Submillimeter star formation rates in interacting pairs
Date
2003
Authors
Klopp, Aaron James Ronald
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Abstract
We have completed a program of observing interacting pairs and field galaxies selected from the CNOC2 survey. Observations were made with the Submillimeter Common User Bolometer Array (SCUBA) at the James Clerk Maxwell Telescope (JCMT). The goal was to use SCUBA fluxes (850/450 µm) to determine star formation rates (SFR's) for 20 interacting pairs (mean redshift of 0.36), and 7 field galaxies chosen on the basis of their large optically-inferred star formation rate. After reducing the data the 850 µm fluxes were used to calculate star formation rates for 18 of those pairs that constituted the best data of the sample. These SFR's were also used to measure the star formation rate per unit blue luminosity of the ensemble of pairs. The data from the 450 µm receivers was insufficiently stable to give reliable fluxes. Two objects were detected at 850 µm above the critical 30' threshold. Another three were detected above 2.50'. The significance of these detections is evident from x~ and Monte Carlo tests, as well as by examining the optical/UV SFR's of CNOC2 galaxies. By inferring a 850 µm flux from an optical/UV SFR we have determined that the chance of obtaining 5 detections(> 2.50') is exceedingly small unless the dust absorbs an average of~ 97% of the bolometric UV energy in a typical CNOC2 galaxy. Given what we know of dust emission at low and moderate redshifts we believe this scenario to be very unlikely, suggesting our pairs constitute a unique ensemble of star formers in their environment.
The ensemble average star formation rate per pair was found to be 5.5 ± 2.4 h M0 yr- 1, an average determined by weighting individual SFR's according to flux error. This value of SFR was used to calculate the SFR per unit blue luminosity (SFR/LB), which was found to range between (4 - 10)x10-10 M0 yr- 1 LB,0 depending on the subset of the sample used. Using values from the literature we determined the (SFR/ L8 ) for field galaxies at moderate redshift . We found that our pairs produced an excess of SFR/ L8 over a comparable sample of field galaxies at the same redshift. The most conservative estimate of this excess is ~ 2 x, but a more consistent value is likely 6 - 9 x. These results provide tantalizing evidence for enhanced star formation in interacting pairs at moderate redshift.