2 Mrk 86

Mrk 86 ( $\alpha(2000)=08^{\rm h}13^{\rm m}14.56^{\rm s}$ $\delta(2000)=+45\hbox{$^\circ$ }59\hbox{$^\prime$ }30.2\hbox{$^{\prime\prime}$ }$) is a well-known object among BCD galaxies (Loose & Thuan 1985; Sage et al. 1992; see Table 1). In the Loose & Thuan (1985) BCD classification, Mrk 86 belongs to the iE class: smooth elliptical Low Surface Brightness (LSB) underlying stellar component on which several knots of star formation are superimposed. The present star formation activity is spread out in several clumps over a relatively large fraction of its entire surface. In fact, Mrk 86 shows the highest ratio of the area covered by star-forming regions to the total projected area of the galaxy within the sample of Papaderos et al. (1996a).

To this moment Mrk 86 has not been the subject of a single and proof study, inasmuch the large number of published data on it. A collection of the published data is given in Table 1. A more detailed description of the previous observations is given by Gil de Paz et al. (1999; GZG hereafter).

   
2.1 Distance

Mrk 86 is a nearby star-forming galaxy. The heliocentric recession velocity is $v_{\hbox{$\odot$ }}=447$kms^-1 (see recession velocities referred to the Local Group in Table 1).

Using the mean blue magnitude of the three brightest blue stars Sharina et al. (1999) derived a distance for this object of 6.9Mpc with an uncertainty of 20 per cent (Sharina, private communication). We can also estimate the distance to Mrk 86 if we assume that it is gravitationally bounded to the edge-on spiral galaxy UGC 4278 (see Paper II). UGC 4278 has a corrected I-band absolute magnitude of $-18.21\pm0.11$ (see Giovanelli et al. 1997) with a logarithmic 21cm line width of $2.220\pm0.019$ (in kms^-1). Therefore, with respect to the Giovanelli et al. (1997) Tully-Fisher template, this galaxy shows an offset of 0.66 ^m, which corresponds to a peculiar radial velocity of -253kms^-1. Thus, its recesion velocity in the CMB reference frame should be 968kms^-1 ( $v_{\hbox{$\odot$ }}=565$kms^-1), which implies a minimum distance for Mrk 86 of 13Mpc (for H₀=75kms^-1Mpc^-1 and assuming that the difference in heliocentric velocity is due to orbital motion). The large difference between this value and that given by Sharina et al. (1999) suggests that these objects are probably not physically bounded. Thus, since no other distance indicator is available for Mrk 86, we have used the distance measured by Sharina et al. (1999) throughout this work. This value leads a projected spatial scale of 33pcarcsec^-1.