Atomic Gas in the Merger Remnant NGC 3921

Image
Minimum credit line: Image courtesy of NRAO/AUI and J. Hibbard(for details, see Image Use Policy).

About this Image

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.

Investigator(s):  J. Hibbard & J. van Gorkom

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Technical Data

    Telescope VLA 
    Date of Observation 1991-01-13 
    Type of Observation Spectral Line Observations 
    Wavelength 21 cm 
    Frequency 1420.4 MHz 
    Species HI 
    Center of Image RA: 11:50:52.24, Dec: 55:05:33.00 (J2000)  
    Field of View 0.1333 x 0.1500 degrees  
    Technical Caption 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.  

  • Astronomical database entries for NGC3921
    • Query NED for images of NGC3921
    • Query SIMBAD for more NGC3921 data

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