METIS will be among the first generation of scientific instruments on the E-ELT. Focusing on highest angular resolution and high spectral resolution, METIS will provide diffraction limited imaging... Show moreMETIS will be among the first generation of scientific instruments on the E-ELT. Focusing on highest angular resolution and high spectral resolution, METIS will provide diffraction limited imaging and coronagraphy from 3-14μm over an 20x20° field of view, as well as integral field spectroscopy at R ~ 100,000 from 2.9-5.3μm. In addition, METIS provides medium-resolution (R ~ 5000) long slit spectroscopy, and polarimetric measurements at N band. While the baseline concept has already been discussed at previous conferences, this paper focuses on the significant developments over the past two years in several areas: The science case has been updated to account for recent progress in the main science areas circum-stellar disks and the formation of planets, exoplanet detection and characterization, Solar system formation, massive stars and clusters, and star formation in external galaxies. We discuss the developments in the adaptive optics (AO) concept for METIS, the telescope interface, and the instrument modelling. Last but not least we provide an overview of our technology development programs, which ranges from coronagraphic masks, immersed gratings, and cryogenic beam chopper to novel approaches to mirror polishing, background calibration and cryo-cooling. These developments have further enhanced the design and technology readiness of METIS to reliably serve as an early discovery machine on the E-ELT. Show less
The metal content of a galaxy, a key property for distinguishing between viable galaxy evolutionary scenarios, strongly influences many of the physical processes in the interstellar medium. An... Show moreThe metal content of a galaxy, a key property for distinguishing between viable galaxy evolutionary scenarios, strongly influences many of the physical processes in the interstellar medium. An absolute and robust determination of extragalactic metallicities is essential in constraining models of chemical enrichment and chemical evolution. Current gas-phase abundance determinations, however, from optical fine-structure lines are uncertain to 0.8 dex as conversion of these optical line fluxes to abundances is strongly dependent on the electron temperature of the ionized gas. In contrast, the far-infrared (far-IR) emission lines can be used to derive an O$^{++}$ abundance that is relatively insensitive to temperature, while the ratio of the optical to far-IR lines provides a consistent temperature to be used in the derivation of an O$^{+}$ abundance. We present observations of the [O III] 88 {$μ$}m fine-structure line in NGC 628 that were obtained as part of the Key Insights on Nearby Galaxies: a Far Infared Survey with Herschel program. These data are combined with optical integrated field unit data to derive oxygen abundances for seven H II regions. We find the abundance of these regions to all lie between the high and low values of strong-line calibrations and to be in agreement with estimates that assume temperature fluctuations are present in the H II regions. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Show less
We use the near-infrared Br{$γ$} hydrogen recombination line as a reference star formation rate (SFR) indicator to test the validity and establish the calibration of the Herschel/PACS 70 {$μ$}m... Show moreWe use the near-infrared Br{$γ$} hydrogen recombination line as a reference star formation rate (SFR) indicator to test the validity and establish the calibration of the Herschel/PACS 70 {$μ$}m emission as a SFR tracer for sub-galactic regions in external galaxies. Br{$γ$} offers the double advantage of directly tracing ionizing photons and of being relatively insensitive to the effects of dust attenuation. For our first experiment, we use archival Canada-France-Hawaii Telescope Br{$γ$} and Ks images of two nearby galaxies: NGC 5055 and NGC 6946, which are also part of the Herschel program KINGFISH (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel). We use the extinction corrected Br{$γ$} emission to derive the SFR(70) calibration for H II regions in these two galaxies. A comparison of the SFR(70) calibrations at different spatial scales, from 200 pc to the size of the whole galaxy, reveals that about 50% of the total 70 {$μ$}m emission is due to dust heated by stellar populations that are unrelated to the current star formation. We use a simple model to qualitatively relate the increase of the SFR(70) calibration coefficient with decreasing region size to the star formation timescale. We provide a calibration for an unbiased SFR indicator that combines the observed H{$α$} with the 70 {$μ$}m emission, also for use in H II regions. We briefly analyze the PACS 100 and 160 {$μ$}m maps and find that longer wavelengths are not as good SFR indicators as 70 {$μ$}m, in agreement with previous results. We find that the calibrations show about 50% difference between the two galaxies, possibly due to effects of inclination. Based on observations obtained with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, France, and the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Show less
We present ~{}kiloparsec spatial resolution maps of the CO-to-H$_{2}$ conversion factor ({$α$}$_{CO}$) and dust-to-gas ratio (DGR) in 26 nearby, star-forming galaxies. We have simultaneously... Show moreWe present ~{}kiloparsec spatial resolution maps of the CO-to-H$_{2}$ conversion factor ({$α$}$_{CO}$) and dust-to-gas ratio (DGR) in 26 nearby, star-forming galaxies. We have simultaneously solved for {$α$}$_{CO}$ and the DGR by assuming that the DGR is approximately constant on kiloparsec scales. With this assumption, we can combine maps of dust mass surface density, CO-integrated intensity, and H I column density to solve for both {$α$}$_{CO}$ and the DGR with no assumptions about their value or dependence on metallicity or other parameters. Such a study has just become possible with the availability of high-resolution far-IR maps from the Herschel key program KINGFISH, $^{12}$CO J = (2-1) maps from the IRAM 30 m large program HERACLES, and H I 21 cm line maps from THINGS. We use a fixed ratio between the (2-1) and (1-0) lines to present our {$α$}$_{CO}$ results on the more typically used $^{12}$CO J = (1-0) scale and show using literature measurements that variations in the line ratio do not affect our results. In total, we derive 782 individual solutions for {$α$}$_{CO}$ and the DGR. On average, {$α$}$_{CO}$ = 3.1 M $_{☉}$ pc$^{–2}$ (K km s$^{–1}$)$^{–1}$ for our sample with a standard deviation of 0.3 dex. Within galaxies, we observe a generally flat profile of {$α$}$_{CO}$ as a function of galactocentric radius. However, most galaxies exhibit a lower {$α$}$_{CO}$ value in the central kiloparsec{mdash}a factor of ~{}2 below the galaxy mean, on average. In some cases, the central {$α$}$_{CO}$ value can be factors of 5-10 below the standard Milky Way (MW) value of {$α$}$_{CO, MW}$ = 4.4 M $_{☉}$ pc$^{–2}$ (K km s$^{–1}$)$^{–1}$. While for {$α$}$_{CO}$ we find only weak correlations with metallicity, the DGR is well-correlated with metallicity, with an approximately linear slope. Finally, we present several recommendations for choosing an appropriate {$α$}$_{CO}$ for studies of nearby galaxies. Show less
While collisionally excited lines in H ii regions allow one to easily probe the chemical composition of the interstellar medium in galaxies, the possible presence of important temperature... Show moreWhile collisionally excited lines in H ii regions allow one to easily probe the chemical composition of the interstellar medium in galaxies, the possible presence of important temperature fluctuations casts some doubt on the derived abundances. To provide new insights into this question, we have carried out a detailed study of a giant H ii region, H 1013, located in the galaxy M101, for which many observational data exist and which has been claimed to harbour temperature fluctuations at a level of t$^{2}$ = 0.03-0.06. We have first complemented the already available optical observational datasets with a mid-infrared spectrum obtained with the Spitzer Space Telescope. Combined with optical data, this spectrum provides unprecedented information on the temperature structure of this giant H ii region. A preliminary analysis based on empirical temperature diagnostics suggests that temperature fluctuations should be quite weak. However, only a detailed photoionization analysis taking into account the geometry of the object and observing apertures can make a correct use of all the observational data. We have performed such a study using the pyCloudy package based on the photoionization code Cloudy. We have been able to produce photoionization models constrained by the observed H{$β$} surface brightness distribution and by the known properties of the ionizing stellar population than can account for most of the line ratios within their uncertainties. Since the observational constraints are both strong and numerous, this argues against the presence of significant temperature fluctuations in H 1013. The oxygen abundance of our best model is 12 + log O/H = 8.57, as opposed to the values of 8.73 and 8.93 advocated by Esteban et al. (2009, ApJ, 700, 654) and Bresolin (2007, ApJ, 656, 186), respectively, based on the significant temperature fluctuations they derived. However, our model is not able to reproduce the intensities of the oxygen recombination lines observed by Esteban et al., as well as the very low Balmer jump temperature inferred by Bresolin. We have argued that the latter might be in error, due to observational difficulties. On the other hand, the discrepancy between model and observation as regards the recombination lines cannot be attributed to observational uncertainties and requires an explanation other than temperature fluctuations. Show less
The focus of this work is to study mid-infrared point sources and the diffuse interstellar medium (ISM) in the low-metallicity (~{}0.2 Z $_{⊙}$) giant H II region N66 in order to determine... Show moreThe focus of this work is to study mid-infrared point sources and the diffuse interstellar medium (ISM) in the low-metallicity (~{}0.2 Z $_{⊙}$) giant H II region N66 in order to determine properties that may shed light on star formation in these conditions. Using the Spitzer Space Telescope's Infrared Spectrograph, we study polycyclic aromatic hydrocarbon (PAH), dust continuum, silicate, and ionic line emission from 14 targeted infrared point sources as well as spectra of the diffuse ISM that is representative of both the photodissociation regions (PDRs) and the H II regions. Among the point source spectra, we spectroscopically confirm that the brightest mid-infrared point source is a massive embedded young stellar object, we detect silicates in emission associated with two young stellar clusters, and we see spectral features of a known B[e] star that are commonly associated with Herbig Be stars. In the diffuse ISM, we provide additional evidence that the very small grain population is being photodestroyed in the hard radiation field. The 11.3 {$μ$}m PAH complex emission exhibits an unexplained centroid shift in both the point source and ISM spectra that should be investigated at higher signal-to-noise and resolution. Unlike studies of other regions, the 6.2 {$μ$}m and 7.7 {$μ$}m band fluxes are decoupled; the data points cover a large range of I $_{7.7}$/I $_{11.3}$ PAH ratio values within a narrow band of I $_{6.2}$/I $_{11.3}$ ratio values. Furthermore, there is a spread in PAH ionization, being more neutral in the dense PDR where the radiation field is relatively soft, but ionized in the diffuse ISM/PDR. By contrast, the PAH size distribution appears to be independent of local ionization state. Important to unresolved studies of extragalactic low-metallicity star-forming regions, we find that emission from the infrared-bright point sources accounts for only 20%-35% of the PAH emission from the entire region. These results make a comparative data set to other star-forming regions with similarly hard and strong radiation fields. Show less
