Can external effects make dense cores unstable? In order to find answer on this question, I selected eight dense cores which were classified as starless from previous literatures, and conducted infrared (3–160 μm) imaging observations with the AKARI telescope and molecular line (HCN and N2H+) mapping observations with the KVN telescope. Combining these data with the archival data, I again examined the starless nature of these eight cores. Two of the eight cores are found to harbor faint protostars having luminosities of ~0.3–4.4 Lsun. The other six cores are found to remain starless and probably are in a dynamically transitional state. For the six starless cores, I analyzed their temperature map, virial parameter, and line asymmetry. Their temperature maps show an enhancement of about 3–6 K toward the outer boundary of these cores, suggesting that they are most likely being heated externally by nearby stars and/or interstellar radiation fields. They also show large virial parameters and an overdominance of red asymmetric line profiles over them, indicating that they are set into either an expansion or an oscillatory motion, probably due to the external heating. In addition, I found that most of the starless cores show a coreshine effect due to the scattering of light by the micron-sized dust grains. This may imply that the age of the cores is of the order of ~10^5 years, which is consistent with the timescale required for the cores to evolve into an oscillatory stage due to external perturbation. Therefore these observational results give us positive answer supporting that the external feedback from nearby stars and/or interstellar radiation fields may play an important role in the dynamical evolution of the cores.

The study of the CI in the nearby Universe and at high redshifts has shown that CI is a very powerful tracer of the molecular gas in the galaxy interstellar medium and starts giving an advantage at z>0.5 because it remains well excited for cooler lower density molecular gas and it is optically thin (no need of the XCO factor). When coupled with high-J CO emission lines the ratio, high-J CO/CI, is a good proxy of (warm, dense, star-forming (SF) gas)/(total H2 gas) mass fraction and provides a unique insight on the main source heating the gas and therefore indicating whether a system is merger driven or disc-like. I show observations of three lensed galaxies at z~3 obtained with the APEX/SEPIA5 receiver and a few ALMA observations towards high-z submm galaxies and derive conclusions on the dominant power source of the molecular ISM of these objects.

Making use of the multiwavelength information of a sample of nearby galaxies selected in the K-band, we build the bivariate mass and luminosity functions for several physical quantities: stellar, dust, atomic and molecular masses, star formation rate and IR luminosity. The analysis shows that the behaviour of the morphological (optically selected) subsamples is quite different: a statistically meaningful result is obtained over the whole sample only for the stellar mass function. Dust and gas mass functions and star-formation rate and far-IR luminosity functions can be computed only for the late-type galaxy subsample. I will discuss the various dependence of the mass and luminosity functions, the comparison with other sample results and with galaxy formation simulations. The analysis allows the characterisation of the sample used (the Herschel Reference Sample, HRS), that, although non homogeneously selected and partially biased towards low IR luminosities, may be considered as representative of the local galaxy population.

The current paradigm of star formation through accretion disks, and magnetohydrodynamically driven gas ejections, predicts the development of collimated outflows, rather than expansion without any preferential direction. However, during the last two decades our group has being studying the massive protostar W75N(B)-VLA2 through radio continuum emission observations (carried out with the VLA), as well as through multi-epoch VLBI observations of water vapor masers (carried out with the VLBA and VERA). Surprisingly, we have seen that in a real time of about 18 years, an expanding water-vapor maser shell found around the radio continuum source, as well as the radio continuum source itself have evolved together from a nearly circular morphology, tracing an almost isotropic outflow, to an elliptical one outlining collimated motions. We have interpreted this very peculiar behaviour (not seen before in massive protostars) in terms of an episodic, short-lived, originally isotropic ionized wind whose morphology evolves as it moves within a toroidal density stratification. Possible observational follow-ups of this singular source will be presented.