Open AccessEvolution of damped Lyman α kinematics and the effect of spatial resolution on 21‐cm measurements
Author(s) -
RyanWeber Emma V.,
StaveleySmith Lister,
Webster Rachel L.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society: letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.067
H-Index - 122
eISSN - 1745-3933
pISSN - 1745-3925
DOI - 10.1111/j.1745-3933.2005.00104.x
Subject(s) - physics , galaxy , astrophysics , redshift , sky , local group , image resolution , telescope , astronomy , resolution (logic) , optics , milky way , artificial intelligence , computer science
We have investigated the effect of spatial resolution on determining pencil‐beam‐like velocity widths and column densities in galaxies. Three 21‐cm data sets are used, the H i Parkes All Sky Survey (HIPASS) galaxy catalogue, a subset of HIPASS galaxies with Australia Telescope Compact Array maps and a high‐resolution image of the Large Magellanic Cloud. Velocity widths measured from 21‐cm emission in local galaxies are compared with those measured in intermediate‐redshift damped Lyman α (DLA) absorbers. We conclude that spatial resolution has a severe effect on measuring pencil‐beam like velocity widths in galaxies. Spatial smoothing by a factor of 240 is shown to increase the median velocity width by a factor of 2. Thus any difference between velocity widths measured from global profiles or low spatial resolution 21‐cm maps at z = 0 and DLAs at z > 1 cannot unambiguously be attributed to galaxy evolution. The effect on column density measurements is less severe and the values of d N DLA /d z from local low‐resolution 21‐cm measurements are expected to be overestimated by only ∼10 per cent.