REST-FRAME OPTICAL SPECTRA OF THREE STRONGLY LENSED GALAXIES AT z ∼ 2

By K. Hainline, A. Shapley, K. Kornei, M. Pettini, Elizabeth Buckley-Geer, Sahar Allam, Douglas L. Tucker. 2009

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We present Keck II NIRSPEC rest-frame optical spectra for three recently discovered lensed galaxies: the Cosmic Horseshoe (z = 2.38), the Clone (z = 2.00), and SDSS J090122.37+181432.3 (z = 2.26). The boost in signal-to-noise ratio (S/N) from gravitational lensing provides an unusually detailed view of the physical conditions in these objects. A full complement of high S/N rest-frame optical emission lines is measured, spanning from rest frame 3600 to 6800 Å, including robust detections of fainter lines such as Hγ, [S ii]λ6717,6732, and in one instance [Ne iii]λ3869. SDSS J090122.37+181432.3 shows evidence for active galactic nucleus activity, and therefore we focus our analysis on star-forming regions in the Cosmic Horseshoe and the Clone. For these two objects, we estimate a wide range of physical properties. Current lensing models for the Cosmic Horseshoe and the Clone allow us to correct the measured Hα luminosity and calculated star formation rate. Metallicities have been estimated with a variety of indicators, which span a range of values of 12+ log(O/H) = 8.3–8.8, between ∼0.4 and ∼1.5 of the solar oxygen abundance. Dynamical masses were computed from the Hα velocity dispersions and measured half-light radii of the reconstructed sources. A comparison of the Balmer lines enabled measurement of dust reddening coefficients. Variations in the line ratios between the different lensed images are also observed, indicating that the spectra are probing different regions of the lensed galaxies. In all respects, the lensed objects appear fairly typical of ultraviolet-selected star-forming galaxies at z ∼ 2. The Clone occupies a position on the emission-line diagnostic diagram of [O iii]/Hβ versus [N ii]/Hα that is offset from the locations of z ∼ 0 galaxies. Our new NIRSPEC measurements may provide quantitative insights into why high-redshift objects display such properties. From the [S ii] line ratio, high electron densities (∼1000 cm−3) are inferred compared to local galaxies, and [O iii]/[O ii] line ratios indicate higher ionization parameters compared to the local population. Building on previous similar results at z ∼ 2, these measurements provide further evidence (at high S/N) that star-forming regions are significantly different in high-redshift galaxies, compared to their local counterparts.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/19e0a4fc9498886ce50783f0fd1a7f05bb35552a

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1. P. Hopkins
2. L. Hernquist
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4. C. Conroy
5. A. Shapley
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7. Naveen A. Reddy
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Citations in the corpus

• Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: physical properties and implications for studies at z > 7 (2014, methodology): “Stellar population ages must be considerably lower and ionisation parameters somewhat larger than are commonly inferred for more massive star forming systems at highredshift (e.g., Hainline et al. 2009, Richard et al. 2011a, Reddy et al. 2012).”
• 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).”
• THE MOSDEF SURVEY: EXCITATION PROPERTIES OF z ∼ 2.3 STAR-FORMING GALAXIES (2014, result): “As noted by Nakajima et al. (2013) and Hainline et al. (2009), the sample of z ≥ 2 galaxies with O32 and R23 measurements tends to exhibit systematically higher O32 values than the bulk of SDSS galaxies, implying higher ionization parameters on average.”
• THE MOSDEF SURVEY: ELECTRON DENSITY AND IONIZATION PARAMETER AT z ∼ 2.3 (2015, background): “Estimates of the electron density at z ∼ 2 have suggested that densities in high-redshift star-forming regions are significantly higher than what is typically observed locally (Hainline et al. 2009; Lehnert et al. 2009; Bian et al. 2010; Shirazi et al. 2014).”
• Spectroscopic detection of C iv λ1548 in a galaxy at z = 7.045: implications for the ionizing spectra of reionization-era galaxies (2015, background): “In high redshift galaxies, observations indicate [CIII]λ1907/CIII]1909 flux ratios in the range 1.2-1.6 (Hainline et al. 2009; James et al. 2014).”
• Spectroscopic detections of C iii] λ1909 Å at z ≃ 6–7: a new probe of early star-forming galaxies and cosmic reionization (2014, background): “Over the range of gas densities typical in high redshift star forming galaxies (102 cm−3 and 104 cm−3; e.g., Hainline et al. 2009; James et al. 2014), the [CIII]λ1907/CIII]λ1909 ratio varies between 1.6 and 1.2 respectively.”
• Modelling the nebular emission from primeval to present-day star-forming galaxies (2016, background): “Near-infrared spectroscopy enables such studies in the optical rest frame of galaxies out to redshifts z ∼ 1– 3 (e.g., Pettini & Pagel 2004; Hainline et al. 2009; Richard et al. 2011; Guaita et al. 2013; Steidel et al. 2014; Shapley et al. 2015).”
• A NEW DIAGNOSTIC OF ACTIVE GALACTIC NUCLEI: REVEALING HIGHLY ABSORBED SYSTEMS AT REDSHIFT >0.3 (2011, background): “Some attributed this trend to varying HII region conditions (Liu et al. 2008; Brinchmann et al. 2008; Hainline et al. 2009) while others claim that additional AGN contribution may be the driving factor (Groves et al. 2006; Wright et al. 2010).”
• SDSS-IV MaNGA : the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements (2016, unknown): “2006; Liu et al. 2008; Brinchmann et al. 2008; Hainline et al. 2009; Wright et al. 2010; Trump et al. 2011 Kewley et al. 2013a,b; Steidel et al. 2014).”
• PHYSICAL CONDITIONS IN A YOUNG, UNREDDENED, LOW-METALLICITY GALAXY AT HIGH REDSHIFT (2010, methodology): “…than the ionization parameters inferred for more typical z ∼ 2 galaxies (which are in turn higher than those inferred for local starforming galaxies); for example, Hainline et al. (2009) use the [O III]/[O II] ratio of two lensed and apparently representative z ∼ 2 galaxies to infer logU ∼ −2.5.”
• Ionization state of inter-stellar medium in galaxies: evolution, SFR-M * -Z dependence, and ionizing photon escape (2013, background): “Nakajima et al. (2013) report that a typical ionization parameter increases towards high-z, and suggest the evolution of ionization parameter (see also, Lilly, Carollo & Stockton 2003; Hainline et al. 2009; Richard et al. 2011).”
• THE COSMIC BPT DIAGRAM: CONFRONTING THEORY WITH OBSERVATIONS (2013, background): “Hainline et al. (2009) show that this effect is likely to be small (0.05−0.2 dex in the [O III]/Hβ and [N II]/Hα line ratios).”
• Chemical abundances in high-redshift galaxies: a powerful new emission line diagnostic (2016, background): “It is likely that a change in both ionization parameter and in the ISM pressure is responsible for this difference (Brinchmann et al. 2008; Liu et al. 2008; Hainline et al. 2009; Bian et al. 2010; Nakajima et al. 2012; Kewley et al. 2013a).”
• DUST EXTINCTION FROM BALMER DECREMENTS OF STAR-FORMING GALAXIES AT 0.75 ⩽ z ⩽ 1.5 WITH HUBBLE SPACE TELESCOPE/WIDE-FIELD-CAMERA 3 SPECTROSCOPY FROM THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY (2012, background): “Figure 6 also shows for comparison the data from two lensed star-forming galaxies located at z ∼ 2 (Hainline et al. 2009).”
• STRONG NEBULAR LINE RATIOS IN THE SPECTRA of z ∼ 2–3 STAR FORMING GALAXIES: FIRST RESULTS FROM KBSS-MOSFIRE (2014, background): “Moreover, except for gravitationally-lensed examples (e.g., Teplitz et al. 2000; Hainline et al. 2009; Finkelstein et al. 2009; Jones et al. 2010; Richard et al. 2011; Rigby et al. 2011; Wuyts et al. 2012; Christensen et al. 2012; Jones et al. 2013; Amorín et al. 2014; James et al. 2014), the low…”
• KECK SPECTROSCOPY OF 3 < z < 7 FAINT LYMAN BREAK GALAXIES: THE IMPORTANCE OF NEBULAR EMISSION IN UNDERSTANDING THE SPECIFIC STAR FORMATION RATE AND STELLAR MASS DENSITY (2012, unknown): “…1.7- 2.0× (the exact value chosen at random from a uniform distribution), consistent with the flux ratios observed in sub-solar galaxies at z ≃ 2−3 (e.g., Hainline et al. 2009, Bian et al. 2010, Erb et al. 2010, Richard et al. 2011) and those predicted by our nebular+stellar population synthesis…”
• THEORETICAL EVOLUTION OF OPTICAL STRONG LINES ACROSS COSMIC TIME (2013, background): “High redshift galaxies typically have larger star formation rates than local galaxies (Shapley et al. 2005; Hainline et al. 2009).”
• PHYSICAL PROPERTIES OF EMISSION-LINE GALAXIES AT z ∼ 2 FROM NEAR-INFRARED SPECTROSCOPY WITH MAGELLAN FIRE (2014, background): “The ionization parameters we measure are, however, in close agreement with those measured in other high redshift samples (e.g., Pettini et al. (2001), Hainline et al. (2009), Richard et al. (2011), Wuyts et al. (2012), Nakajima et al. (2013)).”