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Register a new userAtomic Data Revisions for Transitions Relevant to Observations of Interstellar, Circumgalactic, and Intergalactic Matter
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Measurements of element abundances in galaxies from astrophysical spectroscopy depend sensitively on the atomic data used. With the goal of making the latest atomic data accessible to the community, we present a compilation of selected atomic data for resonant absorption lines at wavelengths longward of 911.753 {AA} (the ion{H}{1} Lyman limit), for key heavy elements (heavier than atomic number 5) of astrophysical interest. In particular, we focus on the transitions of those ions that have been observed in the Milky Way interstellar medium (ISM), the circumgalactic medium (CGM) of the Milky Way and/or other galaxies, and the intergalactic medium (IGM). We provide wavelengths, oscillator strengths, associated accuracy grades, and references to the oscillator strength determinations. We also attempt to compare and assess the recent oscillator strength determinations. For about 22% of the lines that have updated oscillator strength values, the differences between the former values and the updated ones are $gtrsim$~0.1 dex. Our compilation will be a useful resource for absorption line studies of the ISM, as well as studies of the CGM and IGM traced by sight lines to quasars and gamma-ray bursts. Studies (including those enabled by future generations of extremely large telescopes) of absorption by galaxies against the light of background galaxies will also benefit from our compilation.
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PyNeb is a Python package widely used to model emission lines in gaseous nebulae. We take advantage of its object-oriented architecture, class methods, and historical atomic database to structure a practical environment for atomic data assessment. Our aim is to reduce the uncertainties in parameter space (line-ratio diagnostics, electron density and temperature, and ionic abundances) arising from the underlying atomic data by critically selecting the PyNeb default datasets. We evaluate the questioned radiative-rate accuracy of the collisionally excited forbidden lines of the N- and P-like ions (O II, Ne IV, S II, Cl III, and Ar IV), which are used as density diagnostics. With the aid of observed line ratios in the dense NGC 7027 planetary nebula and careful data analysis, we arrive at emissivity-ratio uncertainties from the radiative rates within 10%, a considerable improvement over a previously predicted 50%. We also examine the accuracy of an extensive dataset of electron-impact effective collision strengths for the carbon isoelectronic sequence recently published. By estimating the impact of the new data on the pivotal temperature diagnostics of [N II] and [O III] and by benchmarking the collision strength with a measured resonance position, we question their usefulness in nebular modeling. We confirm that the effective-collision-strength scatter of selected datasets for these two ions does not lead to uncertainties in the temperature diagnostics larger than 10%.
The circumgalactic medium (CGM) of galaxies serves as a record of the influences of outflows and accretion that drive the evolution of galaxies. Feedback from star formation drives outflows that carry mass and metals away from galaxies to the CGM, while infall from the intergalactic medium (IGM) is thought to bring in fresh gas to fuel star formation. Such exchanges of matter between IGM-CGM-galaxies have proven critical to producing galaxy scaling relations in cosmological simulations that match observations. However, the nature of these processes, of the physics that drives outflows and accretion, and their evolution with cosmic time are not fully characterized. One approach to constraining these processes is to characterize the metal enrichment of gas around and beyond galaxies. Measurements of the metallicity distribution functions of CGM/IGM gas over cosmic time provide independent tests of cosmological simulations. We have made great progress over the last decade as direct result of a very sensitive, high-resolution space-based UV spectrograph and the rise of ground-based spectroscopic archives. We argue the next transformative leap to track CGM/IGM metals during the epoch of galaxy formation and transformation into quiescent galaxies will require 1) a larger space telescope with an even more sensitive high-resolution spectrograph covering both the far- and near-UV (1,000-3,000 AA); and 2) ground-based archives housing science-ready data.
We describe a new approach to studying the intergalactic and circumgalactic medium in the local Universe: direct detection through narrow-band imaging of ultra-low surface brightness visible-wavelength line emission. We use the hydrodynamical cosmological simulation EAGLE to investigate the expected brightness of this emission at low redshift ($z$ $lesssim$ 0.2). H$alpha$ emission in extended halos (analogous to the extended Ly$alpha$ halos/blobs detected around galaxies at high redshifts) has a surface brightness of $gtrsim700$ photons cm$^{-2}$ sr$^{-1}$ s$^{-1}$ out to $sim$100 kpc. Mock observations show that the Dragonfly Telephoto Array, equipped with state-of-the-art narrow-band filters, could directly image these structures in exposure times of $sim$10 hours. H$alpha$ fluorescence emission from this gas can be used to place strong constraints on the local ultra-violet background, and on gas flows around galaxies. Detecting H$alpha$ emission from the diffuse intergalactic medium (the cosmic web) is beyond current capabilities, but would be possible with a hypothetical 1000-lens Dragonfly array.
This paper systematically investigates comoving Mpc scale intergalactic medium (IGM) environment around galaxies traced by the Ly$alpha$ forest. Using our cosmological hydrodynamic simulations, we investigate the IGM-galaxy connection at $z=2$ by two methods: (I) cross-correlation analysis between galaxies and the fluctuation of Ly$alpha$ forest transmission ($delta_text{F}$); and (II) comparing the overdensity of neutral hydrogen (HI) and galaxies. Our simulations reproduce observed cross-correlation functions (CCF) between Ly$alpha$ forest and Lyman-break galaxies. We further investigate the variation of the CCF using subsamples divided by dark matter halo mass ($M_text{DH}$), galaxy stellar mass ($M_star$), and star-formation rate (SFR), and find that the CCF signal becomes stronger with increasing $M_text{DH}$, $M_star$, and SFR. The CCFs between galaxies and gas-density fluctuation are also found to have similar trends. Therefore, the variation of the $delta_text{F}$-CCF depending on $M_text{DH}$, $M_star$, and SFR is due to varying gas density around galaxies. We find that the correlation between galaxies and the IGM HI distribution strongly depends on $M_text{DH}$ as expected from the linear theory. Our results support the $Lambda$CDM paradigm, finding a spatial correlation between galaxies and IGM HI, with more massive galaxies being clustered in higher-density regions.
This paper reviews atoms and ions in the upper atmosphere, including the mesospheric metals Na, Fe, Mg$^+$, Si$^+$, Ca$^+$, K and also non-metallic species N, N$^+$, O, H, considering their potential for astronomical adaptive optics. Na and Fe are the best candidates for the creation of polychromatic laser guide stars, with the strongest returns coming from transitions that can be reached by excitation at two wavelengths. Ca$^+$ and Si$^+$ have strong visible-light transitions, but require short wavelengths, beyond the atmospheric cutoff, for excitation from the ground state. Atomic O, N and N$^+$ have strong transitions and high abundances in the mesosphere. The product of column density and cross section for these species can be as high as $10^5$ for O and several hundred for N and N$^+$, making them potential candidates for amplified spontaneous emission. However they require vacuum-ultraviolet wavelengths for excitation.
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