Chemical abundances and ionizing clusters of H ii regions in the LINER galaxy NGC 4258

Abstract

We present long-slit observations in the optical and near infrared of eight H II regions in the spiral galaxy NGC 4258. Six of the observed regions are located in the SE inner spiral arms and the other two are isolated in the northern outer arms.A detailed analysis of the physical conditions of the gas has been performed. For two of the regions an electron temperature has been derived from the [SIII] λ 6312Å line. For the rest, an empirical calibration based on the red and near infrared sulphur lines has been used. The oxygen abundances derived by both methods are found to be significantly lower (by a factor of two) than previously derived by using empirical calibrations based on the optical oxygen lines.In the brightest region, 74C, the observation of a prominent feature due to WolfRayet stars provides an excellent constraint over some properties of the ionizing clusters. In the light of the current evolutionary synthesis models, no consistent solution is found to explain at the same time both the WR feature characteristics and the emission line spectrum of this region. In principle, the presence of WR stars could lead to large temperature fluctuations and also to a hardening of the ionizing radiation. None of these effects are found in region 74C for which the electron temperatures found from the [SIII] λ 6312Å line and the Paschen discontinuity at 8200Å are equal within the errors and the effective temperature of the ionizing radiation is estimated at around 35300 K.Both more observations of confirmed high metallicity regions and a finer metallicity grid for the evolutionary synthesis models are needed in order to understand the ionizing populations of HII regions.

MUSE view of Arp220: Kpc-scale multi-phase outflow and evidence for positive feedback

“…In this section we investigate the dominant ionisation mechanism(s) for the emitting gas across the MUSE FOV using standard emission line ratios (e.g. Baldwin et al 1981;Veilleux & Osterbrock 1987;Díaz et al 2000) and line widths (e.g. Dopita & Sutherland 1995).…”

“…The close wavelengths of the line pairs involved in such diagnostics ensure minimum dust reddening effects. The only exception is the Díaz et al (2000) diagnostic, involving [S II] and [S III] transitions, for which we applied the extinction corrections introduced in Sect. 8. colours identify regions with the lowest line ratios, while greento-orange colours identify the Voronoi bins with highest line ratios.…”

“…In order to measure the U parameter, defined as the number of ionising photons S * per hydrogen atom density n H divided by the speed of light c, we use of the [S III]λλ9069, 9532/[S II]λλ6716, 31 ratio (e.g. Díaz et al 2000). Since [S III]λ9532 is not covered by the wavelength range observed by MUSE, we adopted a theoretical ratio of [S III]λ9532/[S III]λ9069 = 2.5 (Osterbrock & Ferland 2006), fixed by atomic physics.…”

Properties of ionized outflows in MaNGA DR2 galaxies

“…We do that by comparing the values of the ionizing parameter, U , which describes the degree of ionization of the gas, for both kinematic components. Following Diaz et al (2000), we calculate this parameter as the ratio between [Oiii] λ5007 and the sum of the [Oii]λλ3727, 3730 lines 5 . Here we use only regions hosting outflows ionized by star formation, for which we select the sources whose broad component is located in the SF region of the BPT-N diagram in the bottom panels of Figure 6.…”