Question How do stars form?

[Harry Costas]

We are at the initial steps of understanding Star Formation.
So until then, we keep learning.
Yes, we all have opinions; some seem to be the better for now.

[Submitted on 2 Jan 2025]

Photometric Objects Around Cosmic Webs (PAC). VII. Disentangling Mass and Environment Quenching with the Aid of Galaxy-halo Connection in Simulations​

Yun Zheng, Kun Xu, Donghai Zhao, Y.P. Jing, Hongyu Gao, Xiaolin Luo, Ming Li

Star formation quenching in galaxies is a critical process in galaxy formation. It is widely believed that the quenching process is dominated by the mass of galaxies and/or their environment. In Paper V, we addressed the challenge to disentangle the effects of mass and environment by employing the PAC method, which combines spectroscopic and deep photometric surveys. This approach enabled us to measure the excess surface density of blue and red galaxies around massive central galaxies down to 109.0M⊙. However, it is not straightforward to completely separate the two this http URL address this issue, in this paper, we derive the average quenched fraction of central (isolated) galaxies, f¯cenq(M∗), by combining the 3D quenched fraction distribution fsatq(r;M∗,cen,M∗,sat), reconstructed from the n¯2wp(rp) measurements, with the stellar mass-halo mass relation in N-body simulations from Paper IV, and the observed total quenched fraction, f¯allq(M∗). Using fsatq(r;M∗,cen,M∗,sat), f¯cenq(M∗), and the galaxy-halo connection, we assign a quenched probability to each (sub)halo in the simulation, enabling a comprehensive study of galaxy quenching. We find that the mass-quenched fraction increases from 0.3 to 0.87 across the stellar mass range [109.5,1011.0]M⊙, while the environmental quenched fraction decreases from 0.17 to 0.03. The mass effect dominates galaxy quenching across the entire stellar mass range we studied. Moreover, more massive host halos are more effective at quenching their satellite galaxies, while satellite stellar mass has minimal influence on environmental quenching.

 

[Harry Costas]

For those who read these papers, good searching.

[Submitted on 2 Jan 2025]

The long road to the Green Valley: Tracing the evolution of the Green Valley galaxies in the EAGLE simulation​

Apashanka Das, Biswajit Pandey

We study the evolution of the progenitors of the present-day Green Valley (GV) galaxies across redshift z=10−0 using data from the EAGLE simulations. We identify the present-day green valley galaxies using entropic thresholding and track the evolution of the physical properties of their progenitors up to z=10. Our study identifies three distinct phases in their evolution: (i) an early growth phase (z=10−6), where progenitors are gas-rich, efficiently form stars, and experience AGN feedback regulating star formation in massive galaxies, (ii) a transition phase (z=6−2), marked by frequent interactions and mergers in higher-density environments, driving starbursts, depleting gas reservoirs, and strengthening correlations between cold gas and halo properties, and (iii) a quenching phase (z=2−0), dominated by environmental and mass-dependent processes that suppress star formation and deplete cold gas. Our analysis shows that at z<1, environmental factors and cold gas depletion dominate quenching, with tighter correlations between stellar mass, SFR, and cold gas content. The interplay between mass and environmental density during this period drives diverse and distinct evolutionary pathways. Low-mass progenitors evolve gradually in low-density regions due to secular processes and slow gas depletion, while those in high-density environments quench rapidly via environmental mechanisms. High-mass progenitors in low-density environments exhibit prolonged green valley phases driven by internal processes. In contrast, those in dense environments undergo quenching more quickly due to the combined effects of internal and external processes. Our findings provide a comprehensive view of the mechanisms shaping the GV population across cosmic time.