3 The detected sources

Throughout NGC1569 we find at 1.4GHz six sources, M-1 to M-6 listed in Table 2, including their spectral indices $\alpha$ ( $S \propto \nu^{{\alpha}}$, 1.4-5 GHz). The sources are unresolved, except for the source M-6. Because of the (unexplained) high noise of the observations we do not detect any source above the 3$\sigma$ detection threshold at 5GHz. The MERLIN sources detected at 1.4 GHz are also present in the VLA observations of vdHGI.

Table 3 gives the positions where point-like emission of $\sim$0.1mJy/beam peak intensity ($\approx$4$\sigma$$_{\rm n}$) is observed with MERLIN at 1.4GHz. Without further observations we are unable to determine whether or not this emission is real, and associated with an otherwise identified source. However, at positions M-b,c,d the VLA (vdHGI) detects extended emission at a level of 0.7 mJy/beam extending 2'' to the west (possibly containing M-b) and 2'' to the east (possibly containing M-c,d).

The MERLIN-detected sources are shown in Fig. 1; detailed images are shown in Figs. 2 to 7. The stellar clusters located in the surroundings of the sources are listed in Table 4 below. In Figs. 2 to 7 the clusters are identified by the number in the list of Hunter et al. (2000).

We will now discuss the sources relevant to our understanding of the conditions in the galaxy's interstellar medium in more detail.

 

 

Table 3: Tentative 1.4GHz detections with MERLIN.

Source	RA(2000)	Dec(2000)	Figure
	[h m s]	[ $\hbox{$^\circ$ }$ ' '']
M-a	4 30 46.64	64 51 4.7	1
M-b	4 30 46.68	64 51 0.1	1, 2
M-c	4 30 47.08	64 51 0.9	1, 2
M-d	4 30 47.11	64 51 0.7	1, 2

3.1 Sources in the environment of SSC A and B

VLA-8(Fig. 1): this non-thermal radio source with $\alpha = -0.24 \pm 0.10$ is found at $\sim$30pc to the South-West of SSC-A at RA 04$^{\rm h}$30$^{\rm m}$48.0$^{\rm s}$, Dec 64 $\hbox{$^\circ$ }$50'56.3'' (J2000). The peak flux densities are $S(1.4\rm\,GHz) = 0.479 \pm 0.032$ mJy, and $S(5\rm\,GHz) = 0.357 \pm 0.022$ mJy. The source is probably extended ($\sim$20pc) and of low surface brightness since it is not seen with MERLIN; it may be a SNR based on its spectral appearance and extent (ruling out H II regions and RSNe, respectively). The stellar cluster No.18 is located at $\sim$10pc to the North of the source (Table 4). In a region of 2 $''\times2''$ ( $\rm 22\,pc\times22$pc) centered on SSC-A, Heckman et al. (1995) find H$_{\alpha }$ emission of 1400-2300kms^-1 zero-full-width velocity which may be evidence of a Balmer-dominated SNR. In view of the positional uncertainties, it is unclear whether both observations refer to the same object.

3.2 Sources near cluster C and the CO cloud

VLA-16(Fig. 1): this source is found $\sim$25pc to the North of cluster C (No. 10 of Hunter et al. 2000; Table 4). The source is located at RA 4$^{\rm h}$30$^{\rm m}$47.2$^{\rm s}$, Dec 64 $\hbox{$^\circ$ }$51'04.5'' (J2000). It has flux densities of $S(\rm 1.4\,GHz) = 0.681 \pm 0.046$ mJy, and $S(\rm 5\,GHz) = 0.494 \pm 0.049$ mJy, and a non-thermal spectral index of $\alpha = -0.27 \pm 0.14$. This source, not seen with MERLIN, could also be an extended ($\sim$15pc) low surface brightness SNR.

M-1(Fig. 2): when compared with the HST, H$_{\alpha }$, CO and star cluster images shown by Taylor et al. (1999) and Hunter et al. (2000), this source lies within, respectively, 3pc and 12pc distance from the clusters No.6 and No.7 (Hunter et al. 2000; Table 4). This source is located at the North-Eastern edge of a large molecular cloud complex (No.3,2,1 in Taylor et al. 1999) and coincides with the H II region No.2 of Waller (1991). The source is observed with the VLA (VLA-19) and has a thermal spectral index. M-1 may be double and a second source (cf. Fig. 2) may exist just to the North of the central stellar cluster No.6 of Hunter et al. (2000). In this area of the extended H II region No.2 (Waller 1991) lie also the tentative sources M-b,c,d (Table 3).

M-2(Fig. 3): this source is located at the South-Eastern side just outside the large molecular cloud complex (3,2,1) of Taylor et al. (1999). The source lies at a distance of $\sim$15pc from the cluster No.5 (Hunter et al. 2000; Table 4). The source was detected with the VLA (VLA-10) and has a non-thermal spectral index. It is most likely a RSN or a small SNR.

VLA-11: this non-thermal source with $\alpha = -0.74 \pm 0.09$ is located some $\sim$100pc South of C and at the South-Western side just outside the molecular cloud complex (3,2,1) of Taylor et al. (1999) at RA 4$^{\rm h}$30$^{\rm m}$45.79$^{\rm s}$, Dec 64 $\hbox{$^\circ$ }$50'58.3'' (J2000), and with flux densities $S(1.4\rm\,GHz) = 0.541 \pm 0.019$ mJy, $S(5\rm\,GHz) = 0.223 \pm 0.018$ mJy. This source is not detected with MERLIN.

3.3 Other sources

M-3(Fig. 4): this source is located $\sim$2pc to the West of cluster No.8 of Hunter et al. (2000; Table 4). The source is also detected by the VLA (VLA-15). It has a non-thermal spectral index and is most likely a RSN or small SNR.

M-4,5(Figs. 5, 6): the source M-4 (VLA-7) is a thermal source close to the H II region No.5 (Waller 1991); the source M-5 (VLA-6) is a non-thermal source with some thermal emission.

M-6(Fig. 7): this source lies in the area of the H II regions 6,7 and 9 identified by Waller (1991), but does not coincide with any of these objects nor with the H II complex observed by Seaquist et al. (1976). The MERLIN 1.4 GHz observation shows an extended source of $\sim$17pc diameter. The source is detected with the VLA (VLA-1) and has a non-thermal spectrum ( $\alpha = -0.55 \pm 0.02$). In this area a SNR is detected based on [FeII] line emission (Labrie & Pritchet 1998), however, the astrometric precision of this observation is not sufficient to confidently establish full correspondence.

Approximately 500pc to the East of A and B, the VLA observations reveal 3 to 4 non-thermal sources (VLA-2,3,4,5; S(1.4 GHz) 0.4 mJy) in the H II region complex at RA $\approx$ 4$^{\rm h}$30$^{\rm m}$52$^{\rm s}$, Dec 64 $\hbox{$^\circ$ }$50'45'' (J2000) (see Seaquist et al. 1976) which are not seen by MERLIN. If extended, these sources are certainly below the detection limit of MERLIN.

Figure 7: 1.4GHz MERLIN observation of source M-6 (Table 2) associated with the the H II regions 7 and 6 identified by Waller (1991). The contour interval is in steps of 30$\mu$Jy/beam with the first negative and positive contour at 50$\mu$Jy/beam (=2$\sigma$$_{\rm n}$). The synthesized beam is shown in the lower right corner. The cross indicates an intermediate-sized stellar cluster No.45 (Table 4).