Measuring SEDs for individual galaxy components

Abstract

Abstract. Our project, 'MegaMorph', is developing a next-generation tool for decomposing galaxies, in terms of both their structures and stellar populations. By combining data from UV to NIR wavelengths, accounting for morphological peculiarities using non-parametric components, and utilising efficient likelihood sampling methods, we are working to significantly improve the robustness and accuracy of galaxy decomposition. Applying these new techniques to modern large surveys will provide us with a deeper understanding of galaxies.Keywords. galaxies: fundamental parameters, galaxies: structure, galaxies: photometry, methods: data analysis, techniques: image processing Galaxy componentsGalaxies comprise a complex mix of stars, gas, dust and dark matter, with their proportions, distributions and kinematics resulting from a wide variety of physical processes. Even considering just the stars, galaxies typically possess distinct stellar populations, which formed at different times, under varied conditions. To gain more than a superficial understanding of the galaxy population, and the processes that shape it, we need to disentangle these physical components within individual galaxies.This conference primarily focused on separating and characterising galaxy components through their spectral energy distributions. These SEDs are usually, with a few notable exceptions, integrated over the spatial extent of each galaxy. For separating components which dominate at different wavelength ranges, e.g., stars and dust, this approach works well. However, when dividing components with only subtle differences in their SEDs, e.g., multiple stellar populations, any additional discriminatory information is valuable.The various stellar populations within a galaxy often have contrasting spatial distributions. In our simplest models, a galaxy grows through two principal mechanisms: the gradual accretion of gas, which cools and forms a thin disk of stars; and the merging of existing stellar systems, which produces a spheroid. These two structural components thus form through disparate mechanisms, contain different stellar populations, and represent disjoint periods in a galaxy's history (e.g., Cole et al. 2000;Cook et al. 2009;Benson 2010). Using information regarding both the spatial distributions and SEDs of these components will clearly enable a more robust separation of their properties, when compared with trying to use just one of these pieces of information alone. The dichotomy between disk and spheroid stellar components (e.g., Allen et al. 2006;Benson & Devereux 2010) is at the heart of our understanding of galaxy development: measuring their individual properties will provide a deeper understanding of the galaxy population and more effective comparison with theoretical models.

Galaxy And Mass Assembly (GAMA): the wavelength dependence of galaxy structure versus redshift and luminosity

“…In this paper we have followed V14, using optical-NIR imaging and redshifts from the GAMA survey (Driver et al 2009), with multi-band single-Sérsic fits performed using tools developed by the MegaMorph project (Bamford et al 2012), in order to study four further aspects of the wavelength-dependence of galaxy structure. We consider the distributions of N and R for a variety of volume-limited samples subdivided by u − r colour, Sérsic index and morphology.…”

“…Furthermore, even in high-quality data, utilising available colour information can improve the performance of decompositions. To address these issues, the MegaMorph project (Bamford et al 2012) has developed a technique which fits a single, wavelength-dependent model simultaneously to a set of imaging in different filter-bands. These developments have been implemented in an extended version of galfit (Peng et al 2002(Peng et al , 2010 named galfitm (Häußler et al 2013, hereafter H13;Vika et al 2013Vika et al , 2014.…”

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

“…In this paper we build upon the work of La Barbera et al (2010b) and Kelvin et al (2012), by fitting a single, wavelengthdependent model to all the data simultaneously. This is made possible using an extended version of galfit (Peng et al 2002(Peng et al , 2010 developed by the MegaMorph project (Bamford et al 2012, hereafter H13, Vika et al 2013. This approach maximises the signal-to-noise available to constrain the model and ensures that the parameters are optimal for the whole dataset.…”

MegaMorph: classifying galaxy morphology using multi-wavelength Sérsic profile fits

“…We have recently developed and demonstrated a technique for fitting wavelength-dependent Sérsic models to galaxy surface-brightness profiles in a simultaneous and consistent manner (Bamford et al 2012;Häussler et al 2013;Vika et al 2013, hereafter V13). This technique provides measurements of the wavelength variation of Sérsic index (i.e.…”