Galaxies selected on the basis of their emission line strength show low metallicities , regardless of their redshifts .
We conclude this from a sample of faint galaxies at redshifts between 0.6 < z < 2.4 , selected by their prominent emission lines in low-resolution grism spectra in the optical with the Advanced Camera for Surveys ( ACS ) on the Hubble Space Telescope ( HST ) and in the near-infrared using Wide-Field Camera 3 ( WFC3 ) .
Using a sample of 11 emission line galaxies ( ELGs ) at 0.6 < z < 2.4 with luminosities of -22 \lesssim M _ { B } \lesssim - 19 which have [ OII ] , H \beta , and [ OIII ] line flux measurements from the combination of two grism spectral surveys , we use the R 23 method to derive the gas-phase oxygen abundances : 7.5 < 12+log ( O/H ) < 8.5 .
The galaxy stellar masses are derived using Bayesian based Markov Chain Monte Carlo ( \pi MC ^ { 2 } ) fitting of their Spectral Energy Distribution ( SED ) , and span the mass range 8.1 < log ( M _ { * } / M _ { \odot } ) < 10.1 .
These galaxies show a mass-metallicity ( M-L ) and Luminosity-Metallicity ( L-Z ) relation , which is offset by –0.6 dex in metallicity at given absolute magnitude and stellar mass relative to the local SDSS galaxies , as well as continuum selected DEEP2 samples at similar redshifts .
The emission-line selected galaxies most resemble the local “ green peas ” galaxies and Lyman-alpha galaxies at z \simeq 0.3 and z \simeq 2.3 in the M-Z and L-Z relations and their morphologies .
The G - M _ { 20 } morphology analysis shows that 10 out of 11 show disturbed morphology , even as the star-forming regions are compact .
These galaxies may be intrinsically metal poor , being at early stages of formation , or the low metallicities may be due to gas infall and accretion due to mergers .