Star Formation Stochasticity Measured from the Distribution of Burst Indicators

Abstract

One of the key questions in understanding the formation and evolution of galaxies is how starbursts affect the assembly of stellar populations in galaxies over time. We define a burst indicator ($\eta$), which compares a galaxy's star formation rates on short ($\sim 10$ Myr) and long ($\sim 100$ Myr) timescales. To estimate $\eta$, we apply the detailed time-luminosity relationship for H$\alpha$ and near-ultraviolet emission to simulated star formation histories (SFHs) from semi-analytic models and the Mufasa hydrodynamical cosmological simulations. The average of $\eta$ is not a good indicator of star formation stochasticity (burstiness); indeed, we show that this average should be close to zero unless the population has an average SFH which is rising or falling rapidly. Instead, the width of the $\eta$ distribution characterizes the burstiness of a galaxy population's recent star formation. We find this width to be robust to variations in stellar initial mass function and metallicity. We apply realistic noise and selection effects to the models to generate mock HST and JWST galaxy catalogs and compare these catalogs with 3D-HST observations of 956 galaxies at $0.65<z<1.5$ detected in H$\alpha$. Measurements of $\eta$ are unaffected by dust measurement errors under the assumption that $E(B-V{)}_{\mathrm{stars}}=0.44E(B-V{)}_{\mathrm{gas}}$ (i.e., $Q_{\mathrm{sg}}=0.44$). However, setting $Q_{\mathrm{sg}}=0.8_{-0.2}^{+0.1}$ removes an unexpected dependence of the average value of $\eta$ upon dust attenuation and stellar mass in the 3D-HST sample while also resolving disagreements in the distribution of star formation rates. However, even varying the dust law cannot resolve all discrepancies between the simulated and the observed galaxies.

21 pages, 12 figures, submitted to ApJ

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Cited by in corpus (20)

• Non-parametric Star Formation History Reconstruction with Gaussian Processes I: Counting Major Episodes of Star Formation
• Stochastic modelling of star-formation histories II: star-formation variability from molecular clouds and gas inflow
• The Diversity and Variability of Star Formation Histories in Models of Galaxy Evolution
• Stochastic modeling of star-formation histories I: the scatter of the star-forming main sequence
• The Star Formation Burstiness and Ionizing Efficiency of Low-mass Galaxies
• Bursty star formation during the Cosmic Dawn driven by delayed stellar feedback
• Spectral Energy Distributions in Three Deep-Drilling Fields of the Vera C. Rubin Observatory Legacy Survey of Space and Time: Source Classification and Galaxy Properties
• The SAGA Survey. IV. The Star Formation Properties of 101 Satellite Systems around Milky Way-mass Galaxies
• Stochastic Modelling of Star Formation Histories III. Constraints from Physically-Motivated Gaussian Processes
• A spatially resolved analysis of star-formation burstiness by comparing UV and H$\alpha$ in galaxies at z$\sim$1 with UVCANDELS
• ODIN: Improved Narrowband Ly$\alpha$ Emitter Selection Techniques for $z$ = 2.4, 3.1, and 4.5
• Correlations between H$\alpha$ Equivalent Width and Galaxy Properties at $z=0.47$: Physical or Selection-driven?
• Exploring the Correlation between $\mathrm{H}\alpha$-to-UV Ratio and Burstiness for Typical Star-forming Galaxies at $z\sim 2$
• Constraints on Fluctuating Star Formation Rates for Intermediate-mass Galaxies with H$\alpha$ and UV Luminosities
• Constraints on galactic outflows from the metallicity-stellar mass-SFR relation of EAGLE simulation and SDSS galaxies
• A selection of Hα emitters at z = 2.1-2.5 using the Ks-band photometry of ZFOURGE
• Improved Measurements of Galaxy Star Formation Stochasticity from the Intrinsic Scatter of Burst Indicators
• A stochastic model to reproduce the star-formation history of individual galaxies in hydrodynamic simulations
• The recent star formation history of NGC 628 on resolved scales
• The JWST Emission Line Survey (JELS): The sizes and merger fraction of star-forming galaxies during the Epoch of Reionization