Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The SWELLS Survey. VI. hierarchical inference of the initial mass
  functions of bulges and discs   The long-standing assumption that the stellar initial mass function (IMF) is
universal has recently been challenged by a number of observations. Several
studies have shown that a "heavy" IMF (e.g., with a Salpeter-like abundance of
low mass stars and thus normalisation) is preferred for massive early-type
galaxies, while this IMF is inconsistent with the properties of less massive,
later-type galaxies. These discoveries motivate the hypothesis that the IMF may
vary (possibly very slightly) across galaxies and across components of
individual galaxies (e.g. bulges vs discs). In this paper we use a sample of 19
late-type strong gravitational lenses from the SWELLS survey to investigate the
IMFs of the bulges and discs in late-type galaxies. We perform a joint analysis
of the galaxies' total masses (constrained by strong gravitational lensing) and
stellar masses (constrained by optical and near-infrared colours in the context
of a stellar population synthesis [SPS] model, up to an IMF normalisation
parameter). Using minimal assumptions apart from the physical constraint that
the total stellar mass within any aperture must be less than the total mass
within the aperture, we find that the bulges of the galaxies cannot have IMFs
heavier (i.e. implying high mass per unit luminosity) than Salpeter, while the
disc IMFs are not well constrained by this data set. We also discuss the
necessity for hierarchical modelling when combining incomplete information
about multiple astronomical objects. This modelling approach allows us to place
upper limits on the size of any departures from universality. More data,
including spatially resolved kinematics (as in paper V) and stellar population
diagnostics over a range of bulge and disc masses, are needed to robustly
quantify how the IMF varies within galaxies.

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The categories of this paper are: math-ph
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The categories of this paper are: q-fin
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The categories of this paper are: plasm-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: gr-qc
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The categories of this paper are: q-alg
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The categories of this paper are: cond-mat
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The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
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The categories of this paper are: quant-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: math