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Post Info TOPIC: M83
Blobrana


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Southern Pinwheel
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The spectacular new camera installed on NASA's Hubble Space Telescope during Servicing Mission 4 in May has delivered the most detailed view of star birth in the graceful, curving arms of the nearby spiral galaxy M83.

hs-2009-29-a-small_web.jpg
Credit NASA

Nicknamed the Southern Pinwheel, M83 is undergoing more rapid star formation than our own Milky Way galaxy, especially in its nucleus. The sharp "eye" of the Wide Field Camera 3 (WFC3) has captured hundreds of young star clusters, ancient swarms of globular star clusters, and hundreds of thousands of individual stars, mostly blue supergiants and red supergiants.

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Blobrana


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Messier 83
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ESO's Wide Field Imager has captured the intricate swirls of the spiral galaxy Messier 83, a smaller look-alike of our own Milky Way. Shining with the light of billions of stars and the ruby red glow of hydrogen gas, it is a beautiful example of a barred spiral galaxy, whose shape has led to it being nicknamed the Southern Pinwheel.

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Title: The volume densities of giant molecular clouds in M83
Authors: Jonathan S. Heiner, Ronald J. Allen, O. Ivy Wong, Pieter C. van der Kruit

Using observed GALEX far-ultraviolet (FUV) fluxes and VLA images of the 21-cm HI column densities, along with estimates of the local dust abundances, we measure the volume densities of a sample of actively star-forming giant molecular clouds (GMCs) in the nearby spiral galaxy M83 on a typical resolution scale of 170 pc. Our approach is based on an equilibrium model for the cycle of molecular hydrogen formation on dust grains and photodissociation under the influence of the FUV radiation on the cloud surfaces of GMCs. We find a range of total volume densities on the surface of GMCs in M83, namely 0.1 - 400 cm-3 inside R25, 0.5 - 50 cm-3 outside R25 . Our data include a number of GMCs in the HI ring surrounding this galaxy. Finally, we discuss the effects of observational selection, which may bias our results.

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Blobrana


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RE: M83
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Baby stars have been discovered spawning in the otherwise barren outskirts of a galaxy.
The finding has surprised astronomers because the galactic periphery was assumed to lack high concentrations of ingredients needed to form stars.
The stars can be seen in a new image of the Southern Pinwheel galaxy, or M83, obtained by a Nasa space telescope and a ground-based observatory.

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Blobrana


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The outlying regions around the Southern Pinwheel galaxy, or M83, are highlighted in this composite image from NASA's Galaxy Evolution Explorer and the National Science Foundation's Very Large Array in New Mexico. The blue and pink pinwheel in the centre is the galaxy's main stellar disk, while the flapping, ribbon-like structures are its extended arms.

Image1a
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Credit: NASA/JPL-Caltech/VLA/MPIA

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Title: Spitzer Observations of M83 and the Hot Star, H II Region Connection
Authors: Robert H. Rubin, Janet P. Simpson, Sean W.J. Colgan, Reginald J. Dufour, Katherine L. Ray, Edwin F. Erickson, Michael R. Haas, Adalbert W.A. Pauldrach, Robert I. Citron

We have undertaken a program to observe emission lines of SIV 10.5, NeII 12.8, NeIII 15.6, & SIII 18.7 um in a number of extragalactic HII regions with the Spitzer Space Telescope. We report our results for the nearly face-on spiral galaxy M83. The nebulae selected cover a wide range of galactocentric radii (R_G). The observations were made with the Infrared Spectrograph in the short wavelength, high dispersion configuration. The above set of 4 lines is observed cospatially, thus permitting a reliable comparison of the fluxes. From the measured fluxes, we determine the ionic abundance ratios including Ne++/Ne+, S3+/S++, and S++/Ne+ and find that there is a correlation of increasingly higher ionisation with larger R_G. By sampling the dominant ionisation states of Ne and S for HII regions, Ne/S ~ (Ne+ + Ne++)/(S++ + S3+). Our findings of ratios that exceed the benchmark Orion value are more likely due to other effects than a true gradient in Ne/S. Both Ne and S are primary elements produced in alpha- chain reactions. It is expected that Ne/S remains relatively constant throughout a galaxy. This type of observation and method of analysis has the potential for accurate measurements of Ne/S, particularly for HII regions with lower metallicity & higher ionisation than those here, such as those in M33. Our observations may also be used to test the predicted ionising spectral energy distribution of various stellar atmosphere models. We compare the fractional ionisation ratios <Ne++>/<S++> & <Ne++>/<S3+> vs. <S3+>/<S++> with predictions made from our photoionisation models using several state-of-the-art stellar atmosphere model grids. A second paper using Spitzer observations of HII regions in the galaxy M33 will follow.

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Blobrana


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Messier 83
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Hidden Mass Concentration Near the Centre of Starbursting Galaxy M83

Using the near infrared integral field spectrograph CIRPASS at Gemini South, Ruben Diaz and an international team of astronomers, have discovered a previously unknown hidden mass concentration that looks like a second nucleus in the starburst galaxy M83. The mass concentration is located at the youngest end of a giant star forming arc near the galaxy's centre. This concentration probably represents the wreckage of the nucleus of the smaller galaxy which is being "swallowed" by M83.
This double nucleus arrangement is also associated with complex kinematics near the galaxy centre. The masses of the objects were derived from the kinematics of the ionised gas. The nucleus of the intruder body has an estimated mass of about 16 million times the mass of the Sun, compared to 2 million solar masses for the optical "main" nucleus. The two nuclei are about 100 parsecs apart and are probably harbouring black holes. Numerical modelling conducted by the team suggest that the two nuclei would coalesce to form a single massive core in about 60 million years.

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RE: Messier83
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Spiral Galaxy Messier 83


Full Res (JPEG): 2048x2373 - 5.8M image

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Blobrana


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M83
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In a paper entitled "Double Nucleus in M83" published on May 13, 2005, astronomers Damián Mast, Ruben Diaz, and Paz Aguero of Córdoba's National University and the Astronomical Observatory of Cordoba have confirmed "the presence of a secondary nucleus or mass concentration" first suggested by Niranjan Thatte and a team of investigators in the year 2000.
A secondary nucleus is now known to lie about 200 light years (3.9 arc seconds) northwest of the starburst galaxy M83's optical centre.
However, according to Damián Mast, "the mass concentrations could be star clusters instead of black holes."

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The centre of M83, a barred starburst galaxy with a double nucleus, has been observed in the CO(J=2-1) and CO(J=3-2) lines with the Submillimeter Array.
The molecular gas shows a distribution and kinematics typical for barred galaxies at kpc radii, but reveals unusual kinematics around the double nucleus in the central 300 pc. CO velocity data show that the visible nucleus in M83 is at least 3" (65 pc) away from the galaxy's dynamical centre, which most likely coincides with the centre of symmetry previously determined in K band and is suggested to host another nucleus.
High-velocity molecular gas was discovered associated with the visible off-centre nucleus, and also found a steep velocity gradient across it.
Researchers attribute these features to a gas disk rotating around the off-centre nucleus, which may be the remnant of a small galaxy accreted by M83.
The dynamical mass of this component is estimated to be 3x10^8 solar masses within a radius of 40 pc. The dynamical perturbation from the off-centre nucleus may have played a key role in shaping the lopsided starburst.
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M83 is quite a typical barred spiral galaxy - much like our own Milky Way Galaxy.
The galaxy is sometimes called the "Southern Pinwheel".
It forms a small physical group, the M83 group, with the peculiar radio galaxy Centaurus A (NGC 5128) and the unusual galaxy NGC 5253 in Centaurus, all of which lie about 15 million light years distant.
M83 has shown an unusual amount of stellar supernovae explosions - six since the turn of the century - more than any other Messier galaxy.

Position(2000): RA 13 : 37.0 Dec -29 : 52


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