lines (e.g., Hα, Hβ, [OIII]) to map 2D dynamics of
galaxies during the peak epoch of star formation and
AGN accretion. The anticipated S/N ratios for Hα emission from four high-z galaxies as observed using the IRIS IFS 0.05" spatial sampling (see Law et al. 2006). |
| Metallicity
Evolution and Gradients: Tracing
metallicity over cosmic time (1 < z <5) using
multiple optical emission lines to determine the
chemical enrichment history. The IFS will be able to
map metallicity gradients over individual high-z
galaxies from different galactic components
(i.e.,bulge, disk, outflows, and inflows. The figure on the right is a [NII]/Hα ratio map of a z~1.6 galaxy from the Keck AO system, and shows high spatial concentration (yellow) of [NII]/Hα which shows the presence of a weak AGN within this star-forming dominated galaxy (Wright et al. 2009). IRIS will be essential for distinguishing between AGN and star forming emission from different regions of a galaxy. |
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Supermassive
Black Holes: A study of AGN, black hole
demographics and growth throughout cosmic history. The left figure is of the MBH-σ relation plotted for measured black hole masses versus observed dispersions of late-type spirals and nuclear star clusters (Barth et al. 2009). There is a large phase-space regime that requires both higher sensitivity and angular resolution observations of low mass black holes (106 Msun) and high mass black holes (109 Msun). IRIS's finest scale (0.004") is very suitable for this study. |
| Local
Galaxies and Stellar Populations: A study
of stellar populations in galaxies from the local
group to the Virgo cluster. IRIS with its high-angular
resolution and sensitivity will be able to produce
near-infrared spectra and images of individual stars
in nearby galaxies, and will probe the chemical
enrichment and formation histories for a range of
Hubble types. A one-degree image of the Virgo cluster (18 Mpc) from HST, with the lenticular galaxy at the center and other spiral galaxies on the outskirts. IRIS will be able to study each of these galaxies to an unprecedented image depth. |
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Dwarf
Galaxies: A study of local dwarf galaxy's
dynamical and chemical enrichment to probe the dark
matter distribution and differing dark matter models
(warm vs. cold). On the left, the cumulative number of Milky Way satellite galaxies as a function of their observed cicular velocities (black points). These observations are compared to the Via Lactea N-body simulation of predicted number of satellites and how differing reionization epochs influences the expected satellite number distribution (Simon & Geha 2007). |
| Galactic
Center: Studying the properties and
conditions surrounding the supermassive black hole
(SMBH) at the center of the Galaxy. The relative
astrometric accuracy of 30 μas will allow measurements
to better constrain MBH, test General
Relativity, determine GC distance, and the stellar
dynamical history. Right figure is of the current imaging capabilities of the central arcsecond sources from Keck-AO. The image on the right represents the depth and resolution that TMT and IRIS will provide (see UCLA Galactic Center). |
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 |
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Star
Formation: Investigating star formation
properties in star clusters: timescale of star
formation and efficiencies, initial cluster mass
funcion (ICMF), initial mass function, multiplicity
and kinematics The figure on the left illustrates three clusters with varying masses (30Dor: 105 Msun, NGC3603: 104 Msun, Orion: 103 Msun) which will be resolved with IRIS at distances up to 20 Mpc away. |
| Microlensing:
Constraining models of stellar structure and evolution
by determining precise stellar masses from astrometric
microlensing. IRIS, with its high astrometric relative
accuracy, will be able to fit mircolens light curves
to accurately determine stellar masses for a range of
stellar-types. On the right, a proper motion curve for a star over 5 years that has been lensed (solid curve) and without being lens (dashed lens) (Belukurov & Evans 2002). |
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Extrasolar
Planets: The detection and
characterization of extrasolar planets and planet
forming environments. On the left, an image of the first extrasolar multiple planet system ever directly-imaged, around the young star HR 8799 (Marois et al. 2008). The image is a near-infrared color composite of J, H, and K bands taken from both Keck and Gemini telescopes using adaptive optics. Each planet is respectively 70, 40, and 25 AU from the central star. A system such as HR 8799 would be easily studied using IRIS. |
| Solar
System:The formation history of our solar
system. Using near-infrared spectroscopy for
compositional and dynamical studies of Kuiper Belt
Objects (KBO) and transneptunian objects (TNOs). Near infared spectra of Pluto and the TNO, 2005 FY9, show strong methane absorption in the figure on the right (Licandro et al. 2006). |
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Lastly, and perhaps the
most intriguing, are the new discoveries that will likely be
revealed by IRIS. As is stated in The Exploration of the
Unknown by Kellermann el al. 2009, "The excitement of
the next generation of astronomical facilities is not in the
old questions which will be answered, but in the new
questions that they will raise." With IRIS and TMT extending
our current technology by orders of magnitude in sensitivity
and angular resolution it has the promise of doing just
that.
IRIS Team Members
IRIS is a multi-institutional collaboration from USA, Canada, and Japan.
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IRIS technical team: |
IRIS science team: |