Using the SHARC-II camera at the Caltech Submillimeter Observatory to obtain 350 micron images of sources detected with the MIPS instrument on Spitzer, we have discovered a remarkable object at z=1.325+/-0.002 with an apparent Far-Infrared luminosity of 3.2(+/-0.7) x 10^13 Lsun. Unlike other z>1 sources of comparable luminosity selected from mid-IR surveys, MIPS J142824.0+352619 lacks any trace of AGN activity, and is likely a luminous analog of galaxies selected locally by IRAS, or at high redshift in the submillimeter. This source appears to be lensed by a foreground elliptical galaxy at z=1.034, although the amplification is likely modest (~10). We argue that the contribution to the observed optical/Near-IR emission from the foreground galaxy is small, and hence are able to present the rest-frame UV through radio Spectral Energy Distribution of this galaxy. Due to its unusually high luminosity, MIPS J142824.0+352619 presents a unique chance to study a high redshift dusty starburst galaxy in great detail.

C. Borys A. W. Blain A. Dey E. Le Floc'h B. T. Jannuzi V. Barnard C. Bian M. Brodwin K. Men'endez-Delmestre D. Thompson K. Brand M. J. I. Brown C. D. Dowell P. Eisenhardt D. Farrah D. T. Frayer J. Higdon S. Higdon T. Phillips B. T. Soifer D. Stern D. Weedman

We present low-resolution (64 < R < 124) mid-infrared (8--38 micron) Spitzer/IRS spectra of two z~1.3 ultraluminous infrared galaxies (LFIR~10^13) discovered in a Spitzer/MIPS survey of the Bootes field of the NOAO Deep Wide-Field Survey (NDWFS). MIPS J142824.0+352619 is a bright 160 micron source with a large infrared-to-optical flux density ratio and a possible lensing amplification of <~10. The 6.2, 7.7, 11.3, and 12.8 micron PAH emission bands in its IRS spectrum indicate a redshift of z~1.3. The large equivalent width of the 6.2 micron PAH feature indicates that at least 50% of the mid-infrared energy is generated in a starburst, an interpretation that is supported by a large [NeII]/[NeIII] ratio and a low upper limit on the X-ray luminosity. SST24 J142827.19+354127.71 has the brightest 24 micron flux (10.55 mJy) among optically faint (R > 20) galaxies in the NDWFS. Its mid-infrared spectrum lacks emission features, but the broad 9.7 micron silicate absorption band places this source at z~1.3. Given this redshift, SST24 J142827.19+354127.71 has among the largest rest-frame 5 micron luminosities known. The similarity of its SED to those of known AGN-dominated ULIRGs and its lack of either PAH features or large amounts of cool dust indicate that the powerful mid-infrared emission is dominated by an active nucleus rather than a starburst. Our results illustrate the power of the IRS in identifying massive galaxies in the ``redshift desert'' and in discerning their power sources. Because they are bright, MIPS J142824.0+352619 (pending future observations to constrain its lensing amplification) and SST24 J142827.19+354127.71 are useful z>1 templates of a high luminosity starburst and AGN, respectively.

V. Desai L. Armus B. T. Soifer D. W. Weedman S. Higdon C. Bian C. Borys H. W. W. Spoon V. Charmandaris K. Brand M. J. I. Brown A. Dey J. Higdon J. Houck B. T. Jannuzi E. Le Floc'h M. L. N. Ashby H. A. Smith

Spectra have been obtained with the low-resolution modules of the Infrared Spectrograph (IRS) on the Spitzer Space Telescope (Spitzer) for 58 sources having f$_{\nu}$(24 micron) > 0.75 mJy. Sources were chosen from a survey of 8.2 deg$^{2}$ within the NOAO Deep Wide-Field Survey region in Bootes (NDWFS) using the Multiband Imaging Photometer (MIPS) on the Spitzer Space Telescope. Most sources are optically very faint (I > 24mag). Redshifts have previously been determined for 34 sources, based primarily on the presence of a deep 9.7 micron silicate absorption feature, with a median z of 2.2. Spectra are presented for the remaining 24 sources for which we were previously unable to determine a confident redshift because the IRS spectra show no strong features. Optical photometry from the NDWFS and infrared photometry with MIPS and the Infrared Array Camera on the Spitzer Space Telescope (IRAC) are given, with K photometry from the Keck I telescope for some objects. The sources without strong spectral features have overall spectral energy distributions (SEDs) and distributions among optical and infrared fluxes which are similar to those for the sources with strong absorption features. Nine of the 24 sources are found to have feasible redshift determinations based on fits of a weak silicate absorption feature. Results confirm that the "1 mJy" population of 24 micron Spitzer sources which are optically faint is dominated by dusty sources with spectroscopic indicators of an obscured AGN rather than a starburst. There remain 14 of the 58 sources observed in Bootes for which no redshift could be estimated, and 5 of these sources are invisible at all optical wavelengths.

D. W. Weedman B. T. Soifer Lei Hao J. L. Higdon S. J. U. Higdon J. R. Houck E. LeFloc'h M. J. I. Brown A. Dey B. T. Jannuzi M. Rieke V. Desai C. Bian D. Thompson L. Armus H. Teplitz P. Eisenhardt S. P. Willner

We present observations of the starburst galaxy NGC 7714 with the Infrared Spectrograph IRS on board the Spitzer Space Telescope. The spectra yield a wealth of ionic and molecular features that allow a detailed characterization of its properties. NGC 7714 has an HII region-like spectrum with strong PAH emission features. We find no evidence for an obscured active galactic nucleus, and with [NeIII]/[NeII]~0.73, NGC7714 lies near the upper end of normal-metallicity starburst galaxies. With very little slicate absorption and a temperature of the hottest dust component of 340K, NGC 7714 is the perfect template for a young, unobscured starburst

B. R. Brandl D. Devost S. J. U. Higdon V. Charmandaris D. Weedman H. W. W. Spoon T. L. Herter L. Hao J. Bernard-Salas J. R. Houck L. Armus B. T. Soifer C. J. Grillmair P. N. Appleton

We detect bright emission in the far infrared fine structure [O III] 88$\mu$m line from a strong lensing candidate galaxy, H-ATLAS J113526.3-014605, hereafter G12v2.43, at z=3.127, using the $\rm 2^{nd}$ generation Redshift (z) and Early Universe Spectrometer (ZEUS-2) at the Atacama Pathfinder Experiment Telescope (APEX). This is only the fifth detection of this far-IR line from a sub-millimeter galaxy at the epoch of galaxy assembly. The observed [O III] luminosity of $7.1\times10^{9}\,\rm(\frac{10}{\mu})\,\rm{L_{\odot}}\,$ likely arises from HII regions around massive stars, and the amount of Lyman continuum photons required to support the ionization indicate the presence of $(1.2-5.2)\times10^{6}\,\rm(\frac{10}{\mu})$ equivalent O5.5 or higher stars; where $\mu$ would be the lensing magnification factor. The observed line luminosity also requires a minimum mass of $\sim 2\times 10^{8}\,\rm(\frac{10}{\mu})\,\rm{M_{\odot}}\,$ in ionized gas, that is $0.33\%$ of the estimated total molecular gas mass of $6\times10^{10}\,\rm(\frac{10}{\mu})\,\rm{M_{\odot}}\,$. We compile multi-band photometry tracing rest-frame UV to millimeter continuum emission to further constrain the properties of this dusty high redshift star-forming galaxy. Via SED modeling we find G12v2.43 is forming stars at a rate of 916 $\rm(\frac{10}{\mu})\,\rm{M_{\odot}}\,\rm{yr^{-1}}$ and already has a stellar mass of $8\times 10^{10}\,\rm(\frac{10}{\mu})\,\rm{M_{\odot}}\,$. We also constrain the age of the current starburst to be $\leqslant$ 5 million years, making G12v2.43 a gas rich galaxy lying above the star-forming main sequence at z$\sim$3, undergoing a growth spurt and, could be on the main sequence within the derived gas depletion timescale of $\sim$66 million years.

Amit Vishwas Carl Ferkinhoff Thomas Nikola Stephen C. Parshley Justin P. Schoenwald Gordon J. Stacey Sarah J. U. Higdon James L. Higdon Axel Weiß Rolf Güsten Karl M. Menten

We consider positron propagation in the interstellar medium and show that the positrons from the beta-plus decay chains of the radioactive nuclei Ni-56, Ti-44, and Al-26, produced in Galactic supernovae, can fully account for all the features of the diffuse Galactic 511 keV annihilation radiation observed by INTEGRAL/SPI. We also predict additional measurable features that can further test the origin of positrons and provide new information on the nature of the interstellar medium.

J. C. Higdon R. E. Lingenfelter R. E. Rothschild

We review the evidence for cosmic ray acceleration in the superbubble/hot phase of the interstellar medium, and discuss the implications for the composition of cosmic rays and the structure and evolution of the interstellar medium. We show that the bulk of the galactic supernovae, their expanding remnants, together with their metal-rich grain and gas ejecta, and their cosmic ray accelerating shocks, are all confined within the interiors of superbubbles, generated by the multiple supernova explosions of massive stars formed in giant OB associations. This superbubble/hot phase of the ISM provides throughout the age of the Galaxy a cosmic ray source of essentially constant metallicity for acceleration by the shocks of many supernovae over time scales of a few Myr, consistent with both the Be/Fe evolution and ACE observations of Ni-59/Co-59. We also show that if the refractory cosmic ray metals come from the sputtering of fast refractory grains then the accompanying scattering of ambient gas by these fast grains can also account for the relative abundance of cosmic ray volatiles.

R. E. Lingenfelter J. C. Higdon R. Ramaty

Assuming Galactic positrons do not go far before annhilating, a difference between the observed 511 keV annihilation flux distribution and that of positron production, expected from beta-plus decay in Galactic iron nucleosynthesis, was evoked as evidence of a new source and a signal of dark matter. We show, however, that the dark mater sources can not account for the observed positronium fraction without extensive propagation. Yet with such propagation, standard nucleosynthetic sources can fully account for the spatial differences and the positronium fraction, leaving no signal for dark mater to explain.

R. E. Lingenfelter J. C. Higdon R. E. Rothschild

Core collapse supernovae of massive (> 8 Mo) stars are formed primarily in OB associations and help blow giant superbubbles, where their collective shocks accelerate most of the Galactic cosmic rays. The spatial distribution of these stars is thus important to our understanding of the propagation of the observed cosmic rays. In order to better model the Galactic cosmic-ray distribution and propagation, we construct s three-dimensional spatial model of the massive star distribution based primarily on the emission of the H II envelopes surrounding the giant superbubbles which are maintaned by the ionizing radiation of the embedded O stars. The Galactic longitudinal distribution of the 205 micron N II rsdistion emitted by these H II envelopes is used to infer the spatial distribution of the superbubbles. We find that the Galactic superbubble distribution is dominated by the contribution of massive star clusters residing in the spiral arms.

J. C. Higdon R. E. Lingenfelter

We have surveyed a field covering 9.0 degrees^2 within the NOAO Deep Wide-Field Survey region in Bootes with the Multiband Imaging Photometer on the Spitzer Space Telescope (SST) to a limiting 24 um flux density of 0.3 mJy. Thirty one sources from this survey with F(24um) > 0.75 mJy which are optically very faint (R > 24.5 mag) have been observed with the low-resolution modules of the Infrared Spectrograph on SST. Redshifts derived primarily from strong silicate absorption features are reported here for 17 of these sources; 10 of these are optically invisible (R > 26 mag), with no counterpart in B_W, R, or I. The observed redshifts for 16 sources are 1.7 < z < 2.8. These represent a newly discovered population of highly obscured sources at high redshift with extreme infrared to optical ratios. Using IRS spectra of local galaxies as templates, we find that a majority of the sources have mid-infrared spectral shapes most similar to ultraluminous infrared galaxies powered primarily by AGN. Assuming the same templates also apply at longer wavelengths, bolometric luminosities exceed 10^13 L(solar).

J. R. Houck B. T. Soifer D. Weedman S. J. U. Higdon J. L. Higdon T. Herter M. J. I. Brown A. Dey B. T. Jannuzi E. Le Floc'h M. Rieke L. Armus V. Charmandaris B. R. Brandl H. I. Tepliitz