We present data and initial results from VLT/X-Shooter emission-line spectroscopy of 96 galaxies selected by long \gamma -ray bursts ( GRBs ) at 0.1 < z < 3.6 , the largest sample of GRB host spectra available to date .
Most of our GRBs were detected by Swift and 76 % are at 0.5 < z < 2.5 with a median z _ { med } \sim 1.6 .
Based on Balmer and/or forbidden lines of oxygen , nitrogen , and neon , we measure systemic redshifts , star formation rates ( SFR ) , visual attenuations ( A _ { V } ) , oxygen abundances ( 12 + \log ( \mathrm { O / H } ) ) , and emission-line widths ( \sigma ) .
We study GRB hosts up to z \sim 3.5 and find a strong change in their typical physical properties with redshift .
The median SFR of our GRB hosts increases from SFR _ { med } \sim 0.6 M _ { \odot } yr ^ { -1 } at z \sim 0.6 up to SFR _ { med } \sim 15 M _ { \odot } yr ^ { -1 } at z \sim 2 .
A higher ratio of [ O iii ] / [ O ii ] at higher redshifts leads to an increasing distance of GRB-selected galaxies to the locus of local galaxies in the Baldwin-Phillips-Terlevich diagram .
There is weak evidence for a redshift evolution in A _ { V } and \sigma , with the highest values seen at z \sim 1.5 ( A _ { V } ) or z \sim 2 ( \sigma ) .
Oxygen abundances of the galaxies are distributed between 12 + \log ( \mathrm { O / H } ) = 7.9 and 12 + \log ( \mathrm { O / H } ) = 9.0 with a median 12 + \log ( \mathrm { O / H } ) _ { med } \sim 8.5 .
The fraction of GRB-selected galaxies with super-solar metallicities is \sim 20 \% at z < 1 in the adopted metallicity scale .
This is significantly less than the fraction of total star formation in similar galaxies , illustrating that GRBs are scarce in high metallicity environments .
At z \sim 3 , sensitivity limits us to probing only the most luminous GRB hosts for which we derive metallicities of Z \lesssim 0.5 Z _ { \sun } .
Together with a high incidence of Z \sim 0.5 Z _ { \sun } galaxies at z \sim 1.5 , this indicates that a metallicity dependence at low redshift will not be dominant at z \sim 3 .
Significant correlations exist between the hosts ’ physical properties .
Oxygen abundance , for example , relates to A _ { V } ( 12 + \log ( \mathrm { O / H } ) \propto 0.17 \cdot A _ { V } ) , line width ( 12 + \log ( \mathrm { O / H } ) \propto \sigma ^ { 0.6 } ) , and SFR ( 12 + \log ( \mathrm { O / H } ) \propto SFR ^ { 0.2 } ) .
In the last two cases , the normalization of the relations shift to lower metallicities at z > 2 by \sim 0.4 dex .

These properties of GRB hosts and their evolution with redshift can be understood in a cosmological context of star-forming galaxies and a picture in which the hosts ’ properties at low redshift are influenced by the tendency of GRBs to avoid the most metal-rich environments .