Star Formation as a function of environment at z=3
N. Bouché¹, J. D. Lowenthal^2
1 Max Planck Institut fur extraterrestrishe Physik, Garching, DE-85748 ² Smith College, Northampton, USA
We study, for the first time, the star formation rate (SFR) as a function of environment for UV selected Lyman break galaxies (LBGs) at redshift z=3. From deep (m_I,AB(sky) @ 27.6) UBVI MOSAIC images, covering a total of 0.90 deg², we select 334 LBGs in slices 100 Mpc (co-moving) deep spanning the redshift range 2.9 < z < 3.4 using photometric reshifts. We used mock catalogs from the GIF2 cosmological simulations (in a 110 Mpc box) to show that this redshift resolution is sufficient to statistically differentiate the high density from the low density regions using S₅ , the projected density to the 5th nearest neighbor. The large area of the MOSAIC images, ~ 40×40 Mpc (co-moving) per field, allows us to measure the SFR from the dust-corrected UV continuum as a function of S₅. In contrast to low-redshift galaxies, we find that the SFR (or UV luminosity) of LBGs at z = 3 shows no detectable dependence on environment over 2 orders of magnitude in densities. To test the significance of our result, we use Monte Carlo simulations (from the mock catalogs) and the same projected density estimators we applied to our data. We find that we can reject the steep z=0 SFR-density at the 5-s level. We conclude that the SFR-density at z=3 must be at least 3.6 times flatter than it is locally, i.e. the SFR of LBGs is significantly less denpendent on environment than the SFR of local star-forming galaxies. We find that the rest-frame UV colors are also independent of environment.

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