Norbert Geis

[C II] 158 Micron Observations of IC 10: Evidence for Hidden Molecular Hydrogen in Irregular Galaxies

We have mapped the [C II] 158 μm line over 85 × 65 in the Magellanic irregular galaxy IC 10, thus presenting the first complete [C II] map of an entire low-metallicity galaxy. The total luminosity in the [C II] line in IC 10 is 1.5 × 106 L☉. We discuss the origin of the [C II] emission toward different regions in the galaxy. Overall, about 10% of the [C II] emission can originate in standard H I clouds (n ~ 80, T ~ 100 K), while up to about 10% of the emission can originate in ionized gas, either the low-density warm gas or the denser H II regions. For the two brightest regions, most of the [C II] emission is associated with dense photodissociation regions (PDRs). For several regions, however, the [C II] emission may not be explained by standard PDR models. For these regions, emission solely from the atomic medium can also be precluded because the cooling rate per hydrogen atom would be much greater than the heating rate provided by photoelectric UV heating. We speculate that in these regions the presence of an additional column density of H2, 5 times that observed in H I, is required to explain the [C II] emission. The ambient UV fields present in these regions, combined with the low metallicity, create a situation where small CO cores exist surrounded by a relatively large [C II]-emitting envelope where molecular hydrogen is self-shielded. This additional molecular mass is equivalent to at least 100 times the mass in the CO core that one would derive from the CO integrated intensity alone using the standard CO-to-H2 conversion factor. These [C II] observations may, therefore, make a more reliable inventory of the gas reservoir in dwarf irregular galaxies where use of CO alone may significantly underestimate the molecular mass.

A Multiwavelength Study of 30 Doradus: The Interstellar Medium in a Low-Metallicity Galaxy

We report maps of the 158 micron (C II) line, the 63 micron and 146 micron (C I) lines, the 2.2 micron Br gamma line, and the 2.6 mm CO (1-0) line toward the 30 Doradus complex in the Large Magellanic Cloud. The maps of all tracers emphasize the shell-like structure of the 30 Doradus region which is seen edge-on. The fact that the molecular gas as traced by CO (1-0) and the photo dissociated gas as traced by (C II) are co-extensive over tens of parsecs can only be explained by a highly fragmented structure of the interstellar medium which allows UV radiation to penetrate deep into the molecular cloud. Clumpiness is also the key to understanding the extremely high (C II)/CO line intensity ratios.

Far-infrared, submillimeter, and millimeter spectroscopy of the Galactic center : radio arc and +20/+50 kilometer per second clouds

Results are presented from FIR, sub-mm, and mm spectroscopic observations of the radio arc and the +20/+50 km/s molecular clouds in the Galactic center. The results for the radio arc are analyzed, including the spatial distribution of C II forbidden line emission, the spatial distribution of CO emission, the luminosity and mass of C(+) regions, and the CO 7 - 6 emission and line profiles. Model calculations are used to study molecular gas in the radio arc. In addition, forbidden C II, CO 7 - 6, and C(O-18) mapping is presented for the +20/+50 km/x clouds. Consideration is given to the impact of the results on the interpretation of the physical conditions, excitation, and heating of the gas clouds in the arc and near the center. 65 refs.

The MPE/UCB far-infrared imaging Fabry-Perot interferometer (FIFI)

FIFI is an imaging spectrometer with two or three Fabry-Perot interferometers (FPI) in series for airborne astronomical observations in the far-infrared range (λ=40...200μm). It employs 5×5 arrays of photoconducting detectors and offers spectral resolutions as small as 2km/s. Resolution and bandwidth can be set over a wide range to match a variety of astronomical sources. Cryogenic optics minimizes thermal background radiation and provides for in-flight step tunable spatial resolution. At 158 μm wavelength the background-limited NEP is 3 × 10-15W/ℚHz at 40 km/s resolution and with two FPIs; with three FPIs the expected NEP is ≤10-15W√Hz at 5 km/s resolution.The frequency-chopping mode of the high-resolution Fabry-Perot allows for line detection in extended objects. Absolute internal flux calibration ensures adequate “flat fielding” of the array elements.

The European contribution to the SPICA mission

The Japanese led Space Infrared telescope for Cosmology and Astrophysics (SPICA) will observe the universe over the 5 to 210 micron band with unprecedented sensitivity owing to its cold (~5 K) 3.5m telescope. The scientific case for a European involvement in the SPICA mission has been accepted by the ESA advisory structure and a European contribution to SPICA is undergoing an assessment study as a Mission of Opportunity within the ESA Cosmic Vision 1015-2015 science mission programme. In this paper we describe the elements that are being studied for provision by Europe for the SPICA mission. These entail ESA directly providing the cryogenic telescope and ground segment support and a consortium of European insitutes providing a Far Infrared focal plane instrument. In this paper we describe the status of the ESA study and the design status of the FIR focal plane instrument.

Realizing Integral Field Spectroscopy in the Far-Infrared

The optical design of an integral field spectrometer for far-infrared observations, the Far-Infrared Field-Imaging Line Spectrometer (FIFI LS), is presented. The instrument will fly on board the joint NASA/DLR airborne observatory SOFIA, observing in two nearly independent wavelength channels simultaneously: a blue channel (40-105 μm) and a red channel (105-210 μm). To achieve instantaneous integral field spectroscopy for the first time in the far-infrared, a novel reflective image slicer system is utilized that slices the 5 × 5 pixel, two-dimensional field of view into a pseudo-long slit of 25 × 1 pixels. The slicer assembly consists of three sets of five mirrors that have optical power, enabling a compact design. After the sky field has been optically rearranged to the pseudoslit, the image is spectrally dispersed in a standard Littrow-mounted reflective grating spectrometer. The practical concerns for the optical design in the far-infrared and, in particular, the significant effect of diffraction in the entire optical system is discussed.

The SOFIA far-infrared spectrometer FIFI-LS: spearheading a post Herschel era

FIFI-LS (Field-Imaging Far-Infrared Line Spectrometer) is an imaging spectrograph for SOFIA comprised of two medium resolution (R~2200) grating spectrometers feeding two 16x25 pixel detector arrays, which enable simultaneous line observations across two wavelength ranges (42-110 μm and 110-210μm) each across a field of view of 5x5 pixel. FIFI-LS will be the extragalactic spectroscopic workhorse for SOFIA. FIFI-LS has enough sensitivity to observe a substantial sample of nearby galaxies. It also has the right combination of wavelength range and spatial resolution to carry out unique new observations beyond those possible with Herschel, Spitzer, ISO and IRAS. As the effective sensitivity of FIFI-LS is only about a factor of 3-5 lower than the PACS spectrometer onboard Herschel, mainly due to an enhanced multiplexing advantage, FIFI-LS will build upon recent exciting scientific results and spearhead the post- Herschel far-infrared era. FIFI-LS is scheduled for commissioning onboard SOFIA in early 2014. An account on the instrument and its current stratus will be presented.

FIFI LS getting ready to fly aboard SOFIA

FIFI LS is the German far-infrared integral field spectrometer for the SOFIA airborne observatory. The instrument consists of two independent integral field spectrometers for two different wavelength bands (45-110 μm and 100-200 μm). A dichroic filter enables simultaneous observation of two different spectral lines in the same field-of view. This allows very efficient mapping of extended regions with FIFI LS in many important far-infrared cooling lines with line ratios sensitive to temperature and density. FIFI LS will become a facility instrument for SOFIA. In the next two years it will become a fully commissioned facility instrument. After its commission, FIFI LS will be available for general observing with a large science potential. In this paper, we will also discuss the science of FIFI LS.

16 x 25 Ge:Ga detector arrays for FIFI LS

We are developing 2D 16 X 25 pixel detector arrays of both unstressed and stressed Ge:Ga photoconductive detectors for far-infrared astronomy from SOFIA. The arrays, based on earlier 5 X 5 detector arrays used on the KAO, will be for our new instrument, the Far Infrared Field Imaging Line Spectrometer (FIFI LS). The unstressed Ge:Ga detector array will cover the wavelength range from 40 to 120 micrometers , and the stressed Ge:Ga detector array from 120 to 210 micrometers . The detector arrays will be operated with multiplexed integrating amplifiers with cryogenic readout electronics located close to the detector arrays. The design of the stressed detector array and results of current measurements on several prototype 16 pixel linear arrays will be reported. They demonstrate the feasibility of the current concept.

The EUCLID NISP tolerancing concept and results

Within ESAs 2015 - 2025 Cosmic Vision framework the EUCLID mission satellite addresses cosmological questions related to dark matter and dark energy. EUCLID is equipped with two instruments that are simultaneously observing patches of > 0.5 square degree on the sky. The VIS visual light high spacial resolution imager and the NISP near infrared spectrometer and photometer are separated by a di-chroic beam splitter. Having a large FoV (larger than the full moon disk), together with high demands on the optical performance and strong requirements on in flight stability lead to very challenging demands on alignment and post launch { post cool-down optical element position. The role of an accurate and trust-worthy tolerance analysis which is well adopted to the stepwise integration and alignment concept, as well as to the missions stability properties is therefore crucial for the missions success. With this paper we present a new iteration of the baseline tolerancing concept for EUCLID NISP. All 7 operational modes being low resolution slit-less spectroscopy and three band Y, J& H+ band photometry are being toleranced together. During the design process it was noted that the desired performance can only be reached when alignment and tolerancing methods are closely connected and optimized together. Utilizing computer generated - multi zone - holograms to align and cross reference the four lenses of the NISP optical system. We show our plan to verify these holograms and what alignment sensitivities we reach. In the main section we present the result of the tolerancing and the main contributers that drive the mechanical and thermal design of the NISO optical subsystems. This analysis presents the design status of NISP at the system PDR of the mission.