Orion Paper Submitted

Recently I’ve become a silent participant to a huge collaboration intended to map all the molecular hydrogen outflows in Orion-A Molecular Ridge. The submitted paper is entitled: A census of molecular outflows and their sources along the Orion A molecular ridge Characteristics and overall distribution by Davis et al. It is a remarkable work combining data from several wave-bands NIR to MM. Here is the abstract:

Aims. A census of molecular outflows across the entire Orion A Giant Molecular Cloud is sought. With this paper we aim to associate each flow with its progenitor and associated molecular core, so that the characteristics of the outflows and out?ow sources can be established. 

Methods. We present wide-field near-infrared images of Orion A, obtained with the Wide Field Camera, WFCAM, on the United Kingdom Infrared Telescope. Broad-band K and narrow-band H2 1-0S(1) images of a contiguous~8 square degree region are compared to mid-IR photometry from the Spitzer Space Telescope and (sub)millimetre dust-continuum maps obtained with the MAMBO and SCUBA bolometer arrays. Using previously-published H2 images, we also measure proper motions for H2 features in 33 outflows, and use these data to help associated flows with existing sources and/or dust cores. 

Results. Together these data give a detailed picture of dynamical star formation across this extensive region. We increase the number of known molecular outflows to 116. A total of 111 jets were observed with Spitzer; outflow sources are identi?ed for 72 of them (12 more jets have tentative progenitors). The MAMBO 1200 µm maps cover 97 H2 flows; of the 73 observed jets with candidate outflow sources, 57 (78%) are associated with cores or extended emission. The H2 jets are widely distributed and randomly orientated; the jets do not appear to be orthogonal to large-scale filaments or even to the small-scale cores associated with the outflow sources (at least when traced with the 11” resolution of the 1200 µm MAMBO observations). Moreover, jet lengths, L, and jet opening angles, ?, are not obviously correlated with indicators of outflow source age – source spectral index, ? (measured from near- and mid-IR photometry), or (sub)millimetre core flux. It seems clear that excitation requirements limit the usefulness of H2 as a tracer of L and ? (though jet position angles are well defined). 

Conclusions. We demonstrate that H2 jet sources are predominantly protostellar sources with flat or positive near-to-mid-IR spectral indices, rather than disk-excess (or T Tauri) stars. Most, if not all, protostars associated with molecular cores drive molecular outflows. However, not all molecular cores are associated with protostars or H2 jets. On statistical grounds, the H2 jet phase may be marginally shorter than the protostellar phase, though must be considerably (by an order of magnitude) shorter than the prestellar phase. In terms of range and mean value of ?, H2 jet sources are indistinguishable from the more abundant protostars. However, the spread in ? is probably a function of inclination angle as much as source age: the protostars without jets are almost certainly more evolved than their jet-driving counterparts, although these later stages of protostellar evolution (as the source transitions to being a “disk excess” source) are probably relatively brief, since a large fraction of protostars do drive outflows. We also find that protostars that power outflows are no more (nor no less) clustered than protostars that do not. Clearly, outflows weaken and fade rapidly as a source evolves from protostar to pre-main-sequence star, on time-scales much shorter than those associated with the dispersal of young stellar objects.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s