Local Analogs for High-redshift Galaxies: Resembling the Physical Conditions of the Interstellar Medium in High-redshift Galaxies

TL;DR

This study identifies local galaxy analogs with interstellar medium conditions similar to high-redshift galaxies, providing insights into galaxy evolution by comparing physical properties across different cosmic epochs.

Contribution

The paper introduces a new selection method for local analogs that resemble high-redshift galaxies in their ISM conditions, expanding the tools for studying early galaxy formation.

Findings

Local analogs have similar ionization parameters and electron densities to $z\sim2-3$ galaxies.

The mass-metallicity relation in analogs shows a -0.2 dex offset, consistent with high-redshift galaxies.

Analog properties differ from other known analogs like LBAs and GPs in specific ISM parameters.

Abstract

We present a sample of local analogs for high-redshift galaxies selected in the Sloan Digital Sky Survey (SDSS). The physical conditions of the interstellar medium (ISM) in these local analogs resemble those in high-redshift galaxies. These galaxies are selected based on their positions in the [OIII]/H$\beta$ versus [NII]/H$\alpha$ nebular emission-line diagnostic diagram. We show that these local analogs share similar physical properties with high-redshift galaxies, including high specific star formation rates (sSFRs), flat UV continuums and compact galaxy sizes. In particular, the ionization parameters and electron densities in these analogs are comparable to those in $z\simeq2-3$ galaxies, but higher than those in normal SDSS galaxies by $\simeq$0.6~dex and $\simeq$0.9~dex, respectively. The mass-metallicity relation (MZR) in these local analogs shows $-0.2$~dex offset from that in SDSS star-forming galaxies at the low mass end, which is consistent with the MZR of the $z\sim2-3$ galaxies. We compare the local analogs in this study with those in other studies, including Lyman break analogs (LBA) and green pea (GP) galaxies. The analogs in this study share a similar star formation surface density with LBAs, but the ionization parameters and electron densities in our analogs are higher than those in LBAs by factors of 1.5 and 3, respectively. The analogs in this study have comparable ionization parameter and electron density to the GP galaxies, but our method can select galaxies in a wider redshift range. We find the high sSFR and SFR surface density can increase the electron density and ionization parameters, but still cannot fully explain the difference in ISM condition between nearby galaxies and the local analogs/high-redshift galaxies.