Science to Service Academic Program of Distinction: Proposal

A low level of scientific knowledge among the U.S. population has considerably hindered its economic preeminence and social development. Science to Serve is a distinctive framework at GCSU that embraces a significant number of formal and informal interdisciplinary practices with the single purpose of advancing the interest, engagement, and understanding of science and technology by people of all ages and backgrounds. That is, Science to Serve aims to make science “real” to those who might not ordinarily be engaged so that they see the role of science to life, in education, and to the economy. Primary support for this unique framework comes from the Office of Academic Outreach, the Department Biological &Environmental Sciences, the Department of Chemistry & Physics, the Science Education Center, and faculty from Middle Grades Education. This rich tradition of effectively communicating and instilling the usefulness of science to diverse communities has resulted in an impressive host of resources, programs, courses, and activities that are cross-disciplinary in scope. Science to Serve garners broad-based support from the university community and myriad constituencies beyond the campus with faculty and students of all majors serving as ambassadors of science. Partnerships with key statewide and national organizations have further strengthened this initiative and external funding has exceeded $2 million to date. For a relatively small liberal arts university in a rural location, this remarkably large number of resources focused on civic engagement through science is extraordinary. The Science to Serve framework will provide a cohesive, coherent and comprehensive structure that will greatly enhance opportunities for acquiring external support if selected as one of GCSU’s academic programs of distinctio

Compact [C II] emitters around a C IV absorption complex at redshift 5.7

The physical conditions of the circumgalactic medium are probed by intervening absorption-line systems in the spectrum of background quasi-stellar objects out to the epoch of cosmic reionization. A correlation between the ionization state of the absorbing gas and the nature of the nearby galaxies has been suggested by the sources detected either in Lyalpha or [C ii] 158 m near to respectively highly-ionized and neutral absorbers. This is also likely linked to the global changes in the incidence of absorption systems of different types and the process of cosmic reionization. Here we report the detection of two [C ii]-emitting galaxies at redshift $z \sim 5.7$ that are associated with a complex high-ionization C iv absorption system. These objects are part of an overdensity of galaxies and have compact sizes (< 2.4 kpc) and narrow line widths (FWHM $\sim$ 62--64 km s-1). Hydrodynamic simulations predict that similar narrow [C ii] emission may arise from the heating of small ($\lesssim$ 3 kpc) clumps of cold neutral medium or a compact photodissociation region. The lack of counterparts in the rest-frame ultraviolet indicates severe obscuration of the sources that are exciting the [C ii] emission. These results may suggest a connection between the properties of the [C ii] emission, the rare overdensity of galaxies and the unusual high ionization state of the gas in this region.Comment: Published in Nature on 10 May 2023; authors' version; link to the paper: https://www.nature.com/articles/s41586-023-05901-

EIGER I. a large sample of [OIII]-emitting galaxies at 5.3<z<6.95.3 < z < 6.9 and direct evidence for local reionization by galaxies

We present a first sample of 117 [OIII]$\lambda\lambda$4960,5008-selected star-forming galaxies at $5.33 < z < 6.93$ detected in JWST/NIRCam 3.5$\mu$m slitless spectroscopy of a $6.5 \times 3.4$ arcmin$^2$ field centered on the hyperluminous quasar SDSS J0100+2802, obtained as part of the EIGER (Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization) survey. Three prominent galaxy overdensities are observed, one of them at the redshift of the quasar. Galaxies are found within 200 pkpc and 105 km s$^{-1}$ of four known metal absorption-line systems in this redshift range. We focus on the role of the galaxies in ionizing the surrounding intergalactic medium (IGM) during the later stages of cosmic reionization and construct the mean Ly$\alpha$ and Ly$\beta$ transmission as a function of distance from the galaxies. At the lowest redshifts in our study, $5.3 < z < 5.7$, the IGM transmission rises monotonically with distance from the galaxies. This is as expected when galaxies reside at peaks in the overdensity field of an IGM that is ionized by more or less uniform ionizing background, and has been seen at lower redshifts. In contrast, at $5.7 < z < 6.14$, the transmission of both Ly$\alpha$ and Ly$\beta$ first increases with distance, but then peaks at a distance of 5 cMpc before declining. This peak in transmission is qualitatively similar to that seen (albeit at smaller distances and higher redshifts) in the THESAN simulations. Finally, in the region $6.15 < z < 6.26$ where the additional ionizing radiation from the quasar dominates, the monotonic increase in transmission with distance is re-established. This result is interpreted to represent evidence that the transmission of the IGM at $z \sim 5.9$ towards J0100+2802 results from the ``local'' ionizing radiation of galaxies that dominates over the much reduced cosmic background.Comment: 24 pages, 14 figures, submitted to ApJ, comments welcom

EIGER II. first spectroscopic characterisation of the young stars and ionised gas associated with strong Hβ\beta and [OIII] line-emission in galaxies at z=5-7 with JWST

We present emission-line measurements and physical interpretations for a sample of 117 [OIII] emitting galaxies at $z=5.33-6.93$, using the first deep JWST/NIRCam wide field slitless spectroscopic observations. Our 9.7-hour integration is centered upon the $z=6.3$ quasar J0100+2802 -- the first of six fields targeted by the EIGER survey -- and covers $\lambda=3-4$ microns. We detect 133 [OIII] doublets, but merge pairs within $\approx$10 kpc and 600 km s$^{-1}$, motivated by their small scale clustering excess. We detect H$\beta$ in 68 and H$\gamma$ emission in two galaxies. The galaxies are characterised by a UV luminosity M$_{\rm UV}\sim-19.6$ ($-17.7$ to $-22.3$), stellar mass ~$10^8$ $(10^{6.8-10.1})$ M$_{\odot}$, H$\beta$ and [OIII] EWs $\approx$ 850 Angstrom (up to 3000 Angstrom), young ages (~100 Myr), a highly excited interstellar medium ([OIII]/H$\beta\approx6$) and low dust attenuations. These high EWs are very rare in the local Universe, but we show they are ubiquitous at $z\sim6$ based on the measured number densities. The stacked spectrum reveals H$\gamma$ and [OIII]$_{4364}$ which shows that the galaxies are typically dust and metal poor (E(B-V)=0.1, 12+log(O/H)=7.4) with a high electron temperature ($2\times10^4$ K) and a production efficiency of ionising photons ($\xi_{\rm ion}=10^{25.3}$ Hz erg$^{-1}$). We further show the existence of a strong mass-metallicity relation. The young highly ionising stellar populations, moderately low metallicities, low dust attenuations and high ionisation state in z~6 galaxies conspire to maximise the [OIII] output from galaxies, yielding an [OIII] luminosity density at z~6 that is significantly higher than at z~2, despite the order of magnitude decline in cosmic star formation. Thus, [OIII] emission-line surveys with JWST prove a highly efficient method to trace the galaxy density in the epoch of reionization.Comment: Accepted for publication in ApJ. Main text 22 pages, 20 figures. Main results in Figs 14 (Xi_ion), 15 (MEx diagram),17 (MZR), 19 ([OIII] luminosity density

Beyond location and dispersion models: The Generalized Structural Time Series Model with Applications

In many settings of empirical interest, time variation in the distribution parameters is important for capturing the dynamic behaviour of time series processes. Although the fitting of heavy tail distributions has become easier due to computational advances, the joint and explicit modelling of time-varying conditional skewness and kurtosis is a challenging task. We propose a class of parameter-driven time series models referred to as the generalized structural time series (GEST) model. The GEST model extends Gaussian structural time series models by a) allowing the distribution of the dependent variable to come from any parametric distribution, including highly skewed and kurtotic distributions (and mixed distributions) and b) expanding the systematic part of parameter-driven time series models to allow the joint and explicit modelling of all the distribution parameters as structural terms and (smoothed) functions of independent variables. The paper makes an applied contribution in the development of a fast local estimation algorithm for the evaluation of a penalised likelihood function to update the distribution parameters over time \textit{without} the need for evaluation of a high-dimensional integral based on simulation methods

Beyond location and dispersion models: The Generalized Structural Time Series Model with Applications

In many settings of empirical interest, time variation in the distribution parameters is important for capturing the dynamic behaviour of time series processes. Although the fitting of heavy tail distributions has become easier due to computational advances, the joint and explicit modelling of time-varying conditional skewness and kurtosis is a challenging task. We propose a class of parameter-driven time series models referred to as the generalized structural time series (GEST) model. The GEST model extends Gaussian structural time series models by a) allowing the distribution of the dependent variable to come from any parametric distribution, including highly skewed and kurtotic distributions (and mixed distributions) and b) expanding the systematic part of parameter-driven time series models to allow the joint and explicit modelling of all the distribution parameters as structural terms and (smoothed) functions of independent variables. The paper makes an applied contribution in the development of a fast local estimation algorithm for the evaluation of a penalised likelihood function to update the distribution parameters over time \textit{without} the need for evaluation of a high-dimensional integral based on simulation methods

EIGER III. JWST/NIRCam observations of the ultra-luminous high-redshift quasar J0100+2802

We present the first rest-frame optical spectrum of a high-redshift quasar observed with JWST/NIRCam in Wide Field Slitless (WFSS) mode. The observed quasar, J0100+2802, is the most luminous quasar known at $z>6$. We measure the mass of the central supermassive black hole (SMBH) by means of the rest-frame optical H$\beta$ emission line, and find consistent mass measurements of the quasar's SMBH of $M_\bullet\approx10^{10}\,M_\odot$ when compared to the estimates based on the properties of rest-frame UV emission lines CIV and MgII, which are accessible from ground-based observatories. To this end, we also present a newly reduced rest-frame UV spectrum of the quasar observed with X-Shooter/VLT and FIRE/Magellan for a total of 16.8 hours. We readdress the question whether this ultra-luminous quasar could be effected by strong gravitational lensing making use of the diffraction limited NIRCam images in three different wide band filters (F115W, F200W, F356W), which improves the achieved spatial resolution compared to previous images taken with the Hubble Space Telescope by a factor of two. We do not find any evidence for a foreground deflecting galaxy, nor for multiple images of the quasar, and determine the probability for magnification due to strong gravitational lensing with image separations below the diffraction limit of $\Delta\theta\lesssim 0.05''$ to be $\lesssim 2.2\times 10^{-3}$. Our observations therefore confirm that this quasar hosts a ten billion solar mass black hole less than $1$ Gyr after the Big Bang, which is challenging to explain with current black hole formation models.Comment: Accepted for publication in Ap

EIGER V. Characterizing the Host Galaxies of Luminous Quasars at z≳6z\gtrsim6

We report {\em JWST}/NIRCam measurements of quasar host galaxy emissions and supermassive black hole (SMBH) masses for six quasars at $5.9<z<7.1$ in the \textit{Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization} (EIGER) project. We obtain deep NIRCam imaging in the F115W, F200W, and F356W bands, as well as F356W grism spectroscopy of the quasars. We use bright unsaturated stars to construct models of the point spread function (PSF) and estimate the errors of these PSFs. We then measure or constrain the fluxes and morphology of the quasar host galaxies by fitting the quasar images as a point source plus an exponential disk. We successfully detect the host galaxy of three quasars, which have host-to-quasar flux ratios of $\sim1\%-5\%$. Spectral Energy Distribution (SED) fitting suggests that these quasar host galaxies have stellar masses of $M_*\gtrsim10^{10}M_\odot$. For quasars with host galaxy non-detections, we estimate the upper limits of their stellar masses. We use the grism spectra to measure the {\hb} line profile and the continuum luminosity, then estimate the SMBH masses for the quasars. Our results indicate that the positive relation between SMBH masses and host galaxy stellar masses already exists at redshift $z\gtrsim6$. The quasars in our sample show a high black hole to stellar mass ratio of $M_\text{BH}/M_*\sim0.15$, which is about $\sim1-2$ dex higher than the local relations. This result suggests that luminous quasars at $z\gtrsim6$ form a biased sample with overmassive black holes, which might have experienced early SMBH growth compared to their host galaxies' star formation.Comment: 21 pages, 12 figures, submitted to AAS journals. Comments welcome