SQuIGGL⃗E : Studying Quenching in Intermediate-z Galaxies—Gas, AnguL⃗ar Momentum, and Evolution

Abstract

We describe the Studying Quenching in Intermediate-z Galaxies: Gas, angu L → ar momentum, and Evolution ( SQuIGG L ⃗ E ) survey of intermediate-redshift post-starburst galaxies. We leverage the large sky coverage of the Sloan Digital Sky Survey to select ∼ 1300 recently quenched galaxies at 0.5 < z ≤ 0.9 based on their unique spectral shapes. These bright, intermediate-redshift galaxies are ideal laboratories to study the physics responsible for the rapid quenching of star formation: they are distant enough to be useful analogs for high-redshift quenching galaxies, but low enough redshift that multiwavelength follow-up observations are feasible with modest telescope investments. We use the Prospector code to infer the stellar population properties and nonparametric star formation histories (SFHs) of all galaxies in the sample. We find that SQuIGG L ⃗ E galaxies are both very massive (M * ∼ 1011.25 M ⊙) and quenched, with inferred star formation rates ≲1 M ⊙ yr−1, more than an order of magnitude below the star-forming main sequence. The best-fit SFHs confirm that these galaxies recently quenched a major burst of star formation: >75% of SQuIGG L ⃗ E galaxies formed at least a quarter of their total stellar mass in the recent burst, which ended just ∼200 Myr before observation. We find that SQuIGG L ⃗ E galaxies are on average younger and more burst-dominated than most other z ≲ 1 post-starburst galaxy samples. This large sample of bright post-starburst galaxies at intermediate redshift opens a wide range of studies into the quenching process. In particular, the full SQuIGG L ⃗ E survey will investigate the molecular gas reservoirs, morphologies, kinematics, resolved stellar populations, active galactic nucleus incidence, and infrared properties of this unique sample of galaxies in order to place definitive constraints on the quenching process.

The Compact Structures of Massive z ∼ 0.7 Post-starburst Galaxies in the SQuIGGL⃗E Sample

“…The  L SQuIGG E sample is selected from the SDSS DR14 spectroscopic sample (Abolfathi et al 2018) using the rest-frame U m , B m , and V m medium-band filters from Kriek et al (2010) to select galaxies with strong Balmer breaks (indicated by red U m − B m colors) and blue slopes redward of the break (indicated by blue B m − V m colors). In Suess et al (2022), we show that this method reliably selects post-starburst galaxies that were quenched within the last ∼500 Myr, 75% of which formed >25% of their stellar mass in a recent burst, and further discuss the specific selection effects and how they differ from other post-starburst selection techniques. While SDSS imaging exists for the entire sample, the depth and resolution is not sufficient to resolve the galaxies.…”

“…Uncertainties derived by refitting the galaxies using a range of PSF models from nearby locations on the sky are shown in Table 2. For details, see Section 3.1. c The residual-corrected effective radii were derived using the method of Szomoru et al (2012), described in Section 3.3. d The Gini coefficient (G) and the generalized concentration (GC) were measured on the segmentation maps described in Section 3.1, for details see Section 4.3. e The time since quenching (t q ) and the burst fraction are model parameters derived from nonparametric star formation history fitting of the galaxies, see Suess et al (2022) for details.…”

“…Because the youngest, brightest stars in newly formed stellar populations die the most quickly, a central starburst's influence on the size of a galaxy would become weaker with time, leading to size growth as a function of the time since quenching. In Figure 10, we show a subset of the  L SQuIGG E sample divided up into bins of burst mass fraction (as measured in Suess et al 2022) to show trends for galaxies which formed a similar fraction of their stellar mass in the recent burst of star formation. None of these bins show the predicted positive trend for a central starburst; conversely, the smallest and largest burst fraction bins are consistent with a negative slope (Spearman correlations for the 0%-20% bin: ρ = −0.52, p = 0.004; Spearman correlations for the 40%-60% bin: ρ = −0.38, p = 0.01), and the central bin is consistent with no slope (Spearman correlation for the 20%-40% bin: ρ = −0.10, p = 0.45).…”

“…All these methods have in common the goal of selecting galaxies with light dominated by a young stellar population with no ongoing star formation (for a detailed review of post-starburst selection methods, see French 2021). Although a dramatic burst of star formation is not strictly required as suggested by the term post-starburst-the spectral signatures seen in post-starburst galaxies can be produced by the truncation of the existing high star formation rate-it is thought that bursts do accompany quenching in high-mass galaxies (e.g., French et al 2015;Wild et al 2020;Suess et al 2022). Post-starburst galaxies serve as a laboratory for understanding the progenitors of the rapid quenching channel and their evolution immediately after star formation shuts off can shed light on the conditions that caused the galaxies to cease forming new stars.…”

“…However, spectroscopic samples of post-starburst galaxies at intermediate redshift are accessible in the Sloan Digital Sky Survey (SDSS) thanks in large part to the CMASS BOSS sample (Dawson et al 2013), which targeted high-mass red galaxies at intermediate redshift. Leveraging this spectroscopic sample in addition to a handful of ancillary SDSS programs, we have launched the  L SQuIGG E survey (Suess et al 2022), which spectroscopically identified 1318 post-starburst galaxies in the SDSS at z > 0.5 with spectral signatures that indicate that they have recently shut off their primary epoch of star formation. Crucially, these spectra allow us to characterize the properties of the burst to measure the time since star formation was quenched and to track the evolution of the sample in key properties as a function of the time since quenching.…”