PHYSICAL PROPERTIES OF EMISSION-LINE GALAXIES AT z ∼ 2 FROM NEAR-INFRARED SPECTROSCOPY WITH MAGELLAN FIRE

By D. Masters, P. McCarthy, B. Siana, M. Malkan, B. Mobasher, H. Atek, A. Henry, Crystal L. Martin, M. Rafelski, Nimish Hathi and 9 more. 2014

141 citations recorded by the source corpus.

We present results from near-infrared spectroscopy of 26 emission-line galaxies at z ∼ 2.2 and z ∼ 1.5 obtained with the Folded-port InfraRed Echellette (FIRE) spectrometer on the 6.5 m Magellan Baade telescope. The sample was selected from the WFC3 Infrared Spectroscopic Parallels survey, which uses the near-infrared grism of the Hubble Space Telescope Wide Field Camera 3 (WFC3) to detect emission-line galaxies over 0.3 ≲ z ≲ 2.3. Our FIRE follow-up spectroscopy (R ∼ 5000) over 1.0–2.5 μm permits detailed measurements of the physical properties of the z ∼ 2 emission-line galaxies. Dust-corrected star formation rates for the sample range from ∼5–100 M☉ yr−1 with a mean of 29 M☉ yr−1. We derive a median metallicity for the sample of 12 + log(O/H) = 8.34 or ∼0.45 Z☉. The estimated stellar masses range from ∼108.5–109.5 M☉, and a clear positive correlation between metallicity and stellar mass is observed. The average ionization parameter measured for the sample, log U ≈ −2.5, is significantly higher than what is found for most star-forming galaxies in the local universe, but similar to the values found for other star-forming galaxies at high redshift. We derive composite spectra from the FIRE sample, from which we measure typical nebular electron densities of ∼100–400 cm−3. Based on the location of the galaxies and composite spectra on diagnostic diagrams, we do not find evidence for significant active galactic nucleus activity in the sample. Most of the galaxies, as well as the composites, are offset diagram toward higher [O iii]/Hβ at a given [N ii]/Hα, in agreement with other observations of z ≳ 1 star-forming galaxies, but composite spectra derived from the sample do not show an appreciable offset from the local star-forming sequence on the [O iii]/Hβ versus [S ii]/Hα diagram. We infer a high nitrogen-to-oxygen abundance ratio from the composite spectrum, which may contribute to the offset of the high-redshift galaxies from the local star-forming sequence in the [O iii]/Hβ versus [N ii]/Hα diagram. We speculate that the elevated nitrogen abundance could result from substantial numbers of Wolf–Rayet stars in starbursting galaxies at z ∼ 2.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0c8d5bf28d10bdc5b0fb93ac49517a128a71b43b

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Citations in the corpus

STRONG NEBULAR LINE RATIOS IN THE SPECTRA of z ∼ 2–3 STAR FORMING GALAXIES: FIRST RESULTS FROM KBSS-MOSFIRE (2014, background): “…low-redshift star-forming galaxies; • shallower dependence of (N/O) on (O/H) than is typically inferred for galaxies in the local universe, with (N/O) close to the solar value over the full range of inferred (O/H) (see also Masters et al. 2014, which independently reached a similar conclusion).”
THE MOSDEF SURVEY: MASS, METALLICITY, AND STAR-FORMATION RATE AT z ∼ 2.3 (2014, background): “There is mounting evidence in the literature that high-redshift star-forming galaxies have markedly different emission line ratios from those of local starforming galaxies (Shapley et al. 2005; Liu et al. 2008; Hainline et al. 2009; Masters et al. 2014; Steidel et al. 2014).”
ZFIRE: THE KINEMATICS OF STAR-FORMING GALAXIES AS A FUNCTION OF ENVIRONMENT AT z ∼ 2 (2016, methodology): “We also use σint since it can be measured for all galaxies, even those with unresolved rotation, and is robust against PSF effects. σint could trace rotation, velocity dispersion, or a combination of both quantities (Glazebrook 2013; Barro et al. 2014; Masters et al. 2014).”
Chemical abundances in high-redshift galaxies: a powerful new emission line diagnostic (2016, methodology): “Recently Masters et al. (2014) used the Magellan FIRE instrument to observe a sample of z ∼ 2 galaxies in which all of the important diagnostic lines are observed, and Shapley et al. (2015) has extended this sample using galaxies drawn from the MOSFIRE Deep Evolution Field (MOSDEF) Survey.”
Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: physical properties and implications for studies at z > 7 (2014, background): “…development is the discovery of a substantial population ofz ≃ 1.5 − 2 low mass star forming galaxies with very large (200-1000̊A) rest-frame optical emission lines (e.g., Atek et al. 2011, van der Wel et al. 2011, Maseda et al. 2013, Masters et al. 2014, Amorı́n et al. 2014, Atek et al. 2014b).”
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).”
THE MOSDEF SURVEY: EXCITATION PROPERTIES OF z ∼ 2.3 STAR-FORMING GALAXIES (2014, background): “Finally, both Masters et al. (2014) and Steidel et al. (2014) consider gas-phase abundance ratios – specifically, the N/O ratio – which can affect where galaxies fall in the O3N2 BPT diagram.”
THE MOSDEF SURVEY: ELECTRON DENSITY AND IONIZATION PARAMETER AT z ∼ 2.3 (2015, background): “…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.”
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).”
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): “Although the existence of an offset in the N2-BPT plane has been widely reported for other samples of high-redshift galaxies (Masters et al. 2014; Shapley et al. 2015; Sanders et al. 2016), the degree to which the KBSS-MOSFIRE sample differs from typical local galaxies is quite remarkable.”