Bibcode
Jeong, Hyunjin; Yi, Sukyoung K.; Bureau, Martin; Davies, Roger L.; Bacon, Roland; Cappellari, Michele; de Zeeuw, P. Tim; Emsellem, Eric; Falcón-Barroso, J.; Krajnović, Davor; Kuntschner, Harald; McDermid, Richard M.; Peletier, Reynier F.; Sarzi, Marc; van den Bosch, Remco C. E.; van de Ven, Glenn
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 423, Issue 2, pp. 1921-1939.
Advertised on:
6
2012
Número de citas
12
Número de citas referidas
11
Descripción
The unexpected rising flux of early-type galaxies at decreasing
ultraviolet (UV) wavelengths is a long-standing mystery. One important
observational constraint is the correlation between UV-optical colours
and Mg2 line strengths found by Burstein et al. The simplest
interpretation of this phenomenon is that the UV strength is related to
the Mg line strength. Under this assumption, we expect galaxies with
larger Mg gradients to have larger UV colour gradients. By combining UV
imaging from GALEX, optical imaging from MDM and SAURON integral-field
spectroscopy, we investigate the spatially resolved relationships
between UV colours and stellar population properties of 34 early-type
galaxies from the SAURON survey sample. We find that galaxies with old
stellar populations show tight correlations between the far-UV (FUV)
colours (FUV -V and FUV - NUV) and the Mg b index, Hβ index and
metallicity [Z/H]. The equivalent correlations for the Fe5015 index,
α-enhancement [α/Fe] and age are present but weaker. We have
also derived logarithmic internal radial colour, measured line strength
and derived stellar population gradients for each galaxy and again found
a strong dependence of the FUV -V and FUV - NUV colour gradients on both
the Mg b line strength and the metallicity gradients for galaxies with
old stellar populations. In particular, global gradients of Mg b and
[Z/H] with respect to the UV colour [e.g. Δ(Mg b)/Δ(FUV -
NUV) and Δ[Z/H]/Δ(FUV - NUV)] across galaxies are consistent
with their local gradients within galaxies, suggesting that the global
correlations also hold locally. From a simple model based on multiband
colour fits of UV upturn and UV-weak galaxies, we have identified a
plausible range of parameters that reproduces the observed radial colour
profiles. In these models, the centres of elliptical galaxies, where the
UV flux is strong, are enhanced in metals by roughly 60 per cent
compared to UV-weak regions.
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