Dense Cores in Perseus: The Influence of Stellar Content and Cluster Environment

We present the chemistry, temperature, and dynamical state of a sample of 193 dense cores or core candidates in the Perseus Molecular cloud and compare the properties of cores associated with young stars and clusters with those which are not. The combination of our NH3 and CCS observations with previous millimeter, sub-millimeter, and Spitzer data available for this cloud enable us both to determine core properties precisely and to accurately classify cores as starless or protostellar. The properties of cores in different cluster environments and before-and-after star formation provide important constraints on simulations of star-formation, particularly under the paradigm that the essence of star formation is set by the turbulent formation of prestellar cores. We separate the influence of stellar content from that of cluster environment and find that cores within clusters have (1) higher kinetic temperatures and (2) lower fractional abundances of CCS and NH3. Cores associated with protostars have (1) slightly higher kinetic temperatures (2) higher NH3 excitation temperatures), (3) are at higher column density, have (4) slightly more non-thermal/turbulent NH3 linewidths, have (5) higher masses and have (6) lower fractional abundance of CCS. We find that neither cluster environment nor protostellar content makes a significant difference to the dynamical state of cores as estimated by the virial parameter – most cores in each category are gravitationally bound. Overall, cluster environment and protostellar content have a smaller influence on the properties of the cores than is typically assumed, and the variation within categories is larger than the differences between categories.

💡 Research Summary

This paper presents a comprehensive observational study of 193 dense cores (or core candidates) in the Perseus molecular cloud, focusing on how stellar content and cluster environment influence core properties. Using simultaneous NH₃ (1,1) and (2,2) inversion lines together with CCS (2₁–1₀) emission, the authors derive kinetic temperature, column density, velocity dispersion, and molecular abundances for each core. By cross‑matching with existing millimeter/sub‑millimeter continuum maps and Spitzer infrared catalogs, they classify each core as starless or protostellar and as belonging to a clustered or isolated region, thereby separating the effects of embedded young stars from those of the larger‑scale cluster environment.

The main findings can be grouped into three themes. First, cores located within clusters exhibit systematically higher kinetic temperatures (by ~1–2 K) than isolated cores. This temperature elevation is accompanied by a marked reduction in the fractional abundances of both CCS and NH₃. CCS, being a chemically young tracer with a short lifetime, is especially sensitive to enhanced turbulence and heating; it is rapidly destroyed or adsorbed onto dust grains in warmer, more turbulent gas. NH₃, while more robust, also shows decreased abundance, likely due to increased adsorption or mild dissociation under the same conditions. Second, protostellar cores differ from starless ones in several respects: they have slightly higher kinetic temperatures and higher NH₃ excitation temperatures, indicating additional heating from the embedded source. Their column densities and masses are significantly larger, reflecting the accumulation of material during collapse. Non‑thermal NH₃ linewidths are modestly broader, suggesting that protostellar outflows or enhanced internal turbulence contribute to the velocity field. Moreover, CCS abundance is lower in protostellar cores, consistent with chemical evolution driven by heating and UV radiation from the young star. Third, the dynamical state, assessed via the virial parameter α_vir = (5σ²R)/(GM), shows little systematic variation across any of the four categories (clustered vs. isolated, starless vs. protostellar). The majority of cores have α_vir < 2, indicating they are gravitationally bound regardless of environment or stellar content. Small differences in α_vir are not statistically significant, implying that turbulence and gravity remain in near‑balance throughout the early stages of core evolution.

Overall, the authors conclude that while both cluster environment and the presence of a protostar produce measurable changes in temperature and chemistry, these effects are modest compared with the intrinsic scatter of core properties within each category. The variation among individual cores (e.g., in mass, density, chemical age) exceeds the average differences between clustered and isolated or between starless and protostellar samples. This result challenges the common assumption that environment dominates core evolution and supports a picture in which the turbulent formation of prestellar cores sets the primary conditions for star formation, with subsequent stellar feedback and cluster dynamics playing secondary roles. The study highlights the need for high‑resolution, multi‑molecule observations and for simulations that incorporate realistic core‑to‑core variability to better capture the early phases of star formation.