2007ApJ...669L...5B

Low-ionization transitions such as the Mg II λ2796/2803 doublet trace cold gas in the vicinity of galaxies. It is not clear whether this gas is part of the interstellar medium of large protodisks, part of dwarfs, or part of entrained material in supernova-driven outflows. Studies based on Mg II statistics, e.g., stacked images and clustering analysis, have invoked starburst-driven outflows where Mg II absorbers are tracing the denser and colder gas of the outflow. A consequence of the outflow scenario is that the strongest absorbers ought to be associated with starbursts. We use the near-IR integral field spectrograph SINFONI to test whether starbursts are found around z∼1 Mg II absorbers. For 67% (14 out of 21) of the absorbers with rest-frame equivalent width W^λ2796_r> 2 Å, we do detect Hα in emission within ±200 km/s of the predicted wavelength based on the Mg II redshift, and with impact parameter ranging from 0.2" to 6.7" from the QSO. The star formation rate (SFR) inferred from Hα is 1-20 M_☉/yr, i.e., showing a level of star formation larger than in M82 by a factor of >4 on average. Our flux limit (3 σ) is f_Hα<1.2x10^–17 erg/s/cm2, corresponding to a SFR of ∼0.5 M_☉/yr, much below past ground-based Hα surveys of absorption-selected galaxies. We find evidence (at >95%) for a correlation between SFR and equivalent width, indicating a physical connection between starburst phenomena and gas seen in absorption. In the cases where we can extract the velocity field, the host galaxies of Mg II absorbers with W^λ2796_r> 2 Å reside in halos with mean mass <logM_h(M_☉)≳11.2, in good agreement with clustering measurements.