Research projects
# Deep photometric catalog of the VVV survey data
We performed the PSF photometry on the VVV survey data with DaoPHOT. Based on the comparison with the released DoPHOT PSF photometric catalog by Alonso-García et al. (2018), our catalog is ~1 mag deeper in Ks band and include less spurious detections.
The figure shows the source number density map.
The whole catalog will be released in near future. Here we give three sample tile catalogs that covers the region of l~330-334 deg, b~-1-0 deg:
# Star formation in the Galactic giant molecular filaments (GMFs)
GMFs are 100pc-scale, Nessie-like filamentary structures. These objects may be linked to the Galaxy-scale distribution of dense gas and could trace Galaxy-scale star formation patterns or trends. YSO counting method that has been widely-used to estimate SFRs in nearby clouds is applied to the GMFs by assuming the universal and fully sampled IMF and luminosity function. Based on YSO candidates identified in the Galactic plane, the SFRs for ~50 GMFs are estimated. We found that the median SFR surface density and star formation efficiency of GMFs are similar to the nearby star-forming clouds. The star formation rate per free-fall time of GMFs is between 0.002-0.05 with the median value of 0.02. We also find a strong correlation between SFR and dense gas mass that is defined as gas mass above a visual extinction of 7 mag, which suggests that the SFRs of the GMFs scale similarly with dense gas as those of nearby molecular clouds. The corresponding paper has been accepted by A&A and will be published soon. The preprint version can be found in arXiv: 1811.02197.
Distribution of GMFs.
An example of GMFs. Left: background is CO-based extinction map. The contour levels mark the visual extinction of 3, and 7 (black and blue) mag. The identified YSO candidates are labeled with red (Class I) and green (Class II) symbols. Right: average 13CO spectrum. The velocity range of GMF is marked with red lines.
The machine-readable table can be downloaded from here. It's a FITS table, including all information of 57 GMFs.
This figure shows the result if plotting GMFs (black), nearby GB clouds (red) and galaxies from Gao&Solomon(2004) (cyan) together. Note that we have re-estimated SFR and dense gas mass for nearby clouds (see our paper for details). Now the nearby clouds, GMFs and galaxies can be well-fitted with a linear relation with a slope of 0.97. Note that we did not move the position of galaxies as Lada et al. (2012) did.
Does this means an universal SF relation? We DO NOT suggest this conclusion because the possible significant systematic difference. Actually, we use very different method to estimate SFR and mass for nearby clouds, GMFs and galaxies. There is a correlation! However, without cross-calibration, any discussion about fitting slope will have large uncertainties!
# Searching outflows in nearby clouds
Mass outflow plays an essential role in the process of star formation. It is believed that mass outflow is an important way to transfer the excess angular momentum from the dense molecular cores to the ambient interstellar medium. Outflows have been observed in different wavelengths: Herbig-Haro (HH) objects are the optical manifestation of shock-ionized mass outflows and molecular hydrogen emission-line objects (MHOs) are the near-infrared manifestation of mass outflows. We present optical and near-infrared surveys towards several nearby star forming regions, including the ρ Ophiuchi, Aquila, Vela C, Cep OB3, IC5146, M17, and several filaments associated with the Planck Galactic cold clumps (PGCC). The results of ρ Ophiuchi, Aquila, and Vela C have been published (Zhang+13, Zhang+14, Zhang+15). For Cep OB3, IC5146, M17, and PGCCs, we already obtained the imaging data, but the data is still under analysis.
The MHO features detected in Ophiuchus. The newly detected MHO features are marked with black open squares and the previously known MHO features are labeled with red pluses. The YSOs identified by Spitzer photometry are marked with blue circles.
we perform a deep near-infrared search for MHOs towards the ρ Ophiuchi molecular cloud. The survey covers an area of ~0.1 deg2. In total, we discovered six new MHOs and detected 32 known MHOs. Using previously-published H2 images, we measured the proper motions (PMs) for the H2 emission features in 32 MHOs.
Mosaic [S ii] images of the Vela C molecular cloud. The detected HH objects are labeled on left panel. The right panel shows the locations of known YSOs and YSO candidates in the Vela C.
We have performed a deep [SII] λλ6717/6731 wide field survey toward the Vela C. In total, 18 new HH objects, HH 1090-1107, and two previously known HH objects, HH 73-74, are detected.
Spatial distribution of molecular hydrogen outflows detected in Aquila. The 108 MHO features are marked with green circles, and 40 outflow sources are labeled with red filled pentagrams. The blue solid lines connect the outflow sources and their associated MHOs.
We perform an unbiased near-infrared survey toward the Aquila molecular cloud. We identify 45 MHOs, including 11 previously known MHOs and 34 newly discovered objects. After associating 43 MHOs with 40 YSOs, 40 molecular hydrogen outflows are identified. Our estimation of the momentum injection from outflows indicates that a few tens of generation of outflows are needed to match the observed turbulent momentum in our survey region of the Aquila molecular cloud.
The optical view of M17 region. The red box shows the pointings of our proposed observation with the coverage of about 1×1 deg2. The background is DSS red image. The black contours represent visual extinction of 5 and 7 magnitudes as well as the blue contours correspond to the 12CO emission with the contour levels of 150, 170 and 190 K km s−1. The green box shows the coverage of WFI Hα image which is taken from ESO archive data (PID is 69.C-0426(C)).
