4. Results of the Galactic Center Survey

 

In this section, we present the results of the Galactic Center Survey. In Fig. 4 (click here), the full set of survey spectra is given. The mean rms noise per channel of all 357 spectra is . Note that the strongest emission, which appears in the inner Galactic center region at velocities more negative than -200 , is attributed to the ) line.

  
Figure 4: The full set of spectra of the Galactic Center Survey. The x-axis of the spectra is with respect to the line frequency and ranges from -375.2 to +375.2 , the y-axis is and ranges from -0.15 to 0.85 K. The latitude range is, in every case, from b = -09 to +075. Note that the strongest emission, which appears in the inner Galactic center region at velocities lower than -200 , is caused by the ) line. a) Longitude range from l = 36 to 255

 
Figure 4: b) Longitude range from l = 24 to 135

 
Figure 4: c) Longitude range from l = 12 to 015

 
Figure 4: d) Longitude range from l = 00 to -105

4.1. The integrated intensity

  
Figure 5: The integrated intensity of the Galactic center region in . The velocity over which the intensity is integrated ranges from -225.0 to +225.0 . The solid contour levels range from 3.9 to 28.05 in steps of 3.45 K where the lowest level is the -value. The dashed contour is at 2.6 K which is the -value. The circle in the lower left corner of the plot indicates the beam size of 92

   

Source Radio Equatorial Coordinates Galactic Coordinates

name name R.A.(1950) Decl.(1950) SgrA

4.1.1. The total integrated emission

In Fig. 5 (click here), we show a contour map of the integrated intensity, , of the line, covering the velocity range from -225.0 to +225.0 , i.e., the complete emission range of the Galactic center region. To produce smooth contours in the contour map the number of points in the data base for the contour map was increased by a factor of 5 per axis with a standard CLASS interpolation routine, resulting in an increase in the density of points by a factor of 25. The main emission regions coincide with the known continuum and CO peaks SgrA (with the extension to SgrB1), SgrB2 (Lequeux 1962), SgrC and SgrD (Hoffmann et al. 1971). In addition, Clump 2 (Bania 1977) in the range from l=30 to 35 is weak but visible. The most prominent source by far, both in Fig. 5 (click here) and, even more strikingly, in the channel maps (Fig. 6 (click here)) is SgrB2. The sources G 0.5 0.0 and G 0.9+0.1 (Downes & Maxwell 1966), which are distinct emission peaks in radio continuum maps (see e.g. Reich et al. 1984 at 2.695 GHz, Altenhoff et al. 1978 at 4.875 GHz, and Handa et al. 1987 at 10.05 and 10.55 GHz), are not visible. In Table 2 (click here), the coordinates of the main radio and FIR continuum emission sources are summarized.

4.1.2. Channel maps of width

 

In Fig. 6 (click here), we present channel maps integrated over 50  windows. The central velocity of these maps ranges from -200  to +200 .

At -200 , no is visible above the noise; the feature at (l=10, b=-015) is caused by the ) line the emission of which extends to more than +100  at this position (compare the respective feature of in the top panel of Fig. 6 (click here)c).

At -150  and at -100 , only marginal emission is visible, mainly at SgrC (l=-05, b=00) and between l=0 and 1 at about b=-03.

At -50 , the rather widespread emission of the 3-kpc-arm (Rougoor & Oort 1960) can be seen; this peaks at (l=-04, b=-01) and at (l=06, b=-03). The weak emission maximum in the area of l=08 to 11 and b=-02 to +015 might correspond to the radio continuum source G 0.9+0.1.

At 0 , the Galactic center emission is superposed on the emission of local gas. The local component can be distinguished by inspecting the individual spectra; the linewidth of this emission is comparatively narrow (  FWHM) whereas Galactic center emission is characterized by its broad (  FWHM) lines. From this, it is clear that the emission in the area of l=-03 to 06 and b=-09 to -03 is almost exclusively of local origin whereas the emission elsewhere is dominated by Galactic center gas. The Galactic center gas is most widespread and uniformly distributed at this velocity. The Galactic center emission peaks at SgrA (l=00, b=00), at (l=075, b=-01), somewhat east of SgrB2, and at (l=-06, b=-015) (roughly SgrC). The emission covers the inner region of the Galactic center completely, as seen in the contour map of the total emission of the Galactic center region (Fig. 5 (click here)). In addition, the emission extends to b values up to +06 and fills the gap between the inner region and Clump 2. It is possible that the remaining narrow gap at l=24 is connected to Clump 2 by the weak emission at -50  at this longitude. Clump 2 has weak but clearly visible emission in the area of l=26 to 30, b=-015 to +035 and around (l=26, b=00).

  
Figure 6: The integrated intensity of the Galactic center region in in velocity intervals of 50  width. The solid contour levels start at 1.3 K, which is the -level, and increase in steps of 1.15 K. The dashed contour is at 0.8667 K which is the -value. The circle in the lower left corner of the plots indicates the beam size of 92. a) At the top the integrated intensity in the velocity range from -225.0 to -175.0  is plotted, in the middle panel the velocity ranges from -175.0 to -125.0 , and at the bottom the velocity range from -125 to -75.0  is shown

 
Figure 6: b) At the top the integrated intensity of the velocity range from -75.0 to -25  is plotted, in the middle the velocity ranges from -25 to +25 , and at the bottom the velocity range from +25 to +75.0  is shown

 
Figure 6: c) At the top the integrated intensity of the velocity range from +75.0 to +125  is plotted, in the middle the velocity ranges from +125 to +175 , and at the bottom the velocity range from +175 to +225.0  is shown

At +50 , SgrB2 is the most prominent emission feature by far. It peaks at (l=068, b=-006), and it is, with an integrated intensity of more than 15 K, the strongest emission feature in all the channel maps. Compared to SgrB2, the emission from SgrA is rather weak, and SgrC and D are only marginally visible. Again, Clump 2 appears weak but is clearly visible. However, at this velocity the emission peaks at (l=315, b=+06) and covers the area of l=30 to 33, b=+03 to +07 with extensions to (l=28, b=+01) and (l=36, b=+03). In addition, the emission of Clump 2 might be extended to b values beyond the map at (l=31, b=+075) and to larger l values at (l=36, b=+03).

At +100 , SgrD is the dominant emission feature (called the l=15-complex in Bally et al. 1988). It peaks at (l=10, b=00) and ranges from 05 to 15 in l and from -03 to +01 in b. At longitudes greater than 10, this emission feature curves upward to a latitude of +04 at l=135. Apart from this main feature, some emission is visible near SgrA. Clump 2 peaks in the area of l=28 to 34, b=-03 to 00 with an extension to (l=315, b=+03). Some additional emission in the area of l=30 to 34, b=+055 to +075 seems to be present.

At +150 , nearly no emission was observed at our detection level. Some marginal features appear between SgrA and SgrC. However, Clump 2 is still visible in the area of l=285 to 335, b=+005 to +04.

At +200 , no emission is visible.

The channels at very high velocity (+250  to +350 ) were also checked for emission. As expected from the 12 data, with one exception they show no emission in : At +250  some marginal emission might be visible in the area of l=19 to 24, b=-03 to -01.

4.2. Longitude-velocity plots

4.2.1. Plots integrated over ranges of latitude

 

In Fig. 7 (click here), the intensity integrated over two latitude ranges is plotted. These longitude-velocity plots (lv-plots) show the velocity distribution of the emission a) in the complete latitude range from -090 to +075 and b) in the inner latitude range from -030 to +030. To improve the signal-to-noise ratio, four velocity channels were averaged so that the velocity resolution is about 11.7 . The dots in the plot indicate the remaining data points in l and v. The data for the contour maps were interpolated between these points, increasing the number of points by a factor of 5 per axis. The -value was calculated using the following equation:
 
where is the number of latitude points covered by the latitude integration -- which was 12 in case a) and 5 in case b) -- and is the spacing in latitude -- which was 015 in both cases. The mean rms per channel used was 16.85 mK, the value reached by averaging four velocity channels.

  
Figure 7: Longitude-velocity plots showing the velocity distribution of the emission. Note that the strong emission, which appears at velocities lower than -200 , is caused by the ) line. a) The velocity distribution in the complete latitude range from -090 to +075. The solid contour levels range from 0.0282 to 0.2506 in steps of 0.0278 Karcdeg where the lowest level is the -value. The dashed contour is at 0.0188 Karcdeg which is the -value. b) The velocity distribution in the inner latitude range from -030 to +030. The solid contour levels range from 0.018 to 0.222 in steps of 0.017 Karcdeg where the lowest level is the -value. The dashed contour is at 0.012 Karcdeg which is the -value

In general, both plots show the same features. In plot a) one finds that Clump 2, which is more extended in b, is more widespread in the lv-space whereas in plot b) the features toward SgrA to D, which are more concentrated toward the plane, stand out more clearly. The emission of local gas and of Galactic center gas almost at rest with respect to the LSR frame appears mainly in a line from l=-105 to +18 at about -5 . At +18, the emission shifts to a center of about +10  and continues to +33 at about +20 . The 3-kpc-arm at about -50  is visible in the range from -06 to +15 but the emission is not very homogeneous. In the range from -06 to 00 (SgrC) and from +06 to +15 (SgrB2 and D), there are large transition areas between the 3-kpc-arm gas and the gas at rest with respect to the LSR frame. The most prominent feature is the diagonal chain of emission centers ranging from SgrC (6,  ) over SgrA (0,  ), SgrB1 (3,  ), SgrB2 (65,  ) to SgrD (3,  ). Note the weak tail of emission which ranges from SgrA to about (3,  ). At (8,  ), there appears a weak and isolated emission feature which, however, is rather strong in the ) line. From the channel maps (Fig. 6 (click here)b), it is clear that this feature peaks at 15. The main peak of Clump 2 appears at (8,  ), and the emission is extended to (2,  ). At the so-called forbidden velocities (  for l > 0 and   for l < 0) only little C¹⁸O emission is visible. Further significant maxima are located at (5,  ), (1,  ), and (7,  ). Note also the 2-emission features at (5,  ) and (0,  ). The ) emission at velocities lower than -220  in the reference frame will be discussed in Sect. 5 (click here).

4.2.2. Latitude cuts

 

In Fig. 8 (click here), we have plotted the intensity for l versus at a number of individual latitudes. These lv-plots show the spectra (smoothed in velocity as described above) of the emission in a contour map representation covering the whole longitude range. The levels shown are the intensities of the spectra obtained at a certain latitude multiplied by the latitude spacing of the map. The plotted latitude cuts range from b = -045 to b = +030 containing the most interesting features.

  
Figure 8: Longitude-velocity plots of cuts, at single b, showing the (smoothed) spectra of the emission in a contour map representation. The solid contour levels start at 0.0081 Karcdeg (corresponding to 0.054 K), which is the -level, and increase in steps of 0.0075 Karcdeg (corresponding to 0.050 K). The dashed contour is at 0.0054 Karcdeg (corresponding to 0.036 K) which is the 2-value. Note that the strong emission, which appears at velocities lower than -200 , is caused by the ) line. a) In the top panel, the lv-plot at b = -045 is shown. b) In the bottom panel, the lv-plot at b = -030 is shown

 
Figure 8: c) In the top panel, the lv-plot of b = -015 is shown. d) In the bottom panel, the lv-plot of b = 00 is shown

 
Figure 8: e) In the top panel, the lv-plot of b = +015 is shown. f) In the bottom panel, the lv-plot of b = +030 is shown

At b = -045 (plot a) in Fig. 8 (click here), the emission of local origin showing a double peak in v is the prominent feature (see the description of the 0-channel-map in Sect. 4.1.2 (click here)). It peaks at about -5  and +15 .

The features at b = -030 (plot b) in Fig. 8 (click here) show a rather different shape compared to the integrated plots. SgrB2 peaks at -55  (the 3 kpc-arm), and the emission extends from -130  to +65 . In longitude the emission extends to SgrD, with a velocity shift to 0 . An inspection of the spectra makes clear that the two weak lines of emission at about -5  and +15  between SgrA and B2 are again of local origin. At negative longitudes SgrC is weakly visible, ranging from about +20  at l = -05 to about -20  at l = -09.

At b = -015 (plot c) in Fig. 8 (click here), the emission features as described in Sect. 4.2.1 (click here) are present. The more prominent features are the 3-kpc-arm emission, SgrB1 and B2. Note, that at this latitude the ) emission appears abruptly whereas it is not visible at more negative latitudes.

At b = 00 (plot d) in Fig. 8 (click here), the emission features as described in Sect. 4.2.1 (click here) are again present. At this latitude the more prominent features are the emission line at -5  ranging from l = -09 to l = +15, the diagonal chain of emission centers ranging from SgrC to SgrA to SgrB2 and further to SgrD, and the emission associated with SgrA extended to +95 . Note that at this latitude SgrB1 does not appear in this chain. The presence of this feature in the plot at b = -015 and its absence at b = 00 cannot be distinguished in the plot integrated over a range of latitudes.

  
Figure 9: Latitude-velocity plots showing the velocity distribution of the emission. a) The velocity distribution in the longitude range from -105 to +2025 which represents the inner Galactic center region. The solid contour levels range from 0.039 to 0.429 in steps of 0.039 Karcdeg where the lowest level is the -value. The dashed contour is at 0.026 Karcdeg which is the -value. b) The velocity distribution in the longitude range from +2025 to +360 which represents Clump 2. The solid contour levels range from 0.027 to 0.108 in steps of 0.027 Karcdeg where the lowest level is the -value. The dashed contour is at 0.018 Karcdeg which is the -value

At b = +015 (plot e) in Fig. 8 (click here), the emission line at -5  is visible, including the velocity shift at +18 to roughly +10  and the continuation to +31 at about +20 . In addition, SgrD shows an isolated feature at about +95  and a loop-like structure that seems to connect its zero velocity emission to the zero velocity emission of SgrB2, passing over -40  at l = 09. Clump 2 has an additional emission feature at about +150 . Note that at higher latitudes than b = 00 the ) emission disappears abruptly; only at SgrD some emission appears at those latitudes.

The emission at b = +030 (plot f) in Fig. 8 (click here) looks similar to that at b = +015, except that it is somewhat weaker.

4.3. Latitude-velocity plots

In Fig. 9 (click here), we have plotted the intensity integrated over two longitude ranges. These latitude-velocity plots (bv-plots) show the velocity distribution of the emission a) in the longitude range from -105 to +2025, which represents the inner Galactic center region, and b) in the longitude range from +2025 to +360 which represents Clump 2. The averaging of velocity channels, data interpolation and determination of the 1-level were done following the procedures used for the lv-plots.

Plot a) in Fig. 9 (click here) displays the inner Galactic center region. It shows a cross-shaped emission feature in . The horizontal bar follows the b = 0 line in the range from -80  to +110 . SgrC, A, and B2, respectively, can be seen as peaks at -40, -5, and +55 . The extension toward +110  represents SgrD. The vertical bar of the cross toward negative latitude seems to represent gas of local origin. It is partly due to the double-peaked local gas feature already discussed in Sect. 4.2.2 (click here) (plots a) and b) in Fig. 8 (click here). But in general this vertical bar shows the larger b-extension of the emission around v = 0  (see Fig. 6 (click here)b).

In Plot b) of Fig. 9 (click here) mainly Clump 2 is visible. The emission shows the large extent of Clump 2 to positive latitudes at about +15 . In addition, the higher velocity component of Clump 2 becomes visible near (b = -015, v = +105 ).