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slitless

A forward modeling approach of slitless spectroscopy

Version:0.3.0 of 20/04/13, 22:02
Author:Mehdi Outini <mehdi.outini@gmail.com>, Yannick Copin <ycopin@ipnl.in2p3.fr>
Documentation Status
Abstract:Slitless spectroscopy has long been considered a complicated and confused technique. Nonetheless, with the advent of Hubble Space Telescope (HST) instruments, characterized by a low sky background level and a high spatial resolution (most notably WFC3), slitless spectroscopy has become an adopted survey tool to study galaxy evolution from space. We aim to investigate its application to single-object studies to measure not only redshift and integrated spectral features, but also spatially-resolved quantities such as galaxy kinematics. It is used to improve redshifts and constrain basic rotation curve parameters, meaning the plateau velocity v0 (in km/s) and the central velocity gradient w0 (in km/s/arcsec). This forward approach makes it possible to mitigate the self-contamination effect, a primary drawback of slitless spectroscopy, and therefore has the potential to increase precision on redshifts. In a limited sample of well-resolved spiral galaxies from HST surveys (3D-HST and GLASS) train galaxy rotation curve parameters. This proof-of-concept work is promising for future large slitless spectroscopic surveys, such as Euclid and WFIRST.

This code (slitless) made in Python was written in a purpose to simulate and analyse galaxy properties in slitless spectroscopy. It implements both the construction and modelisation of galaxy slitless spectra and the measure of spatially resolved quantities such as kinematics. It also constrains spectral features such as redshift, emission lines, line width etc. The first measure of galaxy kinematics using slitless spectra from 3D-HST and GLASS survey is detailed in [Outini20].

_images/galaxy1134_kinematics.png

Fig. 1 Measure of internal kinematics of the galaxy 1134-MACS-1423 from the GLASS survey. Left: adjusted velocity field (contours) over-imposed on broadband image (gray) of galaxy #1134 from the GLASS survey. Left: input observed (gray) and modeled (contours) peak-normalized spectrogram centered on the Hα+[NII]+[SII] complex. The red dashed lines represents the adjusted rotation curve at the Hα position.