Seminar of Research Postgraduate(RPg) Student:- Mitigating misidentification problem in using high-z LFs to test for Dark Matter models
Wave Dark Matter(ψDM), composed of ultralight bosons with mass ~10-22eV, is a promising candidate to resolve various small scale problems confronted by conventional particle-like Cold Dark Matter(CDM) while having desired properties to explain large scale structure formation. One particular smoking gun signature for ψDM is the predicted suppressed low mass structure formation due to quantum pressure below de Brogile wavelength. And such suppression is detectable as a turnover at the faint end of high-z Luminosity Functions(LFs). Current construction of LFs in blank fields, however, has not been able to reach the faint end where such suppression begins to occur. Gravitational Lensing by galaxy clusters, on the other hand, is able to reach those faint range by magnifying dim distant galaxies behind the lensing cluster. Nevertheless, construction of LFs in lensing fields suffers one critical complication that is contamination by dim cluster members. Intriguingly enough, Shipley et al, 2018 reported a net excess of z~4 galaxies only seen in the Hubble Frontier Fields(HFF) cluster fields and not in accompanying nearby blank fields. Here we suspect this net excess is caused by dim cluster members that have been inaccurately assigned their photometric redshifts of z~4. Such misidentification problem occurs when D4000 break of a dim cluster member is confused with redshifted Lyman break of a high-z star forming galaxy due to similarity in their Spectral Energy Distribution shapes. Accurately quantifying the amount of contamination, and later to remove them, is hence critically important for an accurate construction of LFs in lensing fields. In this talk the speaker will present how magnification bias could be applied to achieve the first aim. And his team found current HFF photometric redshift catalogs suffer greatly this problem, in particular, they found about half of samples in redshift 3.5-5.5 range are in fact low-z dim cluster members. They are currently exploring various strategies to weed out those interlopers, for which they anticipate James Webb Space Telescope(JWST) to have the final say by providing us rest-frame optical Spectral Energy Distributions(SEDs) for high-z galaxies.
時間：2022.06.15(三) 16:30
頻道：Zoom: 351-657-7235
講者：Jiashuo ZHANG(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。
