Probing Cosmic Dawn: Modelling the Assembly History, SEDs, and Dust Content of Selected $z\sim9$ Galaxies
MNRAS
Abstract:
The presence of spectroscopically confirmed Balmer breaks in galaxy spectral energy distributions (SEDs) at $z>9$ provides one of the best probes of the assembly history of the first generations of stars in our Universe. Recent observations of the gravitationally lensed source, MACS 1149_JD1 (JD1), indicate that significant amounts of star formation likely occurred at redshifts as high as $z\simeq15$. The inferred stellar mass, dust mass, and assembly history of JD1, or any other galaxy at these redshifts that exhibits a strong Balmer break, can provide a strong test of our best theoretical models from high-resolution cosmological simulations. In this work, we present the results from a cosmological radiation-hydrodynamics simulation of the region surrounding a massive Lyman-break galaxy. For two of our most massive systems, we show that dust preferentially resides in the vicinity of the young stars thereby increasing the strength of the measured Balmer break such that the simulated SEDs are consistent with the photometry of JD1 and two other $z>9$ systems (GN-z10-3 and GN-z9-1) that have proposed Balmer breaks at high redshift. We find strong variations in the shape and luminosity of the SEDs of galaxies with nearly identical stellar and halo masses, indicating the importance of morphology, assembly history, and dust distribution in making inferences on the properties of individual galaxies at high redshifts. Our results stress the importance that dust may play in modulating the observable properties of galaxies, even at the extreme redshifts of $z>9$.Proposed concepts for the Line Emission Terahertz Observatory (LETO) Band 1 array receiver
Abstract:
The Line Emission Terahertz Observatory (LETO) is a candidate European Space Agency (ESA) M8 mission designed to investigate the interstellar medium, star formation, and the evolution of galaxies through velocity-resolved spectroscopy of key far-infrared emission lines. To meet the demanding sensitivity, spectral-resolution, and mapping-speed requirements of the mission, LETO will employ multi-pixel heterodyne receiver arrays operating across four frequency bands between 0.45 and 5.5 THz.This paper presents proposed concepts for the LETO Band 1 array receiver, which targets the frequency range below 1 THz using superconductor-insulator-superconductor (SIS) mixer technology. A wideband SIS mixer design covering the baseline 450–650 GHz frequency range is described. The design builds upon proven receiver technologies developed for astronomical instruments, thereby reducing technical risk while maintaining near quantum-limited sensitivity.
Two complementary array architectures are investigated. The first employs a conventional single-polarisation mixer configuration that can be reconfigured to support either single- or dual-polarisation observations. The second is based on a fourprobe dual-polarisation mixer concept that eliminates mechanically reconfigurable optical components while providing flexible observing modes. Several operational configurations are presented, demonstrating how the proposed architecture can balance sensitivity, mapping speed, and spacecraft resource constraints. These concepts form the basis for future development of the LETO Band 1 receiver should the mission progress to subsequent study phases.
Revealing new high-redshift quasar populations through Gaussian mixture model selection
Astronomy & Astrophysics, Volume 660, id.A22, 15 pp.
Abstract:
We present a novel method for identifying candidate high-redshift quasars (HzQs; z ≳ 5.5) -which are unique probes of supermassive black hole growth in the early Universe- from large-area optical and infrared photometric surveys. Using Gaussian mixture models to construct likelihoods and incorporating informed priors based on population statistics, our method uses a Bayesian framework to assign posterior probabilities that differentiate between HzQs and contaminating sources. We additionally include deep radio data to obtain informed priors. Using existing HzQ data in the literature, we set a posterior threshold that accepts ∼90% of known HzQs while rejecting > 99% of contaminants such as dwarf stars or lower redshift galaxies. Running the probability selection on test samples of simulated HzQs and contaminants, we find that the efficacy of the probability method is higher than traditional colour cuts, decreasing the fraction of accepted contaminants by 86% while retaining a similar fraction of HzQs. As a test, we apply our method to the Pan-STARRS Data Release 1 (PS1) source catalogue within the HETDEX Spring field area on the sky, covering 400 sq. deg. and coinciding with deep radio data from the LOFAR Two-metre Sky Survey Data Release 1. From an initial sample of ∼5 × 105 sources in PS1, our selection shortlists 251 candidate HzQs, which are further reduced to 63 after visual inspection. Shallow spectroscopic follow-up of 13 high-probability HzQs resulted in the confirmation of a previously undiscovered quasar at z = 5.66 with photometric colours i ‒ z = 1.4, lying outside the typically probed regions when selecting HzQs based on colours. This discovery demonstrates the efficacy of our probabilistic HzQ selection method in selecting more complete HzQ samples, which holds promise when employed on large existing and upcoming photometric data sets.
SDSS-IV MaNGA: The Different Quenching Histories of Fast and Slow Rotators
MNRAS, 473, 2679