Cosmic Star Formation Rate DensityEdit
Cosmic star formation rate density (ρSFR) is a key cosmological quantity that tallies how rapidly stellar mass is being built up per unit volume across the history of the universe. Measured in solar masses per year per cubic megaparsec (M⊙ yr⁻¹ Mpc⁻³), ρSFR(z) traces the global pace of star formation as a function of redshift z, linking the growth of galaxies to the availability of gas, the physics of star formation, and the feedback processes that regulate it. In broad terms, ρSFR rises from early times, peaks in the so-called cosmic noon, and then declines toward the present day, shaping the buildup of the stellar mass density that we observe in galaxies today. star formation rate cosmic star formation history galaxy evolution
In practice, estimating ρSFR requires combining several strands of observation and theory. The two most direct tracers of recent star formation are rest-frame ultraviolet (UV) luminosity, which captures light from short-lived, massive stars, and infrared (IR) luminosity, which comes from dust that absorbs UV/optical photons and re-emits them as heat. Each tracer has its strengths and biases: UV light is sensitive to dust obscuration, while IR observations hinge on how effectively dust converts starlight into infrared emission. Consequently, robust ρSFR estimates typically fuse UV and IR information to account for both unobscured and obscured star formation. This synthesis relies on calibrations that connect luminosity to star formation rate, often anchored to a chosen initial mass function (IMF) such as the Salpeter IMF, the Kroupa IMF, or the Chabrier IMF. The choice of IMF affects inferred SFRs and the normalization of ρSFR(z). See for example discussions around the UV–IR approach and IMF dependence in the context of the Madau–Dickinson diagram and related studies. UV luminosity IR luminosity Calzetti attenuation law star formation rate initial mass function
Dust plays a central role in shaping the observed ρSFR(z). In dusty environments, a large fraction of star formation is hidden from UV surveys and must be inferred from IR or submillimeter measurements. The emergence of sensitive IR and submillimeter facilities has helped reveal substantial, previously missed star formation at intermediate and high redshifts. However, dust corrections remain model-dependent, and uncertainties about dust properties, geometry, and attenuation laws propagate into the final ρSFR estimates. These challenges motivate multiwavelength campaigns and the continued refinement of templates and calibrations used to convert observables into star formation rates. dust infrared astronomy galaxy luminosity function galaxy evolution
The measured trajectory of ρSFR(z) shows a pronounced rise from the earliest epochs, reaching a broad maximum near redshift z ≈ 2–3 (often called the cosmic noon), and then declining toward the present. This pattern mirrors the available gas supply, the efficiency of converting gas into stars, and the cumulative effects of feedback from massive stars and active galactic nuclei (AGN). The amplitude and precise position of the peak, as well as the contributions from different galaxy populations (e.g., low-mass dwarfs versus massive systems), remain active areas of study. High-redshift estimates rely on rest-frame UV measurements and, increasingly, on gravitational lensing, ALMA detections of dusty starbursts, and, with facilities like JWST, deeper probes into the early buildup of stellar mass. See discussions of the cosmic star formation history in terms of its observational footprint across redshift and galaxy populations. cosmic star formation history JWST ALMA Hα UV luminosity dust
Several physical mechanisms shape the global ρSFR(z). Gas accretion from the cosmic web feeds galaxies with fresh fuel, while feedback from supernovae, stellar winds, and AGN can regulate or suppress further star formation by heating or ejecting gas. The balance between gas inflows and these feedback processes, together with the evolving metallicity of the interstellar medium, governs the efficiency of star formation. The interplay among these factors is reflected in correlations such as the mass–metallicity relation and the evolving gas fractions observed in galaxies over cosmic time. See gas accretion and feedback as components of the regulatory network that shapes the cosmic star formation history. cold flow accretion supernova active galactic nucleus mass–metallicity relation metallicity
Debates and uncertainties remain about several aspects of ρSFR(z). One ongoing discussion concerns the faint, low-luminosity galaxies that may contribute significantly to the total SFR density, especially at high redshift; extrapolations of the galaxy luminosity function to these faint ends carry systematic uncertainties. Another area of active work is the possible variation of the IMF with environment or cosmic time; while a universal IMF is a convenient assumption, some models and observational hints invite exploration of potential deviations, particularly in extreme star-forming conditions. Discrepancies between UV- and IR-based estimates, differences in dust attenuation prescriptions, and sample variance across surveys all contribute to the present error budget. Finally, quantifying the contribution of AGN to the infrared background and disentangling it from star formation remains a complex challenge in constructing a complete census of ρSFR. galaxy luminosity function initial mass function dust attenuation law AGN Hα cosmology
The study of ρSFR(z) intersects with broader questions in cosmology and galaxy formation. By informing the rate at which stellar mass is assembled, ρSFR(z) constrains models of gas accretion histories, feedback efficiencies, and the timeline of reionization. Its integral over time connects to the present-day stellar mass density and the chemical enrichment of galaxies and the intergalactic medium. In this context, ρSFR(z) is a bridge between the small-scale physics of star formation and the large-scale evolution of structure in the universe. reionization cosmology galaxy evolution stellar mass density