The spatial relation between young star clusters and molecular clouds in M51 with LEGUS

Abstract

We present a study correlating the spatial locations of young star clusters with those of molecular clouds in NGC 5194, in order to investigate the timescale over which clusters separate from their birth clouds. The star cluster catalogues are from the Legacy ExtraGalactic UV Survey (LEGUS) and the molecular clouds from the Plateau de Bure Interefrometer Arcsecond Whirpool Survey (PAWS). We find that younger star clusters are spatially closer to molecular clouds than older star clusters. The median ages for clusters associated with clouds is 4 Myr whereas it is 50 Myr for clusters that are sufficiently separated from a molecular cloud to be considered unassociated. After ∼6 Myr, the majority of the star clusters lose association with their molecular gas. Younger star clusters are also preferentially located in stellar spiral arms where they are hierarchically distributed in kpc-size regions for 50-100 Myr before dispersing. The youngest star clusters are more strongly clustered, yielding a two-point correlation function with α = −0.28 ± 0.04, than the GMCs (α = −0.09 ± 0.03) within the same PAWS field. However, the clustering strength of the most massive GMCs, supposedly the progenitors of the young clusters for a star formation efficiency of a few percent, is comparable (α = −0.35 ± 0.05) to that of the clusters. We find a galactocentric-dependence for the coherence of star formation, in which clusters located in the inner region of the galaxy reside in smaller star-forming complexes and display more homogeneous distributions than clusters further from the centre. This result suggests a correlation between the survival of a cluster complex and its environment.

An ALMA/HST Study of Millimeter Dust Emission and Star Clusters

“…We find the closest star clusters, as given by LEGUS, to each millimeter source and our analysis suggests that younger star clusters lie closer to the dust than older clusters. This result is in agreement with Grasha et al (2018) with ALMA-LEGUS observations of NGC 7793 and Grasha et al (2019) in M51 who find younger star clusters lie closer on average to giant molecular clouds than the older clusters. Tracking the millimeter/submillimeter continuum slopes with the nearby star cluster ages and masses gives no correlation, suggesting that the hardness and/or intensity of local ISRF generated by the star clusters is not responsible for the flatter dust emissivity we observe.…”

“…The average star cluster-millimeter source separations, for all band 7 sources, are given as colored dashed lines. The older star clusters, on average, lie slightly further from the dust clouds which is in agreement with the results for star clusters and giant molecular clouds in NGC 5194 fromGrasha et al (2019).…”

“…In the LEGUS cluster catalog, the average uncertainty for both a cluster's age and mass is 0.1 dex. Grasha et al (2019) make use of the rich LEGUS dataset by exploring the spatial relation between star clusters and giant molecular clouds (GMCs) in the spiral galaxy NGC 5194 (M51). The authors find a spatial correlation between young (≤10 Myr) star clusters and the GMCs which gives a time-scale for disassociation of the star clusters from the GMCs of ∼ 4-6 Myr.…”

A Variant Stellar-to-nebular Dust Attenuation Ratio on Subgalactic and Galactic Scales

“…In fact, as implied by the two-component dust model (Charlot & Fall 2000;Wild et al 2011), A V,star might reflect the local environment of the diffuse ISM along the line of sight rather than the birth clouds. Studies of young star clusters (YSCs) confirmed that YSCs with ages of ∼ 10 Myr are no longer embedded in their birth clouds (Whitmore et al 2014;Hollyhead et al 2015;Grasha et al 2019). In other words, stellar populations older than this time scale might only suffer dust attenuation from the diffuse ISM.…”

Violent Relaxation in Isolated Star Clusters

“…) [1,2,3,4,5]. Star-formation efficiency (SFE), the fraction of star-forming gas mass converted into stars, reported by observations of nearby star-forming regions to be usually less than 30% [6,7,8].…”