Sarah J,
Here’s a link to the marriage certificate:
5433159.pdf (irishgenealogy.ie)
Griffiths Valuation (1859) lists John Downing in Broagh. He was farming plot 14, a total of about 18 acres. I think the groom also came from that townland as I see Richard Pyke nearby on plot 7, farming 21 acres. The Pike/Pyke farm today is on the Broagh Rd and the Downing farm a few hundred yards away on the Hillhead Rd, not far from the village of Knockloughrim (and some 30 miles from Londonderry but close to Maghera).
Death here for a Richard Pike of Broagh, reported by another Richard Pike:
4872001.pdf (irishgenealogy.ie)
No Pikes in the townland in the 1901 census but there was a Downing household:
National Archives: Census of Ireland 1911
A John Downing there in 1831:
National Archives: Census of Ireland 1911
Two probate abstracts from the PRONI wills site (both died intestate):
Administration of the Estate of John Downing late of Broagh Knockloughrim County Londonderry Farmer who died 7 January 1902 granted at Londonderry to Adam Downing Farmer Effects £148
Downing John of Broagh county Londonderry farmer died 7 August 1920 Administration Londonderry 4 June to Adam Downing farmer. Effects £25.
No sign of the Pike family anywhere in the county in 1831 so possibly they moved into the area sometime after that year.