NGC 1367

Lore & Background

NGC 1367 is a spiral galaxy seen inclined at an angle of 47.5°. It has a bright bulge with a weak bar that ends in ansae, from which low-surface-brightness arms without obvious knots emerge. H-alpha imaging reveals HII regions in the arms and a circumnuclear ring surrounding a central source. The galaxy also possesses a faint outer ring. Star formation occurs in the outer arms, while the bulge shows no significant star formation.

The galaxy's disk emits X-rays, with a central region measuring 31 by 16 arcseconds and faint diffuse X-ray emission beyond. The inner disk emission may arise from supernova remnants, X-ray binary stars, and strong stellar winds. Three individual X-ray sources are nearly coincident with HII regions. The galaxy has an extended hydrogen disk 22.3 arcminutes in diameter.

Radio observations reveal a kiloparsec-scale linear jet-like structure and a bright radio source. Data from the Australian Square Kilometre Array Pathfinder show double radio lobes and jets. The radio jets extend half the length of the inner stellar disk, lie slightly offset from the bar, and coincide with a hole in hydrogen emission. The radio excess indicates an active nucleus, similar to NGC 3079 and the Circinus Galaxy. Chandra X-ray Observatory flux measurements are consistent with a low-luminosity active galactic nucleus, such as a Seyfert galaxy or LINER. A supermassive black hole is predicted at the center, with mass estimates ranging from 0.47 to 4.7 million solar masses based on spiral arm pitch angle, or 25 million solar masses based on the M–sigma relation.

Reader's Guide

NGC 1367 is significant as a nearby example of a spiral galaxy with an active galactic nucleus that produces radio jets and lobes, placing it in the same class as NGC 3079 and the Circinus Galaxy. Its radio jets, which extend half the inner stellar disk and coincide with a hole in the hydrogen disk, provide a laboratory for studying feedback between an active nucleus and its host galaxy's interstellar medium. The galaxy's X-ray emission, partly coincident with HII regions, links star formation processes to high-energy phenomena. The detection of SN 2005ke, an underluminous Type Ia supernova whose shock wave interacted with circumstellar material, adds to the galaxy's legacy as a site for studying supernova physics and progenitor systems. The multiple mass estimates for its central black hole—derived from spiral arm pitch angle and the M–sigma relation—highlight ongoing uncertainties in black hole mass determination. As a member of the Eridanus Cluster, NGC 1367 contributes to the understanding of galaxy evolution in a group environment.

Did You Know?

• NGC 1367 was discovered by William Herschel on November 17, 1784, and independently by Ormond Stone in 1886.
• The galaxy hosts an underluminous Type Ia supernova, SN 2005ke, discovered on 13 November 2005.
• Its radio jets have half the extent of the inner stellar disk and coincide with a hole in hydrogen emission.
• The central supermassive black hole mass is estimated between 0.47 and 4.7 million solar masses (spiral arm pitch angle) or 25 million solar masses (M–sigma relation).