%0 Generic %1 Genzel2011 %A Genzel, R. %A Tacconi, L. J. %A Combes, F. %A Bolatto, A. %A Neri, R. %A Sternberg, A. %A Cooper, M. C. %A Bouche, N. %A Bournaud, F. %A Burkert, A. %A Comerford, J. %A Cox, P. %A Davis, M. %A Schreiber, N. M. Foerster %A Garcia-Burillo, S. %A Gracia-Carpio, J. %A Lutz, D. %A Naab, T. %A Newman, S. %A Saintonge, A. %A Shapiro, K. %A Shapley, A. %A Weiner, B. %D 2011 %K CO conversion factor %T The metallicity dependence of the CO \rightarrow H_2 conversion factor in z>1 star forming galaxies %U http://arxiv.org/abs/1106.2098 %X We use the first systematic samples of CO millimeter line emission in z~1-3 'main-sequence' star forming galaxies (SFGs) for studying the metallicity dependence of the conversion factor \alpha_CO, from CO millimeter line luminosity to molecular gas mass. The molecular gas depletion rate, which is proportional to the ratio of star formation rate to CO line luminosity, is ~1 Gyr^-1 for near-solar metallicity galaxies with stellar masses above M_S~10^11 M_sun. Its value does not vary much between z~0 and 2. Below M_S the depletion rates appear to increase with decreasing metallicity. We show that this trend is probably not caused by starburst events or by changes in the physical parameters of the molecular clouds but instead requires a metallicity dependent conversion factor. The trend is also expected theoretically from the effect of UV-photodissociation of CO at low metallicity. From the available z~0 and z~1-3 samples we constrain the slope of the log(\alpha_CO) -log (metallicity) relation to range between -1.3 and -1.9. Because of the lower metallicities near and beyond the peak of the galaxy formation activity at z~1-2 compared to z~0, our findings suggest that molecular gas masses estimated from CO luminosities have to be substantially corrected upward for galaxies below M_S.

@misc{Genzel2011, abstract = { We use the first systematic samples of CO millimeter line emission in z~1-3 'main-sequence' star forming galaxies (SFGs) for studying the metallicity dependence of the conversion factor {\alpha}_CO, from CO millimeter line luminosity to molecular gas mass. The molecular gas depletion rate, which is proportional to the ratio of star formation rate to CO line luminosity, is ~1 Gyr^-1 for near-solar metallicity galaxies with stellar masses above M_S~10^11 M_sun. Its value does not vary much between z~0 and 2. Below M_S the depletion rates appear to increase with decreasing metallicity. We show that this trend is probably not caused by starburst events or by changes in the physical parameters of the molecular clouds but instead requires a metallicity dependent conversion factor. The trend is also expected theoretically from the effect of UV-photodissociation of CO at low metallicity. From the available z~0 and z~1-3 samples we constrain the slope of the log({\alpha}_CO) -log (metallicity) relation to range between -1.3 and -1.9. Because of the lower metallicities near and beyond the peak of the galaxy formation activity at z~1-2 compared to z~0, our findings suggest that molecular gas masses estimated from CO luminosities have to be substantially corrected upward for galaxies below M_S. }, added-at = {2011-06-13T09:39:26.000+0200}, author = {Genzel, R. and Tacconi, L. J. and Combes, F. and Bolatto, A. and Neri, R. and Sternberg, A. and Cooper, M. C. and Bouche, N. and Bournaud, F. and Burkert, A. and Comerford, J. and Cox, P. and Davis, M. and Schreiber, N. M. Foerster and Garcia-Burillo, S. and Gracia-Carpio, J. and Lutz, D. and Naab, T. and Newman, S. and Saintonge, A. and Shapiro, K. and Shapley, A. and Weiner, B.}, biburl = {https://www.bibsonomy.org/bibtex/29fb6bf904b9cfdf768f9a0fd8ce355c0/miki}, description = {[1106.2098] The metallicity dependence of the CO {\rightarrow} H_2 conversion factor in z>1 star forming galaxies}, interhash = {c9628ce700fdd97959dcb2bad9db6a42}, intrahash = {9fb6bf904b9cfdf768f9a0fd8ce355c0}, keywords = {CO conversion factor}, note = {cite arxiv:1106.2098Comment: submitted to ApJ}, timestamp = {2011-06-13T09:39:26.000+0200}, title = {The metallicity dependence of the CO {\rightarrow} H_2 conversion factor in z>1 star forming galaxies}, url = {http://arxiv.org/abs/1106.2098}, year = 2011 }