Evidence for Shocked Gas Traced by Hydroxyl Masers in Early High-Mass Star -Forming Regions

1. Evidence for Shocked Gas Traced by Hydroxyl Masers in Early High-Mass Star-Forming Regions By Emma Clark Advisors: Natalia Andreev and E.D. Araya Astrophysics Research Laboratory

2. High-Mass Star Formation (Cormac Purcell, http://web.science.mq.edu.au/ ~cpurcell/public/images/sequence_new.png) Monolithic Collapse model Abundant observational evidence shows that outflows and jets are a widespread characteristic of high-mass star formation.

3. Radio Continuum Sources • Rosero et al. (2016) searched for radio continuum in 58 high-mass star forming regions. • 70 detections- half of which should trace ionized jet, which should generate shocks. • They conducted these observations using the Jansky Very Large Array (VLA). • VLA, located in New Mexico

4. Supersonic Jet Photo by Dattatreya Mandal

5. What is a maser? MASER stands for Microwave Amplification by Stimulated Emission of Radiation • It is caused by low energy transitions. • The 1720MHz hydroxyl (OH) maser is well known to trace shocks at the interface between molecular clouds and supernova remnants. (http://hyperphysics.phy-astr.gsu.edu/). The process of stimulated emission

6. THOR Survey • A large field-of-view survey for ground state OH transitions, radio recombination lines and radio continuum in the inner Galaxy. • Conducted with the VLA in C-configuration (Beuther et al. 2016). • The angular resolution and typical RMS are approximately 20” and 10 mJy/b • 1 Jy = 10-26 W/m2Hz

7. Our Objective: Explore the THOR survey to search for evidence of shocks by detection of 1720 MHz hydroxyl (OH) masers in the Rosero et al. (2016) sample.

8. Methods • Using data from the THOR Survey, we searched for 1720 MHz OH masers towards the high-mass star forming regions observed by Rosero et al. (2016). • Of the 58 regions observed by Rosero et al. (2016), 28 had data from the THOR Survey. • We then used the viewer in CASA (Common Astronomy Software Applications) to search for emission lines at the 28 sources.

9. We loaded the data and created 20” circular regions at the coordinates from Rosero et al. (2016).

10. Spectral Cubes Doppler Effect Velocity Frequency

11. If the spectrum shows an emission, we find the image of the channel where the line is located. Radio Velocity (km/s)

12. A more general method was also used to check for any possible maser in the regions but not located within 20” of the Rosero et al. (2016) coordinates: First, we identified regions in the large field-of-view THOR images and extracted sub-cubes

13. Next, we collapsed the sub-cubes to show the maximum intensity at each point of the sky

14. Then, minimum threshold of five times the RMS noise was used to find candidates. Radio Velocity (km/s) We examined the spectra at the remaining points in the image.

15. Detections vs. Tentative Detections Detections were defined as 9 central pixels with intensities above 5xRMS. G15.05+00.07 G35.39-00.33 mm2 Tentative detection Detection

16. G35.39-00.33 mm2 Line parameters: Peak Intensity = 980 mJy/b Velocity = 54.0 km/s FWHM = 1.7 km/s

17. IRAS 18553+0414 Line parameters: Peak Intensity = 368 mJy/b Velocity = 6.0 km/s FWHM = 2.4 km/s

18. IRAS 18440-0148 Line parameters: Peak Intensity = 56 mJy/b Velocity = 103.6 km/s FWHM = 2.9 km/s

19. Tentative detections • Nineteen sources have candidate detections with less than 9 central pixels above 5xRMS. • Because of THOR’s broad channel width, higher resolution images are needed. Example of a tentative detection: G22.73+00.11 mm1 Peak Intensity: 58 mJy/b

20. VLA Proposal

21. Other OH transitions • We examined the 1612 MHz, 1665MHz, and 1667MHz OH maser transitions. • We used the same methods we did in the search for the 1720 MHz masers, directed toward the sources where we had maser detections.

22. 1612 MHz Detections G15.05+00.07 mm1

23. Low velocity peak High velocity peak

24. Further inspection shows that the possible maser is actually a part of some extended source in the larger field of view image

25. 1612 MHz Detections 18437-0216

26. Example of the images before and after the intensity spike Image at the intensity spike

27. Further inspection shows that the possible maser is just artifact from a nearby bright emission

28. 1665 MHz Detections G27.75+00.16 mm2

29. Example of the image at lower velocity than the peak intensity Image at the peak intensity

30. Further inspection shows that the possible maser is just artifact from a nearby bright emission G27.75+00.16 mm2

31. 1665 MHz Detections 18440-0148 Intensity (Jy/b)

32. 1667 MHz Detection 18440-0148 Intensity (Jy/b)

33. OH Detections 18440-0148 Intensity (Jy/b)

34. Summary • We searched for 1720 MHz hydroxyl masers towards the sample of high-mass star forming regions observed by Rosero et al. (2016), getting our data from the THOR survey. • The 1720 MHz OH masers are a known tracer of shocks, and thus, detection in the Rosero et al. (2016) sample would add to the evidence of shocks from jets. • We report detection of three sources, and nineteen tentative detections. • A proposal has been submitted to utilize the VLA for higher spatial and spectral resolution observations to characterize this new sample of 1720 MHz OH masers.