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Title: Concluding Ms. Henrietta Leavitt's Work on Classical Cepheids in the Magellanic System and other updates of the OGLE Collection of Variable Stars
Author: I. Soszynski, A. Udalski, M. K. Szymanski, L. Wyrzykowski, K. Ulaczyk, R. Poleski, P. Pietrukowicz, S. Kozlowski, D. Skowron, J. Skowron, P. Mrz, M. Pawlak

More than a century ago, Ms. Henrietta Leavitt discovered the first Cepheids in the Magellanic Clouds together with the famous period-luminosity relationship revealed by these stars, which soon after revolutionized our view of the Universe. Over the years, the number of known Cepheids in these galaxies has steadily increased with the breakthrough in the last two decades thanks to the new generation of large-scale long-term sky variability surveys.
Here we present the final upgrade of the OGLE Collection of Cepheids in the Magellanic System which already contained the vast majority of known Cepheids. The updated collection now comprises 9649 classical and 262 anomalous Cepheids. Type-II Cepheids will be updated shortly. Thanks to high completeness of the OGLE survey the sample of classical Cepheids includes virtually all stars of this type in the Magellanic Clouds. Thus, the OGLE survey concludes the work started by Ms. Leavitt.
Additionally, the OGLE sample of RR Lyrae stars in the Magellanic System has been updated. It now counts 46 443 variables. A collection of seven anomalous Cepheids in the halo of our Galaxy detected in front of the Magellanic Clouds is also presented.
OGLE photometric data are available to the astronomical community from the OGLE Internet Archive. The time-series photometry of all pulsating stars in the OGLE Collection has been supplemented with new observations.

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Title: First Gaia Local Group Dynamics: Magellanic Clouds Proper Motion and Rotation
Author: Roeland P. van der Marel, Johannes Sahlmann

We use the Gaia data release 1 (DR1) to study the proper motion (PM) fields of the Large and Small Magellanic Clouds (LMC, SMC). This uses the Tycho-Gaia Astrometric Solution (TGAS) PMs for 29 Hipparcos stars in the LMC and 8 in the SMC. The LMC PM in the West and North directions is inferred to be (\mu_W,\mu_N)=(1.8740.039,0.2230.049) mas/yr, and the SMC PM (\mu_W,\mu_N) =0.8760.060,1.2270.042) mas/yr. These results have similar accuracy and agree to within the uncertainties with existing Hubble Space Telescope (HST) PM measurements. Since TGAS uses different methods with different systematics, this provides an external validation of both data sets and their underlying approaches. Residual DR1 systematics may affect the TGAS results, but the HST agreement implies this must be below the random errors. Also in agreement with prior HST studies, the TGAS LMC PM field clearly shows the clockwise rotation of the disk, even though it takes the LMC disk in excess of 108 years to complete one revolution. The implied rotation curve amplitude for young LMC stars is consistent with that inferred from line-of-sight (LOS) velocity measurements. Comparison of the PM and LOS rotation curves implies a kinematic LMC distance modulus m-M=18.530.42, consistent but not yet competitive with photometric methods. These first results from Gaia on the topic of Local Group (LG) dynamics provide an indication of how its future data releases will revolutionize this field.

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Title: The Magellanic Stream: Circumnavigating the Galaxy
Author: Elena D'Onghia (Wisconsin), Andrew J. Fox (STScI)

The Magellanic Clouds are surrounded by an extended network of gaseous structures. Chief among these is the Magellanic Stream, an interwoven tail of filaments trailing the Clouds in their orbit around the Milky Way. When considered in tandem with its Leading Arm, the Stream stretches over 200 degrees on the sky. Thought to represent the result of tidal interactions between the Clouds and ram-pressure forces exerted by the Galactic corona, its kinematic properties reflect the dynamical history of the closest pair of dwarf galaxies to the Milky Way. The Stream is a benchmark for hydrodynamical simulations of accreting gas and cloud/corona interactions. If the Stream survives these interactions and arrives safely in the Galactic disk, its cargo of over a billion solar masses of gas has the potential to maintain or elevate the Galactic star formation rate. In this article, we review the current state of knowledge of the Stream, including its chemical composition, physical conditions, origin, and fate. We also review the dynamics of the Magellanic System, including the proper motions and orbital history of the Large and Small Magellanic Clouds, the first-passage and second-passage scenarios, and the evidence for a Magellanic Group of galaxies.

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The Magellanic Stream
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Title: The Magellanic Stream: break up and accretion onto the hot Galactic corona
Author: Thor Tepper-Garcia, Joss Bland-Hawthorn, Ralph S. Sutherland

The Magellanic HI Stream (2x10^9 Msun [d/55 kpc]^2) encircling the Galaxy at a distance 'd' is arguably the most important tracer of what happens to gas accreting onto a disk galaxy. Recent observations reveal that the Stream's mass is in fact dominated (3:1) by its ionised component. Here we revisit the origin of the mysterious H-alpha (recombination) emission observed along much of its length that is overly bright (150-200 mR) for the known Galactic UV background (20-40 mR [d/55 kpc]^-2). In an earlier model, we proposed that a slow shock cascade was operating along the Stream due to its interaction with the extended Galactic hot corona. But in view of updated parameters for the corona and mounting evidence that most of the Stream must lie far beyond the Magellanic Clouds (d>55 kpc), we revisit the shock cascade model in detail. While slow shocks are important in sustaining the observed levels of ionisation, it now appears unlikely they can account for the bright H-alpha emission if the corona is smooth. The HI gas is broken down by the shock cascade but mostly mixes with the hot corona without significant recombination. We conclude that the corona can be substantially mass-loaded with recent gas debris but this material is very difficult to observe directly.

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Magellanic Bridge
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Title: Spitzer View of Massive Star Formation in the Tidally Stripped Magellanic Bridge
Author: C.-H. Rosie Chen, Remy Indebetouw, Erik Muller, Akiko Kawamura, Karl D. Gordon, Marta Sewilo, Barbara A. Whitney, Yasuo Fukui, Suzanne C. Madden, Marilyn R. Meade, Margaret Meixner, Joana M. Oliveira, Thomas P. Robitaille, Jonathan P. Seale, Bernie Shiao, Jacco Th. van Loon

The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper we present analysis of candidate massive young stellar objects (YSOs), i.e., {in situ, current} massive star formation (MSF) in the Bridge using Spitzer mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are ~10 solar masses, <45 solar masses found in the Large Magellanic Cloud (LMC). The intensity of MSF in the Bridge also appears decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given \hi\ column density, N(HI). We found that the LMC has ~3x higher probability than the Bridge for N(HI) >10x10^20 cm^-2, but the trend reverses at lower N(HI). Investigating whether this lower efficiency relative to HI is due to less efficient molecular cloud formation, or less efficient cloud collapse, or both, will require sensitive molecular gas observations.

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Magellanic Stream
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Hubble finds source of Magellanic Stream

Astronomers using the NASA/ESA Hubble Space Telescope have solved the 40-year-old mystery of the origin of the Magellanic Stream, a long ribbon of gas stretching nearly halfway around the Milky Way. New Hubble observations reveal that most of this stream was stripped from the Small Magellanic Cloud some two billion years ago, with a smaller portion originating more recently from its larger neighbour.
The Magellanic Clouds, two dwarf galaxies orbiting our galaxy, are at the head of a huge gaseous filament known as the Magellanic Stream. Since the Stream's discovery in the early 1970s, astronomers have wondered whether this gas comes from one or both of the satellite galaxies. Now, new Hubble observations show that most of the gas was stripped from the Small Magellanic Cloud about two billion years ago - but surprisingly, a second region of the stream was formed more recently from the Large Magellanic Cloud.

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A Swift Tour of the Nearest Galaxies in UV Light


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NASA's Swift Produces Best Ultraviolet Maps of the Nearest Galaxies

Astronomers at NASA and Pennsylvania State University have used NASA's Swift satellite to create the most detailed ultraviolet light surveys ever of the Large and Small Magellanic Clouds, the two closest major galaxies.
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Title: Dust and Stellar Emission of the Magellanic Clouds
Authors: Ramin A. Skibba, Charles W. Engelbracht, Gonzalo Aniano, Brian Babler, Jean-Philippe Bernard, Caroline Bot, Lynn Redding Carlson, Maud Galametz, Frederic Galliano, Karl Gordon, Sacha Hony, Frank Israel, Vianney Lebouteiller, Aigen Li, Suzanne Madden, Margaret Meixner, Karl Misselt, Edward Montiel, Koryo Okumura, Pasquale Panuzzo, Deborah Paradis, Julia Roman-Duval, Monica Rubio, Marc Sauvage, Jonathan Seale, Sundar Srinivasan, Jacco Th. van Loon

We study the emission by dust and stars in the Large and Small Magellanic Clouds, a pair of low-metallicity nearby galaxies, as traced by their spatially resolved spectral energy distributions (SEDs). This project combines Herschel Space Observatory PACS and SPIRE far-infrared photometry with other data at infrared and optical wavelengths. We build maps of dust and stellar luminosity and mass of both Magellanic Clouds, and analyse the spatial distribution of dust/stellar luminosity and mass ratios. These ratios vary considerably throughout the galaxies, generally between the range 0.01\leq L_{dust}/L_\ast\leq 0.6 and 10^{-4}\leq M_{dust}/M_\ast\leq 4 x 10^{-3}. We observe that the dust/stellar ratios depend on the interstellar medium (ISM) environment, such as the distance from currently or previously star-forming regions, and on the intensity of the interstellar radiation field (ISRF). In addition, we construct star formation rate (SFR) maps, and find that the SFR is correlated with the dust/stellar luminosity and dust temperature in both galaxies, demonstrating the relation between star formation, dust emission and heating, though these correlations exhibit substantial scatter.

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Galactic Thief: "I Would Have Gotten Away With It, If It Weren't for Those Meddling Astronomers"

One of the closest galaxies to the Milky Way almost got away with theft. However, new simulations convicted the Large Magellanic Cloud (LMC) of stealing stars from its neighbour, the Small Magellanic Cloud (SMC). And the crucial evidence came from surveys looking for something entirely different - dark objects on the outskirts of the Milky Way.
Astronomers have been monitoring the LMC to hunt for evidence of massive compact halo objects, or MACHOs. MACHOs were thought to be faint objects, roughly the mass of a star, but their exact nature was unknown. Several surveys looked for MACHOs in order to find out if they could be a major component of dark matter - the unseen stuff that holds galaxies together.

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