The sharp rise in the number of galaxies seen at faint magnitudes in the ultraviolet and blue has been investigated for over 20 years (c.f. reviews by Ellis 1997, and Koo and Kron 1992). To address this problem several large redshift surveys have been conducted using various selection techniques, multi-colour photometry and high-quality spectroscopic observations. These surveys have given a number of significant results:

1. The redshift distribution is dominated by intermediate redshift galaxies to B < 24 – therefore, no large population of ultra-luminous, high redshift galaxies has been detected.
2. The luminosity function of star-forming (i.e. blue) galaxies evolves significantly from intermediate redshift to z ~ 0, although the exact nature of this evolution has not yet been firmly established (c.f. Sullivan et al. 2000, Cowie et al. 1999, Lilly et al. 1995 (CFRS-VI)).
3. The fraction of galaxies exhibiting strong emission lines increases at intermediate redshift compared to magnitude-limited local samples (c.f. Tresse et al. 1999, Tresse et al. 1996 (CFRS-XII), Broadhurst et al. 1988 (BES)).

The "sub-survey" discussed here selected candidates from one field, SA 68 (0.21 deg²), of the KPGRS (Munn et al., 1997). The "sub-survey" is 91% complete for blue galaxies, defined as having U-R_F < 1, fainter than B_J<21.5.

Although not as deep as some other galaxy redshift surveys (e.g. CFRS, Autofib), this survey has the advantage of selecting the galaxies undergoing the most intense star-formation (similar to the UV 2000Å selected survey of Sullivan et al. 2000). The observed U-R_F selection for this sample was chosen because galaxies with spectral energy distributions similar to local galaxies remain above or below U-R_F = 1 to approximately a redshift of 0.6 (Smetanka 1997). Thus, this survey targets the population of galaxies observed to be undergoing the strongest evolution at intermediate redshifts (c.f. Figure 1, Lin et al. 1999, CFRS-VI).

Table 1 summarizes the colour-selected sample showing spectroscopic completeness (percent of sample redshift determination), total completeness (percent of all blue galaxies in SA68 with redshift determination) and the redshift distribution.

This sub-survey is particularly targeted at the galaxies from z = 0 to z = 0.6 that show evidence for intense star-formation activity. Figure 1 shows the correlation between U-R_F color and the equivalent width of [OII] l 3727 for (a) the late type galaxies in Kennicutt (1992) and (b) the galaxies in the KPGRS. Note that the vast majority of galaxies with strong emission-lines have

U - R_F < 1.

The rest-frame color-magnitude diagram for KPGRS galaxies (including the colour-selected sub-survey) with 20 < B_J < 21.5 is shown in figure 2. Notice that ALL the galaxies with M(B_J) < -18 have rest-frame and observed frame U - R_F < 1. This diagram is consistent with a steep rise in the faint end of the blue galaxy luminosity function (a Schechter function with a < -1.25) in contrast to locally-derived galaxy luminosity functions with a flat faint-end (a ~ -1.0). This result is consistent with the luminosity function found in UV and U surveys of Sullivan et al. (2000) and Liu et al. (1998).

Figure 3 shows the distribution of the equivalent width of [OII], l 3727, (W₃₇₂₇) for 26 galaxies with measurable [OII], magnitudes between 20 < B_J < 21.5 and absolute magnitudes between

-21 < M(B_J) < -20 corresponding to a redshift interval from 0.2 < z < 0.4. This same interval has shown that significant evolution is needed to explain comparisons with local galaxies (c.f. Tresse et al. 1999, CFRS-XII, BES). The dashed line indicates a constructed representation of the local W₃₇₂₇ distribution by using Sc galaxy spectra (assumed to be 85% of the local blue galaxies) and non-Seyfert, Markarian galaxy spectra (assumed to be the remaining 15% of the local blue galaxies). All local data is taken from Kennicutt (1992).

Line-ratio diagnostics provide an invaluable tool in attempting to understand the physical processes responsible for the emission-line observed in various extra-galactic objects (Baldwin et al. 1981, Osterbrock and Veilleux 1987). This has been applied to faint galaxies spectroscopically observed in various redshift surveys (c.f. Sullivan et al. 2000, Tresse et al. 1999, Hammer et al. (CFRS-XIV), Smetanka 1997, CFRS-XII). The line-ratio diagnostic diagram for galaxies in the colour-selected sub-survey is shown in Figure 4. These fluxes have been uncorrected for reddening. Reddening will tend to shift individual points to the right on the diagram. However, since Ha is not available for most of the spectra, reddening cannot be independently determined. The line on the diagram shows the trend observed by Baldwin et al. (1981) for spectra resulting from ionization by hot stars. A representative one-sigma error bar is also shown.

Assuming an extinction curve characteristic of local star-burst galaxies (Gordon et al. 1997), points on the diagram will shift approximately 0.3 to the right. Even with this shift, we do not find strong evidence that AGN contribute significantly to the ionizing flux present in these galaxies. Although this statement is primarily due to the uncertainty associated with the data, the galaxies SED derived from broad-band colours supports this conclusion. Specifically, the colours (using our UB_JR_FI_N photometry) of the galaxies in the most extreme portion of this diagram are not distinguishable from the colours of the galaxies definitely in the regime of HII galaxies. This gives further support that non-thermal radiation sources are not needed to explain the emission.

Relative oxygen abundance, [O/H], calculated using the flux ratio R₂₃ (the sum of [OII]₃₇₂₇ and [OIII]_{4959, 5007} to Hb , calibrated by Zaritsky, Kennicutt & Huchra, 1994), can be used to estimate the metalicity of the galaxies in this sample. Figure 5 shows the correlation between [O/H] and M(B_J) for the sample. Galaxies at z > 0.3 are shown as solid circles. The dashed-line shows the correlation between luminosity and [Fe/H] observed for elliptical galaxies (Brodie & Huchra, 1991). If, for instance, the more luminous blue galaxies at intermediate redshift are a result of the temporary brightening of lower luminosity – typically lower metalicity – systems (c.f. BES) we should see these systems in the lower left-hand side of the diagram. Notice two systems fall in this category and both are at z > 0.3, indicating that a small fraction of z > 0.3 star-forming galaxies (<10%) may fall into this category.

Following Couch and Sharples (1987) and BES, we construct a composite spectra from 8 galaxies selected to be representative of all blue galaxies with 20 < B_J < 21.5 and -21 < M(B_J) < -20 again corresponding to a redshift range of 0.2 < z < 0.4. These 8 galaxies were selected solely based on the S/N of their spectra taking care that they spanned the W₃₇₂₇ distribution. Figure 6 shows the comparison of this composite spectrum with three types of local star-forming galaxy spectra from Kennicutt (1992). Panel (a) shows the composite spectrum from this survey (solid line) compared to the composite spectrum of 4 "global starburst" galaxies (dotted line). Panel (b) shows this composite spectrum compared to the composite spectrum of 4 "nuclear starburst" galaxies and panel (c) compares it with the composite spectrum of 4 Sc galaxies. All spectra have been normalized so fl =1 at l =4500Å.

Note that the comparison with the Sc spectrum results in the best fit to both the continuum and observed absorption features. The intense star formation characteristics of local "global starbursts" yields a much bluer continuum than the galaxies used to construct the composite spectrum. Either the 0.2 < z < 0.4 galaxies are reddened significantly more than local galaxies or the star formation rate is closer to local Sc galaxies than local "global starburst" galaxies.

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¹Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.