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198 3MNRAS.205.1191M Mon. Not. R. Astr. Soc. (1983) 205 Mon. Not. R. astr. Soc. (1983) 205,1191-1205 3MNRAS.205.1191M Neutral hydrogen in the haloes of the Galaxy and 198 the LMC R. X. McGee and Lynette M. Newton Division of Radiophysics, CSIRO, PO Box 76, Epping, NSW 2121, Australia Donald C. Morton Anglo-Australian Observatory, PO Box 296, Epping, NSW 2121, Australia Received 1983 April 26; in original form 1982 November 19 Summary. A new low-noise 21-cm line receiver installed on the Parkes 64-m telescope has led to the detection of the Hi counterpart of ionized and neutral elements in the galactic halo. The observations show that very low- intensity Hi exists in three regions at average LSR radial velocities of —40, + 59 and + ISlkms"1 which, if the halo is corotating with the disc, can be interpreted as components of the galactic halo at considerable distances below the galactic plane. Two additional groups of low-intensity Hi features at heliocentric velocities of + 197 and +360kms_1 possibly indicate a similar halo around the Large Magellanic Cloud. Comparison of the column densities obtained by the ultraviolet observa- tions with the International Ultraviolet Explorer and the present H i observa- tion show that Oi in the halo is depleted by a factor between 2 and 10 compared to solar abundance. Of the elements which should be dominant in H i regions A1 and Si are depleted by a factor of < 2 and Fe is close to the solar abundance. Ground-based data on Can show that it is depleted by factors of 4 to 3000, with the greater values occurring at velocities associated with the galactic disc and the Magellanic Clouds. Thus Ca appears to follow the typical pattern of being depleted less in the halo than in the spiral arms. 1 Introduction In the past few years evidence has been mounting for the presence of gaseous haloes around our own Galaxy and the Magellanic Clouds. Savage & de Boer (1981) have examined far- ultraviolet spectra from the International Ultraviolet Explorer {IUE) taken in the directions of stars in the Large Magellanic Cloud (LMC), and note that the weaker low-ion-stage lines show a component structure with strong features near + 60 and +130 km s"1 with respect to the local standard of rest (LSR). Gondhalekar et al (1980) have detected UV components at + 54 and + 134km s_1 in two LMC stars; Songaila (1981) found visible absorption lines at ~+65 and +133kms-1 in four LMC stars. As Savage & de Boer point out, the neutral oxygen they found at these velocities implies that neutral hydrogen should also be present. However, extrapolating the solar abundance ratios would give an Hi column density of © Royal Astronomical Society • Provided by the NASA Astrophysics Data System 1192 R. X. McGee, L. M. Newton and D. C. Morton ~ 4 x 1018 atom cm"2 — at least an order of magnitude below the Hi signal levels previously detected in these directions. A low-noise 21-cm receiver now installed on the Parkes 64-m radio telescope has made it possible for signals from such tenuous H i to be detected in a 3MNRAS.205.1191M reasonable observing time. We report here a series of Hi observations which strongly 198 corroborate the conclusions of Savage & de Boer (1981), especially with respect to inter- mediate and high-velocity gas components, that a galactic halo exists towards the Magellanic Clouds. In addition we have found gas at +197 and +360kms"1 (heliocentric) which we believe indicates a halo around the LMC. 2 Equipment and observations The 21-cm receiver has a 1HE hybrid-mode feed horn with orthogonal probes which act as inputs to two separate channels. The first two stages of each channel are FET amplifiers, cryogenically cooled to 20 K. The system temperatures on cold sky were found to be 44 and 46 K. Intensity calibrations and telescope beam-size measurements were made on the sources Hydra A (S^i =43.5 Jy) and 1934-63 (S21 = 15.4 Jy). The relation between flux density 1 and antenna temperature was S/TA = 1.62JyK' ; the beam efficiency T7B was 0.8. The means of the beamwidths at halfpower were each 14.9 ± 0.1 arcmin. The spectrometer was the 1024-channel digital correlator arranged in configurations to give bandwidths of equivalent radial velocity widths of 0.82, 1.65, 4.1 and 8.2km s"1 per channel. The observations were made in four separate sessions on the telescope. In the first they were in the directions of the nine stars in the Magellanic Clouds reported by Savage & de Boer (1981). The two narrow bandwidths were used (being later Hanning-smoothed to equivalent widths of 1.6 and 3.3kms"1) with velocity ranges of —100 to + lOOkms"1 and — 20 to +400kms_1 respectively. Reference spectra were obtained by switching to a frequency range 2.5 MHz below the observing band. Sufficient numbers of difference spectra, each ‘on and off’ integrated for 15 min, were averaged until the noise level was reduced to a peak-to-peak value of 0.03 K in most cases. The other three sets of data were obtained incidentally during observations of particular objects in the LMC on two occasions (for J. Meaburn, University of Manchester), and in an unsuccessful attempt to detect H1 absorption of extragalactic sources by the Magellanic Stream (for M. V. Pension, Royal Greenwich Observatory). In these cases the bandwidth of 4.1 km s”1 per channel was used with an overall range of -450km s'1. Simultaneous observations were made at 8.2 km s"1 per channel using another quadrant of the correlator. Less integration time was available and the noise levels achieved were worse than in the first set by a factor of 2, but they were still more than adequate to detect the low-intensity Hi features discussed. Seventy-eight profiles have been analysed in the region of sky containing the SMC, part of the Magellanic Stream and the LMC — from galactic longitudes / = 302° to 277° and at galactic latitudes between b = — 30° and — 58°, well clear of the galactic plane. In reporting these low-level 21-cm lines we have considered the possibility of contamina- tion by stray radiation, i.e. 21-cm line radiation entering the receiver through the sidelobes of the telescope from strong H1 sources that may be elsewhere in the sky when the observa- tions are being made. Although we have not had the opportunity of making observations at different times throughout the year with a view of recognizing and eliminating stray radia- tion, our calculations lead us to believe that, apart from contributions to the local profile, the contamination of the features we present here is not serious. Since we cannot rule out the possibility of contamination, we have requested telescope time to investigate this problem. © Royal Astronomical Society • Provided by the NASA Astrophysics Data System Hydrogen in the Galaxy and LMC 1193 3 The data Wideband (10MHz, equivalent to 2100kms"1) observations taken in conjunction with the observations discussed here enabled us to establish and check accurate baseHnes for the 3MNRAS.205.1191M profiles. In displaying the data in Fig. 1 we have truncated the strong Hi signals from the 198 LUX. lSR Heliocentric Radial Velocity (km s_1) Figure 1. Representative HI (21 cm) profiles from directions towards: SMC (a); Magellanic Stream (e), (f); LMC (b), (c), (d), (g), (h). Low-intensity features only are shown, with Gaussian curves superimposed. © Royal Astronomical Society • Provided by the NASA Astrophysics Data System 1194 R. X. McGee, L. M. Newton and D. C. Morton Table 1. Radial velocities, halfwidths and column densities of the low intensity 21 cm H-line components. CD (2) (3) (4) (5) (6) (7)t 3MNRAS.205.1191M Galactic R ial RMS Local Source name Position (1950) coordinates Band- f ® -v LSR noise velocity 198 width velocity velocity R.A. Dec. i b range ÄNh range (km s'1) (km s'1) (cm-2) (km s'1) xlplS HD 5980 00 57 46 72 26 06 302.1 44.9 0.82 - 100 ,+100 -10.8 0.2 64, +36 Sk 80 00 57 52 72 26 00 302.1 45.0 0.82 -100,+100 -10.8 0.2- 65, +40 Sk 108 01 01 48 -72 22 45 301.6 45.1 0.82 -100,+100 -10.9 0.2 73,+40 Fairall 9 01 21 51 -59 03 57 295.1 -57.8 8.2 -150,+300 -11.6 0.1 -84,+30 MS 1.4 01 23 38 61 32 05 295.7 55.4 4.12 70,+400 11.7 0.5 74,+40 MS 1.2 01 25 45 61 17 04 295.2 55.6 4.12 70 ,+400 11.8 0.5 64,+40 MS 1.0 01 25 45 61 32 05 295.3 55.3 4.12 70 ,+400 11.7 0.5 72,+58 MS 1.3 01 25 45 61 47 04 295.4 55.1 4.12 70 ,+400 11.7 0.5 74,+40 MS 1.1 01 27 54 61 32 05 294.9 55.2 4.12 70,+400 11.8 0.5 62,+50 MS 5.4 01 28 35 62 02 06 295.0 54.7 4.12 70,+400 11.8 0.6 74,+40 MS 5.2 01 30 41 61 47 05 294.4 54.9 4.12 70,+400 11.9 0.6 61, +47 MS 5.0 01 30 41 62 02 03 294.6 54.7 4.12 7-0, + 400 11.9 0.6 62, +37 MS 5.3 01 30 41 62 17 04 294.7 54.4 4.12 70,+400 11.9 0.6 61 ,+47 MS 5.1 01 32 49 62 02 05 294.2 54.6 4.12 70,+400 12.0 0.6 72,+39 MS 2.4 02 20 15 71 13 40 293.0 44.4 4.12 70 ,+400 12.6 0.5 74, +44 MS 2.2 02 23 20 70 58 40 292.5 44.4 4.12 70,+ 400 12.7 0.5 77, +45 MS 2.0 02 23 20 71 13 39 292.6 44.2 4.12 70,+400 12.7 0.5 73,+47 MS 2.3 02 23 19 71 28 39 292.8 44.0 4.12 70,+400 12.7 0.5 62,+57 MS 2.1 02 26 23 71 13 39 292.4 44.1 4.12 70,+400 12.8 0.5 75, +45 MS 6.4 02 28 17 66 39 27 288 47.9 4.12 70,+400 13.3 0.6 65,+62 MS 6.2 02 30 51 66 24 27 288 47.9 4.12 70,+400 13.4 0.6 78, + 79 MS 6.0 02 30 50 66 39 26 288 •47.7 4.12 70,+400 13.3 0.6 75,+69 MS 6.3 02 30 50 66 54 27 288 •47.5 4.12 70,+ 400 13.3 0.6 73,+57 MS 6.1 02 33 25 66 39 27 288.0 47.6 4.12 70,+400 13.4 0.6 78,+71 MS 7.4 02 41 45 69 20 33 289.4 45.0 4.12 70 ,+400 13.3 0.6 69, +59 MS 7.2 02 44 42 69 05 33 288.9 45.0 4.12 70,+400 13.4 0.6 70, +54 MS 7.0 02 44 43 69 20 32 289.1 44.8 4.12 70 ,+400 13.3 0.6 77,+57 MS 7.3 02 44 42 69 35 32 289.3 44.6 4.12 70,+400 13.3 0.6
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