SimProp: a Simulation Code for Ultra High Energy Cosmic Ray Propagation

A new Monte Carlo simulation code for the propagation of Ultra High Energy Cosmic Rays is presented. The results of this simulation scheme are tested by comparison with results of another Monte Carlo computation as well as with the results obtained by directly solving the kinetic equation for the propagation of Ultra High Energy Cosmic Rays. A short comparison with the latest flux published by the Pierre Auger collaboration is also presented.Comment: 19 pages, 12 eps figures, version accepted for publication in JCA

NICMOS Snapshot Survey of Damped Lyman Alpha Quasars

We image 19 quasars with 22 damped Lyman alpha (DLA) systems using the F160W filter and the Near-Infrared Camera and Multiobject Spectrograph aboard the Hubble Space Telescope, in both direct and coronagraphic modes. We reach 5 sigma detection limits of ~H=22 in the majority of our images. We compare our observations to the observed Lyman-break population of high-redshift galaxies, as well as Bruzual & Charlot evolutionary models of present-day galaxies redshifted to the distances of the absorption systems. We predict H magnitudes for our DLAs, assuming they are producing stars like an L* Lyman-break galaxy (LBG) at their redshift. Comparing these predictions to our sensitivity, we find that we should be able to detect a galaxy around 0.5-1.0 L* (LBG) for most of our observations. We find only one new possible candidate, that near LBQS0010-0012. This scarcity of candidates leads us to the conclusion that most DLA systems are not drawn from a normal LBG luminosity function nor a local galaxy luminosity function placed at these high redshifts.Comment: 31 pages, 8 figures, Accepted for Feb. 10 issue of Ap

Intensive HST, RXTE and ASCA Monitoring of NGC 3516: Evidence Against Thermal Reprocessing

During 1998 April 13-16, NGC 3516 was monitored almost continuously with HST for 10.3 hr in the UV and 2.8 d in the optical, and simultaneous RXTE and ASCA monitoring covered the same period. The X-rays were strongly variable with the soft (0.5-2 keV) showing stronger variations (~65% peak-to-peak) than the hard (2-10 keV; ~50% peak-to-peak). The optical continuum showed much smaller but highly significant variations: a slow ~2.5% rise followed by a faster ~3.5% decline. The short UV observation did not show significant variability. The soft and hard X-ray light curves were strongly correlated with no significant lag. Likewise, the optical continuum bands (3590 and 5510 A) were also strongly correlated with no measurable lag above limits of <0.15 d. However no significant correlation or simple relationship could be found for the optical and X-ray light curves. These results appear difficult to reconcile with previous reports of correlations between X-ray and optical variations and of measurable lags within the optical band for some other Seyfert 1s. These results also present serious problems for "reprocessing" models in which the X-ray source heats a stratified accretion disk which then reemits in the optical/ultraviolet: the synchronous variations within the optical would suggest that the emitting region is <0.3 lt-d across, while the lack of correlation between X-ray and optical variations would indicate, in the context of this model, that any reprocessing region must be >1 lt-d in size. It may be possible to resolve this conflict by invoking anisotropic emission or special geometry, but the most natural explanation appears to be that the bulk of the optical luminosity is generated by some other mechanism than reprocessing.Comment: 23 pages including 6 figures, accepted for publication in Ap

A low escape fraction of ionizing photons of L>L* Lyman break galaxies at z=3.3

We present an upper limit for the relative escape fraction (f_{esc}^{rel}) of ionizing radiation at z~3.3 using a sample of 11 Lyman Break Galaxies (LBGs) with deep imaging in the U band obtained with the Large Binocular Camera, mounted on the prime focus of the Large Binocular Telescope. We selected 11 LBGs with secure redshift in the range 3.27<z<3.35, from 3 independent fields. We stacked the images of our sources in the R and U band, which correspond to an effective rest-frame wavelength of 1500\AA and 900\AA respectively, obtaining a limit in the U band image of >=30.7(AB)mag at 1 sigma. We derive a 1 sigma upper limit of f_{esc}^{rel}~5%, which is one of the lowest values found in the literature so far at z~3.3. Assuming that the upper limit for the escape fraction that we derived from our sample holds for all galaxies at this redshift, the hydrogen ionization rate that we obtain (Gamma_{-12}<0.3 s^{-1}) is not enough to keep the IGM ionized and a substantial contribution to the UV background by faint AGNs is required. Since our sample is clearly still limited in size, larger z~3 LBG samples, at similar or even greater depths are necessary to confirm these results on a more firm statistical basis.Comment: 15 pages, 2 figures, 1 table, accepted for publication in Ap

Dust enshrouded star-forming activity in Arp 299

We present mid-infrared spectro-imaging (5 - 16 microns) observations of the infrared luminous interacting system Arp 299 (=Mrk171 =IC694+NGC3690) obtained with the ISOCAM instrument aboard ISO. Our observations show that nearly 40% of the total emission at 7 and 15 microns is diffuse, originating from the interacting disks of the galaxies. Moreover, they indicate the presence of large amounts of hot dust in the main infrared sources of the system and large extinctions toward the nuclei. While the observed spectra have an overall similar shape, mainly composed of Unidentified Infrared Bands (UIB) in the short wavelength domain, a strong continuum at ~ 13 microns and a deep silicate absorption band at 10 microns, their differences reveal the varying physical conditions of each component. For each source, the spectral energy distribution (SED) can be reproduced by a linear combination of a UIB "canonical" spectral template and a hot dust continuum due to a 230-300 K black body, after independently applying an extinction correction to both of them. We find that the UIB extinction does not vary much throughout the system (A_V ~ 5 mag) suggesting that most UIBs originate from less enshrouded regions. IC694 appears to dominate the infrared emission of the system and our observations support the interpretation of a deeply embedded nuclear starburst located behind an absorption of about 40 mag. The central region of NGC3690 displays a hard radiation field characterized by a [NeIII]/[NeII] ratio > 1.8. It also hosts a strong continuum from 5 to 16 microns which can be explained as thermal emission from a deeply embedded (A_V ~ 60 mag) compact source, consistent with the mid-infrared signature of an active galactic nucleus (AGN), and in agreement with recent X-ray findings.Comment: to be published in Astronomy and Astrophysics - 12 page

ISO Far-IR Spectroscopy of IR-Bright Galaxies and ULIRGs

Based on far-infrared spectroscopy of a small sample of nearby infrared-bright and ultraluminous infrared galaxies (ULIRGs) with the ISO Long Wavelength Spectrometer, we find a dramatic progression in ionic/atomic fine-structure emission line and molecular/atomic absorption line characteristics in these galaxies extending from strong [O III]52,88 and [N III]57 micron line emission to detection of only faint [C II]158 micron line emission from gas in photodissociation regions in the ULIRGs. The molecular absorption spectra show varying excitation as well, extending from galaxies in which the molecular population mainly occupies the ground state to galaxies in which there is significant population in higher levels. In the case of the prototypical ULIRG, the merger galaxy Arp 220, the spectrum is dominated by absorption lines of OH, H2O, CH, and [O I]. Low [O III]88 micron line flux relative to the integrated far-infrared flux correlates with low excitation and does not appear to be due to far-infrared extinction or to density effects. A progression toward soft radiation fields or very dusty HII regions may explain these effects

Heavy nuclei at the end of the cosmic ray spectrum?

We provide an account of the possible acceleration of iron nuclei up to energies $\sim300$ EeV in the nearby, metally-rich starburst galaxy NGC 253. It is suggested that particles can escape from the nuclear region with energies of $\sim10^{15}$ eV and then could be reaccelerated at the terminal shock of the galactic superwind generated by the starburst, avoiding in this way the photodisintegration expected if the nuclei were accelerated in the central region of high photon density. We have also made estimates of the expected arrival spectrum, which displays a strong dependency with the energy cutoff at the source.Comment: Revised version, to appear in Physical Review

Infrared spectroscopy of NGC 1068: Probing the obscured ionizing AGN continuum

The ISO-SWS 2.5-45 um infrared spectroscopic observations of the nucleus of the Seyfert 2 galaxy NGC 1068 (see companion paper) are combined with a compilation of UV to IR narrow emission line data to determine the spectral energy distribution (SED) of the obscured extreme-UV continuum that photoionizes the narrow line emitting gas in the active galactic nucleus. We search a large grid of gas cloud models and SEDs for the combination that best reproduces the observed line fluxes and NLR geometry. Our best fit model reproduces the observed line fluxes to better than a factor of 2 on average and is in general agreement with the observed NLR geometry. It has two gas components that are consistent with a clumpy distribution of dense outflowing gas in the center and a more extended distribution of less dense and more clumpy gas farther out that has no net outflow. The best fit SED has a deep trough at ~4 Ryd, which is consistent with an intrinsic Big Blue Bump that is partially absorbed by ~6x10^19 cm^-2 of neutral hydrogen interior to the NLR.Comment: 15 pp, 4 figures, ApJ accepte

Observational evidence for AGN fueling. I. The merging of NGC6104 with a companion

We investigate in details the kinematics and morphology of the Seyfert galaxy NGC6104 in order to identify the mechanism of gas transportation to the active galactic nucleus (AGN). Our observational data were obtained at the 6-m Special Astrophysical Observatory telescope with the MPFS integral-field spectrograph and the SCORPIO universal device in three modes: direct imaging, a scanning Fabry-Perot interferometer, and long-slit spectroscopy. Images from the HST archive were invoked to study the structure of the circumnuclear region. An analysis of deep images has revealed that NGC6104 is in the phase of active merging with a companion galaxy. We have been able to study the detailed picture of ionized gas motions up to galactocentric distances of 14 kpc and to construct the stellar velocity field for the inner region. The radial gas motions toward the AGN along the central bar play a significant role at galactocentric distances of 1-5 kpc. In addition, we have detected an outflow of ionized gas from the nucleus that presumably resulted from the intrusion of a radio jet into the ambient interstellar medium. Using diagnostic diagrams, we estimate the contributions from the AGN and star formation to the galactic gas ionization. We estimate the bar pattern speed by the Tremaine-Weinberg method and show that the inner ring observed in the galactic images has a resonant nature. Two possible ring formation scenarios (before and during the interaction with a companion) are discussed.Comment: 12 pages, 2 tables, 6 figures, accepted for publication in Astronomy Letter

SPT 0538-50: Physical conditions in the ISM of a strongly lensed dusty star-forming galaxy at z=2.8

We present observations of SPT-S J053816-5030.8, a gravitationally-lensed dusty star forming galaxy (DSFG) at z = 2.7817, first discovered at millimeter wavelengths by the South Pole Telescope. SPT 0538-50 is typical of the brightest sources found by wide-field millimeter-wavelength surveys, being lensed by an intervening galaxy at moderate redshift (in this instance, at z = 0.441). We present a wide array of multi-wavelength spectroscopic and photometric data on SPT 0538-50, including data from ALMA, Herschel PACS and SPIRE, Hubble, Spitzer, VLT, ATCA, APEX, and the SMA. We use high resolution imaging from HST to de-blend SPT 0538-50, separating DSFG emission from that of the foreground lens. Combined with a source model derived from ALMA imaging (which suggests a magnification factor of 21 +/- 4), we derive the intrinsic properties of SPT 0538-50, including the stellar mass, far-IR luminosity, star formation rate, molecular gas mass, and - using molecular line fluxes - the excitation conditions within the ISM. The derived physical properties argue that we are witnessing compact, merger-driven star formation in SPT 0538-50, similar to local starburst galaxies, and unlike that seen in some other DSFGs at this epoch.Comment: 16 pages, 11 figures. Accepted for publication in Ap