A sample of metal-poor galaxies identified from the LAMOST spectral survey

Abstract

We present a sample of 48 metal-poor galaxies at z < 0.14 selected from 92,510 galaxies in the LAMOST survey. These galaxies are identified for their detection of the auroral emission line [O III]λ4363 above 3σ level, which allows a direct measurement of the electron temperature and the oxygen abundance. The emission line fluxes are corrected for internal dust extinction using Balmer decrement method. With electron temperature derived from [O III]λλ4959, 5007/[O III]λ4363 and electron density from [S II]λ6731/[S II]λ6717, we obtain the oxygen abundances in our sample which range from 12 + log(O/H) = 7.63 (0.09 Z ⊙ ) to 8.46 (0.6 Z ⊙ ). We find an extremely metal-poor galaxy with 12 + log(O/H) = 7.63 ± 0.01. With multiband photometric data from FUV to NIR and Hα measurements, we also determine the stellar masses and star formation rates, based on the spectral energy distribution fitting and Hα luminosity, respectively. We find that our galaxies have low and intermediate stellar masses with 6.39 ≤ log(M/M ⊙ ) ≤ 9.27, and high star formation rates (SFRs) with −2.18 ≤ log(SFR/M ⊙ yr −1 ) ≤ 1.95. We also find that the metallicities of our galaxies are consistent with the local T e -based mass-metallicity relation, while the scatter is about 0.28 dex. Additionally, assuming the coefficient of α = 0.66, we find most of our galaxies follow the local mass-metallicity-SFR relation, while a scatter about 0.24 dex exists, suggesting the mass-metallicity relation is weakly dependent on SFR for those metal-poor galaxies.

What Determines the Local Metallicity of Galaxies: Global Stellar Mass, Local Stellar Mass Surface Density, or Star Formation Rate?

“…Density And Metallicity The global stellar mass -metallicity relation and stellar mass -metallicity -SFR relation have been investigated for decades (e.g. Tremonti et al 2004;Mannucci et al 2010;Gao et al 2017). Previous works suppress the scatter in MZR by introducing the global SFR, finding that at a certain stellar mass, the metallicity scales up remarkably when the stellar mass increases, and scales down slightly when the SFR increases.…”

Strong [OIII]λ5007 emission line compact galaxies in LAMOST DR9: Blueberries, Green Peas and Purple Grapes

“…In this work, 21 galaxies whose specific flux of the [OIII]λ4363 emission lines are above 8.85 × 10 38 erg/s/ Å are used to test the direct T e -based method to calculate the electron temperature and the metallicity referring to Izotov et al (2006) Section 3.1 and Jiang et al (2019). The purpose of this discussion is to show that we have detected the auroral [OIII]λ4363 emission line, which increases the samples of detections in LAMOST (Gao et al 2017), and to demonstrate the current N2-based empirical metallicity relation and direct T e -based metallicity relation in Jiang et al (2019) are in agreement within 1−σ level.…”

“…Then we demonstrate the mass-metallicity relation of 252 sources that have Starlight-derived mass and the N2-based metallicity. Furthermore, we discuss the gas-phase metallicity calculated from the empirical N2-based method and the direct T e -based method with 21 galaxies whose specific flux of the [OIII]λ4363 emission lines are above 8.85 × 10 38 erg/s/ Å, where the detection of [OIII]λ4364 is rare (Gao et al 2017).…”

Sub-galactic scaling relations with T$_{\rm e}$-based metallicity of low metallicity regions in galaxies: metal-poor gas inflow may have important effects?

“…Following the procedure of Gao et al (2017), we use the STARLIGHT software 3 (Cid Fernandes et al 2005) to obtain the best-fit stellar continua, which are then subtracted from the observed spectra. The fitting is based on the built-in stellar library (Bruzual & Charlot 2003) of STARLIGHT and a Chabrier (2003) initial mass function (IMF).…”