skip to main content

SciTech ConnectSciTech Connect

Title: Stars were born in significantly denser regions in the early universe

The density of the warm ionized gas in high-redshift galaxies is known to be higher than what is typical in local galaxies on similar scales. At the same time, the mean global properties of the high- and low-redshift galaxies are quite different. Here, we present a detailed differential analysis of the ionization parameters of 14 star-forming galaxies at redshift 2.6-3.4, compiled from the literature. For each of those high-redshift galaxies, we construct a comparison sample of low-redshift galaxies closely matched in specific star formation rate (sSFR) and stellar mass, thus ensuring that their global physical conditions are similar to the high-redshift galaxy. We find that the median log [O III] 5007/[O II] 3727 line ratio of the high-redshift galaxies is 0.5 dex higher than their local counterparts. We construct a new calibration between the [O III] 5007/[O II] 3727 emission line ratio and ionization parameter to estimate the difference between the ionization parameters in the high- and low-redshift samples. Using this, we show that the typical density of the warm ionized gas in star-forming regions decreases by a median factor of 7.1{sub −5.4}{sup +10.2} from z ∼ 3.3 to z ∼ 0 at fixed mass and sSFR. We show thatmore » metallicity differences cannot explain the observed density differences. Because the high- and low-redshift samples are comparable in size, we infer that the relationship between star formation rate density and gas density must have been significantly less efficient at z ∼ 2-3 than what is observed in nearby galaxies with similar levels of star formation activity.« less
Authors:
; ;  [1]
  1. Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)
Publication Date:
OSTI Identifier:
22356793
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 787; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CALIBRATION; DENSITY; EMISSION; EVOLUTION; GALAXIES; MASS; METALLICITY; MILKY WAY; RED SHIFT; STARS; UNIVERSE