Open AccessHIDEEP – an extragalactic blind survey for very low column‐density neutral hydrogen
Author(s) -
Minchin R. F.,
Disney M. J.,
Boyce P. J.,
De Blok W. J. G.,
Parker Q. A.,
Banks G. D.,
Freeman K. C.,
Garcia D. A.,
Gibson B. K.,
Grossi M.,
Haynes R. F.,
Knezek P. M.,
Lang R. H.,
Malin D. F.,
Price R. M.,
Stewart I. M.,
Wright A. E.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2003.07134.x
Subject(s) - physics , astrophysics , galaxy , surface brightness , telescope , magnitude (astronomy) , astronomy
We have carried out an extremely long integration time (9000 s beam −1 ) 21‐cm blind survey of 60 deg 2 in Centaurus using the Parkes multibeam system. We find that the noise continues to fall as throughout, enabling us to reach an H i column‐density limit of 4.2 × 10 18 cm −2 for galaxies with a velocity width of 200 km s −1 in the central 32 deg 2 region, making this the deepest survey to date in terms of column density sensitivity. The H i data are complemented by very deep optical observations from digital stacking of multi‐exposure UK Schmidt Telescope R ‐band films, which reach an isophotal level of 26.5 R mag arcsec −2 (≃27.5 B mag arcsec −2 ). 173 H i sources have been found, 96 of which have been uniquely identified with optical counterparts in the overlap area. There is not a single source without an optical counterpart. Although we have not measured the column densities directly, we have inferred them from the optical sizes of their counterparts. All appear to have a column density of N H i = 10 20.65±0.38 . This is at least an order of magnitude above our sensitivity limit, with a scatter only marginally larger than the errors on N H i . This needs explaining. If confirmed it means that H i surveys will only find low surface brightness (LSB) galaxies with high M H i / L B . Gas‐rich LSB galaxies with lower H i mass to light ratios do not exist. The paucity of low column‐density galaxies also implies that no significant population will be missed by the all‐sky H i surveys being carried out at Parkes and Jodrell Bank.