An official website of the United States government
Abstract Observed scatter in the Lyαopacity of quasar sightlines atz< 6 has motivated measurements of the correlation between Lyαopacity and galaxy density, as models that predict this scatter make strong and sometimes opposite predictions for how they should be related. Our previous work associated two highly opaque Lyαtroughs atz∼ 5.7 with a deficit of Lyαemitting galaxies (LAEs). In this work, we survey two of the most highly transmissive lines of sight at this redshift toward thez= 6.02 quasar SDSS J1306+0356 and thez= 6.17 quasar PSO J359-06. We find that both fields are underdense in LAEs within 10h−1Mpc of the quasar sightline, somewhat less extensive than underdensities associated with Lyαtroughs. We combine our observations with three additional fields from the literature and find that while fields with extreme opacities are generally underdense, moderate opacities span a wider density range. The results at high opacities are consistent with models that invoke UV background fluctuations and/or late reionization to explain the observed scatter in intergalactic medium (IGM) Lyαopacities. There is tension at low opacities, however, as the models tend to associate lower IGM Lyαopacities with higher densities. Although the number of fields surveyed is still small, the low-opacity results may support a scenario in which the ionizing background in low-density regions increases more rapidly than some models suggest after becoming ionized. Elevated gas temperatures from recent reionization may also be making these regions more transparent.
more »
« less
An Expanded Set of Los Alamos OPLIB Tables in MESA: Type-1 Rosseland-mean Opacities and Solar Models
Abstract We present a set of 1194 Type-1 Rosseland-mean opacity tables for four different metallicity mixtures. These new Los Alamos OPLIB atomic radiative opacity tables are an order of magnitude larger in number than any previous opacity table release, and span regimes where previous opacity tables have not existed. For example, the new set of opacity tables expands the metallicity range toZ= 10−6toZ= 0.2, which allows improved accuracy of opacities at low and high metallicity, increases the table density in the metallicity rangeZ= 10−4toZ= 0.1 to enhance the accuracy of opacities drawn from interpolations across neighboring metallicities, and adds entries for hydrogen mass fractions betweenX= 0 andX= 0.1 includingX= 10−2, 10−3, 10−4, 10−5, 10−6that can improve stellar models of hydrogen deficient stars. We implement these new OPLIB radiative opacity tables inMESAand find that calibrated solar models agree broadly with previously published helioseismic and solar neutrino results. We find differences between using the new 1194 OPLIB opacity tables and the 126 OPAL opacity tables range from ≈20% to 80% across individual chemical mixtures, up to ≈8% and ≈15% at the bottom and top of the solar convection zone respectively, and ≈7% in the solar core. We also find differences between standard solar models using different opacity table sources that are on par with altering the initial abundance mixture. We conclude that this new, open-access set of OPLIB opacity tables does not solve the solar modeling problem, and suggest the investigation of physical mechanisms other than the atomic radiative opacity.
more »
« less
- Award ID(s):
- 1927130
- PAR ID:
- 10513869
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 968
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 56
- Size(s):
- Article No. 56
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The cold neutral medium (CNM) is where neutral atomic hydrogen (Hi) is converted into molecular clouds, so the structure and kinematics of the CNM are key drivers of galaxy evolution. Here we provide new constraints on the vertical distribution of the CNM using the recently developedkinematic_scaleheightsoftware package and a large catalog of sensitive Hiabsorption observations. We estimate the thickness of the CNM in the solar neighborhood to beσz∼ 50–90 pc, assuming a Gaussian vertical distribution. This is a factor of ∼2 smaller than typically assumed, indicating that the thickness of the CNM in the solar neighborhood is similar to that found in the inner Galaxy, consistent with recent simulation results. If we consider only structures with Hioptical depthsτ> 0.1 or column densitiesN(Hi) > 1019.5cm−2, which recent work suggests are thresholds for molecule formation, we findσz∼ 50 pc. Meanwhile, for structures withτ< 0.1 or column densitiesN(Hi) < 1019.5cm−2, we findσz∼ 120 pc. These thicknesses are similar to those derived for the thin- and thick-disk molecular cloud populations traced by CO emission, possibly suggesting that cold Hiand CO are well mixed. Approximately 20% of CNM structures are identified as outliers, with kinematics that are not well explained by Galactic rotation. We show that some of these CNM structures—perhaps representing intermediate-velocity clouds—are associated with the Local Bubble wall. We compare our results to recent observations and simulations, and we discuss their implications for the multiphase structure of the Milky Way’s interstellar medium.more » « less
-
Context.Grids of stellar evolution models with rotation using the Geneva stellar evolution code (GENEC) have been published for a wide range of metallicities. Aims.We introduce the last remaining grid of GENECmodels, with a metallicity ofZ = 10−5. We study the impact of this extremely metal-poor initial composition on various aspects of stellar evolution, and compare it to the results from previous grids at other metallicities. We provide electronic tables that can be used to interpolate between stellar evolution tracks and for population synthesis. Methods.Using the same physics as in the previous papers of this series, we computed a grid of stellar evolution models with GENECspanning masses between 1.7 and 500M⊙, with and without rotation, at a metallicity ofZ = 10−5. Results.Due to the extremely low metallicity of the models, mass-loss processes are negligible for all except the most massive stars. For most properties (such as evolutionary tracks in the Hertzsprung-Russell diagram, lifetimes, and final fates), the present models fit neatly between those previously computed at surrounding metallicities. However, specific to this metallicity is the very large production of primary nitrogen in moderately rotating stars, which is linked to the interplay between the hydrogen- and helium-burning regions. Conclusions.The stars in the present grid are interesting candidates as sources of nitrogen-enrichment in the early Universe. Indeed, they may have formed very early on from material previously enriched by the massive short-lived Population III stars, and as such constitute a very important piece in the puzzle that is the history of the Universe.more » « less
-
Abstract The dust grain size distribution (GSD) likely varies significantly across star-forming environments in the Universe, but its impact on star formation remains unclear. This ambiguity arises because the GSD interacts nonlinearly with processes like heating, cooling, radiation, and chemistry, which have competing effects and varying environmental dependencies. Processes such as grain coagulation, expected to be efficient in dense star-forming regions, reduce the abundance of small grains and increase that of larger grains. Motivated by this, we investigate the effects of similar GSD variations on the thermochemistry and evolution of giant molecular clouds (GMCs) using magnetohydrodynamic simulations spanning a range of cloud masses and grain sizes, which explicitly incorporate the dynamics of dust grains within the full-physics framework of the STARFORGE project. We find that grain size variations significantly alter GMC thermochemistry: the leading-order effect is that larger grains, under fixed dust mass, GSD dynamic range, and dust-to-gas ratio, result in lower dust opacities. This reduced opacity permits interstellar radiation field and internal radiation photons to penetrate more deeply. This leads to rapid gas heating and inhibited star formation. Star formation efficiency is highly sensitive to grain size, with an order-of-magnitude reduction when grain size dynamic range increases from 10−3–0.1μm to 0.1–10μm. Additionally, warmer gas suppresses low-mass star formation, and decreased opacities result in a greater proportion of gas in diffuse ionized structures.more » « less
-
The Sun is the most studied of all stars, and thus constitutes a benchmark for stellar models. However, our vision of the Sun is still incomplete, as illustrated by the current debate on its chemical composition. The problem reaches far beyond chemical abundances and is intimately linked to microscopic and macroscopic physical ingredients of solar models such as radiative opacity, for which experimental results have been recently measured that still await the- oretical explanations. We present opacity profiles derived from helioseismic inferences and compare them with detailed theoretical computations of individual element contributions using three different opacity computation codes, in a complementary way to experimental results. We find that our seismic opacity is about 10% higher than theoretical values used in current solar models around 2 million degrees, but lower by 35% than some recent available theoretical values. Using the Sun as a laboratory of fundamental physics, we show that quantitative comparisons between various opacity tables are required to understand the origin of the discrepancies between reported helioseismic, theoretical and experimental opacity values.more » « less
