2. New Effelsberg HI observations

Observations were performed in 1987/88 and 1991 using the 100 m radio telescope at Effelsberg which has a half power beam width of 9.3 arcmin for the 21 cm HI line. A FET receiver in the first run and a HEMT receiver in the latter run yielded a total system noise of 60 K and 30 K respectively. The total power mode was applied observing an on-source position followed by an empty reference field which was subtracted from the former in order to reduce instrumental effects. Pointing is believed to be about arcsec rms Some of the optical positions are not known to better than 1 arcmin. However, this is small compared to the telescope beam of 9 arcmin. Galaxies with optical velocities were observed with a velocity range of 1250 km s^-1 (with a resolution of 6 km s^-1). The radial velocity range of the M 81 group overlaps with velocities of local hydrogen. This "confusion" essentially could not be solved. Fainter signals adjacent to the range of velocities of local hydrogen were checked by both frequency modulation and rudimentary mapping. All such features which were suspected to be due to galaxies were found to be extended considerably larger compared to known extended haloes and to show velocity gradients different to what one would expect from a rotating galaxy. Therefore they were considered to be local emission.

We aimed for a detection limit of 10⁶ solar masses in HI at the distance of M 81. For comparison, the dwarf M 81 dwA (Lo & Sargent 1979) has an HI flux of 4.2 Jy km s^-1 (line width of 22 km s^-1) which corresponds to 7.2 10⁶ solar masses.

In order to identify background galaxies, a larger range of radial velocities had to be searched. The 1024 channel autocorrelator was split into four banks of 256 channels using a bandwidth of 6.25 MHz each resulting in a resolution of 6 km s^-1 and a velocity coverage from to . Galaxies not detected in this velocity range were searched at higher radial velocities. In Fig.2 (click here) we present the HI profiles of 65 of the 68 detected galaxies. All emission features at negative radial velocities fall into the range of local HI, only two cases are shown in Table1 (click here) (objects 63 and 65), not shown are 211, K63, and 223. In Table1 we present the observational data: the galaxy's name in Col.1 (where a bare number refers to the catalog of Lo et al., a K to that of Karachentseva, and a BK to the catalog of Börngen et al.) is followed by the 1950 position used for the observation (Col.2), the galaxy type follows in Col.3. HI data: the integrated HI flux (Col.4) in Jy km s^-1 is followed by the peak flux and the rms noise in Col.5. The HI velocity (Col.6) and the linewidths at 50%, 25%, and 20% of the peak (Col.7) are followed by comments (Col.8). A colon (:) in Col.7 marks a rather uncertain value.

Recently van Driel et al. (1997, A.A. submitted) searched for HI emission in 23 dwarfs in the area around M 81; they detected three background galaxies (UGC4998, Kar1N, and UGC5658) and improved the existing upper limits.

  
Figure 2: The detected galaxies are plotted as a function of right ascension and radial velocity in this cone diagram. Only the very center ( km s^-1) is the M 81 group

The typical rms noise was in the range 0.003 to 0.01 K; assuming line widths of 15 or 30 km s^-1 (which are typical for small dwarf galaxies) and three times the rms noise this corresponds to an HI line integral of 0.1 to 0.6 Jy km s^-1 or to 0.3 to 1.8 10⁶ solar masses of HI at the distance of the M 81 group (3.6 Mpc). This represents a detection limit much better than needed for the M 81dwA system. However this galaxy remains at the lower end of the HI fluxes of the detected objects. 68 galaxies (a detection rate of 49%) were detected; most of which are background objects. Figure 2 (click here) shows the radial velocity distribution of these galaxies which is like that of a magnitude limited sample of galaxies rather than that of a group of galaxies at a certain distance.

  

Galaxy position (1950.0) type HIflux       HI-       HI-linewidths comment

name R.A. Dec. [mJy] velocity

K37 03 29 00 57 55 1.2 88 97 99

K38 03 29 00 68 12 3.5 208 330 354

OC 05 18 48 73 16 Irr UGC3297, multiple

201 05 19 00 76 24 diffuse

OD 05 23 18 72 25 Irr 11.7 52 69 71 extremely diffuse

UGC3317 05 27 30 73 42 Irr 12.5 110 119 121 DDO38

202 05 53 06 68 33

5 06 11 06 74 50 Irr smooth

7 06 22 00 70 48 Irr 2.3 97 105 125

7A 06 22 00 82 54 S/Irr UGC3461

10 06 38 36 80 10 S/Irr

11 06 38 42 63 46 Irr 2.4 67 71 72

203 06 40 54 84 57 6.3 203 210 213 diffuse

UGC3522 06 41 00 84 58 S/pec 9.0 201 212 216

204 06 45 36 61 40 4.2 45 55 57 UGC3545

205 06 52 36 61 15 7.1 140 142 146

18 06 59 12 64 08

20 07 01 00 66 01 Irr 2.8 109 148 149

K49 07 02 42 71 57

22 07 03 06 78 30 UGC3671

23 07 03 12 65 22 Irr

25 07 06 36 59 20 Irr 4.9 250:

28 07 10 36 65 03 Irr

31 07 16 48 67 12 Irr

33 07 19 30 60 15 Irr

38 07 23 18 60 59 Irr

42 07 25 48 65 29 Irr

44 07 29 36 73 04 Irr 1.3 78 91 92

45 07 30 54 60 35 Irr 2.7 138 171 193

46 07 34 42 59 20 S

50 07 47 42 73 36 0.8 99 101 122

207 07 58 18 86 17 3.4 58 76 78

UGC 4305 08 14 06 70 52 Irr 168.1 53 67 70 DDO50, HoII

63 08 14 12 63 05 Irr 11.7 19 28 30 DDO71

64 08 16 06 65 51 S/Irr

65 08 16 18 66 18 4.3 42 44 49

K52 08 18 42 71 12 Irr 4.2 19 30 36 M81dwA

UGC4363 08 19 18 74 36 SBc 9.2 64 95 105 DDO51

68 08 19 42 74 31 Irr 3.7 50 70 80

69 08 21 42 79 00 Irr 2.1 24 32 34

70 08 23 00 72 26 Irr DDO53

73 08 32 06 69 58 Irr 13.0 32 47 50 UGC4483

75 08 36 42 69 53 S

UGC 4527 08 38 00 77 06 Irr 3.2 72 140 150

208 08 40 54 78 43 UGC4563/4566

79 08 41 30 78 43 Irr 3.9 117 128 158:

82 08 44 36 73 38 Irr

84 08 47 30 78 27 10.4 187 276 293

210 08 50 48 58 40 6.1 33 38 39

6.2 238 258 263

K53 08 50 48 72 12 diffuse

211 08 53 18 60 57 10.4 33 47 48 diffuse

212 08 59 06 79 06 very diffuse

213 09 02 24 59 33

89 09 09 00 60 12

90A 09 17 30 85 32 S/Irr 1.8 28 48 49

K54 09 17 36 75 57 00 2.4 15 27 30

U4998 09 20 48 68 37 00

93A 09 24 00 86 18 Irr diffuse

UGC5139 09 36 00 71 35 Irr 38.7 29 40 44 DDO63, HoI, K57

 

Galaxy position (1950.0) type HIflux       HI-       HI-linewidths comment

name R.A. Dec. [mJy] velocity

97 09 36 24 58 46 S

1N 09 41 00 69 37 12 4.2 53 69 75

101 09 43 18 71 28 Irr diffuse

BK2 09 43 43 69 30 24

103 09 46 06 67 45

K59 09 47 06 72 19 8.4 140 168 171

BK3 09 49 42 69 12 24

215 09 52 30 58 31

108 09 56 30 63 27

BK4 09 59 56 68 25 18

BK5 10 00 44 68 29 54

UGC5423 10 01 25 70 36 27 3.4 47 58 60

K63 10 01 36 66 46 4.2 27 43 50

K64 10 02 12 68 03

UGC5455 10 04 54 70 53 Irr 1.7 142 182 184 K66

117 10 17 36 71 21

UGC5612 10 20 06 71 08 SB DDO77

120 10 22 48 67 54 1.8 210 240 255

U5658 10 23 54 71 29 1.2

UGC 5666 10 24 48 68 40 S 184 77 91 95 DDO81

123 10 25 06 63 25 Irr

UGC5671 10 25 18 67 04 Irr 4.6 70 91 94 K69

124A 10 26 30 74 30 S 3.6 120 129 132

UGC5688 10 26 36 70 19 SBm 13.0 46 61 76 DDO80

126A 10 27 30 78 04 Irr 3.5 38 45 50 UGC5701

126 10 28 48 70 53 DDO82

126B 10 30 30 79 24 SB 3.2 102 124 127 UGC5728 126B

BK6 10 31 02 66 16 12

127A 10 39 00 57 21 Irr diffuse

UGC5846 10 41 12 60 38 Irr 15.1 48 59 62 DDO86

128 10 41 24 73 10 S

A1045+65 10 45 30 65 02

129 10 46 06 65 00 Irr UGC5932

K72 10 46 18 65 49 Irr 15.4 66 76 79 DDO87

BK7 10 47 07 65 22 24

A1047+65 10 47 12 65 00

K73 10 48 48 69 56 2.7 27 35 37

UGC 5979 10 49 12 68 14 Irr 7.4 90 106 109

134 10 49 54 69 48 Irr diffuse

A1050+65 10 50 30 65 31

BK8 10 51 06 65 28 12

K74 10 59 01 70 32 06 Irr

137A 11 04 12 61 48 Irr 4.1 76 88 90

216 11 14 48 68 04

138 11 19 12 69 25 S/Irr UGC6381

138B 11 24 36 79 16 pec UGC6456

217 11 24 42 79 53

218 11 31 06 76 38

140 11 31 30 74 31

140A 11 32 36 57 05 1.7 84 86 89

UGC 6682 11 40 30 59 23 10.9 68 81 83

219 11 46 12 57 41 4.1 100 112 113

UGC 6816 11 48 06 56 44 13.8 116 136 139

UGC 6912 11 53 36 58 29 15.5 91 127 130

K84 11 54 30 56 33

143A 11 56 54 57 22 2.3 35 44 46

143B 11 57 00 85 26 3.2 100 110 118

143C 11 58 00 79 08 4.0 91 101 104 UGC6996

148 12 10 18 69 13

150 12 11 30 59 50

154A 12 17 42 75 27 1.9 86 95 97

 

Galaxy position (1950.0) type HIflux      HI-      HI-linewidths comment

name R.A. Dec. [mJy] velocity

156 12 22 42 61 22 5.1 70 80 83

158 12 24 24 62 40 2.0 34 40 41 UGC7544

159 12 31 54 64 50 2.2 132 141 156 UGC7730

160 12 32 24 73 56 1.8 56 160 165

K162 12 33 00 58 40

162 12 34 48 74 32

K192 12 41 36 54 14 5.8 66 75 77

164 12 42 00 64 05 2.6 113 150 174:

K195 12 42 10 71 03 46

167 12 43 24 63 18

168 12 46 00 60 33

221 12 47 24 78 39 1.9 86 95 101

222 12 47 54 80 16

170 12 49 00 78 40 UGC7995

223 13 22 24 74 38 8.1 79 93 95

176 13 29 06 79 04

K235 17 01 24 70 20 4.0 26 36 39

1 40 42 45