[Paper Review] Blowing out the Candle: How to Quench Galaxies at High Redshift -- an Ensemble of Rapid Starbursts, AGN Feedback and Environment

Lucas C. Kimmig, Rhea–Silvia Remus+4 more|arXiv (Cornell University)|Oct 24, 2023

Astronomy and Astrophysical Research11 citations

TL;DR

The paper uses Magneticum Pathfinder simulations to show that massive quiescent galaxies at z~3.4 form and quench via a rapid, isotropic gas collapse-driven starburst followed by AGN feedback, with environment also playing a role.

ABSTRACT

Recent observations with JWST and ALMA have revealed extremely massive quiescent galaxies at redshifts of z=3 and higher, indicating both rapid onset and quenching of star formation. Using the cosmological simulation suite Magneticum Pathfinder we reproduce the observed number densities and stellar masses, with 36 quenched galaxies of stellar mass larger than 3e10Msun at z=3.42. We find that these galaxies are quenched through a rapid burst of star-formation and subsequent AGN feedback caused by a particularly isotropic collapse of surrounding gas, occurring on timescales of around 200Myr or shorter. The resulting quenched galaxies host stellar components which are kinematically fast rotating and alpha-enhanced, while exhibiting a steeper metallicity and flatter age gradient compared to galaxies of similar stellar mass. The gas of the galaxies has been metal enriched and ejected. We find that quenched galaxies do not inhabit the densest nodes, but rather sit in local underdensities. We analyze observable metrics to predict future quenching at high redshifts, finding that on shorter timescales <500Myr the ratio M_bh/M_* is the best predictor, followed by the burstiness of the preceding star-formation, t50-t90 (time to go from 50% to 90% stellar mass). On longer timescales, >1Gyr, the environment becomes the strongest predictor, followed by t50-t90, indicating that at high redshifts the consumption of old and lack of new gas are more relevant for long-term prevention of star-formation than the presence of a massive AGN. We predict that relics of such high-z quenched galaxies should best be characterized by a strong alpha enhancement.

Motivation & Objective

• Explore how massive quiescent galaxies form and quench at high redshift (z > 3).
• Quantify the roles of rapid starbursts, AGN feedback, and environment in quenching.
• Compare simulated quenched galaxies to observations in number density and stellar mass.
• Characterize the internal structure and chemical properties of quenched vs. non-quenched galaxies.

Proposed method

• Utilize the Magneticum Pathfinder Box3 uhr cosmological hydrodynamical simulation with (128 Mpc/h)^3 volume and high mass/force resolution.
• Identify quenched galaxies at z=3.42 with SFR = 0 or equivalently sSFR < 0.3/tHub as a cross-check.
• Track galaxy progenitors and halos from z~15 to z=2 using L-BaseTree for individual assembly histories.
• Analyze gas density, temperature, and metallicity profiles to study quenching and gas expulsion, including isotropic gas collapse scenarios.
• Compare global star formation rate density and maximum stellar mass evolution against observations from JWST, ALMA and HST.
• Examine observational predictors of future quenching, including Mbh/M* and burstiness t50–t90, across timescales <500 Myr and >1 Gyr.

Experimental results

Research questions

• RQ1 What mechanisms drive the rapid quenching of massive galaxies at z ~ 3–4 in the Magneticum simulation?
• RQ2 How do rapid starbursts, AGN feedback, and environmental factors individually and collectively contribute to quenching?
• RQ3 What are the structural, kinematic, and chemical signatures of quenched vs. non-quenched galaxies at high redshift?
• RQ4 Can observable metrics predict future quenching timescales for high-z galaxies, and which factors dominate on short vs. long timescales?

Key findings

• Quenched galaxies (~36 at z=3.42 in the sample) arise from a rapid starburst coincident with an isotropic gas collapse, followed by strong AGN feedback that ejects gas out to large radii.
• Quenched centrals are kinematically fast-rotating and alpha-enhanced, with steeper metallicity and flatter age gradients compared to similarly massive non-quenched galaxies.
• Quenched galaxies reside in local underdensities rather than the densest nodes of the cosmic web; environment influences quenching on longer timescales.
• On short timescales (<500 Myr), the best predictor of future quenching is Mbh/M* followed by the burstiness of the preceding star formation (t50–t90).
• On timescales >1 Gyr, environment becomes the strongest predictor, followed by t50–t90, suggesting old-gas consumption and lack of fresh gas dominate long-term quenching more than AGN presence.
• Relics of high-z quenched galaxies are expected to show strong alpha-enhancement.