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Register a new userNear-infrared Extinction due to Cool Supernova Dust in Cassiopeia A
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We present the results of extinction measurements toward the main ejecta shell of the Cassiopeia A supernova (SN) remnant using the flux ratios between the two near-infrared (NIR) [Fe II] lines at 1.26 and 1.64 $mu {rm m}$. We find a clear correlation between the NIR extinction ($E(J-H)$) and the radial velocity of ejecta knots, showing that redshifted knots are systematically more obscured than blueshifted ones. This internal self-extinction strongly indicates that a large amount of SN dust resides inside and around the main ejecta shell. At one location in the southern part of the shell, we measure $E(J-H)$ by the SN dust of 0.23$pm$0.05 mag. By analyzing the spectral energy distribution of thermal dust emission at that location, we show that there are warm ($sim$100 K) and cool ($sim$40 K) SN dust components and that the latter is responsible for the observed $E(J-H)$. We investigate the possible grain species and size of each component and find that the warm SN dust needs to be silicate grains such as MgSiO$_{3}$, Mg$_{2}$SiO$_{4}$, and SiO$_{2}$, whereas the cool dust could be either small ($leq$0.01 $mu {rm m}$) Fe or large ($geq$0.1 $mu {rm m}$) Si grains. We suggest that the warm and cool dust components in Cassiopeia A represent grain species produced in diffuse SN ejecta and in dense ejecta clumps, respectively.
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We report the results of broadband (0.95--2.46 $mu$m) near-infrared spectroscopic observations of the Cassiopeia A supernova remnant. Using a clump-finding algorithm in two-dimensional dispersed images, we identify 63 knots from eight slit positions and derive their spectroscopic properties. All of the knots emit [Fe II] lines together with other ionic forbidden lines of heavy elements, and some of them also emit H and He lines. We identify 46 emission line features in total from the 63 knots and measure their fluxes and radial velocities. The results of our analyses of the emission line features based on principal component analysis show that the knots can be classified into three groups: (1) He-rich, (2) S-rich, and (3) Fe-rich knots. The He-rich knots have relatively small, $lesssim 200~{rm km~s}^{-1}$, line-of-sight speeds and radiate strong He I and [Fe II] lines resembling closely optical quasi-stationary flocculi of circumstellar medium, while the S-rich knots show strong lines from O-burning material with large radial velocities up to $sim 2000~{rm km~s}^{-1}$ indicating that they are supernova ejecta material known as fast-moving knots. The Fe-rich knots also have large radial velocities but show no lines from O-burning material. We discuss the origin of the Fe-rich knots and conclude that they are most likely pure Fe ejecta synthesized in the innermost region during the supernova explosion. The comparison of [Fe II] images with other waveband images shows that these dense Fe ejecta are mainly distributed along the southwestern shell just outside the unshocked $^{44}$Ti in the interior, supporting the presence of unshocked Fe associated with $^{44}$Ti.
We present a long-exposure (~10 hr) image of the supernova (SN) remnant Cassiopeia A (Cas A) obtained with the UKIRT 3.8-m telescope using a narrow band filter centered at 1.644 um emission. The passband contains [Fe II] 1.644 um and [Si I] 1.645 um lines, and our `deep [Fe II]+[Si I] image provides an unprecedented panoramic view of Cas A, showing both shocked and unshocked SN ejecta together with shocked circumstellar medium at subarcsec (~0.7 arcsec or 0.012 pc) resolution. The diffuse emission from the unshocked SN ejecta has a form of clumps, filaments, and arcs, and their spatial distribution correlates well with that of the Spitzer [Si II] infrared emission, suggesting that the emission is likely due to [Si I] line not [Fe II] line as in shocked material. The structure of the optically-invisible western area of Cas A is clearly seen for the first time. The area is filled with many Quasi-Stationary Flocculi (QSFs) and fragments of the disrupted ejecta shell. We suggest that the anomalous radio properties in this area could be due to the increased number of such dense clumps. We identified 309 knots in the deep [Fe II]+[Si I] image and classified them into QSFs and fast-moving knots (FMKs). The total H+He mass of QSFs is ~0.23 Msun, implying that the mass fraction of dense clumps in the progenitors red-supergiant wind is 4--13%. The spatial distribution of QSFs suggests that there had been a highly asymmetric mass loss $10^4$--$10^5$ yr before the SN explosion. The mass of the [Fe II] line-emitting, shocked dense Fe ejecta is ~3x$10^{-5}$ Msun. The comparison with the ionic S-line dominated Hubble Space Telescope WFC3/IR image suggests that the outermost FMKs in the southeastern area are Fe-rich.
We apply the supernova(SN) extinction curves to reproduce the observed properties of SST J1604+4304 which is a young infrared (IR) galaxy at z = 1. The SN extinction curves used in this work were obtained from models of unmixed ejecta of type II supernovae(SNe II) for the Salpeter initial mass function (IMF) with a mass range from 8 to 30 M_sun or 8 to 40 M_sun. The effect of dust distributions on the attenuation of starlight is investigated by performing the chi-square fitting method against various dust distributions. These are the commonly used uniform dust screen, the clumpy dust screen, and the internal dust geometry. We add to these geometries three scattering properties, namely, no-scattering, isotropic scattering, and forward-only scattering. Judging from the chi-square values, we find that the uniform screen models with any scattering property provide good approximations to the real dust geometry. Internal dust is inefficient to attenuate starlight and thus cannot be the dominant source of the extinction. We show that the SN extinction curves reproduce the data of SST J1604+4304 comparable to or better than the Calzetti extinction curve. The Milky Way extinction curve is not in satisfactory agreement with the data unless several dusty clumps are in the line of sight. This trend may be explained by the abundance of SN-origin dust in these galaxies; SN dust is the most abundant in the young IR galaxy at z = 1, abundant in local starbursts, and less abundant in the Galaxy. If dust in SST J1604+4304 is dominated by SN dust, the dust production rate is about 0.1 M_sun per SN.
Several methods exist to convert near-infrared (NIR) stellar observations into extinction maps. We present a new method based on NIR multiband observations. The method uses a discretised version of the distribution of intrinsic stellar colours. A number of variations of the basic method are tested, and the results are compared to NICER calculations. When photometric errors are large, the results are close to those of NICER method but some advantages can be seen when the distribution of intrinsic colours cannot be described well with a single covariance matrix. A priori information about relative column density variations at sub-beam scales can result in a significant increase in accuracy. The results may be further improved by considering the magnitude dependence of the intrinsic colours. Thus, the new methods are useful mostly when photometric errors are small, the distribution of intrinsic colours is well known, or one has prior knowledge of the small-scale structures.
We present infrared (IR) and submillimeter observations of the Crab-like supernova remnant (SNR) G54.1+0.3 including 350 micron (SHARC-II), 870 micron (LABOCA), 70, 100, 160, 250, 350, 500 micron (Herschel) and 3-40 micron (Spitzer). We detect dust features at 9, 11 and 21 micron and a long wavelength continuum dust component. The 21 micron dust coincides with [Ar II] ejecta emission, and the feature is remarkably similar to that in Cas A. The IRAC 8 micron image including Ar ejecta is distributed in a shell-like morphology which is coincident with dust features, suggesting that dust has formed in the ejecta. We create a cold dust map that shows excess emission in the northwestern shell. We fit the spectral energy distribution of the SNR using the continuous distributions of ellipsoidal (CDE) grain model of pre-solar grain SiO2 that reproduces the 21 and 9 micron dust features and discuss grains of SiC and PAH that may be responsible for the 10-13 micron dust features. To reproduce the long-wavelength continuum, we explore models consisting of different grains including Mg2SiO4, MgSiO3, Al2O3, FeS, carbon, and Fe3O4. We tested a model with a temperature-dependent silicate absorption coefficient. We detect cold dust (27-44 K) in the remnant, making this the fourth such SNR with freshly-formed dust. The total dust mass in the SNR ranges from 0.08-0.9 Msun depending on the grain composition, which is comparable to predicted masses from theoretical models. Our estimated dust masses are consistent with the idea that SNe are a significant source of dust in the early Universe.
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