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Measurements in the infrared wavelength domain allow direct assessment of the physical state and energy balance of cool matter in space, enabling the detailed study of the processes that govern the formation and evolution of stars and planetary systems in galaxies over cosmic time. Previous infrared missions revealed a great deal about the obscured Universe, but were hampered by limited sensitivity.
SPICA takes the next step in infrared observational capability by combining a large 2.5-meter diameter telescope, cooled to below 8 K, with instruments employing ultra-sensitive detectors. A combination of passive cooling and mechanical coolers will be used to cool both the telescope and the instruments. With mechanical coolers the mission lifetime is not limited by the supply of cryogen. With the combination of low telescope background and instruments with state-of-the-art detectors SPICA provides a huge advance on the capabilities of previous missions.
SPICA instruments offer spectral resolving power ranging from R ~50 through 11 000 in the 17–230 μm domain and R ~28.000 spectroscopy between 12 and 18 μm. SPICA will provide efficient 30–37 μm broad band mapping, and small field spectroscopic and polarimetric imaging at 100, 200 and 350 μm. SPICA will provide infrared spectroscopy with an unprecedented sensitivity of ~5 × 10−20 W m−2 (5σ/1 h)—over two orders of magnitude improvement over what earlier missions. This exceptional performance leap, will open entirely new domains in infrared astronomy; galaxy evolution and metal production over cosmic time, dust formation and evolution from very early epochs onwards, the formation history of planetary systems.
We report the first detection of a mid-J isotopic CO line from an
external galaxy. We detected the 13CO (6-5) line from the
starburst nucleus of NGC 253. The line is suprisingly bright with
an integrated intensity 7% of the 12CO (6-5) line,
indicating optical depth in the 12CO line. Our LVG modeling
shows that a single warm (T ~ 120 K), dense (n ~ 104
cm-3) component emits most of the 12CO and 13CO line
emission from J = 2-1 through J = 7-6. The CO(1-0) line comes from
an additional lower excitation envelope. About 60% of the total
molecular gas mass within 70 pc of the nucleus is in the warm, dense
component. We show that stellar far-UV photons or X-ray photons
from a nuclear source are unlikely to be the primary sources of the
gas heating. The most likely sources of heat are cosmic rays from
the nuclear starburst or microturbulence within molecular clouds.
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