Impact of Colonoscopy Bowel Preparation on Intestinal Microbiota

The gut microbiota is important in maintaining human health, but numerous factors have the potential to alter its composition. Our aim was to examine the impact of a standard bowel preparation on the intestinal microbiota using two different techniques. Fifteen subjects undergoing colonoscopy consumed a bowel preparation comprised of 10 mg bisacodyl and 2 L polyethylene glycol. The microbiota of stool samples, collected one month before, one week before (pre-colonoscopy), and one week, one month, and three to six months after colonoscopy (post-colonoscopy) was evaluated. Two samples were taken three to six months apart from five healthy subjects who did not undergo colonoscopy. Universal primers targeting the V2-V3 region of the 16S rRNA gene were used to PCR amplify all samples for denaturing gradient gel electrophoresis (PCR-DGGE). Pre- and post-colonoscopy samples were compared using Dice's similarity coefficients. Three samples from ten subjects who underwent colonoscopy, and both samples from the five subjects who didn't, were used for high-throughput sequencing of the V1-V3 region of the 16S rRNA gene. Samples were curated and analysed in Mothur. Results of the DGGE analyses show that the fecal microbiota of a small number of subjects had short-term changes. High-throughput sequencing results indicated that the variation between the samples of subjects who underwent colonoscopy was no greater than the variation observed between samples from subjects who did not. We conclude that bowel preparation does not have a lasting effect on the composition of the intestinal microbiota for the majority of subjects.This work was funded by an Australian Post-Graduate Award scholarship. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript

Q1549-C25: A Clean Source of Lyman-Continuum Emission at z=3.15z=3.15

We present observations of Q1549-C25, an ~L* star-forming galaxy at z=3.15 for which Lyman-continuum (LyC) radiation is significantly detected in deep Keck/LRIS spectroscopy. We find no evidence for contamination from a lower-redshift interloper close to the line of sight in the high signal-to-noise spectrum of Q1549-C25. Furthermore, the morphology of Q1549-C25 in V_606, J_125, and H_160 Hubble Space Telescope (HST) imaging reveals that the object consists of a single, isolated component within 1". In combination, these data indicate Q1549-C25 as a clean spectroscopic detection of LyC radiation, only the second such object discovered to date at z~3. We model the spectral energy distribution (SED) of Q1549-C25, finding evidence for negligible dust extinction, an age (assuming continuous star formation) of ~1 Gyr, and a stellar mass of M_*=7.9x10^9 M_sun. Although it is not possible to derive strong constraints on the absolute escape fraction of LyC emission, f_esc(LyC), from a single object, we use simulations of intergalactic and circumgalactic absorption to infer f_esc(LyC)>=0.51 at 95% confidence. The combination of deep Keck/LRIS spectroscopy and HST imaging is required to assemble a larger sample of objects like Q1549-C25, and obtain robust constraints on the average f_esc(LyC) at z~3 and beyond.Comment: 6 pages, 5 figures, accepted to ApJ Letter

A High Fraction of Ly-alpha-Emitters Among Galaxies with Extreme Emission Line Ratios at z ~ 2

Star-forming galaxies form a sequence in the [OIII]/H-beta vs. [NII]/H-alpha diagnostic diagram, with low metallicity, highly ionized galaxies falling in the upper left corner. Drawing from a large sample of UV-selected star-forming galaxies at z~2 with rest-frame optical nebular emission line measurements from Keck-MOSFIRE, we select the extreme ~5% of the galaxies lying in this upper left corner, requiring log([NII]/H-alpha) = 0.75. These cuts identify galaxies with 12 + log(O/H) <~ 8.0, when oxygen abundances are measured via the O3N2 diagnostic. We study the Ly-alpha properties of the resulting sample of 14 galaxies. The mean (median) rest-frame Ly-alpha equivalent width is 39 (36) A, and 11 of the 14 objects (79%) are Ly-alpha-emitters (LAEs) with W_Lya > 20 A. We compare the equivalent width distribution of a sample of 522 UV-selected galaxies at 2.0<z<2.6 identified without regard to their optical line ratios; this sample has mean (median) Ly-alpha equivalent width -1 (-4) A, and only 9% of these galaxies qualify as LAEs. The extreme galaxies typically have lower attenuation at Ly-alpha than those in the comparison sample, and have ~50% lower median oxygen abundances. Both factors are likely to facilitate the escape of Ly-alpha: in less dusty galaxies Ly-alpha photons are less likely to be absorbed during multiple scatterings, while the harder ionizing spectrum and higher ionization parameter associated with strong, low metallicity star formation may reduce the covering fraction or column density of neutral hydrogen, further easing Ly-alpha escape. The use of nebular emission line ratios may prove useful in the identification of galaxies with low opacity to Ly-alpha photons across a range of redshifts.Comment: 12 pages, 5 figures, 2 tables. Accepted for publication in Ap

The Keck Lyman Continuum Spectroscopic Survey (KLCS): The Emergent Ionizing Spectrum of Galaxies at z ∼ 3

We present results of a deep spectroscopic survey quantifying the statistics of the escape of ionizing radiation from star-forming galaxies at z ~ 3. We measure the ratio of ionizing to non-ionizing UV flux density 〈f_(900)/f_(1500) 〉_(obs), where f_(900) is the mean flux density evaluated over the range [880, 910] Å. We quantify the emergent ratio of ionizing to non-ionizing UV flux density by analyzing high signal-to-noise ratio composite spectra formed from subsamples with common observed properties and numbers sufficient to reduce the statistical uncertainty in the modeled IGM+CGM correction to obtain precise values of 〈f_(900)/f_(1500) 〉_(out), including a full-sample average 〈f_(900)/f_(1500) 〉_(out) = 0.057 ± 0.006. We show that 〈f_(900)/f_(1500) 〉_(out) increases monotonically with W_ λ(Lyα), inducing an inverse correlation with UV luminosity as a by-product. We fit the composite spectra using stellar spectral synthesis together with models of the ISM in which a fraction f c of the stellar continuum is covered by gas with column density N_(H1). We show that the composite spectra simultaneously constrain the intrinsic properties of the stars (L_(900)/L_(1500))_(int) along with f_c , N_(H1), E(B - V), and f_(esc,abs), the absolute escape fraction of ionizing photons. We find a sample-averaged f-(esc,abs) = 0.09 ± 0.01, with subsamples falling along a linear relation 〈f_(esc,abs) 〉 ≃ 0.75[W_ λ(Lyα)/110 Å]. Using the far-UV luminosity function, the distribution function n(W(Lyα)), and the relationship between W_ λ(Lyα) and f_(900)/f_(1500) 〉_(out), we estimate the total ionizing emissivity of z ~ 3 star-forming galaxies with M_(uv) ≤ −19.5, which exceeds the contribution of quasi-stellar objects by a factor of ~3, and accounts for ~50% of the total ϵ_(LyC) at z ~ 3 estimated using indirect methods

Column Density, Kinematics, and Thermal State of Metal-bearing Gas within the Virial Radius of z ∼ 2 Star-forming Galaxies in the Keck Baryonic Structure Survey

We present results from the Keck Baryonic Structure Survey (KBSS) including the first detailed measurements of the column densities, kinematics, and internal energy of metal-bearing gas within the virial radius (35–100 physical kpc) of eight ~L* galaxies at z ~ 2. From our full sample of 130 metal-bearing absorbers, we infer that halo gas is kinematically complex when viewed in singly, doubly, and triply ionized species. Broad O vi and C iv absorbers are detected at velocities similar to the lower-ionization gas but with a very different kinematic structure, indicating that the circumgalactic medium (CGM) is multiphase. There is a high covering fraction of metal-bearing gas within 100 kpc, including highly ionized gas such as O vi; however, observations of a single galaxy probed by a lensed background QSO suggest the size of metal-bearing clouds is small (<400 pc for all but the O vi-bearing gas). The mass in metals found within the halo is substantial, equivalent to ≳25% of the metal mass within the interstellar medium. The gas kinematics unambiguously show that 70% of galaxies with detected metal absorption have some unbound metal-enriched gas, suggesting galactic winds may commonly eject gas from halos at z ~ 2. When modeled assuming that ions with different ionization potentials can originate within a single gaseous structure, significant thermal broadening is detected in CGM absorbers that dominates the internal energy of the gas. Some 40% of the detected gas has temperatures in the range 10^(4.5-5.5) K where cooling times are short, suggesting the CGM is dynamic, with constant heating or cooling to produce this short-lived thermal phase

Column Density, Kinematics, and Thermal State of Metal-bearing Gas within the Virial Radius of z ∼ 2 Star-forming Galaxies in the Keck Baryonic Structure Survey

We present results from the Keck Baryonic Structure Survey (KBSS) including the first detailed measurements of the column densities, kinematics, and internal energy of metal-bearing gas within the virial radius (35–100 physical kpc) of eight ~L* galaxies at z ~ 2. From our full sample of 130 metal-bearing absorbers, we infer that halo gas is kinematically complex when viewed in singly, doubly, and triply ionized species. Broad O vi and C iv absorbers are detected at velocities similar to the lower-ionization gas but with a very different kinematic structure, indicating that the circumgalactic medium (CGM) is multiphase. There is a high covering fraction of metal-bearing gas within 100 kpc, including highly ionized gas such as O vi; however, observations of a single galaxy probed by a lensed background QSO suggest the size of metal-bearing clouds is small (<400 pc for all but the O vi-bearing gas). The mass in metals found within the halo is substantial, equivalent to ≳25% of the metal mass within the interstellar medium. The gas kinematics unambiguously show that 70% of galaxies with detected metal absorption have some unbound metal-enriched gas, suggesting galactic winds may commonly eject gas from halos at z ~ 2. When modeled assuming that ions with different ionization potentials can originate within a single gaseous structure, significant thermal broadening is detected in CGM absorbers that dominates the internal energy of the gas. Some 40% of the detected gas has temperatures in the range 10^(4.5-5.5) K where cooling times are short, suggesting the CGM is dynamic, with constant heating or cooling to produce this short-lived thermal phase

Q1549-C25: A Clean Source of Lyman-Continuum Emission at z = 3.15

We present observations of Q1549-C25, an ~L^* star-forming galaxy at z = 3.15 for which Lyman-continuum (LyC) radiation is significantly detected in deep Keck/LRIS spectroscopy. We find no evidence of contamination from a lower-redshift interloper close to the line of sight in the high signal-to-noise spectrum of Q1549-C25. Furthermore, the morphology of Q1549-C25 in V 606, J 125, and H 160 Hubble Space Telescope (HST) imaging reveals that the object consists of a single, isolated component within 1". In combination, these data indicate Q1549-C25 as a clean spectroscopic detection of LyC radiation, only the second such object discovered to date at z ~ 3. We model the spectral energy distribution of Q1549-C25, finding evidence of negligible dust extinction, an age (assuming continuous star formation) of ~1 Gyr, and a stellar mass of M_* =7.9 x 10^9,M_☉. Although it is not possible to derive strong constraints on the absolute escape fraction of LyC emission, f _(esc)(LyC), from a single object, we use simulations of intergalactic and circumgalactic absorption to infer f_(esc)(LyC)⩾ 0.51 at 95% confidence. The combination of deep Keck/LRIS spectroscopy and Hubble Space Telescope imaging is required to assemble a larger sample of objects like Q1549-C25, and obtain robust constraints on the average f _(esc)(LyC) at z ~ 3 and beyond

A High Fraction of Lyα-Emitters Among Galaxies with Extreme Emission Line Ratios at z ~ 2

Star-forming galaxies form a sequence in the [O III] λ5007/Hβ versus [N II] λ6584/Hɑ diagnostic diagram, with low-metallicity, highly ionized galaxies falling in the upper left corner. Drawing from a large sample of UV-selected star-forming galaxies at z ~ 2 with rest-frame optical nebular emission line measurements from Keck-MOSFIRE, we select the extreme ~5% of the galaxies lying in this upper left corner, requiring log([NII]/Hβ) ⩽ -1.1 and log([O III]/Hβ) ⩾/0.75. These cuts identify galaxies with 12 + log(O/H ≾ 8.0, when oxygen abundances are measured via the O3N2 diagnostic. We study the Lyα properties of the resulting sample of 14 galaxies. The mean (median) rest-frame Lyα equivalent width is 39 (36) Å, and 11 of the 14 objects (79%) are Lyα emitters (LAEs) with W_(Lyα) > 20 Å. We compare the equivalent width distribution of a sample of 522 UV-selected galaxies at 2.0 < z < 2.6 identified without regard to their optical line ratios; this sample has mean (median) Lyα equivalent width −1 (−4) Å, and only 9% of these galaxies qualify as LAEs. The extreme galaxies typically have lower attenuation at Lyα than those in the comparison sample and have ~50% lower median oxygen abundances. Both factors are likely to facilitate the escape of Lyα: in less dusty galaxies Lyα photons are less likely to be absorbed during multiple scatterings, while the harder ionizing spectrum and higher ionization parameter associated with strong, low-metallicity star formation may reduce the covering fraction or column density of neutral hydrogen, further easing Lyα escape. The use of nebular emission line ratios may prove useful in the identification of galaxies with low opacity to Lyα photons across a range of redshifts