The LMS-1 stream: A fossil remnant of the early formation of the Milky Way

Data: 
11/08/2021 - 14:00 - 15:00
Local: 
Remoto, com transmissão pela internet

 

The LMS-1 stream: A fossil remnant of the early formation of the Milky Way

 
Khyati Malhan
 
Stockholm University
 
As per the ΛCDM cosmological model, the halo of the Milky Way was built up by the merging of numerous progenitor galaxies, as these dwarf galaxies brought in their own stellar populations (in the form of stars and globular clusters). Over time, the dwarf galaxies were tidally stripped by the Galactic potential, eventually leading to the formation of “stellar streams”. Therefore, stellar streams provide direct evidence of the hierarchical formation of our Galaxy. Surprisingly, most of the known dwarf galaxy streams are dynamically-young systems that were only recently merged into our Galaxy (<~3-6 Gyr ago). However, the hierarchical paradigm of galaxy formation suggests that several dwarf galaxies must have merged into the Milky Way at earlier times (>~8−10 Gyr ago). These dynamically-old streams are likely to be discovered in the inner <~10-20 kpc regions of the Galaxy, and they hold the key to unravel the early formation history of the Galactic Halo. I will talk about the “LMS-1” stellar stream, that we detect by searching for wide streams in the ESA/Gaia EDR3 dataset using my STREAMFINDER algorithm. We detect LMS-1 as a 60° long stream to the north of the Galactic bulge, at a distance of ~15 kpc from the Galactic center, together with additional components that suggest that the overall stream is completely wrapped around the inner Galaxy. Using spectroscopic measurements from LAMOST, SDSS and APOGEE, we infer that the stream is very metal poor (⟨[Fe/H]⟩=−2.1) with a significant metallicity dispersion (σ [Fe/H]=0.4), and it possesses a large radial velocity dispersion (σ_v = 20 ± 4 kms−1). These estimates together imply that LMS-1 is a dwarf galaxy stream. Both the orbit and metallicity of LMS-1 are remarkably similar to the globular clusters NGC~5053, NGC~5024 and another stellar stream “Indus”. Even Pal~5 cluster overlaps with LMS-1 in the dynamical energy-action (E,J) space. These findings make LMS-1 an important contributor to the stellar population of the inner Milky Way halo.
 
 
 
Dr. Khyati Malhan is a postdoc researcher at the Dept. of Physics (2018-2021), Stockholm University. He completed his B.Sc. (Hons) Physics and M.Sc. Physics (2010-2015) from University of Delhi. He then moved to Strasbourg, France to complete his PhD in astrophysics (2015-2018) from Strasbourg Observatory. For his research work, he was awarded the "Best PhD thesis of 2018" by the University of Strasbourg. Dr. Malhan was recently awarded the German Humboldt Fellowship and the IAU/Gruber research grant, and with these, he plans to start his next postdoc position at MPIA in Heidelberg next November.