3 The catalog

3.1 Short description

In the following a sample page of the catalog is given. A short description of the entries in the catalog is given below. Detailed information on the listed properties of the detected galaxies and/or an assessment of the quality of the presented data is presented in the following subsections. A table listing the possible IRAS galaxies is given in Sect. 3.3.
Column 1: RKK running number of the detected 3279 galaxies and galaxy candidates, ordered in Right Ascension (1950.0).
Column 2: Second name.
Column 3: Codes for identifications with objects in the IRAS PSC within a radius of 2 arcmin. The entries signify certain identification (I), possible identification (P), questionable identification (Q) and no credible cross-identification (N).
Columns 4 and 5: Right Ascension and Declination (1950.0).
Columns 6 and 7: Galactic longitude and latitude.
Column 8: Field number of the ESO/SRC Survey on which the galaxy was detected.
Columns 9 and 10: X- and Y-coordinate in mm as measured from the center of the field listed in Col. 8.
Column 11: Large and small diameter $D \times d$ in arcsec.
Column 12: Apparent magnitude $B_{\rm _{\rm J}}$.
Column 13: Galactic reddening based on the DIRBE/IRAS extinction maps (Schlegel et al. 1998).
Column 14: Morphological type including codes with regard to uncertainty of the identification, the orientation and superimposed stars.
Column 15: Descriptive remarks.

3.2 Second names

Most of the second identifications given in Col. 2 of Table 1 originate from the ESO/Uppsala Survey of the ESO(B) Atlas (Lauberts 1982), recognisable as "L'' plus the respective field and running number. After closer inspection, a number of Lauberts galaxies turned out to be two individual galaxies. The Lauberts identification is then given in both case. L126-9 = RKK1251 & RKK1253, corresponding to ESO-LV 126-0090 and ESO-LV 126-0091 in the ESO-LV Catalog (Lauberts & Valentijn 1989). Four galaxies abbreviated as FGCE# are listed in the Flat Galaxy Catalog (Karenchentsev et al. 1993), two in the Arp Madore (1987) Catalog (marked as AM), two in the Parkes-MIT-NRAO 5 GHz Radio Survey (Wright et al. 1994, code PMN), and one in the Catalog of Southern Ring Galaxies (Buta 1995).

  

Table 1: Galaxies in the southern ZOA - I. The Hydra/Antlia extension

97 galaxies (3%) were previously identified by Lauberts (1982), of which four each have two counterparts in the here presented catalog. Including the overlaps in the above mentioned catalogs 112 have entries in earlier optical catalogs (3.4%) and 3167 are newly identified galaxies.

3.3 IRAS identifications

The IRAS PSC (Joint IRAS Science Working Group 1988) has been used extensively for studies of the large-scale structures in the Universe. It is therefore of interest to identify IRAS counterparts of the here uncovered galaxies.

IRAS sources were searched in a radius of 2 arcmin around the optical galaxies. This led to 227 coincidences in the IRAS PSC. In a second step, the possible matches were investigated individually, taking into account
(a) the positional offset between galaxy and IRAS source in combination with the IRAS position uncertainty ellipses
(b) the colors as deduced from the different IRAS wavebands, such as $col_1 = f_{12} \cdot f_{25} /(f_{60})^2$ and col₂ = f₁₀₀/f₆₀,
(c) coincidences with other astronomical objects and their respective colors or color expectation values.

We more or less adopted the selection criteria used by Yamada et al. (1993) in their search for IRAS galaxy candidates in the ZOA as being characteristic of IRAS galaxies, i.e., col₁ < 1 and 0.8 < col₂ < 5. However, neither a lower limit for the $60~\mu$ flux was imposed (0.6 Jy in Yamada et al. 1993), nor a flux quality restriction. Depending on the probability of the cross-identification being correct, the following categories were defined (denoted as such in Col. 3 of Table 1): I: high-certainty identification with IRAS PSC object;

P: possible match in the IRAS PSC, but either the f₆₀ flux was only a lower limit, the separation with regard to the uncertainty ellipse relatively large, or the colors col₁ or col₂ atypical for galaxies;

U: an unlikely cross-identification because of large positional offset and/or unlikely IRAS-colors;

N: the cross-identification is not accepted as credible because of the large positional offset and the unlikely colors and, in addition, that the identification with another object is more likely. If this concerns another galaxy, it is marked as NG (20 cases) in Table 1, if a star as NS (10 cases). If a number is added to the code I, P or Q (e.g., Q2, I3), this number indicates the equally possible galaxy counterparts for a given IRAS source.

Overall, 135 certain IRAS galaxies were identified. For 6 of these sources, two galaxies are equally likely to be the counterpart of the IRAS source (marked as I2), and in 2 cases three galaxies (I3) could match the optical identification, leading to a total of 145 galaxy counterparts for the 135 certain IRAS sources.

The number of galaxies with certain IRAS PSC cross-identification is reduced to 87 (91 galaxies, 87 IRAS sources), if - as in most IRAS color-selected galaxy searches - a strict lower limit for the flux density at $60~\mu$m of f₆₀ = 0.6 Jy is demanded, as well as high flux quality at 60 $\mu$, i.e., Q₆₀=3.

Surprisingly, only 66 IRAS sources were identified by Yamada et al. (1993) in their ZOA IRAS galaxy survey, leaving 22 IRAS galaxies (25%) unaccounted for. Of these, 7 comply with all selection criteria set out by Yamada, hence it is not clear why these IRAS galaxies were missed. The remaining 15 have a high ratio of f₁₀₀ / f₆₀ > 5, though they are bonafida galaxies. Yamada et al. noted already that color-selected, "blind'' IRAS galaxy samples are incomplete because of the f₁₀₀/f₆₀ upper limit restriction which was implemented to avoid the contamination by Galactic cirrus. Overall, the IRAS PSC traces a population of large and bright galaxies (see Woudt 1998, for further details). Nevertheless, "blind'' IRAS galaxy searches apparently miss a significant fraction of nearby galaxies.

There are 21 possible cross-identifications in the IRAS PSC (one with two possible galaxy counterparts) and 27 questionable cross-identifications (3 with two likely galaxy counterparts).

In Table 2, the certain (I and I2 or I3), the possible (P or P2), and questionable (Q and Q2) IRAS sources in the Hydra/Antlia deep optical galaxy catalog are listed with their optical and IRAS properties. The unlikely cross-identifications (NG and NS) are marked in Table 1 but not entered in the IRAS table.

The entries in Table 2 are as follows:
Column 1: Identification in the IRAS Point Source Catalog. If the IRAS name is followed by "Y'', it is also in the IRAS galaxy list of Yamada et al. (1993), if followed by a "*'', it satisfies all the Yamada et al. selection criteria, but is not listed there.
Column 2: Quality parameter of the IRAS PSC cross-identification, I, P and Q as explained above. If followed by a number, the latter indicates the equally likely galaxy counterparts for a given IRAS source.
Column 3: The RKK identification number as in the optical galaxy catalog (Table 1). The "L'' signifies whether this is also a Lauberts galaxy.
Columns 4 - 10: As Cols. 4-7, 11, 12 and 14 of Table 1.
Column 11: Angular separation in arcsec between the optical position (Cols. 4 and 5) and the position given in the IRAS PSC.
Columns 12 - 15: The flux densities at 12 $\mu$m, 25 $\mu$m, 60 $\mu$m, respectively 100 $\mu$m.
Column 16: The IRAS flux qualities at 12 $\mu$m, 25 $\mu$m, 60 $\mu$m, and 100 $\mu$m, where "1'' indicates a lower limit, "2'' an uncertain flux, and "3'' a good flux quality.
Columns 17 - 18: The IRAS colors $col_1 = f_{12} \cdot f_{25} /(f_{60})^2$ and col₂ = f₁₀₀/f₆₀.

  

Table 2: IRAS galaxies in the Hydra/Antlia ZOA region

 

Table 2: continued

 

Table 2: continued

   
3.4 Quality of optical parameters

To assess the quality of the listed positions, diameters and magnitudes, whose derivations are discussed in the following sections, comparisons with three independent samples were made.

The first is an internal consistency check. A generous overlap on the borders of adjacent fields led to independent values for parameters of a given galaxy. In the Hydra/Antlia ZOA survey region, 146 galaxies were found on the borders of two up to four different ESO/SRC survey fields.

A further comparison was made for galaxies in common with "The Surface Photometry Catalogue of the ESO-Uppsala Galaxies'' (Lauberts & Valentijn 1989), henceforth the ESO-LV catalog. Although the ESO-LV catalog generally avoided the ESO/SRC fields close to the Galactic Plane ( ), some exceptions were made. This resulted in an overlap with our survey of the fields F91, F92 and F126 on which we have 49 (12, 14, and 23) of the brighter galaxies in common.

For the field F213 centered at RA = $10^{\rm h} 00^{\rm m}$, Dec = $-50{^\circ}$(1950.0), $\ell = 277\hbox{$.\!\!^\circ$ }3, b = 4\hbox{$.\!\!^\circ$ }0$, MacGillivray used COSMOS to extract the galaxy parameters at the positions of the galaxies identified by us. 330 galaxies are listed in the optical catalog for F213. However, a third of these lie outside the central $5{^\circ}$ $\times$$5{^\circ}$ area of the field, hence have no COSMOS parameters. For 20% of the galaxies within the $5{^\circ}$ $\times$ $5{^\circ}$ boundaries, COSMOS extracted two galaxy candidates at the position of the visually identified galaxy. In general, the parameters of only "one'' of the candidates - sometimes none - matched the actual galaxy. For another 8% of the galaxies, the parameters such as diameters and magnitudes diverged strongly from the visually determined values. After careful inspection on the sky survey plate, it was clear that the superposition of stars on the galaxy images generally caused the confusion: a star superimposed on the border of a galaxy image resulted in a smaller galaxy, stars superimposed more centrally on a galaxy could result in the breaking up of one galaxy into various "COSMOS galaxies''. Quite often the fainter outer parts of LSB spiral were not recognised as being part of a galaxy, and parts of a spiral arms sometimes were lost. About 4% of the galaxies were - for no obvious reasons - not recovered at all by COSMOS.

The above comparison stresses the inherent difficulties in achieving a high success rate of the galaxy identification procedure from automated extraction algorithms at low Galactic latitudes and in obtaining reliable data. Still, the parameters of 186 galaxies could be used for our comparative purposes.

3.5 Positional accuracy of coordinates

The X and Y measurements listed in Cols. 9 and 10 are offsets with respect to the center of the field identified in Col. 8, i.e., the field on which the galaxy was first identified in the course of the galaxy search. This therefore is not necessarily identical to the field on which that galaxy would belong based on its coordinates and the optimal survey fields. Positive X-values indicate increasing RA, negative X-values decreasing RA. Positive Y-values point north, negative values south of the field center.

The positions of the galaxies as well as up to 30 standard stars per field were measured with the measuring machine Optronics at the ESO in Garching (one advantage of working in the ZOA is the availability of numerous standard stars). Fitting a polynomial to the X- and Y-measurements of the standards stars resulted in an rms of the star positions of 0.3 - 0.5 arcsec. For galaxies this precision can not be achieved due to the uncertainties in the determination (by eye) of the center of the extended galaxy images. As this is straightforward for small galaxies, the positions of smaller galaxies generally are of better precision.

Comparing the positions of galaxies derived from the borders of neighboring fields (generally the lowest precision cases) did reveal minor systematic offsets of typically $0 - 1.5\hbox{$^{\prime\prime}$ }$ in RA or Dec with a dispersion of $\sigma = 2\hbox{$^{\prime\prime}$ }$. A comparison of our positions with COSMOS positions for the 186 galaxies in common on field 213 revealed similar trends (offsets in RA and Dec of 2 $\hbox{$^{\prime\prime}$ }$, $\sigma=1\hbox{$.\!\!^{\prime\prime}$ }5$). Positions of ESO-LV galaxies show no offset but a dispersion of 4 $\hbox{$^{\prime\prime}$ }$ compared to the Optronics positions. Taking the quoted error of 3 $\hbox{$^{\prime\prime}$ }$ for the positions in the ESO-LV catalog into account, the 1 $\hbox{$^{\prime\prime}$ }$ for COSMOS, as well as our internal consistency, together indicate that the in Table 1 listed galaxy positions have an accuracy of about 1 arcsec.

The positions of a few galaxies are of lower precision as they were not derived with the measuring machine Optronics. These are marked with a colon following the equatorial coordinates in Cols. 4 and 5 of Table 1.

3.6 Large and small diameters

A comparison of galaxy diameters based on the COSMOS and ESO-LV overlaps, shows a linear correlation with decreasing scatter towards smaller galaxies. On average the present diameters are 10% smaller compared to the COSMOS and ESO-LV values suggesting that the listed diameters correspond approximately to the isophote of 24.5 mag/arcsec² (compared to 25.0 mag/arcsec² of COSMOS and ESO-LV).

An internal consistency check of diameters measured on different plates reveals an error of the order of $1\hbox{$^{\prime\prime}$ }$, while the deviations for the galaxies in common with COSMOS are lower and with ESO-LV slightly higher ( $\varepsilon=0\hbox{$.\!\!^{\prime\prime}$ }3$, respectively $\varepsilon=1\hbox{$.\!\!^{\prime\prime}$ }5$).

In the surveyed region, 103 galaxies have - according to our determinations - a major diameter of $D \ge 60\hbox{$^{\prime\prime}$ }$, i.e., the Lauberts (1982) diameter limit. Of the 97 galaxies identified by Lauberts in the Hydra/Antlia survey region (of which 4 are double systems), 25 actually are smaller than 60 $\hbox{$^{\prime\prime}$ }$, leaving 76 galaxies above the Lauberts diameter limit of $D = 60\hbox{$^{\prime\prime}$ }$. A comparison with the here identified 103 galaxies with $D \ge 60\hbox{$^{\prime\prime}$ }$ hence indicates that 27 galaxies (26%) were missed by Lauberts. These statistics improve somewhat in favor of the Lauberts catalog for galaxies larger than $1\hbox{$.\mkern-4mu^\prime$ }35$, the diameter limit for which the Lauberts catalog is claimed to be complete (Hudson & Lynden-Bell 1991). Still, 5 (of the 49) galaxies larger than $1\hbox{$.\mkern-4mu^\prime$ }35$ have not been identified by Lauberts.

3.7 Apparent magnitude $B_{\rm J}$

Using a KODAK Photographic Step Tablet (exposed and processed acetate photographic silver density film) of 21 steps as a comparison scale (from 0.05 to 3.05 in increments of 0.15 in density), the average surface density (blackness) of each galaxy was determined. The surface densities SD of the two 7-step wedges on the survey fields were determined as well. Applying the log relative intensity scale as given in the UK Schmidt Telescope Handbook (1980) to the step wedges leads to surface density vs. log intensity calibrations of the form:

$$\log ({ I}) = C_1 \cdot SD + C_2.$$ (1)

This relation was found to be linear in the surface density range of the galaxies (density steps 10 - 16.5, cf., Fig. 1.1 in Woudt 1998, Vol. II).

Combining the dimensions of the galaxy (in arcsec) with the relative intensity scale leads to a relative magnitude $B_{\rm J}$ estimate via the equation

$${ B}_{\rm J} = { C_3} - 2.5 \cdot (\log (\pi \cdot { (D/2)} \cdot { (d/2)}) + \log ({ I})). \\$$ (2)

The resulting isophotal magnitudes were then calibrated using the 49 galaxies in common with the ESO-LV catalog (Lauberts & Valentijn 1989), leading to a value of the constant C₃ of

$${ C_3} = 26\hbox{$.\!\!^{\rm m}$ }4.$$ (3)

The here derived magnitude estimates compare best with the B₂₅ of the ESO-LV: as illustrated in the left panel of Fig. 3, no deviation from linearity is observed over the common magnitude range ( $13\hbox{$.\!\!^{\rm m}$ }0 - 17\hbox{$.\!\!^{\rm m}$ }0$), and a surprisingly low dispersion of 1 $\sigma = 0\hbox{$.\!\!^{\rm m}$ }46$.

Figure 3: Comparison of the estimated magnitudes ${B_{\rm J}^{\rm KK}}$ with the 49 galaxies in common with the ESO-LV catalog (left), the 186 galaxies on field 213 in common with COSMOS (middle), and the 146 independent magnitude estimates from the borders of neighbouring fields. For the uncalibrated COSMOS magnitudes a zeropoint correction of $\Delta { B_{\rm J}^{\rm COS}} = +0\hbox{$.\!\!^{\rm m}$ }25$ was applied

A comparison with the COSMOS magnitudes for the 186 galaxies on field 213 is displayed in the middle panel of Fig. 3). As the COSMOS magnitudes were not calibrated a zeropoint correction of $\Delta { B_{\rm J}^{\rm COS}} = +0\hbox{$.\!\!^{\rm m}$ }25$ had to be applied. With the zeropoint set, a linear relationship up to the faintest magnitudes of ${B}_{\rm J} = 19\hbox{$.\!\!^{\rm m}$ }5$ was found with a dispersion of $1\sigma = 0\hbox{$.\!\!^{\rm m}$ }47$

To check the internal consistency, a comparison was made for galaxies found on borders of adjacent fields. Even though measurements on the plate borders are the least reliable, the magnitudes scatter with a dispersion of $\sigma = 0\hbox{$.\!\!^{\rm m}$ }33$ only and show no systematic offsets (right panel of Fig. 3).

Hence, we conclude that our eye-estimates yield magnitudes with no deviations from linearity from the brightest to the faintest galaxies, with a 1$\sigma$ dispersion of $0\hbox{$.\!\!^{\rm m}$ }5$.

3.8 Column 13: Galactic reddening

Column 13 lists the Galactic reddening at the position of the galaxy as given by the DIRBE/IRAS extinction maps (Schlegel et al. 1998). Based on CCD photometry and measurements of the Mg₂-index of 18 early type galaxies at low Galactic latitudes, Woudt (1998) has tested the calibration of the DIRBE/IRAS extinction maps. He found that the extinction for moderate to high DIRBE/IRAS reddenings is systematically underestimated by a factor of f=0.86. As his new calibration so far is based on a small sample of galaxies only which do not cover a substantial fraction of the southern ZOA, we have at this point of time not adopted his correction for this suggested underestimation.

3.9 Column 14: Morphological classification

The morphological types are coded similarly to the precepts of the RC2 (de Vaucouleurs et al. 1976). Due to the varying foreground extinction a homogenous and detailed type classification could not always be accomplished and some codes were added. In the first column, a question mark denotes the uncertainty about the galaxian nature of the object. In the second column, the code F for the Hubble type E-S0 (T=-3in the RC2 classification) was added to the normal designations of E, L, S and I. In the fourth column the subtypes E, M and L are introduced next to the general subtypes 0 to 9. They stand for early spiral (S0/a-Sab), middle spiral (Sb-Sd) and late spiral or irregular (Sdm-Im). The cruder subtypes are a direct indication of the fewer details visible on the obscured galaxy image. The questionmark at the end marks uncertainty of the main type, the colon uncertainty in the subtype. The third column (o) marks the orientation of the galaxy: E, N, F, V stands for edge-on, nearly edge-on, face-on and nearly face-on. The fourth subcolumn (*) indicates the superposition of a single star (1) or multiple stars (S) on the galaxy.

The mixture of galaxy types in our survey - (E-SO: S-I: unclassified) = (11% : 60% : 29%) - is consistent with most optical surveys.

3.10 Column 15: Descriptive remarks

In general, the remarks and abbreviations of Col. 15 are self explanatory. The most common abbreviations are:

* or **	star or stars;
asym.	asymmetric;
blg	bulge;
br.	bright; to indicate bright bulges, nearby or superimposed bright stars or bright bulges;
cl.to br. *	close to bright star;
dbl	double;
diff.	diffuse;
dist.	distinct;
HSB	extremely high surface brightness;
i.a.w.	interacting with; close pair of galaxies which display disturbances in the image or light bridges between the galaxies.
LSB	low surface brightness galaxy. Also vLSB for very low surface brightness, and vvLSB for galaxies just barely visible against the sky background;
neb?	nebula?
neighb. of	neighbor of a listed galaxy. In general, these galaxies are below the diameter limit of $D= 13\hbox{$^{\prime\prime}$ }$ but close to a catalogued galaxy and possibly associated with the named neighbor;

PN	Planetary Nebula;
p.cov.by *	partly covered by star;
poss.larger	possibly larger;
s.p.	superimposed (generally used to note superimposed star or stars on the galaxy image;
sp.	spiral (e.g. spiral arm);
struct.	structure;
in st.diff.pat.	galaxy lies within a stellar diffraction pattern, i.e., generally on darkened background;
trpl syst	triple system, generally followed by the identification of the other members;
v.	very;
v.obs.	very obscured;
vLSB	see LSB;
vvLSB	see LSB;
w.	with;
w.comp.	with companion: a small galaxy, below the diameter limit of the catalog in the vicinity of the galaxy. The companion was not entered into the catalog (contrarily to neighbors, cf. above);
w.sev.comp.	with several companions. Same as w.comp., two or more nearby small galaxies were seen.