Giant molecular clouds in the outer arm of the Galaxy comparable in size and mass to the largest clouds in the inner Galaxy between R about 3 kpc and the solar circle have been detected in a new CO ...survey along the Galactic plane from l = 65 deg to 71 deg centered about b = + 1 deg. These objects at R about 12 kpc are underluminous in CO; the N(H2)/W(CO) ratio determined from either virial masses or the CO luminosity-line width relation is 4 + or - 2 times that in the inner Galaxy. When extrapolated to the entire Galaxy beyond R = 11 kpc, the present survey and related data yield a total molecular mass in the range (1-7) x 10 to the 8th solar masses. The outer arm complexes surveyed contain the two most luminous H II regions known beyond R about 10 kpc; one is the distant component of W58, and the other is a previously unidentified distant component of S98. 20 refs.
In ways similar to experiments in nuclear and particle physics, high-energy astrophysics usesgamma rays and energetic charged particles toprobe processes that involve large energy transfers.Since its ...launch in 2008, the international Fermi Gamma-Ray Space Telescope has been exploringnatural particle accelerators and the interactionsof high-energy particles in the universe. Withsources ranging from thunderstorms on Earth to galaxies and exploding stars in distant parts of the cosmos, the telescopes subjects of study are almostas diverse as were those of the scientist whose name it bears.
We discuss the prospects for indirect detection of dark matter (DM) with the Cherenkov Telescope Array (CTA), a future ground-based gamma-ray observatory that will be sensitive to gamma rays in the ...energy range from a few tens of GeV to 100 TeV. We consider the detectability of DM annihilation in different astrophysical targets with a focus on the Galactic Center (GC) region. With a deep observation of the GC, CTA will be sensitive to DM particles with mass greater than 100 GeV and an annihilation cross section close to the thermal relic value.
We present a catalog of gamma-ray sources at energies above 10 GeV based on data from the Large Area Telescope (LAT) accumulated during the first 3 years of the Fermi Gamma-ray Space Telescope ...mission. This catalog complements the Second Fermi-LAT Catalog, which was based on 2 years of data extending down to 100 MeV and so included many sources with softer spectra below 10 GeV. The First Fermi-LAT Catalog of >10 GeV sources (1FHL) has 514 sources, and includes their locations, spectra, a measure of their variability, and associations with cataloged sources at other wavelengths. We found that 449 (87%) could be associated with known sources, of which 393 (76% of the 1FHL sources) are active galactic nuclei. We also highlight the subset of the 1FHL sources that are the best candidates for detection at energies above 50 GeV with ground-based gamma-ray observatories.
(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast ...sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. LSST will be a wide-field ground-based system sited at Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg\(^2\) field of view, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5\(\sigma\) point-source depth in a single visit in \(r\) will be \(\sim 24.5\) (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg\(^2\) with \(\delta<+34.5^\circ\), and will be imaged multiple times in six bands, \(ugrizy\), covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg\(^2\) region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to \(r\sim27.5\). The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.
The nature of dark matter is a longstanding enigma of physics; it may consist of particles beyond the Standard Model that are still elusive to experiments. Among indirect search techniques, which ...look for stable products from the annihilation or decay of dark matter particles, or from axions coupling to high-energy photons, observations of the \(\gamma\)-ray sky have come to prominence over the last few years, because of the excellent sensitivity of the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope mission. The LAT energy range from 20 MeV to above 300 GeV is particularly well suited for searching for products of the interactions of dark matter particles. In this report we describe methods used to search for evidence of dark matter with the LAT, and review the status of searches performed with up to six years of LAT data. We also discuss the factors that determine the sensitivities of these searches, including the magnitudes of the signals and the relevant backgrounds, considering both statistical and systematic uncertainties. We project the expected sensitivities of each search method for 10 and 15 years of LAT data taking. In particular, we find that the sensitivity of searches targeting dwarf galaxies, which provide the best limits currently, will improve faster than the square root of observing time. Current LAT limits for dwarf galaxies using six years of data reach the thermal relic level for masses up to 120 GeV for the \(b\bar{b}\) annihilation channel for reasonable dark matter density profiles. With projected discoveries of additional dwarfs, these limits could extend to about 250 GeV. With as much as 15 years of LAT data these searches would be sensitive to dark matter annihilations at the thermal relic cross section for masses to greater than 400 GeV (200 GeV) in the \(b\bar{b}\) (\(\tau^+ \tau^-\)) annihilation channels.
The diffuse high-energy gamma-ray emission of the Milky Way arises from interactions of cosmic-rays (CRs) with interstellar gas and radiation field in the Galaxy. The neutral hydrogen (H I) gas ...component is by far the most massive and broadly distributed component of the interstellar medium. Using the 21-cm emission line from the hyperfine structure transition of atomic hydrogen it is possible to determine the column density of H I if the spin temperature (Ts) of the emitting gas is known. Studies of diffuse gamma-ray emission have generally relied on the assumption of a fixed, constant spin temperature for all H I in the Milky Way. Unfortunately, observations of H I in absorption against bright background sources has shown it to vary greatly with location in the Milky Way. We will discuss methods for better handling of spin temperatures for Galactic diffuse emission modeling using the Fermi-LAT data and direct observation of the spin temperature using H I absorption.
We discuss uncertainties and possible sources of errors associated with the determination of the diffuse Galactic
γ-ray emission using the EGRET data. Most of the issues will be relevant also in the ...GLAST era. The focus here is on issues that impact evaluation of dark matter annihilation signals against the diffuse
γ-ray emission of the Milky Way.
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