A European Southern Observatory Very Large Telescope Survey of Near‐Infrared (Z≤ 25) Selected Galaxies at Redshifts 4.5 <z< 6: Constraining the Cosmic Star Formation Rate near the Reionization Epoch

Abstract

We present the results of a Very Large Telescope (VLT) and Hubble Space Telescope imaging survey aimed at the identification of 4:5 < z < 6 galaxies. In the VLT data, a set of broadband and intermediate-band filters has been used to select 13 high-z candidates in a Z AB 25 mag catalog, over an area of about 30 arcmin 2 . Discrimination against lower redshift interlopers (mainly early-type galaxies at high redshift and cool Galactic stars) has been done combining morphological and spectral classification. This sample has been combined with a deeper I AB 27:2 mag sample obtained from the Hubble Deep Field (HDF) campaigns. The VLT final sample consists of 13 high-z candidates, four of which are identified with high confidence as z > 4:5 galaxies. The resulting integral surface density of the Z AB < 25 candidates at z > 4:5 is in the range 0.13-0.44 arcmin À2 , and that in the highest redshift bin 5 < z 6 is between 0.07 and 0.13 arcmin À2 . In the two HDFs, we identify 25 galaxies at I AB 27:2 in the range 4:5 z < 5 and 16 at 5 z 6, corresponding to surface densities of 3.1 and 2 arcmin À2 , respectively. We show that the observed Z AB < 25 UV luminosity density (LD) appears to drop by about 1 order of magnitude from z ' 3 to 6. However, if we apply a threshold to obtain an absolute magnitude-limited sample, the UV LD is roughly constant up to z ' 6. We finally show that recent semianalytic hierarchical models for galaxy formation, while predicting a nearly constant total UV LD up to z ' 6, underpredict the observed UV LD at Z AB 25 and overpredict the I AB 27:2 one. This behavior can be understood in terms of a poor match to the slope of the UV luminosity function.

The bright end of thez ~ 7UVluminosity function from a wide and deep HAWK-I survey

“…Here we present the analysis of two other pointings ( Fig. 1), chosen for the wealth of deep, public observations previously exploited by other authors to search for z ∼ 4−6 LBGs: the BDF field at RA = 336.98 • , Dec = −35.17 • (Lehnert & Bremer 2003), and the New Technology Telescope Deep Field (NTTDF) at RA = 181.36 • , Dec = −7.72 • (Arnouts et al 1999;Fontana et al 2000Fontana et al , 2003. The total exposure time is 15h49m for BDF and 15h03m for the NTTDF in the Y band.…”

“…Along with the main Y-band pointings, we also acquired deep J and Ks Hawk-I observations of both fields. We also obtained ∼7 h of FORS2 Z-band coverage for each field, which we coadded with the already existing FORS2 images (Fontana et al 2003) to reach the required depth. We also re-reduced the archive U, B, V, R, I FORS2 and FORS1 observations of the NTTDF, and the FORS2 R and I images of the BDF.…”

Hubble Space TelescopeImaging and Keck Spectroscopy ofz≈ 6i‐Band Dropout Galaxies in the Advanced Camera for Surveys GOODS Fields

“…Other determinations have been recalculated for our cosmology and higher SFR limit of 15 h À2 70 M yr À1 (instead of 1.5 M yr À1 for Steidel et al 1999), assuming a slope of ¼ À1:6 for z > 2 and ¼ À1:3 for z < 2. Data from the Canada-France Redshift Survey of Lilly et al (1996) are shown by open circles; data from Connolly et al (1997) are squares; and the LBG work of Steidel et al (1999) is plotted by crosses, of Bouwens et al (2003b) by pentagons, of Fontana et al (2003) by inverted triangles, and of Iwata et al (2003) by an open diamond. The three estimates of Bouwens et al (2003a) are shown by crossed circles and indicate three different completeness corrections for one sample of objects (see discussion in x 5.5).…”

“…Fontana et al (2003) presented a sample of z > 4:5 candidates selected at z 0 AB < 25:0 from imaging with the Very Large Telescope (VLT). They find 13 high-redshift candidates, including four in their highest redshift bin of 5 < z < 6 in a total area of 29.9 arcmin 2 , and observe an order-of-magnitude decrease in the UV density between z $ 4:5 and z $ 6.…”

“…This is a relatively small survey, and the authors note significant variance between their two survey fields. In Figure 9 we show star formation densities derived using our prescription from the UV luminosity densities reported by Fontana et al (2003) for their magnitude-limited ''minimal'' sample of objects, which they are confident lie at high redshift. As can be seen, their results are in good agreement with our own although based on very small numbers of objects.…”