Affan Adly Nazri

Multi-epoch very long baseline interferometry (VLBI) observations measure three-dimensional water maser motions in protostellar outflows, enabling analysis of inclination and velocity. However, these analyses assume that water masers and shock surfaces within outflows are co-propagating. We compare VLBI data on maser-traced bow shocks in the high-mass protostar AFGL 5142-MM1, from seven epochs of archival data from the VLBI Exploration of Radio Astrometry (VERA), obtained from 2014 April to 2015 May, and our newly conducted data from the KVN and VERA Array (KaVA), obtained in 2016 March. We find an inconsistency between the expected displacement of the bow shocks and the motions of individual masers. The separation between two opposing bow shocks in AFGL 5142-MM1 was determined to be 337.17 ± 0.07 mas in the KaVA data, which is less than an expected value of 342.1 ± 0.7 mas based on extrapolation of the proper motions of individual maser features measured by VERA. Our measurements imply that the bow shock propagates at a velocity of 24 ± 3 km s-1, while the individual masing gas clumps move at an average velocity of 55 ± 5 km s-1; that is, the water masers are moving in the outflow direction at double the speed at which the bow shocks are propagating. Our results emphasize that investigations of individual maser features are best approached using short-term high-cadence VLBI monitoring, while long-term monitoring on timescales comparable to the lifetimes of maser features is better suited to tracing the overall evolution of shock surfaces. Observers should be aware that masers and shock surfaces can move relative to each other, and that this can affect the interpretation of protostellar outflows.

High-redshift radio(-loud) galaxies (HzRGs) are massive galaxies with powerful radio-loud active galactic nuclei (AGNs) and serve as beacons for protocluster identification. However, the interplay between HzRGs and the large-scale environment remains unclear. To understand the connection between HzRGs and the surrounding obscured star formation, we investigated the overdensity and spatial distribution of submillimeter-bright galaxies (SMGs) in the field of 4C 23.56, a well-known HzRG at z = 2.48. We used SCUBA-2 data (σ \~ 0.6 mJy) to estimate the 850μm source number counts and examine the radial and azimuthal overdensities of the 850μm sources in the vicinity of the HzRG. The angular distribution of SMGs is inhomogeneous around the HzRG 4C 23.56, with fewer sources oriented along the radio jet. We also find a significant overdensity of bright SMGs (S_850 ≥ 5 mJy). Faint and bright SMGs exhibit different spatial distributions. The former are concentrated in the core region, while the latter prefer the outskirts of the HzRG field. High-resolution observations show that the seven brightest SMGs in our sample are intrinsically bright, suggesting that the overdensity of bright SMGs is less likely due to the source multiplicity.