The influence of diffuse scattered light

Abstract

Studies of deep photometry of galaxies have presented discoveries of excess light in surface-brightness and colour profiles at large radii in the form of diffuse faint haloes and thick discs. In a majority of the cases, it has seemed necessary to use exotic stellar populations or alternative physical solutions to explain the excess. Few studies have carefully scrutinized the role of scattered light in this context. I explore the influence of scattered light on ground-based observations of haloes and thick discs around edge-on galaxies, haloes around face-on disc galaxies, host galaxies around blue compact galaxies (BCGs), and haloes around elliptical galaxies. Surfacebrightness structures of all considered types of galaxies are modelled and analysed to compare scattered-light haloes and thick discs with measurements. I simulate the influence of scattered light and accurate sky subtraction on simplified Sérsic-type and face-on disc galaxy models. All galaxy models are convolved with both lower-limit and brighter point spread functions (PSFs); for a few galaxies it was possible to use dedicated PSFs. The results show bright scattered-light haloes and high amounts of red excess at large radii and faint surface brightnesses for nearly all types of galaxies; exceptions are the largest elliptical-type galaxies where the influence of scattered light is smaller. Studies have underestimated the role of scattered light to explain their surface-brightness profiles. My analysis shows surface-brightness profiles that include scattered light that are very similar to and overlap measurements at all radii. The derivation of physical properties of haloes, thick discs, and BCG hosts from diffuse data is misleading since accurate and radially extended PSFs are non-existent. Significantly improved analyses that include new measurements of PSFs are required to study diffuse faint structures further.

Ultraviolet Halos Around Spiral Galaxies. I. Morphology

“…This helps to exclude stars that are close to the galaxy but are not formally detected at different wavelengths or in shorter observations. Sandin (2015) showed that the diffuse light around edge-on galaxies consists in part of light from the galaxy image scattered into the wings of the PSF (the Airy pattern), since the sum of many overlapping Airy patterns leads to a diffuse glow around the galaxy. To measure and subtract this component, a PSF must be measured to at least twice the angular size of the galaxy.…”

“…This conclusion was rehodgeskl@umich.edu 1 Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 inforced by Hutton et al (2014), and Seon et al (2014) detected a UV halo around NGC 891 that they argue is also an eRN. In Hodges- Kluck & Bregman (2014, hereafter, HKB14) we reported that UV halos are ubiquitous around highly inclined galaxies, but Sandin (2015) pointed out that the light scattered into the wings of the point-spread function (PSF) can masquerade as a physical halo. Shinn & Seon (2015) modeled several of the galaxies in HKB14 including this effect, and found that some of the UV halos we had reported are astrophysical while others are artificial.…”

Extragalactic archeology with the GHOSTS Survey

“…A faint second component can now be detected in IC 5052 and NGC 4244. Since we used star count data, this second component cannot be an effect of scattered light and extended PSFs, which might lead to similar detection in integrated light studies, if not modeled carefully (de Jong 2008;Sandin 2014Sandin , 2015. We fit the whole profile with two sech 2 components.…”

A deconvolution technique to correct deep images of galaxies from instrumental scattered light

“…Instrumental contamination affects all A&A 601, A86 (2017) fields; some can be addressed by advanced flat-fielding procedures and sky subtraction; others, like reflections within the camera, which produce artificial halos and ghosts, are much more complex to model and remove (Slater et al 2009;Duc et al 2015). The importance of correcting for light scattering is well documented (Michard 2002;Slater et al 2009;Sandin 2015;Trujillo & Fliri 2016) but the correction process is challenging. In particular, it requires the availability of point spread functions (PSFs) measured up to large radius at the location of the target on the detector.…”

“…The scattering in classical cameras may be reduced with an anti-reflective coating on the detector and on the optical elements (Mihos et al 2005) or largely eliminated by alternative imaging systems, such as photo-lens array . Sandin (2014Sandin ( , 2015 investigate the impact of ghost halos on galaxy profiles by convolving galaxy models with PSFs that correspond to a variety of instruments. He quantifies the importance of scattering as a function of radius for various morphological types.…”