Discovery of a Low-surface-brightness Galaxy in the NGC 2655 Field

We report the discovery of a low surface brightness galaxy (LSB Galaxy) candidate at (α, δ) = (8^h50^m233,78°28'580) (J2000) with projected separation 22'144 from NGC 2655. In addition to evidence and confirmation of its detection, we explore data via The Guide Star Catalog, Version 2.3.2 (Lasker et al. 2008) in support of its apparent presentation.

The LSB Galaxy was first identified in our 14h full-color integration of a field within the NGC 2655 Group (Tully 1988) as acquired from 203 mm Newtonian optics at f/3.9 between 2016 October 23 and 2017 March 02. As depicted in Figure 1, both a compressed linear representation and nonlinear process of the luminance component (23 × 1200 s) reveal an object with diffuse morphology centered at (α, δ) = (8^h50^m233,78°28'580) (J2000) with peak signal at (α, δ) = (8^h50^m259,78°28'518) (J2000). In support of this observation and with analog-digital-units (ADU) in the range [0, 1], we establish Gaussian noise of the source data at σ_k = 3.15e−4 ADU and a mean background reference level of 3.04e−3 ADU. A 7 × 7 pixel (968 × 968) sample at the center of the LSB Galaxy produces a mean signal level of 4.62e−3 ADU, more than 5σ_k greater than the background level. Further, a single-pixel (138 × 138) sample at the peak region is found at 6.64e−3 ADU, more than 6σ_k greater than that of the center of the LSB Galaxy. While this peak signal is later corroborated in our review of data in The Guide Star Catalog, Version 2.3.2 (Lasker et al. 2008), its relationship to the diffuse area is considered here in apparent presentation only.

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Presentation of the LSB Galaxy is confirmed in two additional data sets. Our confirmation luminance integration (6 × 600 s) was acquired with 0.3 m Ritchey-Chrétien optics at f/8 on 2017 March 16, where a nonlinear process reveals the LSB Galaxy (Figure 1). The Pan-STARRS1 Surveys (Chambers et al. 2016) were analyzed for additional confirmation. A FITS-cutout¹ was obtained from the Pan-STARRS1 database (Flewelling et al. 2016) as imaged with the i_PS1 filter with mean wavelength 7545 Å (Tonry et al. 2012). A nonlinear process of this data again reveals the LSB Galaxy with comparative presentation.

The apparent size of the LSB Galaxy is conservatively estimated from the source data at 249 × 277 by identifying right ascension and declination boundaries for which a 5-pixel mean ADU exceeds the background level by 3σ_k. We calculate a projected separation between the LSB Galaxy and NGC 2655 of 22'144, where NGC 2655 is found at (α, δ) = (8^h55^m37731,78°13'2310) (J2000) (Skrutskie et al. 2006). As interactions of NGC 2655 with other galaxies have been identified by Sparke et al. (2008), the LSB Galaxy's proximity to NGC 2655 is of possible related interest.

In consideration of the LSB Galaxy's presentation with a diffuse body and concentrated peak region, we identify three records in The Guide Star Catalog, Version 2.3.2 (Lasker et al. 2008) across the LSB Galaxy (Figure 1), each of which reports magnitude data in the POSS-II IIIaJ+GG385 (B_j) photographic band (Reid et al. 1991). Object N7B0004771² presides near the peak of the LSB Galaxy at 21.44 mag B_j. Object N7B0004791³ is identified near the center of the LSB Galaxy at 21.89 mag B_j. Object N7B0004813⁴ is found opposte the peak signal at 22.11 mag B_j. These data support the source analysis that the LSB Galaxy presents with peak signal near (α, δ) = (8^h50^m259,78°28'518) (J2000).

We extend our gratitude to Roy Gal (University of Hawai'i), Stacy McGaugh (Case Western Reserve University), Thorsten Zilch (Tief Belichtete Galaxien Group) and Peter Riepe (Tief Belichtete Project Group) for their review and consideration of our data.

Software: Aladin (Bonnarel et al. 2000), Astropy (Astropy Collaboration et al. 2013), VizieR Catalog Access Tool (Ochsenbein et al. 2000).