An oxygen abundance gradient into the outer disc of M81

Details An oxygen abundance gradient into the outer disc of M81 An oxygen abundance gradient into the outer disc of M81

May 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012mnras.422..401p&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 422, Issue 1, pp. 401-419.

Astronomy and Astrophysics

Astronomy

H Ii Regions, Galaxies: Abundances, Galaxies: Individual: M81, Galaxies: Individual: Ngc 3031, Galaxies: Ism

Scientific paper

The extended H I disc and tidal tails of M81 present an interesting environment to study the effects of galaxy interaction on star formation and chemical evolution of the outer disc of a large spiral galaxy. We present Hα imaging of the outer disc of M81 and luminosities for 40 H II regions out to ˜3 R25. We have also obtained MMT spectra for 21 H II regions out to more than twice R25. We derive strong-line oxygen abundances for all H II regions using R23-based and [N II]/[O II]-based calibrations and electron temperature abundances for seven regions spanning a galactocentric distance between 5.7 and 32 kpc. We also comment on the abundances of H II regions near KDG 61 and the 'tidal dwarf' candidate HoIX. Our results constitute the most radially extended metallicity study for M81 to date. With this extended data set, we find an overall oxygen abundance gradient of Δ(log (O/H))/ΔRG˜-0.013 dex kpc-1 over the entire radial range. This is significantly flatter than what has been found in previous studies, which were limited to the optical disc. From our temperature-based abundances, we find Δ(log (O/H))/ΔRG˜-0.020 dex kpc-1 and present the possibility of a broken gradient from these data, but note the need to obtain more temperature-based abundances at intermediate galactocentric distances (˜10-20 kpc) to verify whether or not this may be the case. We discuss our main result of a rather flat gradient for M81 in the context of simulations and observations of abundance gradients in other galaxies. We find that the shallow abundance gradient of M81 is likely a result of the interaction history of this galaxy. Locations, galactocentric distances, Hα luminosities (after [N II] correction) and aperture radii for our H II region sample. We assume a distance to M81 of 3.63 Mpc (Freedman et al. 2001), a rotation angle of 157° and inclination of 59° (Kong et al. 2000). We assume the R25 radius is 13.8 arcmin (14.6 kpc at 3.63 Mpc) (de Vaucouleurs et al. 1991). The alternative IDs are from Petit et al. (1988), Hodge & Kennicutt (1983), Münch (1959), Miller & Hodge (1994) and C09. The luminosities and radii marked with † are calculated from Hα+ [N II] fluxes from Lin et al. (2003). The last column indicates whether or not we have spectroscopic data for the region.

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