All Figures

$\begin{figure} \par\includegraphics[width=10.7cm,clip]{2548fig1.ps} \end{figure}$ Figure 1: Contour plots of the BL Lac objects ( center) in the K-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.
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In the text

$\begin{figure} \par\includegraphics[width=12.8cm,clip]{2548fig2.ps} \end{figure}$ Figure 2: The observed K-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 (long-dashed line), and the fitted PSF + host galaxy model profile (solid line). The y-axis is in mag arcsec^-2.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{2548fig3.eps} \end{figure}$ Figure 3: Plot of the apparent K-band magnitude of the host galaxies vs. redshift (Hubble diagram). The high redshift BL Lacs from this work are marked as filled circles, low redshift BL Lcs as open circles (Kotilainen et al. 1998a; Scarpa et al. 2000b; Cheung et al. 2003; Kotilainen & Falomo 2004), FSRQ hosts as open diamonds (Kotilainen et al. 1998b) and high redshift quasar hosts as open squares (Falomo et al. 2004). The solid line is the K-z relation for RGs derived by Willott et al. (2003). These RGs are shown as asterisks. Filter conversion assumes H-K = 0.2.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{2548fig4.eps} \end{figure}$ Figure 4: Plot of the absolute K-band magnitude of the host galaxies vs. redshift. For symbols, see Fig. 3. Additional symbols indicate optical studies of high redshift BL Lacs (filled squares; Heidt et al. 2004, and filled triangles; O'Dowd & Urry 2004). Filter conversions assume R-K = 2.7; I-K = 2.0 and H-K = 0.2. The solid, long-dashed, short-dashed and dotted lines are the luminosities of L* $(M(K)\sim -25.2$ at low redshift; Mobasher et al. 1993), L*-1, L*-2 and L*-3 galaxies, respectively, following the passive evolution model of Bressan et al. (1998).
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In the text

$\begin{figure} \par\includegraphics[width=11cm,clip]{2548fig5.eps} \end{figure}$ Figure 5: Comparison of high and low redshift BL Lacs (filled and open circles, respectively) at various wavelengths. Top left: V-band absolute magnitude. Top right: the 5 GHz radio power. Bottom left: the 5500 Å monochromatic luminosity. Bottom right: the 1 keV luminosity. The first panel uses data from Veron-Cetty & Veron (2003), and the others from Donato et al. (2001).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{2548fig6.eps} \end{figure}$ Figure 6: The K-band $\mu _{\rm e} - r_{\rm e}$ Kormendy relation for the BL Lac host galaxies. Conversion from H- to K-band was made assuming H-K=0.22 colour, typical of normal ellipticals (Recillas-Cruz et al. 1990). Passive evolution of a single age stellar population with formation redshift z = 2 in the K-band was adapted from van Dokkum & Franx (2001). For symbols, see Fig. 3. The solid and long-dashed lines are linear least-square best-fit relations for low redshift BL Lacs (KF04) and normal inactive ellipticals (Pahre et al. 1995), respectively. The short-dashed vertical line is the dividing line between normal and giant ellipticals at R(e) = 3 kpc (Capaccioli et al. 1992).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{2548fig7.eps} \end{figure}$ Figure 7: Plot of the K-band nuclear vs. host luminosity. For symbols, see Fig. 3. The solid lines represent loci of constant ratio between host and nuclear emission. These can be translated into Eddington ratios assuming that the central black hole mass - galaxy luminosity correlation holds at high redshifts and that the observed nuclear power is proportional to the bolometric emission. The two solid lines encompass a spread of 1.5 dex in the nucleus/host luminosity ratio.
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In the text

$\begin{figure} \par\includegraphics[width=10.7cm,clip]{2548fig1.ps} \end{figure}$	Figure 1: Contour plots of the BL Lac objects ( center) in the K-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.
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$\begin{figure} \par\includegraphics[width=12.8cm,clip]{2548fig2.ps} \end{figure}$	Figure 2: The observed K-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 (long-dashed line), and the fitted PSF + host galaxy model profile (solid line). The y-axis is in mag arcsec^-2.
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$\begin{figure} \par\includegraphics[width=11cm,clip]{2548fig5.eps} \end{figure}$	Figure 5: Comparison of high and low redshift BL Lacs (filled and open circles, respectively) at various wavelengths. Top left: V-band absolute magnitude. Top right: the 5 GHz radio power. Bottom left: the 5500 Å monochromatic luminosity. Bottom right: the 1 keV luminosity. The first panel uses data from Veron-Cetty & Veron (2003), and the others from Donato et al. (2001).
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