Stellar systems in the direction of Pegasus I - I. Low surface brightness galaxies

GONZALEZ, N. M.; SMITH CASTELLI, A. V.; FAIFER, F. R.; ESCUDERO, C. G.; CELLONE, S. A.

ASTRONOMY & ASTROPHYSICS. SUPPLEMENT SERIES (PRINT)

EDP Sciences

Lugar: Paris; Año: 2018 vol. 620

0365-0138

To enlarge the sample of known low-surface brightness (LSB) galaxies andto try to provide clues about their nature, we report the detection ofeight of this type of objects ($mu_{{eff}, g´} simeq 27$ magarcsec$^{-2}$) towards the group of galaxies Pegasus I. They are locatedin the very center of Pegasus I, close to the dominant ellipticalgalaxies NGC7619 and NGC7626. Assuming that these galaxies are at thedistance of Pegasus I, we have found that their sizes are intermediateamong similar objects reported in the literature. In particular, wefound that three of these galaxies can be classified as ultra-diffusegalaxies and a fourth one displays a nucleus. The eight new LSB galaxiesshow a significant color dispersion around the extrapolation towardsfaint luminosities of the color-magnitude relation defined by typicalearly-type galaxies. In addition, they display values of the S´ersicindex below 1, in agreement with values obtained for LSB galaxies inother environments. We also show that there seems to be a bias effect inthe size distributions of the detected LSBs in different environments,in the sense that more distant groups/clusters lack small $r_{eff}$objects, while large systems are not found in the Local Group and nearbyenvironments. While there may be an actual shortage of large LSBgalaxies in low-density environments like the Local Group, thenon-detection of small (and faint) systems at large distances is clearlya selection effect. As an example, LSB galaxies with similar sizes tothose of the satellites of Andromeda in the Local Group, will becertainly missed in a visual identification at the distance of PegasusI.