6 The atlas

The atlas is presented in Appendix B and consists of two parts. The first part presents the data for the 30 galaxies which have been fully reduced and analyzed. The second part gives a less elaborate presentation of the remaining 13 galaxies which have been only partially reduced.

The reduction procedures described in Sect. 3 were applied to the data at all three angular resolutions. However, to facilitate the intercomparison of various results for a galaxy, it was decided to present the data of a particular galaxy at the same angular resolution as much as possible. The rotation curves are in some cases a combination of the rotation curves at various resolutions, the inner parts at the highest spatial resolution and the outer parts from data of lower resolution but higher signal-to-noise ratio. The channel maps are sometimes presented at a lower angular resolution than the other data.

Figure 4 shows the graphical layout for each of the 30 galaxies in the first part of the atlas. The data for each of the 13 galaxies in the second part of the atlas are presented on a single page which contains the tables and notes as well as the mosaic of channel maps, the global profile and the XV-diagram along the major axis. The contents of the various tables and panels are described below.

Tables and Notes - There are three tables presented for each galaxy. The upper left table contains information on the observations like date, integration time and correlator settings. The lower left table presents some of the quantities derived from the HI data like global profile widths, integrated HI flux, systemic velocity etc. The upper right table provides the noise and contour levels for the maps in the various panels. The contours in the channel maps, 21 cm continuum maps and XV-diagrams are always drawn at levels which are related to the rms noise.

The notes contain information about specific aspects of a particular galaxy like optical and HI appearance.

Channel maps - The channel maps show how the HI emission behaves as a function of velocity. From these maps it is possible to recognize the presence of warps, non-circular motions and HI-bridges between interacting galaxies like N3769/1135+48 and N3893/N3896. The contours are drawn at levels of -3, -1.5 (dashed), 1.5, 3, 4.5, 6, 9, 12, 15, ...$\sigma$. The value of the rms noise level $\sigma$ is given in the upper right table. In each panel, the cross indicates the adopted dynamical center of the galaxy. The ellipse in the upper left panel is centered on this position and the position angle is set at the kinematic major axis of the inner regions. The ellipticity represents the inclination as derived from the optical axis ratio and the major axis diameter is equal to D^b,i₂₅. The synthesized beam at half power is shown in the lower left corners of the left panels. The panel at the lower right shows the subtracted, "dirty'' continuum map.

Optical image - The optical image of a galaxy was scanned from the blue POSS plates. In the upper left corner, the morphological type according to the RC3 is given. CCD images of far superior quality can be found in Paper I. An example is given for N3726 in which case the CCD image is pasted into the POSS image.

Radio continuum map - The cleaned 21 cm radio continuum map is plotted at the same scale as the optical image. The contours are drawn at levels of -4, -2 (dashed), 2, 4, 8, 16, 32, 64, ...$\sigma$. The value of the rms noise $\sigma$ is given in the upper right table. The ellipse represents the optical image as in the upper left panel in the channels maps. The synthesized beam is plotted in the lower left corner and the small cross indicates the adopted position of the center of rotation.

Global profile - Each point in the global HI profile gives the primary-beam corrected, total HI flux density integrated over a single channel map. The errors are derived as explained in Sect. 3.2. The vertical arrow indicates the systemic velocity (lower left table on the first page) as derived from the HI velocity field and does not necessarily indicate the center of the global HI profile. A significant offset from the center could indicate non-circular motions or a strong lopsidedness. These anomalies can often be traced in the individual channel maps.

Surface density profile - The open and filled symbols indicate the azimuthally averaged radial surface densities for the approaching and receding sides. The solid line follows the average value. At the adopted distance of 18.6 Mpc, 1 arcmin corresponds to 5.4 kpc. The vertical arrow indicates R₂₅^b,i. The profile becomes unreliable for highly inclined systems since no correction for beam smearing was applied.

XV-diagrams - The position-velocity diagrams are shown for two orthogonal cuts through the adopted center of rotation along the kinematic major (left) and minor (right) axes. The position angles of these two axes are printed in the upper right corner of each panel. Note that the quoted position angles refer to the positive offset axes. Consequently, the position angle of the major axis refers to the receding side which also can be inferred from the channel maps. The vertical dashed line indicates the position of the center of rotation. The horizontal dashed line indicates the systemic velocity as derived from either the velocity field for galaxies with fully reduced data, or from the XV-diagram for galaxies in the second part of the atlas. The two vertical arrows show where the ellipse with major axis diameter D₂₅^b,i intersects the XV-slice. The horizontal arrows in the left panel show the systemic velocity $V_{\rm sys}^{\rm GP}$ derived from the global profile and $V_{\rm sys}^{\rm GP}\pm\frac{1}{2} W_{R,I}$ where W_R,I is the width of the global profile at the 20% level of peak flux, corrected for instrumental broadening (see Sect. 3.2) and turbulent motions according to TFq.

Contours are at levels of -3, -1.5 (dashed), 1.5, 3, 4.5, 6, 9, 12, 15, ...$\sigma$. The value of the rms noise $\sigma$ is given in the upper right table. The cross in the lower left corners indicates the angular and velocity resolutions. An offset of 1 arcmin corresponds to a projected distance of 5.4 kpc from the center.

The crosses give the projected rotational velocities as derived from the tilted rings fit. In some cases, at large radii, a cross can be found without any underlying signal in the XV-diagram. In such cases, the rotational velocity at that radius is defined by points in the velocity field away from the major axis. The open and filled circles indicate the projected rotational velocity estimated directly from these XV-diagrams. These points must be deprojected using the appropriate inclination and position angles to obtain the actual rotation curve for both halves of the galaxy.

Total HI map - All pixels in the total HI map with a positive signal have a greyscale value assigned. Because the signal-to-noise ratio along a contour is not constant, the "3$\sigma$-contour'' is not defined. Section 3.3 and the appendix explain why and how the noise varies across an integrated HI map.

The second contour in the total HI maps corresponds to the average value of all pixels with a signal-to-noise ratio between 2.75 and 3.25 and this contour can thus be considered as a pseudo 3$\sigma$-contour. Wherever a contour goes through an area with $(\frac{S}{N})<3$, the contour is plotted much thinner. Consequently, the lowest contour, plotted at the "1.5$\sigma$'' level, is plotted thin over most of its stretch. The various contour levels in atoms cm^-2 are given in the upper right table. The size of the synthesized beam is plotted in the lower left corner. The beamwidths are the same as in the channel maps unless specified otherwise in the note. The small cross indicates the adopted position of the center of rotation (1 arcmin corresponds to 5.4 kpc).

Velocity fields - The greyscales indicate the pixels where a radial velocity was measured. Darker greyscales and white isovelocity contours indicate the receding side. The thick first black contour adjacent to the white ones indicates the adopted systemic velocity. In the ideal case of circular motion and no noise, this thick contour should be a straight line through the center and coinciding with the kinematic minor axis of the galaxy. The isovelocity contours are plotted with constant velocity intervals as given by the upper right table. The synthesized beam is plotted in the lower left corner.

The observed velocity field was modeled by fitting tilted rings to it. The orientation and rotational velocity of each ring were then used to construct the model velocity field. The model velocity field is plotted with the same orientation and on the same scale as the observed velocity field. The isovelocity contours are plotted at the same velocities in the observed as in the model velocity fields. For nearly edge-on systems, the model velocity field is only one or two pixels wide in which case no contours could be drawn.

The residual velocity field was made by subtracting the model from the observed velocity field. White contours indicate positive residuals, black contours indicate negative residuals. The contour levels are ..., -15, -10, -5, 5, 10, 15, ... km s^-1.

Tilted-ring fits - The three combined panels show the results from the tilted-ring fits to the observed velocity field. The upper panel shows the inclination angle, the middle panel the position angle and the lower panel the rotational velocity.

The crosses with errorbars in the panels for inclination and position angle are the results from the second step of the fitting procedure as explained in Sect. 3.6.1. The dashed lines, mostly coinciding with the solid lines, in these upper two panels indicate the final values of the inclination and position angles kept fixed when the rotational velocity was fitted. The resulting rotation curve is shown by crosses with errorbars in the lower panel. The errorbars indicate the formal errors, as given by the least squares minimization algorithm.

The horizontal arrows in the upper two panels indicate the inclination and position angles as derived from the optical isophotes in the outer regions. The diamonds indicate the inclination and position angles as determined from the total HI maps. When the total HI maps are very patchy, these diamonds are very uncertain. The horizontal arrow in the lower panel indicates the rotational velocity as derived from the width of the global HI profile corrected for instrumental broadening, turbulent motion and inclination. The adopted inclination is representative for the outer parts. The vertical arrow in the lower panel indicates R₂₅^b,i.

The solid lines in the upper and middle panels show the inclination and position angles that were adopted to deproject the radial velocities determined from the XV-diagrams. This deprojection results in the rotation curves plotted as open and filled circles in the lower panel (same symbols as in the XV-diagrams). Note that although the rotational velocities at a certain radius may be different for the approaching and receding sides, both sides were assumed to have the same inclination and position angles at that radius. The solid line in the lower panel shows the mean rotation curve derived from the XV-diagram. 1 arcmin on the horizontal axis corresponds to 5.4 kpc.

Tabulated data - The various parameters derived from the HI data presented here are summarized in Table 5.

Column (1) gives the NGC or UGC numbers.
Columns (2)-(5) give the uncorrected widths with formal errors of the global profiles at 20% and 50% of the peak flux.
Column (6) gives the instrumental velocity resolution at which the global profiles were observed.
Columns (7) and (8) contain the heliocentric systemic velocities and their uncertainties as derived from the global profiles.

 

 

Table 5: Results from the HI synthesis observations

Name	$W_{20}\pm$		$W_{50}\pm$		Res.	$V_{\rm hel}\pm$		$\int S{\rm d}v \pm$		$F_\nu \pm$		$R_{\rm HI}$	$R^{\rm lmp}$	$V^{\rm lmp}_{\rm rot}\pm$		shape	$V_{\max}\pm$		$V_{\rm flat}\pm$
	- - - - - - - - km s-1 - - - - - - - -							Jy km s-1		- mJy -		($^\prime$)	($^\prime$)	- km s-1 -			- - - - km s-1 - - - -
(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)	(11)	(12)	(13)	(14)	(15)	(16)	(17)	(18)	(19)	(20)	(21)
Galaxies with fully reduced HI data:
U6399	188.1	1.4	172.5	2.9	8.3	791.5	0.6	10.5	0.3	<2.5		1.68	1.50	88	5	R/F	88	5	88	5
U6446	154.1	1.0	131.9	1.2	5.0	644.3	0.8	40.6	0.5	<7.2		2.96	2.93	80	11	F L	82	4	82	4
N3726	286.5	1.6	260.6	1.8	5.0	865.6	0.9	89.8	0.8	49.7	5.0	4.24	6.22	167	15	F/(D)	162	9	162	9
N3769	265.3	6.7	230.5	3.6	8.3	737.3	1.8	62.3	0.6	12.1	2.9	4.31	7.10	113	11	F/(D)	122	8	122	8
U6667	187.5	1.4	178.1	1.9	5.0	973.2	1.2	11.0	0.4	<2.7		1.64	1.50	86	3	R L	86	3	86	3
N3877	373.4	5.0	344.5	6.2	33.2	895.4	3.8	19.5	0.6	35.6	2.4	2.19	2.17	169	7	F L	167	11	167	11
N3893	310.9	1.0	277.9	4.1	5.0	967.2	1.0	69.9	0.5	137.4	2.9	3.98	3.88	148	19	F/(D)	188	11	188	11
N3917	294.5	1.9	279.1	2.1	8.3	964.6	1.4	24.9	0.6	<7.2		2.69	2.83	137	8	F	135	3	135	3
N3949	286.5	1.4	258.3	1.7	8.3	800.2	1.2	44.8	0.4	134.1	3.6	2.62	1.35	169	8	F L	164	7	164	7
N3953	441.9	2.4	413.9	3.2	33.1	1052.3	2.0	39.3	0.8	50.9	2.5	3.32	3.00	215	10	F	223	5	223	5
N3972	281.2	1.4	260.7	5.5	8.3	852.2	1.4	16.6	0.4	<5.8		1.92	1.67	134	5	R L	134	5	...	..
U6917	208.9	3.2	189.6	1.6	8.3	910.7	1.4	26.2	0.3	<4.4		2.42	2.00	111	7	R/F	104	4	104	4
U6923	166.8	2.4	147.1	4.5	10.0	1061.6	2.2	10.7	0.6	<2.6		1.29	1.02	81	5	R L	81	5	...	..
U6930	136.5	0.5	122.1	0.7	8.3	777.2	0.4	42.7	0.3	<5.8		3.20	3.17	108	7	R/F	107	4	107	4
N3992	478.5	1.4	461.4	2.4	10.0	1048.2	1.2	74.6	1.5	30.2	7.6	4.75	6.67	237	9	F/D	272	6	242	5
U6940	59.3	3.8	40.6	7.8	10.0	1118.0	1.7	2.1	0.3	<1.3		0.61	0.33	37	4	R	37	4	...	..
U6962	220.3	6.6	182.4	3.7	8.3	807.4	3.2	10.0	0.3	13.4	1.7	1.38	1.00	171	7	R L	171	7	...	..
N4010	277.7	1.0	264.1	1.2	8.3	901.9	0.8	38.2	0.3	16.9	1.6	3.36	2.00	122	2	(R)/F L	128	9	128	9
U6969	132.1	6.4	123.5	2.9	10.0	1118.5	2.4	6.1	0.5	<3.8		0.95	0.85	79	5	R	79	5	...	..
U6973	367.8	1.8	350.4	1.2	8.3	700.5	1.0	22.9	0.2	127.5	2.1	2.21	1.50	180	8	F/(D)	173	10	173	10
U6983	188.4	1.3	173.0	1.1	5.0	1081.9	0.8	38.5	0.6	<5.4		3.07	3.00	109	12	F	107	7	107	7
N4051	255.4	1.8	224.6	1.5	5.0	700.3	1.2	35.6	0.8	26.5	2.6	2.89	2.33	153	10	R/F L	159	13	159	13
N4085	277.4	6.6	255.4	7.8	19.8	745.7	5.0	14.6	0.9	44.1	1.3	1.94	1.18	136	7	R/F L	134	6	134	6
N4088	371.4	1.7	342.1	1.9	19.8	756.7	1.2	102.9	1.1	222.3	1.9	4.25	4.10	174	8	F/(D) L	173	14	173	14
N4100	401.8	2.0	380.5	1.8	19.9	1074.4	1.3	41.6	0.7	54.3	1.7	3.45	4.35	159	9	F/D	195	7	164	13
N4102	349.8	2.0	322.4	8.5	8.3	846.3	2.0	8.0	0.2	276.0	1.5	1.16	0.83	178	12	F	178	11	178	11
N4157	427.6	2.2	400.7	3.1	19.9	774.4	1.8	107.4	1.6	179.6	2.3	4.60	5.67	185	14	F/D	201	7	185	10
N4183	249.6	1.2	232.5	1.5	8.3	930.1	1.0	48.9	0.7	<5.8		3.07	4.02	113	11	F/D L	115	6	109	4
N4217	428.1	5.1	395.6	3.8	33.2	1027.0	3.0	33.8	0.7	115.6	2.2	3.19	3.17	178	12	F/D	191	6	178	5
N4389	184.0	1.5	164.9	1.6	8.3	718.4	1.2	7.6	0.2	23.3	1.2	1.30	1.02	110	8	R	110	8	...	..
Galaxies with partially reduced HI data:
N3718	492.8	1.0	465.7	1.0	33.2	993.0	0.8	140.9	0.9	11.4	0.4		6.67	223	12	F	232	11	232	11
N3729	270.8	1.5	253.2	3.9	33.2	1059.8	1.4	5.5	0.3	18.0	0.9		1.00	151	11	F	151	11	151	11
U6773	110.4	2.3	91.1	2.2	8.3	923.6	1.6	5.6	0.4	<2.6			0.67	45	5	R L	45	5	...	..
U6818	166.9	2.3	141.9	5.7	8.3	808.1	2.1	13.9	0.2	2.4	1.0		1.33	74	7	R/(F) L	73	5	73	5
U6894	141.8	1.1	132.2	1.5	8.3	848.6	1.8	5.8	0.2	<2.7			0.67	63	5	R	63	5	...	..
N3985	160.2	3.7	88.0	2.4	8.3	948.2	2.0	15.7	0.6	9.7	1.4		0.50	93	7	R	93	7	...	..
N4013	425.0	0.9	395.0	0.8	33.0	831.3	0.6	41.5	0.2	36.3	0.8		6.12	170	10	F/D	195	3	177	6
U7089	156.7	1.7	97.7	3.0	10.0	770.0	1.5	17.0	0.6	<3.4			1.75	79	7	R L	79	7	...	..
U7094	83.7	1.7	71.9	5.5	10.0	779.6	1.6	2.9	0.2	<2.6			1.00	35	6	R L	35	6	...	..
N4117	289.4	7.5	260.3	5.2	10.0	934.0	1.5	6.9	1.1	3.7	1.2					?
N4138	331.6	4.5	266.0	7.8	19.9	893.8	3.9	19.2	0.7	16.7	4.6		3.55	150	21	F/D	195	7	147	12
N4218	138.0	5.0	79.9	1.9	8.3	729.9	1.7	7.8	0.2	6.3	0.8		0.33	73	7	R	73	7	...	..
N4220	438.1	1.3	423.3	3.3	33.1	914.2	1.2	4.4	0.3	<4.9						?

Figure 5: Correlations between HI mass-to-light ratios and absolute $K^\prime$-band magnitudes (left column) and morphological type (right column). Solid symbols indicate HSB galaxies and open symbols denote galaxies of the LSB type

Columns (9) and (10) provide the integrated HI flux and the uncertainty in Jy km s^-1.
Columns (11) and (12) contain the 21 cm continuum flux density and its uncertainty in mJy. In case no continuum flux was detected, a 3$\sigma$ upper limit for extended emission is given.
Column (13) gives the radius of the HI disk, $R_{\rm HI}$ in arcmin, at the azimuthally averaged surface density of $1~M_{\odot}~{\rm pc}^{-2}$, measured from the radial surface density profiles.
Column (14) gives the radius $R^{\rm lmp}$ of the last measured point of the rotation curve in arcmin. The differences between $R^{\rm lmp}$ and $R_{\rm HI}$ depend on the sensitivity of the measurement and the distribution of the HI gas along the kinematic major axis.
Columns (15) and (16) give the rotational velocity of the last measured point $V^{\rm lmp}$ and its uncertainty.
Column (17) contains information on the overal shape of the rotation curve; R: rising rotation curve, F: the rotation curve shows a flat part, D: the rotation curve shows a declining part, L: lopsided.
Columns (18) and (19) give the maximum observed rotational velocity $V_{\max}$ and its uncertainty. For galaxies with a rising rotation curve (R) $V_{\max}=V^{\rm lmp}$.
Columns (20) and (21) give the average rotational velocity of the flat part of the rotation curve $V_{\rm flat}$ and its uncertainty. For galaxies with a flat rotation curve (F) $V_{\rm flat}=V_{\max}$ may deviate from $V^{\rm lmp}$ because $V_{\rm flat}$ was averaged over the flat part of the rotation curve while $V^{\rm lmp}$ was measured at a single point.

Figure 6: Ratio of HI-to-optical diameter as a function of $K^\prime$ magnitudes, morphological type and disk scale length. The HI diameters were measured at the $1~M_{\odot}~{\rm pc}^{-2}$ isodensity contour. Solid symbols indicate HSB galaxies and open symbols denote galaxies of the LSB type