The Rest-Frame Optical Spectra of Lyman Break Galaxies: Star Formation, Extinction, Abundances, and Kinematics

By M. Pettini, A. Shapley, C. Steidel, J. Cuby, Mark Dickinson, A. Moorwood, K. Adelberger, M. Giavalisco. 2001

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We present the first results of a spectroscopic survey of Lyman break galaxies (LBGs) in the near-infrared aimed at detecting the emission lines of [O II], [O III], and Hβ from the H II regions of normal star-forming galaxies at z ≃ 3. From observations of 15 objects with the Keck telescope and the Very Large Telescope augmented with data from the literature for an additional four objects, we reach the following main conclusions. The rest-frame optical properties of LBGs at the bright end of the luminosity function are remarkably uniform, their spectra are dominated by emission lines, [O III] is always stronger than Hβ and [O II], and projected velocity dispersions are between 50 and 115 km s-1. Contrary to expectations, the star formation rates deduced from the Hβ luminosity are on average no larger than those implied by the stellar continuum at 1500 Å; presumably any differential extinction between rest-frame optical and UV wavelengths is small compared to the relative uncertainties in the calibrations of these two star formation tracers. For the galaxies in our sample, the abundance of oxygen can only be determined to within 1 order of magnitude without recourse to other emission lines ([N II] and Hα), which are generally not available. Even so, it seems well established that LBGs are the most metal-enriched structures at z ≃ 3, apart from quasi-stellar objects, with abundances greater than about 1/10 solar and generally higher than those of damped Lyα systems at the same epoch. They are also significantly overluminous for their metallicities; this is probably an indication that their mass-to-light ratios are low compared to present-day galaxies. At face value, the measured velocity dispersions imply virial masses of about 1010 M☉ within half-light radii of 2.5 kpc. The corresponding mass-to-light ratios, M/L ≈ 0.15 in solar units, are indicative of stellar populations with ages between 108 and 109 yr, consistent with the UV-optical spectral energy distributions. However, we are unable to establish conclusively whether or not the widths of the emission lines reflect the motions of the H II regions within the gravitational potential of the galaxies, even though in two cases we see hints of rotation curves. All 19 LBGs observed show evidence for galactic-scale superwinds; such outflows have important consequences for regulating star formation, distributing metals over large volumes, and allowing Lyman continuum photons to escape and ionize the intergalactic medium.

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Citations in the corpus

• Chemical Abundances of DEEP2 Star-forming Galaxies at z~1.0-1.5 (2005, methodology): “In the sample of Pettini et al. (2001), where the inferred star-formation rates are even more extreme than in the DEEP2 sample, large measured [OIII]/[OII] line ratios indicate significantly higher ionization parameters than those observed in more quiescent samples (Lilly et al. 2003).”
• Gas metallicity diagnostics in star-forming galaxies (2006, background): “…the investigation of the gas metallicity even in high-z galaxies beyond z = 1, such as Lyman-break galaxies (e.g., Teplitz et al. 2000a, 2000b; Pettini et al. 2001), submillimeter-selected high-z galaxies (Swinbank et al. 2004), and so on (see also, e.g., Kobulnicky & Kewley 2004; Savaglio et…”
• THE GASEOUS ENVIRONMENT OF HIGH-z GALAXIES: PRECISION MEASUREMENTS OF NEUTRAL HYDROGEN IN THE CIRCUMGALACTIC MEDIUM OF z ∼ 2–3 GALAXIES IN THE KECK BARYONIC STRUCTURE SURVEY (2012, background): “Spectroscopic observations of star-forming galaxies during this epoch commonly exhibit signatures of strong outflowing winds (Pettini et al. 2001; Shapley et al. 2003; Adelberger et al. 2005a; Steidel et al. 2010).”
• PHYSICAL CONDITIONS IN A YOUNG, UNREDDENED, LOW-METALLICITY GALAXY AT HIGH REDSHIFT (2010, background): “…needed to determine the ionization parameter are few at high redshift, the values inferred similarly do not approach that of BX418, although they are higher than the ionization parameters of local galaxies of similar metallicities (Pettini et al. 2001; Maiolino et al. 2008; Hainline et al. 2009).”
• The evolution of the broad-line region among SDSS quasars (2005, background): “…requests to: T. Nagao on the gas metallicity of high-z galaxies not hosting AGN are extremely difficult and time-consuming, because even the brightest galaxies are much fainter than quasars at the same redshift (but see, e.g., Teplitz et al. 2000; Kobulnicky & Koo 2000; Pettini et al. 2001).”
• Chemical enrichment of the intracluster and intergalactic medium in a hierarchical galaxy formation model (2003, background): “Detailed studies at both optical and infrared wavelengths have shown that at redshifts ∼3, the metallicity of LBGs is relatively high (in the range 0.1–0.5 Z ) (Pettini et al. 2000, 2001).”
• The enrichment of the intergalactic medium with adiabatic feedback – I. Metal cooling and metal diffusion (2009, background): “Observations of galactic winds (e.g., Heckman 2001; Pettini et al. 2001) have found that galactic wind velocities range from hundreds to thousands of km/s and the mass loss rates are comparable to star formation rates.”
• Theoretical Challenges in Galaxy Formation (2016, background): “…nearby Universe (e.g. Heckman, Armus & Miley 1990; Heckman et al. 2000; Martin 1999; Rubin et al. 2014; Veilleux, Cecil & Bland-Hawthorn 2005) but also at higher redshift at the cosmic peak of conversion of gas into stars (Martin et al. 2013, Pettini et al. 2001, Shapley 2011, Steidel et al. 2010).”
• First results from the TNG50 simulation: galactic outflows driven by supernovae and black hole feedback (2019, background): “Pioneering studies have demonstrated the existence of outflows in the local universe (Heckman et al. 1990; Lehnert & Heckman 1996) and at high redshifts z > 2 (Pettini et al. 2001).”
• Feedback and the fundamental line of low-luminosity low-surface-brightness/dwarf galaxies (2002, background): “Spectroscopy of the brighter lensed galaxies at high redshifts reveals using a similar effect typical outflows of 200–800 km s−1 (Franx et al. 1997; Frye & Broadhurst 1998; Pettini et al. 2001; Frye, Broadhurst & Benitez 2002).”
• EXTRAGALACTIC CHEMICAL ABUNDANCES: DO H ii REGIONS AND YOUNG STARS TELL THE SAME STORY? THE CASE OF THE SPIRAL GALAXY NGC 300 (2009, background): “It has recently become possible to extend the nebular techniques to star-forming galaxies at high redshift (Pettini et al. 2001; Shapley et al. 2004), allowing the investigation of cosmic chemical enrichment (Kobulnicky & Kewley 2004; Savaglio et al. 2005; Maier et al. 2006; Liu et al. 2008; Cowie…”
• Keck Absorption-Line Spectroscopy of Galactic Winds in Ultraluminous Infrared Galaxies (2002, methodology): “The observational data set on galactic-scale outflows is slim, however, apart from studies of the local universe (z < 0:1) and high-redshift galaxies (Lyman break galaxies at z 3 [Pettini et al. 2000, 2001] and a few gravitationally lensed objects [Frye et al. 2002]).”
• Lyman Break Galaxies at Redshift z ~ 3: Survey Description and Full Data Set (2003, methodology): “As has been discussed extensively elsewhere (e.g., Steidel et al. 1996a, Steidel et al. 1998, Pettini et al. 2000, 2001), most of the easily identifiable features in LBG spectra are interstellar absorption lines of very strong transitions in the 1200 − 1700Å range in the rest frame.”
• Galaxies and Intergalactic Matter at Redshift z ~ 3: Overview (2002, background): “…at low and high redshift appears to be flowing outwards rapidly enough to escape the galaxies’ gravitational pull (e.g., Heckman et al. 2000; Pettini et al. 2001, 2002); galaxies that experienced intense bursts of star formation in the past now contain little interstellar gas (e.g., Mayall…”
• Rest-Frame Ultraviolet Spectra of z ∼ 3 Lyman Break Galaxies (2003, methodology): “…about the properties of the large-scale outflows of interstellar material which are inferred in LBGs from blueshifted interstellar absorption and redshifted Lyα emission, relative to the systemic stellar redshift (Pettini et al. 2001, 2002; Franx et al. 1997; Lowenthal et al. 1997).”
• RADIATION PRESSURE FROM MASSIVE STAR CLUSTERS AS A LAUNCHING MECHANISM FOR SUPER-GALACTIC WINDS (2010, background): “…ranging from a few tens to several hundred kilometers per second (Heckman, Armus, & Miley 1990; Steidel et al. 1996; Franx et al. 1997; Heckman et al. 2000; Pettini et al. 2000, 2001; Shapley et al. 2003; Martin 2005; Rupke et al. 2005; Tremonti et al. 2007; Weiner et al. 2009; Ménard et al. 2009).”
• Rest-frame ultraviolet-to-optical spectral characteristics of extremely metal-poor and metal-free galaxies (2011, methodology): “At z ∼ 2–3, Lyman break galaxies (LBGs) selected by the so-called drop-out technique have Z ∼ 0.002–0.01 (= 1/10–1/2 Z⊙) (e.g., Pettini et al. 2001; Erb et al. 2006; Mannucci et al. 2009; Erb et al. 2010).”
• The Morphological Diversities among Star-forming Galaxies at High Redshifts in the Great Observatories Origins Deep Survey (2006, background): “The rotation curves derived from spectrosopy of the optical emission lines for small samples of LBGs suggest that there may be rotating disks among them (Pettini et al. 2001; Moorwood et al. 2000).”
• Optical Star Formation Rate Indicators (2005, unknown): “Although in the local universe lowmass galaxies undergoing a strong burst of star formation typically exhibit the highest [O iii]/[O ii] ratios, stronger ionizing radiation fields may be much more common in high-redshift, massive galaxies (e.g., Pettini et al. 2001).”
• MASSIVE HALOS IN MILLENNIUM GAS SIMULATIONS: MULTIVARIATE SCALING RELATIONS (2009, background): “Observational evidence of ubiquitous galactic winds at high and moderate redshifts (Pettini et al. 2001; Weiner et al. 2008) suggest that most of the heating of the ICM occurs at high redshift.”