Atomic Gas in the Merger Remnant NGC 3921

A composite image of the optical light (green), warm gas (yellow and pink), and cold atomic hydrogen gas (blue) in the well known merger remnant NGC 3921, also known as Arp 224. NGC 3921 is the galaxy to the lower left of the image. It is in a small group with three other nearby galaxies (2 of which are labeled in this alternative version of these same data): the spiral galaxy NGC3916 (upper right), the dwarf galaxy known as MCG +09-19-213 (far right), and a small unnamed disk galaxy just to the right of NGC 3921. NGC 3921 is the result of two spiral galaxies which collided and merged into a single object. The atomic hydrogen observations, taken with the VLA in its C- and D-array configurations, show the narrow tail that extends directly south from the galaxy's main body is gas rich, while the tidal loop/plume that emerges from the lower right of the galaxy, loops around, and then extends to the upper left is gas poor, suggesting that this system is the result of the collision between a gas-rich and a gas-poor disk galaxy. The inner regions are relatively free of cold atomic gas, supporting the idea that two disk galaxies can merge together to form a circular gas-poor object similar to an early-type galaxy.

VLA C+D array observations with a resolution of 20". Optical image is an R-band image, and both this image and the continuum subtracted Halpha image were obtained with the KPNO 2.1m telescope. The velocity of MCG +09-19-213 fell to one edge of the bandpass, so its HI has not been completely mapped.

Legacy Astronomical Images

NRAO/AUI/NSF does not hold full copyright for this image. Contact the archivist for details.

Legacy Astronomical Image

NGC3921

J. Hibbard

J. Hibbard, J. van Gorkom

Very Large Array (VLA)

1991-01-13

spectral line

21 cm

1420.4 MHz

HI

RA 11:50:52.240, Dec: 55:5:33.000 (J2000)

0.133333 x 0.150000 degrees

Contact the archivist for a high resolution tif of this image.

Galaxies Series

Peculiar Unit