17 research outputs found
The environments and hosts of metal absorption at z>5
A growing population of metal absorbers are observed at z>5, many showing
strong evolution in incidence approaching the epoch of hydrogen reionization.
Follow-up surveys examining fields around these metals have resulted in galaxy
detections but the direct physical relationship between the detected galaxies
and absorbers is unclear. Upcoming observations will illuminate this
galaxy-absorber relationship, but the theoretical framework for interpreting
these observations is lacking. To inform future z>5 studies, we define the
expected relationship between metals and galaxies using the Technicolor Dawn
simulation to model metal absorption from z=5-7, encompassing the end of
reionization. We find that metal absorber types and strengths are slightly
better associated with their environment than with the traits of their host
galaxies, as absorption system strengths are more strongly correlated with the
local galaxy overdensity than the stellar mass of their host galaxy. For
redshifts prior to the end of the epoch of reionization, strong high ionization
transitions like C IV are more spatially correlated with brighter galaxies on
scales of a few hundred proper kpc than are low ionization systems, due to the
former's preference for environments with higher UVB amplitudes and those ions'
relative rarity at z>6. Post-reionization, the galaxy counts near these
high-ionization ions are reduced, and increase surrounding certain
low-ionization ions due to a combination of their relative abundances and
preferred denser gas phase. We conclude that galaxy-absorber relationships are
expected to evolve rapidly such that high-ionization absorbers are better
tracers of galaxies pre-reionization while low-ionization absorbers are better
post-reionization.Comment: Accepted to MNRA
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Crude, Cash and Culture Change: The Huaorani of Amazonian Ecuador
The idea of indigenous populations around the world as ânoble savagesâ dominated literature for much of the 20th century. Further research into different tribesâ environmental practices as well as their integration into the market economy has begun to change this view. In Ecuadorian Amazon, the Huaorani are the most recently assimilated group, with some sub-groups still resisting contact with the outside. With vast reserves of oil present under Huaorani land, this indigenous group has quickly become integrated into national and international markets. The focus of this study is on one Huaorani community, Gareno, which is located along an oil road within the Amazon. Community members were interviewed in order to better understand why they lived along the oil road and how they felt it impacted their daily lives. Responses showed that the residents have chosen to live and stay in Gareno because of the health and education opportunities and ease of transport, but also because this area is ancestral territory. In addition, they left former villages, which were deep inside the forest, due to social conflict. It is notable that these push and pull factors complicate the notion of ânoble savagesâ (who either continue to be isolated from the market or are unable to cope with it) and highlight indigenous agency and decision-making during a period of rapid cultural, economic, and ecological change. As the people of Gareno look to further improve their quality of life through development, it is important to foster more nuanced views of indigenous peoples to not only devise appropriate conservation and development policies but also to prevent a backlash when they do not conform to idealized Western images
The faint host galaxies of CIV absorbers at z > 5
We explore the expected galaxy environments of CIV absorbers at z > 5 using the Technicolor Dawn simulations. These simulations reproduce the observed history of reionization, the z ~ 6 galaxy stellar mass function, the Ly a forest transmission at z > 5, and the Si IV column density distribution (CDD) at z ~ 5.5. None the less, the CIV CDD remains underproduced. Comparison with observed CII/Si II equivalent width ratios and the CII line incidence suggests that a low carbon yield accounts for some, but not all, of the CIV discrepancy. Alternatively, a density-bounded escape scenario could harden the metagalactic ionizing background more dramatically even than binary stellar evolution, boosting the CIV CDD into near agreement with observations. In this case, galaxies ionize more efficiently and fewer are required to host a given high-ionization absorber. AbsorbersÂŽ environments therefore constrain ionizing escape. Regardless of the escape scenario, galaxies correlate with CIV absorbers out to 300 proper kpc (pkpc). The correlation strengthens independently with galaxy luminosity and CIV column density. Around strong systems (log(NCIV/cm-2) > 14)), the overdensity of galaxies with MUV 41.9 declines from 200-300 within 100 pkpc to 40-60 within 250 pkpc. The previously suggested association between strong CIV absorbers and Ly a emitters at z > 5 is not expected. It may arise if both populations inhabit large-scale voids, but for different reasons. Although most neighbouring galaxies are too faint for HST, JWST will, with a single pointing, identify ~10 neighbouring galaxies per strong CIV absorber at z > 5. Ground-based tests of these predictions are possible via deep surveys for Ly a emission using integral field units.Fil: Finlator, Kristian. Technical University of Denmark; DinamarcaFil: Doughty, Caitlin. New Mexico State University; Estados UnidosFil: Cai, Zheng. Tsinghua University; ChinaFil: Diaz, Carlos Gonzalo. Gemini Observatorysouthern Operations Center; Chile. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - San Juan. Instituto de Ciencias AstronĂłmicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias AstronĂłmicas, de la Tierra y del Espacio; Argentin
Constraining the astrophysics and cosmology from 21 cm tomography using deep learning with the SKA
Future Square Kilometre Array (SKA) surveys are expected to generate huge data sets of 21âcm maps on cosmological scales from the Epoch of Reionization. We assess the viability of exploiting machine learning techniques, namely, convolutional neural networks (CNNs), to simultaneously estimate the astrophysical and cosmological parameters from 21âcm maps from seminumerical simulations. We further convert the simulated 21âcm maps into SKA-like mock maps using the detailed SKA antennae distribution, thermal noise, and a recipe for foreground cleaning. We successfully design two CNN architectures (VGGNet-like and ResNet-like) that are both efficiently able to extract simultaneously three astrophysical parameters, namely the photon escape fraction (fesc), the ionizing emissivity power dependence on halo mass (Cion), and the ionizing emissivity redshift evolution index (Dion), and three cosmological parameters, namely the matter density parameter (Ωm), the dimensionless Hubble constant (h), and the matter fluctuation amplitude (Ï8), from 21âcm maps at several redshifts
Deep Learning Voigt Profiles I. Single-Cloud Doublets
Voigt profile (VP) decomposition of quasar absorption lines is key to
studying intergalactic gas and the baryon cycle governing the formation and
evolution of galaxies. The VP velocities, column densities, and Doppler
parameters inform us of the kinematic, chemical, and ionization conditions of
these astrophysical environments. A drawback of traditional VP fitting is that
it can be human-time intensive. With the coming next generation of large
all-sky survey telescopes with multi-object high-resolution spectrographs, the
time demands will significantly outstrip our resources. Deep learning pipelines
hold the promise to keep pace and deliver science digestible data products. We
explore the application of deep learning convolutional neural networks (CNNs)
for predicting VP fitted parameters directly from the normalized pixel flux
values in quasar absorption line profiles. A CNN was applied to 56
single-component MgII2796, 2803 doublet absorption line systems observed with
HIRES and UVES (). The CNN predictions were statistically indistinct
from a traditional VP fitter. The advantage is that once trained, the CNN
processes systems times faster than a human expert VP fitting
profiles by hand. Our pilot study shows that CNNs hold promise to perform bulk
analysis of quasar absorption line systems in the future.Comment: 22 pages, 12 figures, submitted to the Astrophysical Journa
Astrobites as a Community-led Model for Education, Science Communication, and Accessibility in Astrophysics
Support for early career astronomers who are just beginning to explore
astronomy research is imperative to increase retention of diverse practitioners
in the field. Since 2010, Astrobites has played an instrumental role in
engaging members of the community -- particularly undergraduate and graduate
students -- in research. In this white paper, the Astrobites collaboration
outlines our multi-faceted online education platform that both eases the
transition into astronomy research and promotes inclusive professional
development opportunities. We additionally offer recommendations for how the
astronomy community can reduce barriers to entry to astronomy research in the
coming decade
Extended Sentinel Monitoring of Helicoverpa zea Resistance to Cry and Vip3Aa Toxins in Bt Sweet Corn: Assessing Changes in Phenotypic and Allele Frequencies of Resistance
Transgenic corn and cotton that produce Cry and Vip3Aa toxins derived from Bacillus thuringiensis (Bt) are widely planted in the United States to control lepidopteran pests. The sustainability of these Bt crops is threatened because the corn earworm/bollworm, Helicoverpa zea (Boddie), is evolving a resistance to these toxins. Using Bt sweet corn as a sentinel plant to monitor the evolution of resistance, collaborators established 146 trials in twenty-five states and five Canadian provinces during 2020â2022. The study evaluated overall changes in the phenotypic frequency of resistance (the ratio of larval densities in Bt ears relative to densities in non-Bt ears) in H. zea populations and the range of resistance allele frequencies for Cry1Ab and Vip3Aa. The results revealed a widespread resistance to Cry1Ab, Cry2Ab2, and Cry1A.105 Cry toxins, with higher numbers of larvae surviving in Bt ears than in non-Bt ears at many trial locations. Depending on assumptions about the inheritance of resistance, allele frequencies for Cry1Ab ranged from 0.465 (dominant resistance) to 0.995 (recessive resistance). Although Vip3Aa provided high control efficacy against H. zea, the results show a notable increase in ear damage and a number of surviving older larvae, particularly at southern locations. Assuming recessive resistance, the estimated resistance allele frequencies for Vip3Aa ranged from 0.115 in the Gulf states to 0.032 at more northern locations. These findings indicate that better resistance management practices are urgently needed to sustain efficacy the of corn and cotton that produce Vip3Aa
Aligned metal absorbers and the ultraviolet background at the end of reionization
We use observations of spatially-aligned C ii, C iv, Si ii, Si iv, and O i absorbers to probe the
slope and intensity of the ultraviolet background (UVB) at z ⌠6. We accom- plish this by comparing
observations with predictions from a cosmological hydrody- namic simulation using three trial UVBs
applied in post-processing: a spectrally soft, fluctuating UVB calculated using multi-frequency
radiative transfer; a soft, spatially- uniform UVB; and a hard, spatially-uniform âquasars-onlyâ
model. When considering our paired high-ionization absorbers (Civ/Siiv), the observed statistics
strongly prefer the hard, spatially-uniform UVB. This echoes recent findings that cosmological sim-
ulations generically underproduce strong C iv absorbers at z > 5. A single low/high ionization pair
(Si ii/Si iv), by contrast, shows a preference for the HM12 UVB, while two more (C ii/C iv and O
i/C iv) show no preference for any of the three UVBs. Despite this, future observations of specific
absorbers, particularly Si iv/C iv, with next-generation telescopes probing to lower column
densities should yield tighter con-
ts on the UVB