3 Results

The parameters of the 6848 HV components, which were considered as reliable within 4 rms noise, are given in Table 2. Due to the editorial policy of Astronomy and Astrophysics we publish this table, which comprises 61 printed pages, in electronic form. Thus, only a sample page (The first page of Table 2) is given here. The first column of this table gives the HV detection number; the galactic coordinates are given in the second and third columns; the velocities in the Local (LSR) and Galactic (GSR) standard of rest systems are given in the fourth and fifth columns (the latter velocity is defined as V_GSR = V_LSR +220 sin l cos b). The sixth column gives the brightness temperature of the peak. Figure 1 shows the distribution of these HV components, on an Aitoff projection of galactic coordinates, making a distinction between the 6304 positive (black) and the 544 negative (grey) velocities. The cut off observed in the figure, at latitude -50 $\hbox{$^\circ$ }$, in the region of the Magellanic Clouds, the Bridge and their inmediate surroundings, appears there because only those HV components not detected by Mathewson et al. ([1974]) in these structures have been included in Table 2. As is known from the work of Wannier et al. ([1972]) and Mathewson et al. ([1974]), positive velocities are prevalent in the southern sky and most of the HV components are concentrated in large clouds (Giovanelli & Haynes [1976]; Cohen & Ruellas Mayorga [1980]; Morras [1982]; Morras & Bajaja [1983]; Bajaja et al. [1989]; Cavarischia & Morras [1989]; etc.). However, as can be seen in the figure, many HV components with negative velocities are also present in the southern sky. Most of the new detections are associated with previously known HVC complexes, except for a few which seem to be compact and apparently isolated HVCs.

 

 

Table 2: The catalogue

Number	$l(\hbox{$^\circ$ })$	$b(\hbox{$^\circ$ })$	VLSR	VGSR	Tb	Number	$l(\hbox{$^\circ$ })$	$b(\hbox{$^\circ$ })$	VLSR	VGSR	Tb
1	0.0	-86.5	-82	-82	0.65	56	37.6	-83.5	-90	-74	1.49
2	8.1	-86.5	-82	-80	0.17	57	42.3	-83.5	-98	-81	1.29
3	16.2	-86.5	-82	-78	0.16	58	47.0	-83.5	-98	-79	0.95
4	48.6	-86.5	-90	-81	0.13	59	51.7	-83.5	-90	-70	0.25
5	56.7	-86.5	-90	-78	0.12	60	56.4	-83.5	-115	-94	0.55
6	6.3	-86.0	-82	-80	0.68	61	61.1	-83.5	-124	-102	0.63
7	12.6	-86.0	-90	-86	0.71	62	65.8	-83.5	-124	-101	0.14
8	18.9	-86.0	-90	-85	0.46	63	7.6	-83.0	-90	-86	0.61
9	25.2	-86.0	-90	-83	0.41	64	11.4	-83.0	-98	-92	0.62
10	31.5	-86.0	-90	-81	0.25	65	15.2	-83.0	-98	-90	0.94
11	37.8	-86.0	-90	-80	0.29	66	19.0	-83.0	-107	-98	1.12
12	44.1	-86.0	-90	-79	0.15	67	22.8	-83.0	-90	-79	0.81
13	56.7	-86.0	-98	-85	0.18	68	26.6	-83.0	-98	-85	1.17
14	12.6	-85.5	-82	-78	0.35	69	30.4	-83.0	-98	-84	0.73
15	18.9	-85.5	-82	-76	0.46	70	34.2	-83.0	-98	-82	1.09
16	25.2	-85.5	-82	-74	0.36	71	38.0	-83.0	-98	-81	1.44
17	31.5	-85.5	-90	-80	0.21	72	41.8	-83.0	-98	-80	1.86
18	37.8	-85.5	-90	-79	0.21	73	45.6	-83.0	-107	-87	1.56
19	44.1	-85.5	-82	-70	0.18	74	49.4	-83.0	-107	-86	1.51
20	50.4	-85.5	-98	-84	0.11	75	53.2	-83.0	-107	-85	0.59
21	56.7	-85.5	-98	-83	0.16	76	57.0	-83.0	-115	-92	1.26
22	63.0	-85.5	-107	-91	0.14	77	287.8	-83.0	-149	-174	0.16
23	25.2	-85.0	-90	-81	0.30	78	287.8	-83.0	94	68	0.16
24	37.7	-85.0	-107	-95	0.11	79	291.6	-83.0	-132	-156	0.12
25	44.1	-85.0	-98	-84	0.17	80	291.6	-83.0	103	78	0.35
26	50.4	-85.0	-98	-83	0.12	81	348.6	-83.0	-82	-87	1.05
27	56.7	-85.0	-107	-90	0.20	82	352.4	-83.0	-82	-85	0.54
28	303.3	-85.0	102	85	0.15	83	356.2	-83.0	-82	-83	0.54
29	23.5	-84.5	-90	-81	0.45	84	0.0	-82.5	-82	-82	0.57
30	28.2	-84.5	-90	-80	0.99	85	3.8	-82.5	-82	-80	0.60
31	32.9	-84.5	-90	-78	0.62	86	7.6	-82.5	-90	-86	0.50
32	47.0	-84.5	-82	-66	0.21	87	11.4	-82.5	-98	-92	0.57
33	51.7	-84.5	-90	-73	0.13	88	15.2	-82.5	-107	-99	0.92
34	56.4	-84.5	-107	-89	0.18	89	19.0	-82.5	-107	-97	1.07
35	61.1	-84.5	-107	-88	0.17	90	22.8	-82.5	-115	-103	0.69
36	280.1	-84.5	-190	-210	0.11	91	26.6	-82.5	-115	-102	1.31
37	303.6	-84.5	111	93	0.15	92	30.4	-82.5	-115	-100	1.53
38	308.3	-84.5	111	94	0.34	93	34.2	-82.5	-107	-90	1.52
39	313.0	-84.5	103	87	0.15	94	38.0	-82.5	-107	-89	1.02
40	23.5	-84.0	-98	-88	1.15	95	41.8	-82.5	-107	-87	1.95
41	28.2	-84.0	-98	-87	1.70	96	45.6	-82.5	-107	-86	1.73
42	32.9	-84.0	-90	-77	1.71	97	49.4	-82.5	-107	-85	1.58
43	37.6	-84.0	-90	-75	1.00	98	53.2	-82.5	-107	-84	0.91
44	42.3	-84.0	-98	-82	0.41	99	57.0	-82.5	-107	-82	1.39
45	47.0	-84.0	-82	-65	0.30	100	287.8	-82.5	-132	-159	0.12
46	51.7	-84.0	-90	-71	0.10	101	287.8	-82.5	94	66	0.18
47	56.4	-84.0	-107	-87	0.26	102	291.6	-82.5	94	67	0.23
48	61.1	-84.0	-107	-86	0.17	103	348.6	-82.5	-82	-87	1.77
49	284.8	-84.0	-174	-196	0.34	104	352.4	-82.5	-82	-85	1.31
50	303.6	-84.0	111	91	0.24	105	356.2	-82.5	-82	-83	0.98
51	308.3	-84.0	111	92	0.35	106	0.0	-82.0	-82	-82	0.89
52	313.0	-84.0	103	86	0.18	107	3.8	-82.0	-90	-87	0.64
53	23.5	-83.5	-98	-88	1.33	108	7.6	-82.0	-90	-85	0.43
54	28.2	-83.5	-98	-86	1.09	109	11.4	-82.0	-90	-83	0.33
55	32.9	-83.5	-98	-84	1.42	110	15.2	-82.0	-107	-98	0.49

Figure 4: Same as Fig. 1 for the whole sky from Hulsbosch & Wakker ([1988]) and this database

One of the most remarkable features observed in the figure seems to be the ring-like structure, centered at l $\simeq$ 280$^\circ$; b $\simeq$ 20$^\circ$ (Morras et al. [1999]). It includes both of the most prominent and known HVCs with positive velocities in the region, i.e., HVC 267.5+21+222 (Cavarischia & Morras [1989]) and HVC 287.5+22.5+240 (Morras & Bajaja [1983]). Part of this feature can be seen in Putman & Gibson ([1999a], [1999b]).

The whole sample of HV components detected by us, including the Magellanic Stream (MS), are indicating that, at a level of 0.08 K, the fraction of the southern sky covered by HV gas is about 13%. This value is of the same order as the one derived by Wakker ([1991]), who found that at the limit of 0.05 K, 11% (18% when including the MS and the Outer Arm (OA)) of the sky is covered by gas having $\mid V_{LSR}\mid\,\,\geq$ 100 km s^-1. As quoted by Wakker, the MS and the OA contain a substantial part of the HV gas. The highest positive LSR velocity found in the survey is in the detection number 2820 (V_LSR = 412 km s^-1) around $l \simeq 275\hbox{$.\!\!^\circ$ }5$; $b \simeq -30\hbox{$^\circ$ }$. This detection is not isolated since there are eighteen positive detections around it in the velocity range 360 $\leq V_{LSR} \leq$ 412 km s^-1 (see Table 2). This cloud is probably related to the Magellanic System. The highest negative detected velocity is -280 km s^-1 (number 4389, at l = 359 $.\!\!^\circ$5, $b = 0 \hbox{$.\!\!^\circ$ }5$) which could have been originated in the activity of the galactic center.

Figures 2a and b show, in a similar way as in Giovanelli ([1980]), a plot of V_LSR versus galactic longitude, for the IAR data, in both galactic hemispheres. The figures show that most of the HV gas have positive velocities. They also show that the HV detections with negative velocities are predominantly in the southern galactic hemisphere. Comparing these figures with Fig. 1, it can be seen that a large percentage of the negative velocity gas belongs to the Magellanic Stream. The exceptions could be: 1) z-extensions from features connected to the galactic spiral structure which were not identified as such and, therefore, not deleted from the catalog, and 2) the HV components at low galactic longitude which were suggested as being part of the material that is falling towards the Galactic Center at distances of about 20 kpc or more (Mirabel & Morras [1984]). In Figs. 3a and b we have plotted the distribution of the LSR and GSR velocities, respectively, as a function of the galactic longitude, of our and Hulsbosch & Wakker's ([1988]) data. Figure 3a shows that the distributions of the data points are quite different in the different parts of the sky. As was already noticed by Giovanelli ([1980]), the V_LSR diagram of HVCs visible from the northern sky (which correspond to the galactic regions at l $\leq$ 210 $\hbox{$^\circ$ }$) suggests the presence of two distint populations of HVCs, namely, one with relatively low velocities ( $-150 \leq V_{LSR} \leq -80$ km s^-1) and the other one with relatively high negative values. In spite of the larger number of points available in the IAR data, no similar separation into two populations is apparent in the southern sky. The figure also shows that the highest negative velocities, in absolute values, are larger than the highest positive velocities and that both are much larger than the value of the rotational velocity currently assumed for the LSR in the Galaxy. The new IAR data confirm this asymmetry. The upper limit for the positive V_LSR velocities is about +412 km s^-1 while negative velocities reach values as high as -465 km s^-1 at $l \simeq 111\hbox{$^\circ$ }$, $b \simeq -7\hbox{$^\circ$ }$. Figure 3b also shows that large systematic GSR velocities occur after subtraction of the galactic rotation component.

Finally, Fig. 4 shows the spatial distribution for the whole sky of both databases in the same kind of display as in Fig. 1. A small gap is visible between the southern and northern databases, because the IAR data were taken at Dec $\leq -25\hbox{$^\circ$ }$ and Hulsbosch & Wakker data at Dec $\geq -17\hbox{$.\!\!^\circ$ }2$.

Acknowledgements

This work was supported by the Argentinian National Research Council (CONICET) under project P.I.P 4253/96.