We present Atacama Large Millimeter/submillimeter Array observations of the \(\sim\)10 kAU environment surrounding 21 protostars in the Orion A molecular cloud tracing outflows. Our sample is ...composed of Class 0 to flat-spectrum protostars, spanning the full \(\sim\)1 Myr lifetime. We derive the angular distribution of outflow momentum and energy profiles and obtain the first two-dimensional instantaneous mass, momentum, and energy ejection rate maps using our new approach: the Pixel Flux-tracing Technique (PFT). Our results indicate that by the end of the protostellar phase, outflows will remove \(\sim\)2 to 4 M\(_\odot\) from the surrounding \(\sim\)1 M\(_\odot\) low-mass core. These high values indicate that outflows remove a significant amount of gas from their parent cores and continuous core accretion from larger scales is needed to replenish core material for star formation. This poses serious challenges to the concept of ``cores as well-defined mass reservoirs", and hence to the simplified core-to-star conversion prescriptions. Furthermore, we show that cavity opening angles, and momentum and energy distributions all increase with the protostar evolutionary stage. This is clear evidence that even garden-variety protostellar outflows: (a) effectively inject energy and momentum into their environments on \(10\) kAU scales, and (b) significantly disrupt their natal cores, ejecting a large fraction of the mass that would have otherwise fed the nascent star. Our results support the conclusion that protostellar outflows have a direct impact on how stars get their mass, and that the natal sites of individual low-mass star formation are far more dynamic than commonly accepted theoretical paradigms.
We study the fragmentation of the nearest high line-mass filament, the integral shaped filament (ISF, line-mass \(\sim\) 400 M\(_\odot\) pc\(^{-1}\)) in the Orion A molecular cloud. We have observed ...a 1.6 pc long section of the ISF with the Atacama Large Millimetre/submillimeter Array (ALMA) at 3 mm continuum emission, at a resolution of \(\sim\)3" (1 200 AU). We identify from the region 43 dense cores with masses about a solar mass. 60% of the ALMA cores are protostellar and 40\% are starless. The nearest neighbour separations of the cores do not show a preferred fragmentation scale; the frequency of short separations increases down to 1 200 AU. We apply a two-point correlation analysis on the dense core separations and show that the ALMA cores are significantly grouped at separations below \(\sim\)17 000 AU and strongly grouped below \(\sim\)6 000 AU. The protostellar and starless cores are grouped differently: only the starless cores group strongly below \(\sim\)6 000 AU. In addition, the spatial distribution of the cores indicates periodic grouping of the cores into groups of \(\sim\)30 000 AU in size, separated by \(\sim\)50 000 AU. The groups coincide with dust column density peaks detected by Herschel. These results show hierarchical, two-mode fragmentation in which the maternal filament periodically fragments into groups of dense cores. Critically, our results indicate that the fragmentation models for lower line-mass filaments (\(\sim\) 16 M\(_\odot\) pc\(^{-1}\)) fail to capture the observed properties of the ISF. We also find that the protostars identified with Spitzer and Herschel in the ISF are grouped at separations below \(\sim\)17 000 AU. In contrast, young stars with disks do not show significant grouping. This suggests that the grouping of dense cores is partially retained over the protostar lifetime, but not over the lifetime of stars with disks.
We present near-infrared surveys of the DR22, S184, and W3 high mass star forming regions. Each survey region shows evidence of recent massive star formation, either a maser or compact H scII region. ...We have detected dense clusters in each region. The peak densities (for the listed magnitude range) of the DR22, S184, and W3 clusters are 83 (m$\sb{\rm K} < 17),$ 56 (m$\sb{\rm K} < 17),$ and 216 (m$\sb{\rm K} < 16)$ stars per square arcminute. Deep J (1.25 $\mu$m), H (1.65 $\mu$m) and K (2.2 $\mu$m) images were obtained at the peak density positions for all three clusters. Color-magnitude diagrams show that 68%, 98%, and 73% of the stars in the DR22, S184, and W3 clusters have masses less than $3.6 M\sb\odot$. More than 87% of the stars in each cluster are consistent with the K vs. H-K values of reddened T-Tauri stars. Color-color diagrams reveal that 23%-72% of the sources in S184 show K-band excesses. These excesses are thought to arise in circumstellar disks and are of magnitudes typical for classical T-Tauri stars. In contrast, $<$27% of the stars in DR22 show excesses; and the majority of the stars have colors consistent with reddened naked T-Tauri stars. H-K colors show that the S184 and W3 clusters have several magnitudes of internal extinction, while the DR22 cluster shows little internal extinction ($<$1 mag). We examine the K-band luminosity function, the number of stars detected per K-band magnitude interval, for each cluster. We find a peak at 15th magnitude for the DR22 cluster. A comparison of the peak with existing models results in an age for the DR22 cluster between $3\times10\sp5$ yrs and $1\times10\sp6$ yrs. We do not find similar peaks in the S184 and W3 cluster; however, peaks may be hidden by the high internal extinction observed in both clusters. Finally, we propose that the DR22 cluster is a young cluster which has been unveiled by an advancing H scII region front. We suggest that the paucity of excesses in the DR22 cluster is the result of disk disruption by the advancing H scII region.
