NGC 1543

Lore & Background

NGC 1543 was discovered by James Dunlop on November 5, 1826. The galaxy is seen nearly face on and features a double bar: the inner bar is 23 arcseconds long with its major axis at a 30° northeast angle, while the main bar is about 2.3 arcminutes and lies along an east-west axis. The nucleus shows H-alpha emission and appears to have undergone a star formation event 2 to 5 billion years ago, though the stars in the bulge and disk are old.

The galaxy's outer ring is more visible in the near ultraviolet than in optical wavelengths, with a radius estimated at 160 arcseconds. The ring was also detected in the hydrogen line, while the rest of the galaxy appears devoid of hydrogen. The ring may have formed by the galaxy colliding with a dwarf galaxy while passing through the central region of the Dorado Group. HII regions in the southeastern part of the ring emit ultraviolet and H-alpha, indicating active star formation, and star formation is also observed at the northwest part of the ring. The star formation rate at the ring is estimated at about 0.08 solar masses per year based on ultraviolet radiation, and this rate has been constant over the last hundred million years.

NGC 1543 lies at the outskirts of the Dorado Group, about 1.2 kiloparsecs from the group center where NGC 1553 is located, and is relatively isolated. No extended hydrogen emission was found, indicating the galaxy is not currently interacting.

Reader's Guide

NGC 1543 is significant as a member of the Dorado Group that exhibits a rare double-bar structure and a well-defined outer ring with ongoing star formation. The ring's detection in both ultraviolet and hydrogen line emissions, along with the absence of hydrogen elsewhere in the galaxy, suggests a past collision with a dwarf galaxy as the ring's origin. The constant star formation rate of about 0.08 solar masses per year over the last hundred million years indicates a sustained, moderate level of stellar birth in the ring. The galaxy's isolation at the group outskirts and lack of current interaction make it a valuable case for studying the long-term effects of past mergers on galactic structure and star formation. Its nearly face-on orientation allows detailed observation of the bar and ring morphology, contributing to understanding how such features evolve in lenticular galaxies.

Did You Know?

• NGC 1543 has a double bar: an inner bar 23 arcseconds long and a main bar about 2.3 arcminutes.
• The outer ring of NGC 1543 is more visible in near ultraviolet than in optical light.
• The star formation rate in the ring is about 0.08 solar masses per year, constant over the last hundred million years.
• The galaxy lies about 1.2 kiloparsecs from the center of the Dorado Group and is relatively isolated.