Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...445..152v&link_type=abstract
The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 445, no. 1, p. 152-160
Astronomy and Astrophysics
Astrophysics
44
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
Scientific paper
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 H-alpha + (N II) lambda lambda 6548, 6583 emission-line profiles across the entire disk, with resolution 70 km/s at subarcsecond steps, down to a flux level of approximately 10-17 ergs/s/sq cm (EM approximately equal to 4 cm-6 pc). The DIM contributes approximately 30% of the total disk H-alpha emission within a radius of 10 kpc. The DIM has broader emission lines and larger (N II) H-alpha 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 approximately equal to 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) lambda 6538/H-alpha flux ratio of the DIM increases monotonically with vertical height, reaching unity for absolute value of z greater than or approximately equal to 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 108 - 109 solar mass, 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.
Bland-Hawthorn Jonathan
Cecil Gerald
Veilleux Sylvain
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