Selecting Post-Starburst Galaxies Based on Star Formation History

TL;DR

The paper introduces a direct SFH-based method to identify post-starburst (PSB) galaxies using IFU data from MaNGA, CALIFA, and AMUSING++; by calibrating global SFHs against E+A criteria and applying spatial spaxel analyses, it yields 107 PSBs with diverse quenching morphologies. It finds no strong population of Seyfert 2 PSBs, indicating AGN are not typically dominant throughout the PSB phase, while revealing varied radial quenching patterns, including inside-out rings and mixed trends in centrals and irregulars. The work demonstrates that PSBs selected via SFHs constitute a largely distinct population from traditional SDSS single-fiber PSBs, providing a more nuanced view of quenching pathways and offering a scalable framework for future IFU surveys like AMUSING++. Overall, the study highlights the heterogeneity of PSB evolution and the value of spatially resolved SFHs for understanding galaxy quenching processes.

Abstract

Post-StarBurst (PSB) galaxies are galaxies that have undergone a large burst of star formation followed by rapid quenching. Understanding their properties as a population can help us better understand how galaxies evolve to quiescence. This project aims to use Star Formation History (SFH) measurements from the Integral Field Spectroscopy (IFS) surveys MaNGA, CALIFA, and AMUSING++ processed with the Pipe3D analysis pipeline in order to select PSB galaxies as well as PSB regions in galaxies. Most PSB selection methods use cutoffs determined by spectral features, but in this work we introduce a new PSB selection method based directly on the property we are most interested in; inferred SFHs. IFS data allows us to probe a galaxy's star formation on a spatially resolved scale, enabling us to examine the size, shape, and location of PSB regions within a galaxy. We select 107 PSB galaxies, only 7 of which are among known PSBs selected by other methods. Unlike traditional PSB selection methods, our approach is not biased against Active Galactic Nuclei (AGN). Despite this, we still find no evidence for a significant Seyfert 2 PSB population, suggesting that strong AGN activity is uncommon throughout the PSB phase. Our spatially-resolved SFH selection identifies a wide range of galaxies, including globally quiescent elliptical galaxies with centrally-concentrated PSB spaxels, galaxies with ring-like PSB spaxels and a preference for inside-out age gradients (contrary to what has previously been observed in the literature), and galaxies with widespread PSB regions that have significant star formation elsewhere in the galaxy.

Figures (18)

• Figure 1: An example of the spatially-resolved luminosity fractions from Pipe3D -- each spaxel is colored according to the fraction of the total luminosity that is from stars formed in the corresponding age bin. The left panel of the plot shows the most recent 100 Myrs, the middle panel shows between 100 Myr and 1.5 Gyr, and the right panel shows the SDSS $gri$ image of this galaxy with the MaNGA IFU field overlaid, from Marvin 2019AJ....158...74C. This galaxy is one of our Ring PSBs. Also note that our burst criteria is based off of mass fraction values rather than the luminosity fraction values, which are on average lower than the luminosity fraction values.
• Figure 2: Purity, completeness and F1 score for a range of different mass cuts in the recent age bin on the x axis and the intermediate age bin on the y axis. E+A selection criteria, H$\delta_A$$>$ 4 Å and H$\alpha$$<$ 3 Å were used as the benchmark by which we could measure the purity and completeness of our sample. We chose mass cuts that maximized the F1 score. These mass cuts -- $<0.13$% in the recent age bin and $>4.8$% in the intermediate age bin -- are highlighted on all three plots with a teal square.
• Figure 3: (Left) EW H$\alpha$ vs the mass fraction in the corresponding recent age bin (the past 100 Myr) 2014AA...563A..49S2017MNRAS.469..151B. The vertical line represents H$\alpha$ = 3, where H$\alpha$$<$ 3 is one of the criteria for E+A PSBs, selecting for low sSFRs in the recent age bin. The horizontal line represents the mass cut in the recent age bin, where galaxies must have less than 0.13% of their mass formed in this age bin to meet the Summed Burst criteria. (Right) Lick H$\delta_A$ vs the corresponding intermediate age bin (100 Myr to 1.5 Gyr). Note that a log scale is not used in this panel because the H$\delta_A$ index extends to negative values for quiescent galaxies due to a nearby unrelated feature in the spectra. The vertical line represents H$\delta_A$ = 4, where H$\delta_A$$>$ 4 is one of the criteria for E+A PSBs, selecting for a burst of star formation in the intermediate age bin. The dashed horizontal line represents the mass cut in the intermediate age bin, where galaxies must have greater than 4.83% of their mass formed in this age bin to meet the Summed Burst criteria. This data is shown for every galaxy in the MaNGA sample, and is taken from the pyPipe3D datacubes. Every point represents the light-weighted average of all spaxels in a single galaxy. There is a clear correlation between the star formation history and the emission lines we use to trace the presence of O and A stars.
• Figure 4: Example of the SFH for one of our MaNGA Summed Burst PSBs (8616-12701) plotted over the past 13 Gyr in the main panel, and zoomed in over the past 1.5 Gyr in the inset panel. There is a large spike in star formation at approximately 1 Gyr, and low specific SFR at more recent ages. Teal vertical lines have been drawn at 100 Myr and 1.5 Gyr, and the corresponding regions have been shaded pink and peach respectively. The individual points represent values at the discrete ages.
• Figure 5: Examples of a Ring (indigo), Central (blue), Irregular (orange), and Irregular + Companion (red) distribution of PSB spaxels from MaNGA. According to our selection criteria, PSB spaxels and non-PSB spaxels are shown in green and blue respectively. The limits of the hexagonal IFU are visible. In each panel, the leftmost column shows the IFU data after the signal to noise cut, and the rightmost column shows the image of the galaxy from Marvin 2019AJ....158...74C. The Ring galaxy shows all of its PSB spaxels in a continuous ring, with a clear hole in the center. The Central galaxy shows a concentration of PSB spaxels in the center. The Irregular galaxy does not fit into either of the above categories, and shows a random distribution of PSB spaxels throughout both the center and edges. The Irregular + Companion galaxy has some of its PSB spaxels coming from a nearby galaxy.