The Fourstar Galaxy Evolution Survey (ZFOURGE) was conducted using the FourStar imager (Persson et al. 2013) on the 6.5m Magellan Baade telescope at Las Campanas Observatory. The use of medium-band filters in the near-IR (van Dokkum et al. 2009) allows for accurate sampling at wavelengths that bracket the Balmer break of galaxies leading to more well-constrained photometric redshifts at 1 < z < 4 than with broadband filters alone. In conjunction with existing optical through mid-IR photometry, this dataset provides a comprehensive sampling of the 0.3 – 8 micron spectral energy distribution of galaxies.
ZFOURGE is composed of three 11′ x 11′ pointings with coverage in the CDFS (Giacconi et al. 2002), COSMOS (Capak et al. (2007) and UDS (Lawrence et al. 2007). The 5sigma depth in a circular aperture of D=0.6” in the Ks band is 26.2-26.5 in the CDFS, COSMOS and UDS fields respectively at a typical seeing of ~0.4″. For more information regarding ZFOURGE consult Straatman et al. (2016).
5 sigma AB magnitude depths (CDFS, COSMOS, UDS; D=0.6” apertures)
| J1 | 25.6 | 26.0 | 25.6 |
| J2 | 25.5 | 26.0 | 25.9 |
| J3 | 25.5 | 25.7 | 25.6 |
| Hs | 24.9 | 25.1 | 25.1 |
| Hl | 25.0 | 24.9 | 25.2 |
| Ks | 26.2-26.5 | 25.5 | 25.7 |
Ks depths correspond to a co-addition of the Fourstar imaging with public Ks-band imaging.
| [Field] | [Coordinates] | [Total Survey Area] | [Number of Objects] | [Kband FWHM] |
|---|---|---|---|---|
| CDFS | [03 32 27, -27 45 52] | [128 sq. arcmin] | [30911] | [0.46”] |
| COSMOS | [10 00 31, +02 17 03] | [135 sq. arcmin] | [20786] | [0.47”] |
| UDS | [02 17 15, -05 11 53] | [189 sq. arcmin] | [22093] | [0.44”] |
- Comparison of secure spectroscopic redshifts from the literature to photometric redshifts across all three pointings in ZFOURGE. Top: of the 1,526 sources compared, we find a NMAD scatter in ∆z/(1 +zspec) of 0.10 with about 3% of sources at ∆z/(1 + zspec) > 0.15. Bottom: the residual between the spectroscopic and photometric redshifts, divided by 1+zspec. The red solid, dashed and dotted lines indicate, respectively, ∆z/(1 + zspec) = 0 ± 0, ± 0.05, and ± 0.15.
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- Completeness corrected number counts for each field observed with ZFOURGE. Sources with < 80% completeness are shown with open symbols. We recover at least 80% down to very deep Ks-band magnitudes of 25.4 − 25.9 and 50% down to 25.6 − 26.2. For comparison, the Ks-band completeness corrected number counts of similar galaxy surveys are indicated in grayscale.
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- Three different redshift quality tests, σz from testing against spectroscopic samples, σz,pairs from a redshift pair test (Quadri et al., 2010) for sources with Ks < 23.5 AB mag, and the photometric redshift uncertainty from the p(z) from EAZY, σz,EAZY . These correspond well at all redshifts, indicating excellent redshift accuracies for ZFOURGE: 1 − 2%.
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- The benefit of using medium bandwidth filters in the near-IR on photometric redshift accuracy. σz, derived from a redshift pair test, is clearly smaller if the near-IR medium band filters are used (compared to near-IR broadband), especially at 1.5 < z < 2.5.
