Galaxy And Mass Assembly (GAMA): the wavelength-dependent sizes and profiles of galaxies revealed by MegaMorph

Abstract

We investigate the relationship between colour and structure within galaxies using a large, volume-limited sample of bright, low-redshift galaxies with optical-near-infrared imaging from the GAMA survey. We fit single-component, wavelength-dependent, elliptical Sérsic models to all passbands simultaneously, using software developed by the MegaMorph project. Dividing our sample by n and colour, the recovered wavelength variations in effective radius (R e ) and Sérsic index (n) reveal the internal structure, and hence formation history, of different types of galaxies. All these trends depend on n; some have an additional dependence on galaxy colour. Late-type galaxies (n r < 2.5) show a dramatic increase in Sérsic index with wavelength. This might be a result of their two-component (bulge-disk) nature, though stellar population gradients within each component and dust attenuation are likely to play a role. All galaxies show a substantial decrease in R e with wavelength. This is strongest for early-types (n r > 2.5), even though they maintain constant n with wavelength, revealing that ellipticals are a superimposition of different stellar populations associated with multiple collapse and merging events. Processes leading to structures with larger R e must be associated with lower metallicity or younger stellar populations. This appears to rule out the formation of young cores through dissipative gas accretion as an important mechanism in the recent lives of luminous elliptical galaxies.

Sizes, colour gradients and resolved stellar mass distributions for the massive cluster galaxies in XMMUJ2235-2557 atz= 1.39

“…This wavelength dependence of sizes (or the size-wavelength relation) has been quantified for local passive galaxies in a number of studies (e.g. Barden et al 2005;Hyde & Bernardi 2009;La Barbera et al 2010b;Kelvin et al 2012;Vulcani et al 2014;Kennedy et al 2015). The dependence shown by the above mentioned studies is quite strong, in the sense that galaxy sizes can decrease up to ∼ 38% from g through K band in the GAMA sample (Kelvin et al 2012), or ∼ 32% across the same range in SPIDER (La Barbera et al 2010b).…”

“…Saglia et al 2000;La Barbera et al 2005;Tortora et al 2010), although also affected by age and dust (see, e.g. Vulcani et al 2014). Measuring the colour gradients at high redshift is more challenging due to compact galaxy sizes and limitations on instrumental angular resolution.…”

MegaMorph – multiwavelength measurement of galaxy structure: physically meaningful bulge–disc decomposition of galaxies near and far

“…Furthermore, h is often corrected for inclination-dependent projection and extinction effects, which complicates comparisons. Finally, given the strong wavelength dependence of galaxy effective radius found by Vulcani et al (2014), measurements at optical versus near-infrared wavelengths may be expected to differ significantly, even when an average extinction correction is applied. Nevertheless, we attempt an approximate comparison.…”

“…In Häußler et al (2013) we demonstrate our approach on a large dataset from the GAMA Hill et al 2010) survey, automating both the preparation of the data and the fitting process itself. The resulting measurements -in particular the variation of structural parameters with wavelength -are studied further in Vulcani et al (2014). The objective of the present paper, is to investigate the ability of GALFITM to perform bulge-disc decomposition on galaxy images with a wide range of resolution and signal-to-noise.…”

Predicting the stellar and non-equilibrium dust emission spectra of high-resolution simulated galaxies with dart-ray

“…By using this approach on a set of edge-on galaxies, those authors derived the large scale parameters of the galaxy stellar and dust distributions, such as their scale length/height and the total values for the intrinsic stellar luminosity, dust mass and optical depth. This method has been also generalised for application to statistical samples of any orientation and bulge-to-disk ratio (spiral morphology) by Tuffs et al (2004), and Popescu et al (2011) and has been successfully applied to predict the statistical behaviour of various observables in Driver et al (2007), (2008), (2012), Graham & Worley (2008), Masters et al (2010), Gunawardhana et al (2011), Kelvin et al (2012), (2014), Grootes et al (2013Grootes et al ( , 2014, Pastrav et al (2013a,b) and Vulcani et al (2014). Recently, De Looze et al (2014) extended the applicability of the "decoding technique" to the modelling of a resolved nearby face-on galaxy.…”