N/O in spiral discs: a new algorithm for abundance determinations
We obtain nitrogen abundances in the HII regions of selected spiralgalaxies by using a new algorithm developed from grids ofphotoionization models. The new method requires only the observation ofoptical [NII], [OII] and [OIII] lines. We show the self-consistency ofthe new method, and also the agreement with more detailed modelling ofindividual HII regions. Gradients in [N/O] against effective radius and[O/H] are presented for a well-observed subset of galaxies from theVila-Costas & Edmunds sample.
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Analysis of the ISOPHOT FIR maps of M51 and M101.
The far-IR ISOPHOT maps of the spiral galaxies M51 and M101 at 60, 100,and at 175μm are analysed. For all areas in these galaxies thespectral energy distributions can be fitted with a single-temperatureemission curve. Colours and dust temperatures were estimated forinteresting sub-fields. The temperatures vary between 33K for HIIregions, and 28K for the disk, arm and interarm regimes.
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The H II regions of M101. I - an atlas of 1264 emission regions
A previous survey of the H II regions in M101 (Hodge and Kennicutt) hasbeen extended by a series of CCD images and image tube plates of thegalaxy, approximately tripling the number of known emission regions.This paper provides maps and a catalog of a total of 1264 H II regionsin M101.
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Theoretical models for H II regions. III - The abundance gradient in M101
A previously described theoretical H II region abundance sequencecalibration has been employed to determine oxygen and other heavyelement abundances in a selection of well-observed H II regions in M101.Comparison of abundances derived from the abundance sequence withabundances derived from 'exact' photoionization modeling demonstratethat the accuracy with which H II region abundances may be derived fromthe sequence is about 0.15 dex. The data have been employed to measureradial abundance gradients and heavy element yields for oxygen,nitrogen, and sulfur in M101.
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Turbulent gas motions in giant H II regions. II - The luminosity-velocity dispersion relation
The relation between luminosity L(H-alpha) and velocity dispersion sigmais reinvestigated in view of H-alpha and O III 5007-A forbidden linemeasurements of the velocity dispersion for 43 giant, extragalactic H IIregions. A correlation of L(H-alpha) that varies as sigma (H-alpha) tothe 6.6th power is obtained; O III-line velocity dispersions are notedto obey a similar relation, but are somewhat smaller, and the slope ofboth relations is steeper than expected for gravitationally boundsystems.
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Images in the rocket ultraviolet - Photometry of M101
It is pointed out that ultraviolet imagery of spiral galaxies is asensitive probe of the large-scale morphology of the star-formingregions and the associated interstellar dust. A rocket-borneRitchey-Chretien telescope was employed to obtain three ultravioletimages of the Sc 1 galaxy M101 (NGC 5457). The present investigation isconcerned with the procedures for reduction and absolute calibration ofthe obtained images and an analysis in terms of discrete sources.Attention is also given to the radial variation and the azimuthalvariation of disk and arms. It is found that the emission from M101 inthe UV bandpass is dominated by extreme Population I, in the form ofdiscrete OB/H II complexes.
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