Proper Motions of Young Stellar Outflows in the Mid-Infrared with Spitzer (IRAC). I. The NGC 1333 region

We use two 4.5micron Spitzer (IRAC) maps of the NGC 1333 region taken over approx. 7 yr interval to determine proper motions of its associated outflows. This is a first, successful attempt at obtaining proper motions of stellars outflow from Spitzer observations. For the outflow formed by the Herbig-Haro objects HH7, 8 and 10, we find proper motions of approx. 9-13 km/s, which are consistent with previously determined optical proper motions of these objects. We determine proper motions for a total of 8 outflows, ranging from approx. 10 to 100 km/s. The derived proper motions show that out of these 8 outflows, 3 have tangential velocities less or equal to 20 km/s. This result shows that a large fraction of the observed outflows have low intrinsic velocities, and that the low proper motions are not merely a projection effect.

Spitzer observations of the HH 1/2 system. The discovery of the counterjet

We present unpublished Spitzer IRAC observations of the HH 1/2 young stellar outflow processed with a high angular resolution deconvolution algorithm that produces sub-arcsecond (approx. 0.6 - 0.8) images. In the resulting mid-infrared images the optically invisible counterjet is detected for the first time. The counterjet is approximately half as bright as the jet at 4.5 micron (the IRAC band that best traces young stellar outflows) and has a length of approx. 10. The NW optical jet itself can be followed back in the mid-IR to the position of the exciting VLA 1 source. An analysis of the IRAC colors indicates that the jet/counterjet emission is dominated by collisionally excited H2 pure rotational lines arising from a medium with a neutral Hydrogen gas density of 1000-2000 per cubic cm and a temperature of 1500 K. The observed jet/counterjet brightness asymmetry is consistent with an intrinsically symmetric outflow with extinction from a dense, circumstellar structure of 6 size (along the outflow axis), and with a mean visual extinction of Av=11 mag.

The precession of the HH 111 flow in the infrared

We present Spitzer IRAC images of the HH 111 outflow, that show a wealth of condensations/knots in both jet and counterjet. Studying the positional distribution of these knots, we find very suggestive evidence of a mirror symmetric pattern in the jet/counterjet flow. We model this pattern as the result of an orbital motion of the jet source around a binary companion. From a fit of an analytic, ballistic model to the observed path of the HH 111 system, we find that the motion in a binary with two approx. 1 Msolar stars (one of them being the HH 111 source), in a circular orbit with a separation of approx. 186 AU would produce the mirror symmetric pattern seen in the outflow.

Dust Properties of NGC 147 and NGC 185

We present new mid- to far-infrared images of the two dwarf compact elliptical galaxies that are satellites of M31, NGC 185 and NGC 147, obtained with the Spitzer Space Telescope. Spitzers high sensitivity and spatial resolution enable us for the first time to look directly into the detailed spatial structure and properties of the dust in these systems. The images of NGC 185 at 8 and 24 micron display a mixed morphology characterized by a shell-like diffuse emission region surrounding a central concentration of more intense infrared emission. The lower resolution images at longer wavelengths show the same spatial distribution within the central 50 but beyond this radius, the 160 micron emission is more extended than that at 24 and 70micron. On the other hand, the dwarf galaxy NGC 147 located only a small distance away from NGC 185 shows no significant infrared emission beyond 24 micron and therefore its diffuse infrared emission is mainly stellar in origin. For NGC 185, the derived dust mass based on the best fit to the spectral energy distribution is 1.9e3 Msol, implying a gas mass of ~3.0e5 Msol. These values are in agreement with those previously estimated from infrared as well as from CO and HI observations and are consistent with the predicted mass return from dying stars based on the last burst of star formation ~1.0e9 yr ago. Based on the 70 to 160micron flux density ratio, we estimate a temperature for the dust of ~17K. For NGC 147, we obtain an upper limit for the dust mass of 4.5e2 Msol at 160 micron (assuming a temperature of ~20K), a value consistent with the previous upper limit derived using ISO observations of this galaxy. In the case of NGC 185, we also present full 5-38 micron low-resolution (R~100) spectra of the main emission regions.