We present the catalog of ∼31500 extragalactic HI line sources detected by the completed ALFALFA survey out to z < 0.06 including both high signal-to-noise ratio (> 6.5) detections and ones of lower quality which coincide in both position and recessional velocity with galaxies of known redshift. We review the observing technique, data reduction pipeline, and catalog construction process, focusing on details of particular relevance to understanding the catalog's compiled parameters. We further describe and make available the digital HI line spectra associated with the catalogued sources. In addition to the extragalactic HI line detections, we report nine confirmed OH megamasers and ten OH megamaser candidates at 0.16 < z < 0.22 whose OH line signals are redshifted into the ALFALFA frequency band. Because of complexities in data collection and processing associated with the use of a feed-horn array on a complex single-dish antenna in the terrestrial radio frequency interference environment, we also present a list of suggestions and caveats for consideration by users of the ALFALFA extragalactic catalog for future scientific investigations.

We present Hα-derived star-formation rates (SFRs) for three z ≃ 0.75 galaxy clusters. Our 1σ flux limit corresponds to a star-formation rate of 0.10-0.24 h −2 100 M ⊙ yr −1 , and our minimum reliable Hα + [N II] rest-frame equivalent width is 10Å. We show that Hα narrowband imaging is an efficient method for measuring star formation in distant clusters. In two out of three clusters, we find that the fraction of star-forming galaxies increases with projected distance from the cluster center. We also find that the fraction of star-forming galaxies decreases with increasing local galaxy surface density in the same two clusters. We compare the median rate of star formation among star-forming cluster galaxies to a small sample of star-forming field galaxies from the literature and find that the median cluster SFRs are ∼ 50% less than the median field SFR. We characterize cluster evolution in terms of the mass-normalized integrated cluster SFR and find that the z ≃ 0.75 clusters have more SFR per cluster mass on average than the z ≤ 0.4 clusters from the literature. The interpretation of this result is complicated by the dependence of the mass-normalized SFR on cluster mass and the lack of sufficient overlap in the mass ranges covered by the low and high redshift samples. We find that the fraction and luminosities of the brightest starburst galaxies at z ≃ 0.75 are consistent with their being progenitors of the post-starburst galaxies at z ≃ 0.45 if the post-starburst phase lasts several (∼ 5) times longer than the starburst phase.

Analyzing 24µm MIPS/Spitzer data and the [O II]3727 line of a sample of galaxies at 0.4 ≤ z ≤ 0.8 from the ESO Distant Cluster Survey (EDisCS), we investigate the ongoing star formation rate (SFR) and the specific star formation rate (SSFR) as a function of stellar mass in galaxy clusters and groups, and compare with field studies. As for the field, we find a decline in SFR with time, indicating that star formation (SF) was more active in the past, and a decline in SSFR as galaxy stellar mass increases, showing that the current SF contributes more to the fractional growth of low-mass galaxies than high-mass galaxies. However, we find a lower median SFR (by a factor of ∼1.5) in cluster star-forming galaxies than in the field. The difference is highly significant when all Spitzer and emission-line galaxies are considered, regardless of color. It remains significant at z > 0.6 after removing red emission-line (REL) galaxies, to avoid possible AGN contamination. While there is overlap between the cluster and field SFR-Mass relations, we find a population of cluster galaxies (10-25%) with reduced SFR for their mass. These are likely to be in transition from star-forming to passive. Comparing separately clusters and groups at z > 0.6, only cluster trends are significantly different from the field, and the average cluster SFR at a given mass is ∼ 2 times lower than the field. We conclude that the average SFR in star-forming galaxies varies with galaxy environment at a fixed galaxy mass.

We present the average metallicity and star-formation rate of Lyα emitters (LAEs) measured from our large-area survey with three narrow-band (NB) filters covering the Lyα, [O ii]λ3727, and Hα+[N ii] lines of LAEs at z = 2.2. We select 919 z = 2.2 LAEs from Subaru/Suprime-Cam NB data in conjunction with Magellan/IMACS spectroscopy. Of these LAEs, 561 and 105 are observed with KPNO/NEWFIRM near-infrared NB filters whose central wavelengths are matched to redshifted [O ii] and Hα nebular lines, respectively. By stacking the near-infrared images of the LAEs, we successfully obtain average nebular-line fluxes of LAEs, the majority of which are too faint to be identified individually by narrow-band imaging or deep spectroscopy. The stacked object has an Hα luminosity of 1.7 × 10 42 erg s −1 corresponding to a star formation rate (SFR) of 14 M ⊙ yr −1 . We place, for the first time, a firm lower limit to the average metallicity of LAEs of Z 0.09 Z ⊙ (2σ) based on the [O ii]/(Hα+[N ii]) index together with photo-ionization models and empirical relations. This lower limit of metallicity rules out the hypothesis that LAEs, so far observed at z ∼ 2, are extremely metal poor (Z < 2 × 10 −2 Z ⊙ ) galaxies at the 4σ level. This limit is higher than a simple extrapolation of the observed mass-metallicity relation of z ∼ 2 UV-selected galaxies toward lower masses (5 × 10 8 M ⊙ ), but roughly consistent with a recently proposed fundamental mass-metallicity relation when the LAEs' relatively low SFR is taken into account. The Hα and Lyα luminosities of our NB-selected LAEs indicate that the escape fraction of Lyα photons is ∼ 12 − 30 %, much higher than the values derived for other galaxy populations at z ∼ 2.