The NIBLES bivariate luminosity–H I mass distribution function revised using Arecibo follow-up observations^⋆

¹ University of Massachusetts, Astronomy Program, 536 LGRC, Amherst, MA 01003, USA
e-mail: zbutcher@nrao.edu
² GEPI, Observatoire de Paris, PSL Université, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
³ USN, Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU USR 704, Université d’Orléans OSUC, Route de Souesmes, 18330 Nançay, France

Received: 12 February 2020
Accepted: 18 May 2020

Abstract

We present a modified optical luminosity–H I mass bivariate luminosity function based on H I line observations from the Nançay Interstellar Baryons Legacy Extragalactic Survey (NIBLES), including data from our new, four times more sensitive follow-up H I line observations obtained with the Arecibo radio telescope. The follow-up observations were designed to probe the underlying H I mass distribution of the NIBLES galaxies that were undetected or marginally detected in H I at the Nançay Radio Telescope. Our total follow-up sample consists of 234 galaxies, and it spans the entire luminosity and color range of the parent NIBLES sample of 2600 nearby (900 <  cz <  12 000 km s⁻¹) SDSS galaxies. We incorporated the follow-up data into the bivariate analysis by scaling the NIBLES undetected fraction by an Arecibo-only distribution. We find the resulting increase in low H I mass-to-light ratio densities to be about 10% for the bins −1.0 ≤ log(M_HI/M_⊙/L_r/L_⊙) ≤ −0.5, which produces an increased H I mass function (HIMF) low mass slope of α = −1.14 ± 0.07, being slightly shallower than the values of −1.35 ± 0.05 obtained by recent blind H I surveys. Applying the same correction to the optically corrected bivariate luminosity function from our previous paper produces a larger density increase of about 0.5 to 1 dex in the lowest H I mass-to-light ratio bins for a given luminosity while having a minimal effect on the resulting HIMF low mass slope, which still agrees with blind survey HIMFs. This indicates that while low H I-mass-to-light ratio galaxies do not contribute much to the one-dimensional HIMF, their inclusion has a significant impact on the densities in the two-dimensional distribution.