We present results from 1351 high-resolution spectra of 1215 stars in the Orion Nebula Cluster (ONC) and the surrounding Orion 1c association, obtained with the Hectochelle multiobject echelle spectrograph on the 6.5 m MMT. We confirmed 1111 stars as members, based on their radial velocity and /or H emission. The radial velocity distribution of members shows a dispersion of ¼ 3:1 km s À1. We found a substantial north-south velocity gradient and spatially coherent structure in the radial velocity distribution, similar to that seen in the molecular gas in the region. We also identified several binary and high velocity stars, a region exhibiting signs of triggered star formation, and a possible foreground population of stars somewhat older than the ONC. Stars without infrared excesses (as detected with the IRAC instrument on the Spitzer Space Telescope) exhibit a wider spread in radial velocity than the infrared excess stars; this spread is mostly due to a blueshifted population of stars that may constitute a foreground population. We also identify some accreting stars, based on H, that do not have detectable infrared excesses with IRAC, and thus are potential transitional disk systems (objects with inner disk holes). We propose that the substructure seen in both the stellar and gaseous components is the result of nonuniform gravitational collapse to a filamentary distribution of gas. The spatial and kinematic correlation between the stellar and gaseous components suggests that the region is very young, probably only $1 crossing time old or less, to avoid shock dissipation and gravitational interactions which would tend to destroy the correlation between stars and gas.

Enormous Lyα Nebulae (ELANe), unique tracers of galaxy density peaks, are predicted to lie at the nodes and intersections of cosmic filamentary structures. Previous successful searches for ELANe have focused on wide-field narrowband surveys, or have targeted known sources such as ultraluminous quasi-stellar-objects (QSOs) or radio galaxies. Utilizing groups of coherently strong Lyα absorptions (CoSLAs), we have developed a new method to identify high-redshift galaxy overdensities and have identified an extremely massive overdensity, BOSS1441, at z = 2 − 3 (Cai et al. 2016a). In its density peak, we discover an ELAN that is associated with a relatively faint continuum. To date, this object has the highest diffuse Lyα nebular luminosity of L nebula = 5.1 ± 0.1 × 10 44 erg s −1 . Above the 2σ surface brightness limit of SB Lyα = 4.8 × 10 −18 erg s −1 cm −2 arcsec −2 , this nebula has an end-to-end spatial extent of 442 kpc. This radio-quiet source also has extended C iv λ1549 and He ii λ1640 emission on 30 kpc scales. Note that the Lyα, He ii and C iv emission all have double-peaked line profiles. Each velocity component has a full-width-half-maximum (FWHM) of ≈ 700 − 1000 km s −1 . We argue that this Lyα nebula could be powered by shocks due to an AGN-driven outflow or/and photoionization by a strongly obscured source.

We present a catalog of 1964 isolated, compact neutral hydrogen clouds from the Galactic Arecibo L-Band Feed Array Survey Data Release One. The clouds were identified by a custom machine-vision algorithm utilizing the difference of Gaussian kernels to search for clouds smaller than 20 . The clouds have velocities typically between |V LSR | = 20 and 400 km s −1 , line widths of 2.5-35 km s −1 , and column densities ranging from 1 to 35 × 10 18 cm −2 . The distances to the clouds in this catalog may cover several orders of magnitude, so the masses may range from less than a solar mass for clouds within the Galactic disk, to greater than 10 4 M for high-velocity clouds (HVCs) at the tip of the Magellanic Stream. To search for trends, we separate the catalog into five populations based on position, velocity, and line width: HVCs; galaxy candidates; cold low-velocity clouds (LVCs); warm, low positive-velocity clouds in the third Galactic quadrant; and the remaining warm LVCs. The observed HVCs are found to be associated with previously identified HVC complexes. We do not observe a large population of isolated clouds at high velocities as some models predict. We see evidence for distinct histories at low velocities in detecting populations of clouds corotating with the Galactic disk and a set of clouds that is not corotating.

We present an all sky map of the diffuse Galactic far ultraviolet (1344-1786Å) background using GALEX data, covering 65% of the sky with 11.79 arcmin 2 pixels. We investigate the dependence of the background on Galactic coordinates, finding that a standard cosecant model of intensity is not a valid fit. Furthermore, we compare our map to Galactic all sky maps of 100 µm emission, N HI column, and Hα intensity. We measure a consistent low level FUV intensity at zero-points for other Galactic quantities, indicating a 300 CU non-scattered isotropic component to the diffuse FUV. There is also a linear relationship between FUV and 100 µm emission below 100 µm values of 8 MJy/sr. We find a similar linear relationship between FUV and N HI below 10 21 cm −2 . The relationship between FUV and Hα intensity has no such constant cutoff. For all Galactic quantities, the slope of the linear portion of the relationship decreases with Galactic latitude. A modified cosecant model, taking into account dust scattering asymmetry and albedo, is able to accurately fit the diffuse FUV at latitudes above 20 • . The best fit model indicates an albedo, a, of 0.62 ± 0.04 and a scattering asymmetry function, g, of 0.78 ± 0.05. Deviations from the model fit may indicate regions of excess FUV emission from fluorescence or shock fronts, while low latitude regions with depressed FUV emission are likely the result of self-shielding dusty clouds.

Enormous Lyα nebulae (ELANe) represent the extrema of Lyα nebulosities. They have detected extents of >200 kpc in Lyα and Lyα luminosities >10 44 erg s −1. The ELAN population is an ideal laboratory to study the interactions between galaxies and the intergalactic/circumgalactic medium (IGM/CGM) given their brightness and sizes. The current sample size of ELANe is still very small, and the few z≈2 ELANe discovered to date are all associated with local overdensities of active galactic nuclei (AGNs). Inspired by these results, we have initiated a survey of ELANe associated with quasi-stellar object (QSO) pairs using the Palomar and Keck Cosmic Web Imagers (PCWI/KCWI). In this Letter, we present our first result: the discovery of ELAN0101+0201 associated with a QSO pair at z=2.45. Our PCWI discovery data shows that, above a 2σ surface brightness of 1.2×10 −17 erg s −1 cm −2 arcsec −2 , the end-to-end size of ELAN0101+0201 is 232 kpc. We have conducted follow-up observations using KCWI, resolving multiple Lyα emitting sources within the rectangular field of view of ≈130×165 projected kpc 2 , and obtaining their emission line profiles at high signal-to-noise ratios (S/Ns). Combining both KCWI and PCWI, our observations confirm that ELAN0101+0201 resides in an extremely overdense environment. Our observations further support that a large amount of cool (T ∼ 10 4 K) gas could exist in massive halos (M 10 13 M e) at z≈2. Future observations on a larger sample of similar systems will provide statistics of how cool gas is distributed in massive overdensities at high redshift and strongly constrain the evolution of the intracluster medium.