New Observations of the Interstellar Medium in the Lyman Break Galaxy MS 1512–cB58

By M. Pettini, S. Rix, C. Steidel, K. Adelberger, M. Hunt, A. Shapley. 2001

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We present the results of a detailed study of the interstellar medium (ISM) of MS 1512-cB58 (cB58 for short), an ~L* Lyman break galaxy at z = 2.7276, based on new spectral observations obtained with the Echelle Spectrograph and Imager on the Keck II telescope at 58 km s-1 resolution. We focus in particular on the chemical abundances and kinematics of the interstellar gas deduced from the analysis of 48 ultraviolet absorption lines, at rest wavelengths between 1134 and 2576 Å, due to elements from H to Zn. Our main findings are as follows. Even at this relatively early epoch, the ISM of this galaxy is already highly enriched in elements released by Type II supernovae; the abundances of O, Mg, Si, P, and S are all ~2/5 of their solar values. In contrast, N and the Fe-peak elements Mn, Fe, and Ni are underabundant by a factor of ~3. Based on current ideas of stellar nucleosynthesis, these results can be understood if most of the metal enrichment in cB58 has taken place within the last ~300 Myr, the timescale for the release of N from intermediate-mass stars. Such a young age is consistent with the UV-optical spectral energy distribution. Thus, cB58 seems to be an example of a galaxy in the process of converting its gas into stars on a few dynamical timescales—quite possibly we are witnessing the formation of a galactic bulge or an elliptical galaxy. The energetic star formation activity has stirred the interstellar medium to high velocities; the strongest absorption lines span a velocity interval of ~1000 km s-1. The net effect is a bulk outflow of the ISM at a speed of ~255 km s-1 and at a rate that exceeds the star formation rate. It is unclear whether this gas will be lost or retained by the galaxy. On the one hand, the outflow probably has sufficient energy to escape the potential well of cB58, for which we derive a baryonic mass of ~1010 M☉. On the other hand, at least some of the elements manufactured by previous generations of stars must have mixed efficiently with the ambient, neutral, ISM to give the high abundances we measure. We point out that the chemical and kinematic properties of cB58 are markedly different from those of most damped Lyα systems at the same redshift.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/259ee601f1670155c9af88e2ba601db62f5b59fd

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Heating cooling flows with jets (2003, background): “Bipolar outflows are observed around most accreting objects, be they forming stars (Arce & Goodman 2002), accreting black holes that power AGNs (Pounds et al. 2003) and micro-quasars (Mirabel & Rodriguez 1999), or forming galaxies (Pettini et al. 2002).”
Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: physical properties and implications for studies at z > 7 (2014, background): “Deep spectra of the low luminosity galaxies in our sample thus provide a verycomplementary picture to existing samples of luminous lensed galaxies with deep rest-UV spectra (e.g., Pettini et al. 2002, Quideret al. 2009, Quider et al. 2010, Bayliss et al. 2013, James et al. 2013).”
THE KILOPARSEC-SCALE KINEMATICS OF HIGH-REDSHIFT STAR-FORMING GALAXIES (2009, background): “…into the IGM surrounding these galaxies, creating the ubiquitous blueshifted interstellar absorption features observed in rest-frame UV spectra (e.g., Pettini et al. 2002; Shapley et al. 2003), and the corresponding redshifts of the resonantly scattered Lyα emission line (Verhamme et al. 2008).”
An ALMA survey of the SCUBA-2 CLS UDS field: physical properties of 707 sub-millimetre galaxies (2019, positive): “We also overlay on to the figure lines corresponding to constant gas depletion (or star-formation efficiency), which we estimate assuming half of the gas is available to form stars (the other half being expelled) (Pettini et al. 2002): τdep ∼ 0.5 × Mgas SFR .”
The Distribution of Metallicity in the Intergalactic Medium at z ~ 2.5: O VI and C IV Absorption in the Spectra of Seven QSOs (2003, background): “The stellar physics and populations basically resemble those in the local neighborhood, except that at z & 2.5 the star formation rate in the typical galaxy was much higher, and the IMF may have been tilted towards high mass (Pettini et al. 2002).”
A Survey of Star-forming Galaxies in the 1.4 ≲ z ≲ 2.5 Redshift Desert: Overview (2004, background): “The latter have provided information on the kinematics and chemistry of outflowing gas that may have very significant implications for the galaxy formation process (see, e.g., Pettini et al. 2002a; Shapley et al. 2003, Adelberger et al. 2003).”
Lyman Break Galaxies at Redshift z ~ 3: Survey Description and Full Data Set (2003, methodology): “As has been discussed extensively elsewhere (e.g., Franx et al. 1997; Steidel et al. 1998; Pettini et al. 1998, 2000, 2001, 2002; Adelberger et al. 2003; Shapley et al. 2003) the Ly α emission and interstellar absorption features are almost universally separated by at least several hundred km s−1.”
Where Are the Baryons? II. Feedback Effects (2005, background): “We find that this velocity roughly corresponds to the observed outflow velocities of Lyman break galaxies (e.g., Pettini et al. 2002).”
Formation of z~6 Quasars from Hierarchical Galaxy Mergers (2006, background): “…(e.g., Martin 1999, 2005; Heckman et al. 2000; Rupke et al. 2002, 2005) and Lyman break galaxies at z 3 as indicated by blueshifted interstellar absorption lines and redshifted Ly emission lines (e.g., Pettini et al. 2002; Shapley et al. 2003), aswell as Ly emitters at z 5:7 (Ajiki et al. 2002).”
THE CHARACTERISTIC STAR FORMATION HISTORIES OF GALAXIES AT REDSHIFTS z ∼ 2–7 (2012, background): “Pettini et al. (2002) estimated the mass outflow rate of the low-ionization and HI gas of the lensed Lyman Break galaxy cB58, finding ηout ≃ 1.75.”
A primer on hierarchical galaxy formation: the semi-analytical approach (2006, methodology): “The superwind model is motivated by the observations of outflows of gas from large, star forming galaxies at high and low redshift (Pettini et al. 2001, 2002; Dawson et al. 2002; Adelberger et al. 2003; Shapley et al. 2003; Martin 2005; Wilman et al. 2005b).”
LSD: Lyman-break galaxies Stellar populations and Dynamics – I. Mass, metallicity and gas at z∼ 3.1 (2009, methodology): “Numerous studies have shown that outflows are already present at high redshifts (Pettini et al. 2001, 2002; Frye, Broadhurst & Benı́tez 2002; Weiner et al. 2008).”