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O/H-N/O: The curious case of NGC 4670

Accepted version
Peer-reviewed

Type

Article

Change log

Authors

Kumari, N 
James, BL 
Irwin, MJ 
Amorín, R 
Pérez-Montero, E 

Abstract

We use integral field spectroscopic (IFS) observations from Gemini North Multi-Object Spectrograph (GMOS-N) of a group of four H II regions and the surrounding gas in the central region of the blue compact dwarf (BCD) galaxy NGC 4670. At spatial scales of 9 pc, we map the spatial distribution of a variety of physical properties of the ionised gas: internal dust attenuation, kinematics, stellar age, star-formation rate, emission line ratios and chemical abundances. The region of study is found to be photoionised. Using the robust direct Te-method, we estimate metallicity, nitrogen-to-oxygen ratio and helium abundance of the four H II regions. The same parameters are also mapped for the entire region using the HII-CHI-mistry code. We find that log(N/O) is increased in the region where the Wolf-Rayet bump is detected.The region coincides with the continuum region, around which we detect a slight increase in He abundance. We estimate the number of WC4, WN2-4 and WN7-9 stars from the integrated spectrum of WR bump region. We study the relation between log(N/O) and 12 + log(O/H) using the spatially-resolved data of the FOV as well as the integrated data of the H II regions from ten BCDs. We find an unexpected negative trend between N/O and metallicity. Several scenarios are explored to explain this trend, including nitrogen enrichment, and variations in star formation efficiency via chemical evolution models.

Description

Keywords

HII regions, galaxies: abundances, galaxies: dwarf, galaxies: individual: NGC 4670

Journal Title

Monthly Notices of the Royal Astronomical Society

Conference Name

Journal ISSN

0035-8711
1365-2966

Volume Title

476

Publisher

Oxford University Press (OUP)
Sponsorship
European Research Council (695671)
Science and Technology Facilities Council (ST/N000927/1)
Science and Technology Facilities Council (ST/N005805/1)