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Astron. Astrophys. 326, 59-68 (1997)

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3. Results

3.1. Formaldehyde

The parameters of Gaussian fits to the detected lines are given in Table 2. Spectra are displayed in Fig. 1. Since not all lineshapes are exactly Gaussian, we have also determined the integrated line intensities by adding the channels with emission, calculating the errors from the rms noise per channel. The results are identical, with the errors of the Gaussian typically being slightly larger than the errors obtained using the rms noise.

[FIGURE] Fig. 1. H2 CO spectra for those positions and transitions where we detected, at least tentatively, a line. All spectra have been smoothed to a resolution of 10 [FORMULA] @ The central positions (1950.0) and distances of the galaxies are: NGC 253: [FORMULA] [FORMULA], [FORMULA], 2.5 Mpc, Maffei 2: [FORMULA], [FORMULA], 5 Mpc, IC 342: [FORMULA] [FORMULA], [FORMULA], 1.8 Mpc, M 82: [FORMULA], [FORMULA] [FORMULA], 3.3 Mpc, NGC 6946: [FORMULA], [FORMULA], 11 Mpc.

[TABLE]

Table 2. Parameters of [FORMULA] lines observed toward nearby spiral galaxies. The offsets from the central position are given in arcseconds. Errors (1 [FORMULA]) are given in parenthesis.


We detected mm wavelength [FORMULA] transitions toward all galaxies that were observed, although the detection of the [FORMULA] line in NGC 6946 is tentative.

Toward NGC 253, four of the five transitions observed could be detected; in M 82, all five lines were found. The three positions observed in M 82 are detected in the [FORMULA] line, while the [FORMULA] line is not seen toward the (10 [FORMULA],10 [FORMULA]) offset. Toward this position, the [FORMULA] twin lines thus have different intensities.

In IC 342, four out of six transitions were detected. It is interesting to note that the [FORMULA] transition was detected both toward the central and (tentatively) toward an offset position, while its twin transition, the [FORMULA] line, only observed toward the offset position, was not detected at an rms level of [FORMULA] 12 mK. As in M 82, the intensities of the [FORMULA] twin lines differ. Toward the center, the [FORMULA] line is considerably stronger than its counterpart, the [FORMULA] transition, which is not detected. Toward a northern offset position however, the [FORMULA] line is stronger than the (tentatively detected) [FORMULA] line.

Toward Maffei 2, two out of four lines were found. The profiles show a double peaked structure. This double feature is also visible in the HNC(1-0) transition (Hüttemeister et al. 1995), but is not seen in other molecular species.

3.2. Methanol

The results of Gaussian fits for all observations of single positions are given in Table 3; spectra are displayed in Fig. 2. We also obtained a map of NGC 253 in the [FORMULA] transitions at 145 GHz with a 10 [FORMULA] spacing (Fig. 3).

[FIGURE] Fig. 2. [FORMULA] transitions detected toward NGC 253, Maffei 2, IC 342 and NGC 6964.
[FIGURE] Fig. 3. Map of [FORMULA] ([FORMULA]) toward NGC 253. The upper left panel shows the spectra with a [FORMULA] range of 50-450 kms and [FORMULA] ranging from -70 to 200 mK. The total integrated intensity map is given in the upper left panel; solid contours start at 5.25 K [FORMULA] (3 [FORMULA]) in steps of 1.75 K [FORMULA] (1 [FORMULA]). The dashed contour denotes the 2 [FORMULA] level at 3.5 K [FORMULA] @ In the lower panel, we present channel maps of 50 [FORMULA] width. The first solid contour is at 1.8 K [FORMULA] (3 [FORMULA]), the steps are 0.9 K [FORMULA] @ the dashed contour is 1.2 K [FORMULA] (2 [FORMULA]).

[TABLE]

Table 3. Parameters of [FORMULA] lines observed toward nearby spiral galaxies. The offsets from the central position are given in arcseconds.


As is the case for the [FORMULA] transitions at 96 GHz, the [FORMULA] 'line' is actually a blend of several individual transitions (see Table 1) with frequencies ranging from 145.09375 GHz to 145.13346 GHz, corresponding to a velocity shift of 82 [FORMULA]. We adopted a rest frequency of 145.10323 GHz, corresponding to the [FORMULA] [FORMULA] transition. The [FORMULA] transitions were detected with relative ease in all sources we observed, with the notable exception of M 82. In Maffei 2, the [FORMULA] line was also easily detected. The [FORMULA] transition in NGC 253 is clearly detected.

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© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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