The Mid-Infrared ELT Imager and Spectrograph (METIS) is one of three first light instruments on the ELT. It will provide high-contrast imaging and medium resolution, slit-spectroscopy from 3 - 19um, as well as high resolution (R ∼ 100,000) integral field spectroscopy from 2.9-5.3μm. All modes observe at the diffraction limit of the ELT, by means of adaptive optics, yielding angular resolutions of a few tens of milliarcseconds. The range of METIS science is broad, from Solar System objects to active galactic nuclei (AGN). We will present an update on the main science drivers for METIS: circum-stellar disks and exoplanets. The METIS project is now in full steam, approaching its preliminary design review (PDR) in 2018. In this paper we will present the current status of its optical, mechanical and thermal design as well as operational aspects. We will also discuss the challenges of building an instrument for the ELT, and the required technologies.

We present [C ii] 158 μm measurements from over 15,000 resolved regions within 54 nearby galaxies of the Kingfish program to investigate the so-called [C ii] "line-cooling deficit" long known to occur in galaxies with different luminosities. The [C ii]/TIR ratio ranges from above 1% to below 0.1% in the sample, with a mean value of 0.48 ± 0.21%. We find that the surface density of 24 μm emission dominates this trend, with [C ii]/TIR dropping as vI_v (24 μm)increases. Deviations from this overall decline are correlated with changes in the gas-phase metal abundance, with higher metallicity associated with deeper deficits at a fixed surface brightness. We supplement the local sample with resolved [C ii] measurements from nearby luminous infrared galaxies and high-redshift sources from z = 1.8-6.4, and find that star formation rate density drives a continuous trend of deepening [C ii] deficit across six orders of magnitude in Σ_SFR. The tightness of this correlation suggests that an approximate can be estimated directly from global measurements of [C ii]/TIR, and a relation is provided to do so. Several low-luminosity active galactic nucleus (AGN) hosts in the sample show additional and significant central suppression of [C ii]/TIR, but these deficit enhancements occur not in those AGNs with the highest X-ray luminosities, but instead those with the highest central starlight intensities. Taken together, these results demonstrate that the [C ii] line-cooling line deficit in galaxies likely arises from local physical phenomena in interstellar gas.

We present calibrations for star formation rate (SFR) indicators in the ultraviolet, mid-infrared, and radiocontinuumbands, including one of the first direct calibrations of 150 MHz as an SFR indicator. Our calibrationsutilize 66 nearby star-forming galaxies with Balmer-decrement-corrected Hα luminosities, which span five ordersof magnitude in SFR and have absolute magnitudes of -24 < Mr < -12. Most of our photometry andspectrophotometry are measured from the same region of each galaxy, and our spectrophotometry has beenvalidated with SDSS photometry, so our random and systematic errors are small relative to the intrinsic scatter seenin SFR indicator calibrations. We find that the Wide-field Infrared Space Explorer W4 (22.8 μm), Spitzer 24 μm,and 1.4 GHz bands have tight correlations with the Balmer-decrement-corrected Hα luminosity, with a scatter ofonly 0.2 dex. Our calibrations are comparable to those from the prior literature for L∗ galaxies, but for dwarfgalaxies, our calibrations can give SFRs that are far greater than those derived from most previous literature.

With its relatively low ionization potential, C⁺ can be found throughout the interstellar medium (ISM) and provides one of the main cooling channels of the ISM via the [C ii] 157 μm emission. While the strength of the [C ii] line correlates with the star formation rate, the contributions of the various gas phases to the [C ii] emission on galactic scales are not well established. In this study we establish an empirical multi-component model of the ISM, including dense H ii regions, dense photon dissociation regions (PDRs), the warm ionized medium (WIM), low density and surfaces of molecular clouds (SfMCs), and the cold neutral medium (CNM). We test our model on ten luminous regions within the two nearby galaxies NGC 3184 and NGC 628 on angular scales of 500-600 pc. Both galaxies are part of the Herschel key program KINGFISH, and are complemented by a large set of ancillary ground- and space-based data. The five modeled phases together reproduce the observed [C ii] emission quite well, overpredicting the total flux slightly (about 45%) averaged over all regions. We find that dense PDRs are the dominating component, contributing 68% of the [C ii] flux on average, followed by the WIM and the SfMCs, with mean contributions of about half of the contribution from dense PDRs, each. CNM and dense H ii regions are only minor contributors with less than 5% each. These estimates are averaged over the selected regions, but the relative contributions of the various phases to the [C ii] flux vary significantly between these regions.

Exoplanet Proxima b will be an important laboratory for the search for extraterrestrial life for the decades ahead. Here, we discuss the prospects of detecting carbon dioxide at 15 μm using a spectral filtering technique with the Medium Resolution Spectrograph (MRS) mode of the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST). At superior conjunction, the planet is expected to show a contrast of up to 100 ppm with respect to the star. At a spectral resolving power of R = 1790-2640, about 100 spectral CO₂ features are visible within the 13.2-15.8 μm (3B) band, which can be combined to boost the planet atmospheric signal by a factor of 3-4, depending on the atmospheric temperature structure and CO₂ abundance. If atmospheric conditions are favorable (assuming an Earth-like atmosphere), with this new application to the cross-correlation technique, carbon dioxide can be detected within a few days of JWST observations. However, this can only be achieved if both the instrumental spectral response and the stellar spectrum can be determined to a relative precision of ≤1 10^-4 between adjacent spectral channels. Absolute flux calibration is not required, and the method is insensitive to the strong broadband variability of the host star. Precise calibration of the spectral features of the host star may only be attainable by obtaining deep observations of the system during inferior conjunction that serve as a reference. The high-pass filter spectroscopic technique with the MIRI MRS can be tested on warm Jupiters, Neptunes, and super-Earths with significantly higher planet/star contrast ratios than the Proxima system.

The [C ii] 158 μm fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [C ii] balances the heating, including that due to far-ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [C ii] emission remains unclear because C⁺ can be found in multiple phases of the interstellar medium. Here we measure the fractions of [C ii] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [N ii] 205 μm fine-structure line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of [C ii]/[N ii] 122 μm. Using the FIR [C ii] and [N ii] emission detected by the KINGFISH (Key Insights on Nearby Galaxies: a Far- Infrared Survey with Herschel) and Beyond the Peak Herschel programs, we show that 60%-80% of [C ii] emission originates from neutral gas. We find that the fraction of [C ii] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and has a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [C ii] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.

METIS is one the first three instruments on the E-ELT. Apart from diffraction limited imaging, METIS will provide coronagraphy and medium resolution slit spectroscopy over the 3 - 19μm range, as well as high resolution (R ∼ 100,000) integral field spectroscopy from 2.9 - 5.3μm, including a mode with extended instantaneous wavelength coverage. The unique combination of these observing capabilities, makes METIS the ideal instrument for the study of circumstellar disks and exoplanets, among many other science areas. In this paper we provide an update of the relevant science drivers, the METIS observing modes, the status of the simulator and the data analysis. We discuss the preliminary design of the optical system, which is driven by the need to calibrate observations at thermal IR wavelengths on a six-mirror ELT. We present the expected adaptive optics performance and the measures taken to enable high contrast imaging. We describe the opto-mechanical system, the location of METIS on the Nasmyth instrument platform, and conclude with an update on critical subsystem components, such as the immersed grating and the focal plane detectors. In summary, the work on METIS has taken off well and is on track for first light in 2025.