Near-infrared image of NGC 1068 - Bar-driven star formation and the circumnuclear composition
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Abstract
Images of the inner 1.5' (7.9 kpc) of the Seyfert galaxy NGC 1068 at H (1.6 microns) and K (2.2 microns) both show an impressive stellar bar not found by shorter visual wavelength observations. We discuss a pair of reasons why the core of this galaxy appears so different over a pair of wavelength regimes that are both dominated by stellar photospheric emission: substantial stellar population variations with position or the effects of dust obscuration or both. Due to the close spatial proximity between the bar, the bright mid-infrared dust emission, and the J = 1 -> 0 CO emission, the bar is likely to be directly responsible for confining the molecular gas, leading to extremely active star formation in a partial ring that surrounds the central disk. There may be little star formation within the bar itself, and the visual and near-infrared colors of the bar/disk region indicate that our images are dominated by emission from photospheres of evolved late-type giant or asymptotic giant branch stars, modified by the effects of dust both in absorption and in emission. The ring of near-infrared emission that surrounds the bar, as well as the spiral arms, are bright at K, probably due either to emission from warm dust or from newly formed supergiant stars. We estimate the mass of the central disk and bar of the galaxy and find M_core_ = 2-3 x 10^10^ M_sun_, within a radius of about 15" (1.3 kpc) of the center. We conclude that the high current rate of star formation, about 100 M_sun_ yr^-1^, is due primarily to a large mass of molecular gas, rather than an extremely efficient mechanism of stellar birth.
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