An H-alpha survey aiming at the detection of extraplanar diffuse ionized gas in halos of edge-on spiral galaxies. I. How common are gaseous halos among non-starburst galaxies?

TL;DR

This survey investigates how common gaseous halos are in edge-on spiral galaxies and finds a correlation between star formation activity and the presence of extraplanar diffuse ionized gas.

Contribution

It provides the first large-scale statistical analysis of extraplanar diffuse ionized gas in a diverse sample of non-starburst spiral galaxies.

Findings

Extraplanar emission detected in 30 out of 74 galaxies.

Correlation between FIR flux ratio and extraplanar gas presence.

Minimum star formation rate per area for halo detection established.

Abstract

In a series of two papers we present results of a new H-alpha imaging survey, aiming at the detection of extraplanar diffuse ionized gas in halos of late-type spiral galaxies. We have investigated a sample of 74 nearby edge-on spirals, covering the northern and southern hemisphere. In 30 galaxies we detected extraplanar diffuse emission at mean distances of |z|~1-2 kpc. Individual filaments can be traced out to |z|<= 6 kpc in a few cases. We find a good correlation between the FIR flux ratio (S_60/S_100) and the SFR per unit area (L_FIR/D^2_25), based on the detections/non-detections. This is actually valid for starburst, normal and for quiescent galaxies. A minimal SFR per unit area for the lowest S_60/S_100 values, at which extended emission has been detected, was derived, which amounts to (dE/dt)_A25^thres = (3.2+-0.5)x10E+40 erg/s/kpc^2. There are galaxies where extraplanar emission was detected at smaller values of L_FIR/D^2_25, however, only in combination with a significantly enhanced dust temperature. The results corroborate the general view that the gaseous halos are a direct consequence of SF activity in the underlying galactic disk.