%0 Generic %1 faisst2017empirical %A Faisst, Andreas L. %A Masters, Daniel %A Wang, Yun %A Merson, Alexander %A Capak, Peter %A Malhotra, Sangeeta %A Rhoads, James E. %D 2017 %K Halpha NII prediction ratio %T Empirical Modeling of the Redshift Evolution of the NII/H$\alpha$ ratio for Galaxy Redshift Surveys %U http://arxiv.org/abs/1710.00834 %X We present an empirical parameterization of the NII/H$\alpha$ flux ratio as a function of stellar mass and redshift valid at 0 < z < 2.7 and 8.5 < log(M) < 11.0. This description can easily be applied to (i) simulations for modeling NII line emission, (ii) deblend NII and H$\alpha$ in current low-resolution grism and narrow-band observations to derive intrinsic H$\alpha$ fluxes, and (iii) to reliably forecast the number counts of H$\alpha$ emission line galaxies for future surveys such as those planned for Euclid and WFIRST. Our model combines the evolution of the locus on the BPT diagram measured in spectroscopic data out to z ~ 2.5 with the strong dependence of NII/H$\alpha$ on stellar mass and OIII/H$\beta$ observed in local galaxy samples. We find large variations in the NII/H$\alpha$ flux ratio at a fixed redshift due to its dependency on stellar mass, hence the assumption of a constant NII contamination fraction can lead to a significant under- or over-estimate of H$\alpha$ luminosities. Specifically, measurements of the intrinsic H$\alpha$ luminosity function derived from current low-resolution grism spectroscopy assuming a constant 29% contamination of NII are likely over-estimated by factors of 2-4 at log(L) > 43.0 and systematically under-estimated by ~50 at log(L) < 42.5 at redshifts z ~ 1.5. This has implications on the prediction of H-alpha emitters for Euclid and WFIRST. We also study the impact of blended H$\alpha$ and NII on the accuracy of measured spectroscopic redshifts.

@misc{faisst2017empirical, abstract = {We present an empirical parameterization of the [NII]/H$\alpha$ flux ratio as a function of stellar mass and redshift valid at 0 < z < 2.7 and 8.5 < log(M) < 11.0. This description can easily be applied to (i) simulations for modeling [NII] line emission, (ii) deblend [NII] and H$\alpha$ in current low-resolution grism and narrow-band observations to derive intrinsic H$\alpha$ fluxes, and (iii) to reliably forecast the number counts of H$\alpha$ emission line galaxies for future surveys such as those planned for Euclid and WFIRST. Our model combines the evolution of the locus on the BPT diagram measured in spectroscopic data out to z ~ 2.5 with the strong dependence of [NII]/H$\alpha$ on stellar mass and [OIII]/H$\beta$ observed in local galaxy samples. We find large variations in the [NII]/H$\alpha$ flux ratio at a fixed redshift due to its dependency on stellar mass, hence the assumption of a constant [NII] contamination fraction can lead to a significant under- or over-estimate of H$\alpha$ luminosities. Specifically, measurements of the intrinsic H$\alpha$ luminosity function derived from current low-resolution grism spectroscopy assuming a constant 29% contamination of [NII] are likely over-estimated by factors of 2-4 at log(L) > 43.0 and systematically under-estimated by ~50 at log(L) < 42.5 at redshifts z ~ 1.5. This has implications on the prediction of H-alpha emitters for Euclid and WFIRST. We also study the impact of blended H$\alpha$ and [NII] on the accuracy of measured spectroscopic redshifts.}, added-at = {2017-10-04T10:37:15.000+0200}, author = {Faisst, Andreas L. and Masters, Daniel and Wang, Yun and Merson, Alexander and Capak, Peter and Malhotra, Sangeeta and Rhoads, James E.}, biburl = {https://www.bibsonomy.org/bibtex/24a7e2aca33e65a4c6bdd67495eb16863/miki}, description = {[1710.00834] Empirical Modeling of the Redshift Evolution of the [NII]/H$\alpha$ ratio for Galaxy Redshift Surveys}, interhash = {76acfda4249c56575949075fa1f45423}, intrahash = {4a7e2aca33e65a4c6bdd67495eb16863}, keywords = {Halpha NII prediction ratio}, note = {cite arxiv:1710.00834Comment: 14 pages, 10 figures, 1 table, submitted to ApJ}, timestamp = {2017-10-04T10:37:15.000+0200}, title = {Empirical Modeling of the Redshift Evolution of the [NII]/H$\alpha$ ratio for Galaxy Redshift Surveys}, url = {http://arxiv.org/abs/1710.00834}, year = 2017 }