Open AccessAn ultraviolet‐selected galaxy redshift survey – II. The physical nature of star formation in an enlarged sample
Author(s) -
Sullivan Mark,
Treyer Marie A.,
Ellis Richard S.,
Bridges Terry J.,
Milliard Bruno,
Donas José
Publication year - 2000
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 - 10.1046/j.1365-8711.2000.03140.x
Subject(s) - physics , astrophysics , redshift , galaxy , star formation , luminosity , astronomy , metallicity , redshift survey , context (archaeology) , emission spectrum , ultraviolet , luminosity function , line (geometry) , spectral line , paleontology , geometry , mathematics , quantum mechanics , biology
We present further spectroscopic observations for a sample of galaxies selected in the vacuum ultraviolet (UV) at 2000 Å from the FOCA balloon‐borne imaging camera of Milliard et al. This work represents an extension of the initial study by Treyer et al. Our enlarged catalogue contains 433 sources (≃3 times as many as in our earlier study) across two FOCA fields. 273 of these are galaxies, nearly all with redshifts z ≃0–0.4. Nebular emission‐line measurements are available for 216 galaxies, allowing us to address issues of excitation, reddening and metallicity. The UV and H α luminosity functions strengthen our earlier assertions that the local volume‐averaged star formation rate is higher than indicated from earlier surveys. Moreover, internally within our sample, we do not find a steep rise in the UV luminosity density with redshift over 0< z <0.4. Our data are more consistent with a modest evolutionary trend, as suggested by recent redshift survey results. Investigating the emission‐line properties, we find no evidence for a significant number of AGN in our sample; most UV‐selected sources to z ≃0.4 are intense star‐forming galaxies. We find that the UV flux indicates a consistently higher mean star formation rate than that implied by the H α luminosity for typical constant or declining star formation histories. Following Glazebrook et al., we interpret this discrepancy in terms of a starburst model for our UV‐luminous sources. We develop a simple algorithm which explores the scatter in the UV flux–H α relation in the context of various burst scenarios. Whilst we can explain most of our observations in this way, there remains a small population with extreme UV–optical colours which cannot be understood.