2018ApJ...856..166H -
Astrophys. J., 856, 166-166 (2018/April-1)
Extraplanar H II regions in spiral galaxies. I. Low-metallicity gas accreting through the disk-halo interface of NGC 4013.
HOWK J.C., RUEFF K.M., LEHNER N., WOTTA C.B., CROXALL K. and SAVAGE B.D.
Abstract (from CDS):
The interstellar thick disks of galaxies serve as the interface between the thin star-forming disk, where feedback-driven outflows originate, and the distant halo, the repository for accreted gas. We present optical emission line spectroscopy of a luminous, thick disk H II region located at z = 860 pc above the plane of the spiral galaxy NGC 4013 taken with the Multi-Object Double Spectrograph on the Large Binocular Telescope. This nebula, with an Hα luminosity ∼4-7 times that of the Orion nebula, surrounds a luminous cluster of young, hot stars that ionize the surrounding interstellar gas of the thick disk, providing a measure of the properties of that gas. We demonstrate that strong emission line methods can provide accurate measures of relative abundances between pairs of H II regions. From our emission line spectroscopy, we show that the metal content of the thick disk H II region is a factor of ≃2 lower than gas in H II regions at the midplane of this galaxy (with the relative abundance of O in the thick disk lower by -0.32 ± 0.09 dex). This implies incomplete mixing of material in the thick disk on small scales (hundreds of parsecs) and that there is accretion of low-metallicity gas through the thick disks of spirals. The inclusion of low-metallicity gas this close to the plane of NGC 4013 is reminiscent of the recently proposed "fountain-driven" accretion models.
Abstract Copyright:
© 2018. The American Astronomical Society. All rights reserved.
Journal keyword(s):
galaxies: abundances - galaxies: individual: NGC 4013 - galaxies: ISM
Nomenclature:
Fig. 1, Table 1: [HRL2018] NGC 4013 EHR 1 N=1, [HRL2018] NGC 4013 disk N (Nos disk 1- disk 2).
Simbad objects:
10
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