The influence of diffuse scattered light

Abstract

All telescopes and instruments are to some degree affected by scattered light. It is possible to estimate the amount of such scattered light, and even correct for it, with a radially extended point spread function (PSF). The outer parts of the PSF have only rarely been determined, since they are faint and therefore difficult to measure. A mostly complete overview of existing properties and measurements of radially extended PSFs is presented, to both show their similarities and to indicate how bright extended objects can be used to measure the faintest regions. The importance of the far wings of the PSF and their possible temporal variations are demonstrated in three edge-on galaxy models. The same study is applied to the first edge-on galaxy where earlier observations reveal a halo, NGC 5907. All PSFs were collected in two diagrams, after they were offset or normalized, when that was possible. Surfacebrightness structures of edge-on galaxies were modelled and analysed to study scattered-light haloes that result when there is an exponential disc. The models were convolved with both a lower-limit PSF and a more average PSF. The PSF of the observed data could be used in the case of NGC 5907. The comparison of the PSFs demonstrates a lower-limit r −2 power-law decline at larger radii. The analysis of the galaxy models shows that the outer parts of the PSF also are important to correctly model and analyse observations and, in particular, fainter regions. The reassessed analysis of the earlier measurements of NGC 5907 reveals an explanation for the faint halo in scattered light, within the quoted level of accuracy.

HERschelObservations of Edge-on Spirals (HEROES)

“…We note that we use the same geometrical parameters at all wavelengths for the dust disc and that only the luminosities of the bulge and the stellar discs are determined individually at each wavelength. This simulates the wavelengthdependent behaviour of their luminosity ratios (De Geyter et al 2013, 2014. We also note that, at this stage, we do not make any assumptions about the characteristics of the stellar populations.…”

“…4.1 to describe the stellar components of the galaxy, plus a dust disc represented by the doubleexponential disc (see e.g. Xilouris et al 1999;Baes et al 2010;Verstappen et al 2013;De Geyter et al 2013, 2014:…”

“…Among the other reasons could be the emission of obscured star-forming regions deeply embedded in dense dust clouds which do not contribute notably to the observed UV flux, but have a clear impact on the FIR emission (see e.g. De Looze et al 2012, 2014De Geyter et al 2015).…”

The IAC Stripe 82 Legacy Project: a wide-area survey for faint surface brightness astronomy

“…Zibetti et al 2004;Sandin 2014;Trujillo & Fliri 2015). To estimate this effect in the Stripe 82 data, we provide ultra-deep PSFs reaching out to 8 arcmin in radius and extending over 20 mag in dynamical range.…”

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.…”