EPoS Contribution
EPoS Contribution
Initial phases of high-mass star formation: A multiwavelength study towards the extended green object G12.42+0.50

Namitha Issac
IIST, Trivandrum, IN
Extended Green Objects (EGOs) provide a promising tool towards understanding the early evolutionary phases of high mass stars. These sources, that show enhanced and extended emission in the 4.5 μm Spitzer IRAC band, are believed to be driven by outflows from massive YSOs, in which case the spectral carriers would be atomic and molecular shock indicators like H2 and [Fe II] lines and broad CO(v=1-0) bandheads. A multiwavelength study of the extended green object, G12.42+0.50 is presented here. Radio continuum emission mapped at 610 and 1390 MHz, using the Giant Meterwave Radio Telescope (GMRT), India, advocates for a scenario of coexistence of an UC H II region and an ionized thermal jet possibly powered by the MYSO, IRAS 18079-1756, with an estimated spectral type of B1-B0.5. Shock-excited lines of H2 and [Fe II], as seen in the near-infrared spectra obtained with UKIRT-UIST, lend support to this picture. In order to examine the nature of the dust associated with G12.42+0.50, we use the data at the IRAC, Hi-Gal, ATLASGAL-Planck and SMA wavelengths. The cold dust emission reveals a massive clump of mass 1375 Msol enveloping G12.42+0.50, along with several other less massive clumps identified from hydrogen column density map. The high resolution 1.1 mm SMA observation probes the inner regions of the cold dust that reveals two dense and bright compact cores, both of which qualify as potential high-mass star forming cores. Data from the MALT90 survey and JCMT archives are used to probe the molecular gas kinematics of the region associated with G12.42+0.50. The optically thick line HCO+ show signatures of protostellar infall. From the observations of J = 3-2 transition of 12CO, 13CO and C18O, we detect the presence of a wide-angle bipolar outflow. Signatures of a hub-filament system is seen in the 8.0 μm and the FIR images and is supported by the constructed hydrogen column density and dust temperature maps. A detailed study of the gas kinematics agrees with the bulk motion in the filaments and suggest a likely picture of gas inflow along the filaments to the massive central clump. A conjectured hypothesis of the EGO, G12.42+0.50, satisfying the multiwavelength observations, could be an active star forming complex harbouring very early evolutionary cores.
Caption: (a)The Spitzer IRAC colour composite image of G12.42+0.50, overlaid with the SMA 1.1 mm emission contours in black. The 12CO(3-2) emission integrated from the peak of the blueshifted profile to the blue wings is represented using blue contours and from the peak of the red profile to the red wings is represented using red contours. The contours start from the 5σ level for both the red and blue lobes and increases in steps of 3σ and 4σ , respectively (σ = 2.7 K km s-1 for red lobe and σ = 2.3 K km s-1 for blue lobe). The yellow line defines the direction of the proposed outflow. The red and blue lobes of the molecular outflow lie along a similar axis as the ionized jet. (b) The colour scale represents the 1.1 mm continuum emission from SMA observed towards G12.42+0.50. Radio emission at 1390 MHz is represented by yellow contours. The restoring beams of the 1390 MHz map and 1.1-mm map are indicated at the bottom right and left of the image, respectively. The "x"'s mark the positions of radio components, R1 and R2. The white circle shows the position of the H2O maser in the vicinity of G12.42+0.50. (c) The velocity peaks of 12CO(3-2) line extracted along the filaments is overlaid on the column density map shown in grey scale. The positions of all the filaments are also labelled.
Collaborators:
A. Tej, IIST, IN
T. Liu, SHAO, CH
W. Varricatt, UKIRT, US
S. Vig, IIST, IN
C.H. Ishwara-Chandra, NCRA-TIFR, IN
M. Schultheis, UCA, FR
Key publication

Suggested Session: High-Mass Star Formation