Background and first results from the new AAO/UKST H survey

The need for the survey

Despite the importance of star formation in our own Galaxy, its variation between galaxies and the need to understand the resultant gaseous emission line structures visible on a wide range of angular scales, little survey work has been undertaken in a form that combines both large area coverage, high sensitivity and good resolution. The nearest star forming complexes may lie as close as 100 parsecs with sizes of tens of parsecs. Such structures often subtend angular sizes of a degree or more yet exhibit fine detail at arcsecond level. To study the interaction of these ionized structures with their large scale environment we need surveys of considerable extent at good angular resolution. Most work to date has concentrated on relatively small regions for specific study at high spatial or velocity resolution (e.g. Russeil et al. these proceedings) or very large areas at low resolution (e.g. Rodgers et al. 1960, Kogure et al. 1982, and more recently Buxton et al., Dennison et al. - these proceedings). It is only now that surveys are beginning to simultaneously tackle issues of coverage, sensitivity and resolution in either a spatial sense (our survey) or in velocity space (e.g. Reynolds et al. - these proceedings). There is a clear need for a high angular resolution optical survey to complement studies at other wavebands.

The only existing UKST wide area H survey work dates to the late 1970's (e.g. Davies, Elliot & Meaburn, 1976) using mainly coarse grained (though fast) 098-04 emulsion and a far from optimum filter. Many parts of the galactic plane are unsurveyed at decent resolutions, particularly the outer extensions beyond a few degrees from the galactic equator. The Northern Milky-Way above Dec has not been covered at all. Progress in other wavebands highlights the urgent need for an optical counterpart for the detailed study of galactic gas. Table 1 gives a list of the various H surveys currently underway and known to the authors together with the KYOTO survey (Kogure et al. 1982) as an example from the older photographic work. Our new survey will clearly contribute much to the detailed investigation of star formation and the general ISM in terms of its coverage and resolution.

Table 1: Basic characteristics of various current H surveys

Survey	Area	Res	Sens.	FOV	Finish	Telescope/Detector	Filter
	(sq.deg)	(arcsec)	Rayl.	(degrees)	date		FWHM(Å)
AAO/UKST	4000	1	5-10?		1999	UKST, Tech Pan film	70
WHAM	30000	3600	0.25	1	1998	0.6m, Faby-Perot, CCD	0.25
MSSSO	4000	12	?		1998	400mm F/4.5, 2K CCD	55
MARSEILLE	280	9	0.2		1999	36cm, Fabry-P	5km/s
VIRGINIA	4000	96	0.3		?	f/1.2 lens,CCD	17
MICHIGAN	100	3	20		1999	Curtis Schmidt,2K CCD	30
KYOTO	4000	30		17	1982	14.3cm+103aE	280

1: WHAM - Reynolds et al., 2: MSSSO - Buxton et al., 3: MARSEILLE - Russeil et al., 4: VIRGINIA - Dennison et al., 5: MICHIGAN - Smith et al. (all these proceedings) 6: Kogure et al. 1982. There is a lack of consistent units for measuring H sensitivity levels (emission measures) which are given in either Rayleighs `R', cm/pc or in ergs/cm/s/arc. The conversion factors are: 0.3R = 1cm/pc = 2ergs/cm/s/arc.

© Copyright Astronomical Society of Australia 1997