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There are two ways to start a story about the axion. One is to explain that this hypothetical particle could be the key to a major problem in the Standard [...]

Gravitational interactions between the Large Magellanic Cloud (LMC) and the stellar and dark matter halo of the Milky Way are expected to give rise to disequilibrium phenomena in the outer Milky Way.sup.1-7. A local wake is predicted to trail the orbit of the LMC, and a large-scale overdensity is predicted to exist across a large area of the northern Galactic hemisphere. Here we report the detection of both the local wake and northern overdensity (hereafter the 'collective response') in a map of the Galaxy based on 1,301 stars at Galactocentric distances between 60 and 100 kiloparsecs. The location of the wake is in good agreement with an N-body simulation that includes the dynamical effect of the LMC on the Milky Way halo. The density contrast of the wake and collective response are stronger in the data than in the simulation. The detection of a strong local wake is independent evidence that the Magellanic clouds are on their first orbit around the Milky Way. The wake traces the path of the LMC, which will provide insight into the orbit of the LMC, which in turn is a sensitive probe of the mass of the LMC and the Milky Way. These data demonstrate that the outer halo is not in dynamical equilibrium, as is often assumed. The morphology and strength of the wake could be used to test the nature of dark matter and gravity. The detection of structure in the distribution of giant stars in the outer Galactic halo shows the substantial global impact of the Magellanic clouds on our Galaxy., Author(s): Charlie Conroy [sup.1] , Rohan P. Naidu [sup.1] , Nicolás Garavito-Camargo [sup.2] , Gurtina Besla [sup.2] , Dennis Zaritsky [sup.2] , Ana Bonaca [sup.1] , Benjamin D. Johnson [sup.1] [...]

The specifics of how galaxies form from, and are fuelled by, gas from the intergalactic medium remain uncertain. Hydrodynamic simulations suggest that 'cold accretion flows'--relatively cool (temperatures of the order of 104 kelvin), unshocked gas streaming along filaments of the cosmic web into dark-matter halos (1-3)--are important. These flows are thought to deposit gas and angular momentum into the circumgalactic medium, creating disk- or ring-like structures that eventually coalesce into galaxies that form at filamentary intersections (4, 5). Recently, a large and luminous filament, consistent with such a cold accretion flow, was discovered near the quasi-stellar object QSO UM287 at redshift 2.279 using narrow-band imaging (6). Unfortunately, imaging is not sufficient to constrain the physical characteristics of the filament, to determine its kinematics, to explain how it is linked to nearby sources, or to account for its unusual brightness, more than a factor of ten above what is expected for a filament. Here we report a two-dimensional spectroscopic investigation of the emitting structure. We find that the brightest emission region is an extended rotating hydrogen disk with a velocity profile that is characteristic of gas in a darkmatter halo with a mass of [10.sup.13] solar masses. This giant protogalactic disk appears to be connected to a quiescent filament that may extend beyond the virial radius of the halo. The geometry is strongly suggestive of a cold accretion flow., We observed the UM287 filament with the Palomar Cosmic Web Imager (PCWI) (7), an integral field spectrograph that is designed for low surface brightness measurements using a 40' X 60' [...]

For almost two decades the properties of 'dwarf galaxies have challenged the cold dark matter (CDM) model of galaxy formation (1). Most observed dwarf galaxies consist of a rotating stellar disk (2) embedded in a massive dark-matter halo with a near-constant-density core (3). Models based on the dominance of CDM, however, invariably form galaxies with dense spheroidal stellar bulges and steep central dark-matter profiles (4-6), because low-angular-momentum baryons and dark matter sink to the centres of galaxies through accretion and repeated mergers (7). Processes that decrease the central density of CDM halos$ have been identified, but have not yet reconciled theory with observations of present-day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different dark-matter particle candidate (9). Here we report hydrodynamical simulations (in a frameworks (10) assuming the presence of CDM and a cosmological constant) in which the inhomogeneous interstellar medium is resolved. Strong outflows from supernovae remove low-angular-momentum gas, which inhibits the formation of bulges and decreases the dark-matter density to less than half of what it would otherwise be within the central kiloparsec. The analogues of dwarf galaxies--bulgeless and with shallow central dark-matter profiles--arise naturally in these simulations., In an expanding ACDM Universe (the favoured theory of cosmic structure formation), galaxy disks form as gas cools and collapses inside spinning halos of collisionless dark matter, reaching centrifugal equilibrium [...]

The unambiguous detection of dark matter annihilation in our Galaxy would unravel one of the most outstanding puzzles in particle physics and cosmology. Recent observations have motivated models in which the annihilation rate is boosted by the Sommerfeld effect, a nonperturbative enhancement arising from a long-range attractive force. We applied the Sommerfeld correction to Via Lactea II, a high-resolution N-body simulation of a Milky Way--sized galaxy, to investigate the phase-space structure of the galactic halo. We found that the annihilation luminosity from kinematically cold substructure could be enhanced by orders of magnitude relative to previous calculations, leading to the prediction of gamma-ray fluxes from as many as several hundred dark clumps that should be detectable by the Fermi satellite.

The significant developments that took place in the study of cold dark clouds are presented. Findings reveal that by clarifying the combined structure of physical properties and complex chemical, the condition for star formation can be understood.

The Hubble Space Telescope shows that galactic 'lenses' of the invisible material are more common than computer models of galaxy clumping predict. The Hubble Space Telescope shows that galactic 'lenses' of the invisible material are more common than computer models of galaxy clumping predict., Author Affiliations: Among the galactic clusters examined by researchers seeking to understand the distribution of dark matter is MACSJ1206 (spread across centre of image), which distorts other galaxies' light into [...]

Byline: Toshifumi Yanagisawa (1), Yasushi Muraki (2), Yutaka Matsubara (2), Fumio Abe (2), Kimiaki Masuda (2), Sachiyo Noda (2), Takahiro Sumi (2), Yuji Kato (2), Mitsuaki Fujimoto (2), Shuji Sato (2), Ian Bond (3), Nicholas Rattenbury (3), Philip Yock (3), Pam Kilmartin (4), John Hearnshaw (4), Micheal Reid (5), Denis Sullivan (5), Brian Carter (6), Richard Dodd (6), Garry Nankivell (6), Noiman Rumsey (6), Morihiro Honda (7), Maki Sekiguchi (7), Masanori Yoshizawa (8), Takashi Nakamura (9), Humitaka Sato (9), Seiji Kabe (10), Makoto Kobayashi (10), Yoshiyuki Watase (10), Jun Jugaku (11), Toshiharu Saito (12), Barbel Koribalsky (13) Keywords: dark matter; MACHO; wide-field camera Abstract: We have constructed a large, mosaic CCD camera called MOA-cam2 which has 4096 x 6144-pixelsto search for gravitational microlensing events. MOA-cam2 has three4096 x 2048-pixel SITe CCD chips, which have a very high quantum efficiency (nearly 80% in the wave region 500 to 800 nm),and three buttable sides. We have placed the threechips side by side with 100 um dead space. MOA-cam2 has been installed on the 61 cm Boller and Chivens telescope of the MOA collaboration at the Mt. John University Observatory (MJUO) in NewZealand since July 1998. The field coverage is 0.92deg x 1.38deg per exposure. The technical details of MOA-cam2 and the first images obtained with the Boller and Chivens telescope are presented. MOA-cam2 introduces a second phase of research on gravitational microlensing by the MOA collaboration. Author Affiliation: (1) Nagoya University, Japan (2) Nagoya University, Japan (3) University of Auckland, New Zealand (4) University of Canterbury, New Zealand (5) Victoria University of Wellington, New Zealand (6) Carter National Observatory, New Zealand (7) University of Tokyo, Japan (8) National Astronomical Observatory, Japan (9) Kyoto University, Japan (10) High Energy Accelerator Research Organization (KEK), Japan (11) Tokai University, Japan (12) Tokyo Metropolitan College of Aeronautics, Japan (13) Australia Telescope National Facility, Australia Article History: Registration Date: 07/10/2004

Observations of brown dwarfs, which are in the interval between the least massive star and the most massive planet, are discussed. They may be almost as common as stars, but seem not to have a dynamically interesting amount of mass. A rough idea of how many occur as solitary objects and how many are in binary systems has now been developed. A first glimpse of atmospheres with temperatures between those of stars and those of planets, in which dust formation is a crucial process has been obtained and led to the proposal of the first new spectral classes in several decades and the need for new diagnostics for classification and setting the temperature scale. All current masses depend on models.