Bright galaxy sample in the Kilo-Degree Survey Data Release 4

Abstract

We present a bright galaxy sample with accurate and precise photometric redshifts (photo-zs), selected using ugriZYJHKs photometry from the Kilo-Degree Survey (KiDS) Data Release 4. The highly pure and complete dataset is flux-limited at r < 20 mag, covers ∼1000 deg2, and contains about 1 million galaxies after artifact masking. We exploit the overlap with Galaxy And Mass Assembly spectroscopy as calibration to determine photo-zs with the supervised machine learning neural network algorithm implemented in the ANNz2 software. The photo-zs have a mean error of |⟨δz⟩|∼5 × 10−4 and low scatter (scaled mean absolute deviation of ∼0.018(1 + z)); they are both practically independent of the r-band magnitude and photo-z at 0.05 < zphot < 0.5. Combined with the 9-band photometry, these allow us to estimate robust absolute magnitudes and stellar masses for the full sample. As a demonstration of the usefulness of these data, we split the dataset into red and blue galaxies, used them as lenses, and measured the weak gravitational lensing signal around them for five stellar mass bins. We fit a halo model to these high-precision measurements to constrain the stellar-mass–halo-mass relations for blue and red galaxies. We find that for high stellar mass (M⋆ > 5 × 1011 M⊙), the red galaxies occupy dark matter halos that are much more massive than those occupied by blue galaxies with the same stellar mass.

Galaxy And Mass Assembly (GAMA): Data Release 4 and the z < 0.1 total and z < 0.08 morphological galaxy stellar mass functions

“…3.4). We note however, that the accuracy of these redshifts is surpassed by those recently presented for the KiDS-bright sample (Bilicki et al 2021) using ANNz, where SMAD and mean[(1 + z) −1 ∆z] values of 0.0180 and 0.00012 respectively were achieved.…”

Around the Spindle Galaxy: The Dark Halo Mass of NGC 3115

“…Generally, the available data on the motions of faint satellites around isolated high-luminosity galaxies definitely indicate a (2-3)-fold excess of dark matter around bulge-dominated galaxies compared to disk-dominated ones of the same stellar mass. This conclusion is consistent with the assertions: "we find that passive central galaxies have halos that are at least twice massive as those of star-forming objects of the same stellar mass" (Mandelbaum et al 2016) and "the red galaxies occupy dark matter halos that are much more massive that those occupied by blue galaxies with the same stellar mass" (Bilicki et al 2021), both obtained from the weak gravitational lensing data. Despite the limited statistics, there is also a noticeable tendency according to which the variation in the ratio of darkto-light matter (M T /M * ) in late-type galaxies is much wider than in early-type galaxies.…”

“…In addition to the dependence on the mass (luminosity) of a galaxy, the ratio M T /M * also depends on its morphological type. Spiral galaxies of type Milky Way and M 31 have an M T /M * ∼ 25, while early-type (ET) galaxies with dominant bulges are characterized by an M T /M * ratio that is 2-3 times higher (Karachentseva et al 2011;Mandelbaum et al 2016;Bilicki et al 2021). This difference may be due to the fact that star formation in disk-dominated galaxies occurs fairly evenly throughout the entire cosmological scale of 13.8 Gyr, while the main (violent) formation of stars in E and S0 galaxies ended in an early epoch, almost ceasing in the last 10 Gyr.…”

The halo model with beyond-linear halo bias: unbiasing cosmological constraints from galaxy-galaxy lensing and clustering

“…In this work we forecast the impact of including a beyond-linear halo bias correction 𝛽 NL for a galaxy clustering sample similar to the bright galaxy sample in the Kilo-Degree Survey Data Release 4 (Bilicki et al 2021). This sample is flux-limited at 𝑟 < 20 mag and contains approximately 1 million galaxies with a mean redshift of 0.23.…”