ALBERT

Description: The flow of baryons to and from a galaxy, which is fundamental for galaxy formation and evolution, can be studied with galaxy-metal absorption system pairs. Our search for galaxies around C iv absorption systems at z  ~ 5.7 showed an excess of photometric Lyman α emitter (LAE) candidates in the fields J1030+0524 and J1137+3549. Here, we present spectroscopic follow-up of 33 LAEs in both fields. In the first field, three out of the five LAEs within 10 h –1 projected comoving Mpc from the C iv system are within ±500 km s –1 from the absorption at $z_{{\rm C\,{\small iv}}}=5.7242\pm 0.0001$ . The closest candidate (LAE 103027+052419) is robustly confirmed at $212.8^{+14}_{-0.4}\;h^{-1}$ physical kpc from the C iv system. In the second field, the LAE sample is selected at a lower redshift ( z  ~ 0.04) than the C iv absorption system as a result of the filter transmission and, thus, do not trace its environment. The observed properties of LAE 103027+052419 indicate that it is near the high-mass end of the LAE distribution, probably having a large H i column density and large-scale outflows. Therefore, our results suggest that the C iv system is likely produced by a star-forming galaxy which has been injecting metals into the intergalactic medium since z  〉 6. Thus, the C iv system is either produced by LAE 103027+052419, implying that outflows can enrich larger volumes at z  〉 6 than at z  ~ 3.5, or an undetected dwarf galaxy. In either case, C iv systems like this one trace the ionized intergalactic medium at the end of cosmic hydrogen reionization and may trace the sources of the ionizing flux density.

Description: Lyman-break galaxies (LBGs) at z  ~ 3–4 are targeted to measure the fraction of Lyman-continuum (LyC) flux that escapes from high-redshift galaxies. However, z  ~ 3–4 LBGs are identified using the Lyman-break technique which preferentially selects galaxies with little or no LyC. We re-examine the standard LBG selection criteria by performing spectrophotometry on composite spectra constructed from 794 $U_nG{\cal R}$ -selected z  ~ 3 LBGs from the literature while adding LyC flux of varying strengths. The modified composite spectra accurately predict the range of redshifts, properties, and LyC flux of LBGs in the literature that have spectroscopic LyC measurements while predicting the existence of a significant fraction of galaxies outside the standard selection region. These galaxies, termed Lyman-continuum galaxies (LCGs), are expected to have high levels of LyC flux and are estimated to have a number density ~30–50 per cent that of the LBG population. We define R obs ( U n ) as the relative fraction of observed LyC flux, integrated from 912 Å to the shortest rest-frame wavelength probed by the U n filter, to the observed non-ionizing flux (here measured at 1500 Å). We use the 794 spectra as a statistical sample for the full z  ~ 3 LBG population, and find ${{R_{\rm obs}(U_n)}=5.0^{+1.0}_{-0.4} (4.1^{+0.5}_{-0.3})}$  per cent, which corresponds to an intrinsic LyC escape fraction of ${{f_{\rm esc}^{\rm LyC}}=10.5^{+2.0}_{-0.8} (8.6^{+1.0}_{-0.6})}$  per cent (contamination corrected). From the composite spectral distributions we estimate ${{R_{\rm obs}(U_n)}\sim 16\pm 3,\ {f_{\rm esc}^{\rm LyC}}\sim 33\pm 7}$  per cent for LCGs and ${{R_{\rm obs}(U_n)}\sim 8\pm 3,\ {f_{\rm esc}^{\rm LyC}}\sim 16\pm 4}$  per cent for the combined LBG+LCG z  ~ 3 sample. All values are measured in apertures defined by the ultraviolet continuum and do not include extended and/or offset LyC flux. A complete galaxy census and the total emergent LyC flux at high redshift are essential to quantify the contribution of galaxies to the ionizing photon budget of the Universe, particularly during the epoch of reionization.

Description: We performed a detailed study of the extended cool gas, traced by Mg ii absorption [ W r (2796) ≥ 0.3 Å], surrounding 14 narrow-line active galactic nuclei (AGNs) at 0.12 ≤ z ≤ 0.22 using background quasar sightlines. The background quasars probe the AGNs at projected distances of 60 ≤ D ≤ 265 kpc. We find that, between 100 ≤ D ≤ 200 kpc, AGNs appear to have lower Mg ii gas covering fractions (0.09 $^{+0.18}_{-0.08}$ ) than quasars (0.47 $^{+0.16}_{-0.15}$ ) and possibly lower than inactive field galaxies (0.25 $^{+0.11}_{-0.09}$ ). We do not find a statistically significant azimuthal angle dependence for the Mg ii covering fraction around AGNs, though the data hint at one. We also study the ‘down-the-barrel’ outflow properties of the AGNs themselves and detect intrinsic Na i D absorption in 8/8 systems and intrinsic Mg ii absorption in 2/2 systems, demonstrating that the AGNs have significant reservoirs of cool gas. We find that 6/8 Na i D and 2/2 Mg ii intrinsic systems contain blueshifted absorption with v  〉 50 km s –1 , indicating outflowing gas. The 2/2 intrinsic Mg ii systems have outflow velocities a factor of ~4 higher than the Na i D outflow velocities. Our results are consistent with AGN-driven outflows destroying the cool gas within their haloes, which dramatically decreases their cool gas covering fraction, while starburst-driven winds are expelling cool gas into their circumgalactic media (CGM). This picture appears contrary to quasar–quasar pair studies which show that the quasar CGM contains significant amounts of cool gas whereas intrinsic gas found ‘down-the-barrel’ of quasars reveals no cool gas. We discuss how these results are complementary and provide support for the AGN unified model.

Description: We examine the effects of magnitude, colour and Lyα equivalent width (EW) on the spatial distribution of z  ~ 3 Lyman break galaxies (LBGs) and report significant differences in the two-point autocorrelation functions. The results are obtained using samples of ~10 000–55 000 LBGs from the Canada–France–Hawaii Telescope Legacy Survey Deep Fields. We find that magnitude has a larger effect on the autocorrelation function amplitude on small scales (1 $h^{-1}_{70}$ Mpc, the one-halo term) and that colour is more influential on large scales (1 $h^{-1}_{70}$ Mpc, the two-halo term). We find the most significant differences between autocorrelation functions for LBGs with dominant net Lyα EW in absorption (aLBGs) and dominant net Lyα EW in emission (eLBGs) determined from 95 per cent pure samples of each population using a photometric technique calibrated from ~1000 spectra. The aLBG autocorrelation function has a higher two-halo amplitude than the full LBG sample and has a one-halo term departure from a power-law fit near ~1 $h^{-1}_{70}$ Mpc, corresponding to the virial radii of M DM ~ 10 13 M dark matter haloes. In contrast, the eLBG autocorrelation function has a one-halo term departure at ~0.12 $h^{-1}_{70}$ Mpc, suggesting parent haloes of M DM ~ 10 11 M and a two-halo term that exhibits a curious ‘hump’ on intermediate scales that we localize to the faintest, bluest members. The aLBG–eLBG cross-correlation function exhibits an anticorrelation component that reinforces different physical locations for a significant fraction of aLBGs and eLBGs. We introduce a ‘shell’ model for the eLBG autocorrelation function and find that the form can be reproduced assuming that a significant fraction of eLBGs have a shell-like spatial distribution. Based on the analysis of all LBG subsamples, and considering the natural asymmetric distribution of LBGs on the colour–magnitude diagram, we conclude that aLBGs are more likely to reside in group-like environments hosting multiple luminous ( i '  〈 26.4) LBGs whereas eLBGs are more likely to be found on group outskirts and in the field. Because Lyα is a tracer of several intrinsic properties, including morphology, the results presented here imply that the mechanisms behind the morphology–density relation at low redshift are in place at z  ~ 3 and that Lyα EW may be a key environment diagnostic. Finally, our results show that the LBG autocorrelation function amplitude is lower than the true average as a result of the spatial anticorrelation of the spectral types. This result holds broad consequences for all autocorrelation functions measured for any population that contains members residing in different environments as the average amplitude, and hence the inferred average dark matter mass, will always be underestimated.

Description: Timely responses to environmental cues enable the synchronization of phenological life-history transitions essential for the health and survival of north-temperate and boreal tree species. While photoperiodic cues will remain persistent under climate change, temperature cues may vary, contributing to possible asynchrony in signals influencing developmental and physiological transitions essential to forest health. Understanding the relative contribution of photoperiod and temperature as determinants of the transition from active growth to dormancy is important for informing adaptive forest management decisions that consider future climates. Using a combination of photoperiod (long = 20 h or short = 8 h day lengths) and temperature (warm = 22 °C/16 °C and cool = 8 °C/4 °C day/night, respectively) treatments, we used microscopy, physiology and modeling to comprehensively examine hallmark traits of the growth–dormancy transition—including bud formation, growth cessation, cold hardiness and gas exchange—within two provenances of white spruce [ Picea glauca (Moench) Voss] spanning a broad latitude in Alberta, Canada. Following exposure to experimental treatments, seedlings were transferred to favorable conditions, and the depth of dormancy was assessed by determining the timing and ability of spruce seedlings to resume growth. Short photoperiods promoted bud development and growth cessation, whereas longer photoperiods extended the growing season through the induction of lammas growth. In contrast, cool temperatures under both photoperiodic conditions delayed bud development. Photoperiod strongly predicted the development of cold hardiness, whereas temperature predicted photosynthetic rates associated with active growth. White spruce was capable of attaining endodormancy, but its release was environmentally determined. Dormancy depth varied substantially across experimental treatments suggesting that environmental cues experienced within one season could affect growth in the following season, which is particularly important for a determinate species such as white spruce. The joint influence of these environmental cues points toward the importance of including local constant photoperiod and shifting temperature cues into predictive models that consider how climate change may affect northern forests.

Description: Metal absorption systems are products of star formation. They are believed to be associated with massive star-forming galaxies, which have significantly enriched their surroundings. To test this idea with high column density C iv absorption systems at z  ~ 5.7, we study the projected distribution of galaxies and characterize the environment of C iv systems in two independent quasar lines of sight: J103027.01+052455.0 and J113717.73+354956.9. Using wide-field photometry (~80 60 h –1 comoving Mpc), we select bright ( M UV (1350 Å)  –21.0 mag.) Lyman break galaxies (LBGs) at z  ~ 5.7 in a redshift slice z  ~ 0.2 and we compare their projected distribution with z  ~ 5.7 narrow-band selected Lyman alpha emitters (LAEs, z  ~ 0.08). We find that the C iv systems are located more than 10  h –1 projected comoving Mpc from the main concentrations of LBGs and no candidate is closer than ~5 h –1 projected comoving Mpc. In contrast, an excess of LAEs – lower mass galaxies – is found on scales of ~10 h –1 comoving Mpc, suggesting that LAEs are the primary candidates for the source of the C iv systems. Furthermore, the closest object to the system in the field J1030+0524 is a faint LAE at a projected distance of 212 h –1 physical kpc. However, this work cannot rule out undiscovered lower mass galaxies as the origin of these absorption systems. We conclude that, in contrast with lower redshift examples ( z 3.5), strong C iv absorption systems at z  ~ 5.7 trace low-to-intermediate density environments dominated by low-mass galaxies. Moreover, the excess of LAEs associated with high levels of ionizing flux agrees with the idea that faint galaxies dominate the ionizing photon budget at this redshift.

Description: The mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins), a major pine forest pest native to western North America, has extended its range north and eastward during an ongoing outbreak. Determining how the MPB has expanded its range to breach putative barriers, whether physical (nonforested prairie and high elevation of the Rocky Mountains) or climatic (extreme continental climate where temperatures can be below –40 °C), may contribute to our general understanding of range changes as well as management of the current epidemic. Here, we use a panel of 1,536 single nucleotide polymorphisms (SNPs) to assess population genetic structure, connectivity, and signals of selection within this MPB range expansion. Biallelic SNPs in MPB from southwestern Canada revealed higher genetic differentiation and lower genetic connectivity than in the northern part of its range. A total of 208 unique SNPs were identified using different outlier detection tests, of which 32 returned annotations for products with putative functions in cholesterol synthesis, actin filament contraction, and membrane transport. We suggest that MPB has been able to spread beyond its previous range by adjusting its cellular and metabolic functions, with genome scale differentiation enabling populations to better withstand cooler climates and facilitate longer dispersal distances. Our study is the first to assess landscape-wide selective adaptation in an insect. We have shown that interrogation of genomic resources can identify shifts in genetic diversity and putative adaptive signals in this forest pest species.

Description: Hubble Space Telescope spectroscopic observations of the nearby Type Ia supernova (SN Ia) SN 2011fe, taken on 10 epochs from –13.1 to +40.8 d relative to B -band maximum light, and spanning the far-ultraviolet (UV) to the near-infrared (IR) are presented. This spectroscopic coverage makes SN 2011fe the best-studied local SN Ia to date. SN 2011fe is a typical moderately luminous SN Ia with no evidence for dust extinction. Its near-UV spectral properties are representative of a larger sample of local events (Maguire et al.). The near-UV to optical spectra of SN 2011fe are modelled with a Monte Carlo radiative transfer code using the technique of ‘abundance tomography’, constraining the density structure and the abundance stratification in the SN ejecta. SN 2011fe was a relatively weak explosion, with moderate Fe-group yields. The density structures of the classical model W7 and of a delayed detonation model were tested. Both have shortcomings. An ad hoc density distribution was developed which yields improved fits and is characterized by a high-velocity tail, which is absent in W7. However, this tail contains less mass than delayed detonation models. This improved model has a lower energy than one-dimensional explosion models matching typical SNe Ia (e.g. W7, WDD1; Iwamoto et al.). The derived Fe abundance in the outermost layer is consistent with the metallicity at the SN explosion site in M101 (~0.5 Z ). The spectroscopic rise-time (~19 d) is significantly longer than that measured from the early optical light curve, implying a ‘dark phase’ of ~1 d. A longer rise-time has significant implications when deducing the properties of the white dwarf and binary system from the early photometric behaviour.

Description: We report on the discovery of a new fast radio burst (FRB), FRB 150215, with the Parkes radio telescope on 2015 February 15. The burst was detected in real time with a dispersion measure (DM) of 1105.6 ± 0.8 pc cm−3, a pulse duration of 2.8$$^{+1.2}_{-0.5}$$ ms, and a measured peak flux density assuming that the burst was at beam centre of 0.7$$^{+0.2}_{-0.1}$$ Jy. The FRB originated at a Galactic longitude and latitude of 24.66°, 5.28° and 25° away from the Galactic Center. The burst was found to be 43 ± 5 per cent linearly polarized with a rotation measure (RM) in the range −9 〈 RM 〈 12 rad m−2 (95 per cent confidence level), consistent with zero. The burst was followed up with 11 telescopes to search for radio, optical, X-ray, γ-ray and neutrino emission. Neither transient nor variable emission was found to be associated with the burst and no repeat pulses have been observed in 17.25 h of observing. The sightline to the burst is close to the Galactic plane and the observed physical properties of FRB 150215 demonstrate the existence of sight lines of anomalously low RM for a given electron column density. The Galactic RM foreground may approach a null value due to magnetic field reversals along the line of sight, a decreased total electron column density from the Milky Way, or some combination of these effects. A lower Galactic DM contribution might explain why this burst was detectable whereas previous searches at low latitude have had lower detection rates than those out of the plane.