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TOPIC: Milky Way
Blobrana


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Title: The Edge of the Milky Way Stellar Disk Revealed Using Clump Giant Stars as Distance Indicators
Authors: D. Minniti, R. K. Saito, J. Alonso-García, P. W. Lucas, M. Hempel

We use the clump giants of the disk as standard candles calibrated from Hipparcos parallaxes in order to map their distribution with two new near-IR surveys of the Galactic plane: UKIDSS-GPS and VVV. We explore different selection cuts of clump giants. We conclude that there is an edge of the stellar disk of the Milky Way at R=13.9±0.5kpc along various lines of sight across the galaxy. The effect of the warp is considered, taking fields at different longitudes and above and below the plane. We demonstrate that the edge of the stellar disk of the Milky Way can now be mapped in the near infrared in order to test different models, and to establish our own place within the galaxy.

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Blobrana


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Title: A Molecular Spiral Arm in the Far Outer Galaxy
Authors: T. M. Dame, P. Thaddeus

We have identified a spiral arm lying beyond the Outer Arm in the first Galactic quadrant ~15 kpc from the Galactic center. After tracing the arm in existing 21 cm surveys, we searched for molecular gas using the CfA 1.2 meter telescope and detected CO at 10 of 220 positions. The detections are distributed along the arm from l = 13 deg, v = -21 km/s to l = 55 deg, v = -84 km/s and coincide with most of the main H I concentrations. One of the detections was fully mapped to reveal a large molecular cloud with a radius of 47 pc and a molecular mass of ~50,000 Mo. At a mean distance of 21 kpc, the molecular gas in this arm is the most distant yet detected in the Milky Way. The new arm appears to be the continuation of the Scutum-Centaurus Arm in the outer Galaxy, as a symmetric counterpart of the nearby Perseus Arm.

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Blobrana


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Stars Gather in 'Downtown' Milky Way

The region around the center of our Milky Way galaxy glows colourfully in this new version of an image taken by NASA's Spitzer Space Telescope.
The data were previously released as part of a long, 120-degree view of the plane our galaxy. Now, data from the very center of that picture are being presented at a different contrast to better highlight this jam-packed region. In visible-light pictures, it is all but impossible to see the heart of our galaxy, but infrared light penetrates the shroud of dust giving us this unprecedented view.
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Blobrana


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Title: Constraining the Milky Way Dark Matter Density Profile with Gamma-Rays with Fermi-LAT
Authors: Nicolas Bernal (Bonn U.), Sergio Palomares-Ruiz (Lisbon, CFTP-IST)

We study the abilities of the Fermi-LAT instrument on board of the Fermi mission to simultaneously constrain the Milky Way dark matter density profile and some dark matter particle properties, as annihilation cross section, mass and branching ratio into dominant annihilation channels. A single dark matter density profile is commonly assumed to determine the capabilities of gamma-ray experiments to extract dark matter properties or to set limits on them. However, our knowledge of the Milky Way halo is far from perfect, and thus in general, the obtained results are too optimistic. Here, we study the effect these astrophysical uncertainties would have on the determination of dark matter particle properties and conversely, we show how gamma-ray searches could also be used to learn about the structure of the Milky Way halo, as a complementary tool to other type of observational data that study the gravitational effect caused by the presence of dark matter. In addition, we also show how these results would improve if external information on the annihilation cross section and on the local dark matter density were included and compare our results with the predictions from numerical simulations.

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Blobrana


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High-velocity clouds
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Title: The collisions of high-velocity clouds with the galactic halo
Authors: Petr Jelinek, Gerhard Hensler

Spiral galaxies are surrounded by a widely distributed hot coronal gas and seem to be fed by infalling clouds of neutral hydrogen gas with low metallicity and high velocities. We numerically study plasma waves produced by the collisions of these high-velocity clouds (HVCs) with the hot halo gas and with the gaseous disk. In particular, we tackle two problems numerically: 1) collisions of HVCs with the galactic halo gas and 2) the dispersion relations to obtain the phase and group velocities of plasma waves from the equations of plasma motion as well as further important physical characteristics such as magnetic tension force, gas pressure, etc. The obtained results allow us to understand the nature of MHD waves produced during the collisions in galactic media and lead to the suggestion that these waves can heat the ambient halo gas. These calculations are aiming at leading to a better understanding of dynamics and interaction of HVCs with the galactic halo and of the importance of MHD waves as a heating process of the halo gas.

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Blobrana


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Maser to predict Milky Way's fate

Will the Milky Way slam into its giant neighbour, Andromeda, in a few billion years? A laser-like spot of light in the galaxy hints at an answer.
The speed at which Andromeda is moving towards the Milky Way can be determined from the Doppler shift of the light it emits. But the galaxy is too spread out for its subtle sideways motion in the sky to be detected. If it moves fast enough in this direction it may miss the Milky WayMovie Camera altogether.
Now Loránt Sjouwerman of the National Radio Astronomy Observatory in Socorro, New Mexico, and colleagues have glimpsed a bright, laser-like spot of microwave radiation, called a maser, in Andromeda that could help determine its sideways motion.
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Blobrana


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High-Velocity Clouds
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Title: The 21cm "Outer Arm" and the Outer-Galaxy High-Velocity Clouds: Connected by Kinematics, Metallicity, and Distance
Authors: Todd M. Tripp, Limin Song (UMass)

We compare and discuss the metallicity, kinematics, and distance of the gaseous "Outer Arm" (OA) and the high-velocity clouds (HVCs) in the outer Galaxy. Using high-resolution ultraviolet spectra obtained with the HST Space Telescope Imaging Spectrograph (STIS) and FUSE, we detect the OA in a variety of absorption lines toward two QSOs, H1821+643 and HS0624+6907. We show that the OA is not detected in absorption in STIS spectra of several stars in the OA direction, consistent with the OA distance constraint of Lehner & Howk, which brackets the Galactocentric radius to 9-18 kpc. We also show that HVC Complex G, which is near the OA at a similar velocity, is detected in absorption toward the two stars; this HVC is in the solar vicinity at R(G)=8.3-10.2 kpc. HVC Complex C is known to be at a similar distance. Comparison of the low- and high-ion absorption profiles clearly shows that the OA is a multiphase cloud. Toward H1821+643, the low-ionisation metals lines are composed of multiple narrow components, indicating the presence of several cold clouds and rapid cooling and fragmentation. High-ion profiles also contain narrow components, but the high ions and low ions are not cospatial. Nevertheless, some of the highly ionised gas is also surprisingly cold. Accounting for ionisation corrections, the OA metallicity is Z=0.2-0.5 Z(Solar), but nitrogen is underabundant and some species are depleted by dust. The OA and nearby HVCs are not consistent with Galactic rotation, and we suggest that these HVCs could be detritus from a merging satellite galaxy.

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Blobrana


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Ca ne tourne pas rond dans la Voie lactée !

Plutôt que de tourner en cercles autour du centre de la Voie lactée, l'ensemble des étoiles de notre Galaxie adopte des trajectoires différentes, s'éloignant du centre galactique. C'est ce que viennent de montrer Arnaud Siebert et Benoit Famaey, astronomes à l'Observatoire astronomique de Strasbourg (CNRS/Université de Strasbourg) et leurs collègues étrangers. Pourquoi ce comportement étrange ? Ce serait la barre centrale et les bras spiraux de notre Galaxie qui auraient perturbé l'ensemble des étoiles et les auraient fait sortir de leurs trajectoires circulaires normales pour leur faire prendre ces chemins de traverse.
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Blobrana


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Nasa discovers galaxy 'bubbles'

Nasa's Fermi Gamma-Ray Space Telescope has discovered a previously unseen structure in the Milky Way.
Astronomer David Whitehouse examines the importance of the huge "bubbles" discovered within our galaxy.
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Blobrana


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Data from the Fermi Large Area Telescope (LAT) unveil the new feature after several processing steps, illustrated here. First, the data are smoothed to eliminate features smaller than 2 degrees across, then the contrast is increased (stretched). Even without additional processing, the edge of the southern bubble can be seen. Next, astronomers mask out bright point sources, such as pulsars and distant galaxies. Then, using models developed from Fermi LAT observations, astronomers remove the diffuse gamma-ray emission from the image. This reveals the entire new structure, which is further brightened by another contrast stretch.
Credit: NASA/DOE/Fermi LAT/D. Finkbeiner et al.

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