Extragalactic Sources for Ultra High Energy Cosmic Ray Nuclei

In this article we examine the hypothesis that the highest energy cosmic rays are complex nuclei from extragalactic sources. Under reasonable physical assumptions, we show that the nearby metally rich starburst galaxies (M82 and NGC 253) can produce all the events observed above the ankle. This requires diffusion of particles below $10^{20}$ eV in extragalactic magnetic fields $B \approx 15$ nG. Above $10^{19}$ eV, the model predicts the presence of significant fluxes of medium mass and heavy nuclei with small rate of change of composition. Notwithstanding, the most salient feature of the starburst-hypothesis is a slight anisotropy induced by iron debris just before the spectrum-cutoff.Comment: To appear in Phys. Rev. D, reference adde

The Formation and Evolution of Massive Stellar Clusters in IC 4662

We present a multiwavelength study of the formation of massive stellar clusters, their emergence from cocoons of gas and dust, and their feedback on surrounding matter. Using data that span from radio to optical wavelengths, including Spitzer and Hubble ACS observations, we examine the population of young star clusters in the central starburst region of the irregular Wolf-Rayet galaxy IC 4662. We model the radio-to-IR spectral energy distributions of embedded clusters to determine the properties of their HII regions and dust cocoons (sizes, masses, densities, temperatures), and use near-IR and optical data with mid-IR spectroscopy to constrain the properties of the embedded clusters themselves (mass, age, extinction, excitation, abundance). The two massive star-formation regions in IC 4662 are excited by stellar populations with ages of ~ 4 million years and masses of ~ 3 x 10^5 M_sun (assuming a Kroupa IMF). They have high excitation and sub-solar abundances, and they may actually be comprised of several massive clusters rather than the single monolithic massive compact objects known as Super Star Clusters (SSCs). Mid-IR spectra reveal that these clusters have very high extinctions, A_V ~ 20-25 mag, and that the dust in IC 4662 is well-mixed with the emitting gas, not in a foreground screen.Comment: 7 pages, 11 figures, to appear in proceedings of the conference "Young Massive Star Clusters: Initial Conditions and Environments ", held in Granada, Spain, September 200

Spitzer observations of the SCUBA/VLA sources in the Lockman Hole: Star formation history of infrared-luminous galaxies

We present Spitzer Space Telescope imaging observations at 3.6, 4.5, 5.8, 8.0, and 24 mum of the SCUBA submillimeter sources and muJy VLA radio sources in a 5' x 5' area in the Lockman Hole East region. Out of the similar to 40 SCUBA/VLA sources in the field, Spitzer counterparts were detected for nearly all except for the few low-weight SCUBA detections. We show that the majority (80% - 90%) of the detected sources are cold (i.e., starburst-like) infrared-luminous galaxies (L-IR > 10(11) L-.) at redshift 0.5 < z < 3.5, whose star-formation rate density (SFRD) is comparable to that of the optically selected star-forming galaxies

Submillimeter detections of Spitzer Space Telescope galaxy populations

We present submillimeter statistical detections of galaxies discovered in the 5' x 5' Spitzer Early Release Observations (to similar to4 - 15 muJy 5 sigma at 3.6 - 8 mum, 170 muJy at 24 mum) through a stacking analysis of our reanalyzed SCUBA 8 mJy survey maps and a Spitzer identification of a new submillimeter point source in the 8 mJy survey region. For sources detected at 5.8 or 8 mum ( 154 and 111 sources, respectively), we detect positive skews in the submillimeter flux distributions at 99.2% - 99.8% confidence using Kolmogorov-Smirnov tests, at both 850 and 450 mum. We also marginally detect the Spitzer 24 mum galaxies at 850 mum at 97% confidence and place limits on the mean submillimeter fluxes of the 3.6 and 4.5 mum sources. Integrating the submillimeter fluxes of the Spitzer populations, we find the 5.8 mum galaxies contribute 0.12 +/- 0.05 nW m(-2) sr(-1) to the 850 mum background and 2.4 +/- 0.7 nWm(-2) sr(-1) to the 450 mum background; similar contributions are made by the 8 mum-selected sample. We infer that the populations dominating the 5.8 and 8 mum extragalactic background light also contribute around a quarter of the 850 mum background and the majority of the 450 mum background

Spitzer Observations of MAMBO Galaxies: Weeding Out Active Nuclei in Starbursting Protoellipticals

We present 3.6 - 24 mum Spitzer observations of an unbiased sample of nine luminous, dusty galaxies selected at 1200 mum by MAMBO on the IRAM 30 m telescope, a population akin to the well-known submillimeter or SCUBA galaxies ( hereafter SMGs). Owing to the coarse resolution of submillimeter/millimeter cameras, SMGs have traditionally been difficult to identify at other wavelengths. We compare our multiwavelength catalogs to show that the overlap between 24 and 1200 mum must be close to complete at these flux levels. We find that all (4/4) of the most secure greater than or equal to4 sigma SMGs have greater than or equal to 4 sigma counterparts at 1.4 GHz, while the fraction drops to 7/9 using all greater than or equal to 3 sigma SMGs. We show that combining mid-infrared (MIR) and marginal ( greater than or equal to 3 sigma) radio detections provides plausible identifications in the remaining cases, enabling us to identify the complete sample. Accretion onto an obscured central engine is betrayed by the shape of the MIR continuum emission for several sources, confirming Spitzer's potential to weed out active galaxies. We demonstrate the power of an S-24 mum/S-8 mum versus S-8 mum/S-4.5 mum color-color plot as a diagnostic for this purpose. However, we conclude that the majority ( similar to 75%) of SMGs have rest-frame mid/far-IR spectral energy distributions commensurate with obscured starbursts. Sensitive 24 mum observations are clearly a useful route to identify and characterize reliable counterparts to high-redshift far-IR-bright galaxies, complementing what is possible via deep radio imaging

Dust and Starlight Maps for Galaxies in the KINGFISH Sample

Dust and starlight have been modeled for the KINGFISH project galaxies. For each pixel in each galaxy, we estimate: (1) dust surface density; (2) q_PAH, the dust mass fraction in PAHs; (3) distribution of starlight intensities heating the dust; (4) luminosity emitted by the dust; and (5) dust luminosity from regions with high starlight intensity. The modeling is as described in the paper "Modeling Dust and Starlight in Galaxies Observed by Spitzer and Herschel: The KINGFISH Sample", by G. Aniano, B.T. Draine, L.K. Hunt, K. Sandstrom, D. Calzetti, R.C. Kennicutt, D.A, Dale, and 26 other authors, accepted for publication in The Astrophysical Journal.Please consult the file readme.tx