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Figure 1: 12CO(1-0) velocity-channel maps observed with the PdBI in the nucleus of NGC 4826 with a spatial resolution of at (beam is plotted as a filled ellipse in the bottom left corner of each panel). We show a field of view of 75 , i.e. 1.8 times the diameter of the primary beam at 115 GHz. The phase tracking center is indicated by a cross at and . Velocity-channels are displayed from v=-190 km s-1 to v=190 km s-1 in steps of 10 km s-1. Velocities are in LSR scale and referred to  km s-1. Contour levels are -3, 3, 10, 20, 40 and 78 where the 1-sigma rms  mJy beam-1. There are very few pixels with negative fluxes below -3inside the field-of-view.

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In the text

Figure 2: Same as Fig. 1 but for the 2-1 line of 12CO. Spatial resolution reaches at (beam is plotted as a filled ellipse in the bottom left corner of each panel). We show a field of view of 43 , i.e. 2 times the diameter of the the primary beam at 230 GHz. Velocity-channels are displayed from v=-172.5 km s-1 to v=167.5 km s-1 in steps of 10 km s-1, with same reference as used in Fig. 1. Contour levels are -4, 4, 8, 16, 32 and 62, where the 1-sigma rms  mJy beam-1. There are very few pixels with negative fluxes below -4inside the field-of-view.

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In the text

	Figure 3: The VLA radio-continuum map at 6 cm from Turner and Ho (1994), in grey logarithmic scale from 0.2 to 12mJy beam-1. We highlight the position of the dynamical center derived from CO (star marker) which coincides with a strong non-thermal source.
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In the text

Figure 4: a) 12CO(1-0) integrated intensity contours in the inner 58 of NGC 4826. Contours beyond the displayed field-of-view have been screened as S/N ratio is lower than 3 for . and are offsets (in arcsec) with respect to the phase tracking center. Contours are -1.75, -0.88, 1.75, 4, 6, 8, 10, 12, 15, 18, 22 to 34 in steps of 5 Jy km s-1 beam-1. The dynamical center is indicated by the star marker. The white contour highlights the nuclear region here defined as CND. 1- noise = 0.25 Jy km s-1 beam-1 at the center of the image (1-noise = 0.90 Jy km s-1 beam-1 at the edge of the displayed field-of-view) b) same as a) but for the 12CO(2-1) line. The zoomed view shows emission coming from the inner 24 . Contours beyond the displayed field-of-view have been screened as S/N ratio is lower than 3 for . Contours are -2.4 -1.4 2.4 to 19.4 in steps of 2.4 Jy km s-1 beam-1. Thick contours inside the CND highlight the asymmetrical pattern. 1-noise = 0.36 Jy km s-1 beam-1 (1- noise = 0.8 Jy km s-1 beam-1 at the edge of the displayed field-of-view). Positions of Arm I and II are indicated. Beam-sizes are represented by filled ellipses.

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In the text

Figure 5: a) Peak brightness 12CO(1-0) map deprojected into the galaxy plane in Loge(r)-, where r (in arcsec) and (in degrees) are the polar coordinates. Variable r is the galaxy deprojected radius in relative to the dynamical center and is the azimuthal angle in degrees, measured counter-clockwise from the western side of the major axis. We assume an inclination of and position angle for the NGC 4826 disk (see Sect. 3.3.1). The locations of the two m=1 spirals (Arms I and II), appearing as two straight ridges, are high-lighted by the white-shaded lines. b) Same as a) but for the 12CO(2-1) line. Arm I and the beginning of Arm II are detected.

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In the text

Figure 6: a) Overlay of the mean-velocity field derived from the 1-0 data, in line contours, spanning the range (-160 km s-1, 160 km s-1) in steps of 20 km s-1on the integrated intensity map of 12CO(1-0). Integrated intensity as in Fig. 4 starting by 1.75 Jy km s-1 beam-1. Velocities are here referred to  km s-1 (thick contour). Solid black (grey) lines are used for positive (negative) velocities. The straight line at indicates the position of NGC 4826's major axis. The star marks the AGN position. b) Same as a) but for the 12CO(2-1) line. Integrated intensity contours as in Fig. 4 starting by 2.4 Jy km s-1 beam-1. Velocities span the range (-120 km s-1, 120 km s-1) in steps of 20 km s-1.

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In the text

	Figure 7: a) We show the 12CO(1-0) position-velocity (p-v) diagram along the major axis of NGC 4826 (line contours and grey scale range: 0.015, 0.035 to 0.27 Jy beam-1 in steps of 0.035 Jy beam-1). Velocities have been re-scaled to  km s-1and x' offsets are relative to the dynamical center. b) Same as a) but for the 12CO(2-1) line in the inner . Contours are the same as in a).
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In the text

	Figure 8: Rotation curve obtained from the combined 1-0 + 2-1 CO data in NGC 4826 to a radius of R=700 pc.
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In the text

	Figure 9: 12CO(2-1) position-velocity plot taken along the NGC 4826's minor axis. We indicate the position of Arm I, and the N/S crossings of the CND lopsided instability. The gas kinematics show local signatures of outflow motions at these positions.
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In the text

Figure 10: We display the velocity perturbations of the gas flow, projected into the plane of the sky (v ), due to a fast (  km s-1 kpc-1) ( a) and a slow (  km s-1 kpc-1) ( b) m=1 trailing spiral wave. x and y axes are parallel to the major and minor galaxy axes (x>0 eastwards, y>0 northwards), and we assume (i.e., northern side is closer to us). Thin line contours and gray scale range from -10, -8 to 16 in steps of 2 km s-1 (dashed contours for negative values). Isovelocities v=-80 km s-1(dashed line) and v=80 km s-1 (thick line) define the orientation of circular rotation in the disk (clockwise). The potential minimum locus is represented by the logarithmic spiral. The position of corotation is indicated by the dotted circle in the top panel.

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In the text

Figure 11: We display the overlay of the Pa integrated intensity image, derived from the HST F187N and F160W NICMOS filters (grey logarithmic scale ranges from -  erg s-1 cm-2 pix-1 in the top panel and from -  erg s-1 cm-2 pix-1 in the bottom panel; grey scale increases from light to dark), and the integrated intensity maps obtained for the 1-0 (top) and 2-1(bottom) lines of 12CO in the disk of NGC 4826 (same contours as Fig. 6).

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In the text

	Figure 12: The VLA radio-continuum map at 2 cm (mostly thermal emission) taken from Turner and Ho (1994) (in contours from 35% to 95%, in steps of 10% of the maximum = 1 mJy beam-1) is overlaid on the Pa image of NGC 4826 (in grey scale, as shown). The lopsided star formation in the nucleus has a strong maximum offset by 16 pc northward from the position of the AGN (marked with a square).
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In the text

Figure 13: a) (left) The F450W image of the galaxy with the "cut'' aperture superposed. The brightness peak is shown with a cross in the black (brightest) central region, while a bright H II region is marked with a cross at a radial distance of 17 . b) (right) The surface brightness profile along the minor axis, together with the F450W-F814W and F450W-F160W colors. The center and H II region at shown by crosses in a) (left) are denoted here by vertical dotted lines. The F160W profile is shown by a dotted line, F814W by a solid line, F450W by a dashed line, and CO(1-0) by a heavy line (from top to bottom). Y axis units are magnitudes for all profiles, "including'' CO (in logarithmic scale with an arbitrary offset). In the top panel (for all curves except that for F450W), we plot the reflection of the southern half of the surface brightness profile underneath the northern half of the profile, showing the asymmetry induced by the dust lane. The horizontal dashed lines in the lower panels show the intrinsic color as estimated from the southern region, i.e., at negative offsets along the cuts.

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In the text

	Figure 14: Same CO contours as in Fig. 11 overlaid on extinction AV derived from the HST broad-band B-I color map. Greyscale ranges from AV=0 to 2.
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In the text

Figure 15: a) (top) Strength of the i-Fourier components of the stellar potential of NGC 4826 derived from the HST-NICMOS image of the galaxy nucleus. We represent the main components-Q1 and Q2-and the sum QT. b) (middle) The phases of the potential components are plotted for i=1,2. c) (bottom) Radial variation of the average torque-t(R)-per unit mass. We indicate the radial extent of CND, Arm I and Arm II.

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In the text

	Figure 16: Estimation of the order of magnitude of the Toomre Q parameter (grey scale ranges from 1-3 in the top panel and from 0.7-2.5 in the bottom panel) overlaid on the integrated intensity maps obtained for the 1-0 (top) and 2-1 (bottom) lines of 12CO in the disk of NGC 4826 (same contours as Fig. 6).
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In the text

	Figure 17: The principal epicyclic frequencies , and in the inner disk of NGC 4826. The pattern speed  km s-1 kpc-1 has been purposely chosen to locate the inner m=1 mode of Arm I between its corotation and OLR.
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In the text