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 [OIII] 5007/ [OII] 3727 line ratio of the high-redshift galaxies is 0.5 dex higher than their local counterparts. We construct a new calibration between the [OIII] 5007/ [OII] 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 $7.1^{+10.2}_{-5.4}$ from z ~ 3.3 to z ~ 0 at fixed mass and sSFR. We show that 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.Comment: 16 pages, 6 figures, accepted for publication in Ap

Relative merits of different types of rest-frame optical observations to constrain galaxy physical parameters

We present a new approach to constrain galaxy physical parameters from the combined interpretation of stellar and nebular emission in wide ranges of observations. This approach relies on the Bayesian analysis of any type of galaxy spectral energy distribution using a comprehensive library of synthetic spectra assembled using state-of-the-art models of star formation and chemical enrichment histories, stellar population synthesis, nebular emission and attenuation by dust. We focus on the constraints set by 5-band photometry and low- and medium-resolution spectroscopy at optical rest wavelengths on a set of physical parameters characterizing the stars and the interstellar medium. Since these parameters cannot be known a priori for any galaxy sample, we assess the accuracy to which they can be retrieved by simulating `pseudo-observations' using models with known parameters. Assuming that these models are good approximations of true galaxies, we find that the combined analysis of stellar and nebular emission in low-resolution galaxy spectra provides valuable constraints on all physical parameters. At higher resolution, the analysis of the combined stellar and nebular emission in 12,660 SDSS star-forming galaxies using our approach yields likelihood distributions of stellar mass, gas-phase oxygen abundance, optical depth of the dust and specific star formation rate similar to those obtained in previous separate analyses of the stellar and nebular emission at the original (twice higher) SDSS spectral resolution. We show that the constraints derived on galaxy physical parameters from these different types of observations depend sensitively on signal-to-noise ratio. Our approach can be extended to the analysis of any type of observation across the wavelength range covered by spectral evolution models. [abridged]Comment: 24 pages, 19 figures, accepted for publication in MNRAS. Full-resolution version available from ftp://ftp.iap.fr/pub/from_users/pacifici/paper_pacifici_hr.pd

Immune relevant molecules identified in the skin mucus of fish using omics technologies

Author's accepted version (postprint)

Charting the evolution of the ages and metallicities of massive galaxies since z=0.7

The stellar populations of intermediate-redshift galaxies can shed light onto the growth of massive galaxies in the last 8 billion years. We perform deep, multi-object rest-frame optical spectroscopy with IMACS/Magellan of ~70 galaxies in the E-CDFS with redshift 0.6522.7 and stellar mass >10^{10}Msun. Following the Bayesian approach adopted for previous low-redshift studies, we constrain the stellar mass, mean stellar age and stellar metallicity of individual galaxies from stellar absorption features. We characterize for the first time the dependence of stellar metallicity and age on stellar mass at z~0.7 for all galaxies and for quiescent and star-forming galaxies separately. These relations for the whole sample have a similar shape as the z=0.1 SDSS analog, but are shifted by -0.28 dex in age and by -0.13 dex in metallicity, at odds with simple passive evolution. We find that no additional star formation and chemical enrichment are required for z=0.7 quiescent galaxies to evolve into the present-day quiescent population. However, this must be accompanied by the quenching of a fraction of z=0.7 Mstar>10^{11}Msun star-forming galaxies with metallicities comparable to those of quiescent galaxies, thus increasing the scatter in age without affecting the metallicity distribution. However rapid quenching of the entire population of massive star-forming galaxies at z=0.7 would be inconsistent with the age/metallicity--mass relation for the population as a whole and with the metallicity distribution of star-forming galaxies only, which are on average 0.12 dex less metal-rich than their local counterparts. This indicates chemical enrichment until the present in at least a fraction of the z=0.7 massive star-forming galaxies.[abridged]Comment: accepted for publication on ApJ, 26 pages, 13 figure

The ages and metallicities of galaxies in the local universe

We derive stellar metallicities, light-weighted ages and stellar masses for a magnitude-limited sample of 175,128 galaxies drawn from the Sloan Digital Sky Survey Data Release Two (SDSS DR2). We compute median-likelihood estimates of these parameters using a large library of model spectra at medium-high resolution, covering a comprehensive range of star formation histories. The constraints we derive are set by the simultaneous fit of five spectral absorption features, which are well reproduced by our population synthesis models. By design, these constraints depend only weakly on the alpha/Fe element abundance ratio. Our sample includes galaxies of all types spanning the full range in star formation activity, from dormant early-type to actively star-forming galaxies. We show that, in the mean, galaxies follow a sequence of increasing stellar metallicity, age and stellar mass at increasing 4000AA-break strength (D4000). For galaxies of intermediate mass, stronger Balmer absorption at fixed D4000 is associated with higher metallicity and younger age. We investigate how stellar metallicity and age depend on total galaxy stellar mass. Low-mass galaxies are typically young and metal-poor, massive galaxies old and metal-rich, with a rapid transition between these regimes over the stellar mass range 3x10^9<M/Msun<3x10^10. Both high- and low-concentration galaxies follow these relations, but there is a large dispersion in stellar metallicity at fixed stellar mass, especially for low-concentration galaxies of intermediate mass. Despite the large scatter, the relation between stellar metallicity and stellar mass is similar to the correlation between gas-phase oxygen abundance and stellar mass for star-forming galaxies. [abriged]Comment: 22 pages, 14 figures, accepted for publication on MNRAS, data available at http://www.mpa-garching.mpg.de/SDSS

Alien Registration- Brinchmann, Christian Aron Juel N. (Portland, Cumberland County)

https://digitalmaine.com/alien_docs/21343/thumbnail.jp