[Paper Review] The Evolution of Luminous Matter in the Universe

Piero Madau|arXiv (Cornell University)|Sep 15, 1997

Photocathodes and Microchannel Plates3 citations

TL;DR

This paper presents a spectrophotometric model that traces the evolution of luminous matter by using rest-frame UV and near-IR continua to infer star formation rates and stellar masses in galaxies. It shows that ~60% of today's stars formed recently (z < 1.5), consistent with hierarchical cosmologies, and accounts for the entire extragalactic background light down to faint magnitudes, with dust absorption being the largest uncertainty in early starlight budgeting.

ABSTRACT

I review a technique for interpreting faint galaxy data which traces the evolution with cosmic time of the galaxy luminosity density, as determined from several deep spectroscopic samples and the HDF. The method relies on the rest frame UV and near-IR continua of galaxies as indicators, for a given IMF and dust content, of their instantaneous SFR and total stellar mass, and offers the prospect of addressing in a coherent framework an important set of subjects: cosmic star formation history, dust in primeval galaxies, shape of the IMF, stellar mass-to-light ratios of present-day galaxies, extragalactic background light, Type II supernovae and heavy element enrichment history of the universe. The global spectrophotometric properties of field galaxies are well fit by a simple stellar evolution model, defined by a time-dependent SFR per unit comoving volume, a universal IMF which is relatively rich in massive stars, and a modest amount of dust reddening. The model is able to account for the entire background light recorded in the galaxy counts down to the very faint magnitude levels probed by the HDF, and produces visible mass-to-light ratios at the present epoch which are consistent with the values observed in nearby galaxies of various morphological types. The bulk (&gt;60%) of the stars present today formed relatively recently (z&lt;1.5), consistently with the expectations from a broad class of hierarchical clustering cosmologies, and in good agreement with the low level of metal enrichment observed at high redshifts in the damped Lyman-alpha systems. Throughout this review I emphasize how the poorly constrained amount of starlight that was absorbed by dust and reradiated in the far-IR at early epochs represents one of the biggest uncertainties in our understanding of the evolution of luminous matter in the universe.

Motivation & Objective

• To interpret faint galaxy data from deep surveys and the Hubble Deep Field to reconstruct the cosmic history of luminous matter.
• To resolve uncertainties in the star formation history, initial mass function (IMF), dust content, and stellar mass-to-light ratios in galaxies.
• To account for the entire extragalactic background light (EBL) using a consistent model of star formation and dust absorption.
• To assess the role of dust in absorbing early starlight and reradiating it in the far-IR, a major source of uncertainty in luminous matter evolution.

Proposed method

• Uses rest-frame UV and near-IR spectral energy distributions (SEDs) as proxies for instantaneous star formation rate (SFR) and total stellar mass.
• Applies a simple stellar population (SSP) model with a time-dependent SFR per unit comoving volume.
• Employs a universal initial mass function (IMF) rich in massive stars and a modest dust reddening law to fit observed galaxy SEDs.
• Calibrates the model against deep spectroscopic samples and Hubble Deep Field (HDF) data to constrain SFR and stellar mass density evolution.
• Fits the observed galaxy counts and background light to validate the model's consistency with the total extragalactic background light.
• Incorporates dust reprocessing by estimating the fraction of starlight absorbed and reradiated in the far-IR, highlighting its uncertainty.

Experimental results

Research questions

• RQ1 What is the cosmic history of star formation, as inferred from the rest-frame UV and near-IR properties of faint galaxies?
• RQ2 How much of the extragalactic background light is accounted for by known galaxies and their evolved stellar populations?
• RQ3 To what extent does dust absorption and re-emission in the far-IR affect the inferred luminous matter budget in the early universe?
• RQ4 Is the initial mass function (IMF) consistent across cosmic time, and does it favor massive stars in early star formation?
• RQ5 How well do the model-predicted stellar mass-to-light ratios match observations of local galaxies?

Key findings

• Approximately 60% of the stars in the present-day universe formed at redshift z < 1.5, indicating a significant recent star formation epoch.
• The model accounts for the entire extragalactic background light recorded in galaxy counts down to the faintest HDF magnitudes.
• The predicted present-day stellar mass-to-light ratios are consistent with observations of nearby galaxies across morphological types.
• The star formation history inferred is broadly consistent with hierarchical clustering cosmologies and low metallicity levels seen in high-redshift damped Lyman-alpha systems.
• Dust absorption of early starlight, reradiated in the far-IR, remains the largest uncertainty in reconstructing the full luminous matter budget.
• The model's success in fitting both SEDs and integrated background light supports the use of rest-frame UV and near-IR continua as robust indicators of SFR and stellar mass.