Direct Oxygen Abundances for Low-Luminosity LVL Galaxies

Abstract

We present MMT spectroscopic observations of H II regions in 42 low luminosity galaxies in the Spitzer Local Volume Legacy (LVL) survey. For 31 of the 42 galaxies in our sample, we were able to measure the temperature sensitive [O III] λ4363 line at a strength of 4σ or greater, and thus determine oxygen abundances using the "direct" method. Our results provide the first "direct" estimates of oxygen abundance for 19 of these galaxies. "Direct" oxygen abundances were compared to B -band luminosities, 4.5 µm luminosities, and stellar masses in order to characterize the luminosity-metallicity and mass-metallicity relationships at low-luminosity.We present and analyze a "Combined Select" sample composed of 38 objects (drawn from a sub-set of our parent sample and the literature) with "direct" oxygen abundances and reliable distance determinations (based on the tip of the red giant branch or Cepheid variables). Consistent with previous studies, the B-band and 4.5 µm luminosity-metallicity relationships for the 38 objects were found to be 12 + log (O/H) = (6.27±0.21)+(−0.11±0.01)M B and 12 + log(O/H) = (6.10±0.21)+(−0.10±0.01)M [4.5] † Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. arXiv:1205.6782v1 [astro-ph.CO] 30 May 2012 Low-Luminosity LVL SampleWe selected a sample of 42 low luminosity galaxies in the LVL survey in order to obtain new MMT high-resolution spectra. These low luminosity spirals and dwarf irregulars span a range in distance of 2.5 ≤ D ≤ 14.0 Mpc 2 . The luminosities for this sample range in the near-IR (determined from IRAC (Fazio et al. 2004) photometry) from M [4.5] = −13.1 to −21.7, with B -band magnitudes of −10.8 ≥ M B ≥ −18.8. Most of the objects were chosen because they lack "direct" oxygen abundances in the literature, their abundance estimates are dated, or were studied with instruments which were known to have problems.Although not LVL objects, two additional galaxies were added to the sample (increasing the sample total to 44 objects) because they played a role in motivating this project. Both UGC 4393 and UGC 10818 were identified by Engelbracht et al. (2008) as low metallicity outliers from the global trend of 70/160 µm color temperature as a function of metallicity. These two galaxies affect the interpretation of the trend for aromatic emission to weaken below 12 + log(O/H) = 7.9 in the mid-IR (see e.g., Engelbracht et al. 2008) and the far-IR (see e.g., Draine et al. 2007;Engelbracht et al. 2008).

New candidates for extremely metal-poor emission-line galaxies in the SDSS/BOSS DR10

“…We also show the XMD emission-line galaxies with 12 + log O/H ≤ 7.35 by and Izotov et al (2012) in small red filled circles. The small open squares in magenta, green, and blue are the data derived by Berg et al (2012), Pustilnik et al (2011), andJames et al (2015), respectively (see text). The most-metal deficient BCDs I Zw 18, SBS 0335-052W, and SBS 0335-052E are shown with filled blue triangles and are labelled.…”

“…The position of all XMD candidates from this paper and from and Izotov et al (2012) are also plotted. Berg et al (2012) studied a sample of 42 low-luminosity galaxies aiming to fill the relatively sparse low-luminosity end of the relation with intrinsically faint galaxies. For comparison we show their data in small open squares in magenta.…”

“…Pustilnik et al 2005;Izotov et al 2006b;Guseva et al 2007;Pustilnik et al 2011;Izotov et al 2012;Berg et al 2012). More than ten galaxies with 12 + log O/H ≤ 7.35 were found among the galaxies from the Sloan Digital Sky Survey data release 7 (SDSS DR7; Izotov et al 2012).…”

Study of the Lynx-Cancer void galaxies. – V. The extremely isolated galaxy UGC 4722

“…In particular, we compare their metallicities with that expected from the relation derived for the Local Volume dwarfs with well-known distances and O/H by Berg et al (2012). The scatter in this relation is quite small, σ (O/H) =0.15 dex.…”

The slow flow model of dust efflux in local star-forming galaxies

“…The heavy element content of star-forming galaxies is characterized by a strong relation between the stellar mass and average gas-phase oxygen abundance (Lequeux et al 1979;Tremonti et al 2004). This so-called mass-metallicity relation (MZR) extends to low stellar mass galaxies (∼ 10 7 M⊙ Lee et al 2006;Zahid et al 2012a;Berg et al 2012) and is observed at intermediate (Savaglio et al 2005;Cowie & Barger 2008;Zahid et al 2011;Moustakas et al 2011;Zahid et al 2013a) and high redshifts (Erb et al 2006;Mannucci et al 2009;Laskar et al 2011). The metallicity at all stellar masses increases with time and the high mass end of the relation flattens at late times as galaxies enrich to an empirical upper limit in the gas-phase abundance (Zahid et al 2013a).…”