We present a description of the Dragonfly Wide Field Survey (DWFS), a deep photometric survey of a wide area of sky. The DWFS covers 330 deg2 in the equatorial GAMA fields and the Stripe 82 fields in the SDSS g and r bands. It is carried out with the 48-lens Dragonfly Telephoto Array, a telescope that is optimized for the detection of low surface brightness emission. The main goal of the survey is to study the dwarf galaxy population beyond the Local Group. In this paper, we describe the survey design and show early results. We reach 1σ depths of μ g  ≈ 31 mag arcsec−2 on arcminute scales and show that Milky Way satellites such as Sextans, Bootes, and Ursa Major should be detectable out to D ≳ 10 Mpc. We also provide an overview of the elements and operation of the 48-lens Dragonfly telescope and a detailed description of its data reduction pipeline. The pipeline is fully automated, with individual frames subjected to a rigorous series of quality tests. The sky subtraction is performed in two stages, ensuring that emission features with spatial scales up to ∼0.°9 × 0.°6 are preserved. The DWFS provides unparalleled sensitivity to low surface brightness features on arcminute scales.

We present an extensive compendium of photometrically-determined structural properties for all CALIFA galaxies in the Third Data Release (DR3). We exploit Sloan Digital Sky Survey (SDSS) images in order to extract one-dimensional (1D) gri surface brightness profiles for all CALIFA DR3 galaxies. We also derive a variety of non-parametric quantities and parametric models fitted to 1D i-band profiles. The galaxy images are decomposed using the 2D bulge-disc decomposition programs imfit and galfit. The relative performance and merit of our 1D and 2D modelling approaches are assessed. Where possible, we compare and augment our photometry with existing measurements from the literature. Close agreement is generally found with the studies of Walcher et al. (2014) and Méndez-Abreu et al. (2017), though some significant differences exist. Various structural metrics are also highlighted on account of their tight dispersion against an independent variable, such as the circular velocity.

In 2008 it was reported that the stellar stream of the edge-on spiral NGC 5907 loops twice around the galaxy, enveloping it in a giant corkscrew-like structure. Here we present imaging of this iconic object with the Dragonfly Telephoto Array, reaching a 1σ surface brightness level of µ g = 30.3 mag arcsec −2 on spatial scales of 1 (the approximate width of the stream). We find a qualitatively different morphology from that reported in the 2008 study. The Dragonfly data do not show two loops but a single curved stream with a total length of 45 (220 kpc). The surface brightness of the stream ranges from µ g ≈ 27.6 mag arcsec −2 to µ g ≈ 28.8 mag arcsec −2 , and it extends significantly beyond the region where tidal features had previously been detected. We find a density enhancement near the luminosity-weighted midpoint of the stream which we identify as the likely remnant of a nearly-disrupted progenitor galaxy. A restricted N-body simulation provides a qualitative match to the detected features. In terms of its spatial extent and stellar mass the stream is similar to Sagittarius, and our results demonstrate the efficacy of low surface brightness-optimized telescopes for obtaining maps of such large streams outside the Local Group. The census of these rare, relatively high mass events complements the census of common, low mass ones that is provided by studies of streams in the Milky Way halo.

Uncertainty in the wide-angle point-spread function (PSF) at large angles (tens of arcseconds and beyond) is one of the dominant sources of error in a number of important quantities in observational astronomy. Examples include the stellar mass and shape of galactic halos and the maximum extent of starlight in the disks of nearby galaxies. However, modeling the wide-angle PSF has long been a challenge in astronomical imaging. In this paper, we present a self-consistent method to model the wide-angle PSF in images. Scattered light from multiple bright stars is fitted simultaneously with a background model to characterize the extended wing of the PSF using a Bayesian framework operating on a pixel-by-pixel level. The method is demonstrated using our software elderflower and is applied to data from the Dragonfly Telephoto Array to model its PSF out to 20′–25′. We compare the wide-angle PSF of Dragonfly to that of a number of other telescopes, including the SDSS PSF and show that, on scales of arcminutes, the scattered light in the Dragonfly PSF is markedly lower than that of other wide-field imaging telescopes. The energy in the wings of the Dragonfly PSF is sufficiently low that optical cleanliness plays an important role in defining the PSF. This component of the PSF can be modeled accurately, highlighting the power of our self-contained approach.