Galactic cirri in deep optical imaging

Abstract

The ubiquitous presence of Galactic cirri in deep optical images represents a major obstacle to study the low surface brightness features of extragalactic sources. To address this issue, we have explored the optical properties of cirri using g, r, i, and z bands in the Sloan Digital Sky Survey (SDSS) Stripe82 region. Using state-of-the-art, custom made, image processing techniques, including the modeling and removal of the instrumental scattered light produced by the stars, we managed to isolate the optical diffuse emission by the cirri, allowing their photometric characterization. We find that their optical colors are driven by the dust column density: The cirri become redder as their 100 μm emission increases. Remarkably, the optical colors of the Galactic cirri differ significantly from those of extragalactic sources, with a characteristic bluer r-i color for a given g-r, allowing one to detect these by using a simple color relation. Our results show the high potential of deep multi-band optical photometry, on its own, identifying the presence of cirri at a higher spatial resolution than those provided by far-infrared observations. The combination of very deep data and multi-band photometry (as the one produced by LSST and Euclid) would make it possible to build dust maps of unprecedented quality.

Discovery and analysis of low-surface-brightness galaxies in the environment of NGC 1052

“…The depth of the data in the environment of NGC 1052 is remarkable, however we found that it is not homogeneous, varying from 29.2 to 29.9 mag arcsec −2 in the g band, from 28.7 to 29.1 mag arcsec −2 in the r band, and from 27.5 to 27.6 mag arcsec −2 in the z band, all measured as 3σ in 10×10 arcsec boxes following the depth definition by Román et al (2020), Appendix A. This range in depth is from approximately 0.5 to 1 mag arcsec −2 deeper than the typical depth of the DECaLS data in other regions (see Martinez-Delgado et al 2021b).…”

“…Given the large radius expected for the LSBGs in our sample, there is a wide margin to carry out this loss-of-resolution process by rebinning the pixel scale. This method of enhancing the diffuse emission by averaging small spatial scales has been used in previous works with good results (Zaritsky et al 2019;Román et al 2020). The operation of this pipeline is the following: We create a deep g + r image that is going to be used as a detection image.…”

A photometric and kinematic analysis of UDG1137+16 (dw1137+16): Probing ultradiffuse galaxy formation in a group environment

“…The co-addition of frames was performed using a pipeline with a resistant median-based combination algorithm, efficiently rejecting satellite tails, cosmic rays and other artefacts. The depth of the final coadded image is 28.4 mag arcsec −2 (3 sigma in a 10x10 box) following the definition provided in appendix A of Román et al (2020).…”

A feather on the hat: tracing the giant stellar stream around the Sombrero galaxy

“…For this, we carried out specific observations of bright stars to produce a high signal-to-noise large-radius point spread function (PSF) model. We follow a processing similar to that carried out by Román et al (2020) and Infante-Sainz, Trujillo & Román (2020). Given the excellent circular symmetry of the PSF of this telescope, we constructed a PSF model averaging the flux in the azimuthal direction, hence maximizing the signal-to-noise of the model.…”

“…Given the excellent circular symmetry of the PSF of this telescope, we constructed a PSF model averaging the flux in the azimuthal direction, hence maximizing the signal-to-noise of the model. Finally we run the scattered-light modelling pipeline developed by Román et al (2020) producing the model of the light scattered by the stars in the field (see Fig. 4).…”