分类： 天文学 >> 天文学 提交时间： 2023-02-19
Sharon Lapiner
Avishai Dekel
Jonathan Freundlich
Omri Ginzburg
Fangzhou Jiang
Michael Kretschmer
Sandro Tacchella
Daniel Ceverino
Joel Primack
摘要： We utilize high-resolution cosmological simulations to reveal that high-redshift galaxies tend to undergo a robust `wet compaction' event when near a `golden' stellar mass of $\sim 10^{10} M_{\odot}$. This is a gaseous shrinkage to a compact star-forming phase, a `blue nugget' (BN), followed by central quenching of star formation to a compact passive stellar bulge, a `red nugget' (RN), and a buildup of an extended gaseous disc and ring. Such nuggets are observed at cosmic noon and seed today's early-type galaxies. The compaction is triggered by a drastic loss of angular momentum due to, e.g., wet mergers, counter-rotating cold streams, or violent disc instability. The BN phase marks drastic transitions in the galaxy structural, compositional and kinematic properties. The transitions are from star-forming to quenched inside-out, from diffuse to compact with an extended disc-ring and a stellar envelope, from dark matter to baryon central dominance, from prolate to oblate stellar shape, from pressure to rotation support, from low to high metallicity, and from supernova to AGN feedback. The central black hole growth, first suppressed by supernova feedback when below the golden mass, is boosted by the compaction, and the black hole keeps growing once the halo is massive enough to lock in the supernova ejecta.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jorge A. Zavala
Veronique Buat
Caitlin M. Casey
Denis Burgarella
Steven L. Finkelstein
Micaela B. Bagley
Laure Ciesla
Emanuele Daddi
Mark Dickinson
Henry C. Ferguson
Maximilien Franco
E. F. Jim'enez-Andrade
Jeyhan S. Kartaltepe
Anton M. Koekemoer
Aurélien Le Bail
E. J. Murphy
Casey Papovich
Sandro Tacchella
Stephen M. Wilkins
Itziar Aretxaga
摘要： Lyman Break Galaxy (LBG) candidates at z>10 are rapidly being identified in JWST/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts (z10 LBGs, representing potential contaminants in LBG candidate samples. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but detected at longer wavelengths. Combining the JWST data with (sub)millimeter constraints, including deep NOEMA interferometric observations, we show that this source is a dusty star-forming galaxy (DSFG) at z~5.1. We also present a tentative 2.6sigma SCUBA-2 detection at 850um around a recently identified z~16 LBG candidate in the same field and show that, if the emission is real and associated with this candidate, the available photometry is consistent with a z~5 dusty galaxy with strong nebular emission lines despite its blue near-IR colors. Further observations on this candidate are imperative to mitigate the low confidence of this tentative submillimeter emission and its positional uncertainty. Our analysis shows that robust (sub)millimeter detections of NIRCam dropout galaxies likely imply z=4-6 redshift solutions, where the observed near-IR break would be the result of a strong rest-frame optical Balmer break combined with high dust attenuation and strong nebular line emission, rather than the rest-frame UV Lyman break. This provides evidence that DSFGs may contaminate searches for ultra high-redshift LBG candidates from JWST observations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We propose an analytic model, CuspCore II, for the response of dark matter (DM) haloes to central gas ejection, as a mechanism for generating DM-deficient cores in dwarfs and high-z massive galaxies. We test this model and three other methods using idealized N-body simulations. The current model is physically justified and provides more accurate predictions than the earlier version, CuspCore I (Freundlich et al. 2020). The CuspCore model assumes an instantaneous change of potential, followed by a relaxation to a new Jeans equilibrium. The relaxation turns out to be violent relaxation during the first orbital period, followed by phase mixing. By tracing the energy diffusion dE=dU(r) iteratively, the model reproduces the simulated DM profiles with ~10% accuracy or better. A method based on adiabatic invariants shows similar precision for moderate mass change but underestimates the DM expansion for strong gas ejection. A method based on a simple empirical relation between DM and total mass ratios makes slightly inferior predictions. The crude assumption used in CuspCore I, of energy conservation for shells that encompass a fixed DM mass, turns out to underestimate the DM response, which can be partially remedied by introducing an alternative "energy" definition. Our model is being generalized to address the differential response of a multi-component system of stars and DM in the formation of DM-deficient galaxies.
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