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This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 survey that publicly releases infrared spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the subsurvey Time Domain Spectroscopic Survey data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey subsurvey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated value-added catalogs. This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper, Local Volume Mapper, and Black Hole Mapper surveys.

An excess γ-ray signal toward the outer halo of M31 has recently been reported. Although other explanations are plausible, the possibility that it arises from dark matter (DM) is valid. In this work we interpret the excess in the framework of DM annihilation, using as our representative case WIMP DM annihilating to bottom quarks, and we perform a detailed study of the systematic uncertainty in the J-factor for the M31 field. We find that the signal favors a DM particle with a mass of ~45-72 GeV. While the mass is well constrained, the systematic uncertainty in the cross section spans 3 orders of magnitude, ranging from ~5 × 10-27-5 × 10-24 cm3 s-1. This high uncertainty is due to two main factors, namely, an uncertainty in the substructure nature and geometry of the DM halos for both M31 and the Milky Way (MW), and correspondingly, an uncertainty in the contribution to the signal from the MW's DM halo along the line of sight. However, under the conditions that the minimum subhalo mass is ≲10-6M⊙ and the actual contribution from the MW's DM halo along the line of sight is at least ~30% of its total value, we show that there is a large overlap with the DM interpretations of both the Galactic center (GC) excess and the antiproton excess, while also being compatible with the limits for the MW dwarf spheroidals. More generally, we summarize the results from numerous complementary DM searches in the energy range 10 GeV-300 GeV corresponding to the GC excess and identify a region in parameter space that still remains viable for discovery of the DM particle.

ABSTRACT: We present the first public data release of the GOGREEN (Gemini Observations of Galaxies in Rich Early Environments) and GCLASS (Gemini CLuster Astrophysics Spectroscopic Survey) surveys of galaxies in dense environments, spanning a redshift range 0.8 < z < 1.5. The surveys consist of deep, multiwavelength photometry and extensive Gemini GMOS spectroscopy of galaxies in 26 overdense systems ranging in halo mass from small groups to the most massive clusters. The objective of both projects was primarily to understand how the evolution of galaxies is affected by their environment, and to determine the physical processes that lead to the quenching of star formation. There was an emphasis on obtaining unbiased spectroscopy over a wide stellar mass range (M ≳ 2 × 1010 M⊙), throughout and beyond the cluster virialized regions. The final spectroscopic sample includes 2771 unique objects, of which 2257 have reliable spectroscopic redshifts. Of these, 1704 have redshifts in the range 0.8 < z < 1.5, and nearly 800 are confirmed cluster members. Imaging spans the full optical and near-infrared wavelength range, at depths comparable to the UltraVISTA survey, and includes Hubble Space Telescope/Wide Field Camera 3 F160W (GOGREEN) and F140W (GCLASS). This data release includes fully reduced images and spectra, with catalogues of advanced data products including redshifts, line strengths, star formation rates, stellar masses, and rest-frame colours. Here, we present an overview of the data, including an analysis of the spectroscopic completeness and redshift quality.

In the local Universe, there is a strong division in the star-forming properties of low-mass galaxies, with star formation largely ubiquitous amongst the field population while satellite systems are predominantly quenched. This dichotomy implies that environmental processes play the dominant role in suppressing star formation within this low-mass regime (M ★ ~ 105.5-8 M☉). As shown by observations of the Local Volume, however, there is a non-negligible population of passive systems in the field, which challenges our understanding of quenching at low masses. By applying the satellite quenching models of Fillingham et al. (2015) to subhalo populations in the Exploring the Local Volume In Simulations suite, we investigate the role of environmental processes in quenching star formation within the nearby field. Using model parameters that reproduce the satellite quenched fraction in the Local Group, we predict a quenched fraction - due solely to environmental effects - of ~0.52 ± 0.26 within 1 < R/R vir < 2 of the Milky Way and M31. This is in good agreement with current observations of the Local Volume and suggests that the majority of the passive field systems observed at these distances are quenched via environmental mechanisms. Beyond 2R vir, however, dwarf galaxy quenching becomes difficult to explain through an interaction with either the Milky Way or M31, such that more isolated, field dwarfs may be self-quenched as a result of star-formation feedback.

The Type Ia supernova (SN Ia) 2016coj in NGC 4125 (redshift z = 0.00452 ± 0.00006) was discovered by the Lick Observatory Supernova Search 4.9 days after the fitted first-light time (FFLT; 11.1 days before B-band maximum). Our first detection (prediscovery) is merely 0.6 ± 0.5 days after the FFLT, making SN 2016coj one of the earliest known detections of an SN Ia. A spectrum was taken only 3.7 hr after discovery (5.0 days after the FFLT) and classified as a normal SN Ia. We performed high-quality photometry, low- and high-resolution spectroscopy, and spectropolarimetry, finding that SN 2016coj is a spectroscopically normal SN Ia, but the velocity of Si ii λ6355 around peak brightness (∼12,600 kms-1) is a bit higher than that of typical normal SNe. The Si ii λ6355 velocity evolution can be well fit by a broken-power-law function for up to a month after the FFLT. SN 2016coj has a normal peak luminosity (MB ≈ -18.9 ± 0.2 mag), and it reaches a B-band maximum ∼16.0 days after the FFLT. We estimate there to be low host-galaxy extinction based on the absence of Na i D absorption lines in our low- and high-resolution spectra. The spectropolarimetric data exhibit weak polarization in the continuum, but the Si ii line polarization is quite strong (∼0.9% ± 0.1%) at peak brightness.

Recent studies of galaxies in the local Universe, including those in the Local Group, find that the efficiency of environmental (or satellite) quenching increases dramatically at satellite stellar masses below ~ 108M⊙. This suggest a physical scalewhere quenching transitions from a slow 'starvation' mode to a rapid 'stripping' mode at low masses. We investigate the plausibility of this scenario using observed HI surface density profiles for a sample of 66 nearby galaxies as inputs to analytic calculations of ram-pressure and turbulent viscous stripping. Across a broad range of host properties, we find that stripping becomes increasingly effective at M* ≲ 108-9M⊙, reproducing the critical mass scale observed. However, for canonical values of the circumgalactic medium density (nhalo < 10-3.5 cm-3), we find that stripping is not fully effective; infalling satellites are, on average, stripped of only ≲40-60 per cent of their cold gas reservoir, which is insufficient to match observations. By including a host halo gas distribution that is clumpy and therefore contains regions of higher density, we are able to reproduce the observed HI gas fractions (and thus the high quenched fraction and short quenching timescale) of Local Group satellites, suggesting that a host halo with clumpy gas may be crucial for quenching low-mass systems in Local Group-like (and more massive) host haloes.

The vast majority of dwarf satellites orbiting the Milky Way and M31 arequenched, while comparable galaxies in the field are gas-rich and star-forming.Assuming that this dichotomy is driven by environmental quenching, we use theELVIS suite of N-body simulations to constrain the characteristic timescaleupon which satellites must quench following infall into the virial volumes oftheir hosts. The high satellite quenched fraction observed in the Local Groupdemands an extremely short quenching timescale (~ 2 Gyr) for dwarf satellitesin the mass range Mstar ~ 10^6-10^8 Msun. This quenching timescale issignificantly shorter than that required to explain the quenched fraction ofmore massive satellites (~ 8 Gyr), both in the Local Group and in more massivehost halos, suggesting a dramatic change in the dominant satellite quenchingmechanism at Mstar < 10^8 Msun. Combining our work with the results ofcomplementary analyses in the literature, we conclude that the suppression ofstar formation in massive satellites (Mstar ~ 10^8 - 10^11 Msun) is broadlyconsistent with being driven by starvation, such that the satellite quenchingtimescale corresponds to the cold gas depletion time. Below a critical stellarmass scale of ~ 10^8 Msun, however, the required quenching times are muchshorter than the expected cold gas depletion times. Instead, quenching must acton a timescale comparable to the dynamical time of the host halo. We posit thatram-pressure stripping can naturally explain this behavior, with the criticalmass (of Mstar ~ 10^8 Msun) corresponding to halos with gravitational restoringforces that are too weak to overcome the drag force encountered when movingthrough an extended, hot circumgalactic medium.

The vast majority of dwarf satellites orbiting the Milky Way and M31 arequenched, while comparable galaxies in the field are gas-rich and star-forming.Assuming that this dichotomy is driven by environmental quenching, we use theELVIS suite of N-body simulations to constrain the characteristic timescaleupon which satellites must quench following infall into the virial volumes oftheir hosts. The high satellite quenched fraction observed in the Local Groupdemands an extremely short quenching timescale (~ 2 Gyr) for dwarf satellitesin the mass range Mstar ~ 10^6-10^8 Msun. This quenching timescale issignificantly shorter than that required to explain the quenched fraction ofmore massive satellites (~ 8 Gyr), both in the Local Group and in more massivehost halos, suggesting a dramatic change in the dominant satellite quenchingmechanism at Mstar < 10^8 Msun. Combining our work with the results ofcomplementary analyses in the literature, we conclude that the suppression ofstar formation in massive satellites (Mstar ~ 10^8 - 10^11 Msun) is broadlyconsistent with being driven by starvation, such that the satellite quenchingtimescale corresponds to the cold gas depletion time. Below a critical stellarmass scale of ~ 10^8 Msun, however, the required quenching times are muchshorter than the expected cold gas depletion times. Instead, quenching must acton a timescale comparable to the dynamical time of the host halo. We posit thatram-pressure stripping can naturally explain this behavior, with the criticalmass (of Mstar ~ 10^8 Msun) corresponding to halos with gravitational restoringforces that are too weak to overcome the drag force encountered when movingthrough an extended, hot circumgalactic medium.