To cite the service as such, we suggest the following BibTeX entry:
@MISC{vo:GAVO_DC_IRK, year=2012, title={A Name Mapping Authority Host for {IVOIDs}}, author={{GAVO} Data Center}, url={https://dc.zah.uni-heidelberg.de/rr/q/nmah/info}, howpublished={{VO} resource provided by the {GAVO} Data Center} }