Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2010-02-02
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
25 pages, 15 figures. Accepted to AJ
Scientific paper
We measure the strength, frequency, and timescale of tidally triggered star formation at redshift z=0.08-0.38 in a spectroscopically complete sample of galaxy pairs drawn from the magnitude-limited redshift survey of 9,825 Smithsonian Hectospec Lensing Survey (SHELS) galaxies with R<20.3. To examine the evidence for tidal triggering, we identify a volume-limited sample of major (|\Delta M_R|<1.75, corresponding to mass ratio >1/5) pair galaxies with $M_R < -20.8 in the redshift range z=0.08-0.31. The size and completeness of the spectroscopic survey allows us to focus on regions of low local density. The spectrophotometric calibration enables the use of the 4000 Ang break (D_n4000), the H\alpha specific star formation rate (SSFR_{H\alpha}), and population models to characterize the galaxies. We show that D_n4000 is a useful population classification tool; it closely tracks the identification of emission line galaxies. The sample of major pair galaxies in regions of low local density with low D_n4000 demonstrates the expected anti-correlation between pair-wise projected separation and a set of star formation indicators explored in previous studies. We measure the frequency of triggered star formation by comparing the SSFR_{H\alpha} in the volume-limited sample in regions of low local density: 32 +/-7% of the major pair galaxies have SSFR_{H\alpha} at least double the median rate of the unpaired field galaxies. Comparison of stellar population models for pair and for unpaired field galaxies implies a timescale for triggered star formation of ~300-400 Myr.
Dell'Antonio Ian
Fabricant Daniel G.
Freedman Woods Deborah
Geller Margaret J.
Kurtz Michael J.
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