The nature of the two nuclei in the young merger NGC 3256: an obscured AGN?

Details The nature of the two nuclei in the young merger NGC 3256: an obscured AGN? The nature of the two nuclei in the young merger NGC 3256: an obscured AGN?

Jan 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...305..107k&link_type=abstract

Astronomy and Astrophysics, v.305, p.107

Astronomy and Astrophysics

Astrophysics

23

Galaxies: Individual (Ngc 3256), Galaxies: Interactions, Galaxies: Nuclei, Galaxies: Seyfert, Galaxies: Starburst, Infrared: Galaxies

Scientific paper

We present new high resolution images of the starburst galaxy NGC 3256 in the near-infrared broad band continuum (JHK'L') and in the H_2_ 1-0 S(1) 2.121μm, Brγ 2.165μm and [Fe II] 1.644μm lines. The line images are dominated by a primary peak with a secondary peak to the south and fainter extended emission covering ~10-20arcsec^2^ (~2.7-5.4kpc^2^). The Brγ , [Fe II] and radio morphology are well correlated, while the H_2_ emission is least enhanced on the primary peak, and its morphology is clearly different from the other lines. Several methods were used to estimate the effects of extinction, which we derive to be A_V_~2.4 and ~5.3mag (continuum), and A_V_~7.8 and ~10.7mag (emission lines), towards the northern and southern peaks, respectively. The difference in these values probably reflects the uncertainty inherent in each method. Corrected for this extinction, luminosities of the peaks become approximately equal in H_2_ , whereas the northern peak still dominates the Brγ , [Fe II] and JHK' emission. The L' band image shows two equally bright emission peaks, strongly supporting the previous radio evidence for the existence of two nuclei in this relatively recent merger. Because of the large, possibly underestimated extinction, the S nucleus may even be the intrinsically brighter nucleus; mid-infrared imaging is needed to estimate the relative luminosities. From the Brγ and [Fe II] luminosities, we derive high mass star forming rates of 1.3 and 0.4Msun_yr^-1^, total star formation rates of 6.7 and 1.8Msun_yr^-1^ and SN rates of 0.5 and 0.3yr^-1^, for the N and S nucleus, respectively. Finally, we discuss evidence for and against the existence of a heavily obscured Seyfert nucleus in the S, as suggested by the infrared line ratios, low Brγ luminosity, shallow CO 2.3μm feature and the large unresolved soft X-ray luminosity. Near-infrared spectroscopy of coronal lines and mid-IR spectroscopy on the S nucleus, and spatially resolved X-ray observations are needed to definitely answer this question.

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