Confirmation of a faint red halo around NGC 5907 |
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Authors: | P A James & M M Casali |
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Institution: | Astrophysics Group, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF,;Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ |
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Abstract: | We report the detection of extended infrared emission 5.2 kpc above the plane of the edge-on spiral galaxy NGC 5907 in the J K bands. This provides confirmation at two other wavelengths of the R -band result of Sackett et al. The halo J − K colour is found to be 1.3 ± 0.3. If we make the assumption that the halo emission is of the form necessary to give a flat rotation curve at large radii, with a power-law index in projection of −1.0, the K surface brightness, M/LK ratio and R − K colour are found to be 23.0 mag arcsec−2, 100 and 3.5 respectively, at 95-arcsec radius. Adopting a halo index of −2.5 in projection, typical of known stellar haloes but inconsistent with the halo measured by Sackett et al., the K surface brightness at 95 arcsec drops to 24.0 mag arcsec−2 and the J − K colour to 2.5, while the M/LK ratio is undetermined since such a halo would be unrelated to the dark matter component. If the emission is interpreted as arising from the massive halo, then it is broadly consistent with a population of stars at the very lowest masses, possibly extending into the brown dwarf regime. |
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Keywords: | stars: low-mass brown dwarfs galaxies: haloes galaxies: individual: NGC 5907 galaxies: spiral dark matter infrared: galaxies |
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