Search

We use Spitzer/IRAC deep exposure data covering two significantly larger than before sky areas to construct maps suitable for evaluating source-subtracted fluctuations in the cosmic infrared background (CIB). The maps are constructed using the self-calibration methodology eliminating artifacts to sufficient accuracy and subset maps are selected in each area containing approximately uniform exposures. These maps are clipped and removed of known sources and then Fourier transformed to probe the CIB anisotropies to new larger scales. The power spectrum of the resultant CIB anisotropies is measured from the data to >1 degree revealing the component well above that from remaining known galaxies on scales >1 arcmin. The fluctuations are demonstrated to be free of Galactic and Solar System foreground contributions out to the largest scales measured. We discuss the proposed theories for the origin of the excess CIB anisotropies in light of the new data. Out of these, the model where the CIB fluctuation excess originates from the granulation power due to LIGO-observed primordial black holes as dark matter appears most successful in accounting for all observations related to the measured CIB power amplitude and spatial structure, including the measured coherence between the CIB and unresolved cosmic X-ray background (CXB). Finally we point out the use of the data to probe the CIB-CXB cross-power to new scales and higher accuracy. We also discuss the synergy of these data with future CIB programs at shorter near-IR wavelengths with deep wide surveys and sub-arcsecond angular resolution as provided by Euclid and Roman space missions., Comment: Astrophysical Journal Letters, to be published

JWST observations of the young Galactic supernova remnant Cassiopeia A revealed an unexpected structure seen as a green emission feature in colored composite MIRI F1130W and F1280W images - hence dubbed the Green Monster - that stretches across the central parts of the remnant in projection. Combining the kinematic information from NIRSpec and MIRI MRS with the multi-wavelength imaging from NIRCam and MIRI, we associate the Green Monster with circumstellar material that was lost during an asymmetric mass-loss phase. MIRI images are dominated by dust emission but its spectra show emission lines from Ne, H and Fe with low radial velocities indicative of a CSM nature. An X-ray analysis of this feature in a companion paper (Vink et al. 2024) supports its CSM nature and detects significant blue shifting, thereby placing the Green Monster on the near side, in front of the Cas A SN remnant. The most striking features of the Green Monster are dozens of almost perfectly circular 1" - 3" sized holes, most likely created by interaction between high-velocity SN ejecta material and the CSM. Further investigation is needed to understand whether these holes were formed by small 8000-10500 km/s N-rich ejecta knots that penetrated and advanced out ahead of the remnant's 5000 - 6000 km/s outer blastwave, or by narrow ejecta fingers that protrude into the forward-shocked CSM. The detection of the Green Monster provides further evidence of the highly asymmetric mass-loss that Cas A's progenitor star underwent prior to explosion., Comment: 28 pages, 12 figures, resubmitted to ApJL after minor revision, comments welcome

We present a procedure for calculating the heating of, and the infrared emission from, dust in a homogeneous spherical shell surrounded by a spherically symmetric source of radiation. The results are applicable to newly formed dust either in supernova ejecta or in the circumstellar medium that has been swept up by the expanding shock wave. They can also be applied to the heating and IR emission from dust in clumps or clouds embedded in a homogeneous radiation field.

JWST/NIRCam obtained high angular-resolution (0.05-0.1''), deep near-infrared 1--5 micron imaging of Supernova (SN) 1987A taken 35 years after the explosion. In the NIRCam images, we identify: 1) faint H2 crescents, which are emissions located between the ejecta and the equatorial ring, 2) a bar, which is a substructure of the ejecta, and 3) the bright 3-5 micron continuum emission exterior to the equatorial ring. The emission of the remnant in the NIRCam 1-2.3 micron images is mostly due to line emission, which is mostly emitted in the ejecta and in the hot spots within the equatorial ring. In contrast, the NIRCam 3-5 micron images are dominated by continuum emission. In the ejecta, the continuum is due to dust, obscuring the centre of the ejecta. In contrast, in the ring and exterior to the ring, synchrotron emission contributes a substantial fraction to the continuum. Dust emission contributes to the continuum at outer spots and diffuse emission exterior to the ring, but little within the ring. This shows that dust cooling and destruction time scales are shorter than the synchrotron cooling time scale, and the time scale of hydrogen recombination in the ring is even longer than the synchrotron cooling time scale. With the advent of high sensitivity and high angular resolution images provided by JWST/NIRCam, our observations of SN 1987A demonstrate that NIRCam opens up a window to study particle-acceleration and shock physics in unprecedented details, probed by near-infrared synchrotron emission, building a precise picture of how a SN evolves., Comment: Accepted for publication in MNRAS; 18 pages

We present initial results from a JWST survey of the youngest Galactic core-collapse supernova remnant Cassiopeia A (Cas A), made up of NIRCam and MIRI imaging mosaics that map emission from the main shell, interior, and surrounding circumstellar/interstellar material (CSM/ISM). We also present four exploratory positions of MIRI/MRS IFU spectroscopy that sample ejecta, CSM, and associated dust from representative shocked and unshocked regions. Surprising discoveries include: 1) a web-like network of unshocked ejecta filaments resolved to 0.01 pc scales exhibiting an overall morphology consistent with turbulent mixing of cool, low-entropy matter from the progenitor's oxygen layer with hot, high-entropy matter heated by neutrino interactions and radioactivity, 2) a thick sheet of dust-dominated emission from shocked CSM seen in projection toward the remnant's interior pockmarked with small (approximately one arcsecond) round holes formed by knots of high-velocity ejecta that have pierced through the CSM and driven expanding tangential shocks, 3) dozens of light echoes with angular sizes between 0.1 arcsecond to 1 arcminute reflecting previously unseen fine-scale structure in the ISM. NIRCam observations place new upper limits on infrared emission from the neutron star in Cas A's center and tightly constrain scenarios involving a possible fallback disk. These JWST survey data and initial findings help address unresolved questions about massive star explosions that have broad implications for the formation and evolution of stellar populations, the metal and dust enrichment of galaxies, and the origin of compact remnant objects., Comment: 27 pages, 10 figures, now published in ApJL

JWST NIRCam observations at 1.5-4.5 $\mu$m have provided broad and narrow band imaging of the evolving remnant of SN 1987A with unparalleled sensitivity and spatial resolution. Comparing with previous marginally spatially resolved Spitzer IRAC observations from 2004-2019 confirms that the emission arises from the circumstellar equatorial ring (ER), and the current brightness at 3.6 and 4.5 $\mu$m was accurately predicted by extrapolation of the declining brightness tracked by IRAC. Despite the regular light curve, the NIRCam observations clearly reveal that much of this emission is from a newly developing outer portion of the ER. Spots in the outer ER tend to lie at position angles in between the well-known ER hotspots. We show that the bulk of the emission in the field can be represented by 5 standard spectral energy distributions (SEDs), each with a distinct origin and spatial distribution. This spectral decomposition provides a powerful technique for distinguishing overlapping emission from the circumstellar medium (CSM) and the supernova (SN) ejecta, excited by the forward and reverse shocks respectively., Comment: Accepted for publication in ApJ. 16 pages, 12 figures. 2 animations not included here

At a distance of 50 kpc, Supernova 1987A is an ideal target to study how a young supernova (SN) evolves in time. Its equatorial ring, filled with material expelled from the progenitor star about 20,000 years ago, has been engulfed with SN blast waves. Shocks heat dust grains in the ring, emitting their energy at mid-infrared (IR) wavelengths We present ground-based 10--18$\mu$m monitoring of the ring of SN 1987A from day 6067 to 12814 at a resolution of 0.5", together with SOFIA photometry at 10-30 $\mu$m. The IR images in the 2000's (day 6067-7242) showed that the shocks first began brightening the east side of the ring. Later, our mid-IR images from 2017 to 2022 (day 10952-12714) show that dust emission is now fading in the east, while it has brightened on the west side of the ring. Because dust grains are heated in the shocked plasma, which can emit X-rays, the IR and X-ray brightness ratio represent shock diagnostics. Until 2007 the IR to X-ray brightness ratio remained constant over time, and during this time shocks seemed to be largely influencing the east side of the ring. However, since then, the IR to X-ray ratio has been declining, due to increased X-ray brightness. Whether the declining IR brightness is because of dust grains being destroyed or being cooled in the post-shock regions will require more detailed modelling., Comment: MNRAS accepted

The diffuse, unresolved sky provides most of the photons that the Hubble Space Telescope (HST) receives, yet remains poorly understood. HST Archival Legacy program SKYSURF aims to measure the 0.2-1.6 $\mu$m sky surface brightness (sky-SB) from over 140,000 HST images. We describe a sky-SB measurement algorithm designed for SKYSURF that is able to recover the input sky-SB from simulated images to within 1% uncertainty. We present our sky-SB measurements estimated using this algorithm on the entire SKYSURF database. Comparing our sky-SB spectral energy distribution (SED) to measurements from the literature shows general agreements. Our SKYSURF SED also reveals a possible dependence on Sun angle, indicating either non-isotropic scattering of solar photons off interplanetary dust or an additional component to Zodiacal Light. Finally, we update Diffuse Light limits in the near-IR based on the methods from Carleton et al. (2022), with values of 0.009 MJy sr$^{-1}$ (22 nW m$^{-2}$ sr$^{-1}$) at 1.25 $\mu$m, 0.015 MJy sr$^{-1}$ (32 nW m$^{-2}$ sr$^{-1}$) at 1.4 $\mu$m, and 0.013 MJy sr$^{-1}$ (25 nW m$^{-2}$ sr$^{-1}$) at 1.6 $\mu$m. These estimates provide the most stringent all-sky constraints to date in this wavelength range. SKYSURF sky-SB measurements are made public on the official SKYSURF website and will be used to constrain Diffuse Light in future papers., Comment: Revised based on helpful comments from the reviewer, and accepted to AJ on April 12th, 2023. Main paper: 18 pages, 9 figures, 4 tables. Appendices: 16 pages, 10 figures, 1 table. Main results shown in Figure 7 and Table 4

We give an overview and describe the rationale, methods, and first results from NIRCam images of the JWST "Prime Extragalactic Areas for Reionization and Lensing Science" ("PEARLS") project. PEARLS uses up to eight NIRCam filters to survey several prime extragalactic survey areas: two fields at the North Ecliptic Pole (NEP); seven gravitationally lensing clusters; two high redshift proto-clusters; and the iconic backlit VV 191 galaxy system to map its dust attenuation. PEARLS also includes NIRISS spectra for one of the NEP fields and NIRSpec spectra of two high-redshift quasars. The main goal of PEARLS is to study the epoch of galaxy assembly, AGN growth, and First Light. Five fields, the JWST NEP Time-Domain Field (TDF), IRAC Dark Field (IDF), and three lensing clusters, will be observed in up to four epochs over a year. The cadence and sensitivity of the imaging data are ideally suited to find faint variable objects such as weak AGN, high-redshift supernovae, and cluster caustic transits. Both NEP fields have sightlines through our Galaxy, providing significant numbers of very faint brown dwarfs whose proper motions can be studied. Observations from the first spoke in the NEP TDF are public. This paper presents our first PEARLS observations, their NIRCam data reduction and analysis, our first object catalogs, the 0.9-4.5 $\mu$m galaxy counts and Integrated Galaxy Light. We assess the JWST sky brightness in 13 NIRCam filters, yielding our first constraints to diffuse light at 0.9-4.5 {\mu}m. PEARLS is designed to be of lasting benefit to the community., Comment: Accepted to AJ, comments welcome. We ask anyone who uses our public PEARLS (NEP TDF) data to refer to this overview paper

We present the first results from the HST Archival Legacy project "SKYSURF." As described in Windhorst et al. 2022, SKYSURF utilizes the large HST archive to study the diffuse UV, optical, and near-IR backgrounds and foregrounds in detail. Here we utilize SKYSURF's first sky-surface brightness measurements to constrain the level of near-IR diffuse Extragalactic Background Light (EBL). Our sky-surface brightness measurements have been verified to an accuracy of better than 1%, which when combined with systematic errors associated with HST, results in sky brightness uncertainties of $\sim$2-4% $\simeq$ 0.005 MJy/sr in each image. We put limits on the amount of diffuse EBL in three near-IR filters (F125W, F140W, and F160W) by comparing our preliminary sky measurements of $> 30,000$ images to Zodiacal light models, carefully selecting the darkest images to avoid contamination from stray light. In addition, we investigate the impact that instrumental thermal emission has on our measurements, finding that it has a limited impact on F125W and F140W measurements, whereas uncertainties in the exact thermal state of HST results in significant uncertainties in the level of astrophysical diffuse light in F160W images. When compared to the Kelsall et al. (1998) Zodiacal model, an isotropic diffuse background of $30$ nW m$^{-2}$ sr$^{-1}$ remains, whereas using the Wright (1998) Zodiacal model results in no discernible diffuse background. Based primarily on uncertainties in the foreground model subtraction, we present limits on the amount of diffuse EBL of 29 nW m$^{-2}$ sr$^{-1}$, 40 nW m$^{-2}$ sr$^{-1}$, and 29 nW m$^{-2}$ sr$^{-1}$ for F125W, F140W, and F160W respectively. While this light is generally isotropic, our modeling at this point does not distinguish between a cosmological origin or a Solar System origin (such as a dim, diffuse, spherical cloud of cometary dust)., Comment: Accepted with Windhorst et al. 2022 to AJ. Main figures are Fig. 10 and 11. Comments welcome!

We give an overview and describe the rationale, methods, and testing of the Hubble Space Telescope (HST) Archival Legacy project "SKYSURF." SKYSURF uses HST's unique capability as an absolute photometer to measure the ~0.2-1.7 $\mu$m sky surface brightness (SB) from 249,861 WFPC2, ACS, and WFC3 exposures in ~1400 independent HST fields. SKYSURF's panchromatic dataset is designed to constrain the discrete and diffuse UV to near-IR sky components: Zodiacal Light (ZL; inner Solar System), Kuiper Belt Objects (KBOs; outer Solar System), Diffuse Galactic Light (DGL), and the discrete plus diffuse Extragalactic Background Light (EBL). We outline SKYSURF's methods to: (1) measure sky-SB levels between its detected objects; (2) measure the integrated discrete EBL, most of which comes from AB$\simeq$17-22 mag galaxies; and (3) estimate how much diffuse light may exist in addition to the extrapolated discrete galaxy counts. Simulations of HST WFC3/IR images with known sky-values and gradients, realistic cosmic ray (CR) distributions, and star plus galaxy counts were processed with nine different algorithms to measure the "Lowest Estimated Sky-SB" (LES) in each image between the discrete objects. The best algorithms recover the inserted LES values within 0.2% when there are no image gradients, and within 0.2-0.4% when there are 5-10% gradients. SKYSURF requires non-standard re-processing of these HST images that includes restoring the lowest sky-level from each visit into each drizzled image. We provide a proof of concept of our methods from the WFC3/IR F125W images, where any residual diffuse light that HST sees in excess of the Kelsall et al. (1998) Zodiacal model prediction does not depend on the total object flux that each image contains. This enables us to present our first SKYSURF results on diffuse light in Carleton et al. (2022)., Comment: Accepted to AJ; see accompanying paper Carleton et al. 2022: arXiv:2205.06347. Comments welcome!

Here we present new - and, nevertheless, last - mid-infrared (mid-IR) data for supernovae (SNe) based on measurements with the Spitzer Space Telescope. Comparing our recent 3.6 and 4.5 $\mu$m photometry with previously published mid-IR and further multiwavelength datasets, we were able to draw some conclusions about the origin and heating mechanism of the dust in these SNe or in their environments, as well as on possible connection with circumstellar matter (CSM) originating from pre-explosion mass-loss events in the progenitor stars. We also present new results regarding both certain SN classes and single objects. We highlight the mid-IR homogeneity of SNe Ia-CSM, which may be a hint of their common progenitor type and of their basically uniform circumstellar environments. Regarding single objects, it is worth highlighting the late-time interacting Type Ib SNe 2003gk and 2004dk, for which we present the first-ever mid-IR data, which seem to be consistent with clues of ongoing CSM interaction detected in other wavelength ranges. Our current study suggests that long-term mid-IR follow-up observations play a key role in a better understanding of both pre- and post-explosion processes in SNe and their environments. While Spitzer is not available any more, the expected unique data from the James Webb Space Telescope, as well as long-term near-IR follow-up observations of dusty SNe, can bring us closer to the hidden details of this topic., Comment: 25 pages, 10 figures, 4 tables; accepted for publication in ApJ

SN 2010jl is a Type IIn core collapse supernova whose radiative output is powered by the interaction of the SN shock wave with its surrounding dense circumstellar medium (CSM). After day ~60, its light curve developed a NIR excess emission from dust. This excess could be a thermal IR echo from pre-existing CSM dust, or emission from newly-formed dust either in the cooling postshock region of the CSM, or in the cooling SN ejecta. Recent analysis has shown that dust formation in the CSM can commence only after day ~380, and has also ruled out newly-formed ejecta dust as the source of the NIR emission. The early (< 380 d) NIR emission can therefore only be attributed to an IR echo. The H-K color temperature of the echo is about 1250 K. The best fitting model requires the presence of about 1.6e-4 Msun of amorphous carbon dust at a distance of 2.2e16 cm from the explosion. The CSM-powered luminosity is preceded by an intense burst of hard radiation generated by the breakout of the SN shock through the stellar surface. The peak burst luminosity seen by the CSM dust is significantly reduced by Thomson scattering in the CSM, but still has the potential of evaporating the dust needed to produce the echo. We show that the survival of the echo-producing dust provides important constraints on the intensity, effective temperature, and duration of the burst., Comment: Accepted for publication in the ApJ, 20 pages, 1 table, and 17 figures

We present an analysis of the 4-2600 $\mu$m spectral energy distributions (SEDs) of the west and east nuclei and the diffuse infrared (IR) region of the merger-driven starburst Arp 220. We examine several possible source morphologies and dust temperature distributions using a mixture of silicate and carbonaceous grains. From fits to the SEDs we derive dust masses, temperatures, luminosities, and dust inferred gas masses. We show that the west and east nuclei are powered by central sources deeply enshrouded behind $\sim 10^{26}$ cm$^{-2}$ column densities of hydrogen with an exponential density distribution, and that the west and east nuclei are optically thick out to wavelengths of $\sim 1900$ and $\sim 770$ $\mu$m, respectively. The nature of the central sources cannot be determined from our analysis. We derive star formation rates or black hole masses needed to power the IR emission, and show that the [C II] 158$\mu$m line cannot be used as a tracer of the star formation rate in heavily obscured systems. Dust inferred gas masses are larger than those inferred from CO observations, suggesting either larger dust-to-H mass ratios, or the presence of hidden atomic H that cannot be inferred from CO observations. The luminosities per unit mass in the nuclei are $\sim 450$, in solar units, smaller that the Eddington limit of $\sim 1000 - 3000$ for an optically thick star forming region, suggesting that the observed gas outflows are primarily driven by stellar winds and supernova shock waves instead of radiation pressure on the dust., Comment: Accepted for publication in The Astrophysical Journal

Spitzer's final Infrared Array Camera (IRAC) observations of SN 1987A show the 3.6 and 4.5 $\mu$m emission from the equatorial ring (ER) continues a period of steady decline. Deconvolution of the images reveals that the emission is dominated by the ring, not the ejecta, and is brightest on the west side. Decomposition of the marginally resolved emission also confirms this, and shows that the west side of the ER has been brightening relative to the other portions of the ER. The infrared (IR) morphological changes resemble those seen in both the soft X-ray emission and the optical emission. The integrated ER light curves at 3.6 and 4.5 $\mu$m are more similar to the optical light curves than the soft X-ray light curve, though differences would be expected if dust is responsible for this emission and its destruction is rapid. Future observations with the James Webb Space Telescope will continue to monitor the ER evolution, and will reveal the true spectrum and nature of the material responsible for the broadband emission at 3.6 and 4.5 $\mu$m. The present observations also serendipitously reveal a nearby variable source, subsequently identified as a Be star, that has gone through a multi-year outburst during the course of these observations., Comment: 12 pages, 9 figures. Accepted for publication in the ApJ

We have used the Goddard IRAM 2-Millimeter Observer (GISMO) with the 30 m IRAM telescope to carry out a 2 mm survey of the Galaxy's central molecular zone (CMZ). These observations detect thermal emission from cold ISM dust, thermal free-free emission from ionized gas, and nonthermal synchrotron emission from relatively flat-spectrum sources. Archival data sets spanning $3.6 \mu$m to 90 cm are used to distinguish different emission mechanisms. After the thermal emission of dust is modeled and subtracted, the remaining 2 mm emission is dominated by free-free emission, with the exception of the brightest nonthermal filament (NTF) that runs though the middle of the bundle of filaments known as the Radio Arc. This is the shortest wavelength at which any NTF has been detected. The GISMO observations clearly trace this NTF over a length of ~0.2$^\circ$, with a mean 2 mm spectral index which is steeper than at longer wavelengths. The 2 mm to 6 cm (or 20 cm) spectral index steepens from $\alpha \approx -0.2$ to $-0.7$ as a function distance from the Sickle H II region, suggesting that this region is directly related to the NTF. A number of unresolved (at $21''$) 2 mm sources are found nearby. One appears to be thermal dust emission from a molecular cloud that is associated with an enigmatic radio point source whose connection to the Radio Arc is still debated. The morphology and colors at shorter IR wavelengths indicate other 2 mm unresolved sources are likely to be compact H II regions., Comment: 17 pages, 11 figures. Accepted for publication in the ApJ

The Central Molecular Zone (CMZ), covering the inner ~1$^\circ$ of the Galactic plane has been mapped at 2 mm using the GISMO bolometric camera on the 30 m IRAM telescope. The $21''$ resolution maps show abundant emission from cold molecular clouds, from star forming regions, and from one of the Galactic center nonthermal filaments. In this work we use the Herschel Hi-GAL data to model the dust emission across the Galactic center. We find that a single-temperature fit can describe the 160 -- 500 $\mu$m emission for most lines of sight, if the long-wavelength dust emissivity scales as $\lambda^{-\beta}$ with $\beta \approx 2.25$. This dust model is extrapolated to predict the 2 mm dust emission. Subtraction of the model from the GISMO data provides a clearer look at the 2 mm emission of star-forming regions and the brightest nonthermal filament., Comment: 18 pages, 15 figures. Accepted for publication in the ApJ

We study the coherence of the near-infrared and X-ray background fluctuations and the X-ray spectral properties of the sources producing it. We use data from multiple Spitzer and Chandra surveys, including the UDS/SXDF surveys, the Hubble Deep Field North, the EGS/AEGIS field, the Chandra Deep Field South and the COSMOS surveys, comprising $\sim$2275 Spitzer/IRAC hours and $\sim$~16 Ms of Chandra data collected over a total area of $\sim$~1~deg$^2$. We report an overall $\sim$5$\sigma$ detection of a cross-power signal on large angular scales $>$ 20$''$ between the 3.6 and 4.5\mum\ and the X-ray bands, with the IR vs [1-2] keV signal detected at 5.2$\sigma$. The [0.5-1] and [2-4] keV bands are correlated with the infrared wavelengths at a $\sim$1$-$3$\sigma$ significance level. The hardest X-ray band ([4-7] keV) alone is not significantly correlated with any infrared wavelengths due to poor photon and sampling statistics. We study the X-ray SED of the cross-power signal. We find that its shape is consistent with a variety of source populations of accreting compact objects, such as local unabsorbed AGNs or high-z absorbed sources. We cannot exclude that the excess fluctuations are produced by more than one population. Because of poor statistics, the current relatively broad photometric bands employed here do not allow distinguishing the exact nature of these compact objects or if a fraction of the fluctuations have instead a local origin., Comment: 14 Pages, 4 figures, Accepted by ApJ, for inquires please contact author N. Cappelluti

Astrophysical measurements away from the 1 AU orbit of Earth can enable several astrophysical science cases that are challenging or impossible to perform from Earthbound platforms, including: building a detailed understanding of the extragalactic background light throughout the electromagnetic spectrum; measurements of the properties of dust and ice in the inner and outer solar system; determinations of the mass of planets and stellar remnants far from luminous stars using gravitational microlensing; and stable time-domain astronomy. Though potentially transformative for astrophysics, opportunities to fly instrumentation capable of these measurements are rare, and a mission to the distant solar system that includes instrumentation expressly designed to perform astrophysical science, or even one primarily for a different purpose but capable of precise astronomical investigation, has not yet been flown. In this White Paper, we describe the science motivations for this kind of measurement, and advocate for future flight opportunities that permit intersectional collaboration and cooperation to make these science investigations a reality., Comment: Science white paper submitted for the Astro2020 decadal review, 5 pages + references

We describe the results of principal component analysis (PCA) of up-the-ramp sampled IR array data from the HST WFC3 IR, JWST NIRSpec, and prototype WFIRST WFI detectors. These systems use respectively Teledyne H1R, H2RG, and H4RG-10 near-IR detector arrays with a variety of IR array controllers. The PCA shows that the Legendre polynomials approximate the principal components of these systems (i.e. they roughly diagonalize the covariance matrix). In contrast to the monomial basis that is widely used for polynomial fitting and linearization today, the Legendre polynomials are an orthonormal basis. They provide a quantifiable, compact, and (nearly) linearly uncorrelated representation of the information content of the data. By fitting a few Legendre polynomials, nearly all of the meaningful information in representative WFC3 astronomical datacubes can be condensed from 15 up-the-ramp samples down to 6 compressible Legendre coefficients per pixel. The higher order coefficients contain time domain information that is lost when one projects up-the-ramp sampled datacubes onto 2-dimensional images by fitting a straight line, even if the data are linearized before fitting the line. Going forward, we believe that this time domain information is potentially important for disentangling the various non-linearities that can affect IR array observations, i.e. inherent pixel non-linearity, persistence, burn in, brighter-fatter effect, (potentially) non-linear inter-pixel capacitance (IPC), and perhaps others., Comment: 26 pages, 10 figures, accepted by Journal of Astronomical Telescopes, Instruments, and Systems (JATIS)

Infrared (IR) observations of core collapse supernovae (CCSNe) have been used to infer the mass of dust that has formed in their ejecta. A plot of inferred dust masses versus supernova (SN) ages shows a trend of increasing dust mass with time, spanning a few decades of observations. This trend has been interpreted as evidence for the slow and gradual formation of dust in CCSNe. Observationally, the trend exhibits a $ t^2$ behavior, exactly what is expected from an expanding optically thick ejecta. In this case, the observed dust resides in the infrared (IR)-thin "photosphere" of the ejecta, and constitutes only a fraction of the total dust mass. We therefore propose that dust formation proceeds very rapidly, condensing most available refractory elements within two years after the explosion. At early epochs, only a fraction of the dust emission escapes the ejecta accounting for the low observed dust mass. The ejecta's entire dust content is unveiled only a few decades after the explosion, with the gradual decrease in its IR opacity. Corroborating evidence for this picture includes the early depletions of refractory elements in the ejecta of SN1987A and the appearance of a silicate emission band around day 300 in SN~2004et., Comment: Accepted for publication in the ApJ Letters. The manuscript contains 7 pages, including 2 figures

The equatorial ring of Supernova (SN) 1987A has been exposed to forward shocks from the SN blast wave, and it has been suggested that these forward shocks have been causing on-going destruction of dust in the ring. We obtained SOFIA FORCAST 11.1, 19.7 and 31.5 micron photometry of SN\,1987A in 2016. Compared with Spitzer measurements 10 years earlier, the 31.5 micron flux has significantly increased. The excess at 31.5 micron appears to be related to the Herschel 70 micron excess, which was detected 5 years earlier. The dust mass needed to account for the the 31.5--70 micron excess is 3--7x10^-4 Msun, more than ten times larger than the ring dust mass (1x10^-5 Msun) estimate from the data 10-years earlier. We argue that dust grains are re-formed or grown in the post-shock regions in the ring after forward shocks have destroyed pre-existing dust grains in the ring and released refractory elements into gas. In the post-shock region, atoms can stick to surviving dust grains, and the dust mass may have increased (grain growth), or dust grains might have condensed directly from the gas. An alternative possibility is that the outer part of the expanding ejecta dust might have been heated by X-ray emission from the circumstellar ring. The future development of this excess could reveal whether grains are reformed in the post-shocked region of the ring or eject dust is heated by X-ray., Comment: 10 mages; MNRAS accented

We study the source-subtracted near-infrared and X-ray background fluctuations of the COSMOS field using data from the Spitzer SPLASH program ($\sim$1272 hours) and Chandra COSMOS Legacy Survey (4.6 Ms). The new auto power spectra of the cosmic infrared and X-ray background fluctuations reach maximum angular scales of $\sim$ 3000$''$ and $\sim$ 5000$''$, respectively. We measure the cross power spectra between each infrared and X-ray band and calculate the mean power above 20$''$. We find that the soft X-ray band is correlated with 3.6 and 4.5$\mu$m at $\sim$ 4 $\sigma$ significance level. The significance between hard X-ray and the 3.6$\mu$m (4.5$\mu$m) band is $\sim$2.2 $\sigma$ ($\sim$3.8$\sigma$). The combined infrared (3.6 + 4.5$\mu$m) data are correlated with the X-ray data in soft ([0.5-2] keV), hard ([2-7] keV) and broad ([0.5-7] keV) bands at $\sim$5.6$\sigma$, $\sim$4.4$\sigma$ and $\sim$6.6$\sigma$ level, respectively. We compare the new measurements with existing models for the contributions from known populations at $z$$<$7, which are not subtracted. The model predictions are consistent with the measurements but we cannot rule out contributions from other components, such as Direct Collapse Black Holes (DCBH). However, the stacked cross-power spectra, combining other available data, show excess fluctuations about an order of magnitude on average at $\sim$4$\sigma$ confidence at scales within $\sim$300$''$. By studying the X-ray SED of the cross-power signal, assuming no significant variation from the infrared, we find that its shape is consistent with DCBHs., Comment: 20 pages, 20 figures, 4 tables

The light curves of Type IIn supernovae are dominated by the radiative energy released through the interaction of the supernova shockwaves with their dense circumstellar medium (CSM). The ultraluminous Type IIn supernova SN 2010jl exhibits an infrared emission component that is in excess of the extrapolated UV-optical spectrum as early as a few weeks post-explosion. This emission has been attributed by some as evidence for rapid formation of dust in the cooling postshock CSM. We investigate the physical processes that may inhibit or facilitate the formation of dust in the CSM. When only radiative cooling is considered, the temperature of the dense shocked gas rapidly drops below the dust condensation temperature. However, by accounting for the heating of the postshock gas by the downstream radiation from the shock, we show that dust formation is inhibited until the radiation from the shock weakens, as the shock propagates into the less dense outer regions of the CSM. In SN 2010jl dust formation can therefore only commence after day 380. Only the IR emission since that epoch can be attributed to the newly formed CSM dust. Observations on day 460 and later show that the IR luminosity exceeds the UV-optical luminosity. The post-shock dust cannot extinct the radiation emitted by the expanding SN shock. Therefore, its IR emission must be powered by an interior source, which we identify with the reverse shock propagating through the SN ejecta. IR emission before day 380 must therefore be an IR echo from preexisting CSM dust., Comment: Accepted for publication in The Astrophysical Journal, 26 Pages

A search for the progenitor of SN~2010jl, an unusually luminous core-collapse supernova of Type~IIn, using pre-explosion {\it Hubble}/WFPC2 and {\it Spitzer}/IRAC images of the region, yielded upper limits on the UV and near-infrared (IR) fluxes from any candidate star. These upper limits constrain the luminosity and effective temperature of the progenitor, the mass of any preexisting dust in its surrounding circumstellar medium (CSM), and dust proximity to the star. A {\it lower} limit on the CSM dust mass is required to hide a luminous progenitor from detection by {\it Hubble}. {\it Upper} limits on the CSM dust mass and constraints on its proximity to the star are set by requiring that the absorbed and reradiated IR emission not exceed the IRAC upper limits. Using the combined extinction-IR emission constraints we present viable $M_d-R_1$ combinations, where $M_d$ and $R_1$ are the CSM dust mass and its inner radius. These depend on the CSM outer radius, dust composition and grain size, and the properties of the progenitor. The results constrain the pre-supernova evolution of the progenitor, and the nature and origin of the observed post-explosion IR emission from SN~2010jl. In particular, an $\eta$~Car-type progenitor will require at least 4~mag of visual extinction to avoid detection by the {\it Hubble}. This can be achieved with dust masses $\gtrsim 10^{-3}$~\msun\ (less than the estimated 0.2-0.5~\msun\ around $\eta$~Car) which must be located at distances of $\gtrsim 10^{16}$~cm from the star to avoid detection by {\it Spitzer}., Comment: Accepted for publication in the ApJ. 14 pages 10 figures. The complete figure set for Figure 10 (24 images) is available in the online journal

Near-infrared array detectors, like the \JWST NIRSpec's Teledyne's H2RGs, often provide reference pixels and a reference output. These are used to remove correlated noise. Improved Reference Sampling and Subtraction (\IRSSquare, pronounced "IRS-square") is a statistical technique for using this reference information optimally in a least squares sense. Compared to "traditional" H2RG readout, \IRSSquare uses a different clocking pattern to interleave many more reference pixels into the data than is otherwise possible. Compared to standard reference correction techniques, \IRSSquare subtracts the reference pixels and reference output using a statistically optimized set of frequency dependent weights. The benefits include somewhat lower noise variance and much less obvious correlated noise. NIRSpec's \IRSSquare images are cosmetically clean, with less $1/f$ banding than in traditional data from the same system. This article describes the \IRSSquare clocking pattern and presents the equations that are needed to use \IRSSquare in systems other than NIRSpec. For NIRSpec, applying these equations is already an option in the calibration pipeline. As an aid to instrument builders, we provide our prototype \IRSSquare calibration software and sample \JWST NIRSpec data. The same techniques are applicable to other detector systems, including those based on Teledyne's H4RG arrays. The H4RG's "interleaved reference pixel readout" mode is effectively one \IRSSquare pattern.

While theoretical dust condensation models predict that most refractory elements produced in core-collapse supernovae (SNe) efficiently condense into dust, a large quantity of dust has so far only been observed in SN 1987A. We present the analysis of Spitzer Space Telescope, Herschel Space Observatory, Stratospheric Observatory for Infrared Astronomy (SOFIA), and AKARI observations of the infrared (IR) shell surrounding the pulsar wind nebula in the supernova remnant G54.1+0.3. We attribute a distinctive spectral feature at 21 $\mu$m to a magnesium silicate grain species that has been invoked in modeling the ejecta-condensed dust in Cas A, which exhibits the same spectral signature. If this species is responsible for producing the observed spectral feature and accounts for a significant fraction of the observed IR continuum, we find that it would be the dominant constituent of the dust in G54.1+0.3, with possible secondary contributions from other compositions, such as carbon, silicate, or alumina grains. The smallest mass of SN-formed dust required by our models is 1.1 $\pm$ 0.8 $\rm M_{\odot}$. We discuss how these results may be affected by varying dust grain properties and self-consistent grain heating models. The spatial distribution of the dust mass and temperature in G54.1+0.3 confirms the scenario in which the SN-formed dust has not yet been processed by the SN reverse shock and is being heated by stars belonging to a cluster in which the SN progenitor exploded. The dust mass and composition suggest a progenitor mass of 16$-$27 $\rm M_{\odot}$ and imply a high dust condensation efficiency, similar to that found for Cas A and SN 1987A. The study provides another example of significant dust formation in a Type IIP SN and sheds light on the properties of pristine SN-condensed dust., Comment: 16 pages, 3 tables, 11 figures, accepted for publication in ApJ

The nature of the progenitor star (or system) for the Type IIn supernova (SN) subclass remains uncertain. While there are direct imaging constraints on the progenitors of at least four Type IIn supernovae, one of them being SN 2010jl, ambiguities remain in the interpretation of the unstable progenitors and the explosive events themselves. A blue source in pre-explosion HST/WFPC2 images falls within the 5 sigma astrometric error circle derived from post-explosion ground-based imaging of SN 2010jl. At the time the ground-based astrometry was published, however, the SN had not faded sufficiently for post-explosion HST follow-up observations to determine a more precise astrometric solution and/or confirm if the pre-explosion source had disappeared, both of which are necessary to ultimately disentangle the possible progenitor scenarios. Here we present HST/WFC3 imaging of the SN 2010jl field obtained in 2014 and 2015, when the SN had faded sufficiently to allow for new constraints on the progenitor. The SN, which is still detected in the new images, is offset by 0."099 +/- 0."008 (24 +/- 2 pc) from the underlying and extended source of emission that contributes at least partially, if not entirely, to the blue source previously suggested as the candidate progenitor in the WFPC2 data. This point alone rules out the possibility that the blue source in the pre-explosion images is the exploding star, but may instead suggest an association with a young (<5-6 Myr) cluster and still argues for a massive (>30 solar masses) progenitor. We obtain new upper limits on the flux from a single star at the SN position in the pre-explosion WFPC2 and Spitzer/IRAC images that may ultimately be used to constrain the progenitor properties., Comment: Submitted to ApJ/AAS Journals; 6 Pages; 4 figures

Stellar streams have become central to studies of the interaction histories of nearby galaxies. To characterize the most prominent parts of the stellar stream around the well-known nearby (d = 17 Mpc) edge-on disk galaxy NGC 5907, we have obtained and analyzed new, deep gri Subaru/Suprime-Cam and 3.6 micron Spitzer/Infrared Array Camera (IRAC) observations. Combining the near-infrared 3.6 micron data with visible-light images allows us to use a long wavelength baseline to estimate the metallicity and age of the stellar population along a ~60 kpc long segment of the stream. We have fitted the stellar spectral energy distribution (SED) with a single-burst stellar population synthesis model and we use it to distinguish between the proposed satellite accretion and minor/major merger formation models of the stellar stream around this galaxy. We conclude that a massive minor merger (stellar mass ratio of at least 1:8) can best account for the metallicity of -0.3 inferred along the brightest parts of the stream., Comment: 16 pages, 11 figures, 1 table, accepted for publication in the Astronomical Journal

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 ApJ

Spitzer observations of SN 1987A have now spanned more than a decade. Since day ~4,000, mid-infrared (mid-IR) emission has been dominated by that from shock-heated dust in the equatorial ring (ER). From 6,000 to 8,000 days after the explosion, Spitzer observations included broadband photometry at 3.6 - 24 micron, and low and moderate resolution spectroscopy at 5 - 35 micron. Here we present later Spitzer observations, through day 10,377, which include only the broadband measurements at 3.6 and 4.5 micron. These data show that the 3.6 and 4.5 micron brightness has clearly begun to fade after day ~8,500, and no longer tracks the X-ray emission as well as it did at earlier epochs. This can be explained by the destruction of the dust in the ER on time scales shorter than the cooling time for the shocked gas. We find that the evolution of the late time IR emission is also similar to the now fading optical emission. We provide the complete record of the IR emission lines, as seen by Spitzer prior to day 8,000. The past evolution of the gas as seen by the IR emission lines seems largely consistent with the optical emission, although the IR [Fe II] and [Si II] lines show different, peculiar velocity structures., Comment: Accepted for publication in AJ. 22 pages, 18 figures

Two millimeter observations of the MACS J1149.6+2223 cluster have detected a source that was consistent with the location of the lensed MACS1149-JD galaxy at z=9.6. A positive identification would have rendered this galaxy as the youngest dust forming galaxy in the universe. Follow up observation with the AzTEC 1.1 mm camera and the IRAM NOrthern Extended Millimeter Array (NOEMA) at 1.3 mm have not confirmed this association. In this paper we show that the NOEMA observations associate the 2 mm source with [PCB2012] 2882 ([PCB2012] 2882 is the NED-searchable name for this source.), source number 2882 in the Hubble Space Telescope ( HST) Cluster Lensing and Supernova (CLASH) catalog of MACS J1149.6+2223. This source, hereafter referred to as CLASH 2882, is a gravitationally lensed spiral galaxy at z=0.99. We combine the GISMO 2 mm and NOEMA 1.3 mm fluxes with other (rest frame) UV to far-IR observations to construct the full spectral energy distribution (SED) of this galaxy, and derive its star formation history, and stellar and interstellar dust content. The current star formation rate of the galaxy is 54/mu Msun yr-1, and its dust mass is about 5 10^7/mu Msun, where mu is the lensing magnification factor for this source, which has a mean value of 2.7. The inferred dust mass is higher than the maximum dust mass that can be produced by core collapse supernovae (CCSN) and evolved AGB stars. As with many other star forming galaxies, most of the dust mass in CLASH 2882 must have been accreted in the dense phases of the ISM., Comment: Accepted for publication in The Astrophysical Journal

We present a new analysis of the infrared (IR) emission from the ejecta of SN1987A covering days 615, 775, 1144, 8515, and 9090 after the explosion. We show that the observations are consistent with the rapid formation of about 0.4 Msun of dust, consisting of mostly silicates, near day 615, and evolving to about 0.45 Msun of composite dust grains consisting of ~0.4 Msun of silicates and ~ 0.05 Msun of amorphous carbon after day ~8500. The proposed scenario challenges previous claims that dust in SN ejecta is predominantly carbon, and that it grew from an initial mass of ~1e-3 Msun, to over 0.5 Msun by cold accretion. It alleviates several problems with previous interpretations of the data: (1) it reconciles the abundances of silicon, magnesium, and carbon with the upper limits imposed by nucleosynthesis calculations; (2) it eliminates the requirement that most of the dust observed around day 9000 grew by cold accretion onto the1e-3 Msun of dust previously inferred for days 615 and 775 after the explosion; and (3) establishes the dominance of silicate over carbon dust in the SN ejecta. At early epochs, the IR luminosity of the dust is powered by the radioactive decay of 56Co, and at late times by at least (1.3-1.6)e-4 Msun 44Ti. Even if only a fraction greater than ~10% of the silicate dust survives the injection into the ISM, the observations firmly establish the role of core collapse SNe as the major source of thermally condensed silicate dust in the universe., Comment: Accepted for publication in The Astrophysical Journal. The manuscript has 10 pages, 6 figures, and 4 tables

NGC 6872, hereafter the Condor, is a large spiral galaxy that is interacting with its closest companion, the S0 galaxy IC 4970. The extent of the Condor provides an opportunity for detailed investigation of the impact of the interaction on the current star formation rate and its history across the galaxy, on the age and spatial distribution of its stellar population, and on the mechanism that drive the star formation activity. To address these issues we analyzed the far-ultraviolet (FUV) to near-infrared (near-IR) spectral energy distribution (SED) of 17, 10 kpc diameter, regions across the galaxy, and derived their star formation history, current star formation rate, and stellar population and mass. We find that most of the star formation takes place in the extended arms, with very little star formation in the central 5 kpc of the galaxy, in contrast to what was predicted from previous numerical simulations. There is a trend of increasing star formation activity with distance from the nucleus of the galaxy, and no evidence for a recent increase in the current star formation rate (SFR) due to the interaction. The nucleus itself shows no significant current star formation activity. The extent of the Condor also provides an opportunity to test the applicability of a single standard prescription for conversion of the FUV + IR (22 micron) intensities to a star formation rate for all regions. We find that the conversion factor differs from region to region, arising from regional differences in the stellar populations., Comment: 14 pages. 10 figures. Accepted for publication in ApJ

Re-examination of the COBE DIRBE data reveals the thermal emission of several comet dust trails. The dust trails of 1P/Halley, 169P/NEAT, and 3200 Phaethon have not been previously reported. The known trails of 2P/Encke, and 73P/Schwassmann-Wachmann 3 are also seen. The dust trails have 12 and 25 micron surface brightnesses of <0.1 and <0.15 MJy/sr, respectively, which is <1% of the zodiacal light intensity. The trails are very difficult to see in any single daily image of the sky, but are evident as rapidly moving linear features in movies of the DIRBE data. Some trails are clearest when crossing through the orbital plane of the parent comet, but others are best seen at high ecliptic latitudes as the Earth passes over or under the dust trail. All these comets have known associations with meteor showers. This re-examination also reveals one additional comet and 13 additional asteroids that had not previously been recognized in the DIRBE data., Comment: 11 pages. Accepted for publication in AJ. The movies (which will appear in the AJ) are not included here

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 Letters

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 ApJ

We present deep continuum observations using the GISMO camera at a wavelength of 2 mm centered on the Hubble Deep Field (HDF) in the GOODS-N field. These are the first deep field observations ever obtained at this wavelength. The 1 sigma sensitivity in the innermost approx. 4 arcminutes of the 7 utes map is approx. 135 uJy/beam, a factor of three higher in flux/beam sensitivity than the deepest available SCUBA 850 um observations, and almost a factor of four higher in flux / beam sensitivity than the combined MAMBO/AzTEC 1.2 mm observations of this region. Our source extraction algorithm identifies 12 sources directly, and another 3 through correlation with known sources at 1.2 mm and 850 um. Five of the directly detected GISMO sources have counterparts in the MAMBO/AzTEC catalog, and four of those also have SCUBA counterparts. HDF850.1, one of the first blank-field detected submillimeter galaxies, is now detected at 2 mm. The median redshift of all sources with counterparts of known redshifts is med(z) = 2.91 +/- 0.94. Statistically, the detections are most likely real for 5 of the seven 2 mm sources without shorter wavelength counterparts, while the probability for none of them being real is negligible., Comment: Accepted for publication in ApJ

Recent infrared (IR) observations of freshly-formed dust in supernova remnants (SNRs) have yielded significantly lower dust masses than predicted by theoretical models and measured from high redshift observations. The Crab Nebula's pulsar wind is thought to be sweeping up freshly-formed supernova (SN) dust along with the ejected gas. The evidence for this dust was found in the form of an IR excess in the integrated spectrum of the Crab and in extinction against the synchrotron nebula that revealed the presence of dust in the filament cores. We present the first spatially resolved emission spectra of dust in the Crab Nebula acquired with the Infrared Spectrograph aboard the Spitzer Space Telescope. The IR spectra are dominated by synchrotron emission and show forbidden line emission from from S, Si, Ne, Ar, O, Fe, and Ni. We derived a synchrotron spectral map from the 3.6 and 4.5 microns images, and subtracted this contribution from our data to produce a map of the residual continuum emission from dust. The dust emission appears to be concentrated along the ejecta filaments and is well described by an amorphous carbon or silicate grain compositions. We find a dust temperature of 55+/- 4 K for silicates and 60 +/- 7 K for carbon grains. The total estimated dust mass is 0.0012-0.012 solar masses, well below the theoretical dust yield predicted for a core-collapse supernova. Our grain heating model implies that the dust grain radii are relatively small, unlike what is expected for dust grains formed in a Type IIP SN., Comment: 10 pages, 3 tables, 6 figures, accepted to ApJ

We present deep Chandra observations and Spitzer Space Telescope infrared (IR) spectroscopy of the shell in the composite supernova remnant (SNR) Kes 75 (G29.7-0.3). The remnant is composed of a central pulsar wind nebula and a bright partial shell in the south that is visible at radio, IR, and X-ray wavelengths. The X-ray emission can be modeled by either a single thermal component with a temperature of ~ 1.5 keV, or with two thermal components with temperatures of 1.5 and 0.2 keV. Previous studies suggest that the hot component may originate from reverse-shocked SN ejecta. However, our new analysis shows no definitive evidence for enhanced abundances of Si, S, Ar, Mg, and Fe, as expected from supernova (SN) ejecta, or for the IR spectral signatures characteristic of confirmed SN condensed dust, thus favoring a circumstellar or interstellar origin for the X-ray and IR emission. The X-ray and IR emission in the shell are spatially correlated, suggesting that the dust particles are collisionally heated by the X-ray emitting gas. The IR spectrum of the shell is dominated by continuum emission from dust with little, or no line emission. Modeling the IR spectrum shows that the dust is heated to a temperature of ~ 140 K by a relatively dense, hot plasma, that also gives rise to the hot X-ray emission component. The density inferred from the IR emission is significantly higher than the density inferred from the X-ray models, suggesting a low filling factor for this X-ray emitting gas. The total mass of the warm dust component is at least 0.013 solar masses, assuming no significant dust destruction has occurred in the shell. The IR data also reveal the presence of an additional plasma component with a cooler temperature, consistent with the 0.2 keV gas component. Our IR analysis therefore provides an independent verification of the cooler component of the X-ray emission., Comment: 12 pages, 4 tables, 11 figures, accepted for publication in ApJ

Analyses of high-redshift ultraluminous infrared (IR) galaxies traditionally use the observed optical to submillimeter spectral energy distribution (SED) and estimates of the dynamical mass as observational constraints to derive the star formation rate (SFR), the stellar mass, and age of these objects. An important observational constraint neglected in the analysis is the mass of dust giving rise to the IR emission. In this paper we add this constraint to the analysis of AzTEC-3. Adopting an upper limit to the mass of stars and a bolometric luminosity for this object, we construct stellar and chemical evolutionary scenarios, constrained to produce the inferred dust mass and observed luminosity before the associated stellar mass exceeds the observational limit. We find that the model with a Top Heavy IMF provided the most plausible scenario consistent with the observational constraints. In this scenario the dust formed over a period of ~200 Myr, with a SFR of ~500 Msun/yr. These values for the age and SFR in AzTEC-3 are significantly higher and lower, respectively, from those derived without the dust mass constraint. However, this scenario is not unique, and others cannot be completely ruled out because of the prevailing uncertainties in the age of the galaxy, its bolometric luminosity, and its stellar and dust masses. A robust result of our models is that all scenarios require most of the radiating dust mass to have been accreted in molecular clouds. Our new procedure highlights the importance of a multiwavelength approach, and of the use of dust evolution models in constraining the age and the star formation activity and history in galaxies., Comment: Accepted for publication in the ApJ. 12 pages with 11 embedded figures

We present results from our spectroscopic study, using the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, designed to identify massive young stellar objects (YSOs) in the Galactic Center (GC). Our sample of 107 YSO candidates was selected based on IRAC colors from the high spatial resolution, high sensitivity Spitzer/IRAC images in the Central Molecular Zone (CMZ), which spans the central ~300 pc region of the Milky Way Galaxy. We obtained IRS spectra over 5um to 35um using both high- and low-resolution IRS modules. We spectroscopically identify massive YSOs by the presence of a 15.4um shoulder on the absorption profile of 15um CO2 ice, suggestive of CO2 ice mixed with CH3OH ice on grains. This 15.4um shoulder is clearly observed in 16 sources and possibly observed in an additional 19 sources. We show that 9 massive YSOs also reveal molecular gas-phase absorption from CO2, C2H2, and/or HCN, which traces warm and dense gas in YSOs. Our results provide the first spectroscopic census of the massive YSO population in the GC. We fit YSO models to the observed spectral energy distributions and find YSO masses of 8 - 23 Msun, which generally agree with the masses derived from observed radio continuum emission. We find that about 50% of photometrically identified YSOs are confirmed with our spectroscopic study. This implies a preliminary star formation rate of ~0.07 Msun/yr at the GC., Comment: Accepted for publication in ApJ

We have used the Spitzer satellite to monitor the mid-IR evolution of SN 1987A over a 5 year period spanning the epochs between days 6000 and 8000 since the explosion. The supernova (SN) has evolved into a supernova remnant (SNR) and its radiative output is dominated by the interaction of the SN blast wave with the pre-existing equatorial ring (ER). The mid-IR spectrum is dominated by emission from ~180 K silicate dust, collisionally-heated by the hot X-ray emitting gas with a temperature and density of ~5x10^6 K and 3x10^4 cm-3, respectively. The mass of the radiating dust is ~1.2x10^(-6) Msun on day 7554, and scales linearly with IR flux. The infrared to soft-X-ray flux ratio is roughly constant with a value of 2.5. Gas-grain collisions therefore dominate the cooling of the shocked gas. The constancy of of this ratio suggests that very little grain processing or gas cooling have occurred throughout this epoch. The shape of the dust spectrum remained unchanged during the observations while the total flux increased with a time dependence of t^(0.87), t being the time since the first encounter between the blast wave and the ER. These observations are consistent with the transitioning of the blast wave from free expansion to a Sedov phase as it propagates into the main body of the ER., Comment: Accepted for publication in the ApJ, 11 pages, 11 figures

We report the detection of several molecular gas-phase and ice absorption features in three photometrically-selected young stellar object (YSO) candidates in the central 280 pc of the Milky Way. Our spectra, obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, reveal gas-phase absorption from CO2 (15.0um), C2H2 (13.7um) and HCN (14.0um). We attribute this absorption to warm, dense gas in massive YSOs. We also detect strong and broad 15um CO2 ice absorption features, with a remarkable double-peaked structure. The prominent long-wavelength peak is due to CH3OH-rich ice grains, and is similar to those found in other known massive YSOs. Our IRS observations demonstrate the youth of these objects, and provide the first spectroscopic identification of massive YSOs in the Galactic Center., Comment: Accepted for publication in ApJ Letters

(Condensed form) - The serendipitous discovery of infrared echoes around the supernova remnant of Cas A by the Spitzer satellite has provided astronomers with a unique opportunity to study the properties of the echoing material and the history and nature of the outburst that generated these echoes. All the echoes located within a distance of ~15 arcmin from the SN are caused by the delayed arrival of thermal emission from dust located at a distance of 160 lyr (corresponding to half the adopted age of the remnant) directly behind the origin of the explosion. The spectra of the echoes are distinct from that of the general diffuse interstellar medium (ISM) revealing hot silicate grains that are either stochastically heated to temperatures in excess of ~150 K, or radiating at an equilibrium temperature of this value. We show that the optical light curve from the supernova, is not capable of producing such spectra, and could therefore not have given rise to the echoes. Instead, we find that the echoes were generated by an intense and short burst of EUV-UV radiation with a luminosity of ~ 1.5E11 Lsun. The average H-column density of the IR emitting region in the echoing clouds is about 5E17 cm-2. Taking a burst time of ~1 d gives a cloud density of ~200 cm-3, typical of dense IR cirrus., Comment: Submitted to The Astrophysical Journal - 33 pages including 13 figures - Accepted for publication in The ApJ - revised text and added references and figure

We have obtained Spitzer/IRAC observations of the central 2.0 x 1.4 degrees (~280 x 200 pc) of the Galaxy at 3.6-8.0 microns. A point source catalog of 1,065,565 objects is presented. The catalog includes magnitudes for the point sources at 3.6, 4.5, 5.8, and 8.0 microns, as well as JHK photometry from 2MASS. The point source catalog is confusion limited with average limits of 12.4, 12.1, 11.7, and 11.2 magnitudes for [3.6], [4.5], [5.8], and [8.0], respectively. We find that the confusion limits are spatially variable because of stellar surface density, background surface brightness level, and extinction variations across the survey region. The overall distribution of point source density with Galactic latitude and longitude is essentially constant, but structure does appear when sources of different magnitude ranges are selected. Bright stars show a steep decreasing gradient with Galactic latitude, and a slow decreasing gradient with Galactic longitude, with a peak at the position of the Galactic center. From IRAC color-magnitude and color-color diagrams, we conclude that most of the point sources in our catalog have IRAC magnitudes and colors characteristic of red giant and AGB stars., Comment: 44 pages, 13 figures, ApJS in press

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, 2007