Surface photometry of galaxies in low density regions

Abstract

Abstract. -We perform detailed surface photometry, based on B-and/or R-band CCD images of 92 faint galaxies. They are a subsample of those galaxies which were studied by Hopp et al. (1994) in the direction of three nearby voids. We derive integral photometric parameters and radial surface brightness profiles and compare them to those of several faint galaxy samples, located in different environments, and of a bright field galaxy sample. According to the obtained photometric characteristics, our sample is a mixture of intrinsically bright and faint galaxies, about 60% of them belonging to the bright subsample (MB −19.0). These bright ones show mean characteristics of typical Freeman's disks and are mainly located in the background of the observed voids. The faint subsample (MB ≥ −19.0) has parameters typical for the low-surface-brightness (LSB) galaxies. There are a few well isolated galaxies both among the bright and faint subsamples. About 40% of studied galaxies reveal ellipticity and position angle variations along of the radius. The (B − R) colour indices of the observed galaxies span over a wide range of 0.5−1.8 mag with a median value at 1.11 mag, rather blue. About 30% of the observed galaxies reveal radial colour gradients at a 5σ significance level. These galaxies show typically red centers and are getting bluer towards the periphery. The most isolated galaxies in our sample show relatively blue colours (BT − RT 0.8). About 40% of the studied galaxies have surface brightness profiles which can be described by the model of single exponential disk. 38% of our galaxies have more complicated profiles and either can be approximated by two exponentials or show the presence of a small bulge. 20% of the observed galaxies have central light depression and outer irregularities -typical for some dwarf galaxies. These profile type frequencies are similar to those of faint field galaxy sample. The evolutionary history of both the isolated and clustered galaxies obviously results in similar photometric and structural characteristics. Thus the photometric methods alone are inadequate for selecting galaxies with different isolation properties.

Surface photometry of emission-line galaxies in low density regions

“…The filter strength, defined by the minimum signal to noise ratio for the detection of a local signal, was generally between 2.0 − 2.5 σ, where σ is the rms noise level of the sky background at each scale length. After the filtering, a careful sky background level determination and subtraction was performed on the smoothed frame, as described in more detail in Vennik et al (1996). After the background subtraction the galaxy image was extracted from the large CCD frame and interactively cleaned from disturbing objects like e.g.…”

“…As a result, a sample of galaxies of late morphological type and of low surface brightness was identified, with several very isolated galaxies and galaxies populating the rims of the voids. Vennik et al (1996) performed B and R surface photometry of a subsample of these galaxies and concluded that both isolated and non-isolated galaxies show similar photometric and structural characteristics.…”

Studies of galaxies in voids

“…In the Hopp et al sample in the direction of voids only nine dwarf galaxies are located fully within voids (three objects), or in some intermediate regions near the void boundaries (six galaxies). These galaxies were observed in the H i 21 cm line by Huchtmeier et al (1997) (hereafter HHK) and their morphology and colors were studied by Vennik et al (1996). In the sample of Popescu et al there were also 17 void BCGs (eight fully located in voids), but these were not observed in H i.…”

A Concise Reference to (Projected) Sérsic R1/n Quantities, Including Concentration, Profile Slopes, Petrosian Indices, and Kron Magnitudes

“…Early papers include Andredakis, Peletier, & Balcells (1995), Schwarzkopf & Dettmar (1997), Seigar & James (1998), Iodice, D'Onofrio, & Capaccioli (1997, Khosroshahi, Wadadekar, & Kembhavi (2000), D'Onofrio (2001), Graham (2001a), Möllenhoff & Heidt (2001), and Prieto et al (2001). In either case, since the work of Capaccioli in the late 1980s and in particular Caon, Capaccioli, & D'Onofrio (1993) and D'Onofrio, , the past decade has seen an explosion in the application of the R 1/n model (e.g., Cellone, Forte, & Geisler 1994;Vennik & Richter 1994;Young & Currie 1994Graham et al 1996;Karachentseva 1996;Vennik et al 1996, to mention just a few early papers), yet no single resource exists for the expressions and quantities pertaining to the R 1/n model. Moreover, no one reference provides more than a few of the relevant equations, and many textbooks still only refer to the R 1/4 model.…”