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MCG+04-29-060
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Universe's ultraviolet background could provide clues about missing galaxies

Astronomers have developed a way to detect the ultraviolet (UV) background of the Universe, which could help explain why there are so few small galaxies in the cosmos. UV radiation is invisible but shows up as visible red light when it interacts with gas. An international team of researchers led by Durham University, UK, has now found a way to measure it using instruments on Earth.
Researchers pointed the Multi Unit Spectroscopic Explorer (MUSE), an instrument of the European Southern Observatory's Very-Large Telescope, in Chile, at the galaxy UGC 7321, which lies at a distance of 30 million light years from Earth.

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UGC 7321
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Title: Dark matter dominance at all radii in the superthin galaxy UGC 7321
Authors: Arunima Banerjee (IISc, India), Lynn D. Matthews (CFA-Harvard, USA), Chanda J. Jog (IISc, India)

We model the shape and density profile of the dark matter halo of the low surface brightness, superthin galaxy UGC 7321, using the observed rotation curve and the HI scale height data as simultaneous constraints. We treat the galaxy as a gravitationally coupled system of stars and gas, responding to the gravitational potential of the dark matter halo. An isothermal halo of spherical shape with a core density in the range of 0.039 - 0.057 M_sun/pc^3 and a core radius between 2.5 - 2.9 kpc, gives the best fit to the observations for a range of realistic gas parameters assumed. We find that the best-fit core radius is only slightly higher than the stellar disc scale length (2.1 kpc), unlike the case of the high surface brightness galaxies where the halo core radius is typically 3-4 times the disc scale length of the stars. Thus our model shows that the dark matter halo dominates the dynamics of the low surface brightness, superthin galaxy UGC 7321 at all radii, including the inner parts of the galaxy.

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