https://phys.org/news/2020-11-family-tree-milky-deciphered.html
Family tree of the Milky Way deciphered
by Morgan Hollis, Royal Astronomical Society
Galaxy merger tree of the Milky Way inferred by applying the insights gained from the E-MOSAICS simulations to the Galactic globular cluster population. The main progenitor of the Milky Way is denoted by the trunk of the tree, coloured by its stellar mass. Black lines indicate the five identified satellites. Grey dotted lines illustrate other mergers that the Milky Way is predicted to have experienced, but could not be linked to a specific progenitor. From left to right, the six images along the top of the figure indicate the identified progenitor galaxies: Sagittarius, Sequoia, Kraken, the Milky Way’s Main progenitor, the progenitor of the Helmi streams, and Gaia-Enceladus-Sausage. Credit: D. Kruijssen / Heidelberg University/Licence
Scientists have known for some time that galaxies can grow by the merging of smaller galaxies, but the ancestry of our own Milky Way galaxy has been a long-standing mystery. Now, an international team of astrophysicists has succeeded in reconstructing the first complete family tree of our home galaxy by analyzing the properties of globular clusters orbiting the Milky Way with artificial intelligence. The work is published in Monthly Notices of the Royal Astronomical Society.
Scientists have known for some time that galaxies can grow by the merging of smaller galaxies, but the ancestry of our own Milky Way galaxy has been a long-standing mystery. Now, an international team of astrophysicists has succeeded in reconstructing the first complete family tree of our home galaxy by analyzing the properties of globular clusters orbiting the Milky Way with artificial intelligence. The work is published in Monthly Notices of the Royal Astronomical Society.
more at link.........................
the paper:
https://academic.oup.com/mnras/article-abstract/498/2/2472/5893320?redirectedFrom=fulltext
Kraken reveals itself – the merger history of the Milky Way reconstructed with the E-MOSAICS simulations:
ABSTRACT
Globular clusters (GCs) formed when the Milky Way experienced a phase of rapid assembly. We use the wealth of information contained in the Galactic GC population to quantify the properties of the satellite galaxies from which the Milky Way assembled. To achieve this, we train an artificial neural network on the E-MOSAICS cosmological simulations of the co-formation and co-evolution of GCs and their host galaxies. The network uses the ages, metallicities, and orbital properties of GCs that formed in the same progenitor galaxies to predict the stellar masses and accretion redshifts of these progenitors. We apply the network to Galactic GCs associated with five progenitors: Gaia-Enceladus, the Helmi streams, Sequoia, Sagittarius, and the recently discovered ‘low-energy’ GCs, which provide an excellent match to the predicted properties of the enigmatic galaxy ‘Kraken’. The five galaxies cover a narrow stellar mass range [M⋆ = (0.6–4.6) × 108 M⊙], but have widely different accretion redshifts (zacc=0.57−2.65" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">zacc=0.57−2.65zacc=0.57−2.65). All accretion events represent minor mergers, but Kraken likely represents the most major merger ever experienced by the Milky Way, with stellar and virial mass ratios of rM⋆=1" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">rM⋆=1rM⋆=1:31−16+34" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">31+34−1631−16+34 and rMh=1" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">rMh=1rMh=1:7−2+4" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">7+4−27−2+4, respectively. The progenitors match the z = 0 relation between GC number and halo virial mass, but have elevated specific frequencies, suggesting an evolution with redshift. Even though these progenitors likely were the Milky Way’s most massive accretion events, they contributed a total mass of only log (M⋆, tot/M⊙) = 9.0 ± 0.1, similar to the stellar halo. This implies that the Milky Way grew its stellar mass mostly by in-situ star formation. We conclude by organizing these accretion events into the most detailed reconstruction to date of the Milky Way’s merger tree.
Family tree of the Milky Way deciphered
by Morgan Hollis, Royal Astronomical Society
Galaxy merger tree of the Milky Way inferred by applying the insights gained from the E-MOSAICS simulations to the Galactic globular cluster population. The main progenitor of the Milky Way is denoted by the trunk of the tree, coloured by its stellar mass. Black lines indicate the five identified satellites. Grey dotted lines illustrate other mergers that the Milky Way is predicted to have experienced, but could not be linked to a specific progenitor. From left to right, the six images along the top of the figure indicate the identified progenitor galaxies: Sagittarius, Sequoia, Kraken, the Milky Way’s Main progenitor, the progenitor of the Helmi streams, and Gaia-Enceladus-Sausage. Credit: D. Kruijssen / Heidelberg University/Licence
Scientists have known for some time that galaxies can grow by the merging of smaller galaxies, but the ancestry of our own Milky Way galaxy has been a long-standing mystery. Now, an international team of astrophysicists has succeeded in reconstructing the first complete family tree of our home galaxy by analyzing the properties of globular clusters orbiting the Milky Way with artificial intelligence. The work is published in Monthly Notices of the Royal Astronomical Society.
Scientists have known for some time that galaxies can grow by the merging of smaller galaxies, but the ancestry of our own Milky Way galaxy has been a long-standing mystery. Now, an international team of astrophysicists has succeeded in reconstructing the first complete family tree of our home galaxy by analyzing the properties of globular clusters orbiting the Milky Way with artificial intelligence. The work is published in Monthly Notices of the Royal Astronomical Society.
more at link.........................
the paper:
https://academic.oup.com/mnras/article-abstract/498/2/2472/5893320?redirectedFrom=fulltext
Kraken reveals itself – the merger history of the Milky Way reconstructed with the E-MOSAICS simulations:
ABSTRACT
Globular clusters (GCs) formed when the Milky Way experienced a phase of rapid assembly. We use the wealth of information contained in the Galactic GC population to quantify the properties of the satellite galaxies from which the Milky Way assembled. To achieve this, we train an artificial neural network on the E-MOSAICS cosmological simulations of the co-formation and co-evolution of GCs and their host galaxies. The network uses the ages, metallicities, and orbital properties of GCs that formed in the same progenitor galaxies to predict the stellar masses and accretion redshifts of these progenitors. We apply the network to Galactic GCs associated with five progenitors: Gaia-Enceladus, the Helmi streams, Sequoia, Sagittarius, and the recently discovered ‘low-energy’ GCs, which provide an excellent match to the predicted properties of the enigmatic galaxy ‘Kraken’. The five galaxies cover a narrow stellar mass range [M⋆ = (0.6–4.6) × 108 M⊙], but have widely different accretion redshifts (zacc=0.57−2.65" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">zacc=0.57−2.65zacc=0.57−2.65). All accretion events represent minor mergers, but Kraken likely represents the most major merger ever experienced by the Milky Way, with stellar and virial mass ratios of rM⋆=1" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">rM⋆=1rM⋆=1:31−16+34" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">31+34−1631−16+34 and rMh=1" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">rMh=1rMh=1:7−2+4" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; font-size: 14px; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">7+4−27−2+4, respectively. The progenitors match the z = 0 relation between GC number and halo virial mass, but have elevated specific frequencies, suggesting an evolution with redshift. Even though these progenitors likely were the Milky Way’s most massive accretion events, they contributed a total mass of only log (M⋆, tot/M⊙) = 9.0 ± 0.1, similar to the stellar halo. This implies that the Milky Way grew its stellar mass mostly by in-situ star formation. We conclude by organizing these accretion events into the most detailed reconstruction to date of the Milky Way’s merger tree.