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Astron. Astrophys. 343, 367-372 (1999)

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4. The Maximum Entropy Method (MEM) deconvolution

The angular resolution of the total integrated line intensity map has been improved by using a MEM deconvolution algorithm (Wilczek & Drapatz 1985). The SEST HPBW of the [FORMULA] CO observations was [FORMULA] and the observational grid spacing was generally [FORMULA] in the central region, i.e. appropriate for MEM-deconvolution. The best deconvolution was obtained after 14 smoothly converging iterations resulting in a [FORMULA]-value of 5.7 for the final map. The expected resolution of the MEM map is about a third of the beamwidth used, i.e. [FORMULA].

The MEM map is presented in Fig. 5 and Fig. 6. In Fig. 5, the image has been rotated clockwise by [FORMULA], so that the new x- and y-axes are the galaxy's minor and major axes, respectively. Here the deconvolved integrated intensities are displayed in a grey-scale representation to emphasize the detailed structure of the CO distribution. The major axis of the galaxy is the y-axis, which is the same as in Fig. 4, thus facilitating direct comparison of the molecular gas spatial and velocity structure along the major axis.

[FIGURE] Fig. 5. SEST MEM grey-scale map of NGC 1365 (effective resolution [FORMULA]) in the J = 3 - 2 CO line over an approximately [FORMULA]c [FORMULA] [FORMULA] region, centered on the optical nucleus and covering the bar; the image has been rotated clockwise by [FORMULA]; northeast is up and southwest is down

[FIGURE] Fig. 6. Contours: SEST MEM map of NGC 1365 (effective resolution [FORMULA]) in the J = 3 - 2 CO line, centered on the optical nucleus and covering the bar (North is up and East to the left). The contour values are [0.01, 0.05, 0.1, 0.15, 0.3, 0.5, 0.7] [FORMULA] 958 [FORMULA]. Greyscale: B - Gunnz colour index image ([FORMULA] [FORMULA] [FORMULA]), which emphasizes the dust lanes (light areas) as well as hot-star- and H II -regions (dark areas)

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© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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