MS 0440+0204 BCG

Lore & Background

MS 0440+0204 BCG has a compact appearance and is composed of six close galaxies or components merging together. The velocity difference between two known components is estimated at 2,600 kilometers per second. A low surface brightness halo with a diameter of 157 kiloparsecs envelops these components. The core appears red, with a total near ultraviolet magnitude of 21.84 ± 0.44. The galaxy contains an intermediate red stellar population but no young stellar component; stars in the inner regions have an estimated age of 4,370 ± 160 million years, while outer-region stars are around 15,400 ± 6,280 million years old. A study published in 1993 found 15 gravitational lensing arc features surrounding the BCG based on CCD imaging. The largest known arc has a length of 10 arcseconds but is unresolved, while the other arcs trace out a 90 kiloparsec radius. Detections of hydrogen-alpha emission suggest cooling flow may be present. In 2009, the BCG was found to contain a radio source, classifying it as a radio galaxy, with a radio power of 34.2 ± 0.1 × 10^23 W Hz−1 and a radio flux density of 30.2 ± 0.07 mJy.

Reader's Guide

MS 0440+0204 BCG is significant as a massive cD galaxy at the center of its cluster, exhibiting multiple nuclei that reveal an ongoing merger of six components. Its gravitational lensing arcs—15 features detected in 1993, including a 10-arcsecond unresolved arc—provide a natural laboratory for studying dark matter distribution and galaxy cluster mass. The presence of hydrogen-alpha emission and a cooling flow signature suggests ongoing gas accretion and star formation suppression, consistent with its lack of a young stellar population. The galaxy's classification as a radio galaxy, confirmed in 2009, adds to its importance as a source of non-thermal emission. The age gradient—inner stars at 4,370 million years and outer stars at 15,400 million years—indicates a complex formation history, with older stars in the halo and younger stars in the core from mergers. Its total mass of 0.53 × 10^12 M☉ and low surface brightness halo of 157 kiloparsecs make it a key object for understanding the assembly of brightest cluster galaxies.

Did You Know?

• MS 0440+0204 BCG contains six close galaxies or components merging together.
• The largest gravitational lensing arc around the BCG is 10 arcseconds long but unresolved.
• The galaxy's radio power is estimated at 34.2 ± 0.1 × 10^23 W Hz−1.
• Stars in the outer regions of the BCG are around 15,400 ± 6,280 million years old.