The sample of normal galaxies

**Figure 1:** Distribution of the normal galaxies included in this Guide, in celestial coordinates on an equal-area display. The dotted grid represents the Galactic coordinate system. As expected, most UV observations of normal galaxies concentrate at high Galactic latitudes.
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The catalog of normal galaxies here presented includes 274 galaxies distributed over the sky. The distribution is shown in Figure 1. This large collection of data, resulting from many individual research projects, does not constitute a homogeneous sample. The total B magnitude ${B_{T}}$ (Figure 2) spans a relative wide range (from 6 to 19 mag), with a mean value of 12.5 and a peak between 13-15 mag, confirming that very few faint galaxies were observed by IUE.

**Figure 2:** Distribution of total B-band magnitudes for the galaxies included in this Guide.
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The sample contains galaxies of all the morphological types, from ellipticals to irregulars (Figure 3). The elliptical galaxies, some of which are intrinsically strong UV emitters due to the the UV-upturn phenomenon, represent about one-quarter of the total number of the galaxies in this sample. Figure 3 shows the distribution of galaxies as a function of the continuous T-type morphological parameter. The objects were binned according to their morphological classes: E, E-S0, S0, S0a, Sa, Sab, Sb, Sbc, Sc, Scd, Sd, Sm, Irr.

**Figure 3:** Distribution of morphological T-types of galaxies included in this Guide. The T-types are adopted from LEDA.
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The distribution of galaxies with redshift is shown in Figure 4. It is clear that IUE observed normal galaxies only in the very nearby Universe.

**Figure 4:** Distribution of galaxies included in this Guide vs. redshift.
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Many of the galaxies observed by IUE are extended objects with respect to the large aperture of the spectrograh. The large IUE apertures are 10" $\times$ 20" and oval-like, each corresponding to the area of a circular diaphragm having a diameter of 15.1 arcsec (Longo & Capaccioli 1992). In order to estimate the fraction of the galaxy area observed by IUE, we calculated for each galaxy the ``coverage parameter'' C, defined as the logarithmic ratio between the surface area of the galaxy and the area of the large IUE aperture.

Here D $_{25}$ and R $_{25}$ are the major axis and the axial ratio of the optical image of the galaxy as listed in LEDA, in units of arcsec. The numerator approximates the surface area of the galaxy, represented as an ellipse with the major and minor axes of the galaxy.

A C-value of zero implies that the entire galaxy was measured by in the IUE spectrum. The distribution of galaxies as a function of the C parameter is shown in Figure 5 . For 17 faint galaxies, where the axes are not measurable and which are not shown in Figure 5, the C parameter is $\leq 0$ . For $90 \%$ of the sample, the IUE aperture covered less than the $10 \%$ of the galaxy.

**Figure 5:** Distribution of the logarithmic coverage factor for galaxies included in this Guide. A value of unity implies that only 10% of the galaxy was actually measured by IUE. In most cases, IUE sampled a region that was 1% to 0.1% of the target galaxy area.
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Figure 6 shows the number of available spectra per galaxy. For 40% of the galaxies included in this Guide to Normal Galaxies only one spectrum, either SW or LW, was obtained. A few galaxies were observed extensively. Among those are the starburst galaxies NGC 4449, NGC 5253, and NGC 5236.

**Figure 6:** Number of spectra available in INES for each galaxy included in this Guide.
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Figure 7 shows the number of galaxies in our sample as a function of the observation date of the two spectra included here. The distribution indicates two periods of enhanced interest in UV spectra of galaxies. From the launch of IUE to the mid-80s there was presumably a learning period of UV properties of galaxies, when many objects were observed. After this, the exploitation of IUE began in earnest. The peak in 1994-5 was probably due to ``last-minute'' observations, prior to the closing of the IUE Observatory.

**Figure 7:** IUE observations of normal galaxies vs. the years of observation.
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In conclusion, the IUE data set for normal galaxies represents mostly a sample of UV spectra of the innermost regions of bright nearby galaxies.