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$\begin{figure} \par\includegraphics[width=13cm,clip]{0344fig2a.ps}\end{figure}$ Figure 2: The observed H-band azimuthally averaged radial surface brightness profile (solid points with error bars) for each BL Lac object, overlaid with the scaled PSF model (dotted line), the de Vaucouleurs r^1/4 model convolved with the PSF (dashed line), and the fitted PSF + host model profile (solid line). The y-axis is plotted in mag arcsec^-2.
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In the text

$\begin{figure} \par\includegraphics[width=13cm,clip]{0344fig2b.ps}\end{figure}$ Figure 2: continued.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0344fig3.eps}\end{figure}$ Figure 3: Plot of the apparent H magnitude of the host galaxies vs. redshift (Hubble diagram). The BL Lacs are marked as filled circles (this work), filled squares (K98), open squares (S00) and open circles (C03). The solid line is the K-z relation for RGs derived by Willott et al. (2003), converted to the H-band assuming H-K = 0.2. The dashed line is the extrapolation of the relation towards lower redshift. The RGs are shown as asterisks.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0344fig4.eps}\end{figure}$ Figure 4: Plot of the absolute H band magnitude of the host galaxies vs. redshift. For symbols, see Fig. 3. The solid, short-dashed and long-dashed lines are the luminosities of L* (M(H) $\sim$ -25.0 at low redshift; Mobasher et al. 1993), L*-1 and L*-2 galaxies, respectively, following the passive evolution model of Bressan et al. (1998).
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0344fig5.eps}\end{figure}$ Figure 5: The H-band $\mu _{\rm e}-r_{\rm e}$ relation for the full sample of BL Lac host galaxies. For symbols, see Fig. 3. The solid and dashed lines are the linear least-square best-fit relations for the BL Lacs and for normal inactive ellipticals (Pahre et al. 1995), respectively.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0344fig6.eps}\end{figure}$ Figure 6: The R-H vs. H colour-magnitude diagram for the BL Lac host galaxies. For symbols, see Fig. 3. The other symbols indicate low redshift (z < 0.2) elliptical quasar hosts (crosses; from Jahnke et al. 2003) and elliptical galaxies (filled triangles) and S0 galaxies (open triangles) in the Virgo cluster, and elliptical galaxies (filled inverted triangles) and S0 galaxies (open inverted triangles) in the Coma cluster (from Bower et al. 1992a,b). The solid line shows the best-fit regression line for Virgo and Coma clusters (Bower et al. 1992b). The V-K vs. V diagram of Bower et al. (1992b) has been transformed into R-H vs. H assuming V-R = 0.6, H-K = 0.2 (see text), and distance moduli for Virgo and Coma clusters m-M = 31.0 and 34.6, respectively (Bower et al. 1992b).
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{0344fig7a.ps}\end{figure}$ Figure 7: The host galaxy R-H radial colour profile for all the BL Lacs in the sample, calculated using the R-band data from Falomo & Kotilainen (1999) and Falomo & Kotilainen (in prep.). The dashed vertical lines refer to the effective radius derived from the fit of the R-band data. The profiles indicate that the host galaxies are predominantly bluer further away from the nuclei, but there are marked exceptions with bluer inner regions, e.g. MS 0317, Mrk 180 and 1ES 1853.
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In the text

$\begin{figure} \par\includegraphics[width=12.8cm,clip]{0344fig7b.ps}\end{figure}$ Figure 7: continued.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{0344fig8.eps}\end{figure}$ Figure 8: Upper panel: histogram of the host galaxy R-H colour gradient for all the BL Lac samples. The solid histogram shows the BL Lacs in this work. Lower panel: histogram of the host galaxy V-K colour gradient for normal ellipticals (from Peletier et al. 1990; Schombert et al. 1993).
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{0344fig1a.ps}\end{figure}$ Figure 1: Contour images of the BL Lac objects in the H-band. The distance between major tick marks is 10 px (2 $.\!\!^{\prime\prime}$ 35). Successive isophotes are separated by 0.5 mag intervals. North is up and east to the left. The host galaxy is resolved in all objects.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{0344fig1b.ps}\end{figure}$ Figure 1: continued.
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In the text

$\begin{figure} \par\includegraphics[width=13cm,clip]{0344fig2a.ps}\end{figure}$	Figure 2: The observed H-band azimuthally averaged radial surface brightness profile (solid points with error bars) for each BL Lac object, overlaid with the scaled PSF model (dotted line), the de Vaucouleurs r^1/4 model convolved with the PSF (dashed line), and the fitted PSF + host model profile (solid line). The y-axis is plotted in mag arcsec^-2.
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$\begin{figure} \par\includegraphics[width=13cm,clip]{0344fig2b.ps}\end{figure}$	Figure 2: continued.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0344fig4.eps}\end{figure}$	Figure 4: Plot of the absolute H band magnitude of the host galaxies vs. redshift. For symbols, see Fig. 3. The solid, short-dashed and long-dashed lines are the luminosities of L* (M(H) $\sim$ -25.0 at low redshift; Mobasher et al. 1993), L-1 and L-2 galaxies, respectively, following the passive evolution model of Bressan et al. (1998).
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{0344fig5.eps}\end{figure}$	Figure 5: The H-band $\mu _{\rm e}-r_{\rm e}$ relation for the full sample of BL Lac host galaxies. For symbols, see Fig. 3. The solid and dashed lines are the linear least-square best-fit relations for the BL Lacs and for normal inactive ellipticals (Pahre et al. 1995), respectively.
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$\begin{figure} \par\includegraphics[width=12.8cm,clip]{0344fig7b.ps}\end{figure}$	Figure 7: continued.
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$\begin{figure} \par\includegraphics[width=12.5cm,clip]{0344fig8.eps}\end{figure}$	Figure 8: Upper panel: histogram of the host galaxy R-H colour gradient for all the BL Lac samples. The solid histogram shows the BL Lacs in this work. Lower panel: histogram of the host galaxy V-K colour gradient for normal ellipticals (from Peletier et al. 1990; Schombert et al. 1993).
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$\begin{figure} \par\includegraphics[width=12cm,clip]{0344fig1a.ps}\end{figure}$	Figure 1: Contour images of the BL Lac objects in the H-band. The distance between major tick marks is 10 px (2 $.\!\!^{\prime\prime}$ 35). Successive isophotes are separated by 0.5 mag intervals. North is up and east to the left. The host galaxy is resolved in all objects.
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$\begin{figure} \par\includegraphics[width=12cm,clip]{0344fig1b.ps}\end{figure}$	Figure 1: continued.
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