Affan Adly Nazri

We present a comprehensive study of formaldehyde (H₂CO) absorption and radio recombination line (H_110α) emission in 215 molecular clouds from the Bolocam Galactic Plane Survey, observed using the Nanshan 25 m radio telescope. H₂CO was detected in 88 sources (40.93%) with 59 being new detections, while H_110α emission was found in only 11 sources (5.12%), all coincident with H₂CO absorption. There exists a correlation of H₂CO fluxes with millimeter fluxes below a \(3~\mathrm{Jy}\) threshold and an increased dispersion above it, suggesting the sub-cosmic microwave background cooling of H₂CO. Cross-matching with kinematic distance catalogs revealed H₂CO spanning galactocentric distances from \(0.216\) to \(10.769~\mathrm{kpc}\), with column densities ranging from \(7.82 \times 10^{11}\) to \(6.69 \times 10^{14}~\mathrm{cm}^{-2}\). A significant inverse correlation was observed between H₂CO detection fraction and galactocentric distance, suggesting enhanced star-forming activity closer to the Galactic Center. These findings challenge traditional Galactic Habitable Zone (GHZ) models by demonstrating the presence of biogenic precursors in the inner Galaxy, shielded within dense molecular clouds. Our results underscore the importance of incorporating chemical tracers such as H₂CO, alongside physical constraints to refine the boundaries of the GHZ and advance the research of prebiotic chemistry in the Milky Way.

Extensive radio frequency interference (RFI) monitoring is essential in the site selection process before constructing radio astronomy observatories, followed by mitigation strategies to minimize its adverse effects. Malaysia has an enormous prospect for radio astronomy due to its prominent location in the centre of Southeast Asia, but is challenged by its relatively high population density. In this research article, we perform high-cadence, low-frequency RFI monitoring at two sites, each representing an urban and a rural environment. Using modified generalized spectral kurtosis (GSK) as an RFI detection method, we ascertain the suitability of Glami Lemi, a rural area in the centre of Peninsular Malaysia previously assigned as a candidate radio notification zone (RNZ), as a potential site for radio astronomy observations due to its lower RFI contamination in our high-cadence monitoring, especially when compared with urban areas. We identified a number of persistent and transient RFI in our dataset, associate each of them with their potential origins and, if present, characterize their temporal evolution. A few types of RFI mitigation strategies were also tested and discussed. This study lays the groundwork for Malaysia's endeavours in establishing its first research-grade radio telescope, emphasizing the importance of robust RFI detection and mitigation strategies in optimizing observational outcomes.

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 \(337.17 \pm 0.07~\mathrm{mas}\) in the KaVA data, which is less than an expected value of \(342.1 \pm 0.7~\mathrm{mas}\) 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 \(24 \pm 3~\mathrm{km}~\mathrm{s}^{-1}\), while the individual masing gas clumps move at an average velocity of \(55 \pm 5~\mathrm{km}~\mathrm{s}^{-1}\); 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.