THE MOSDEF SURVEY: EXCITATION PROPERTIES OF z ∼ 2.3 STAR-FORMING GALAXIES

By A. Shapley, Naveen A. Reddy, M. Kriek, William Robert Freeman, R. Sanders, B. Siana, A. Coil, B. Mobasher, I. Shivaei, S. Price and 1 more. 2014

140 citations recorded by the source corpus.

We present results on the excitation properties of z ∼ 2.3 galaxies using early observations from the MOSFIRE Deep Evolution Field (MOSDEF) Survey. With its coverage of the full suite of strong rest-frame optical emission lines, MOSDEF provides an unprecedented view of the rest-frame optical spectra of a representative sample of distant star-forming galaxies. We investigate the locations of z ∼ 2.3 MOSDEF galaxies in multiple emission-line diagnostic diagrams. These include the [O iii]λ5007/Hβ vs. [N ii]/Hα and [O iii]λ5007/Hβ vs. [S ii]λλ6717, 6731/Hα “BPT” diagrams, as well as the O32 vs. R23 excitation diagram. We recover the well-known offset in the star-forming sequence of high-redshift galaxies in the [O iii]λ5007/Hβ vs. [N ii]/Hα BPT diagram relative to Sloan Digital Sky Survey star-forming galaxies. However, the shift for our rest-frame optically selected sample is less significant than for rest-frame-UV selected and emission-line selected galaxies at z ∼ 2. Furthermore, we find that the offset is mass-dependent, only appearing within the low-mass half of the z ∼ 2.3 MOSDEF sample, where galaxies are shifted toward higher [N ii]/Hα at fixed [O iii]/Hβ. Within the [O iii]λ5007/Hβ vs. [S ii]/Hα and O32 vs. R23 diagrams, we find that z ∼ 2.3 galaxies are distributed like local ones, and therefore attribute the shift in the [O iii]λ5007/Hβ vs. [N ii]/Hα BPT diagram to elevated N/O abundance ratios among lower-mass ( M * < 10 10 M ⊙ ?> ) high-redshift galaxies. The variation in N/O ratios calls into question the use at high redshift of oxygen abundance indicators based on nitrogen lines, but the apparent invariance with redshift of the excitation sequence in the O32 vs. R23 diagram paves the way for using the combination of O32 and R23 as an unbiased metallicity indicator over a wide range in redshift. This indicator will allow for an accurate characterization of the shape and normalization of the mass–metallicity relationship over more than 10 Gyr.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

View Paper: https://www.semanticscholar.org/paper/717168221ffeb7d6ae74341d1c9e7275e6a25ba5

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. P. V. van Dokkum
2. P. Hopkins
3. L. Hernquist
4. C. Conroy
5. M. Franx
6. R. Dav'e
7. A. Dekel
8. T. Naab

In Electrical and Electronic Engineering

1. P. Oesch
2. G. Illingworth
3. M. Franx
4. M. Trenti
5. P. V. van Dokkum
6. M. Stiavelli
7. C. Carollo
8. S. Charlot

In Instrumentation

1. P. V. van Dokkum
2. M. Franx
3. C. Conroy
4. P. Hopkins
5. L. Hernquist
6. I. Labbé
7. A. Dekel
8. A. Shapley

Citations in the corpus

• THE GRISM LENS-AMPLIFIED SURVEY FROM SPACE (GLASS). I. SURVEY OVERVIEW AND FIRST DATA RELEASE (2015, background): “Alternatively, recent work has shown that N-based indicators could be biased tracers of oxygen (Amorín et al. 2010; Andrews & Martini 2013; Masters et al. 2014; Shapley et al. 2015).”
• Chemical abundances in high-redshift galaxies: a powerful new emission line diagnostic (2016, methodology): “Both of these authors interpret this result in terms of an enhanced population of Wolf-Rayet stars at high redshift, leading to an enhancement in the relative N abundance, and a much hotter ionising spectrum (modelled by Shapley et al. (2015) as a hot Black Body).”
• SDSS IV MaNGA – spatially resolved diagnostic diagrams: a proof that many galaxies are LIERs (2016, methodology): “…lines in the BPT diagrams have been the main classification tool to distinguish star formation from other sources of ionisation in several studies based on the SDSS and more distant galaxy samples (Kauffmann et al. 2003b; Tremonti et al. 2004; Kewley et al. 2006, 2013; Shapley et al. 2015).”
• The SINS/zC-SINF Survey of z ∼ 2 Galaxy Kinematics: SINFONI Adaptive Optics–assisted Data and Kiloparsec-scale Emission-line Properties (2018, background): “…ratio, as amply discussed in the literature 5 (e.g., Kewley & Dopita 2002; Kewley et al. 2013; Pérez-Montero & Contini 2009; Yuan et al. 2012; Andrews & Martini 2013; Steidel et al. 2014; Shapley et al. 2015; Sanders et al. 2015, 2017; Kashino et al. 2017; Strom et al. 2017; Cresci et al. 2017).”
• RECONCILING THE STELLAR AND NEBULAR SPECTRA OF HIGH-REDSHIFT GALAXIES (2016, background): “Anomalously high N/O at a given O/H has been advocated as the primary driver of the N2 BPT “offset” (Masters et al. Stellar and Nebular Spectra at z∼ 2.4 27 2014; Shapley et al. 2015; Sanders et al. 2015; Jones et al. 2015).”
• Modelling the nebular emission from primeval to present-day star-forming galaxies (2016, background): “…of H ii regions and galaxies in the nearby Universe, which increasingly appear as inappropriate to study the star formation and ISM conditions of chemically young galaxies (e.g., Erb et al. 2010; Steidel et al. 2014, 2016; Shapley et al. 2015; see also Brinchmann et al. 2008; Shirazi et al. 2014).”
• Nebular Emission Line Ratios in z ≃ 2–3 Star-forming Galaxies with KBSS-MOSFIRE: Exploring the Impact of Ionization, Excitation, and Nitrogen-to-Oxygen Ratio (2016, methodology): “…dex larger values of log(N/O) with respect to SDSS galaxies matched in O32 and R23 (as described in §5.3), consistent with the results reported by Shapley et al. (2015) for z ∼ 2 MOSDEF galaxies, but we argue that samples matched in O32 and R23 are more likely to share ionizing radiation fields…”
• SDSS-IV MaNGA : the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements (2016, background): “A higher N/O abundance has been claimed to explain the offset in the BPT Diagram (Masters et al. 2014, Shapley et al. 2015, Sanders et al. 2016).”
• FORMING COMPACT MASSIVE GALAXIES (2015, background): “Although this limit is observed to be higher atz& 2 (e.g., Brinchmann, Pettini, & Charlot 2008; Steidel et al. 2014; Shapley et al. 2015), values of [NII ]/Hα> 1 are extreme at any redshift (see, e.g., Leja et al. 2013b; Shapley et al. 2015).”
• THE MOSDEF SURVEY: ELECTRON DENSITY AND IONIZATION PARAMETER AT z ∼ 2.3 (2015, methodology): “…al. 2013a), systematically harder ionizing spectra (Steidel et al. 2014), higher ionization parameters (Brinchmann et al. 2008), or an enhancement in the N/O ratio (Masters et al. 2014; Shapley et al. 2015) in high-redshift galaxies in comparison to what is typically observed in the local universe.”