The spatial clustering of mid-IR selected star forming galaxies at z ∼1 in the GOODS fields

Abstract

We present the first spatial clustering measurements of z ~ 1, 24 μm-selected, star forming galaxies in the Great Observatories Origins Deep Survey (GOODS). The sample under investigation includes 495 objects in GOODS-South and 811 objects in GOODS-North selected down to flux densities of f_(24) > 20 μJy and z_(AB) < 23.5 mag, for which spectroscopic redshifts are available. The median redshift, IR luminosity and star formation rate (SFR) of the sample are z ~ 0.8, L_(IR) ~ 4.4 × 10^(10) L_☉, and SFR ~ 7.6 M_☉ yr^(−1), respectively. We measure the projected correlation function w(r_p) on scales of r_p = 0.06−10 h^(−1) Mpc, from which we derive a best fit comoving correlation length of r_0 = 4.0 ± 0.4 h^(−1) Mpc and slope of γ = 1.5 ± 0.1 for the whole f_(24) > 20 μJy sample after combining the two fields. We find indications of a larger correlation length for objects of higher luminosity, with Luminous Infrared Galaxies (LIRGs, L_(IR) > 10^(11) L_☉) reaching r_0 ~ 5.1 h^(−1) Mpc. This would imply that galaxies with larger SFRs are hosted in progressively more massive halos, reaching minimum halo masses of ~3 × 10^(12) M_☉ for LIRGs.We compare our measurements with the predictions from semi-analytic models based on the Millennium simulation. The variance in the models is used to estimate the errors in our GOODS clustering measurements, which are dominated by cosmic variance. The measurements from the two GOODS fields are found to be consistent within the errors. On scales of the GOODS fields, the real sources appear more strongly clustered than objects in the Millennium-simulation based catalogs, if the selection function is applied consistently. This suggests that star formation at z ~ 0.5−1 is being hosted in more massive halos and denser environments than currently predicted by galaxy formation models. Mid-IR selected sources appear also to be more strongly clustered than optically selected ones at similar redshifts in deep surveys like the DEEP2 Galaxy Redshift Survey and the VIMOS-VLT Deep Survey (VVDS), although the significance of this result is ≲3σ when accounting for cosmic variance. We find that LIRGs at z ~ 1 are consistent with being the direct descendants of Lyman Break Galaxies and UV-selected galaxies at z ~ 2−3, both in term of number densities and clustering properties, which would suggest long lasting star-formation activity in galaxies over cosmological timescales. The local descendants of z ~ 0.5−1 star forming galaxies are not luminous IR galaxies but are more likely to be normal, L < L_∗ ellipticals and bright spirals.

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