All Figures

$\begin{figure} \par\includegraphics[clip,angle=-90,width=14cm]{m2415f01.ps} \end{figure}$ Figure 1: The Digitized Sky Survey (DSS-II) blue image of the field in the vicinity of BCG HS 0822+3542. North is up, East is to the left. At the adopted distance of HS 0822+3542 (11 Mpc) the scale is $\sim$ 54 pc = 1 $^{\prime \prime }$ . The two marked galaxies - LSBD SAO 0822+3545 and Anon J0825+3534 have been checked as possible companions of the BCG. On our data the LSBD has $V_{\rm hel} \sim 700$ km s^-1, close to that of HS 0822+3542. Its projected distance to the BCG is 213 $^{\prime \prime }$ or 11.4 kpc. The galaxy Anon J0825+3534, very close to the position of 2MASXi J0825440+353459 (NED), is a distant background object with $V_{\rm hel}=15590$ km s^-1.
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In the text

$\begin{figure} \par\includegraphics[clip,width=8.1cm]{m2415f02.ps} \end{figure}$ Figure 2: Top panel: 2D spectrum of SAO 0822+3545 with the H $\alpha$ line at $\lambda$ 6579 Å. Positive Y corresponds to the NW direction for the slit position shown in Fig. 3. H $\alpha$ -emission is clearly seen on top of the continuum in the region of $\pm \sim$ 5 $^{\prime \prime }$ from the central position. Furthermore, some very faint H $\alpha$ -emission (with S/N ratio of $\sim$ 1) can be traced out to $\pm \sim$ 10 $^{\prime \prime }$ , in the regions without detectable continuum. Bottom panel: 1D spectrum of the central region ( $\pm$ 3 $^{\prime \prime }$ ), summed along the slit, EW(H $\alpha$ ) = 17 Å.
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=7.8cm]{m2415f03.ps} \includegraphics[width=7.8cm]{m2415f04.ps} } \end{figure}$ Figure 3: Left panel: B-band image of SAO 0822+3545 from the NOT. N is up, E is to the left. The 2 $^{\prime \prime }$ -wide long slit of the 6 m telescope spectrum is superimposed. Highly irregular structure is seen in the inner $\sim$ 15 $^{\prime \prime }$ . Two knots near the center and two arcs to the N and W are indicative of some activity in this galaxy. The isophotal contour corresponds to a B-band SB of $\sim$ 25 $.\!\!^{\rm m}$ 7 arcsec^-2, or 2 $\sigma$ of background (for 2D Gaussian smoothing with FWHM=1 $^{\prime \prime }$ ). Two faint objects, probable background galaxies in the vicinity of SAO 0822+3545, are marked as S $_{\rm 1}$ and S $_{\rm 2}$ . Right panel: The same B-band image of SAO 0822+3545, deconvolved after 15 iterations using the FFT based Lucy algorithm (Adorf et al. 1992). The angular resolution has improved from 1 $.\!\!^{\prime\prime}$ 25 to $\sim$ 0 $.\!\!^{\prime\prime}$ 85 ( FWHM). Several filaments and many knots are easily visible within the brighter part of the galaxy. Knots are marked by letters from "a'' to "i'', respectively.
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In the text

$\begin{figure} \par\includegraphics[clip,width=7.7cm]{m2415f05.ps} \par\end{figure}$ Figure 4: Grey-scale map of (B-V)-colour for SAO 0822+3545 smoothed with 2D median with the window size of 1 $.\!\!^{\prime\prime}$ 6 $\times$ 1 $.\!\!^{\prime\prime}$ 6. The extinction corrected ( E(B-V)=0.047) colour distribution is shown only for regions with S/N ratio larger than 4. The colour scale is shown in the right side column. B-band surface brightness (SB) isolines are superimposed, with the lowest SB level of 25 $.\!\!^{\rm m}$ 7 arcsec^-2. The other levels are: 24.5, 24.0, 23.6, 23.3, 23.1, 22.9, 22.8 and 22.6 mag arcsec^-2.
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In the text

$\begin{figure} \par\mbox{\includegraphics[clip,width=8.3cm]{m2415f06.ps} \includegraphics[clip,width=8.3cm]{m2415f07.ps} } \end{figure}$ Figure 5: Left panel: the NOT B-band image of HS 0822+3542, deconvolved with 40 iterations using FFT based Lucy algorithm. The angular resolution is improved from 1 $.\!\!^{\prime\prime}$ 25 to $\sim$ 0 $.\!\!^{\prime\prime}$ 6. N is up, E is to the left. The slit position for H $\alpha$ velocity curve is superimposed. The isophotal contour corresponds to $\mu _{\rm B} =$ 25 $.\!\!^{\rm m}$ 0 arcsec^-2 or 4 $\sigma$ of background (for 2D Gaussian smoothing with FWHM=1 $^{\prime \prime }$ ). The arrow indicates the extent of H $\alpha$ emission on the 6 m telescope spectrum. All features marked as "a'' to "f'' are resolved in B,V,R deconvolved images. Knot "b'' is $\sim$ 8 time fainter than "a'' (see Sect. 3.3). Right panel: same as before, but for NOT V-band image. The filamentary structure on NW edge is well seen on both images.
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In the text

$\begin{figure} \par\includegraphics[clip,width=7.9cm]{m2415f08.ps} % \end{figure}$ Figure 6: Upper panel: H $\alpha$ intensity in HS 0822+3542 along the slit position shown in Fig. 5. Lower panel: P-V diagram of ionized gas in HS 0822+3542 based on the H $\alpha$ line from the same spectrum. Its form within a radius of $\pm$ 4 $^{\prime \prime }$ , and the characteristic diameter and velocity amplitude ( $\sim$ 480 pc and $\sim$ 30 km s^-1), are consistent with the appearance of supershells observed in many star-bursting galaxies. Filled boxes show the velocities on both sides of the shell as derived from the Gaussian decomposition of the H $\alpha$ line at several positions along the slit. For details see Sect. 3.3.
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In the text

$\begin{figure} \par\includegraphics[clip,angle=-90,width=15.2cm]{m2415f09.ps} \end{figure}$ Figure 7: 1D spectrum of HS 0822+3542 with a sampling of 4.6 Å pixel^-1. The spectrum in the bottom is scaled by 1/27 to show the relative intensities of strong lines.
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In the text

$\begin{figure} \par \includegraphics[clip,width=8.4cm]{m2415f10.ps} \end{figure}$ Figure 8: BVR tracks based on PEGASE.2 evolution models from Fioc & Rocca-Volmerange (1997). Solid and dotted lines are for instantaneous starburst stellar populations with Z of 1/20 $Z_{\odot }$ and 1/50 $Z_{\odot }$ , respectively (Salpeter IMF, $M_{\rm up}$ and $M_{\rm low}$ are 120 and 0.1 $M_{\odot }$ ). The dashed line is for 1/20 $Z_{\odot }$ continuous SF at a constant rate. Time scales (in Gyr) for respective tracks are shown in the bottom. The filled triangle with error bars shows corrected for Galactic extinction of E(B-V)= 0.047 the total BVR colours of SAO 0822+3545. Filled squares show the sequence of BVR colors for composite stellar populations with a "young'' (10 Myr) starburst and an admixture of a 10 Gyr ("old'') coeval population. The mass ratio $\eta = M_{\rm old}/M_{\rm young}$ varies along the sequence as 0,2,5,10,20,30,40,50,60 and 80. Open circles show the colours of a composite population with the same 10 Myr "young'' population mixed with a 250 Myr ("old'') coeval population. For this case the mass ratio $\eta$ sequence is shown for values 0,2,5,10,20,40 and 80. Two open stars show the BVR colours of a stellar population resulting from continuous SF with a steep IMF ( $\alpha =3.35$ ), lasting 100 and 250 Myr, while the cross shows the colours for the case of continuous SF, lasting 1 Gyr, but for a Salpeter IMF with $M_{\rm up}=30$ $M_{\odot }$ (see text).
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In the text

$\begin{figure} \par\includegraphics[clip,angle=-90,width=14.7cm]{m2415f11.ps} \end{figure}$ Figure 9: The position of HS 0822+3542 and SAO 0822+3545 (in the box) is shown relative to the other galaxies from LEDA in the redshift range between $V_{\rm hel} = 427$ and 1027 km s^-1. The blue luminosities of galaxies are indicated by the size of the filled circle. The nearest neighbour to the pair, at the position ${\rm RA}\sim 8^{\rm h}$ , ${\rm DEC}\sim 36$ $^\circ$ (D=1.15 Mpc) has $M_{\rm B}= -$ 14.7. Dotted, dashed and dot-dashed lines show the projection of galactic latitudes $b^{\rm II} =$ 30 $^\circ$ , 25 $^\circ$ and 20 $^\circ$ , respectively. Galactic extinction should more strongly affect the detection of faint galaxies. The absence of bright galaxies is not a selection effect, since some of them are found in the zone of $b^{\rm II} < 25$ $^\circ$ ,
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In the text

$\begin{figure} \par\includegraphics[clip,angle=-90,width=15.2cm]{m2415f09.ps} \end{figure}$	Figure 7: 1D spectrum of HS 0822+3542 with a sampling of 4.6 Å pixel^-1. The spectrum in the bottom is scaled by 1/27 to show the relative intensities of strong lines.
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