Seminar of Research Postgraduate(RPg) Student:- Role of galactic outflows in the early universe
Feedback from star formation is thought to drive gas out of the disks of galaxies and hence regulate their further growth in stellar mass. In the local universe, galactic outflows containing atomic, ionised, and molecular gas, as well as dust, are seen from starburst galaxies. In the early universe, where the universal star formation rate is higher, ubiquitous outflows of atomic/ionised gas are inferred from star-forming galaxies using Lyman-α spectral profiles. Outflows of cooler molecular gas at high-z are of particular interest because molecular gas provides the direct fuel for star formation; however, observational evidence remains scarce. A recent study claims to have detected numerous molecular outflows in the spectra of star-forming galaxies at z>4 traced in OH 119μm absorption. In the first part of this seminar, the speaker presents a thorough re-examination of two of the eight sources from this study claimed to show unambiguous signatures of OH outflows. He shows that a proper treatment of the uncertainties in the spectra reveals that the purported outflows are of low statistical significance, and that absorption lines from the Earth’s atmosphere may also contaminate the measurements. He discusses improvements to the observing strategy used to search for high-z outflows seen in OH absorption. Outflows from star-forming regions are also thought to play an important role in the reionization of the universe, punching holes in the surrounding neutral InterStellar Medium(ISM) and creating ionised channels through which Lyman continuum(LyC, λ<912Å) photons can escape. In the second part of this seminar, the speaker presents future work to search for leakage of LyC from gravitationally-lensed high-z star-forming galaxies, taking advantage of archival observations of massive lensing clusters. This can help to constrain the escape fraction of LyC photons from star forming galaxies in the early universe, which models of reionization predict to be significantly greater than is seen in the local universe.
時間：2022.12.02(三) 15:00
地點：香港大學 莊月明物理樓518室
講者：James Michael George NIANIAS(香港大學)
語言：英語
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【此屬轉載訊息，以主事單位發佈為準】
此活動由香港大學物理系.主辦。
