5 Notes on individual objects

 We hereafter present some notes on each dwarf galaxy in the final list. The optical velocities of companion galaxies and the location of some HII regions mentioned were derived from long-slit spectroscopic data obtained in March 1998 with the ESO 3.6 m telescope. These observations will be presented in detail in Paper II.

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H1031-2818: This system is the most luminous dwarf in our sample, at $M_B\approx -17.5$ mag. Its surface brightness profiles in both B and I suggest a central depression with respect to a normal exponential fitting law. This flattening appears more pronounced in B, where the extrapolation of the outer slope of the LSB component to R^*=0$^{\prime\prime}$ leads to a central surface brightness $\sim 0.7$ B mag brighter than the observed value. In Fig. 14 the intensity distribution of the LSB component in B is fitted with a modified exponential distribution of the form Eq. (2) with (b,q)=(1.8,0.65). We determined the apparent B luminosity of the LSB component as 15.83 mag and that of the component in excess of it as 18.79 mag. Thus, the latter luminosity component, due to ongoing star-forming activity, represents only a minor contribution, $\sim 6$%, to the total luminosity of the system.

Within an area $\sim 14$$^{\prime\prime}$ in diameter there are three moderately blue ($B-I\sim 1.3$ mag) off-center regions immersed in the relatively red ($B-I \sim 1.8$) LSB stellar continuum. The latter knots host HII regions. For radii $\ge$ 4$^{\prime\prime}$ the radially averaged B-I profile shows a monotonic color increase with a gradient of $\sim 0.18$ mag kpc^-1.

This HI source is the only VLA HI source re-observed at Nançay but not reconfirmed. The upper limit to the integrated HI line flux listed in Table 2 is a 3$\sigma$ upper limit for an assumed line FWHM of 75 km s^-1, the average observed for the 15 confirmed primary list dwarf galaxies.

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H1031-2632: A low surface brightness object with a central blue surface brightness of only 23 ${\rm mag\,\,arcsec^{-2 }}$. The galaxy is quite red (B-I=1.5); it does not show any significant color gradient ($\Delta(B-I)=-0.11$ mag kpc^-1), nor evidence for star formation. The clump located roughly 8$^{\prime\prime}$ West of the center ($B-I\sim 2$) is presumably a background galaxy, which was also detected in K' (m_K= 17.3). It was removed for the computation of surface brightness profiles. The Nançay HI spectrum shows a second signal, centered on $V_{\rm hel}=3745$ km s^-1 with a FWHM of 155 km s^-1. In the NED and LEDA databases 2 small, highly inclined galaxies were found in an area 1.5 times the size of the telescope HPBW: FGCE 818, an $0\hbox{$.\mkern-4mu^\prime$}9$ diameter superthin Scd-type edge-on system (see Fig. 4) and ESO 501- G017, an S0 at a redshift of 4429 km s^-1. FGCE 818 is the obvious candidate for this HI signal, as shown by the VLA imaging of McMahon (1993) who measured $V_{\rm hel}=3743$ km s^-1 for the VLA source.

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H1032-2638: Edge-on dwarf galaxy. Two foreground stars, a blue and a red one, indicated in the color map (Fig. 16; top-right) by crosses, were removed when computing SBPs (though there may still remain some small residuals). The galaxy itself was not detected in K'. The blue region to the South-West hosts a strong HII region.

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H1032-2722: A low surface brightness object exhibiting an off-center blue clump. Its surface brightness profiles in both B and I suggest for radii $\le 7$$^{\prime\prime}$ a central depression with respect to a normal exponential fitting law. In Fig. 17 the intensity distribution of the LSB component in B is fitted with a modified exponential distribution of the form Eq. (2) with (b,q)=(1.8,0.7).

The central surface brightness of the modified exponential distribution (23.13 B mag arcsec^-2) is 1.3 mag fainter than the extrapolated value of the outer slope (21.82 mag arcsec^-2). The apparent B luminosity of the LSB component was determined as 17.64 mag and that of the excess light as 20.62 mag (representing $\sim\!\!\!6$% of the total B luminosity of the system). This HI-dwarf exhibits an off-center blue clump to the East. The latter shows up in K' whereas the low-surface brightness disk is barely detected in this band. Within the inner 1 kpc ($\le$ 4$^{\prime\prime}$) the radially averaged color profile shows a strong color gradient (0.57 mag kpc^-1) whereas a constant blue color ($B-I = 1.09 \pm 0.08$) is measured in the LSB component. Widespread star formation is detected through spectroscopy. It is more active at the location of the blue clump.

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H1032-2819: As discussed in Sect. 4.1, no optical counterpart was found to this HI cloud, situated less than 60 kpc away from the spiral galaxy ESO 436-G046 (see Fig. 3). One cannot exclude that this cloud has been detached from the spiral by tidal interaction. Although the latter does not exhibit strong signs of interaction, it has a nearby companion, ESO 436-IG042 whose Nançay HI spectra is shown in Fig. 10.

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H1033-2707: A rather blue, high-surface brightness object, with an integrated B-I index of $\sim 1.0$ mag. Colors are getting even bluer to the North along its major axis, where they attain a value $\sim 0.75$; a star forming region is observed there.

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H1033-2642: A red low-surface brightness object showing a truncation of its exponential profile at levels mag arcsec^-2. The galaxy is interacting with the S0 galaxy to the South-East (labeled as G1 in Fig. 19) which is at the same optical redshift ($V_{\rm opt}=2510$ km s^-1; m_B=15.2; m_I=13.2). H1033-2642 has a red ($B-I\sim 1.45$ mag) central region with a B-I index getting bluer ($-0.09 \pm 0.015$ mag kpc^-1) with increasing galactocentric radius. It is barely detected in K'. A low level of star-formation is seen all along the South-North axis.

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H1033-2722: A red low-surface brightness object with a decreasing B-I color towards larger radii ($-0.145 \pm$ 0.015 mag kpc^-1). An off-centered blue region associated with an HII region is seen to the North-West.

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H1034-2558: A blue compact dwarf galaxy detected previously in the objective-prism survey by Maza et al. (1991) and catalogued as CTS 1015 and M01.13. It shows an extended, blue off-centered nucleus ( mag) and a relatively constant color ($\sim$ 0.9 - 1.0 mag) in the LSB component. The averaged color gradient for radii $\le 0.5$ kpc is as strong as $\sim 1.76$ mag kpc^-1. The luminosity component in excess (m_B=19.31 mag) of the LSB component as modelled by a pure exponential law (m_B=18.61) contributes % of the total light of H1034-2558, contrary to other HI-detected dwarfs in our sample, which generally show a moderate (if any) luminosity contribution of a younger stellar population superimposed on their LSB components. Very strong emission lines typical of a BCD are associated with the blue compact nucleus. The latter is detected in K', at which wavelength another clump is seen 10$^{\prime\prime}$ to the South-East without any counterpart in the I-band.

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H1034-2758: A distorted object with off-centered blue knots. Two galaxies lie at a small projected distance from H1034-2758 (see Fig. 22): G1 (m_B=17.5, m_B=16.1) and G2 (m_B=18.3, m_I=17.3). The northern object, G2, is a background starburst galaxy at $V_{\rm opt}=10577$ km s^-1. G1 with $V_{\rm opt}=3630$ km s^-1 appears as a quiescent dwarf galaxy, a very close interacting companion to H1034-2758 at a projected distance of only 26$^{\prime\prime}$ or 5.7 kpc. The inner isophotes of H1034-2758 seem to be slightly distorted. However, contrary to H1033-2642, no signs of truncation in the SBPs profiles are seen in the outer part of the galaxy. The exponential profile of H1034-2758 reveals an excess in the central core, though less pronounced than in H1034-2558. The diffuse relatively blue ( 0.9 mag) region $\sim 6$$^{\prime\prime}$ West of the nuclear region corresponds to a strong HII region.

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H1035-2756: A peculiar galaxy showing two distinct luminosity knots embedded in a patchy very low-surface brightness ( mag arcsec^-2) continuum. Only the eastern clump shows signs of current star formation.

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H1035-2605: An elongated face-on object having the reddest integrated color in the sample (B-I=1.7). The galaxy shows two relatively bluer knots at each extremity of its disk with in between a very red region ($B-I\sim 2$) probably affected by dust extinction. The radially averaged B-I profile shows a negative color gradient of -0.17 mag kpc^-1. The galaxy is well detected in K'. The I and K' peaks occur at the same position. Despite its red color, the optical spectrum indicates an extended starburst. The red nearby objects, designated G1 (m_B=18.3, m_I=16.0) and G2 (m_B=18.6, m_I=16.3) in Fig. 24 are probably background galaxies, although their optical velocities are yet unknown.

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H1035-2502: A blue low-surface brightness object. Extended weak emission lines are observed along a blue bar that shows up in the B-I color map. The Nançay HI spectrum shows a second, narrow peak centered on $V_{\rm hel}=3620$ km s^-1 with a FWHM of 40 km s^-1. In the NED and LEDA databases a single large spiral was found in the neighborhood, NGC 3313, whose outer HI disk should be readily detectable at Nançay as its center lies $2\hbox{$.\mkern-4mu^\prime$}5$ W of the dwarf galaxy (see Fig. 5). HI line observations (VLA imaging by McMahon 1993, Nançay profile by Theureau et al. 1998) show that this face-on 12.4 mag SBb-type spiral is the obvious candidate for the HI signal, with a central velocity of 3706 km s^-1, a FWHM of 107 km s^-1 and a mean flux density of 156 mJy.

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H1035-2740: A relatively blue compact galaxy (B-I=0.92). This is, with H1034-2558, the only object for which the optical maximum of the galaxy coincides with a blue clump. Emission lines are detected all along the galaxy. The very red object to the North-West, designated as G1 in Fig. 26, was marginally detected in B ($m_B \sim 20.9$) and well seen in I ($m_I\sim 17.5$). It is most probably a distant background galaxy.

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H1038-2733 A low surface galaxy with a bar-like structure. It is the galaxy with the highest HI-mass-to-blue luminosity ratio in the sample (2.3 $M_{\odot}/L_{\odot,B}$). The radially averaged B-I profile shows between $\sim 0.2$ kpc and $\sim 2.2$ kpc radius a weak negative color gradient of -0.12 mag kpc^-1. Star formation is observed mainly to the West at the location of a blue region.

The galaxy to the North designated as G1 in Fig. 27 is very red ($B-I\sim 2.7$) and likely a background galaxy. The Nançay HI spectrum shows a second signal, centered on $V_{\rm hel}=3975$ km s^-1 with a W₂₀ width of 330 km s^-1. In the NED and LEDA databases a large spiral, NGC 3336, and a smaller pair of galaxies, AM 1038-273, were found in an area 1.5 times the size of the telescope HPBW (see Fig. 8). The 13$^{\rm th}$ mag Sc-type spiral NGC 3336 is the obvious candidate for this HI signal, as shown by the VLA imaging of McMahon (1993) and the Effelsberg detection of Richter & Huchtmeier (1983), who find a central velocity of 4000 km s^-1, a FWHM of 300 km s^-1 and a mean flux density of 57 mJy.

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H1038-2730: An edge-on system with isophote twisting. The radially averaged B-I profile shows a weak negative color gradient of $\sim -0.19$ mag kpc^-1. We do not see any evidence of current star-formation occurring in this object. This object has an intriguingly broad HI line width (FWHM 155 km s^-1) given its luminosity and compared to the other edge-on objects in the sample.