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TOPIC: Milky Way
Blobrana


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RE: Milky Way
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Title: The long bar as seen by the VVV survey: I. Colour-magnitude diagrams
Authors: C. González-Fernández (1), M. López-Corredoira (2 and 3), E. B. Amôres (4 and 5), D. Minniti (6 and 7), P. Lucas (8), I. Toledo (9) ((1) Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, (2) Instituto de Astrofísica de Canarias, (3) Departamento de Astrofísica, Universidad de La Laguna, (4) FCUL, Lisboa, Portugal, (5) Laboratório Nacional de Astrofísica MCTI, Brazil, (6) Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, (7) Vatican Observatory, (8) Centre for Astrophysics Research, University of Hertfordshire)

The VISTA Variable Survey (VVV) is able to map the Galaxy at l<0 with an unpaired depth (at least 3 mag deeper than 2MASS), opening new possibilities for studying the inner structure of the Milky Way. In this paper we concentrate on the exploitation of these data to better understand the spatial disposition and distribution of the structures present in the inner Milky Way, particularly the Long Bar and its interaction with the inner disc.
The observations show the presence of a clear overdensity of stars with associated recent stellar formation that we interpret as the traces of the Long Bar, and we derive an angle for it of 41±5 with the Sun-Galactic centre line, touching the disc near l=27 and l=-12. The colour-magnitude diagrams presented here also show a lack of disc stars in several lines of sight, a fact that we associate with the truncation of the disc by the potential of this bar for Galactocentric radius less than 5kpc.

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Blobrana


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Title: The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
Authors: Jo Bovy (IAS), Carlos Allende Prieto, Timothy C. Beers, Dmitry Bizyaev, Luiz N. da Costa, Katia Cunha, Garrett L. Ebelke, Daniel J. Eisenstein, Peter M. Frinchaboy, Ana Elia García Pérez, Léo Girardi, Fred R. Hearty, David W. Hogg, Jon Holtzman, Marcio A. G. Maia, Steven R. Majewski, Elena Malanushenko, Viktor Malanushenko, Szabolcs Mészáros, David L. Nidever, Robert W. O'Connell, Christine O'Donnell, Audrey Oravetz, Kaike Pan, Helio J. Rocha-Pinto, Ricardo P. Schiavon, Donald P. Schneider, Mathias Schultheis, Michael Skrutskie, Verne V. Smith, David H. Weinberg, John C. Wilson, Gail Zasowski

We measure the Milky Way's rotation curve over the Galactocentric range 4 kpc <~ R <~ 14 kpc from the first year of data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We model the line-of-sight velocities of 3,365 stars in fourteen fields with b = 0 deg between 30 deg < l < 210 deg out to distances of 10 kpc using an axisymmetric kinematical model that includes a correction for the asymmetric drift of the warm tracer population (\sigma_R ~ 35 km/s). We determine the local value of the circular velocity to be V_c(R_0) = 218 ± 6 km/s and find that the rotation curve is approximately flat with a local derivative between -3.0 km/s/kpc and 0.4 km/s/kpc. We also measure the Sun's position and velocity in the Galactocentric rest frame, finding the distance to the Galactic center to be 8 kpc < R_0 < 9 kpc, radial velocity V_{R,sun} = -10 ± 1 km/s, and rotational velocity V_{\phi,sun} = 242^{+10}_{-3} km/s, in good agreement with local measurements of the Sun's radial velocity and with the observed proper motion of Sgr A*. We investigate various systematic uncertainties and find that these are limited to offsets at the percent level, ~2 km/s in V_c. Marginalising over all the systematics that we consider, we find that V_c(R_0) < 235 km/s at >99% confidence. We find an offset between the Sun's rotational velocity and the local circular velocity of 26 ± 3 km/s, which is larger than the locally-measured solar motion of 12 km/s. This larger offset reconciles our value for V_c with recent claims that V_c >~ 240 km/s. Combining our results with other data, we find that the Milky Way's dark-halo mass within the virial radius is ~8x10^{11} solar masses.

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Blobrana


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Milky Way Bar
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Title: A New Model for the Milky Way Bar
Authors: Yougang Wang, Hongsheng Zhao, Shude Mao, R. M. Rich

We use Schwarzschild's orbit-superposition technique to construct self-consistent models of the Galactic bar. Using \chi^2 minimisation, we find that the best-fit Galactic bar model has a pattern speed \Omega_{p}=60 km s^{-1} kpc^{-1}, disk mass M_{d}=1.0 x 10^{11}solar masses and bar angle \theta_{bar}=20° for an adopted bar mass M_{bar}=2 x 10^{10}solar masses. The model can reproduce not only the three-dimensional and projected density distributions but also velocity and velocity dispersion data from the BRAVA survey. We also predict the proper motions in the range l=[-12°,12°], b=[-10°,10°], which appear to be higher than observations in the longitudinal direction. The model is stable within a timescale of 0.5 Gyr, but appears to deviate from steady-state on longer timescales. Our model can be further tested by future observations such as those from GAIA.

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Blobrana


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RE: Milky Way
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This image is directed roughly towards the centre of our galaxy, and shows cold dust laced between the stars. The colder material looks redder in this image, which is created by combining Planck data with shorter wavelength data from NASA's Infrared Astronomical Satellite (IRAS) satellite.

planck-tendrils-of-cold-dust-500.jpg

The plane of our galaxy is seen running across the bottom, with the galactic centre in the lower-right. The "forked" feature on the right is a cloud of gas and dust around the star rho Ophiuchi, and is a region where stars are currently forming. 
Planck measures the cold material between the stars. Reddish tones in this image correspond to temperatures as cold as 12 degrees above absolute zero, and whitish tones to significantly warmer ones (on order a few tens of degrees) in regions where massive stars are currently forming. The dust structures are local, within 500 light-years of the sun.
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Title: Reddening and Extinction Toward the Galactic Bulge from OGLE-III: The Inner Milky Way's Rv ~ 2.5 Extinction Curve
Authors: David M. Nataf, Andrew Gould, Pascal Fouqué, Oscar A. Gonzalez, Jennifer A. Johnson, Jan Skowron, Andrzej Udalski, Michal K. Szymanski, Marcin Kubiak, Grzegorz Pietrzynski, Igor Soszynski, Krzysztof Ulaczyk, Lukasz Wyrzykowski, Radoslaw Poleski

We combine VI photometry from OGLE-III with VVV and 2MASS measurements of E(J-K_{s}) to resolve the longstanding problem of the non-standard optical extinction toward the Galactic bulge. We show that the extinction is well-fit by the relation A_{I} = 0.7465*E(V-I) + 1.3700*E(J-K_{s}), or, equivalently, A_{I} = 1.217*E(V-I)(1+1.126*(E(J-K_{s})/E(V-I)-0.3433)). The optical and near-IR reddening law toward the inner Galaxy approximately follows an R_{V} ~ 2.5 extinction curve with a dispersion {\sigma}_{R_{V}} ~ 0.2, consistent with extragalactic investigations of the hosts of type Ia SNe. Differential reddening is shown to be significant on scales as small as as our mean field size of 6', with the 1{\sigma} dispersion in reddening averaging 9% of total reddening for our fields. The intrinsic luminosity parameters of the Galactic bulge red clump (RC) are derived to be (M_{I,RC}, \sigma_{I,RC,0}, (V-I)_{RC,0}, \sigma_{(V-I)_{RC}}, (J-K_{s})_{RC,0}) = (-0.12, 0.09, 1.06, 0.121, 0.66). Our measurements of the RC brightness, brightness dispersion and number counts allow us to estimate several Galactic bulge structural parameters. We estimate a distance to the Galactic center of 8.20 kpc, resolving previous discrepancies in distance determinations to the bulge based on I-band observations. We measure an upper bound on the tilt {\alpha} ~ 40°. between the bar's major axis and the Sun-Galactic center line of sight, though our brightness peaks are consistent with predictions of an N-body model oriented at {\alpha} ~25°. The number of RC stars suggests a total stellar mass for the Galactic bulge of 2.0*10^{10} solar masses, if one assumes a Salpeter IMF.

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Title: Galactic Chemical Evolution and the Oxygen Isotopic Composition of the Solar System
Authors: Larry R. Nittler, Eric Gaidos

We review current observational and theoretical constraints on the Galactic chemical evolution (GCE) of oxygen isotopes in order to explore whether GCE plays a role in explaining the lower 17O/18O ratio of the Sun, relative to the present-day interstellar medium, or the existence of distinct 16O-rich and 16O-poor reservoirs in the Solar System. Although the production of both 17O and 18O are related to the metallicity of progenitor stars, 17O is most likely produced in stars that evolve on longer timescales than those that produce 18O. Therefore the 17O/18O ratio need not have remained constant over time, contrary to preconceptions and the simplest models of GCE. An apparent linear, slope-one correlation between delta17O and delta18O in the ISM need not necessarily reflect an O isotopic gradient, and any slope-one galactocentric gradient need not correspond to evolution in time. Instead, increasing 17O/18O is consistent both with observational data from molecular clouds and with modeling of the compositions of presolar grains. Models in which the rate of star formation has decelerated over the past few Gyr or in which an enhanced period of star formation occurred shortly before solar birth ("starburst") can explain the solar-ISM O-isotopic difference without requiring a local input of supernova ejecta into the protosolar cloud. "Cosmic chemical memory" models in which interstellar dust is on average older than interstellar gas predict that primordial Solar System solids should be 16O-rich, relative to the Sun, in conflict with observations. However, scenarios in which the 16O-rich contribution of very massive stars could lead to 16O-poor solids and a 16O-rich bulk Sun, if the Solar System formed shortly after a starburst, independent of the popular scenario of photochemical self-shielding of CO.

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Milky Way struck 100 million years ago, still rings like a bell

An international team of astronomers have discovered evidence that our Milky Way had an encounter with a small galaxy or massive dark matter structure perhaps as recently as 100 million years ago, and as a result of that encounter it is still ringing like a bell.
The discovery is based on observations of 300,000 nearby Milky Way stars by the Sloan Digital Sky Survey (SDSS). Stars in the disk of the Milky Way move up and down at a speed of about 20-30 kilometres per second while orbiting the center of the galaxy at a brisk 220 kilometres per second. The positions and motions of these nearby stars weren't quite as regular as previously thought, according to the study results.
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Hubble times Milky Way and Andromeda galaxy pile-up

Astronomers have used the Hubble Space Telescope to work out when precisely our Milky Way Galaxy will crash into its neighbour, Andromeda.
The pair are being pulled together by their mutual gravity and the scientists expect them to begin to merge in about four billion years' time.
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 Ghostly Gamma-ray Beams Blast from Milky Way's Center

As galaxies go, our Milky Way is pretty quiet. Active galaxies have cores that glow brightly, powered by supermassive black holes swallowing material, and often spit twin jets in opposite directions. In contrast, the Milky Way's center shows little activity. But it wasn't always so peaceful. New evidence of ghostly gamma-ray beams suggests that the Milky Way's central black hole was much more active in the past.
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 The definitive guide to the milky way galaxy



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