| Input | Action |
|---|---|
| click (or SPC or A) | show wavelength at cursor |
| drag | rubber-band zoom, like e — a purely
horizontal drag zooms X only; purely vertical, Y only |
| right-click | quick line menu — pick a line to set the redshift at that position (same as ESC + shortcut key) |
| Key | Action |
|---|---|
| ESC key | mark known line at cursor via shortcut key (see below; backquote works as ESC) |
| ESC ESC | refine redshift using nearest line |
| g | guess redshift (enter wavelength of probable line) |
| = | enter redshift directly |
| r | remove features from plot |
Shortcut keys after ESC:
| Key | Line | Key | Line |
|---|---|---|---|
| l | Lyα 1216 | g | G 4304 |
| c | CIV 1549 | b | Hβ 4861 |
| m | MgII 2800 | O | [OIII] 5007 |
| o | [OII] 3727 | d | NaD 5892 |
| k | K 3933 | a | Hα 6563 |
| h | H 3969 |
| Key | Action |
|---|---|
| [ ] | pan left/right |
| z / u | zoom / unzoom X axis |
| i / o | zoom / unzoom Y axis ("in" / "out") |
| x / y | set X range / Y range (two cursor picks) |
| e | expand plot (two corner picks) |
| w | whole X range |
| a | autoscale Y axis |
| h | home — restore initial display range |
| d | display again |
| Key | Action |
|---|---|
| _ | continuum fit and estimate noise |
| m | measure EW/flux of line (define continuum first) |
| b | plot binned up spectrum |
| s | plot smoothed spectrum |
| t | overlay template spectrum (currently {template}) |
| k | kill nearest line from list |
| B | bodge cosmic rays/sky by replacing with ZERO |
| Key | Action |
|---|---|
| p | print to PDF (pyredshift.pdf) |
| ? | this help |
| q | quit |
All wavelengths are VACUUM, in Ångstroms (from pyredshift.lines, colours as plotted):
{linelist}pyredshift is a tool for measuring the redshift of a galaxy or quasar
from a 1D spectrum, by eye. Run it as pyredshift file —
the format (FITS image or table, SDSS, JWST, XSHOOTER, OutThere, CSV,
2-column ascii) is auto-detected, with -f to force one,
-z to start from a known redshift and --retro
for a retro PGPLOT-style black background. It plots the spectrum histogram-style with a
crosshair cursor, and overlays rest-frame line identifications that
follow the trial redshift shown at top left.
The basic game: spot a feature you can identify, put the crosshair on
it and press ESC then the line's shortcut key (or
g to type any rest wavelength) — the line labels jump
to that redshift. Now check the other features line up, panning and
zooming (mouse drag works), binning (b) or smoothing
(s) to dig in the noise, and refining with
ESC ESC on the sharpest line. Along the way you can fit a
continuum (_) and measure equivalent widths and line fluxes
(m), and print to PDF (p). q
quits and reports the final redshift to the terminal. It is the Python
descendant of Karl's venerable redshift.f (Fortran, 1990s)
via pdlredshift (Perl/PDL).
From a Jupyter notebook, call
pyredshift.redshift.redshift(wave, flux) with numpy arrays:
the interactive window opens outside the notebook, and when you quit the
final view is embedded in the cell and the redshift returned.