University of Hertfordshire

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From the same journal

By the same authors

The Rotation of the halo of NGC 6822 from the radial velocities of carbon stars

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Original languageEnglish
Pages (from-to)3376-3385
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Early online date20 May 2016
Publication statusPublished - 1 Nov 2016


Using spectra taken with the AAOmega spectrograph, we measure the radial velocities of over 100 stars, many of which are intermediate age carbon stars, in the direction of the dwarf irregular galaxy NGC 6822. Kinematic analysis suggests that the carbon stars in the sample are associated with NGC 6822, and estimates of its radial velocity and galactic rotation are made from a star-by-star analysis of its carbon star population. We calculate a heliocentric radial velocity for NGC 6822 of −51±3 kms-1 and show that the population rotates with a mean rotation speed of 11.2±2.1 kms-1 at a mean distance of 1.1 kpc from the galactic centre, about a rotation axis with a position angle of 26 ∘ ±13 ∘ , as projected on the sky. This is close to the rotation axis of the HI gas disk and suggests that NGC 6822 is not a polar ring galaxy, but is dynamically closer to a late type galaxy. However, the rotation axis is not aligned with the minor axis of the AGB isodensity profiles and this remains a mystery.


© The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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