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Post Info TOPIC: Andromeda galaxy (M31)


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Title: Andromeda and its satellites - a kinematic perspective
Authors: Michelle L. M. Collins, R. Michael Rich, Scott C. Chapman

Using spectroscopic data taken with Keck II DEIMOS by the Z-PAndAS team in the Andromeda-Triangulum region, I present a comparison of the disc and satellite systems of Andromeda with those of our own Galaxy. I discuss the observed discrepancies between the masses and scale radii of Andromeda dwarf spheroidal galaxies of a given luminosity with those of the Milky Way. I also also present an analysis of the newly discovered M31 thick disc, which is measured to be hotter, more extended and thicker than that seen in the Milky Way.

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Hubble Zooms in on Double Nucleus in Andromeda Galaxy

A new Hubble Space Telescope image centers on the 100-million-solar-mass black hole at the hub of the neighbouring spiral galaxy M31, or the Andromeda galaxy, one of the few galaxies outside the Milky Way visible to the naked eye and the only other giant galaxy in the Local Group. This is the sharpest visible-light image ever made of the nucleus of an external galaxy.
The Hubble image is being presented today at the meeting of the American Astronomical Society in Austin, Texas.

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Rare Ultra-blue Stars Found in Neighbouring Galaxy's Hub

hs-2012-03-a-web.jpg

Peering deep inside the hub of the neighbouring Andromeda galaxy, NASA's Hubble Space Telescope has uncovered a large, rare population of hot, bright stars. While Hubble has spied these ultra-blue stars before in Andromeda, the new observation covers a much broader area, revealing that these stellar misfits are scattered throughout the galaxy's bustling center.
Astronomers used Hubble's Wide Field Camera 3 to find roughly 8,000 of the ultra-blue stars in a stellar census made in ultraviolet light, which traces the glow of the hottest stars. The study is part of the multi-year Panchromatic Hubble Andromeda Treasury survey to map stellar populations across the Andromeda galaxy. The team's results are being presented today at the American Astronomical Society meeting in Austin, Texas.

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In 1612 German astronomer Simon Marius measured the diameter of the Andromeda nebula and discerned it as having a dull, pale light which increased in brightness toward its center, like "a candle shining through horn".
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The first description of the Andromeda Galaxy based on telescopic observation was given by German astronomer Simon Marius in 1612. Charles Messier catalogued it as object M31 in 1764 and incorrectly credited Marius as the discoverer, unaware of Al Sufi's earlier work.
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Andromeda galaxy
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Title: Hide and seek between Andromeda's halo, disk, and giant stream
Authors: Gisella Clementini (1), Rodrigo Contreras Ramos (1 and 2), Luciana Federici (1), Giulia Macario (1 and 2), Giacomo Beccari (3), Vincenzo Testa (4), Michele Cignoni (2), Marcella Marconi (5), Vincenzo Ripepi (5), Monica Tosi (1), Michele Bellazzini (1), Flavio Fusi Pecci (1), Emiliano Diolaiti (1), Carla Cacciari (1), Bruno Marano (2), Emanuele Giallongo (4), Roberto Ragazzoni (6), Andrea Di Paola (4), Stefano Gallozzi (4), Riccardo Smareglia (7) ((1) INAF, Osservatorio Astronomico di Bologna, Bologna, Italy, (2) Dipartimento di Astronomia, Universita' di Bologna, Bologna, Italy, (3) European Southern Observatory, Garching bei Munchen, Germany, (4) INAF, Osservatorio Astronomico di Roma, Monteporzio, Italy, (5) INAF, Osservatorio Astronomico di Capodimonte, Napoli, Italy, (6) INAF, Osservatorio Astronomico di Padova, Padova, Italy, (7) INAF, Osservatorio Astronomico di Trieste, Trieste, Italy.)

Photometry in B, V (down to V ~ 26 mag) is presented for two 23' x 23' fields of the Andromeda galaxy (M31) that were observed with the blue channel camera of the Large Binocular Telescope during the Science Demonstration Time. Each field covers an area of about 5.1kpc x 5.1kpc at the distance of M31 ((m-M)o ~ 24.4 mag), sampling, respectively, a northeast region close to the M31 giant stream (field S2), and an eastern portion of the halo in the direction of the galaxy minor axis (field H1). The stream field spans a region that includes Andromeda's disk and the giant stream, and this is reflected in the complexity of the colour magnitude diagram of the field. One corner of the halo field also includes a portion of the giant stream. Even though these demonstration time data were obtained under non-optimal observing conditions the B photometry, acquired in time-series mode, allowed us to identify 274 variable stars (among which 96 are bona fide and 31 are candidate RR Lyrae stars, 71 are Cepheids, and 16 are binary systems) by applying the image subtraction technique to selected portions of the observed fields. Differential flux light curves were obtained for the vast majority of these variables. Our sample includes mainly pulsating stars which populate the instability strip from the Classical Cepheids down to the RR Lyrae stars, thus tracing the different stellar generations in these regions of M31 down to the horizontal branch of the oldest (t ~ 10 Gyr) component.

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andromea211011b.jpg
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Date: 21st October 2011



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m31b.jpg
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Find the Andromeda Galaxy

The most easily visible neighbouring galaxy is now well seen in the evening. The Great Andromeda Galaxy, also known as M31, is one of the closest galaxies to our own and is part of what is called the "Local Group," an assembly of galaxies in this neighbourhood of the Universe which travel together, bound by one another's gravity. On the next clear, dark night, have a look yourself. M31 appears as an elliptical, hazy smudge, quite dim but readily seen once you know what to expect and where to look.
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Title: PAndromeda - first results from the high-cadence monitoring of M31 with Pan-STARRS 1
Authors: C.-H. Lee, A. Riffeser, J. Koppenhoefer, S. Seitz, R. Bender, U. Hopp, C. Goessl, R. P. Saglia, J. Snigula, W. E. Sweeney, W. S. Burgett, K. C. Chambers, T. Grav, J. N. Heasley, K. W. Hodapp, R. Jedicke, N. Kaiser, R.-P. Kudritzki, G. A. Luppino, R. H. Lupton, E. A. Magnier, D. G. Monet, J. S. Morgan, P. M. Onaka, P. A. Price, C. W. Stubbs, J. L. Tonry, R. J. Wainscoat

The Pan-STARRS 1 (PS1) survey of M31 (PAndromeda) is designed to identify gravitational microlensing events, caused by bulge and disk stars (self-lensing) and by compact matter in the halos of M31 and the Milky Way (halo lensing, or lensing by MACHOs). With the 7 deg2 FOV of PS1, the entire disk of M31 can be imaged with one single pointing. Our aim is to monitor M31 with this wide FOV with daily sampling (20 mins/day). In the 2010 season we acquired in total 91 nights towards M31, with 90 nights in the rP1 and 66 nights in the iP1. The total integration time in rP1 and iP1 are 70740s and 36180s, respectively. As a preliminary analysis, we study a 40' x 40' sub-field in the central region of M31, a 20' x 20' sub-field in the disk of M31 and a 20' x 20' sub-field for the investigation of astrometric precision. We demonstrate that the PSF is good enough to detect microlensing events. We present light curves for 6 candidate microlensing events. This is a competitive rate compared to previous M31 microlensing surveys. We finally also present one example light curve for Cepheids, novae and eclipsing binaries in these sub-fields.

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Title: Possible detection of the M31 rotation in WMAP data
Authors: F. De Paolis, V.G. Gurzadyan, G. Ingrosso, Ph. Jetzer, A.A. Nucita, A. Qadir, D. Vetrugno, A.L. Kashin, H.G. Khachatryan, S. Mirzoyan

Data on the cosmic microwave background (CMB) radiation by the Wilkinson Microwave Anisotropy Probe (WMAP) had a profound impact on the understanding of a variety of physical processes in the early phases of the Universe and on the estimation of the cosmological parameters. Here, the 7-year WMAP data are used to trace the disk and the halo of the nearby giant spiral galaxy M31. We analysed the temperature excess in three WMAP bands (W, V, and Q) by dividing the region of the sky around M31 into several concentric circular areas. We studied the robustness of the detected temperature excess by considering 500 random control fields in the real WMAP maps and simulating 500 sky maps from the best-fitted cosmological parameters. By comparing the obtained temperature contrast profiles with the real ones towards the M31 galaxy, we find that the temperature asymmetry in the M31 disk is fairly robust, while the effect in the halo is weaker. An asymmetry in the mean microwave temperature in the M31 disk along the direction of the M31 rotation is observed with a temperature contrast up to about 130 microK/pixel. We also find a temperature asymmetry in the M31 halo, which is much weaker than for the disk, up to a galactocentric distance of about 10 degrees (120 kpc) with a peak temperature contrast of about 40 microK/pixel. Although the confidence level of the signal is not high, if estimated purely statistically, which could be expected due to the weakness of the effect, the geometrical structure of the temperature asymmetry points towards a definite effect modulated by the rotation of the M31 halo. This result might open a new way to probe these relatively less studied galactic objects using high-accuracy CMB measurements, such as those with the Planck satellite or planned balloon-based experiments, which could prove or disprove our conclusions.

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