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.

 

[Harry Costas]

Scientists have gone beyond where no man has gone before.
We are living in amazing times.


[Submitted on 25 Jan 2025]

Spatially-resolved spectro-photometric SED Modeling of NGC 253's Central Molecular Zone I. Studying the star formation in extragalactic giant molecular clouds​

Pedro K. Humire, Subhrata Dey, Tommaso Ronconi, Victor H. Sasse, Roberto Cid Fernandes, Sergio Martín, Darko Donevski, Katarzyna Małek, Juan A. Fernández-Ontiveros, Yiqing Song, Mahmoud Hamed, Jeffrey G. Mangum, Christian Henkel, Víctor M. Rivilla, Laura Colzi, N. Harada, Ricardo Demarco, Arti Goyal, David S. Meier, Swayamtrupta Panda, Ângela C. Krabbe, Yaoting Yan, Amanda R. Lopes, K. Sakamoto, S. Muller, K. Tanaka, Y. Yoshimura, K. Nakanishi, Antonio Kanaan, Tiago Ribeiro, William Schoenell, Claudia Mendes de Oliveira

Studying the interstellar medium in nearby starbursts is essential for understanding the physical mechanisms driving these objects, thought to resemble young star-forming galaxies. This study aims to analyze the physical properties of the first spatially-resolved multi-wavelength SED of an extragalactic source, spanning six decades in frequency (from near-UV to cm wavelengths) at an angular resolution of 3′′ (51 pc at the distance of NGC,253). We focus on the central molecular zone (CMZ) of NGC,253, which contains giant molecular clouds (GMCs) responsible for half of the galaxy's star formation. We use archival data, spanning optical to centimeter wavelengths, to compute SEDs with the GalaPy and CIGALE codes for validation, and analyze stellar optical spectra with the \textsc{starlight} code.
Our results show significant differences between central and external GMCs in terms of stellar and dust masses, star formation rates (SFRs), and bolometric luminosities. We identify the best SFR tracers as radio continuum bands at 33 GHz, radio recombination lines, and the total infrared luminosity (LIR; 8-1000μm), as well as 60μm IR emission. BPT and WHAN diagrams indicate shock signatures in NGC~253's nuclear region, associating it with AGN/star-forming hybrids, though the AGN fraction is negligible (≤7.5%). Our findings show significant heterogeneity in the CMZ, with central GMCs exhibiting higher densities, SFRs, and dust masses compared to external GMCs. We confirm that certain centimeter photometric bands can reliably estimate global SFR at GMC scales.

 

[Harry Costas]

Dust to dust. Could this be how stars formed?
Trillions upon trillions of stars would take infinity to form in this way.

[Submitted on 26 Jan 2025]

The influence of dust growth on the observational properties of circumplanetary discs​

Matthäus Schulik, Bertram Bitsch, Anders Johansen, Michiel Lambrechts

Dust growth is often indirectly inferred observationally in star-forming environments, theoretically predicted to produce mm-sized particles in circumstellar discs, and also presumably witnessed by the predecessors of the terrestrial meteoritic record. For those reasons it is believed that young gas giants under formation in protoplanetary discs with putative circumplanetary discs (CPDs) surrounding them, such as PDS 70c, should be containing mm-sized particles. We model the spectra of a set of CPDs, which we obtained from radiation hydrodynamic simulations at varying Rosseland opacities kappa_R. The kappa_R from the hydrodynamic simulations are matched with consistent opacity sets of ISM-like composition, but grown to larger sizes. Our high kappa_R hydro data nominally corresponds to 10 mum-sized particles, and our low kappa_R-cases correspond to mm-sized particles. We investigate the resulting broad spectral features at first while keeping the overall optical depth in the planetary envelope constant. Dust growth to size distributions dominated by millimeter particles generally results in broad, featureless spectra with black-body like slopes in the far-infrared, while size distributions dominated by small dust develop steeper slopes in the far-infrared and maintain some features stemming from individual minerals. We find that significant dust growth from microns to millimeters can explain the broad features of the PDS 70c data, when upscaling the dust masses from our simulations by x100. Furthermore our results indicate that the spectral range of 30-500 mum is an ideal hunting ground for broadband features arising from the CPD, but that longer wavelengths observed with ALMA can also be used for massive circumplanetary discs