Magellan/MMIRS near-infrared multi-object spectroscopy of nebular emission from star-forming galaxies at 2 <z< 3

Abstract

Aims. To investigate the ingredients, which allow star-forming galaxies to present Lyα line in emission, we studied the kinematics and gas phase metallicity of the interstellar medium. Methods. We used multi-object near-infrared spectroscopy with Magellan/MMIRS to study nebular emission from z 2−3 starforming galaxies discovered in three MUSYC fields. Results. We detected emission lines from four active galactic nuclei and 13 high-redshift star-forming galaxies, including Hα lines down to a flux of (4 ± 1)E-17 erg s −1 cm −2 . This yielded seven new redshifts. The most common emission line detected is [OIII]5007, which is sensitive to metallicity. We were able to measure metallicity (Z) for two galaxies and to set upper (lower) limits for another two (two). The metallicity values are consistent with 0.3 < Z/Z < 1.2, 12 + log (O/H) ∼ 8.2−8.8. Comparing the Lyα central wavelength with the systemic redshift, we find ∆v Lyα−[OIII]5007 = 70−270 km s −1 . Conclusions. High-redshift star-forming galaxies, Lyα emitting (LAE) galaxies, and Hα emitters appear to be located in the low mass, high star-formation rate (SFR) region of the SFR versus stellar mass diagram, confirming that they are experiencing burst episodes of star formation, which are building up their stellar mass. Their metallicities are consistent with the relation found for z ≤ 2.2 galaxies in the Z versus stellar mass plane. The measured ∆v Lyα−[OIII]5007 values imply that outflows of material, driven by star formation, could be present in the z ∼ 2−3 LAEs of our sample. Comparing with the literature, we note that galaxies with lower metallicity than ours are also characterized by similar ∆v Lyα−[OIII]5007 velocity offsets. Strong F([OIII]5007) is detected in many Lyα emitters. Therefore, we propose the F(Lyα)/F([OIII]5007) flux ratio as a tool for the study of high-redshift galaxies; while influenced by metallicity, ionization, and Lyα radiative transfer in the ISM, it may be possible to calibrate this ratio to primarily trace one of these effects.

A CLOSE COMPARISON BETWEEN OBSERVED AND MODELED LyαLINES FORz∼ 2.2 LyαEMITTERS

“…The ∆v Lyα,r value has been measured in more than 60 LAEs (McLinden et al 2011;Finkelstein et al 2011;Hashimoto et al 2013;Guaita et al 2013;Chonis et al 2013;Shibuya et al 2014b;Song et al 2014;Erb et al 2014). These studies have shown that LAEs at z ∼ 2 − 3 have a mean ∆v Lyα,r of ≃ 200 km s −1 , which is significantly smaller than that of LBGs at a similar redshift, ∆v Lyα,r ≃ 400 km s −1 (e.g., Steidel et al 2010;Rakic et al 2011;Kulas et al 2012).…”

The VIMOS Ultra Deep Survey

“…To estimate z sys , we started with the VUDS redshift as a guess, and we fit together the CIII]1908 emission line and the continuum around it. We used the optimize.leastsq python function (as applied also in Guaita et al 2013) by assuming a Gaussian profile, that the continuum has a well-defined slope (linear fit), and including the VUDS noise spectrum in the minimization procedure. This noise contains the information of the observation and the instrumental uncertainty.…”

Extreme emission-line galaxies out toz~ 1 in zCOSMOS

“…An alternative selection criterion based on other strong emission lines would have the drawback that we could only select a smaller number of galaxies over a smaller redshift range, e.g., Hα emitters can be selected at z < ∼ 0.5. Finally, the choice of a sample of strong [O iii] emitters has also been motivated by the aim of collecting a representative and statistically significant sample of star-forming galaxies that would be easily detectable at higher redshifts (z ∼ 2−3) in deep wide-field NIR surveys (e.g., van der Wel et al 2011;Atek et al 2011;Xia et al 2012;Guaita et al 2013;Maseda et al 2013Maseda et al , 2014. Since they would be affected by similar biases, our sample is intended to offer a valuable benchmark for future direct comparison with other probes of strong emission-line galaxies at higher redshifts.…”