Issue |
A&A
Volume 460, Number 2, December III 2006
|
|
---|---|---|
Page(s) | 397 - 413 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20065554 | |
Published online | 12 September 2006 |
3D Lyα radiation transfer
I. Understanding Lyα line profile morphologies
1
Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland e-mail: daniel.schaerer@obs.unige.ch
2
Laboratoire d'Astrophysique (UMR 5572), Observatoire Midi-Pyrénées, 14 avenue E. Belin, 31400 Toulouse, France
3
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85748 Garching, Germany
Received:
5
May
2006
Accepted:
26
July
2006
Aims.The development of a general code for 3D Lyα radiation transfer in galaxies to understand the diversity of Lyα line profiles observed in star-forming galaxies and related objects.
Methods.Using a Monte Carlo technique, we developed a 3D Lyα radiation transfer code that allows for prescribed arbitrary hydrogen density, ionisation, temperature structures, dust distributions, arbitrary velocity fields, and UV photon sources. As a first test and application we examined the Lyα line profiles predicted for several simple geometrical configurations and their dependence on the main input parameters.
Results.Overall, we find line profiles reaching from doubly peaked symmetric
emission to symmetric Voigt (absorption) in static configurations with
increasing dust content, and asymmetric red- (blue-) shifted emission
lines with a blue (red) counterpart ranging from absorption to
emission (with increasing line/continuum strength) in expanding
(infalling) media.
In particular we find the following results to be interesting
for the interpretation of Lyα profiles from galaxies.
1) Standard Lyα absorption line fitting of global spectra of
galaxies may lead to an underestimation of the true hydrogen column
density in certain geometrical conditions;
2) Normal (inverted) P-Cygni-like Lyα profiles
can be obtained in expanding (infalling) media from objects without
any intrinsic Lyα emission, as a natural consequence of radiation
transfer effects;
3) The formation and the detailed shape of Lyα profiles resulting from expanding shells has been thoroughly revised.
In particular we find that, for sufficiently large column densities
( cm-2), the position of the main Lyα
emission peak is quite generally redshifted by approximately twice the
expansion velocity.
This is in excellent agreement with the observations of
LBGs,
which show that Lyα is redshifted by ~
, where Vexp
is the expansion velocity measured from the interstellar absorption
lines blueshifted with respect to the stellar redshift.
This finding also indicates that large-scale, fairly symmetric shell
structures must be a good description of the outflows in LBGs.
Key words: galaxies: starburst / galaxies: ISM / galaxies: high-redshift / utraviolet: galaxies / radiative transfer / line: profiles
© ESO, 2006
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