Bibcode
Peletier, Reynier F.; Kutdemir, Elif; van der Wolk, Guido; Falcón-Barroso, J.; Bacon, Roland; Bureau, Martin; Cappellari, Michele; Davies, Roger L.; de Zeeuw, P. Tim; Emsellem, Eric; Krajnović, Davor; Kuntschner, Harald; McDermid, Richard M.; Sarzi, Marc; Scott, Nicholas; Shapiro, Kristen L.; van den Bosch, Remco C. E.; van de Ven, Glenn
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 419, Issue 3, pp. 2031-2053.
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1
2012
Número de citas
27
Número de citas referidas
26
Descripción
We investigate the [3.6]-[4.5] Spitzer-IRAC colour behaviour of the
early-type galaxies of the SAURON survey, a representative sample of 48
nearby ellipticals and lenticulars. We investigate how this colour,
which is unaffected by dust extinction, can be used to constrain the
stellar populations in these galaxies.
We find a tight relation between the [3.6]-[4.5] colour and effective
velocity dispersion, a good mass indicator in early-type galaxies:
([3.6]-[4.5])e = (-0.109 ? 0.007)?+ (0.154 ? 0.016). Contrary
to other colours in the optical and near-infrared, we find that the
colours become bluer for larger galaxies. The relations are tighter when
using the colour inside re (scatter 0.013 mag), rather than
the much smaller re/8 aperture (scatter 0.023 mag), due to
the presence of young populations in the central regions. We also obtain
strong correlations between the [3.6]-[4.5] colour and three strong
absorption lines (H?, Mgb and Fe 5015). Comparing our data with the
models of Marigo et al., which show that more metal rich galaxies are
bluer, we can explain our results in a way consistent with results from
the optical, by stating that larger galaxies are more metal rich. The
blueing is caused by a strong CO absorption band, whose line strength
increases strongly with decreasing temperature and which covers a
considerable fraction of the 4.5-?m filter. In galaxies that contain a
compact radio source, the [3.6]-[4.5] colour is generally slightly
redder (by 0.015 ? 0.007 mag using the re/8 aperture) than in
the other galaxies, indicating small amounts of either hot dust,
non-thermal emission, or young stars near the centre.
We find that the large majority of the galaxies show redder colours with
increasing radius. Removing the regions with evidence for young stellar
populations (from the H? absorption line) and interpreting the colour
gradients as metallicity gradients, we find that our galaxies are more
metal poor going outwards. The radial [3.6]-[4.5] gradients correlate
very well with the metallicity gradients derived from optical line
indices. We do not find any correlation between the gradients and galaxy
mass; at every mass, galaxies display a real range in metallicity
gradients.
Consistent with our previous work on line indices, we find a tight
relation between local [3.6]-[4.5] colour and local escape velocity. The
small scatter from galaxy to galaxy, although not negligible, shows that
the amount and distribution of the dark matter relative to the visible
light cannot be too different from galaxy to galaxy. Due to the lower
sensitivity of the [3.6]-[4.5] colour to young stellar populations, this
relation is more useful to infer the galaxy potential than the
Mgb-vesc relation.
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