Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21724503h&link_type=abstract
American Astronomical Society, AAS Meeting #217, #245.03; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
We investigate the ionization structure of nebular gas in M83 using the line diagnostic diagram, [SII](6716+6731A)/Hα vs. [OIII](5007A)/Hβ with the newly available narrowband images from the Wide Field Camera 3(WFC3) of the Hubble Space Telescope(HST). We produce the diagnostic diagram on a pixel-by-pixel (0.2"x0.2") basis and compare it with several photo- and shock-ionization models. We select four regions from the center to the outer spiral arm and compare them in the diagnostic diagram. For the photo-ionized gas, we observe a gradual increase of the log([OIII]/Hβ) ratios from the center to the spiral arm, consistent with the metallicity gradient from the center to the spiral arm, as the HII regions go from super solar abundance to roughly solar abundance. Using the diagnostic diagram, we separate the photo-ionized from the shock-ionized component of the gas. We find that the shock-ionized Hα emission ranges from 2% to about 15-20% of the total, depending on the separation criteria used. An interesting feature in the diagnostic diagram is an horizontal distribution around log([OIII]/Hβ) ≈ 0. This shows a good fit with a shock-ionization model at 2.0 Z&sun; metallicity and shock velocities in the range of 300 km/s to 400 km/s. A low velocity shock component, < 200 km/s, is also detected, and is located at the boundary between the outer ring and the spiral arm. The low velocity shock component can be due to 1) supernova remnants located nearby, 2) dynamical interaction between the outer ring and the spiral arm, 3) abnormal line ratios from extreme local dust extinction.
This paper is based on Early Release Science observations made by the WFC3 Scientific Oversight Committee. We are grateful to the Director of the Space Telescope Science Institute for awarding Director's Discretionary time for this program.
Calzetti Daniela
Dopita Mike A.
Hong Sungryong
SOC WFC3
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