Refereed journal article or data article (A1)

The multifarious ionization sources and disturbed kinematics of extraplanar gas in five low-mass galaxies

List of Authors: Rautio RPV, Watkins AE, Comerón S, Salo H, Díaz-García S, Janz J


Publication year: 2022

Journal: Astronomy and Astrophysics

Journal name in source: ASTRONOMY & ASTROPHYSICS

Journal acronym: ASTRON ASTROPHYS

Volume number: 659

Number of pages: 21

ISSN: 0004-6361

eISSN: 1432-0746




Aims. We investigate the origin of the extraplanar di ffuse ionized gas (eDIG) and its predominant ionization mechanisms in five nearby (17-46 Mpc) low-mass (10(9)-10(10) M-circle dot) edge-on disk galaxies: ESO 157-49, ESO 469-15, ESO 544-27, IC 217, and IC 1553.

Methods. We acquired Multi Unit Spectroscopic Explorer (MUSE) integral field spectroscopy and deep narrowband H alpha imaging of our sample galaxies. To investigate the connection between in-plane star formation and eDIG, we measure the star formation rates (SFRs) and perform a photometric analysis of our narrowband H alpha imaging. Using our MUSE data, we investigate the origin of eDIG via kinematics, specifically the rotation velocity lags. We also construct standard diagnostic diagrams and emission-line maps (EW(H alpha), [N II] /H alpha, [S II] //H alpha, [O III]/H beta) and search for regions consistent with ionization by hot low-mass evolved stars (HOLMES) and shocks.

Results. We measure eDIG scale heights of h(zeDIG) = 0.59-1.39 kpc and find a positive correlation between them and specific SFRs. In all galaxies, we also find a strong correlation between extraplanar and midplane radial H alpha profiles. These correlations along with diagnostic diagrams suggest that OB stars are the primary driver of eDIG ionization. However, we find regions consistent with mixed OB-HOLMES and OB-shock ionization in all galaxies and conclude that both HOLMES and shocks may locally contribute to the ionization of eDIG to a significant degree. From H alpha kinematics, we find rotation velocity lags above the midplane with values between 10 and 27 km s(-1) kpc(-1). While we do find hints of an accretion origin for the ionized gas in ESO 157-49, IC 217, and IC 1553, overall the ionized gas kinematics of our galaxies do not match a steady galaxy model or any simplistic model of accretion or internal origin for the gas.

Conclusions. Despite our galaxies' similar structures and masses, our results support a surprisingly composite image of ionization mechanisms and a multifarious origin for the eDIG. Given this diversity, a complete understanding of eDIG will require larger samples and composite models that take many different ionization and formation mechanisms into account.

Last updated on 2022-13-05 at 14:22