TNG50 sightlines

How to read

• Rows are lines, cool to hot. Columns are instrument cases (Layout).
• Flux is normalised to the continuum; v is the velocity relative to the galaxy's systemic velocity.
• Stepped line: the degraded spectrum, a Gaussian line-spread function of FWHM c/R with 5 pixels and the given S/N per resolution element. Shading: the noiseless model. Intrinsic (dashed): the noiseless spectrum before the line-spread function.
• Fitted components: the fitted model in ink, each component in the line colour and a tick at its centre. A hollow tick marks a component on a bound, cut by the time cap, or unconstrained (log N error above 1 dex). An arrow marks a saturated component: its log N is only a lower limit, read as “log N > 14.5 sat”. The readout gives the fitted values, their errors and flags.
• Drag or use the arrow keys to pan; ctrl or cmd with the wheel, or + and −, zoom; Home resets.
• 3D: drag to orbit, scroll to zoom, click a sightline to open its spectra.

Data and methods

Sightlines through the circumgalactic medium of one TNG50-1 galaxy (subhalo 488530 at z = 0), labelled by orientation, impact parameter b and azimuth from the projected major axis.

Optical depths from Trident on a 0.25 km/s grid, stored at 1 km/s. Velocities are relative to the galaxy's systemic velocity.

H I: TNG neutral fraction (self-shielding included); metal ions: Trident HM2012 table, solar ratios scaled by metallicity.

Atomic data follow Trident 1.4.2 (O VI 1031.912 Å and C IV 1548.187 Å, 3 to 4 km/s from Morton 2003); O VII from Verner et al. 1996. Damped H I wings use Trident's Γ = 4.69 × 10⁸ s⁻¹ against the standard damping constant 6.265 × 10⁸ (Morton 2003), so damped log N fitted here sits about 0.13 dex above VPFIT-style fits of the same wings. Saturated components are lower limits.

The degradation and the Voigt fits run in your browser: Levenberg–Marquardt on (log N, b, v) through the line-spread function, seeded from the intrinsic component catalogue and pruned by ΔBIC. Noise matches the publication figure only statistically.

3D: every gas cell and star particle deposited into nested cubes (±400, ±100 and ±25 kpc), fetched from a public Hugging Face dataset. Find searches the fitted components of every sightline. Ask is an optional chat that drives the page through the same tools; its local model downloads about 1 GB, and the Claude backend sends your messages through the sightline server.

Licence and credits

Simulation: IllustrisTNG, TNG50-1 (Nelson et al. 2019; Pillepich et al. 2019), used under the IllustrisTNG data policy. Spectra: Trident (Hummels, Smith and Silvia 2017) on yt (Turk et al. 2011); metal-ion table HM2012, H I from the TNG neutral fraction.

Code MIT; yt and the patched Trident BSD-3; three.js MIT; WebLLM and the Qwen2.5-1.5B-Instruct weights Apache-2.0 (loaded only for the chat's local model); TNG50-derived spectra under the IllustrisTNG data policy (see THIRD_PARTY_LICENSES).

Source: github.com/tanmay-starslab/cgm-absorber-requirements. Companion page: Detect and resolve.

New sightline

Library sightlines load at once; new ones are cast on the sightline server.

Find by components