The Interstellar Disk--Halo Connection in the Spiral Galaxy NGC 3079
Abstract
We discuss the morphology and excitation of ionized gas in the nearby Sc galaxy NGC 3079. The almost edge-on orientation is ideal for studying the vertical structure of the gaseous disk, and especially the diffuse ionized medium (DIM) found between the bright H II regions. We used the Hawaii Imaging Fabry-Perot Interferometer (HIFI) to map 150,000 Hα + [N II] λλ6548, 6583 emission-line profiles across the entire disk, with resolution 70 km s^-1^ at subarcsecond steps, down to a flux level of ~10^-17^ ergs s^-1^ cm^-2^ (EM ~ 4 cm^-6^ pc). The DIM contributes ~30% of the total disk Hα emission within a radius of 10 kpc. The DIM has broader emission lines and larger [NII]/Hα flux ratios than the adjacent H II regions. Within a radius of 5 kpc, we find that the X-shaped filaments reported in previous studies emerge from the inner (R ~ 1.5 kpc) disk, and rise more than 4 kpc above the disk plane. The morphology, kinematics, and excitation of the filaments suggest that they form a biconic interface between the undisturbed disk gas, and gas entrained in the wide-angle outflow. The DIM beyond 5 kpc radius is more vertically extended than the thick ionized disk detected in our Galaxy and in a few nearby edge-on systems. After correcting for dust, the vertical profile of this DIM has an exponential scale height of about 1.1 kpc, similar to that of the H I disk. The [N II] λ6583/Hα flux ratio of the DIM increases monotonically with vertical height, reaching unity for |z| ~> 2.5 kpc. The flux required to keep the DIM ionized at R = 8 kpc is similar to that near the solar circle of our Galaxy. Highly dilute radiation from O stars in the galactic plane probably maintains the DIM. The total mass of the DIM is of order 10^8^-10^9^ M_sun_, representing less than 1% of the total dynamical mass of NGC 3079. Mechanical energy from intense star formation in the disk probably lifts the DIM above the disk. The several bubbles and filaments within 1 kpc of the disk plane is direct evidence for gas flow between the disk and halo.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 1995
- DOI:
- 10.1086/175681
- Bibcode:
- 1995ApJ...445..152V
- Keywords:
-
- Galactic Halos;
- Galactic Structure;
- H Ii Regions;
- Interstellar Gas;
- Kinematics;
- Line Spectra;
- Spiral Galaxies;
- Star Formation;
- Flux Density;
- H Alpha Line;
- Ionization;
- Luminosity;
- Spectrum Analysis;
- Stellar Spectrophotometry;
- Astronomy;
- GALAXIES: INDIVIDUAL NGC NUMBER: NGC 3079;
- GALAXIES: ISM;
- GALAXIES: KINEMATICS AND DYNAMICS;
- GALAXIES: SPIRAL;
- GALAXIES: STRUCTURE