Browsing by Author "Jarvis, Matt J."

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    Cosmological 3D Hi Gas Map with HETDEX Lyα Emitters and eBOSS QSOs at z = 2: IGM-Galaxy/QSO Connection and a ∼ 40-Mpc Scale Giant Hii Bubble Candidate
    (IOP Publishing, 2020) Jarvis, Matt J.; Mukae, Shiro; Ouchi, Masami
    We present cosmological (30−400 Mpc) distributions of neutral hydrogen (H i) in the intergalactic medium (IGM) traced by Lyα emitters (LAEs) and QSOs at z = 2.1–2.5, selected with the data of the ongoing Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) and the eBOSS survey. Motivated by a previous study of Mukae et al., we investigate spatial correlations of LAEs and QSOs with H i tomography maps reconstructed from H i Lyα forest absorption in the spectra of background galaxies and QSOs obtained by the CLAMATO survey and this study, respectively. In the cosmological volume far from QSOs, we find that LAEs reside in regions of strong H i absorption, i.e., H i rich, which is consistent with results of previous galaxy−background QSO pair studies. Moreover, there is an anisotropy in the H i distribution plot of transverse and line-of-sight distances; on average the H i absorption peak is blueshifted by ~200 km s−1 from the LAE Lyα redshift, reproducing the known average velocity offset between the Lyα emission redshift and the galaxy systemic redshift. We have identified a ~40 Mpc scale volume of H i underdensity that is a candidate for a giant H ii bubble, where six QSOs and an LAE overdensity exist at $\left\langle z\right\rangle =2.16$.
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    First HETDEX Spectroscopic Determinations of Lyα and UV Luminosity Functions at z=2–3: Bridging a Gap between Faint AGNs and Bright Galaxies
    (The Astrophysical Journal, 2021) Jarvis, Matt J.
    We present Lyα and ultraviolet (UV)-continuum luminosity functions (LFs) of galaxies and active galactic nuclei (AGNs) at z = 2.0–3.5 determined by the untargeted optical spectroscopic survey of the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). We combine deep Subaru imaging with HETDEX spectra resulting in 11.4 deg2 of fiber spectra sky coverage, obtaining 18,320 galaxies spectroscopically identified with Lyα emission, 2126 of which host type 1 AGNs showing broad (FWHM > 1000 km s−1 ) Lyα emission lines. We derive the Lyα (UV) LF over 2 orders of magnitude covering bright galaxies and AGNs in log erg s 43.3 45.5 LLya [] – -1 = (−27 < MUV < −20) by the 1/Vmax estimator. Our results reveal that the bright-end hump of the Lyα LF is composed of type 1 AGNs. In conjunction with previous spectroscopic results at the faint end, we measure a slope of the best-fit Schechter function to be a = - - + Sch 1.70 0.14 0.13, which indicates that αSch steepens from z = 2–3 toward high redshift. Our UV LF agrees well with previous AGN UV LFs and extends to faint-AGN and bright-galaxy regimes. The number fraction of Lyαemitting objects (XLAE) increases from MUV* ~ -21 to bright magnitude due to the contribution of type 1 AGNs, while previous studies claim that XLyα decreases from faint magnitudes to M* UV, suggesting a valley in the XLyα–magnitude relation at M* UV. Comparing our UV LF of type 1 AGNs at z = 2–3 with those at z = 0, we find that the number density of faint (MUV > −21) type 1 AGNs increases from z ∼ 2 to 0, as opposed to the evolution of bright (MUV < −21) type 1 AGNs, suggesting AGN downsizing in the rest-frame UV luminosity
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    A flexible method for estimating luminosity functions via Kernel Density Estimation
    (IOP Publishing, 2020) Jarvis, Matt J.; Yuan, Zunli; Wang, Jiancheng
    We propose a flexible method for estimating luminosity functions (LFs) based on kernel density estimation (KDE), the most popular nonparametric density estimation approach developed in modern statistics, to overcome issues surrounding binning of LFs. One challenge in applying KDE to LFs is how to treat the boundary bias problem, since astronomical surveys usually obtain truncated samples predominantly due to the flux-density limits of surveys. We use two solutions, the transformation KDE method (φˆ t), and the transformation-reflection KDE method (φˆ tr) to reduce the boundary bias. We develop a new likelihood cross-validation criterion for selecting optimal bandwidths, based on which, the posterior probability distribution of bandwidth and transformation parameters for φˆ t and φˆ tr are derived within a Markov chain Monte Carlo (MCMC) sampling procedure. The simulation result shows that φˆ t and φˆ tr perform better than the traditional binned method, especially in the sparse data regime around the flux-limit of a survey or at the bright-end of the LF. To further improve the performance of our KDE methods, we develop the transformation-reflection adaptive KDE approach (φˆ tra). Monte Carlo simulations suggest that it has a good stability and reliability in performance, and is around an order of magnitude more accurate than using the binned method. By applying our adaptive KDE method to a quasar sample, we find that it achieves estimates comparable to the rigorous determination in a previous work, while making far fewer assumptions about the LF. The KDE method we develop has the advantages of both parametric and non-parametric methods.
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    Measuring the HI mass function below the detection threshold
    (Royal Astronomical Society, 2020) Pan, Hengxing; Jarvis, Matt J.; Santos, Mario G.
    We present a Bayesian stacking technique to directly measure the H I mass function (HIMF) and its evolution with redshift using galaxies formally below the nominal detection threshold. We generate galaxy samples over several sky areas given an assumed HIMF described by a Schechter function and simulate the H I emission lines with different levels of background noise to test the technique. We use MULTINEST to constrain the parameters of the HIMF in a broad redshift bin, demonstrating that the HIMF can be accurately reconstructed, using the simulated spectral cube far below the H I mass limit determined by the 5σ flux-density limit, i.e. down to MHI=107.5 M⊙ over the redshift range 0 < z < 0.55 for this particular simulation, with a noise level similar to that expected for the MIGHTEE survey. We also find that the constraints on the parameters of the Schechter function, ϕ⋆, M⋆, and α can be reliably fit, becoming tighter as the background noise decreases as expected, although the constraints on the redshift evolution are not significantly affected. All the parameters become better constrained as the survey area increases. In summary, we provide an optimal method for estimating the H I mass at cosmological distances that allows us to constrain the HIMF below the detection threshold in forthcoming H I surveys. This study is a first step towards the measurement of the HIMF at high (z > 0.1) redshifts.
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    Non-Gaussianity constraints using future radio continuum surveys and the multitracer technique
    (Oxford University Press, 2019) Camera, Stefano; Gomes, Zahra; Jarvis, Matt J.
    Tighter constraints on measurements of primordial non-Gaussianity (PNG) will allow the differentiation of inflationary scenarios. The cosmic microwave background bispectrum – the standard method of measuring the local non-Gaussianity – is limited by cosmic variance. Therefore, it is sensible to investigate measurements of non-Gaussianity using the large-scale structure. This can be done by investigating the effects of non-Gaussianity on the power spectrum on large scales. In this study, we forecast the constraints on the local PNG parameter fNL that can be obtained with future radio surveys.