Using the Infrared Spectrograph on the Spitzer Space Telescope, we observed the Antennae galaxies obtaining spectral maps of the entire central region and high signal-to-noise 5 − 38µm spectra of the two galactic nuclei and six infrared-luminous regions.The total infrared luminosity of our six IR peaks plus the two nuclei is L IR = 3.8·10 10 L ⊙ , with their derived star formation rates ranging between 0.2 and 2 M ⊙ /yr, with a total of 6.6 M ⊙ /yr. None of the typical mid-infrared tracers of AGN activity is detected in either nucleus of the system, excluding the presence of an dust enshrouded accretion disk. The hardest and most luminous radiation originates from two compact clusters in the southern part of the overlap region, which also have the highest dust temperatures. PAH emission and other tracers of softer radiation are spatially extended throughout and beyond the overlap region, but regions with harder and intenser radiation field show a reduced PAH strength.The strong H 2 emission is rather confined around the nucleus of NGC 4039, where shocks appear to be the dominant excitation mechanism, and the southern part of the overlap region, where it traces the most recent starburst activity. The luminosity ratio between the warm molecular gas (traced by the H 2 lines) and the total far-IR emission is ∼ 1.6 · 10 −4 , similar to that found in many starburst and ULIRGs. The total mass of warm H 2 in the Antennae is 2.5 · 10 7 M ⊙ , with a fraction of warm to total H 2 gas mass of about 0.35%. The average warm H 2 temperature is 302 ± 26 K and appears anti-correlated with the radiation field hardness, possibly due to an evolution of the PDR morphology. The previously reported tight correlation between the H 2 and PAH emission was not found but higher total PAH emission to continuum ratios were found in PDRs with warmer gas.

Recently, mid-infrared instruments have become available on several large ground-based telescopes, resulting in data sets with unprecedented spatial resolution at these long wavelengths. In this paper we examine 'ground-based-only' diagnostics, which can be used in the study of star-forming regions in starburst galaxies. By combining output from the stellar population synthesis code Starburst 99 with the photoionization code Mappings, we model stellar clusters and their surrounding interstellar medium, focusing on the evolution of emission lines in the N-and Q-band atmospheric windows (8 -13 and 16.5 -24.5 µm respectively) and those in the near-infrared. We address the detailed sensitivity of various emission line diagnostics to stellar population age, metallicity, nebular density, and ionization parameter. Using our model results, we analyze observations of two stellar clusters in the overlap region of the Antennae galaxies obtained with VLT Imager and Spectrometer for mid Infrared (VISIR). We find evidence for clumpy, high density, ionized gas. The two clusters are young (younger than 2.5 and 3 Myr respectively), the surrounding interstellar matter is dense (≥ 10 4 cm −3 ) and can be characterized by a high ionization parameter (logU ≥ -1.53). Detailed analysis of the mid-infrared spectral features shows that a (near-)homogeneous medium cannot account for the observations, and that complex structure on scales below the resolution limit, containing several young stellar clusters embedded in clumpy gas, is more likely.

In this letter we present ground-based subarcsecond mid-infrared imaging and spectroscopy of young super star clusters in the overlap region of the merging galaxies NGC4038/4039 (the Antennae) obtained with the VLT Imager and Spectrometer for mid-Infrared (VISIR). With its unprecedented spatial resolution VISIR begins to resolve the H ii/PDR complexes around the star-forming regions for the first time. In the N-band spectra of two young star clusters unexpectedly low polycyclic aromatic hydrocarbon (PAH) emission is observed, compared to what is seen with the Infrared Space Observatory (ISO) and with the Spitzer Space Telescope. We conclude that a large fraction of the PAH emission cannot directly be associated with the super star clusters, but originate from an extended region of at least 215 pc radius around the clusters. In the distribution of [Ne ii] 12.81 µm emission a highly obscured cluster is discovered that does not have an optical or near-infrared counterpart.

Hyperspectral imaging is applied to a Mixtec codex in order to reveal an abundance of never 9 before seen pictographic scenes hidden underneath a layer of gypsum and chalk gesso. 10 Because of the organic nature of these paints, no other technique has been able to reveal them 11 in a non-invasive manner. The results thus far indicate that the covered text contains unique 12 genealogic information which may prove invaluable for the interpretation of archaeological 13 remains from southern Mexico.

Abstract. Recent research has suggested that long-duration gamma-ray bursts (LGRBs) occur preferentially in low-metallicity environments, but the exact nature of this correlation is currently a matter of intense debate. We use the newest generation of the Starburst99/Mappings code to generate an extensive suite of cutting-edge stellar population synthesis models, covering a wide range of physical parameters specifically tailored for modeling the ISM environments of metal-poor galaxies and LGRB host galaxies. With our models, we generate optical emission line diagnostics, which will allow us to examine the ISM properties and stellar populations of a variety of galaxy populations in unprecedented detail. While accurately modeling low-metallicity galaxies still poses a challenge to these models, future improvements to these grids will have profound consequences for our understanding of metal-poor galaxies, their ISM environments, and the nature of their role as the hosts of LGRBs.