A Caltech Library Service

Empirical Modeling of the Redshift Evolution of the [N II]/Hα Ratio for Galaxy Redshift Surveys

Faisst, Andreas L. and Masters, Daniel and Wang, Yun and Merson, Alexander and Capak, Peter and Malhotra, Sangeeta and Rhoads, James E. (2018) Empirical Modeling of the Redshift Evolution of the [N II]/Hα Ratio for Galaxy Redshift Surveys. Astrophysical Journal, 855 (2). Art. No. 132. ISSN 1538-4357. doi:10.3847/1538-4357/aab1fc.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


We present an empirical parameterization of the [N ii]/Hα flux ratio as a function of stellar mass and redshift valid at 0 < z < 2.7 and 8.5 < log(M/M_⊙) < 11.0. This description can (i) easily be applied to simulations for modeling [N ii]λ6584 line emission, (ii) deblend [N ii] and Hα in current low-resolution grism and narrow-band observations to derive intrinsic Hα fluxes, and (iii) reliably forecast the number counts of Hα emission-line galaxies for future surveys, such as those planned for Euclid and the Wide Field Infrared Survey Telescope (WFIRST). Our model combines the evolution of the locus on the Baldwin, Phillips & Terlevich (BPT) diagram measured in spectroscopic data out to z ~ 2.5 with the strong dependence of [N ii]/Hα on stellar mass and [O iii]/Hβ observed in local galaxy samples. We find large variations in the [N ii]/Hα flux ratio at a fixed redshift due to its dependency on stellar mass; hence, the assumption of a constant [N ii] flux contamination fraction can lead to a significant under- or overestimate of Hα luminosities. Specifically, measurements of the intrinsic Hα luminosity function derived from current low-resolution grism spectroscopy assuming a constant 29% contamination of [N ii] can be overestimated by factors of ~8 at log(L) > 43.0 for galaxies at redshifts z ~ 1.5. This has implications for the prediction of Hα emitters for Euclid and WFIRST. We also study the impact of blended Hα and [N ii] on the accuracy of measured spectroscopic redshifts.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Faisst, Andreas L.0000-0002-9382-9832
Masters, Daniel0000-0001-5382-6138
Capak, Peter0000-0003-3578-6843
Malhotra, Sangeeta0000-0002-9226-5350
Rhoads, James E.0000-0002-1501-454X
Additional Information:© 2018. The American Astronomical Society. Received 2017 September 8; revised 2018 February 12; accepted 2018 February 15; published 2018 March 16. The authors thank J. Colbert for helpful comments and discussions. We also thank the referee for the very useful comments, which helped to improve this paper. A.M. acknowledges sponsorship of a NASA Postdoctoral Program Fellowship. A.M. was supported by JPL, which is run under contract by the California Institute of Technology for NASA.
Group:Infrared Processing and Analysis Center (IPAC), COSMOS
Funding AgencyGrant Number
NASA Postdoctoral ProgramUNSPECIFIED
Subject Keywords:cosmology: observations; galaxies: fundamental parameters; galaxies: ISM
Issue or Number:2
Record Number:CaltechAUTHORS:20180328-133307813
Persistent URL:
Official Citation:Andreas L. Faisst et al 2018 ApJ 855 132
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85480
Deposited By: George Porter
Deposited On:29 Mar 2018 15:13
Last Modified:15 Nov 2021 20:29

Repository Staff Only: item control page