| Name: | Shankar Ray |
| Affiliation: | CHRIST (Deemed to be University) |
| Conference ID : | ASI2024_594 |
| Title : | Unlocking the Enigma of Extremely Fast Rotating Massive Spirals: Star Formation, Missing Baryons, and Early Stellar Growth |
| Authors : | Shankar Ray1,2, Suraj Dhiwar3,4, Joydeep Bagchi1, M.B. Pandge2 |
| Authors Affiliation: | 1 Department of Physics and Electronics, Christ University, Hosur Road, Bengaluru-560029, India
2 Department of Physics and Electronics, Dayanand Science College, Latur-413512, India
3 Inter-University Centre for Astronomy and Astrophysics, Pune-411007, India
4 Savitribai Phule Pune University, Pune-411007, India |
| Mode of Presentation: | Poster |
| Abstract Category : | Galaxies and Cosmology |
| Abstract : | We analyse highly sensitive AstroSat UVIT data for a sample of five extremely massive galaxies with rotational velocities > 300km/s. We find that these massive spirals have a very low to moderate recent star formation (~ 1.4-13.7 Msun yr^-1) falling far below the star formation main-sequence relation with the specific star formation rates < 10^(-10.5) yr^-1. We resolve the star-forming clumps of these objects in far-ultraviolet and find the mean star formation rate density to be ~ 0.01-0.07 Msun yr^-1 kpc^-2 showing localised young star formation. It is observed that the galaxies with relatively recent high star formation have noticeable asymmetry in their structures, perhaps contributing to their recent uprise in star formation. However, we find that these galaxies are extremely inefficient (star formation efficiency ≲ 31 percent) when it comes to condensing their dark-matter halo baryons into stars in the galactic disc. Modelling the spectral energy distributions covering far-ultraviolet to far-infrared emissions indicates that these galaxies have experienced the peak of their star formation much before the `cosmic high noon'/`quasar epoch' around redshift ~ 1-3. We find much of their stellar mass grew rapidly by that time with ~ 31-42 percent of the stellar mass accumulated in ~ (1/16) - (1/5)th the age of the Universe. However, we find that these galaxies have a baryonic mass of ~ 10^11 Msun making them fall far below the Baryonic Tully-Fisher relation. Despite the detections of soft X-ray emitting gas in the huge halo ( > 10^13 Msun) of some of these galaxies, we find these galaxies lack upto ~ 67-92 percent of baryons in their halo as per the expectations from the `cosmological baryon fraction', termed as the `missing baryons'. Understanding these ultra-rapidly rotating objects within our immediate cosmic vicinity perhaps could offer invaluable insights into the processes involved in the formation and evolution of galaxies.
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