Properties of the giant H iiregions and bar in the nearby spiral galaxy NGC 5430

Abstract

In order to better understand the impact of the bar on the evolution of spiral galaxies, we measure the properties of giant H ii regions and the bar in the SB(s)b galaxy NGC 5430. We use two complementary data sets, both obtained at the Observatoire du Mont‐Mégantic: a hyperspectral data cube from the imaging Fourier transform spectrograph SpIOMM (Spectromètre‐Imageur à transformée de Fourier de l‐Observatoire du Mont‐Mégantic) and high‐resolution spectra across the bar from a long‐slit spectrograph. We flux‐calibrate SpIOMM spectra for the first time, and produce Hα and [N ii]λ6584 Å intensity maps from which we identify 51 giant H ii regions in the spiral arms and bar. We evaluate the type of activity, the oxygen abundance and the age of the young populations contained in these giant H ii regions and in the bar. Thus, we confirm that NGC 5430 does not harbour a strong active galactic nucleus, and that its Wolf–Rayet knot shows a pure H ii region nature. We find no variation in abundance or age between the bar and spiral arms, nor as a function of galactocentric radius. These results are consistent with the hypothesis that a chemical mixing mechanism is at work in the galaxy's disc to flatten the oxygen abundance gradient. Using the starburst99 model, we estimate the ages of the young populations, and again find no variations in age between the bar and the arms or as a function of radius. Instead, we find evidence for two galaxy‐wide waves of star formation, about 7.1 and 10.5 Myr ago. While the bar in NGC 5430 is an obvious candidate to trigger these two episodes, it is not clear how the bar could induce widespread star formation on such a short time‐scale.

Confined massive circumstellar shell in type IIL SN 2008fq

“…The nebular lines with Gaussian profiles and the ratio H /[N II] = 2 indicated by the spectrum on day 71 are superimposed on the computed H . Remarkably, the adopted line ratio is consistent with the median value for the sample of giant H II regions in the ordinary spiral galaxy (Brière et al 2012). The case of = 800 km s −1 is apparently preferred (Fig.…”

Constraints on the minor merging and star formation history of the Wolf–Rayet galaxy NGC 5430 through observations

“…The Galactic level SFR is confirmed by adding up the local extinction-corrected SFR of individual HII regions identified by other independent observations. Figure 9(c) shows the HII regions identified by Brière et al (2012) by using the imaging Fourier transform spectrograph SpIOMM on the 1.6-m-diameter Ritchey-Chretien telescopes. The total SFR in the HII regions is 2.4 M⊙ yr −1 , including ∼ 0.6 M⊙ yr −1 from the central region and 1 M⊙ yr −1 from the W-R region.…”

“…In this section, we compare star formation activity and molecular gas. Since the Hα flux is not spatially calibrated on the image of the GHASP survey (Figure 9(b)) due to the strategy of the survey, we used the calibrated flux of HII regions from Brière et al (2012) and the 12 CO flux of the beam at the same positions for the analyses in this section. Typical size of HII regions is 1 -2.5 kpc 2 , comparable to our beam area of ∼ 1.5 kpc 2 , but we suggest that the results still have to be treated with care.…”

“…We found that the 12 CO distribution of NGC 5430 is correlated with star formation rate surface density. Figure 9(d) compares the HII regions of Brière et al (2012) (circles) and our 12 CO image (color scale). Physical areas of HII regions are indicated by the circles sizes.…”

“…The current SFE is quantified as SFR(Hα)/MH 2 , where MH 2 is the molecular gas traced by the 12 CO. The total SFR(Hα) in the 12 CO region is ∼ 2.2 M⊙ yr −1 obtained by using the measurements of Brière et al (2012). The total MH 2 in our map is ∼ 4.7 × 10 9 M⊙, for the total flux of 5.7 × 10 4 Jy beam −1 km s −1 and the CO-to-H2 conversion factor of 2 × 10 20 cm −2 (K km s −1 ) −1 .…”