Galaxy formation and evolution

Abstract:

As the closest known active galactic nucleus, Centaurus A (Cen A) provides a rich environment for astrophysical exploration. It has been observed across wavelengths from radio to gamma-rays, and indications of ongoing particle acceleration have been found on different scales. Recent measurements of very-high-energy (VHE) gamma-rays ( GeV) by the HESS observatory have inferred the presence of ultra-relativistic electrons along Cen A’s jet, yet the underlying acceleration mechanism remains uncertain. Various authors have proposed that jet substructures, known as knots, may serve as efficient particle accelerators. In this study, we investigate the hypothesis that knots are the particle acceleration sites along Cen A’s jets. We focus on stationary knots, and assume that they result from interactions between the jet and the stellar winds of powerful stars. By combining relativistic hydrodynamic simulations and shock acceleration theory with the radio and X-ray data, we compare theoretical predictions with morphological and spectral data from different knots. We estimate the maximum electron energy and the resulting VHE gamma-ray emission. Our findings suggest that electrons accelerated at the knots are responsible for the gamma-ray spectrum detected in the VHE band.

Abstract:

The ALMACAL −22 surv e y includes o v er 2700 h of observations of ALMA phase and amplitude calibrators, spanning frequencies from 84 to 950 GHz across bands 3 to 10. In total, 687 out of the 1047 calibrators have redshifts confirmed with spectroscopy and we find an additional 50 featureless blazars. The redshift distribution of the ALMACAL-22 sample peaks at z ≈1 and spans a wide range, from the nuclei of nearby galaxies at z ≪0 . 01 to quasars at z = 3 . 742. 70 new VLT/X-Shooter spectra of these sources co v ering UV to NIR wavelengths are also presented, which will be used in future stacking experiments to search for cold gas in the circumgalactic medium. Infrared magnitudes from WISE indicate that the majority of the sources are consistent with being quasars or blazars. After fitting the radio spectral energy distributions of the calibrators, we find that most ALMA calibrators exhibit peaked spectra or are re-triggered which is surprising given the large number of blazars in the sample. The peak frequencies span three orders of magnitude from 100 MHz to 170 GHz, corresponding to linear sizes ranging from sub-pc to > 10 kpc. In the future, when combined with high-resolution radio imaging, these results will of fer v aluable constraints on the molecular gas content of the CGM, as well as the ages and duty cycles of AGN jets. The e ver-gro wing ALMACAL data set will remain an indispensable resource for studying the various aspects of galaxy formation and evolution.

Abstract:

Understanding the sources that power nebular emission in high-redshift galaxies is fundamentally important not only for shedding light on to the drivers of reionization, but to constrain stellar populations and the growth of black holes. Here, we focus on an individual object, GS9422, a galaxy at with exquisite data from the JWST Advanced Deep Extragalactic Survey (JADES), JWST Extragalactic Medium-band Survey (JEMS), and First Reionization Epoch Spectroscopically Complete Observations (FRESCO) surveys, including 14-band JWST/NIRCam photometry and deep NIRSpec prism and grating spectroscopy. We map the continuum emission and nebular emission lines across the galaxy on 0.2-kpc scales. GS9422 has been claimed to have nebular-dominated continuum and an extreme stellar population with top-heavy initial mass function. We find clear evidence for different morphologies in the emission lines, the rest-ultraviolet and rest-optical continuum emission, demonstrating that the full continuum cannot be dominated by nebular emission. While multiple models reproduce the spectrum reasonably well, our preferred model with a type-2 active galactic nucleus (AGN) and local damped Ly (DLA) clouds can explain both the spectrum and the wavelength-dependent morphology. The AGN powers the off-planar nebular emission, giving rise to the Balmer jump and the emission lines, including Ly, which therefore does not suffer DLA absorption. A central, young stellar component dominates the rest-UV emission and – together with the DLA clouds – leads to a spectral turn over. A disc-like, older stellar component explains the flattened morphology in the rest-optical continuum. We conclude that GS9422 is consistent with being a normal galaxy with an obscured, type-2 AGN – a simple scenario, without the need for exotic stellar populations.

Abstract:

Like many areas of astrophysics and cosmology, the Vera C. Rubin Observatory will be transformational for almost all the applications of strong lensing, thanks to the dramatic increase in the number of known strong lenses by two orders of magnitude or more and the readily available time-domain data for the lenses with transient sources. In this article, we provide an overview of the forecasted number of discovered lenses of different types and describe the primary science cases these large lens samples will enable. We provide an updated forecast on the joint constraint for the dark energy equation-of-state parameters, w0 and wa, from combining all strong-lensing probes of dark energy. We update the previous forecast from the Rubin Observatory Dark Energy Science Collaboration’s Science Review Document by adding two new crucial strong-lensing samples: lensed type Ia supernovae and single-deflector lenses with measured stellar kinematics. Finally, we describe the current and near-future activities and collaborative efforts within the strong-lensing community in preparation for the arrival of the first real dataset from Rubin in 2026. This article is part of the Theo Murphy meeting issue ‘Multi-messenger gravitational lensing (Part 2)’.