Multi-wavelength constraints on cosmic-ray leptons in the Galaxy

Cosmic rays (CRs) interact with the gas, the radiation field and the magnetic field in the Milky Way, producing diffuse emission from radio to gamma rays. Observations of this diffuse emission and comparison with detailed predictions are powerful tools to unveil the CR properties and to study CR propagation. We present various GALPROP CR propagation scenarios based on current CR measurements. The predicted synchrotron emission is compared to radio surveys, and synchrotron temperature maps from WMAP and Planck, while the predicted interstellar gamma-ray emission is compared to Fermi-LAT observations. We show how multi-wavelength observations of the Galactic diffuse emission can be used to help constrain the CR lepton spectrum and propagation. Finally we discuss how radio and microwave data could be used in understanding the diffuse Galactic gamma-ray emission observed with Fermi-LAT, especially at low energies.Comment: 8 pages, 5 figures; in Proceedings of the 34th International Cosmic Ray Conference (ICRC 2015), The Hague (The Netherlands); Oral contributio

EGRET Observations of the Diffuse Gamma-Ray Emission in Orion: Analysis Through Cycle 6

We present a study of the high-energy diffuse emission observed toward Orion by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory. The total exposure by EGRET in this region has increased by more than a factor of two since a previous study. A simple model for the diffuse emission adequately fits the data; no significant point sources are detected in the region studied ($l = 195^\circ$ to $220^\circ$ and $b = -25^\circ to -10^\circ$) in either the composite dataset or in two separate groups of EGRET viewing periods considered. The gamma-ray emissivity in Orion is found to be $(1.65 \pm 0.11) \times 10^{-26} {s sr}^{-1}$ for E > 100 MeV, and the differential emissivity is well-described as a combination of contributions from cosmic-ray electrons and protons with approximately the local density. The molecular mass calibrating ratio is $N(H_2)/W_{CO} = (1.35 \pm 0.15) \times 10^{20} cm^{-2} (K km/s)^{-1}$.Comment: 16 pages, including 5 figures. 3 Tables as three separate files. Latex document, needs AASTEX style files. Accepted for publication in Ap

Diffuse Gamma Rays: Galactic and Extragalactic Diffuse Emission

"Diffuse" gamma rays consist of several components: truly diffuse emission from the interstellar medium, the extragalactic background, whose origin is not firmly established yet, and the contribution from unresolved and faint Galactic point sources. One approach to unravel these components is to study the diffuse emission from the interstellar medium, which traces the interactions of high energy particles with interstellar gas and radiation fields. Because of its origin such emission is potentially able to reveal much about the sources and propagation of cosmic rays. The extragalactic background, if reliably determined, can be used in cosmological and blazar studies. Studying the derived "average" spectrum of faint Galactic sources may be able to give a clue to the nature of the emitting objects.Comment: 32 pages, 28 figures, kapproc.cls. Chapter to the book "Cosmic Gamma-Ray Sources," to be published by Kluwer ASSL Series, Edited by K. S. Cheng and G. E. Romero. More details can be found at http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm

High-Latitude Molecular Clouds as gamma-ray Sources for GLAST

For about two decades, a population of relative small and nearby molecular clouds has been known to exist at high Galactic latitudes. Lying more than 10$^\circ$ from the Galactic plane, these clouds have typical distances of $\sim$150 pc, angular sizes of $\sim1^\circ$, and masses of order tens of solar masses. These objects are passive sources of high-energy $\gamma$-rays through cosmic ray-gas interactions. Using a new wide-angle CO survey of the northern sky, we show that typical high-latitude clouds are not bright enough in $\gamma$-rays to have been detected by EGRET, but that of order 100 of them will be detectable by the Large Area Telescope (LAT) on GLAST. Thus, we predict a new steady population of $\gamma$-ray sources at high Galactic latitudes, perhaps the most numerous after active galactic nuclei.Comment: Accepted for publication in the Astrophysical Journal Letter

Multifrequency study of the ring nebula SG13

We investigate the morphology and kinematics of the interstellar medium in the environs of the open cluster Mrk50, which includes the Wolf-Rayet star WR157 and a number of early B-type stars. The analysis was performed using radio continuum images at 408 and 1420 MHz, and HI 21cm line data taken from the Canadian Galactic Plane Survey, molecular observations of the 12CO (J=1-0) line at 115 GHz from the Five College Radio Astronomy Observatory and available mid and far IR observations obtained with the MSX and IRAS satellites, respectively. This study allowed identification of the radio continuum and molecular counterpart of the ring nebula SG13, while no neutral atomic structure was found to be associated. The nebula is also detected in images in the mid and far infrared, showing the existence of dust well mixed with the ionized gas. We estimate the main physical parameters of the material linked to the nebula. The interstellar gas distribution in the environs of Mrk50 is compatible with a stellar wind bubble created by the mass loss from WR157. The distribution of young stellar object (YSO) candidates in the region shows that stellar formation activity may be present in the molecular shell that encircles the ring nebula.Comment: Accepted for publication in MNRAS, 13 pages, 11 figure

The radio and IR counterparts of the ring nebula around HD211564

We report the detection of the radio and infrared counterparts of the ring nebula around the WN3(h) star HD211564 (WR152), located to the southwest of the HII region Sh2132. Using radio continuum data from the Canadian Galactic Plane Survey, we identified the radio counterparts of the two concentric rings, of about 9' and 16' in radius, related to the star. After applying a filling factor f = 0.05-0.12, electron densities and ionized masses are in the range 10-16 cm^-3 and 450-700 Mo, respectively. The analysis of the HI gas emission distribution allowed the identification of 5900 Mo of neutral atomic gas with velocities between -52 and -43 km/s probably linked to the nebula. The region of the nebula is almost free of molecular gas. Only four small clumps were detected, with a total molecular mass of 790 Mo. About 310 Mo are related to a small infrared shell-like source linked to the inner ring, which is also detected in the MSX band A. An IRAS YSO candidate is detected in coincidence with the shell-like IR source. We suggest that the optical nebula and its neutral counterparts originated from the stellar winds from the WR star and its massive progenitor, and are evolving in the envelope of a slowly expanding shell centered at (l,b) = (102 30, -0 50), of about 31 pc in radius. The bubble's energy conversion efficiency is in agreement with recent numerical analysis and with observational results.Comment: 11 pages, 7 figures, accepted in MNRA

Galactic interstellar 18O/17O ratios - a radial gradient?

(Abridged) Our aim is to determine 18O/17O abundance ratios across the entire Galaxy. These provide a measure of the amount of enrichment by high-mass versus intermediate-mass stars. Such ratios, derived from the C18O and C17O J=1-0 lines alone, may be affected by systematic errors. Therefore, the C18O and C17O (1-0), (2-1), and (3-2), as well as the 13CO (1-0) and (2-1) lines, were observed towards 18 prominent galactic targets (a total of 25 positions). The combined dataset was analysed with an LVG model, accounting for optical depth effects. The data cover galactocentric radii R between 0.1 and 16.9 kpc (solar circle at 8.5 kpc). Near the centre of the Galaxy, 18O/17O = 2.88 +/- 0.11. For the galactic disc out to an R of ca. 10 kpc, 18O/17O = 4.16 +/- 0.09. At ca. R = 16.5 kpc, 18O/17O = 5.03 +/- 0.46. Assuming that 18O is synthesised predominantly in high-mass stars (M > 8 Msun), while C17O is mainly a product of lower-mass stars, the ratio from the inner Galaxy indicates a dominance of CNO-hydrogen burning products that is also apparent in the C- and N-isotope ratios. The high 18O/17O value of the solar system (5.5) relative to that of the ambient ISM suggests contamination by nearby high-mass stars during its formation. High values in the metal-poor environment of the outer Galaxy are not matched by the low values observed towards the even more metal-poor LMC. Apparently, the outer Galaxy cannot be considered as an intermediate environment between the solar neighbourhood and the ISM of small metal-poor galaxies. The apparent 18O/17O gradient along the galactic disc and the discrepancy between outer disc and LMC isotope ratios may be explained by different ages of the respective stellar populations.Comment: Accepted by Astron. & Astroph.; 10 pages + 4 pages on-line material (figs