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An (in)complete NIRSpec census of Balmer absorption in Type 1 AGN -- radiation-driven outflows in little red dots, quasars and variable stars
Ignas Juod\v{z}balis, Xihan Ji, Francesco D'Eugenio, Jan Scholtz, Roberto Maiolino, Amanda Stoffers, Alessandro Marconi, Elena Bertola, Andrew J. Bunker, Stefano Carniani, Giovanni Cresci, Emma Curtis-Lake, Zheng Ma, Cosimo Marconcini, Eleonora Parlanti, Pierluigi Rinaldi, Brant Robertson, Hannah \"Ubler, Giacomo Venturi, Junyu Zhang
https://arxiv.org/abs/2607.19057 https://arxiv.org/pdf/2607.19057 https://arxiv.org/html/2607.19057
arXiv:2607.19057v1 Announce Type: new
Abstract: A notable achievement of the first generation of JWST surveys was the discovery of an abundance of faint high-redshift ($z > 4$) broad-line active galactic nuclei (AGN) in the $L_{\rm bol} < 10^{45}$~erg~s$^{-1}$ regime, previously only accessible at $z < 1$. The high prevalence of absorption features in their broad hydrogen lines is one of the peculiarities of a significant fraction of this new population. In this paper, we conduct a broad census of Balmer absorption in a sample of 47 Type-1 AGN spanning $2 < z < 7$. Accounting for incompleteness of JWST spectroscopic data, we estimate that $44_{-6}^{ 21}$~\% of Little Red Dots (LRDs) have absorption in \Has while the incidence rate is $< 25$~\% (at 2$\sigma$) in Little Blue Dots (LBDs). Additionally, R1000 JWST/NIRSpec data is strongly resolution limited, implying an inability to disentangle Doppler broadening in the absorption from optical depth effects. This is alleviated with R2700 observations, although some degeneracies remain. We find a significant correlation between the velocity of the Balmer absorption and the [OIII]5007 narrow line luminosity, suggesting a common driving mechanism. We do not find any other significant correlations (and do not confirm previously claimed correlations) between Balmer absorption and other spectral properties of LRDs (except for the expected correlation between \Has and \Hbs absorption velocities). Comparing LRDs, quasars and stellar \Has absorbers, we establish that absorption in both LRDs and broad absorption line quasars is consistent with radiatively driven outflows, echoing the physics of variable stars yet occurring at vastly different scales.
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Fast ungated five-dimensional cardiac MRI on a 1.5 T MR-linac for MRI-guided radiotherapy
M. L. Terpstra, T. E. Olausson, M. M. N. Aubert, C. Beijst, A. Sbrizzi, C. A. T. van den Berg, M. F. Fast
https://arxiv.org/abs/2607.16033 https://arxiv.org/pdf/2607.16033 https://arxiv.org/html/2607.16033
arXiv:2607.16033v1 Announce Type: new
Abstract: Background: Stereotactic arrhythmia radio-ablation (STAR) for patients with ventricular tachycardia is currently limited by complex cardiorespiratory motion. Current 5D-MRI motion models require long acquisition and reconstruction times, limiting clinical viability. Objective: To develop a fast, ungated 5D-MRI reconstruction method for personalized motion characterization to support MRI-guided STAR treatments. Methods: We propose a fast, ungated 5D-MRI reconstruction method based on the CMR-MOTUS framework. The method uses a 3D Cartesian acquisition with a joint optimization framework to reconstruct a motion-corrected reference image and low-rank deformation vector fields (DVFs). By exploiting the low rank structure, we explicitly disentangle respiratory and cardiac motion during optimization. Then, the DVFs are used for 5D-MRI reconstruction with a retrospectively adjustable number of motion states. Validation was performed using digital and physical cardiorespiratory phantoms. Furthermore, the approach was evaluated using 10 healthy volunteers, comparing motion consistency with 2D cine MRI. Results: Validation of 5D CMR-MOTUS using digital and physical phantoms demonstrated accurate 5D-MRI reconstruction. In the physical phantom, 5D CMR-MOTUS achieved a left-ventricle DICE of 0.96 /- 0.01. In the volunteer cohort, the 5D-MRI scans showed strong motion to 2D cine MRI, with a cardiac motion error of 0.1 /- 0.9 mm and a respiratory motion error of 0.2 /- 2.9 mm. Crucially, 5D-MRI data were acquired in 1 minute and reconstructed in 6 minutes. Conclusions: The proposed 5D-MRI method enables rapid, high-quality, and personalized motion characterization, demonstrating potential for integration into MRI-guided STAR treatments. Data Availability: The 3D k-space data and 5D reconstructions for the ten volunteers are publicly available at https://doi.org/10.5281/zenodo.21278894
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