Bibcode
Alonso-Herrero, A.; García-Marín, M.; Rodríguez Zaurín, J.; Monreal-Ibero, A.; Colina, L.; Arribas, S.
Bibliographical reference
Astronomy and Astrophysics, Volume 522, id.A7
Advertised on:
11
2010
Journal
Citations
29
Refereed citations
28
Description
Context. The general properties (e.g., activity class, star formation
rates, metallicities, extinctions, average ages, etc.) of luminous
(LIRGs) and ultraluminous infrared galaxies (ULIRGs) in the local
universe are well known because large samples of these objects have been
the subject of numerous spectroscopic works over the past three decades.
There are, however, relatively few studies of the spatially-resolved
spectroscopic properties of large samples of LIRGs and ULIRGs using
integral field spectroscopy (IFS). Aims: We are carrying out an
IFS survey of local (z<0.26) samples of LIRGs and ULIRGs to
characterize their two-dimensional spectroscopic properties. The main
goal of this paper is to study the spatially resolved properties of the
stellar populations and the excitation conditions in a sample of LIRGs.
Methods: We analyze optical (3800-7200 Å) IFS data taken
with the Potsdam Multi-Aperture Spectrophotometer (PMAS) of the central
few kiloparsecs of eleven LIRGs. To study these stellar populations, we
fit the optical stellar continuum and the hydrogen recombination lines
of selected regions in the galaxies. We analyzed the excitation
conditions of the gas using the spatially resolved properties of the
brightest optical emission lines. We complemented the PMAS observations
with existing HST/NICMOS near-infrared continuum and Paα imaging.
Results: The optical continua of selected regions in our LIRGs
are well fitted with a combination of an evolved (~0.7-10 Gyr) stellar
population with an ionizing stellar population (1-20 Myr). The latter
population is more obscured than the evolved population, and has visual
extinctions in good agreement with those obtained from the Balmer
decrement. Except for NGC 7771, we find no clear that there is an
important contribution to the optical light from an intermediate-aged
stellar population (~100-500 Myr). Even after correcting for the
presence of stellar absorption, a large number of spaxels with low
observed equivalent widths of Hα in emission still show enhanced
[N ii]λ6584/Hα and [S ii]λλ6717,
6731/Hα ratios. These ratios are likely to be produced by a
combination of photoionization in H ii regions and diffuse emission.
These regions of enhanced line ratios are generally coincident with low
surface-brightness H ii regions and diffuse emission detected in the
Hα and Paα images. We used the PMAS spatially resolved line
ratios and the NICMOS Paα photometry of H ii regions to derive the
fraction of diffuse emission in LIRGs. We find that this fraction varies
from galaxy to galaxy, and it is generally less than 60%, as found in
other starburst galaxies.
Based on observations collected at the German-Spanish Astronomical
Center, Calar Alto, jointly operated by the Max-Planck-Institut für
Astronomie Heidelberg and the Instituto de Astrofísica de
Andalucía (CSIC).Figures 1b-1j and 2b-2j are only available in
electronic form at http://www.aanda.org