Dust-Gas Interaction in SNR 1987A

Multiwavelength observations of SNR 1987A show that its morphology is rapidly changing at X-ray, radio, and optical wavelengths as the blast wave from the explosion expands into the circumstellar equatorial ring. Infrared emission arises from the interaction of dust grains with the hot X-ray emitting gas. We show that the IR emission provides important complementary information on the interaction of the SN blast wave with the circumstellar equatorial ring that cannot be obtained at any other wavelength.Comment: 8 pages, 4 figures; review talk to appear in the AIP Proceedings of the Conference " Supernova 1987A: 20 Years after - Supernovae and Gamma-Ray Bursters" held in Aspen Co USA, Feb 19-23, 200

Cosmic Infrared Background Fluctuations and Zodiacal Light

We have performed a specific observational test to measure the effect that the zodiacal light can have on measurements of the spatial fluctuations of the near-IR background. Previous estimates of possible fluctuations caused by zodiacal light have often been extrapolated from observations of the thermal emission at longer wavelengths and low angular resolution, or from IRAC observations of high latitude fields where zodiacal light is faint and not strongly varying with time. The new observations analyzed here target the COSMOS field, at low ecliptic latitude where the zodiacal light intensity varies by factors of $\sim2$ over the range of solar elongations at which the field can be observed. We find that the white noise component of the spatial power spectrum of the background is correlated with the modeled zodiacal light intensity. Roughly half of the measured white noise is correlated with the zodiacal light, but a more detailed interpretation of the white noise is hampered by systematic uncertainties that are evident in the zodiacal light model. At large angular scales ($\gtrsim100"$) where excess power above the white noise is observed, we find no correlation of the power with the modeled intensity of the zodiacal light. This test clearly indicates that the large scale power in the infrared background is not being caused by the zodiacal light.Comment: 17 pp. Accepted for publication in the Ap

The Near Infrared Background: Interplanetary Dust or Primordial Stars?

The intensity of the diffuse ~ 1 - 4 micron sky emission from which solar system and Galactic foregrounds have been subtracted is in excess of that expected from energy released by galaxies and stars that formed during the z < 5 redshift interval (Arendt & Dwek 2003, Matsumoto et al. 2005). The spectral signature of this excess near-infrared background light (NIRBL) component is almost identical to that of reflected sunlight from the interplanetary dust cloud, and could therefore be the result of the incomplete subtraction of this foreground emission component from the diffuse sky maps. Alternatively, this emission component could be extragalactic. Its spectral signature is consistent with that of redshifted continuum and recombination line emission from HII regions formed by the first generation of very massive stars. In this paper we analyze the implications of this spectral component for the formation rate of these Population III stars, the redshift interval during which they formed, the reionization of the universe and evolution of collapsed halo masses. We find that to reproduce the intensity and spectral shape of the NIRBL requires a peak star formation rate that is higher by about a factor of 4 to 10 compared to those derived from hierarchical models. Furthermore, an extragalactic origin for the NIRBL leads to physically unrealistic absorption-corrected spectra of distant TeV blazars. All these results suggest that Pop III stars contribute only a fraction of the NIRBL intensity with zodiacal light, star forming galaxies, and/or non-nuclear sources giving rise to the remaining fraction.Comment: 28 pages including 7 embedded figures. Submitted to Ap

Interstellar and Ejecta Dust in the Cas A Supernova Remnant

Infrared continuum observations provide a means of investigating the physical composition of the dust in the ejecta and swept up medium of the Cas A supernova remnant. Using low resolution Spitzer IRS spectra (5-35 $\mu$m), and broad-band Herschel PACS imaging (70, 100, and 160 $\mu$m), we identify characteristic dust spectra, associated with ejecta layers that underwent distinct nuclear burning histories. The most luminous spectrum exhibits strong emission features at $\sim9$ and 21 $\mu$m and is closely associated with ejecta knots with strong Ar emission lines. The dust features can be reproduced by magnesium silicate grains with relatively low Mg to Si ratios. Another dust spectrum is associated with ejecta having strong Ne emission lines. It has no indication of any silicate features, and is best fit by Al$_2$O$_3$ dust. A third characteristic dust spectrum shows features that are best matched by magnesium silicates with a relatively high Mg to Si ratio. This dust is primarily associated with the X-ray emitting shocked ejecta, but it is also evident in regions where shocked interstellar or circumstellar material is expected. However, the identification of dust composition is not unique, and each spectrum includes an additional featureless dust component of unknown composition. Colder dust of indeterminate composition is associated with emission from the interior of the SNR, where the reverse shock has not yet swept up and heated the ejecta. Most of the dust mass in Cas A is associated with this unidentified cold component, which is $\lesssim0.1$ $M_{\odot}$. The mass of warmer dust is only $\sim 0.04$ $M_{\odot}$.Comment: 45 pages. 21 Figures. Accepted for publication in Ap

Dust formation, evolution, and obscuration effects in the very high-redshift universe

The evolution of dust at redshifts z>9, and consequently the dust properties, differs greatly from that in the local universe. In contrast to the local universe, core collapse supernovae (CCSNe) are the only source of thermally-condensed dust. Because of the low initial dust-to-gas mass ratio, grain destruction rates are low, so that CCSNe are net producers of interstellar dust. Galaxies with large initial gas mass or high mass infall rate will therefore have a more rapid net rate of dust production comported to galaxies with lower gas mass, even at the same star formation rate. The dust composition is dominated by silicates, which exhibit a strong rise in the UV opacity near the Lyman break. This "silicate-UV break" may be confused with the Lyman break, resulting in a misidentification of a galaxies' photometric redshift. In this paper we demonstrate these effects by analyzing the spectral energy distribution (SED) of MACS1149-JD, a lensed galaxy at z=9.6. A potential 2mm counterpart of MACS1149-JD has been identified with GISMO. While additional observations are required to corroborate this identification, we use this possible association to illustrate the physical processes and the observational effects of dust in the very high redshift universe.Comment: Accepted for publication in ApJ Letter