2015MNRAS.452..597Z

Using the Oxford Short Wavelength Integral Field specTrograph, we investigate radial variations of several initial mass function (IMF) dependent absorption features in M31 and M32. We obtain high signal-to-noise spectra at six pointings along the major axis of M31 out to ∼ 700arcsec(2.7kpc) and a single pointing of the central 10pc for M32. In M31 the sodium Nai λ8190 index shows a flat equivalent width profile at ∼ 0.4Å through the majority of the bulge, with a strong gradient up to 0.8Å in the central 10arcsec(38pc); the Wing-Ford FeH λ9916 index is measured to be constant at 0.4Å for all radii; and calcium triplet CaT λλ8498, 8542, 8662 shows a gradual increase through the bulge towards the centre. M32 displays flat profiles for all three indices, with FeH at ∼ 0.5Å, very high CaT at ∼ 0.8Å and low Nai at ∼ 0.1Å. We analyse these data using stellar population models. We find that M31 is well described on all scales by a Chabrier IMF, with a gradient in sodium enhancement of [Na/Fe] ∼ +0.3dex in the outer bulge, rising within the central 10arcsec to perhaps [Na/Fe] ∼ +1.0dex in the nuclear region. We find M32 is described by a Chabrier IMF and young stellar age in line with other studies. Models show that CaT is much more sensitive to metallicity and [α/Fe] than to IMF. We note that the centres of M31 and M32 have very high stellar densities and yet we measure Chabrier IMFs in these regions.