To investigate galaxy properties as a function of their total stellar mass, we obtained 21 cm H i line observations at the 100-m class Nançay Radio Telescope of 2839 galaxies from the Sloan Digital Sky Survey (SDSS) in the Local Volume (900 < cz < 12 000 km s −1 ), dubbed the Nançay Interstellar Baryons Legacy Extragalactic Survey (NIBLES) sample. They were selected evenly over their entire range of absolute SDSS z-band magnitudes (M z ∼ −13.5 to −24 mag), which were used as a proxy for their stellar masses. In this paper, a first, global presentation of the observations and basic results is given; their further analysis will be presented in other papers in this series. The galaxies were originally selected based on their properties, as listed in SDSS DR5. Comparing this photometry to their total H i masses, we noted that, for a few percent, the SDSS magnitudes appeared severely misunderestimated, as confirmed by our re-measurements for selected objects. Although using the later DR9 results eliminated this problem in most cases, 384 still required manual photometric source selection. Usable H i spectra were obtained for 2600 of the galaxies, of which 1733 (67%) were clearly detected and 174 (7%) marginally. The spectra for 241 other observed galaxies could not be used for further analysis owing to problems with either the H i or the SDSS data. We reached the target number of about 150 sources per half-magnitude bin over the M z range −16.5 to −23 mag. Down to −21 mag the overall detection rate is rather constant at the ∼75% level but it starts to decline steadily towards the 30% level at −23 mag. Making regression fits by comparing total H i and stellar masses for our sample, including our conservatively estimated H i upper limits for non-detections, we find the relationship log(M H I /M ) = −0.59 log(M ) + 5.05, which lies significantly below the relationship found in the M H I /M -M plane when only using H i detections.

H i stacking has proven to be a highly effective tool to statistically analyse average H i properties for samples of galaxies which may or may not be directly detected. With the plethora of H i data expected from the various upcoming H i surveys with the SKA Precursor and Pathfinder telescopes, it will be helpful to standardize the way in which stacking analyses are conducted. In this work we present a new python-based package, HISS, designed to stack H i (emission and absorption) spectra in a consistent and reliable manner. As an example, we use HISS to study the H i content in various galaxy sub-samples from the NIBLES survey of SDSS galaxies which were selected to represent their entire range in total stellar mass without a prior colour selection. This allowed us to compare the galaxy colour to average H i content in both detected and non-detected galaxies. Our sample, with a stellar mass range of 10 8 < M (M ) < 10 12 , has enabled us to probe the H i-to-stellar mass gas fraction relationship more than half an order of magnitude lower than in previous stacking studies.

The Arecibo L-band Feed Array Zone of Avoidance (ALFA ZOA) Deep Survey is the deepest and most sensitive blind H I survey undertaken in the ZOA. ALFA ZOA Deep will cover about 300 square degrees of sky behind the Galactic Plane in both the inner ( l b 30 7 5; 2°⩽ ⩽°⩽ |°|) and outer ( l b 175 207 ; 2 1°⩽ ⩽°−°⩽ ⩽ +°) Galaxy, using the Arecibo Radio Telescope. First results from the survey have found 61 galaxies within a 15 square degree area centered on l 192 =°and b = −2°. The survey reached its expected sensitivity of rms = 1 mJy at 9 km s −1 channel resolution, and is shown to be complete above integrated flux, F HI = 0.5 Jy km s −1 . The positional accuracy of the survey is 28″ and detections are found out to a recessional velocity of nearly 19,000 km s −1 . The survey confirms the extent of the Orion and Abell 539 clusters behind the plane of the Milky Way and discovers expansive voids, at 10,000 and 18,000 km s −1 . Twenty-six detections (43%) have a counterpart in the literature, but only two of these have known redshifts. Counterparts are 20% less common beyond v hel = 10,000 km s −1 and 33% less common at extinctions higher than A B = 3.5 mag. The ALFA ZOA Deep survey is able to probe large scale structure beyond redshifts that even the most modern wide-angle surveys have been able to detect in the ZOA at any wavelength.

We present a new optical luminosity-Hi mass bivariate luminosity function (BLF) based on Hi line observations from the Nançay Interstellar Baryons Legacy Extragalactic Survey (NIBLES). NIBLES sources lie within the local universe (900 ≤ cz ≤ 12,000 km s −1 ) and were chosen from SDSS DR5 such that the optical luminosity function was sampled as uniformly as possible. The Hi mass function (HIMF) derived from our raw-data BLF, which is based on Hi detections only, is consistent with the HIMFs derived from other optically selected surveys in that the low-mass slope is flatter than those derived from blind Hi surveys. However, spanning the entire luminosity range of NIBLES, we identify a highly consistent distribution of the Hi gas mass to luminosity ratio (gas-to-light ratio) with a predictable progression in the mean M HI /L r ratio as a function of L r . This consistency allows us to construct plausible gasto-light ratio distributions for very low-luminosity bins which lie outside the NIBLES sample. We also identify a ∼ 10% decrease in detection fraction for galaxies fainter than log(L r ) = 9.25, consistent with the expected decrease due to distance and sensitivity effects. Accounting for these trends, we reconstruct plausible gas-to-light distributions spanning luminosity bins down to log(L r ) = 5.25, thus producing a corrected BLF. This corrected BLF is in good qualitative agreement with optical luminosity-Hi mass distributions from the ALFALFA survey and is able to accurately reproduce blind survey HIMFs, lending credibility that this two dimensional optical luminosity-Hi mass distribution is an accurate representation of the volume density distribution of galaxies in the local universe. We also note that our agreement with HIMFs from other surveys is dependent on accounting for all systematic differences such as selection method, Hubble constant and Hi flux scale.

We obtained Arecibo Hi line follow-up observations of 154 of the 2600 galaxies in the Nançay Interstellar Baryons Legacy Extragalactic Survey (NIBLES) sample. These observations are on average four times more sensitive than the original observations at the Nançay Radio Telescope. The main goal of this survey is to characterize the underlying Hi properties of the NIBLES galaxies which were undetected or marginally detected at Nançay. Of the Nançay non-detections, 85% were either clearly or marginally detected at Arecibo, while 89% of the Nançay marginal detections were clearly detected. Based on the statistics of the detections relative to g − i color and r-band luminosity (L r ) distribution among our Arecibo observations, we anticipate ∼60% of our 867 Nançay non-detections and marginal detections could be detected at the sensitivity of our Arecibo observations. Follow-up observations of our low luminosity (L r < 10 8.5 L ) blue sources indicate that they have, on average, more concentrated stellar mass distributions than the Nançay detections in the same luminosity range, suggesting we may be probing galaxies with intrinsically different properties. These follow-up observations enable us to probe Hi mass fractions, log(M HI /M ) 0.5 dex and 1 dex lower, on average, than the NIBLES and ALFALFA surveys respectively.