* Astronomy

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Small Magellanic Cloud

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Festive Nebulas Light Up Milky Way Galaxy Satellite

Two glowing nebulas in the Small Magellanic Cloud, a dwarf galaxy that is a satellite of our Milky Way galaxy, have been observed by NASA's Hubble Space Telescope. Young, brilliant stars at the center of each nebula are heating hydrogen, causing these clouds of gas and dust to glow red. The image is part of a study called Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE). Astronomers are using Hubble to probe the Milky Way satellite to understand how dust is different in galaxies that have a far lower supply of heavy elements needed to create dust.
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RE: The Small Magellanic Cloud

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A Dwarf Galaxy's Star Bar and Dusty Wing

This new image shows the Small Magellanic Cloud galaxy in infrared light from the Herschel Space Observatory a European Space Agency-led mission with important NASA contributions, and NASA's Spitzer Space Telescope. The Large and Small Magellanic Clouds are the two biggest satellite galaxies of our home galaxy, the Milky Way, though they are still considered dwarf galaxies compared to the big spiral of the Milky Way.

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Title: The Spitzer Survey of the Small Magellanic Cloud (S3MC): Insights into the Life-Cycle of Polycyclic Aromatic Hydrocarbons
Authors: Karin M. Sandstrom, Alberto D. Bolatto, Bruce Draine, Caroline Bot, Snezana Stanimirovic

We present the results of modelling dust SEDs across the SMC with the aim of mapping the distribution of PAHs in a low-metallicity environment. Using Spitzer Survey of the SMC (S3MC) photometry from 3.6-160 um over the main star-forming regions of the Wing and Bar along with spectral mapping from 5-38 um from the Spitzer Spectroscopic Survey of the SMC (S4MC) in selected regions, we model the dust SED and emission spectrum to determine the fraction of dust in PAHs across the SMC. We use the regions of overlapping photometry and spectroscopy to test the reliability of the PAH fraction as determined from SED fits alone. The PAH fraction in the SMC is low compared to the Milky Way and variable--with relatively high fractions (q_PAH~1-2%) in molecular clouds and low fractions in the diffuse ISM (<q_PAH>=0.6%). We use the map of PAH fraction across the SMC to test a number of ideas regarding the production, destruction and processing of PAHs in the ISM. We find weak or no correlation between the PAH fraction and the distribution of carbon AGB stars, the location of supergiant H I shells and young SN remnants, or the turbulent Mach number. We find that the PAH fraction is correlated with CO intensity, peaks in the dust surface density and the molecular gas surface density as determined from 160 um emission. The PAH fraction is high in regions of active star-formation, as predicted by its correlation with molecular gas, but is suppressed in H II regions. Because the PAH fraction in the diffuse ISM is generally very low--in accordance with previous work on modelling the SED of the SMC--and the PAH fraction is relatively high in molecular regions, we suggest that PAHs are destroyed in the diffuse ISM of the SMC and/or PAHs are forming in molecular clouds. We discuss the implications of these observations for our understanding of the PAH life cycle, particularly in low-metallicity galaxies.

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NASA's Spitzer Space Telescope has captured an action-packed picture of the nearby Small Magellanic Cloud, a small galaxy that looks like a wispy cloud when seen from Earth.
From Spitzer's perch up in space, the galaxy's clouds of dust and stars come into clear view. The telescope's infrared vision reveals choppy piles of recycled stardust -- dust that is being soaked up by new star systems and blown out by old ones.
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Recycled piles of stardust - and the stars that suck them up and spit them out - have been revealed in a new image of a dwarf galaxy near our own Milky Way.
The image, taken by NASA's Spitzer Space Telescope, shows the Small Magellanic Cloud and gives astronomers an opportunity to study the entire life cycle of stars up close, as well as the different environments in which stars form. It was unveiled here today at the 215th meeting of the American Astronomical Society.
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The infrared portrait of the Small Magellanic Cloud, taken by NASA's Spitzer Space Telescope, reveals the stars and dust in this galaxy as never seen before. The Small Magellanic Cloud is a nearby satellite galaxy to our Milky Way galaxy, approximately 200,000 light-years away.
The image shows the main body of the Small Magellanic Cloud, which is comprised of the "bar" and "wing" on the left and the "tail" extending to the right. The bar contains both old stars (in blue) and young stars lighting up their natal dust (green/red). The wing mainly contains young stars. The tail contains only gas, dust and newly formed stars. Spitzer data has confirmed that the tail region was recently torn off the main body of the galaxy. Two of the tail clusters, which are still embedded in their birth clouds, can be seen as red dots.
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Title: SMC in space and time: a project to study the evolution of the prototype interacting late-type dwarf galaxy
Authors: M.Tosi (1), J.Gallagher (2), E.Sabbi (3), K.Glatt (4,5), E.K.Grebel (4), C.Christian (3), M.Cignoni (6,1), G.Clementini (1), A.Cole (7), G.Da Costa (8), D.Harbeck (2), M.Marconi (9), M.Meixner (3), A.Nota (3), M.Sirianni (3), T.Smecker-Hane (10) ((1)INAF - Osservatorio Astronomico di Bologna, I, (2) University of Wisconsin, Madison, WI, USA,(3)STScI, Baltimore, MD, USA, (4) Heidelberg University, Heidelberg, D, (5)Basel University, Basel, CH, (6)Bologna University, Bologna, I, (7)University of Tasmania, AU,(8)Research School of Astronomy & Astrophysics, ANU, AU, (9)INAF - OA Capodimonte, Napoli, I,(10) University of California, Irvine, CA, USA)

We introduce the SMC in space and time, a large coordinated space and ground-based program to study star formation processes and history, as well as variable stars, structure, kinematics and chemical evolution of the whole SMC. Here, we present the Colour-Magnitude Diagrams(CMDs) resulting from HST/ACS photometry, aimed at deriving the star formation history (SFH) in six fields of the SMC. The fields are located in the central regions, in the stellar halo, and in the wing toward the LMC. The CMDs are very deep, well beyond the oldest Main Sequence Turn-Off, and will allow us to derive the SFH over the entire Hubble time.

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Title: Formation of the Small Magellanic Cloud: ancient major merger as a solution to the kinematical differences between old stars and HI gas
Authors: Kenji Bekki, Masashi Chiba

Recent observations of the Small Magellanic Cloud (SMC) have revealed that the HI gas shows a significant amount of rotation (V_c 60 km/s), while no or little rotation is evident for the old stellar populations. We suggest that this unique kinematical difference between these components in the SMC can be caused by a major merger event which occurred in the early stage of the SMC formation. Our simulations show that dissipative dwarf-dwarf merging can transform two gas-rich dwarf irregulars into a new dwarf, which consists of a spheroidal stellar component and a rotating extended HI disk. The remnant of this dwarf-dwarf merging shows significantly different kinematics between stars and gas, in the sense that a gas disk rotates rapidly while a stellar component shows little rotation. We thus suggest that the simulated dwarf having a dynamically hot spheroid and an extended gas disk finally evolves into the present SMC after efficient stripping of the outer gas via tidal fields of the Galaxy and the Large Magellanic Cloud. We also suggest that spatial distributions and kinematics of RGB and AGB stars with different ages in the possible spheroidal component of the SMC can provide valuable information on whether and when a past major merger event really occurred in the SMC.

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