1 Introduction

Most of the radio sources in the luminosity range $P_{408} \sim 10^{23}-10^{25}$ W Hz^-1 (H₀=75 km s^-1 Mpc^-1 and q₀=0 is assumed throughout the paper) and at low redshift are found in elliptical galaxies. These galaxies form the population referred to as "Low Luminosity Radio Galaxies'' (hereafter LLRGs), within the class of active galactic nuclei. LLRGs have lower radio luminosity than "Powerful Radio Galaxies'' (hereafter PRGs) - whose radio power is similar to that of radio quasars-, but larger radio luminosity than starburst galaxies. Optical studies of the elliptical hosts of LLRGs show that their photometric parameters resemble the class of brightest cluster members (hereafter BCMs), exhibiting similar absolute magnitudes in average, shallow light profiles, and presenting extended envelopes (cD type) for a significant fraction of sources (Lilly & Prestage [1987]; Owen & Laing [1989]; Smith & Heckman [1989a], [1989b]; González-Serrano et al. [1993]). Regarding the local environment, Heckman et al. ([1985]) and González-Serrano et al. ([1993]) found that LLRGs were located in higher density regions that radio quiet ellipticals, considering a radius of 133 kpc around the radio galaxy. Heckman et al. ([1985]) concluded from this result that galaxy interactions could foster the nuclear activity. Alternatively, Ledlow & Owen ([1995]) claimed from their study of LLRGs in Abell clusters that the radio detection rate was influenced by the optical properties, i.e. the optical luminosity, rather than the galaxy density around the radio galaxy (hereafter RG).

Quantitative analysis of the morphological structure of the galaxy isophotes, obtained from surface photometry, has revealed morphological peculiarities in LLRGs which are likely related to gravitational interaction and merging processes (Colina & Pérez-Fournon [1990]; González-Serrano et al. [1993]). These characteristics include strong isophote twisting, off-centering, excesses from a de Vaucouleurs light profile at large radii and the presence of features like shells, tails and bridges. This type of peculiarities had been previously observed in PRGs ( P>10²⁵-10^25.5 W Hz^-1, Heckman et al. [1986]; Smith & Heckman [1989b]), where they are generally more significant. PRGs differ from LLRGs in other respects. The former typically have an FR II (Fanaroff & Riley [1974]) radio morphology (whereas the latter are generally FR I), are located in poorer local environments, their Hubble type and surface brightness profiles are more diverse, and they have stronger emission lines and a larger fraction of systems showing dust patches (Heckman et al. [1986]). Heckman et al. ([1986]) argued that PRGs could originate from galaxy mergers involving at least a dynamically cold gas-rich system (a disk galaxy) whereas that LLRGs could be fueled by accretion of their own atmospheres or of an intracluster or intragroup gaseous medium. Smith & Heckman ([1989b]) suggested that mergers could be common to both classes, but that mergers for LLRGs would occur between ellipticals, and the lack of a cool interstellar medium would prevent the formation of the strong tidal perturbations shown in PRGs.

  

Table 1: Source list

 

Table 1: continued

González-Serrano et al. ([1993]) reported an exhaustive photometric study of a sample of 24 LLRGs from the B2 sample (Colla et al. [1975]; Fanti et al. [1978]), with the common characteristic of presenting a well-defined radio jet in Parma et al. ([1987]). Various general properties were established for this sample, like the shape of the light profiles, the absolute magnitudes, local environment, incidence of isophote peculiarities and fraction of systems undergoing gravitational interaction/merging. It was concluded that, at least among galaxies with radio jets, the local galaxy density and the interactions likely play an important role in the production of this type of radio sources. One question arising from this study was whether LLRGs with and without a well-defined jet have similar environments and optical properties. The answer will help to understand the origin of the different kinds of radio sources and the relation of radio morphology with the environment.

The present paper reports surface photometry for 72 B2 galaxies (including some spirals and irregulars), based on V-band CCD images, and complements our previous optical studies of B2 galaxies with well-defined radio jets. The following results are presented: (i) V-band contour plots of the galaxies and qualitative morphological classification, (ii) surface brightness profiles of the elliptical galaxies and de Vaucouleurs fits, obtaining the parameters $\mu_{\rm e}$ and $r_{\rm e}$, (iii) profiles of the isophote parameters ellipticity, position angle and B₄, and (iv) description of the isophote peculiarities of the galaxies, relative to an elliptical model, as well as other morphological features such as tails, shells and/or nuclear dust. The relation of the optical properties with radio morphology for the complete B2 sample will be presented in a forthcoming paper.