We present results of 2 mm observations of the Crab Nebula, obtained using the Goddard-IRAM Superconducting 2 Millimeter Observer (GISMO) bolometer camera on the IRAM 30 m telescope. Additional 3.3 mm observations with the MUSTANG bolometer array on
the Green Bank Telescope are also presented. The integrated 2 mm flux density of the Crab Nebula provides no evidence for the emergence of a second synchrotron component that has been proposed. It is consistent with the radio power law spectrum, extrapolated up to a break frequency of log(nu_{b} [GHz]) = 2.84 +/- 0.29 or nu_{b} = 695^{+651}_{-336} GHz. The Crab Nebula is well-resolved by the ~16.7 beam (FWHM) of GISMO. Comparison to radio data at comparable spatial resolution enables us to confirm significant spatial variation of the spectral index between 21 cm and 2 mm. The main effect is a spectral flattening in the inner region of the Crab Nebula, correlated with the toroidal structure at the center of the nebula that is prominent in the near-IR through X-ray regime.
A mid-infrared (3.6-8 um) survey of the Galactic Center has been carried out with the IRAC instrument on the Spitzer Space Telescope. This survey covers the central 2x1.4 degree (~280x200 pc) of the Galaxy. At 3.6 and 4.5 um the emission is dominated
by stellar sources, the fainter ones merging into an unresolved background. At 5.8 and 8 um the stellar sources are fainter, and large-scale diffuse emission from the ISM of the Galaxys central molecular zone becomes prominent. The survey reveals that the 8 to 5.8 um color of the ISM emission is highly uniform across the surveyed region. This uniform color is consistent with a flat extinction law and emission from polycyclic aromatic hydrocarbons (PAHs). Models indicate that this broadband color should not be expected to change if the incident radiation field heating the dust and PAHs is <10^4 times that of the solar neighborhood. The few regions with unusually red emission are areas where the PAHs are underabundant and the radiation field is locally strong enough to heat large dust grains to produce significant 8 um emission. These red regions include compact H II regions, Sgr B1, and wider regions around the Arches and Quintuplet Clusters. In these regions the radiation field is >10^4 times that of the solar neighborhood. Other regions of very red emission indicate cases where thick dust clouds obscure deeply embedded objects or very early stages of star formation.
Multiwavelength observations of supernova remnant (SNR) 1987A show that its morphology and luminosity are rapidly changing at X-ray, optical, infrared, and radio wavelengths as the blast wave from the explosion expands into the circumstellar equatori
al ring, produced by mass loss from the progenitor star. The observed infrared (IR) radiation arises from the interaction of dust grains that formed in mass outflow with the soft X-ray emitting plasma component of the shocked gas. Spitzer IRS spectra at 5 - 30 microns taken on day 6190 since the explosion show that the emission arises from ~ 1.1E-6 Msun of silicate grains radiating at a temperature of ~180+20-15 K. Subsequent observations on day 7137 show that the IR flux had increased by a factor of 2 while maintaining an almost identical spectral shape. The observed IR-to-X-ray flux ratio (IRX) is consistent with that of a dusty plasma with standard Large Magellanic Cloud dust abundances. IRX has decreased by a factor of ~ 2 between days 6190 and 7137, providing the first direct observation of the ongoing destruction of dust in an expanding SN blast wave on dynamic time scales. Detailed models consistent with the observed dust temperature, the ionization timescale of the soft X-ray emission component, and the evolution of IRX suggest that the radiating silicate grains are immersed in a 3.5E6 K plasma with a density of (0.3-1)E4 cm^{-3}, and have a size distribution that is confined to a narrow range of radii between 0.023 and 0.22 microns. Smaller grains may have been evaporated by the initial UV flash from the supernova.
Determination of the cosmic infrared background (CIB) at far infrared wavelengths using COBE/DIRBE data is limited by the accuracy to which foreground interplanetary and Galactic dust emission can be modeled and subtracted. Previous determinations of
the far infrared CIB (e.g., Hauser et al. 1998) were based on the detection of residual isotropic emission in skymaps from which the emission from interplanetary dust and the neutral interstellar medium were removed. In this paper we use the Wisconsin H-alpha Mapper (WHAM) Northern Sky Survey as a tracer of the ionized medium to examine the effect of this foreground component on determination of the CIB. We decompose the DIRBE far infrared data for five high Galactic latitude regions into H I and H-alpha correlated components and a residual component. We find the H-alpha correlated component to be consistent with zero for each region, and we find that addition of an H-alpha correlated component in modeling the foreground emission has negligible effect on derived CIB results. Our CIB detections and 2 sigma upper limits are essentially the same as those derived by Hauser et al. and are given by nu I_nu (nW m-2 sr-1) < 75, < 32, 25 +- 8, and 13 +- 3 at 60, 100, 140, and 240 microns, respectively. Our residuals have not been subjected to a detailed anisotropy test, so our CIB results do not supersede those of Hauser et al. We derive upper limits on the 100 micron emissivity of the ionized medium that are typically about 40% of the 100 micron emissivity of the neutral atomic medium. This low value may be caused in part by a lower dust-to-gas mass ratio in the ionized medium than in the neutral medium, and in part by a shortcoming of using H-alpha intensity as a tracer of far infrared emission.
