Star Formation Histories from Spectral Energy Distributions and Color–magnitude Diagrams Agree: Evidence for Synchronized Star Formation in Local Volume Dwarf Galaxies over the Past 3 Gyr

Abstract

Star formation histories (SFHs) reveal physical processes that influence how galaxies form their stellar mass. We compare the SFHs of a sample of 36 nearby (D ⪅ 4 Mpc) dwarf galaxies from the ACS Nearby Galaxy Survey Treasury (ANGST), inferred from the color–magnitude diagrams (CMDs) of individually resolved stars in these galaxies, with those reconstructed by broadband spectral energy distribution (SED) fitting using the dense basis SED-fitting code. When comparing individual SFHs, we introduce metrics for evaluating SFH reconstruction techniques. For both the SED and CMD methods, the median normalized SFH of galaxies in the sample shows a period of quiescence at lookback times of 3–6 Gyr followed by rejuvenated star formation over the past 3 Gyr that remains active until the present day. To determine if these represent special epochs of star formation in the D <4 Mpc portion of the Local Volume, we break this ANGST dwarf galaxy sample into subsets based on specific star formation rate and spatial location. Modulo offsets between the methods of about 1 Gyr, all subsets show significant decreases and increases in their median normalized SFHs at the same epochs, and the majority of the individual galaxy SFHs are consistent with these trends. These results motivate further study of potential synchronized star formation quiescence and rejuvenation in the Local Volume as well as development of a hybrid method of SFH reconstruction that combines CMDs and SEDs, which have complementary systematics.

AstroSat/UVIT Cluster Photometry in the Northern Disk of M31

“…However, the differences are smaller than 2σ for the majority of clusters. This is consistent with the studies of Olsen et al (2021) and Johnson et al (2013), which compared CMD and SED fitting methods.…”

The Sparkler: Evolved High-redshift Globular Cluster Candidates Captured by JWST

“…Spectral energy distributions (SEDs) derived from our aperture photometry were analysed using the DENSE BASIS method 18 (Iyer & Gawiser 2017;Iyer et al 2019) to determine nonparametric star formation histories (SFHs), masses, ages, metallicities, and dust extinction values for our compact sources. The DENSE BASIS fits were run with a single t 50 parameter, following the prescription of Iyer et al (2019), with the full methodology and validation tests presented by Iyer et al (2018Iyer et al ( , 2019 and Olsen et al (2021). The primary advantages of using nonparametric SFHs is that they allow us to account for multiple stellar populations, robustly derive SFH-related quantities including masses, star formation rates (SFRs), and ages, and allow us to set explicit priors in SFH space to prevent outshining due to younger stellar populations that could otherwise bias the estimates of these properties (Iyer & Gawiser 2017;Leja et al 2019;Lower et al 2020).…”

Searching for Conformity Across Cosmic Time with Local Group and Local Volume Star Formation Histories

“…The ANGST sample contains a diverse set of galaxies that, while nearby enough to be resolved, are also distant enough for integrated photometric observations. Olsen et al (2021) used these observations to compare the SFHs of Local Volume dwarf galaxies out to ∼4 Mpc from two SFH reconstruction methods corresponding to two types of observations. The first method is the CMD reconstruction method of Dolphin (2002) using Hubble Space Telescope (HST) images from the ANGST survey as shown in Weisz et al (2011a), and the second using the Dense Basis nonparametric spectral energy distribution (SED) fitting code (Iyer et al 2019) that fits the matched photometry from Johnson et al (2013) for 36 of the galaxies with good wavelength coverage.…”