We present a catalogue of Molecular Hydrogen emission-line Objects (MHOs) in outflows from young stars, most of which are deeply embedded. All objects are identified in the near-infrared lines of molecular hydrogen, all reside in the Milky Way, and all are associated with jets or molecular outflows. Objects in both low and high-mass star forming regions are included. This catalogue complements the existing database of Herbig-Haro objects; indeed, for completeness, HH objects that are detected in H_2_ emission are included in the MHO catalogue.
We present the analysis of 35.5deg^2^ of images in the 1-0 S(1) line of H_2_ from the UK Widefield Infrared Survey for H_2_ (UWISH2) towards Cassiopeia and Auriga. We have identified 98 Molecular Hydrogen emission-line Objects (MHOs) driven by Young Stellar Objects, 60 per cent of which are bipolar outflows and all are new discoveries. We estimate that the UWISH2-extended emission object catalogue contains fewer than 2 per cent false positives and is complete at the 95 per cent level for jets and outflows brighter than the UWISH2 detection limit. We identified reliable driving source candidates for three quarters of the detected outflows, 40 per cent of which are associated with groups and clusters of stars. The driving source candidates are 20 per cent protostars, the remainder are Classical T-Tauri Stars. We also identified 15 new star cluster candidates near MHOs in the survey area. We find that the typical outflow identified in the sample has the following characteristics: the position angles are randomly orientated; bipolar outflows are straight within a few degrees; the two lobes are slightly asymmetrical in length and brightness; the length and brightness of the lobes are not correlated; typical time gaps between major ejections of material are 1-3 kyr, hence FU-Ori or EX-Ori eruptions are most likely not the cause of these, but we suggest MNors as a possible source. Furthermore, we find that outflow lobe length distributions are statistically different from the widely used total length distributions. There are a larger than expected number of bright outflows indicating that the flux distribution does not follow a power law.
Jets and outflows from young stellar objects (YSOs) are important signposts of currently ongoing star formation. In order to study these objects, we are conducting an unbiased survey along the Galactic plane in the 1-0 S(1) emission line of molecular hydrogen at 2.122 um using the United Kingdom Infrared Telescope. In this paper, we are focusing on a 33-deg^2^-sized region in Serpens and Aquila (18{deg}<l<30{deg}; -1.5{deg}<b<+1.5{deg}). We trace 131 jets and outflows from YSOs, which results in a 15-fold increase in the total number of known molecular hydrogen outflows. Compared to this, the total integrated 1-0 S(1) flux of all objects just about doubles, since the known objects occupy the bright end of the flux distribution. Our completeness limit is 3x10^-18^W/m^2^ with 70 per cent of the objects having fluxes of less than 10^-17^W/m^2^.
The [CII] 158um FIR fine-structure line is one of the most important cooling lines of the star-forming ISM. It is used as a tracer of star formation efficiency in external galaxies and to study feedback effects in parental clouds. High spectral resolution observations have shown complex structures in the line profiles of the [CII] emission. To determine whether the complex profiles observed in [^12^CII] are due to individual velocity components along the line-of-sight or due to self-absorption, one has to compare the [^12^CII] and isotopic [^13^CII] line profiles. Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in the sources M43, Horsehead PDR, Monoceros R2 and M17 SW allow to detect with high S/N the optically thin [^13^CII] and simultaneously the [^12^CII] emission lines. We first derive the [^12^CII] optical depth and the [CII] column density from a single component model. However, the complex line profiles observed require a double layer model with an emitting background and an absorbing foreground. A multi-component velocity fit allows to derive the physical conditions of the [CII] gas: column density and excitation temperature. We find moderate to high [^12^CII] optical depths in all four sources, and self-absorption of [^12^CII] in Mon R2 and M17 SW. The high column density of the warm background emission corresponds to an equivalent Av of up to 41mag. The foreground absorption requires substantial column densities of cold and dense [CII] gas, with an equivalent Av ranging up to about 13mag. The column density of the warm background material requires multiple PDR surfaces stacked along the line of sight and in velocity. The substantial column density of dense and cold foreground [CII] gas detected in absorption cannot be explained with any known scenario and we can only speculate about its origin.
We present the results of a narrow-band near-infrared imaging survey for Molecular Hydrogen emission-line Objects (MHOs) toward 26 regions containing high-mass protostellar candidates and massive molecular outflows. We have detected a total of 236 MHOs, 156 of which are new detections, in 22 out of the 26 regions. We use H_2_2.12{mu}m/H_2_2.25{mu}m flux ratios, together with morphology, to separate the signatures of fluorescence associated with photo- dissociation regions (PDRs) from shocks associated with outflows in order to identify the MHOs. PDRs have typical low flux ratios of ~1.5-3, while the vast majority of MHOs display flux ratios typical of C-type shocks (~6-20). A few MHOs exhibit flux ratios consistent with expected values for J-type shocks (~3-4), but these are located in regions that may be contaminated with fluorescent emission. Some previously reported MHOs have low flux ratios, and are likely parts of PDRs rather than shocks indicative of outflows. We identify a total of 36 outflows across the 22 target regions where MHOs were detected. In over half these regions, MHO arrangements and fluorescent structures trace features present in CO outflow maps, suggesting that the CO emission traces a combination of dynamical effects, which may include gas entrained in expanding PDRs as well as bipolar outflows. Where possible, we link MHO complexes to distinct outflows and identify candidate driving sources.
We present a radio survey carried out with the Australia Telescope Compact Array. A motivation for the survey was to make a complete inventory of the diffuse emission components as a step towards a study of the cosmic evolution in radio source structure and the contribution from radio-mode feedback on galaxy evolution. The Australia Telescope Low-Brightness Survey (ATLBS) at 1388MHz covers 8.42deg^2^ of the sky in an observing mode designed to yield images with exceptional surface brightness sensitivity and low confusion. The survey was carried out in two adjacent regions on the sky centred at 00:35:00-67:00:00 and 00:59:17=-67:00:00 (J2000.0). The ATLBS radio images, made with 0.08mJy/beam rms noise and 50arcsec beam, detect a total of 1094 sources with peak flux exceeding 0.4mJy/beam. The ATLBS source counts were corrected for blending, noise bias, resolution and primary beam attenuation; the normalized differential source counts are consistent with no upturn down to 0.6mJy.
A radio survey has been conducted with the Westerbork Synthesis Radio Telescope for nine fields in four high latitude areas for which deep, multicolor Kitt Peak 4-m plates are available. A total of 471 sources are tabulated; 306 of these form a well defined, complete sample. The influence of the selection criteria on sample completeness is discussed. Angular size distribution has been precisely derived, in virtue of the 3 km resolution obtainable with the present instrument, and a smaller fraction of sources larger than about 20arcsec is noted for the 1-10mJy range than for the 10-100mJy. The 1412MHz source counts are consistent at different cutoff levels, showing that the statistical corrections for population and resolution bias are reliable. The present counts are consistent with previous 1.4GHz counts, which are here given for the 1-100000mJy flux range.
A deep multicolor optical identification program is presented for a complete sample of 302 radio sources that were observed with the Westerbork Synthesis Radio Telescope within 5.52{deg}^2^ down to S_1.4GHz_>~0.6mJy (5{sigma}). Optical identifications are made from multicolor prime focus plates taken with the Kitt Peak 4 meter telescope in the passbands U,J,F and N with approximate respective limiting magnitudes of ~23.3, 23.7, 22.7 and 21.1. The astrometry has systematic errors smaller than 0.2"-0.3", while the random errors are of order 0.4". The agreement between the radio and optical coordinate frames is on average better than 0.25". Identifications are based on positional coincidence using the likelihood ratio method. For 171 out of the 302 radio sources likely identifications are proposed with an a posteriori identification percentage of 53%, 14 expected spurious objects (or 5% of all radio sources), while not more than 4 identifications have been missed. The sample reliability is 92% and its completeness 98%. About 20% of the identifications are stellar objects, the remaining have extended images or are too faint to be classified. About 15% of the identifications appear in possible clusters. The identification statistics are roughly constant from field to field, except for the Hercules 2 field which has an unusually high identification fraction (74%). The identification fraction is presented as a function of 21 cm flux density and limiting magnitude, and amounts to 15% for 1<~S_1.4GHz_<~100mJy down to the Palomar Sky Survey limit and 29% down to the effective 48" Schmidt limit. For S_1.4_<~100mJy the identification fraction remains roughly constant with flux density, contrary to the prediction of higher fractions by some models for cosmological evolution. The magnitude distributions for galaxies plus objects of unknown type generally increase towards fainter magnitudes; the quasar magnitude distributions are also increasing but not as steeply as for the radio galaxies.
The ongoing radio continuum TIFR GMRT Sky Survey (TGSS) using the Giant Metrewave Radio Telescope (GMRT) at 150MHz offers an unprecedented opportunity to undertake a fairly deep search for low-frequency radio emission from nearby extrasolar planets. Currently TGSS images are available for a little over a steradian, encompassing 175 confirmed exoplanetary systems. We have searched for their radio counterparts in the TGSS (150MHz), supplemented with a search in the NRAO VLA Sky Survey (NVSS) and the VLA FIRST survey at 1.4GHz. For 171 planetary systems, we find no evidence of radio emission in the TGSS maps, placing a 3{sigma} upper limit between 8.7mJy and 136mJy (median ~24.8mJy) at 150MHz.