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There is growing evidence that high-mass star formation and hub-filament systems (HFS) are intricately linked. The gas kinematics along the filaments and the forming high-mass star(s) in the central hub are in excellent agreement with the new generation of global hierarchical high-mass star formation models. In this paper, we present an observational investigation of a typical HFS cloud, G310.142+0.758 (G310 hereafter) which reveals unambiguous evidence of mass inflow from the cloud scale via the filaments onto the forming protostar(s) at the hub conforming with the model predictions. Continuum and molecular line data from the ATOMS and MALT90 surveys are used that cover different spatial scales. Three filaments (with total mass $5.7\pm1.1\times 10^3~M_{\odot}$) are identified converging toward the central hub region where several signposts of high-mass star formation have been observed. The hub region contains a massive clump ($1280\pm260~M_{\odot}$) harbouring a central massive core. Additionally, five outflow lobes are associated with the central massive core implying a forming cluster. The observed large-scale, smooth and coherent velocity gradients from the cloud down to the core scale, and the signatures of infall motion seen in the central massive clump and core, clearly unveil a nearly-continuous, multi-scale mass accretion/transfer process at a similar mass infall rate of $\sim 10^{-3}~M_{\odot}~yr^{-1}$ over all scales, feeding the central forming high-mass protostar(s) in the G310 HFS cloud., Accepted to publish in ApJ. 10 pages with 6 figures and 2 tables

The fifth iteration of the Sloan Digital Sky Survey (SDSS-V) is set to obtain optical and near-infrared spectra of $\sim$5 million stars of all ages and masses throughout the Milky Way. As a part of these efforts, APOGEE & BOSS Young Star Survey (ABYSS) will observe $\sim10^5$ stars with ages $, 18 pages, 12 pages. Accepted to ApJS. Part of SDSS DR18

We present a Spitzer/Herschel focused survey of the Aquila molecular clouds ($d \sim 436$~pc) as part of the eHOPS (extension of HOPS Out to 500 ParSecs) census of nearby protostars. For every source detected in the Herschel/PACS bands, the eHOPS-Aquila catalog contains 1-850~$\mu$m SEDs assembled from 2MASS, Spitzer, Herschel, WISE, and JCMT/SCUBA-2 data. Using a newly developed set of criteria, we classify objects by their SEDs as protostars, pre-ms sequence stars with disks, and galaxies. A total of 172 protostars are found in Aquila, tightly concentrated in the molecular filaments that thread the clouds. Of these, 71 (42\%) are Class 0 protostars, 54 (31\%) are Class I protostars, 43 (25\%) are flat-spectrum protostars, and 4 (2\%) are Class II sources. Ten of the Class 0 protostars are young PACS Bright Red Sources similar to those discovered in Orion. We compare the SEDs to a grid of radiative transfer models to constrain the luminosities, envelope densities, and envelope masses of the protostars. A comparison of the eHOPS-Aquila to the HOPS protostars in Orion finds that the protostellar luminosity functions in the two star-forming regions are statistically indistinguishable, the bolometric temperatures/envelope masses of eHOPS-Aquila protostars are shifted to cooler temperatures/higher masses, and the eHOPS-Aquila protostars do not show the decline in luminosity with evolution found in Orion. We briefly discuss whether these differences are due to biases between the samples, diverging star formation histories, or the influence of environment on protostellar evolution., Comment: Accepted in ApJS. NASA IPAC/IRSA Data Release DOI: 10.26131/IRSA553

We present an 870 $μ$m continuum survey of 300 protostars from the Herschel Orion Protostar Survey using the Atacama Compact Array (ACA). These data measure protostellar flux densities on envelope scales $\leq$8000 au (20") and resolve the structure of envelopes with 1600 au (4") resolution, a factor of 3-5 improvement in angular resolution over existing single-dish 870 $μ$m observations. We compare the ACA observations to Atacama Large Millimeter/submillimeter Array 12 m array observations at 870 $μ$m with $\sim$0.1 (40 au) resolution. Using the 12 m data to measure the fluxes from disks and the ACA data within 2500 au to measure the combined disk plus envelope fluxes, we calculate the 12 m/ACA 870 $μ$m flux ratios. Our sample shows a clear evolution in this ratio. Class 0 protostars are mostly envelope-dominated with ratios $

APOGEE-2 is a dual-hemisphere, near-infrared (NIR), spectroscopic survey with the goal of producing a chemo-dynamical mapping of the Milky Way Galaxy. The targeting for APOGEE-2 is complex and has evolved with time. In this paper, we present the updates and additions to the initial targeting strategy for APOGEE-2N presented in Zasowski et al. (2017). These modifications come in two implementation modes: (i) "Ancillary Science Programs" competitively awarded to SDSS-IV PIs through proposal calls in 2015 and 2017 for the pursuit of new scientific avenues outside the main survey, and (ii) an effective 1.5-year expansion of the survey, known as the Bright Time Extension, made possible through accrued efficiency gains over the first years of the APOGEE-2N project. For the 23 distinct ancillary programs, we provide descriptions of the scientific aims, target selection, and how to identify these targets within the APOGEE-2 sample. The Bright Time Extension permitted changes to the main survey strategy, the inclusion of new programs in response to scientific discoveries or to exploit major new datasets not available at the outset of the survey design, and expansions of existing programs to enhance their scientific success and reach. After describing the motivations, implementation, and assessment of these programs, we also leave a summary of lessons learned from nearly a decade of APOGEE-1 and APOGEE-2 survey operations. A companion paper, Santana et al. (submitted), provides a complementary presentation of targeting modifications relevant to APOGEE-2 operations in the Southern Hemisphere., Comment: 59 pages; 11 Figures; 7 Tables; 2 Appendices; Submitted to Journal and Under Review; Posting to accompany papers using the SDSS-IV/APOGEE-2 Data Release 17 scheduled for December 2021

Direct collisions between finite-sized particles occur commonly in many areas of astrophysics. Such collisions are typically mediated by chaotic, bound gravitational interactions involving small numbers of particles. An important application is stellar collisions, which occur commonly in dense star clusters, and their relevance for the formation of various types of stellar exotica. In this paper, we return to our study of the collision rates and probabilities during small-number chaotic gravitational interactions ($N$ $\lesssim$ 10), moving beyond the small-number particle limit and into the realm of larger particle numbers ($N$ $\gtrsim$ 10$^3$) to test the extent of validity of our analytic model as a function of the particle properties and the number of interacting particles. This is done using direct $N$-body simulations of stellar collisions in dense star clusters, by varying the relative numbers of particles with different particle masses and radii. We compute the predicted rate of collisions using the mean free path approximation, adopting the point-particle limit and using the sticky-star approximation as our collision criterion. We evaluate its efficacy in the regime where gravitational-focusing is important by comparing the theoretical rates to numerical simulations. Using the tools developed in previous papers in this series, in particular Collision Rate Diagrams, we illustrate that our predicted and simulated rates are in excellent agreement, typically consistent with each other to within one standard deviation., 11 pages, 6 figures and 3 tables; submitted for publication; comments welcome

We report ALMA and VLA continuum observations that potentially identify the four youngest protostars in the Orion Molecular Clouds taken as part of the Orion VANDAM program. These are distinguished by bright, extended, irregular emission at 0.87 mm and 8 mm and are optically thick at 0.87 mm. These structures are distinct from the disk or point-like morphologies seen toward the other Orion protostars. The 0.87 mm emission implies temperatures of 41-170 K, requiring internal heating. The bright 8 mm emission implies masses of 0.5 to 1.2 M_sun assuming standard dust opacity models. One source has a Class 0 companion, while another exhibits substructure indicating a companion-candidate. Three compact outflows are detected, two of which may be driven by companions, with dynamical times of ~300 to ~400 years. The slowest outflow may be driven by a first hydrostatic core. These protostars appear to trace an early phase when the centers of collapsing fragments become optically thick to their own radiation and compression raises the gas temperature. This phase is thought to accompany the formation of hydrostatic cores. A key question is whether these structures are evolving on free fall times of ~100 years, or whether they are evolving on Kelvin-Helmholtz times of several thousand years. The number of these sources imply a lifetime of ~6000 years, in closer agreement with the Kelvin-Helmholtz time. In this case, rotational and/or magnetic support could be slowing the collapse., accepted by ApJ, 22 pages, 11 figures, 5 tables

This paper documents the sixteenth data release (DR16) from the Sloan Digital Sky Surveys; the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the southern hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey (TDSS) and new data from the SPectroscopic IDentification of ERosita Survey (SPIDERS) programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17)., Comment: DR16 release: Monday Dec 9th 2019. This is the alphabetical order SDSS-IV collaboration data release paper. 25 pages, 6 figures, accepted by ApJS on 11th May 2020. Minor changes clarify or improve text and figures relative to v1

The Integral Shaped Filament (ISF) is the nearest molecular cloud with rapid star formation, including massive stars, and it is therefore a star-formation laboratory. We use Gaia parallaxes, to show that the distances to young Class II stars ('disks') projected along the spine of this filament are related to the gas radial velocity by $$ v = -{D\over\tau} + K;\qquad \tau = 4\,{\rm Myr}, $$ where $K$ is a constant. This implies that the ISF is a standing wave, which is consistent with the Stutz & Gould (2016) 'Slingshot' prediction. The $\tau=4\,{\rm Myr}$ timescale is consistent with the 'Slingshot' picture that the Orion Nebula Cluster (ONC) is the third cluster to be violently split off from the Orion A cloud (following NGC 1981 and NGC 1987) at few-Myr intervals due to gravito-magnetic oscillations. We also present preliminary evidence that the truncation of the ISF is now taking place $16^\prime$ south of the ONC and is mediated by a torsional wave that is propagating south with a characteristic timescale $\tau_{\rm torsion} = 0.5\,{\rm Myr}$, i.e. eight times shorter. The relation between these two wave phenomena is not presently understood., Comment: 5 pages, 5 figures, submitted to MNRAS Letters

Stars form from the gravitational collapse of dense molecular cloud cores. In the protostellar phase, mass accretes from the core onto a protostar, likely through an accretion disk, and it is during this phase that the initial masses of stars and the initial conditions for planet formation are set. Over the past decade, new observational capabilities provided by the Spitzer Space Telescope and Herschel Space Observatory have enabled wide-field surveys of entire star-forming clouds with unprecedented sensitivity, resolution, and infrared wavelength coverage. We review resulting advances in the field, focusing both on the observations themselves and the constraints they place on theoretical models of star formation and protostellar evolution. We also emphasize open questions and outline new directions needed to further advance the field., Comment: Accepted for publication as a chapter in Protostars and Planets VI, University of Arizona Press (2014), eds. H. Beuther, R. Klessen, C. Dullemond, Th. Henning

We present a hierarchical Bayesian method for fitting infrared spectral energy distributions (SEDs) of dust emission to observed fluxes. Under the standard assumption of optically thin single temperature (T) sources the dust SED as represented by a power--law modified black body is subject to a strong degeneracy between T and the spectral index beta. The traditional non-hierarchical approaches, typically based on chi-square minimization, are severely limited by this degeneracy, as it produces an artificial anti-correlation between T and beta even with modest levels of observational noise. The hierarchical Bayesian method rigorously and self-consistently treats measurement uncertainties, including calibration and noise, resulting in more precise SED fits. As a result, the Bayesian fits do not produce any spurious anti-correlations between the SED parameters due to measurement uncertainty. We demonstrate that the Bayesian method is substantially more accurate than the chi-square fit in recovering the SED parameters, as well as the correlations between them. As an illustration, we apply our method to Herschel and sub millimeter ground-based observations of the star-forming Bok globule CB244. This source is a small, nearby molecular cloud containing a single low-mass protostar and a starless core. We find that T and beta are weakly positively correlated -- in contradiction with the chi-square fits, which indicate a T-beta anti-correlation from the same data-set. Additionally, in comparison to the chi-square fits the Bayesian SED parameter estimates exhibit a reduced range in values., Comment: 20 pages, 9 figures, ApJ format, revised version matches ApJ-accepted version

We present Spitzer observations of a sample of 12 starless cores selected to have prominent 24 micron shadows. The Spitzer images show 8 and 24 micron shadows and in some cases 70 micron shadows; these spatially resolved absorption features trace the densest regions of the cores. We have carried out a 12CO (2-1) and 13CO (2-1) mapping survey of these cores with the Heinrich Hertz Telescope (HHT). We use the shadow features to derive optical depth maps. We derive molecular masses for the cores and the surrounding environment; we find that the 24 micron shadow masses are always greater than or equal to the molecular masses derived in the same region, a discrepancy likely caused by CO freeze--out onto dust grains. We combine this sample with two additional cores that we studied previously to bring the total sample to 14 cores. Using a simple Jeans mass criterion we find that ~ 2/3 of the cores selected to have prominent 24 micron shadows are collapsing or near collapse, a result that is supported by millimeter line observations. Of this subset at least half have indications of 70 micron shadows. All cores observed to produce absorption features at 70 micron are close to collapse. We conclude that 24 micron shadows, and even more so the 70 micron ones, are useful markers of cloud cores that are approaching collapse., 41 pages, 28 figures, 5 tables; accepted by ApJ

We present Spitzer observations of a sample of 12 starless cores selected to have prominent 24 mum shadows. The Spitzer images show 8 mum and 24 mum shadows and in some cases 70 mum shadows; these spatially resolved absorption features trace the densest regions of the cores. We have carried out a {sup 12}CO (2-1) and {sup 13}CO (2-1) mapping survey of these cores with the Heinrich Hertz Telescope (HHT). We use the shadow features to derive optical depth maps. We derive molecular masses for the cores and the surrounding environment; we find that the 24 mum shadow masses are always greater than or equal to the molecular masses derived in the same region, a discrepancy likely caused by CO freezeout onto dust grains. We combine this sample with two additional cores that we studied previously to bring the total sample to 14 cores. Using a simple Jeans mass criterion, we find that approx2/3 of the cores selected to have prominent 24 mum shadows are collapsing or near collapse, a result that is supported by millimeter line observations. Of this subset at least half have indications of 70 mum shadows. All cores observed to produce absorption features at 70 mummore » are close to collapse. We conclude that 24 mum shadows, and even more so the 70 mum ones, are useful markers of cloud cores that are approaching collapse.« less

We study the nature of faint, red-selected galaxies at z ~ 2-3 using the Hubble Ultra Deep Field (HUDF) and Spitzer IRAC photometry. We detect candidate galaxies to H < 26 mag, probing lower-luminosity (lower mass) galaxies at these redshifts. We identify 32 galaxies satisfying the (J - H) > 1.0 mag color selection, 16 of which have unblended [3.6um] and [4.5um] IRAC photometry. We derive photometric redshifts, masses, and stellar population parameters for these objects. We find that the selected objects span a diverse range of properties over a large range of redshifts, 1 < z < 3.5. A substantial fraction (11/32) appear to be lower-redshift (z < 2.5), heavily obscured dusty galaxies or edge-on spiral galaxies, while others (12/32) appear to be galaxies at 2 < z < 3.5 whose light at rest-frame optical wavelengths is dominated by evolved stellar populations. Interestingly, by including Spitzer data many candidates for galaxies dominated by evolved stellar populations are rejected, and for only a subset of the sample (6/16) do the data favor this interpretation. We place an upper limit on the space and stellar mass density of candidate massive evolved galaxies. The z > 2.5 objects that are dominated by evolved stellar populations have a space density at most one-third that of z ~ 0 red, early-type galaxies. Therefore, at least two-thirds of present-day early-type galaxies assemble or evolve into their current configuration at redshifts below 2.5. We find a dearth of candidates for low-mass galaxies at 1.5 < z < 3 that are dominated by passively evolving stellar populations even though the data should be sensitive to them; thus, at these redshifts, galaxies whose light is dominated by evolved stellar populations are restricted to only those galaxies that have assembled high stellar mass.[Abridged], 18 pages, 10 figures, and 4 tables. Accepted for publication in ApJ

We announce the initial release of data from the Ohio State University Bright Spiral Galaxy Survey, a BVRJHK imaging survey of a well-defined sample of 205 bright, nearby spiral galaxies. We present H-band morphological classification on the Hubble sequence for the OSU Survey sample. We compare the H-band classification to B-band classification from our own images and from standard galaxy catalogs. Our B-band classifications match well with those of the standard catalogs. On average, galaxies with optical classifications from Sa through Scd appear about one T-type earlier in the H-band than in the B-band, but with large scatter. This result does not support recent claims made in the literature that the optical and near-IR morphologies of spiral galaxies are uncorrelated. We present detailed descriptions of the H-band morphologies of our entire sample, as well as B- and H-band images for a set of 17 galaxies chosen as type examples, and BRH color-composite images of six galaxies chosen to demonstrate the range in morphological variation as a function of wavelength. Data from the survey are accessible at http://www.astronomy.ohio-state.edu/~survey/, Comment: LaTeX with AASTeX style file, 56 pages with 4 multi-part figures. Accepted for publication in The Astrophysical Journal Supplement. Data available at http://www.astronomy.ohio-state.edu/~survey/EDR/

We measure the ratio of total to selective extinction, R_{VI}=A_V/E(V-I), toward Baade's Window by comparing the VIK colors of 132 Baade's Window G and K giants from Tiede, Frogel, & Terndrup with the solar-neighborhood (V-I),(V-K) relation from Bessell & Brett. We find R_{VI}=2.283 +/- 0.016, and show that our measurement has no significant dependence on stellar type from G0 to K4. Adjusting the Paczynski et al. determination of the centroid of the dereddened Baade's Window clump for this revised value of $R_{VI}$, we find I_{0,RC}=14.43 and (V-I)_{0,RC}=1.058. This implies a distance to the Baade's Window clump of d_{BW} = 8.63 +/- 0.16 kpc, where the error bar takes account of statistical but not systematic uncertainties., 8 pages, 1 figure, submitted to ApJ

We present ALMA (0.87~mm) and VLA (9~mm) observations toward OMC2-FIR4 and OMC2-FIR3 within the Orion integral-shaped filament that are thought to be the nearest regions of intermediate mass star formation. We characterize the continuum sources within these regions on $\sim$40~AU (0\farcs1) scales and associated molecular line emission at a factor of $\sim$30 better resolution than previous observations at similar wavelengths. We identify six compact continuum sources within OMC2-FIR4, four in OMC2-FIR3, and one additional source just outside OMC2-FIR4. This continuum emission is tracing the inner envelope and/or disk emission on less than 100~AU scales. HOPS-108 is the only protostar in OMC2-FIR4 that exhibits emission from high-excitation transitions of complex organic molecules (e.g., methanol and other lines) coincident with the continuum emission. HOPS-370 in OMC2-FIR3 with L~$\sim$~360~\lsun, also exhibits emission from high-excitation methanol and other lines. The methanol emission toward these two protostars is indicative of temperatures high enough to thermally evaporate methanol from icy dust grains; overall these protostars have characteristics similar to hot corinos. We do not identify a clear outflow from HOPS-108 in \twco, but find evidence of interaction between the outflow/jet from HOPS-370 and the OMC2-FIR4 region. The multitude of observational constraints indicate that HOPS-108 is likely a low to intermediate-mass protostar in its main mass accretion phase and it is the most luminous protostar in OMC2-FIR4. The high resolution data presented here are essential for disentangling the embedded protostars from their surrounding dusty environments and characterizing them.