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Hidden Mass Concentration Near the Center of Starbursting Galaxy M83

October 13, 2006

Figure 1.

CIRPASS integral field is depicted and superposed on a HST pseudo color optical image of the center of Messier 83. The rotation center of the galaxy (intruder nucleus) is at the youngest end of the partial ellipse that describes the positions of the main star forming regions of the giant arc.

Figure 2.

Left: radial velocity of the ionized gas, corresponding to the main integral field observed. Note the position of the optical nucleus at the upper right of the CIRPASS field, the bulge center, and the intruder nucleus inside the yellow circle. Right: image generated from the continuum in the spectral region of 1.28 microns. The achieved resolution is 0.6 arcseconds.

Using the near infrared integral field spectrograph CIRPASS at Gemini South, Ruben Diaz and an international team of astronomers, have discovered a previously unknown hidden mass concentration that looks like a second nucleus in the starburst galaxy M83. The mass concentration is located at the youngest end of a giant star forming arc near the galaxy's center (Figure 1). This concentration probably represents the wreckage of the nucleus of the smaller galaxy which is being "swallowed" by M83.

This double nucleus arrangement is also associated with complex kinematics near the galaxy center (Figure 2). The masses of the objects were derived from the kinematics of the ionized gas. The nucleus of the intruder body has an estimated mass of about 16 million times the mass of the Sun, compared to 2 million solar masses for the optical "main" nucleus. The two nuclei are about 100 parsecs apart and are probably harboring black holes. Numerical modeling conducted by the team suggest that the two nuclei would coalesce to form a single massive core in about 60 million years.

Located at about 12 million light-years (3.7 megaparsecs) away, Messier 83 is a nearby grand design galaxy displaying intense star forming activity. This activity is likely the result of a recent merger of an accreted satellite galaxy.

See more details in the paper "Hidden Trigger for the Giant Starburst Arc in M83" by Ruben Diaz et al., The Astrophysical Journal, 2006, in press.