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We present the analysis of cloud–cloud collision (CCC) process in the Galactic molecular complex S235. Our new CO observations performed with the PMO-13.7 m telescope reveal two molecular clouds, namely the S235-Main and the S235-ABC, with ∼4 km s−1 velocity separation. The bridge feature, the possible colliding interface and the complementary distribution of the two clouds are significant observational signatures of cloud–cloud collision in S235. The most direct evidence of cloud–cloud collision process in S235 is that the S235-Main (in a distance of 1547$^{+44}_{-43}$ pc) and S235-ABC (1567$^{+33}_{-39}$ pc) meet at almost the same position (within 1σ error range) at a supersonic relative speed. We identified ten 13CO clumps from PMO-13.7 m observations, 22 dust cores from the archival SCUBA-2 data, and 550 YSOs from NIR–MIR data. 63 per cent of total YSOs are clustering in seven MST groups (M1−M7). The tight association between the YSO groups (M1 $\&$ M7) and the bridge feature suggests that the CCC process triggers star formation there. The collisional impact subregion (the South) shows 3 ∼ 5 times higher CFE and SFE (average value of 12.3 and 10.6 per cent, respectively) than the non-collisional impact subregion (2.4 and 2.6 per cent, respectively), suggesting that the CCC process may have enhanced the CFE and SFE of the clouds compared to those without collision influence.

 

The Orion Nebula Cluster (ONC) hosts protoplanetary disks experiencing external photoevaporation by the cluster’s intense UV field. These “proplyds” are comprised of a disk surrounded by an ionization front. We present ALMA Band 3 (3.1 mm) continuum observations of 12 proplyds. Thermal emission from the dust disks and free–free emission from the ionization fronts are both detected, and the high-resolution (0.″057) of the observations allows us to spatially isolate these two components. The morphology is unique compared to images at shorter (sub)millimeter wavelengths, which only detect the disks, and images at longer centimeter wavelengths, which only detect the ionization fronts. The disks are small (r_d= 6.4–38 au), likely due to truncation by ongoing photoevaporation. They have low spectral indices (α≲ 2.1) measured between Bands 7 and 3, suggesting the dust emission is optically thick. They harbor tens of Earth masses of dust as computed from the millimeter flux using the standard method although their true masses may be larger due to the high optical depth. We derive their photoevaporative mass-loss rates in two ways: first, by invoking ionization equilibrium and second, by using the brightness of the free–free emission to compute the density of the outflow. We find decent agreement between these measurements and$\dot{M}$= 0.6–18.4 × 10⁻⁷M_⊙yr⁻¹. The photoevaporation timescales are generally shorter than the ∼1 Myr age of the ONC, underscoring the known “proplyd lifetime problem.” Disk masses that are underestimated due to being optically thick remains one explanation to ease this discrepancy.

 

Airborne fine particles favor the infection and lifecycle of H1N1 viruses and their translocation into extra-pulmonary organs. 

The line widths of broad-line regions (BLRs) of active galactic nuclei (AGNs) are key parameters for understanding central supermassive black holes. However, owing to obscuration from dusty tori, optical recombination lines from BLRs in type II AGNs cannot be directly detected. Radio recombination lines (RRLs), with low extinction, could be ideal tracers to probe the emission from BLRs in type II AGNs. We performed RRL observations for H35α and H36α towards the centre of the Circinus galaxy with Atacama Large Millimeter/submillimeter Array (ALMA). The narrow components of H35α and H36α, which are thought to be mainly from star-forming regions around the nuclear region, are detected. However, only upper limits are obtained for broad H35α and H36α. Because Circinus is one of the nearest AGNs, the non-detection of broad RRLs in Circinus in this band tells us that it is hopeless to try to detect broad RRL emission in local AGNs with current facilities. Submillimetre RRLs, with flux densities that are dozens of times higher than those at the millimetre level, could be the tools to directly detect BLRs in type II AGNs with ALMA, once its backend frequency coverage has been upgraded to several times better than its current capabilities.

 

ABSTRACT Submillimetre galaxies represent a rapid growth phase of both star formation and massive galaxies. Mapping SMGs in galaxy protoclusters provides key insights into where and how these extreme starbursts take place in connections with the assembly of the large-scale structure in the early Universe. We search for SMGs at 850 $\rm{\mu m}$ using JCMT/SCUBA-2 in two massive protoclusters at z = 2.24, BOSS1244 and BOSS1542, and detect 43 and 54 sources with S850 > 4 mJy at the 4σ level within an effective area of 264 arcmin2, respectively. We construct the intrinsic number counts and find that the abundance of SMGs is 2.0 ± 0.3 and 2.1 ± 0.2 times that of the general fields, confirming that BOSS1244 and BOSS1542 contain a higher fraction of dusty galaxies with strongly enhanced star formation. The volume densities of the SMGs are estimated to be ∼15–30 times the average, significantly higher than the overdensity factor (∼6) traced by H α emission-line galaxies (HAEs). More importantly, we discover a prominent offset between the spatial distributions of the two populations in these two protoclusters – SMGs are mostly located around the high-density regions of HAEs, and few are seen inside these regions. This finding may have revealed for the first time the occurrence of violent star formation enhancement in the outskirts of the HAE density peaks, likely driven by the boosting of gas supplies and/or starburst triggering events. Meanwhile, the lack of SMGs inside the most overdense regions at z ∼ 2 implies a transition to the environment disfavouring extreme starbursts.