The optical morphology of galaxies holds the
cumulative record of their assembly history, and techniques for
its quantitative characterization offer a promising avenue toward
understanding galaxy formation and evolution. However, the
morphology of star-forming galaxies is generally dictated by the
youngest stellar component, which can readily overshine faint
structural/morphological features in the older underlying stellar
background (e.g., relics from recent minor mergers) that could
hold important insights into the galaxy build-up process.
Stripping off galaxy images from the emission from stellar
populations younger than an adjustable age cutoff t_cut
can therefore provide a valuable tool in extragalactic research.
RemoveYoung (RY), a publicly available tool that was
presented in Gomes
& Papaderos (2016, A&A 594, A49)
exploits the combined power of integral field spectroscopy (IFS)
and population spectral synthesis (PSS) toward this goal.
Two-dimensional post-processing of PSS models to IFS data cubes
with RY permits computation of the spectral energy, surface
brightness, and stellar surface density distribution of stellar
populations older than a user-defined t_cut. This suggests
a variety of applications to star-forming galaxies, such as
interacting or merging galaxy pairs and lower-mass starburst
galaxies near and far, and blue compact and tidal dwarf galaxies.
RemoveYoung (RY) requires as input the Population
Vector (PV) obtained by fitting a galaxy spectrum with a PSS code. The PV is essentially an array holding the
best-fitting set of mass fractions of Simple Stellar
Populations (SSPs) picked up by the PSS code from a base
library. The latter may contain SSPs spanning a range in
stellar age and metallicity from, e.g., Bruzual & Charlot
(2003; MNRAS, 344, 1000; available online here) or MILES.
The current version (v.01) of RY is
adapted to the post-processing of PVs computed with the Starlight code (Cid
Fernandes et al. 2005, MNRAS 358, 363). An example of the PV
obtained by fitting the optical spectrum of an emission-line
galaxy with Starlight can be found here.
A PV can be post-processed with RY by executing in a Linux terminal the command:
$ ./RY01.exe par1 par2 ... par10
where
par1 | spectrum.PV (PV obtained
from PSS modeling of a galaxy spectrum) |
par2 | distance to the galaxy in
Mpc |
par3 | directory where the PV is
stored |
par4 | directory where the
library SSPs are stored |
par5 | directory where the
photometric filter transmission curves are stored |
par6 | requested time cutoff
t_cut in Gyr |
par7 | flux units of the modeled
galaxy spectrum |
par8 | 1: correction for
the intrinsic extinction A_V inferred from the PSS fit
(and included in spectrum.PV) 0: no correction for intrinsic extinction will be applied |
par9 | 0: execution of RY
without storage of its output 1: storage of a list of synthetic magnitudes for a set of photometric filters 2: additionally, storage of the spectroscopic output from the code |
par10 | verbosity level of the
terminal output (0/1: no terminal
output/terminal output) |
|
$ ./RY01.exe < grid.in |
100 | [number of PVs in the
list] |
/home/RY_user/PVs/ | [ PV_Dir ] |
/home/RY_user/SSPs/ | [ SSP_Dir ] |
/home/RY_user/PhotometricFilters/ | [Filter_Dir] |
0.10 |
[t_cut Gyr ] |
1.0e-16 |
[Flux_units] |
1 |
[ Ext_Corr ] |
1 |
[ Output ] 0-only
run RY 1-MAG file 2-MAG & SPC files |
0 |
[Verbosity ] 0/1:
no terminal output/terminal output |
spectrum.PV 010.000 | [PV file ] [Distance] |
spectrum1.PV 022.400 | [PV file ] [Distance] |
spectrum2.PV 006.700 | [PV file ] [Distance] |
... |
... |
spectrum99.PV 047.200 | [PV file ] [Distance] |
col 01 | Filter |
col 02 | An estimate of the
fraction of the filter transmission curve within the
spectral range of the modeled spectrum |
col 03 | As in column 02, but only
for pixels with a flux > 0.0 |
col 04 | Effective lambda of the
filter transmission curve |
col 05 | Calibration zero point |
col 06 | MAG_OBS: MAG computed
from the observed spectrum |
col 07 | MAG_FIT: computed from
the FIT to the observed spectral continuum (i.e. excluding
the contribution of emission lines) |
col 08 | MAG_FIT_Y: MAG obtained
from the FIT for the young stellar component (i.e. for
SSPs with an age .leq.
t_cut) |
col 09 | MAG_FIT_O: MAG obtained
from the FIT for the old stellar component (i.e. for SSPs
with an age > t_cut) |
col 10 |
MAG_OBS - MAG_SYNTH (i.e. luminosity increase in mag due to the nebular line emission) |
col 11 |
MAG_OBS - MAG_FIT_Y |
col 12 |
MAG_OBS - MAG_FIT_O (i.e.
magnitude corresponding to the young stellar component and
nebular line emission) |
col 15 |
logM_cor: log of
currently available stellar mass (i.e. corrected for the
stellar mass fraction returned to the ISM in the course of
stellar evolution) |
col 16 |
logM: log of stellar mass
ever formed |
col 17 |
logM_cor_y: as in col. 15
but for the young stellar component |
col 18 |
logM_cor : as in
col. 16 but for the young stellar component |
col 19 |
logM_cor_o: as in col. 15
but for the old stellar component |
col 20 | logM_cor : as in
col. 16 but for the old stellar component |
col 01 | Wavelength covered by SSP
models from Bruzual & Charlot (2003) (91 Å - 1600000
Å) |
col 02 | Obs + synthetic over the
spectral range between 91 Å and 1600000 Å |
col 03 | Wavelength covered by the
observed spectrum |
col 04 | Observed spectrum |
col 05 | as in col. 01 |
col 06 | Synthetic spectrum best fit spectrum |
col 07 | Synthetic spectrum for
the young stellar component |
col 08 | Synthetic spectrum for
the old stellar component |
col 09 | Internal |
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