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Reionisation-era galaxies often display intense nebular emission lines, both in rest-frame optical ([OIII]+H$\beta$) and ultraviolet (UV; CIII], CIV). How such strong nebular emission is powered remains unclear, with both active galactic nuclei (AGN) and hot stars considered equally viable. The UV continuum slopes of these early systems tend to be very blue ($\beta-1$) than typical star-forming systems in the reionisation era. To investigate the properties of AGN in the reionisation era, we have conducted a search for potential examples of rare analogues with blue continua at intermediate redshift ($z\sim2-3$). Our goals are to determine whether AGN with intense line emission and blue continua exist and thereby to establish the range of rest-frame UV and optical line ratios in this population. In this paper we report the detection of a X-ray luminous AGN at $z=3.21$ (UDS-24561) with extreme [OIII]+H$\beta$ line emission (EW $=1300$ \r{A}) and a blue UV continuum slope ($\beta=-2.34$). MMT/Binospec and Keck/MOSFIRE spectra indicate rest-frame UV line ratios consistent with AGN photoionisation models and rest-frame optical lines with both a narrow component (FWHM $=154$ km$/$s) and extended broad wings (FWHM $=977$ km$/$s), consistent with outflowing gas. We describe how such objects can be identified in future JWST emission line surveys in the reionisation era, thereby providing a valuable census of AGN activity at $z>6$ and understanding their contribution to cosmic reionisation., Comment: 11 pages, 7 figures, accepted by MNRAS

Deep spectroscopy of galaxies in the reionization-era has revealed intense CIII] and CIV line emission (EW $>15-20$ \r{A}). In order to interpret the nebular emission emerging at $z>6$, we have begun targeting rest-frame UV emission lines in galaxies with large specific star formation rates (sSFRs) at $1.36$ only in large sSFR galaxies with [OIII]+H$\beta$ EW $>1500$ \r{A}. In contrast to previous studies, we find that many galaxies with intense [OIII] have weak CIII] emission (EW $=5-8$ \r{A}), suggesting that the radiation field associated with young stellar populations is not sufficient to power strong CIII]. Photoionization models demonstrate that the spread in CIII] among systems with large sSFRs ([OIII]+H$\beta$ EW $>1500$ \r{A}) is driven by variations in metallicity, a result of the extreme sensitivity of CIII] to electron temperature. We find that the strong CIII] emission seen at $z>6$ (EW $>15$ \r{A}) requires metal poor gas ($\simeq0.1\ Z_\odot$) whereas the weaker CIII] emission in our sample tends to be found at moderate metallicities ($\simeq0.3\ Z_\odot$). The luminosity distribution of the CIII] emitters in our $z\simeq1-3$ sample presents a consistent picture, with stronger emission generally linked to low luminosity systems ($M_{\rm{UV}}>-19.5$) where low metallicities are more likely. We quantify the fraction of strong CIII] and CIV emitters at $z\simeq1-3$, providing a baseline for comparison against $z>6$ samples. We suggest that the first UV line detections at $z>6$ can be explained if a significant fraction of the early galaxy population is found at large sSFR ($>200$ Gyr$^{-1}$) and low metallicity ($, Comment: 21 pages, 10 figures, accepted by MNRAS

The James Webb Space Telescope (JWST) is expected to observe galaxies at $z>10$ that are presently inaccessible. Here, we use a self-consistent empirical model, the UniverseMachine, to generate mock galaxy catalogues and lightcones over the redshift range $z=0-15$. These data include realistic galaxy properties (stellar masses, star formation rates, and UV luminosities), galaxy-halo relationships, and galaxy-galaxy clustering. Mock observables are also provided for different model parameters spanning observational uncertainties at $z10^7 M_\odot$ and/or $M_{1500}12$ expand dramatically, so efforts to detect $z>12$ galaxies will provide the most valuable constraints on galaxy formation models. The faint-end slopes of the stellar mass/luminosity functions at a given mass/luminosity threshold steepen as redshift increases. This is because observable galaxies are hosted by haloes in the exponentially falling regime of the halo mass function at high redshifts. Hence, these faint-end slopes are robustly predicted to become shallower below current observable limits ($M_\ast < 10^7M_\odot$ or $M_\mathrm{1500}>-17$). For reionization models, extrapolating luminosity functions with a constant faint-end slope from $M_{1500}=-17$ down to $M_{1500}=-12$ gives the most reasonable upper limit for the total UV luminosity and cosmic star formation rate up to $z\sim 12$. We compare to three other empirical models and one semi-analytic model, showing that the range of predicted observables from our approach encompasses predictions from other techniques. Public catalogues and lightcones for common fields are available online., Comment: 17 pages, MNRAS submitted. Catalogs and lightcones available at https://www.peterbehroozi.com/data.html

Spectroscopic observations of massive $z>7$ galaxies selected to have extremely large [OIII]+H$\beta$ equivalent width (EW $\sim1500$ \r{A}) have recently revealed large Ly$\alpha$ detection rates, in contrast to the weak emission seen in the general population. Why these systems are uniquely visible in Ly$\alpha$ at redshifts where the IGM is likely significantly neutral is not clear. With the goal of better understanding these results, we have begun a campaign with MMT and Magellan to measure Ly$\alpha$ in galaxies with similar [OIII]+H$\beta$ EWs at $z\simeq2-3$. At these redshifts, the IGM is highly ionized, allowing us to clearly disentangle how the Ly$\alpha$ properties depend on the [OIII]+H$\beta$ EW. Here we present Ly$\alpha$ EWs of $49$ galaxies at $z=2.2-3.7$ with intense [OIII]+H$\beta$ line emission (EW $=300-3000$ \r{A}). Our results demonstrate that strong Ly$\alpha$ emission (EW $>20$ \r{A}) becomes more common in galaxies with larger [OIII]+H$\beta$ EW, reflecting a combination of increasingly efficient ionizing photon production and enhanced transmission of Ly$\alpha$. Among the galaxies with the most extreme [OIII]+H$\beta$ emission (EW $\sim1500$ \r{A}), we find that strong Ly$\alpha$ emission is not ubiquitous, with only $50$ per cent of our population showing Ly$\alpha$ EW $>20$ \r{A}. Our data suggest that the range of Ly$\alpha$ strengths is related to the observed ellipticity, with those systems that appear edge-on or elongated having weaker Ly$\alpha$ emission. We use these results to interpret the anomalous Ly$\alpha$ properties seen in $z>7$ galaxies with extreme [OIII]+H$\beta$ emission and discuss implications for the escape of ionizing radiation from these extreme line emitting galaxies.

Reionization-era galaxies tend to exhibit weak Ly$\alpha$ emission, likely reflecting attenuation from an increasingly neutral IGM. Recent observations have begun to reveal exceptions to this picture, with strong Ly$\alpha$ emission now known in four of the most massive z=7$-$9 galaxies in the CANDELS fields, all of which also exhibit intense [OIII]$+$H$\beta$ emission (EW$>$800 $\mathrm{\mathring{A}}$). To better understand why Ly$\alpha$ is anonymously strong in a subset of massive z$\simeq$7$-$9 galaxies, we have initiated an MMT/Binospec survey targeting a larger sample (N=22) of similarly luminous ($\simeq$1$-$6 L$^{\ast}_{\mathrm{UV}}$) z$\simeq$7 galaxies selected over very wide-area fields ($\sim$3 deg$^2$). We confidently ($>$7$\sigma$) detect Ly$\alpha$ in 78% (7/9) of galaxies with strong [OIII]$+$H$\beta$ emission (EW$>$800 $\mathrm{\mathring{A}}$) as opposed to only 8% (1/12) of galaxies with more moderate (EW=200$-$800 $\mathrm{\mathring{A}}$) [OIII]$+$H$\beta$. We argue that the higher Ly$\alpha$ EWs of the strong [OIII]$+$H$\beta$ population likely reflect enhanced ionizing photon production efficiency owing to their large sSFRs ($\gtrsim$30 Gyr$^{-1}$). We also find evidence that Ly$\alpha$ transmission from massive galaxies declines less rapidly over $6, Comment: 20 pages, 11 figures. Accepted in MNRAS with minor revisions

Over the past decades, rest-frame ultraviolet (UV) observations have provided large samples of UV luminous galaxies at redshift (z) greater than 6, during the so-called epoch of reionization. While a few of these UV identified galaxies revealed significant dust reservoirs, very heavily dust-obscured sources at these early times have remained elusive. They are limited to a rare population of extreme starburst galaxies, and companions of rare quasars. These studies conclude that the contribution of dust-obscured galaxies to the cosmic star formation rate density at $z>6$ is sub-dominant. Recent ALMA and Spitzer observations have identified a more abundant, less extreme population of obscured galaxies at $z=3-6$. However, this population has not been confirmed in the reionization epoch so far. Here, we report the discovery of two dust-obscured star forming galaxies at $z=6.6813\pm0.0005$ and $z=7.3521\pm0.0005$. These objects are not detected in existing rest-frame UV data, and were only discovered through their far-infrared [CII] lines and dust continuum emission as companions to typical UV-luminous galaxies at the same redshift. The two galaxies exhibit lower infrared luminosities and star-formation rates than extreme starbursts, in line with typical star-forming galaxies at $z\sim7$. This population of heavily dust-obscured galaxies appears to contribute 10-25 per cent to the $z>6$ cosmic star formation rate density., 16 pages, 7 figures, 4 tables, published in Nature

We quantify the distribution of [OIII]+H$\beta$ line strengths at z$\simeq$7 using a sample of 20 bright (M$_{\mathrm{UV}}$ $\lesssim$ $-$21) galaxies. We select these systems over wide-area fields (2.3 deg$^2$ total) using a new colour-selection which precisely selects galaxies at z$\simeq$6.63$-$6.83, a redshift range where blue Spitzer/IRAC [3.6]$-$[4.5] colours unambiguously indicate strong [OIII]$+$H$\beta$ emission. These 20 galaxies suggest a log-normal [OIII]$+$H$\beta$ EW distribution with median EW = 759$^{+112}_{-113}$ $\mathrm{\mathring{A}}$ and standard deviation = 0.26$^{+0.06}_{-0.05}$ dex. We find no evidence for strong variation in this EW distribution with UV luminosity. The typical [OIII]+H$\beta$ EW at z$\simeq$7 implied by our sample is considerably larger than that in massive star forming galaxies at z$\simeq$2, consistent with a shift toward larger average sSFR (4.4 Gyr$^{-1}$) and lower metallicities (0.16 Z$_\odot$). We also find evidence for the emergence of a population with yet more extreme nebular emission ([OIII]+H$\beta$ EW$>$1200 $\mathrm{\mathring{A}}$) that is rarely seen at lower redshifts. These objects have extremely large sSFR ($>$30 Gyr$^{-1}$), as would be expected for systems undergoing a burst or upturn in star formation. While this may be a short-lived phase, our results suggest that 20% of the z$\simeq$7 population has such extreme nebular emission, implying that galaxies likely undergo intense star formation episodes regularly at z$>$6. We argue that this population may be among the most effective ionizing agents in the reionization era, both in terms of photon production efficiency and escape fraction. We furthermore suggest that galaxies passing through this large sSFR phase are likely to be very efficient in forming bound star clusters., Comment: 20 pages, 11 figures. Accepted in MNRAS with minor revisions

The NIRCam instrument on the upcoming James Webb Space Telescope (JWST) will offer an unprecedented view of the most distant galaxies. In preparation for future deep NIRCam extragalactic surveys, it is crucial to understand the color selection of high-redshift galaxies using the Lyman dropout technique. To that end, we have used the JAdes extraGalactic Ultradeep Artificial Realizations (JAGUAR) mock catalog to simulate a series of extragalactic surveys with realistic noise estimates. This enables us to explore different color selections and their impact on the number density of recovered high-redshift galaxies and lower-redshift interlopers. We explore how survey depth, detection signal-to-noise ratio, color selection method, detection filter choice, and the presence of the Ly$\alpha$ emission line affects the resulting dropout selected samples. We find that redder selection colors reduce the number of recovered high-redshift galaxies, but the overall accuracy of the final sample is higher. In addition, we find that methods that utilize two or three color cuts have higher accuracy because of their ability to select against low-redshift quiescent and faint dusty interloper galaxies. We also explore the near-IR colors of brown dwarfs and demonstrate that, while they are predicted to have low on-sky densities, they are most likely to be recovered in F090W dropout selection, but there are color cuts which help to mitigate this contamination. Overall, our results provide NIRCam selection methods to aid in the creation of large, pure samples of ultra high-redshift galaxies from photometry alone., Comment: 24 pages, 20 figures, accepted for publication in the Astrophysical Journal

Galaxy clustering measurements can be used to constrain many aspects of galaxy evolution, including galaxy host halo masses, satellite quenching efficiencies, and merger rates. We simulate JWST galaxy clustering measurements at z$\sim$4$-$10 by utilizing mock galaxy samples produced by an empirical model, the UniverseMachine. We also adopt the survey footprints and typical depths of the planned joint NIRCam and NIRSpec Guaranteed Time Observation program planned for Cycle 1 to generate realistic JWST survey realizations and to model high-redshift galaxy selection completeness. We find that galaxy clustering will be measured with $\gtrsim$5$\sigma$ significance at z$\sim$4$-$10. Halo mass precisions resulting from Cycle 1 angular clustering measurements will be $\sim$0.2 dex for faint (-18 $\gtrsim$ $\mathit{M}_{\mathrm{UV}}^{ }$ $\gtrsim$ -19) galaxies at z$\sim$4$-$10 as well as $\sim$0.3 dex for bright ($\mathit{M}_{\mathrm{UV}}^{ }$ $\sim$ -20) galaxies at z$\sim$4$-$7. Dedicated spectroscopic follow-up over $\sim$150 arcmin$^2$ would improve these precisions by $\sim$0.1 dex by removing chance projections and low-redshift contaminants. Future JWST observations will therefore provide the first constraints on the stellar-halo mass relation in the epoch of reionization and substantially clarify how this relation evolves at z$>$4. We also find that $\sim$1000 individual satellites will be identifiable at z$\sim$4$-$8 with JWST, enabling strong tests of satellite quenching evolution beyond currently available data (z$\lesssim$2). Finally, we find that JWST observations can measure the evolution of galaxy major merger pair fractions at z$\sim$4$-$8 with $\sim$0.1$-$0.2 dex uncertainties. Such measurements would help determine the relative role of mergers to the build-up of stellar mass into the epoch of reionization., Comment: 17 pages, 7 figures

We present the results of a new sensitive survey of neutral hydrogen above and below the Galactic Center with the Green Bank Telescope. The observations extend up to Galactic latitude | b | < 10 deg with an effective angular resolution of 9.5' and an average rms brightness temperature noise of 40 mK in a 1 km/s channel. The survey reveals the existence of a population of anomalous high-velocity clouds extending up to heights of about 1.5 kpc from the Galactic Plane and showing no signature of Galactic rotation. These clouds have local standard of rest velocities | Vlsr | < 360 km/s and, assuming a Galactic Center origin, they have sizes of a few tens of parsecs and neutral hydrogen masses spanning $10-10^5 \, M_\odot$. Accounting for selection effects, the cloud population is symmetric in longitude, latitude, and Vlsr. We model the cloud kinematics in terms of an outflow expanding from the Galactic Center and find the population consistent with being material moving with radial velocity Vw ~ 330 km/s distributed throughout a bi-cone with opening angle $��>140$ deg. This simple model implies an outflow luminosity $Lw > 3 \times 10^{40}$ erg/s over the past 10 Myr, consistent with star formation feedback in the inner region of the Milky Way, with a cold gas mass-loss rate $\lesssim 0.1 \, M_\odot$/yr. These clouds may represent the cold gas component accelerated in the nuclear wind driven by our Galaxy, although some of the derived properties challenge current theoretical models of the entrainment process., 16 pages, 9 figures. Accepted for publication in ApJ

This paper describes the Polarization Spectroscopic Telescope Array (PolSTAR), a mission proposed to NASA's 2014 Small Explorer (SMEX) announcement of opportunity. PolSTAR measures the linear polarization of 3-50 keV (requirement; goal: 2.5-70 keV) X-rays probing the behavior of matter, radiation and the very fabric of spacetime under the extreme conditions close to the event horizons of black holes, as well as in and around magnetars and neutron stars. The PolSTAR design is based on the technology developed for the Nuclear Spectroscopic Telescope Array (NuSTAR) mission launched in June 2012. In particular, it uses the same X-ray optics, extendable telescope boom, optical bench, and CdZnTe detectors as NuSTAR. The mission has the sensitivity to measure ~1% linear polarization fractions for X-ray sources with fluxes down to ~5 mCrab. This paper describes the PolSTAR design as well as the science drivers and the potential science return., Comment: (Astroparticle Physics in press, 34 pages, 23 figures, 6 tables)

X-ray polarimetry promises to give qualitatively new information about high-energy astrophysical sources, such as binary black hole systems, micro-quasars, active galactic nuclei, neutron stars, and gamma-ray bursts. We designed, built and tested a X-ray polarimeter, X-Calibur, to be used in the focal plane of the balloon-borne InFOCuS grazing incidence X-ray telescope. X-Calibur combines a low-Z scatterer with a CZT detector assembly to measure the polarization of 20-80keV X-rays making use of the fact that polarized photons scatter preferentially perpendicular to the electric field orientation. X-Calibur achieves a high detection efficiency of ~80%. The X-Calibur detector assembly is completed, tested, and fully calibrated. The response to a polarized X-ray beam was measured successfully at the Cornell High Energy Synchrotron Source. This paper describes the design, calibration and performance of the X-Calibur polarimeter. In principle, a similar space-borne scattering polarimeter could operate over the broader 2-100keV energy band., 53 pages, 32 figures, accepted by the Journal of Astronomical Instrumentation