Gas Accretion via Lyman Limit Systems

In cosmological simulations, a large fraction of the partial Lyman limit systems (pLLSs; 16<log N(HI)<17.2) and LLSs (17.2log N(HI)<19) probes large-scale flows in and out of galaxies through their circumgalactic medium (CGM). The overall low metallicity of the cold gaseous streams feeding galaxies seen in these simulations is the key to differentiating them from metal rich gas that is either outflowing or being recycled. In recent years, several groups have empirically determined an entirely new wealth of information on the pLLSs and LLSs over a wide range of redshifts. A major focus of the recent research has been to empirically determine the metallicity distribution of the gas probed by pLLSs and LLSs in sizable and representative samples at both low (z2) redshifts. Here I discuss unambiguous evidence for metal-poor gas at all z probed by the pLLSs and LLSs. At z<1, all the pLLSs and LLSs so far studied are located in the CGM of galaxies with projected distances <100-200 kpc. Regardless of the exact origin of the low-metallicity pLLSs/LLSs, there is a significant mass of cool, dense, low-metallicity gas in the CGM that may be available as fuel for continuing star formation in galaxies over cosmic time. As such, the metal-poor pLLSs and LLSs are currently among the best observational evidence of cold, metal-poor gas accretion onto galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springe

The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

CO J = 1–0 SPECTROSCOPY OF FOUR SUBMILLIMETER GALAXIES WITH THE ZPECTROMETER ON THE GREEN BANK TELESCOPE

We report detections of three z ∼ 2.5 submillimeter-selected galaxies (SMGs; SMM J14011+0252, SMM J14009+0252, SMM J04431+0210) in the lowest rotational transition of the carbon monoxide molecule (CO J = 1–0) and one nondetection (SMM J04433+0210). For the three galaxies we detected, we find a line-integrated brightness temperature ratio of the J = 3–2 and 1–0 lines of 0.68 ± 0.08; the 1–0 line is stronger than predicted by the frequent assumption of equal brightnesses in the two lines and by most single-component models. The observed ratio suggests that mass estimates for SMGs based on J = 3–2 observations and J = 1–0 column density or mass conversion factors are low by a factor of 1.5. Comparison of the 1–0 line intensities with intensities of higher-J transitions indicates that single-component models for the interstellar media in SMGs are incomplete. The small dispersion in the ratio, along with published detections of CO lines with Jupper&gt; 3 in most of the sources, indicates that the emission is from multi-component interstellar media with physical structures common to many classes of galaxies. This result tends to rule out the lowest scaling factors between CO luminosity and molecular gas mass, and further increases molecular mass estimates calibrated against observations of galaxie

The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies. © 2023. The Author(s). Published by IOP Publishing Ltd on behalf of the Astronomical Society of the Pacific (ASP). All rights reservedOpen access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least 4 m. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the 6.5 m James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 yr, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit. © 2023. The Author(s). Published by IOP Publishing Ltd on behalf of the Astronomical Society of the Pacific (ASP). All rights reserved.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]