Luminosity Function Of Lyman Break Galaxies Research Articles

Large Equivalent Width L[CLC]y[/CLC]α line Emission at [FORMULA][F]z=4.5[/F][/FORMULA]: Young Galaxies in a Young Universe?

The Large Area Lyman Alpha survey has found ≈150 Lyα emitters at z = 4.5. While stellar models predict a maximum Lyα equivalent width (EW) of 240 A, 60% of the Lyα emitters have EWs exceeding this value. We attempt to model the observed EW distribution by combining stellar population models with an extrapolation of a Lyman break galaxy luminosity function at z = 4, incorporating observational selection effects and Malmquist bias. To reproduce the high EWs seen in the sample, we need to postulate a stellar initial mass function with an extreme slope of α = 0.5 (instead of 2.35), zero-metallicity stars, or narrow-line active galactic nuclei (AGNs). Not all the high-EW sources can be AGNs without exceeding the X-ray background or postulating a very steep redshift evolution. Only 7.5%-15% of galaxies need to show Lyα emission to explain the observed number counts. This raises the possibility either that star formation in high-redshift galaxies is episodic or that the Lyα galaxies we are seeing are the youngest 7.5%-15% and that Lyα is strongly quenched by dust at about 107 yr of age.

The Rest‐Frame Optical Properties ofz ≃ 3 Galaxies

We present the results of a near-infrared imaging survey of z ~ 3 Lyman break galaxies (LBGs). The survey covers a total of 30 arcmin2 and includes 118 photometrically selected LBGs with Ks-band measurements, 63 of which also have J-band measurements, and 81 of which have spectroscopic redshifts. Using the distribution of optical magnitudes from previous work and -Ks colors for this subsample, we compute the rest-frame optical luminosity function of LBGs. This luminosity function is described by an analytic Schechter fit with a very steep faint-end slope of ? = -1.85 ? 0.15, and it strikingly exceeds locally determined optical luminosity functions at brighter magnitudes, where it is fairly well constrained. The V-band luminosity density of only the observed bright end of the z ~ 3 LBG luminosity function already approaches that of all stars in the local universe. For the 81 galaxies with measured redshifts, we investigate the range of LBG stellar populations implied by the photometry that generally spans the range 900-5500 ? in the rest frame. The parameters under consideration are the star formation rate as a function of time, the time since the onset of star formation, and the degree of reddening and extinction by dust. While there are only weak constraints on the parameters for most of the individual galaxies, there are strong trends in the sample as a whole. With a wider wavelength baseline than most previous studies at similar redshifts, we confirm the trend that intrinsically more luminous galaxies are dustier. We also find that there is a strong correlation between extinction and the age of the star formation episode, in the sense that younger galaxies are dustier and have much higher star formation rates. The strong correlation between extinction and age, which we show is unlikely to be an artifact of the modeling procedure, has important implications for an evolutionary sequence among LBGs. A unified scenario that accounts for the observed trends in bright LBGs is one in which a relatively short period of very rapid star formation (hundreds of M? yr-1) lasts for roughly 50-100 Myr, after which both the extinction and star formation rate are considerably reduced and stars are formed at a more quiescent, but still rapid, rate for at least a few hundred megayears. In our sample, a considerable fraction (~20%) of the LBGs have best-fit star formation ages 1 Gyr, implied stellar masses of 1010 M?, and are still forming stars at ~30 M? yr-1.

The nature of high-redshift galaxies

Using semi-analytic models of galaxy formation, we investigate the properties of z∼3 galaxies and compare them with the observed population of Lyman-break galaxies (LBGs). In addition to the usual quiescent mode of star formation, we introduce a physical model for starbursts triggered by galaxy–galaxy interactions. We find that with the merger rate that arises naturally in the CDM-based merging hierarchy, a significant fraction of bright galaxies identified at high redshift ( z≳2) are likely to be low-mass, bursting satellite galaxies. The abundance of LBGs as a function of redshift and the luminosity function of LBGs both appear to be in better agreement with the data when the starburst mode is included, especially when the effects of dust are considered. The objects that we identify as LBGs have observable properties including low velocity dispersions that are in good agreement with the available data. In this “Bursting Satellite” scenario, quiescent star formation at z≳2 is relatively inefficient and most of the observed LBGs are starbursts triggered by satellite mergers within massive halos. In high-resolution N-body simulations, we find that the most massive dark matter halos cluster at redshift z∼3 much as the Lyman-break galaxies (LBGs) are observed to do. This is true for both the Ω=1 CHDM model and low- Ω ΛCDM and OCDM models, all of which have fluctuation power spectra P( k) consistent with the distribution of low-redshift galaxies. The Bursting Satellite scenario can resolve the apparent paradox of LBGs that cluster like massive dark matter halos but have narrow linewidths and small stellar masses.