arXiv subjects

Ryan Endsley

Publications and source records attributed to Ryan Endsley.

88 records · Page 5Linked to original sources

arXiv2022

Strong Ly$α$ Emission in an Overdense Region at $z=6.8$: A Very Large ($R\sim3$ physical Mpc) Ionized Bubble in COSMOS?

Our understanding of reionization has advanced considerably over the past decade, with several results now demonstrating that the IGM transitioned from substantially neutral at $z=7$ to largely reionized at $z=6$. However, little remains known about the sizes of ionized bubbles at $z\gtrsim7$ as well as the galaxy overdensities which drive their growth. Fortunately, rest-UV spectroscopic observations offer a pathway towards characterizing these ionized bubbles thanks to the resonant nature of Lyman-alpha photons. In a previous work, we presented Ly$α$ detections from three closely-separated Lyman-break galaxies at $z\simeq6.8$, suggesting the presence of a large ($R>1$ physical Mpc) ionized bubble in the 1.5 deg$^2$ COSMOS field. Here, we present new deep Ly$α$ spectra of ten UV-bright ($\mathrm{M}_{\mathrm{UV}}^{} \leq -20.4$) $z\simeq6.6-6.9$ galaxies in the surrounding area, enabling us to better characterize this potential ionized bubble. We confidently detect (S/N$>$7) Ly$α$ emission at $z=6.701-6.882$ in nine of ten observed galaxies, revealing that the large-scale volume spanned by these sources (characteristic radius $R = 3.2$ physical Mpc) traces a strong galaxy overdensity ($N/\langle N\rangle \gtrsim 3$). Our data additionally confirm that the Ly$α$ emission of UV-bright galaxies in this volume is significantly enhanced, with 40% (4/10) showing strong Ly$α$ emission (equivalent width$>$25 $\mathrm{\mathring{A}}$) compared to the 8$-$9% found on average at $z\sim7$. The median Ly$α$ equivalent width of our observed galaxies is also $\approx$2$\times$ that typical at $z\sim7$, consistent with expectations if a very large ($R\sim3$ physical Mpc) ionized bubble is allowing the Ly$α$ photons to cosmologically redshift far into the damping wing before encountering HI.

astro-ph.GA↗

arXiv2022

The ALMA REBELS Survey: Efficient Ly$α$ Transmission of UV-Bright z$\simeq$7 Galaxies from Large Velocity Offsets and Broad Line Widths

Recent work has shown that UV-luminous reionization-era galaxies often exhibit strong Lyman-alpha emission despite being situated at redshifts where the IGM is thought to be substantially neutral. It has been argued that this enhanced Ly$α$ transmission reflects the presence of massive galaxies in overdense regions which power large ionized bubbles. An alternative explanation is that massive galaxies shift more of their Ly$α$ profile to large velocities (relative to the systemic redshift) where the IGM damping wing absorption is reduced. Such a mass-dependent trend is seen at lower redshifts, but whether one exists at $z\sim7$ remains unclear owing to the small number of existing systemic redshift measurements in the reionization era. This is now changing with the emergence of [CII]-based redshifts from ALMA. Here we report MMT/Binospec Ly$α$ spectroscopy of eight UV-bright ($\mathrm{M_{UV}}^{}\sim-22$) galaxies at $z\simeq7$ selected from the ALMA REBELS survey. We detect Ly$α$ in 4 of 8 galaxies and use the [CII] systemic redshifts to investigate the Ly$α$ velocity profiles. The Ly$α$ lines are significantly redshifted from systemic (average velocity offset=223 km/s) and broad (FWHM$\approx$300$-$650 km/s), with two sources showing emission extending to $\approx$750 km/s. We find that the broadest Ly$α$ profiles are associated with the largest [CII] line widths, suggesting a potential link between the Ly$α$ FWHM and the dynamical mass. Since Ly$α$ photons at high velocities transmit efficiently through the $z=7$ IGM, our data suggest that velocity profiles play a significant role in boosting the Ly$α$ visibility of the most UV-luminous reionization-era galaxies.

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arXiv2021

Spectroscopy of an extreme [OIII] emitting active galactic nucleus at $z=3.212$: implications for the reionisation era

Reionisation-era galaxies often display intense nebular emission lines, both in rest-frame optical ([OIII]+H$β$) 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 ($β<-2$), reflecting minimal dust obscuration, young ages, and low metallicities. This contrasts with narrow-lined AGN at $z\sim2-3$, whose UV slopes are significantly redder ($β>-1$) 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$β$ line emission (EW $=1300$ Å) and a blue UV continuum slope ($β=-2.34$). 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.

astro-ph.GA↗

arXiv2021

MMT Spectroscopy of Lyman-alpha at z$\simeq$7: Evidence for Accelerated Reionization Around Massive Galaxies

Reionization-era galaxies tend to exhibit weak Ly$α$ emission, likely reflecting attenuation from an increasingly neutral IGM. Recent observations have begun to reveal exceptions to this picture, with strong Ly$α$ emission now known in four of the most massive z=7$-$9 galaxies in the CANDELS fields, all of which also exhibit intense [OIII]$+$H$β$ emission (EW$>$800 $\mathrm{\mathring{A}}$). To better understand why Ly$α$ 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$). We confidently ($>$7$σ$) detect Ly$α$ in 78% (7/9) of galaxies with strong [OIII]$+$H$β$ 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$β$. We argue that the higher Ly$α$ EWs of the strong [OIII]$+$H$β$ population likely reflect enhanced ionizing photon production efficiency owing to their large sSFRs ($\gtrsim$30 Gyr$^{-1}$). We also find evidence that Ly$α$ transmission from massive galaxies declines less rapidly over $6<z<7$ than in low-mass lensed systems. In particular, our data suggest no strong evolution in Ly$α$ transmission, consistent with a picture wherein massive z$\simeq$7 galaxies often reside in large ionized regions. We detect three closely-separated ($R$ = 1.7 physical Mpc) z$\simeq$7 Ly$α$ emitters in our sample, conceivably tracing a large ionized structure that is consistent with this picture. We detect tentative evidence for an overdensity in this region, implying a large ionizing photon budget in the surrounding volume.

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arXiv2021

The Detection of Ionized Carbon Emission at z~8

We present deep Keck/MOSFIRE $H$-band spectroscopic observations covering the [CIII],CIII]$λ\lambda1907,1909$ doublet for three $z\sim8$ galaxy candidates in the AEGIS field. Along with non-detections in two galaxies, we obtain one of the highest-redshift detections to-date of [CIII]$λ1907$ for the galaxy AEGIS-33376, finding $z_{\rm spec}=7.945\pm0.001$. We measure a [CIII]$λ$1907 flux of $2.24\pm0.71\times10^{-18} \mbox{ erg}\mbox{ s}^{-1} \mbox{ cm}^{-2}$, corresponding to a rest-frame equivalent width of $20.3\pm6.5 \unicode{x212B}$ for the single line. Given the not very constraining upper limit for CIII]$λ1909$ based on strong sky-line contamination, we assume a [CIII]$λ$1907/CIII]$λ1909$ doublet ratio of 1.5 and infer a total [CIII],CIII]$λ\lambda1907,1909$ equivalent width of $33.7\pm 10.8 \unicode{x212B}$. We repeat the same reductions and analysis on multiple subsets of our raw data divided on the basis of time and observing conditions, verifying that the [CIII]$λ1907$ emission is present for AEGIS-33376 throughout our observations. We also confirm that the significance of the [CIII]$λ1907$ detection in different subsets of our data tracks that of brighter emission features detected on the same multi-slit mask. These multiple tests suggest that the observed emission line is real and associated with the $z\sim 8$ target. The strong observed [CIII],CIII]$λ\lambda1907,1909$ in AEGIS-33376 likely indicates ISM conditions of low metallicity, high ionization parameter, and a hard ionizing spectrum, although AGN contributions are possible. This single detection represents a sizable increase in the current sample [CIII],CIII]$λ\lambda1907,1909$ detections at $z>7$, while $\textit{JWST}$ will provide the first statistical samples of such measurements at these redshifts.

astro-ph.GA↗

arXiv2021

Lyman-alpha spectroscopy of extreme [OIII] emitting galaxies at $z\simeq2-3$: Implications for Ly$α$ visibility and LyC leakage at $z>6$

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

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arXiv2020

Rest-frame UV spectroscopy of extreme [OIII] emitters at $1.3<z<3.7$: Toward a high-redshift UV reference sample for JWST

Deep spectroscopy of galaxies in the reionization-era has revealed intense CIII] and CIV line emission (EW $>15-20$ Å). 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 $1.3 6$ only in large sSFR galaxies with [OIII]+H$β$ EW $>1500$ Å. In contrast to previous studies, we find that many galaxies with intense [OIII] have weak CIII] emission (EW $=5-8$ Å), 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$β$ EW $>1500$ Å) 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 $>15$ Å) 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 ($<0.1\ Z_\odot$).

astro-ph.GA↗

arXiv2020

The [OIII]$+$H$β$ Equivalent Width Distribution at z$\simeq$7: Implications for the Contribution of Galaxies to Reionization

We quantify the distribution of [OIII]+H$β$ 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$6.63$-$6.83, a redshift range where blue Spitzer/IRAC [3.6]$-$[4.5] colours unambiguously indicate strong [OIII]$+$H$β$ emission. These 20 galaxies suggest a log-normal [OIII]$+$H$β$ 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$β$ 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$). We also find evidence for the emergence of a population with yet more extreme nebular emission ([OIII]+H$β$ 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.

astro-ph.GA↗

arXiv2020

The Universe at z>10: Predictions for JWST from the UniverseMachine DR1

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 $z<10$. We predict that Cycle 1 JWST surveys will very likely detect galaxies with $M_*>10^7 M_\odot$ and/or $M_{1500}<-17$ out to at least $z\sim 13.5$. Number density uncertainties at $z>12$ 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.

astro-ph.GA↗

arXiv2020

Simulating JWST/NIRCam Color Selection of High-Redshift Galaxies

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$α$ 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.

astro-ph.GA↗

arXiv2019

Clustering with JWST: Constraining Galaxy Host Halo Masses, Satellite Quenching Efficiencies, and Merger Rates at z=4-10

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$5$σ$ 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.

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arXiv2019

Unveiling the Phase Transition of the Universe During the Reionization Epoch with Lyman-alpha

The epoch of reionization (6 < z < 10) marks the period in our universe when the first large galaxies grew to fruition, and began to affect the universe around them. Massive stars, and potentially accreting supermassive black holes, filled the universe with ionizing radiation, burning off the haze of neutral gas that had filled the intergalactic medium (IGM) since recombination (z~1000). The evolution of this process constrains key properties of these earliest luminous sources, thus observationally constraining reionization is a key science goal for the next decade. The measurement of Lyman-alpha emission from photometrically-identified galaxies is a highly constraining probe of reionization, as a neutral IGM will resonantly scatter these photons, reducing detectability. While significant work has been done with 8-10m telescopes, these observations require extremely large telescopes (ELTs); the flux limits available from today's 10m class telescopes are sufficient for only the brightest known galaxies (m < 26). Ultra-deep surveys with the Giant Magellan Telescope (GMT) and Thirty Meter Telescope (TMT) will be capable of detecting Lyman-alpha emission from galaxies 2-3 magnitudes fainter than today's deepest surveys. Wide-field fiber spectroscopy on the GMT combined with narrow-field AO-assisted slit spectroscopy on the TMT will be able to probe the expected size of ionized bubbles throughout the epoch of reionization, following up degree scale deep imaging surveys with the Wide Field Infrared Space Telescope. These data will provide the first resolved Lyman-alpha-based maps of the ionized intergalactic medium throughout the epoch of reionization, constraining models of both the temporal and spatial evolution of this phase change.

astro-ph.CO↗

arXiv2019

UV Diagnostics of Galaxies from the Peak of Star-Formation to the Epoch of Reionization

The rest-frame UV emission from massive stars contains a wealth of information about the physical nature and conditions of star formation in galaxies. Using studies of the rest-frame UV, the past decade has witnessed the beginning of knowledge about the existence and properties of galaxies during the first few billion years after the Big Bang. This period of history corresponds to the formation of the first stars, the rapid formation of galaxy stellar populations, the reionization of the IGM, the production and dissemination of heavy elements, and the formation of the first black holes. Massive stars in these galaxies drive all of these events, and their light dominates the spectral energy distributions of galaxies. As we look to the 2020s, fundamental questions remain about the nature of these stellar populations and their evolution, from just before the peak of the cosmic star formation density (z~3), up to the epoch of reionization (z > 6). This next decade will provide transformative gains both in our ability to identify star-forming galaxies and accreting supermassive black holes at these early epochs with imaging surveys in the rest-frame UV (e.g., LSST, WFIRST). Ground-based, rest-frame UV spectroscopy on >20 m-class telescopes (e.g., GMT/TMT) offers the ability to investigate the astrophysical conditions in galaxies at the earliest cosmic times. This includes studies of the evolution in galaxy stellar populations, gas ionization (temperature, pressure), metallicity, and interstellar (and circumgalactic) gas kinematics and covering fractions. In this white paper, we describe the scientific prospects and the requirements for research in this area.

astro-ph.GA↗

arXiv2018

The JWST Extragalactic Mock Catalog: Modeling galaxy populations from the UV through the near-IR over thirteen billion years of cosmic history

We present an original phenomenological model to describe the evolution of galaxy number counts, morphologies, and spectral energy distributions across a wide range of redshifts (0.2 6]. Our model follows observed mass and luminosity functions of both star-forming and quiescent galaxies, and reproduces the redshift evolution of colors, sizes, star-formation and chemical properties of the observed galaxy population. Unlike other existing approaches, our model includes a self-consistent treatment of stellar and photoionized gas emission and dust attenuation based on the BEAGLE tool. The mock galaxy catalogs generated with our new model can be used to simulate and optimize extragalactic surveys with future facilities such as the James Webb Space Telescope (JWST), and to enable critical assessments of analysis procedures, interpretation tools, and measurement systematics for both photometric and spectroscopic data. As a first application of this work, we make predictions for the upcoming JWST Advanced Deep Extragalactic Survey (JADES), a joint program of the JWST/NIRCam and NIRSpec Guaranteed Time Observations teams. We show that JADES will detect, with NIRCam imaging, thousands of galaxies at z>6, and tens at z>10 at m_AB<30 (5-sigma) within the 236 arcmin^2 of the survey. The JADES data will enable accurate constraints on the evolution of the UV luminosity function at z>8, and resolve the current debate about the rate of evolution of galaxies at z>8. Ready to use mock catalogs and software to generate new realizations are publicly available as the JAdes extraGalactic Ultradeep Artificial Realizations (JAGUAR) package.

astro-ph.GA↗

arXiv2018

Blowing in the Milky Way wind: neutral hydrogen clouds tracing the Galactic nuclear outflow

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 $α>140$ 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.

astro-ph.GA↗

arXiv2015

X-Ray Polarimetry with the Polarization Spectroscopic Telescope Array (PolSTAR)

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.

astro-ph.IM↗