Characterizing the ELG luminosity functions in the nearby Universe^⋆

¹ Instituto de Astrofísica de Canarias, s/n, 38205 La Laguna, Tenerife, Spain
e-mail: gfavole@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
³ Departamento de Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049, Spain
⁴ Centro de Investigación Avanzada en Física Fundamental, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
⁵ Australian Astronomical Optics, Macquarie University, 105 Delhi Rd, North Ryde, NSW 2113, Australia
⁶ Departamento de Física, Universidad Técnica Federico Santa María, Casilla 110-V, Avda. España, 1680 Valparaíso, Chile
⁷ Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101, USA
⁸ Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching bei München, Germany
⁹ Instituto de Astrofísica de La Plata (CCT La Plata, CONICET, UNLP), Paseo del Bosque s/n, B1900FWA La Plata, Argentina
¹⁰ Facultad de Ciencias Astronómicas y Geofísicas, UNLP, Paseo del Bosque s/n, B1900FWA La Plata, Argentina
¹¹ Centre for Astrophysics & Supercomputing, Swinburne University of Technology, POB 218 Hawthorn, Victoria 3122, Australia
¹² Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Shanghai 200030, PR China
¹³ Dipartimento di Fisica “G. Occhialini”, Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
¹⁴ INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
¹⁵ International Centre for Radio Astronomy Research, The University of Western Australia, Crawley, WA 6009, Australia
¹⁶ PlantTech Research Institute Limited., South British House, 4th Floor, 35 Grey Street, Tauranga 3110, New Zealand
¹⁷ Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Campus San Joaquín, Avda. Vicuña Mackenna 4860, Santiago, Chile
¹⁸ Facultad de Físicas, Universidad de Sevilla, Avda. Reina Mercedes s/n, Campus de Reina Mercedes, 41012 Sevilla, Spain
¹⁹ Instituto de Investigación Multidisciplinar en Ciencia y Tecnología, Universidad de La Serena, Raúl Bitrán 1305, La Serena, Chile
²⁰ Departamento de Astronomía, Universidad de La Serena, Av. Juan Cisternas 1200 Norte, La Serena, Chile

Received: 17 March 2023
Accepted: 15 November 2023

Abstract

Context. Nebular emission lines are powerful diagnostics for the physical processes at play in galaxy formation and evolution. Moreover, emission-line galaxies (ELGs) are one of the main targets of current and forthcoming spectroscopic cosmological surveys.

Aims. We investigate the contributions to the line luminosity functions (LFs) of different galaxy populations in the local Universe, providing a benchmark for future surveys of earlier cosmic epochs.

Methods. The large statistics of the observations from the SDSS DR7 main galaxy sample and the MPA-JHU spectral catalog enabled us to precisely measure the Hα, Hβ, [O II], [O III], and, for the first time, the [N II], and [S II] emission-line LFs over ∼2.4 Gyrs in the low-z Universe, 0.02 < z < 0.22. We present a generalized 1/V_max LF estimator capable of simultaneously correcting for spectroscopic, r-band magnitude, and emission-line incompleteness. We studied the contribution to the LF of different types of ELGs classified using two methods: (i) the value of the specific star formation rate (sSFR), and (ii) the line ratios on the Baldwin–Phillips–Terlevich (BPT) and the WHAN (i.e., Hα equivalent width, EW_Hα, versus the [N II]/Hα line ratio) diagrams.

Results. The ELGs in our sample are mostly star forming, with 84 percent having sSFR > 10⁻¹¹ yr⁻¹. When classifying ELGs using the BPT+WHAN diagrams, we find that 63.3 percent are star forming, only 0.03 are passively evolving, and 1.3 have nuclear activity (Seyfert). The rest are low-ionization narrow emission-line regions (LINERs) and composite ELGs. We found that a Saunders function is the most appropriate to describe all of the emission-line LFs, both observed and dust-extinction-corrected (i.e., intrinsic). They are dominated by star-forming regions, except for the bright end of the [O III] and [N II] LFs (i.e., L_[N II] > 10⁴² erg s⁻¹, L_[O III] > 10⁴³ erg s⁻¹), where the contribution of Seyfert galaxies is not negligible. In addition to the star-forming population, composite galaxies, and LINERs are the ones that contribute the most to the ELG numbers at L < 10⁴¹ erg s⁻¹. We do not observe significant evolution with redshift of our ELGs at 0.02 < z < 0.22. All of our results, including data points and analytical fits, are publicly available.

Conclusions. Local ELGs are dominated by star-forming galaxies, except for the brightest [N II] and [O III] emitters, which have a large contribution of Seyfert galaxies. The local line luminosity functions are best described by Saunders functions. We expect these two conclusions to hold up at higher redshifts for the ELG targeted by current cosmological surveys, such as DESI and Euclid.