Complex Structure in Class 0 Protostellar Envelopes. Ii. Kinematic Structure From Single-Dish and Interferometric Molecular Line Mapping

Abstract

We present a study of dense molecular gas kinematics in seventeen nearby protostellar systems using single-dish and interferometric molecular line observations. The non-axisymmetric envelopes around a sample of Class 0/I protostars were mapped in the N 2 H + (J = 1 → 0) tracer with the IRAM 30m, CARMA and PdBI as well as NH 3 (1,1) with the VLA. The molecular line emission is used to construct line-center velocity and linewidth maps for all sources to examine the kinematic structure in the envelopes on spatial scales from 0.1 pc to ∼1000 AU. The direction of the large-scale velocity gradients from single-dish mapping is within 45 • of normal to the outflow axis in more than half the sample. Furthermore, the velocity gradients are often quite substantial, the average being ∼2.3 km s −1 pc −1 . The interferometric data often reveal small-scale velocity structure, departing from the more gradual large-scale velocity gradients. In some cases, this likely indicates accelerating infall and/or rotational spin-up in the inner envelope; the median velocity gradient from the interferometric data is ∼10.7 km s −1 pc −1 . In two systems, we detect high-velocity HCO + (J = 1 → 0) emission inside the highestvelocity N 2 H + emission. This enables us to study the infall and rotation close to the disk and estimate the central object masses. The velocity fields observed on large and small-scales are more complex than would be expected from rotation alone, suggesting that complex envelope structure enables other dynamical processes (i.e. infall) to affect the velocity field. 1 Based on observations carried out with the IRAM 30m Telescope and IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).-5with 20kHz channels and in 2009 we used 40 MHz with 20kHz channels; see Table 2 the list of sources observed and more detail.We conducted our observations using frequency-switched on-the-fly (OTF) mapping mode. The maps varied in size depending on the extent of the source being observed, most being 3 × 3 . Most maps were integrated down to at least σ T ∼ 150mK for the N 2 H + (J = 1 → 0) transition, noise levels for each map are listed in Table 2. We mapped the sources by scanning in the northsouth direction and again in the east-west direction to minimize striping in the final map. The scan legs were stepped by 5 and we repeated the maps to gain a higher signal-to-noise ratio. Calibration scans were taken about every 10 minutes between scan legs and the final maps took approximately 2 hours to complete. Pointing was checked about every two hours, azimuth and elevation offsets were typically ±5 ; the pointing offset remained stable, typically within ∼2 during an observation. These values agree well with the rms pointing accuracy of ∼2 .

A study on subarcsecond scales of the ammonia and continuum emission toward the G16.59−0.05 high-mass star-forming region

“…9b along a NE-SW line, which looks consistent with the A145, page 8 of 11 bipolar structure seen in HCO + . This result weakens the outflow interpretation significantly, because N 2 H + is a well known tracer of dense gas, but is only exceptionally detected in outflows (see the case of L1157; Tobin et al 2011). Moreover, for a bipolar outflow one would not expect such a sharp change in velocity because the line peak should shift from red to blue velocities gradually, going from one lobe to the other.…”

Water in star-forming regions withHerschel(WISH)

“…3.2) could be due to a variety of reasons, including asymmetric densities and UV fields across the core. Different densities on the two sides could be caused by irregularities or gradients of the surrounding cloud material distribution (Liu et al 2012;Tobin et al 2011) and can lead to different excitation of the molecules. The density also affects the penetration of the UV field, which in turn results in abundance variations.…”

CHARACTERIZING THE YOUNGESTHERSCHEL-DETECTED PROTOSTARS. I. ENVELOPE STRUCTURE REVEALED BY CARMA DUST CONTINUUM OBSERVATIONS

“…How slowly (or rapidly) the amplitude decreases with increasing uv distance Note. The collection of 2.7 mm data at the top are from Looney et al (2000), the 3.4 mm data are from Tobin et al (2011), and the collection of 2.7 mm data at the bottom are from (Arce & Sargent 2006). reveals how concentrated the emission is toward a particular source, in addition to structural changes in the emitting material.…”

“…Plots of the 2.9 mm luminosity (L 2.9 mm ) vs. L bol (top) and the L 2.9 mm / L bol ratio vs. L bol (bottom). We also include sources observed by Tobin et al (2011) at 3.4 mm, by Looney et al (2000) at 2.7 mm, and by Arce & Sargent (2006) at 2.7 mm. For luminosities of about 1 L , the PBRS have the highest 2.9 mm luminosity ratios and at higher luminosities they are comparable to or larger than those from Looney et al (2000).…”