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Subsections

3 Results

The observational results are summarised in Table 2 and the maps are shown in Figs. 1 to 6, where the intensity scale is $T_{\rm A}^*$ and velocities are shown relative to local standard of rest. Note that although the SEST maps are shown at their observed spacings, the global integrated intensities (Table 2), like the OSO observations, are calculated for a map spacing of one beam (as in Table 1).

  \begin{figure}
\includegraphics[angle=-90,width=10cm]{10582f1.ps}\par\includegraphics[angle=-90,width=10cm]{10582f2.ps}\end{figure} Figure 1: Top: CO  $1\rightarrow 0$ in NGC 1068 over the full mapped region. The spacing is 44'' and the velocity resolution is 10 km s-1. Bottom: HCN  $1\rightarrow 0$ in NGC 1068 over the full mapped region. The spacing is 57'' and the velocity resolution is 40 km s-1


  \begin{figure}
\includegraphics[angle=-90,width=10cm]{10582f3.ps}\par\includegraphics[angle=-90,width=10cm]{10582f4.ps}\end{figure} Figure 2: Top: CO  $1\rightarrow 0$ in NGC 1365 over the full mapped region. The spacing is 44'' and the velocity resolution is 10 km s-1. Bottom: HCN  $1\rightarrow 0$ in NGC 1365 over $68''\times 68''$ of the $136''\times 136''$ region mapped. The spacing is 34'' and the velocity resolution is 40 km s-1


  \begin{figure}
\includegraphics[angle=-90,width=10cm]{10582f5.ps}
\includegraphics[angle=-90,width=10cm]{10582f6.ps}\end{figure} Figure 3: Top: CO  $1\rightarrow 0$ in NGC 2273 over the full mapped region. The spacing is 30'' and the velocity resolution is 80 km s-1. There were no HCN detections in this galaxy. Bottom: HCN  $1\rightarrow 0$ in NGC 4945 over $100''\times 80''$ of the $140''\times 120''$ mapped region. The spacing is 20'' and the velocity resolution is 80 km s-1


  \begin{figure}
\includegraphics[angle=-90,width=10cm]{10582f7.ps}\par\includegraphics[angle=-90,width=10cm]{10582f8.ps}\end{figure} Figure 4: Top: CO  $1\rightarrow 0$ in NGC 5033 over the full mapped region. The spacing is 30'' and the velocity resolution is 80 km s-1. Bottom: HCN  $1\rightarrow 0$ in NGC 5033 over the full mapped region. The spacing is 44'' and the velocity resolution is 80 km s-1. The emission at ( -44'',44'') could correspond to that in position ( -30'',30'') of the CO map


  \begin{figure}
\includegraphics[angle=-90,width=10cm]{10582f9.ps}\par\includegraphics[angle=-90,width=10cm]{10582f10.ps}\end{figure} Figure 5: Top: CO  $1\rightarrow 0$ in Circinus over $120''\times 360''$ of the $120''\times 500''$ mapped region. The antenna temperature increment is 0.1 K, the spacing is 20'' and the velocity increment, of 10 km s-1 resolution, is 500 km s-1. Bottom: HCN  $1\rightarrow 0$ in Circinus over the full mapped region. The spacing is 30'' and the velocity resolution is 100 km s-1


  \begin{figure}
\includegraphics[angle=-90,width=10cm]{10582f11.ps}\par\includegraphics[angle=-90,width=10cm]{10582f12.ps}\end{figure} Figure 6: Top: CO  $1\rightarrow 0$ in NGC 6814 over the full mapped region. The spacing is 44'' and the velocity resolution is 10 km s-1. Bottom: HCN  $1\rightarrow 0$ in NGC 6814 over the full mapped region. The spacing is 57'' and the velocity resolution is 100 km s-1


 

 
Table 2: The 5 galaxies of Curran et al. (2000) with v<4000 km s-1 in which HCN was detected. NGC 4945 and Circinus have been added in order to increase the sample (see Curran et al. 2001b). In the table "Teles.'' refers to the telescope used with the observed date given. The final three main columns refer to the main-beam brightness temperatures, $I_{\rm mb}$ (centre) and $\int I_{\rm mb}$ (global) [K km s-1], measured for the corresponding transition, where the results have been rounded to two figures (because of $\eta _{\rm mb}$) and the errors and upper limits are according to $1\sigma $ (defined by the noise). Concerning the larger uncertainties: In NGC 1365 these arise from differences over the 4 day observing run due to the uncertainty in the focusing of the telescope over this period (April 2000). The resulting values compare well with those previously (Curran et al. 2000). For NGC 4945 the CO  $1\rightarrow 0$ results are from the data of Dahlem et al. (1993) and the CO  $2\rightarrow 1$ data from our own December 1998 observations: The uncertainties are obtained by comparing the central spectra with those of Curran et al. (2001b), after taking into account the slightly different main beam efficiences between the 1988 and post 1993 epochs. In Circinus the same focusing uncertainties responsible in the case of NGC 1365 during the CO observations, caused a reduction in antenna temperature (cf. Curran et al. 1998), thus giving the larger uncertainties. *In NGC 6814 since our map quality is so poor (Fig. 6), this value is taken from Fig. 3 of Curran et al. (2000). We also used our original detection to determine the moment/baseline boxes over the map, giving the values quoted as well as a central value of $0.60\pm 0.15$ K km s-1

Galaxy
Teles. Date(s) HCN  $1\rightarrow 0$ CO  $1\rightarrow 0$ CO  $2\rightarrow 1$
      Centre Global Centre Global Centre Global

NGC 1068
SEST 9/00 & 11/00 $10\pm1$ $13\pm2$ $107\pm3$ $360\pm10$ $133\pm1$ $320\pm10$
NGC 1365 SEST 4/00 $5.5\pm0.5$ $13\pm1$ $100\pm10$ $300\pm30$ $150\pm10$ >300
NGC 2273 OSO 9/00 $0.5\pm0.3$ <0.7 $4\pm1$ $\approx$4 - -
NGC 4945 SEST 12/98 & 6/00 $23\pm1$ $41\pm2$ $510\pm30$ $3400\pm700$ $740\pm40$ $3700\pm500$
NGC 5033 OSO 9/00 $2.2\pm0.7$ $8\pm2$ $30\pm3$ $200\pm60$ - -
Circinus SEST 6/99, 4/00 & 6-7/00 $7\pm1$ $24\pm5$ $150\pm30$ $550\pm100$ $190\pm30$ $2100\pm300$
NGC 6814 SEST 8/00 $0.45\pm0.08^*$ $1.1\pm0.3$ $6.4\pm0.6$ $31\pm3$ $4.4\pm0.6$ $18\pm3$


In Table 3 the luminosities are summmarised. These are calculated by multiplying the average integrated intensity by the area of the map (e.g. as in Sandqvist et al. 1995). Since there may be some ambiguity due to how much area is actually mapped[*], we constrain the value by multiplying the global integrated intensity at single beam spacing over the estimated source size[*], which gives a similar result as calculated by the average integrated intensity over the mapped area.

 

 
Table 3: The luminosities of the near-by sample over the beam, HCN extent of emission and mapped region [ $\times 10^{3}$ K km s-1 kpc2]. Here and in Table 5, D refers to the distance to the galaxy [Mpc] (assuming a Hubble parameter of H0=75 km s-1 Mpc-1) and $L_{\rm FIR}$ [ $10^{10}~L_{\odot}$] is the far infrared luminosity computed using the FIR flux (Lonsdale et al. 1985, Heckman et al. 1989). Note that the CO in NGC 1068 was observed at SEST as opposed to OSO (Curran et al. 2000) and so the larger beam gives a correspondingly larger value of $L_{\rm CO~1\rightarrow0}$ over the central beam

Galaxy
D $L_{\rm HCN~1\rightarrow0}$ $L_{\rm CO~1\rightarrow0}$ $L_{\rm CO~2\rightarrow1}$ $L_{\rm FIR}$
    Beam Map Beam HCN Map Map Beam Map  

NGC 1068
15 $0.12\pm0.03$ 0.91 $\approx$1.1 2.4 0.28 $1.62\pm0.07$ 7.4
NGC 1365 20 $0.13\pm0.01$ $\approx$0.25 $1.4\pm0.1$ $\approx$2.7 $\approx$4.7 $0.54\pm0.07$ $\approx$5.0 6.8
NGC 2273 25 $\approx$0.01 <0.07 $0.05\pm0.01$ $\approx$0.06 $\approx$0.08 - - 0.66
NGC 4945 4 $\approx$0.02 $0.04\pm0.01$ $0.25\pm0.01$ $\approx$0.8 $\approx$1.4 $0.09\pm0.01$ $\approx$0.6 0.91
NGC 5033 12 $0.011\pm0.003$ $0.022\pm0.005$ $0.08\pm0.01$ $\approx$0.3 $0.6\pm0.1$ - - 0.53
Circinus 4 $0.006\pm0.002$ $0.09\pm0.02$ $\approx$0.20 $\approx$0.27 0.03 $\approx$0.35 0.62
NGC 6814 21 $0.011\pm0.002$ $0.035\pm0.006$ $0.10\pm0.01$ $\approx$0.42 $0.017\pm0.002$ $0.19\pm0.03$ 0.66

Average
14 0.04 0.08 0.4 0.8 1.4 0.2 1.6 2.5


In Table 3 the values given are:
1.
The luminosity over the central beam[*], i.e. as in Table 3 of Curran et al. (2000);
2.
Over the full CO mapped region;
3.
Over the HCN[*] mapped region.
The last two values allow us to state the CO/HCN luminosity ratios, not only over the central beam, but also over the whole (molecular gas region) of the galaxy as well as over the region of the HCN emission. We discuss our results for each source below and compare them with previously published CO observations. We are not aware of any large-scale HCN maps of these galaxies.

3.1 NGC 1068

Our value of the global CO luminosity (Table 3) is comparable with that Planesas et al. (1989) who get, also from single dish observations, $L_{{\rm
CO}~1\rightarrow0}=3.8~10^{3}$ K km s-1 kpc2 over a partial map spanning $120''\times 120''$ (cf. Fig. 1). Both results are consistent with those of Young et al. (1995), see Sect. 4.

Concerning HCN, note that the central integrated intensity is similar to that obtained previously at Onsala ($11\pm1$ K km s-1, Curran et al. 2000), although, due to the larger SEST beam, the central luminosity is slightly higher (cf. $0.09\pm0.01~10^{3}$ K km s-1 kpc2).

3.2 NGC 1365

Our CO values agree well with those previously published by Sandqvist et al. (1995); 1.7 103 K km s-1 kpc2 over the central beam and 5.3 103 K km s-1 kpc2 at 20'' spacing over $204''\times 164''$.

Again the central HCN result agrees well with our previous measurement of $0.16\pm0.031~10^{3}$ K km s-1 kpc2 (Curran et al. 2000).

3.3 NGC 2273

We are not aware of any large-scale maps of either CO or HCN in this galaxy. The central CO value agrees well with that of $0.041\pm0.003~10^{3}$ K km s-1 kpc2(Curran et al. 2000).

3.4 NGC 4945

We adopt a distance of 3.7 Mpc (Mauersberger et al. 1996) (although distance estimates to NGC 4945 vary somewhat, e.g. 6.7 Mpc according to Dahlem et al. 1993, Forbes & Norris 1998). The choice of value has no effect on the relative luminosities (i.e. ratios). Note that while the central CO  $1\rightarrow 0$integrated intensity compares well with that obtained by Mauersberger et al. (1996) ($\approx$450 K km s-1), the global value from this data is around 3 times greater than actually published by Dahlem et al.(1993) ($900\pm50$ K km s-1), Table 2.

The central HCN integrated intensity compares well with that of Curran et al. (2001b) ($24\pm2$ K km s-1).

3.5 NGC 5033

Again we are not aware of any large-scale maps, although both the CO and HCN luminosities agree with those previously determined, i.e. $0.093\pm0.006$ and $0.014\pm0.002~10^{3}$ K km s-1 kpc2, respectively (Curran et al. 2000).

Note that due to the relatively close proximity and vastness of this galaxy, we may be far from having global CO values and that the "structure'' in our map may be due to some structure within the galaxy, e.g. spiral arms (Thean et al. 1997 and references therein).

3.6 Circinus

The new values agree well with those from the maps of 1988 and 1993 (see Curran et al. 1998), i.e. $\approx$0.3 103 K km s-1 kpc2 for both the CO $1\rightarrow 0$ and $2\rightarrow 1$transitions.

Concerning the HCN, the central integrated intensity agrees (within uncertainties) with that of Curran et al. (2001b), i.e. $5.2\pm0.8$ K km s-1. Note that (blue-shifted) HCN may also be detected at -60'' along the minor axis, which corresponds to the (approaching) NW molecular outflow (Curran et al. 1999) and where a tentative detection of HCO+ has been made (see Curran 2000a).

3.7 NGC 6814

With no large-scale maps available, again the CO luminosity agrees with that previously obtained, i.e. $0.118\pm0.002~10^{3}$ K km s-1 kpc2, although due to the weak emission (a central integrated intensity of $\approx$0.5 K km s-1, Curran et al. 2000), no HCN was detected over the time allocated to map this molecule[*].


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