Astronomy and Astrophysics – Astronomy
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aas...204.1505g&link_type=abstract
American Astronomical Society Meeting 204, #15.05; Bulletin of the American Astronomical Society, Vol. 36, p.680
Astronomy and Astrophysics
Astronomy
Scientific paper
We present the first direct measurements of electron temperatures and element abundances for two H II regions in the spiral galaxy M51. H II regions in M51 have very low excitation, which led previous studies to infer that the abundances in this galaxy were quite high (log O/H = -2.9 to -2.6) compared to the solar value, based on photoionization models or extrapolation of empirical relations of abundances vs. strong emission line intensities. We have detected the [N II] λ 5755 line for the first time in the regions M51-CCM72 and M51-CCM10, which allows us to derive electron temperatures from the [N II] λ 6583/λ 5755 intensity ratio. We find T(N II) = 6000±300 K for CCM72 and 7400(+1000,-600) K for CCM10. Based on these temperature measurements, we derive log O/H = -3.2±0.1 for CCM72 and -3.5±0.2 for CCM10. These abundances are a factor of 2-3 smaller than values derived previously from photoionization models or extrapolation of strong-line calibrations. If confirmed, the new results imply that the inner parts of spirals are not as metal-rich as previously thought, and that the excitation of metal-rich H II regions is relatively insensitive to abundances. Lower abundances in spiral disks could affect the derivation of quantities that may have metallicity dependence, e.g. the Cepheid P-L relation, or the mass of molecular gas derived from CO observations.
Bresolin Fabio
Garnett Don R.
Kennicutt Robert C.
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