Multi-Wavelength Study of a Complete IRAC 3.6micron-Selected Galaxy Sample: a Fair Census of Red and Blue Populations at Redshifts 0.4-1

TL;DR

This study uses multi-wavelength data to analyze a galaxy sample at redshifts 0.4-1, revealing that massive quiescent galaxies existed by z≈1 and lower mass galaxies stopped forming stars later.

Contribution

It introduces a new multi-wavelength approach combined with neural network photometric redshifts to study galaxy populations at intermediate redshifts.

Findings

Massive quiescent galaxies are already in place by z≈1.

Lower mass galaxies tend to cease star formation at later times.

The photometric redshift errors are well-characterized with a standard deviation of ~0.025(1+z).

Abstract

We present a multi-wavelength study of a 3.6 $\mu$m-selected galaxy sample in the Extended Groth strip. The sample is complete for galaxies with stellar mass $>10^{9.5}$ \Msun and redshift $0.4<z<1.2$. In this redshift range, the IRAC 3.6 $\mu$m band measures the rest-frame near-infrared band, permitting nearly unbiased selection with respect to both quiescent and star-forming galaxies. The numerous spectroscopic redshifts available in the EGS are used to train an Artificial Neural Network to estimate photometric redshifts. The distribution of photometric redshift errors is Gaussian with standard deviation ${\sim}0.025(1+z)$, and the fraction of redshift failures (${>}3\sigma$ errors) is about 3.5%. A new method of validation based on pair statistics confirms the estimate of standard deviation even for galaxies lacking spectroscopic redshifts. Basic galaxy properties measured include rest-frame $U-B$ colors, $B$- and $K$-band absolute magnitudes, and stellar masses. We divide the sample into quiescent and star-forming galaxies according to their rest-frame $U-B$ colors and 24 to 3.6 \micron\ flux density ratios and derive rest $K$-band luminosity functions and stellar mass functions for quiescent, star forming, and all galaxies. The results show that massive, quiescent galaxies were in place by $z\approx1$, but lower mass galaxies generally ceased their star formation at later epochs.