We describe the automated spectral classification, redshift determination, and parameter measurement pipeline in use for the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III (SDSS-III) as of the survey's Ninth Data Release (DR9), encompassing 831,000 moderateresolution optical spectra. We give a review of the algorithms employed, and describe the changes to the pipeline that have been implemented for BOSS relative to previous SDSS-I/II versions, including new sets of stellar, galaxy, and quasar redshift templates. For the color-selected "CMASS" sample of massive galaxies at redshift 0.4 z 0.8 targeted by BOSS for the purposes of large-scale cosmological measurements, the pipeline achieves an automated classification success rate of 98.7% and confirms 95.4% of unique CMASS targets as galaxies (with the balance being mostly M stars). Based on visual inspections of a subset of BOSS galaxies, we find that approximately 0.2% of confidently reported CMASS sample classifications and redshifts are incorrect, and about 0.4% of all CMASS spectra are objects unclassified by the current algorithm which are potentially recoverable. The BOSS pipeline confirms that ∼51.5% of the quasar targets have quasar spectra, with the balance mainly consisting of stars and low signal-to-noise spectra. Statistical (as opposed to systematic) redshift errors propagated from photon noise are typically a few tens of km s −1 for both galaxies and quasars, with a significant tail to a few hundreds of km s −1 for quasars. We test the accuracy of these statistical redshift error estimates using repeat observations, finding them underestimated by a factor of 1.19 to 1.34 for galaxies, and by a factor of 2 for quasars. We assess the impact of sky-subtraction quality, signal-to-noise ratio, and other factors on galaxy redshift success. Finally, we document known issues with the BOSS DR9 spectroscopic data set, and describe directions of ongoing development.

Quiescent galaxies with little or no ongoing star formation dominate the galaxy population above M * ∼ 2 × 10 10 M⊙, where their numbers have increased by a factor of ∼ 25 since z ∼ 2 1-4 . Once star formation is initially shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole [5][6][7] , an unknown mechanism must remove or heat subsequently accreted gas from stellar mass loss 8 or mergers that would otherwise cool to form stars 9, 10 . Energy output from a black hole accreting at a low rate has been proposed 11-13 , but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centers of clusters 14,15 , which are too rare to explain the vast majority of the quiescent population 16 . Here we report bisymmetric emission features co-aligned with strong ionized gas velocity gradients from which we infer the presence of centrallydriven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as 10% of the population at M * ∼ 2 × 10 10 M⊙. In a prototypical example, we calculate that the energy input from the galaxy's low-level active nucleus is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.Using optical imaging spectroscopy from the Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory 17 (SDSS-IV MaNGA) program, we define a new class of quiescent galaxies (required to have red rest-frame colors, NUV − r > 5) that is characterized by the presence of narrow bisymmetric patterns in equivalent width (EW) maps of strong emission lines, such as Hα and [O III]. Our selection employs multiband imaging to exclude galaxies with dust lanes and other disk signatures. The observed enhanced emission features are oriented randomly with respect to the optical surface brightness morphology, but roughly align with strong, systematic velocity gradients as traced by the ionized gas emission lines. The gas velocity fields in these galaxies are decoupled from their stellar motions. These galaxies are surprisingly common among the quiescent population, accounting for ∼10% of quiescent galaxies with log M * /M⊙ ∼ 10.3. To illuminate the salient features of this class, we focus on a prototypical example, nicknamed "Akira" (Fig. 1). The SDSS imaging shows Akira to be an unremarkable spheroidal galaxy of moderate stellar mass (log M * /M⊙ = 10.78) that is interacting with a low-mass companion (nicknamed "Tetsuo") at a projected separation of ≈ 32 kpc (67 ′′ ); they are not classified as members of a larger galaxy group 18 and the properties of both galaxies are listed in Table 1. Spectral energy distribution (SED) fitting indicates that Akira is nearly dormant, with almost no detection of ongoing star formation 19 . Resolved spectroscopy, however, reveals intriguing and complex patterns among spectral tracers of gas in Ak...

We measure the strength of He ii λ4686 nebular emission in passively evolving ("retired") galaxies, aiming to constrain their populations of hot accreting white dwarfs (WDs) in the context of the single degenerate (SD) scenario of Type Ia supernovae (SNe Ia). In the SD scenario, as a WD burns hydrogen-rich material accreted from a companion star, it becomes a powerful source of ionizing UV emission. If significant populations of such sources exist in galaxies, strong emission in the recombination lines of He ii should be expected from the interstellar medium. To explore this conjecture, we select from the Sloan Digital Sky Survey ∼ 11 500 emission line galaxies with stellar ages > 1 Gyr showing no signs of AGN activity and co-add their spectra in bins of stellar population age. For the first time, we detect He ii λ4686 nebular emission in retired galaxies and find it to be significantly weaker than that expected in the SD scenario, especially in the youngest age bin (1 − 4 Gyr) where the SN Ia rate is the highest. Instead, the strength of the observed He ii λ4686 nebular emission is consistent with post-asymptotic giant branch stars being the sole ionizing source in all age bins. These results limit populations of accreting WDs with photospheric temperatures (T eff ) in the range ∼ (1.5 − 6) · 10 5 K to the level at which they can account for no more than ∼ 5 − 10% of the observed SN Ia rate. Conversely, should all WD progenitors of SN Ia go through the phase of steady nuclear burning with T eff ∼ (1.5 − 6) · 10 5 K, they do not increase their mass by more than ∼ 0.03 M ⊙ in this regime.

Galaxies grow through both internal and external processes. In about 10% of nearby red galaxies with little star formation, gas and stars are counter-rotating, demonstrating the importance of external gas acquisition in these galaxies. However, systematic studies of such phenomena in blue, star-forming galaxies are rare, leaving uncertain the role of external gas acquisition in driving evolution of blue galaxies. Here, based on new measurements with integral field spectroscopy of a large representative galaxy sample, we find an appreciable fraction of counter-rotators among blue galaxies (9 out of 489 galaxies). The central regions of blue counter-rotators show younger stellar populations and more intense, ongoing star formation than their outer parts, indicating ongoing growth of the central regions. The result offers observational evidence that the acquisition of external gas in blue galaxies is possible; the interaction with pre-existing gas funnels the gas into nuclear regions (<1 kpc) to form new stars.