• Three dwarf spheroidal galaxies found to

    From ScienceDaily@1:317/3 to All on Tue Jul 27 21:30:50 2021
    Three dwarf spheroidal galaxies found to rotate

    Date:
    July 27, 2021
    Source:
    Instituto de Astrofi'sica de Canarias (IAC)
    Summary:
    Astrophysicists have discovered the presence of transverse rotation
    (in the plane of the sky) in three dwarf spheroidal galaxies, a very
    faint type of galaxies and difficult to observe, which are orbiting
    round the Milky Way; this helps to trace their evolutionary history.



    FULL STORY ==========================================================================
    An international team of astrophysicists from the Instituto de
    Astrofi'sica de Canarias (IAC), the University of La Laguna (ULL)
    and the Space Telescope Science Institute (STScI, USA) has discovered
    the presence of transverse rotation (in the plane of the sky) in three
    dwarf spheroidal galaxies, a very faint type of galaxies and difficult
    to observe, which are orbiting round the Milky Way; this helps to trace
    their evolutionary history. The finding was made using the most recent
    data from the GAIA satellite of the European Space Agency. The results
    of the study have just been published in the journal Monthly Notices of
    the Royal Astronomical Society (MNRAS).


    ========================================================================== Dwarf galaxies have a particular interest for cosmology. The standard cosmological model suggests that this type of galaxies was the first
    to form.

    Many of them, the majority, have been destroyed and cannibalized by
    large galaxies such as the Milky Way. However, those that remain can be
    studied and contain valuable information about the early Universe.

    One subclass of dwarf galaxies are the dwarf spheroidals. They are very diffuse, with low luminosity, they contain large proportions of dark
    matter and little or no gas. Since their discovery they have been deeply studied. However, their internal kinematics are still little known,
    due to the technical difficulties needed for their detailed study.

    Various previous studies have shown that the dwarf spheroidals do not
    have patterns of internal rotation, but their stars move on random orbits predominantly towards and away from the centre of the galaxy. But the
    galaxies within the other major sub-class of dwarfs, the irregulars, have
    large quantites of gas, and in some cases do have internal rotation. These differences suggest a different origin for the two types of dwarfs,
    or to a very different evolutionary history in which interactions with
    large galaxies, in our case with the Milky Way, have played a crucial
    role in eliminating the internal rotation of the spheroidals.

    To carry out their present research, the team of astrophysicists form
    the IAC and the STScI have used the latest data from ESA's Gaia to study
    the internal kinematics of six dwarf spheroidal galaxies, satellites
    of the Milky Way, and have discovered the presence of transverse
    rotation (in the plane of the sky) in three of them: Carina, Fornax,
    and Sculptor. These are the first detections of this type of rotation in
    dwarf spheroidal galaxies, except for the Sagittarius spheroidal, which
    is strongly distorted by the gravitational potential of the Milky Way,
    and is therefore not representative of its type.

    "The importance of this result is because, in general, the internal
    kinematics of galaxies, in this case their rotation, is an important
    tracer of their evolutionary history, and of the conditions in which the
    system was formed," explains Alberto Manuel Marti'nez-Garci'a, doctoral
    student at the IAC and the ULL, and first author of the article.

    "Although the standard model of cosmology assumes that the dwarf galaxies
    were the first to form, it is not clear if they are simple systems or
    whether those we observe are formed by the agglomeration of other even
    simpler systems, smaller and older. The presence of rotation suggests the second option. It also suggests a common origin for all dwarf galaxies,
    those that are at present rich in gas (the irregulars) and those which
    are not (the spheroidals)," explains Andre's del Pino, researcher at
    the STScI and a co-author of the article.

    "The Gaia satellite has revolutionised our knowledge of the Milky Way and
    its neighbourhood, giving us very precise measurements of the positions
    and motions of almost two thousand million stars. Although the data
    from Gaia are used mainly to study our Galaxy, this ESA mission has
    also opened a new window on the study of the satellite galaxies of the
    Milky Way, giving specific access to their internal kinematics," says
    Antonio Aparicio, a researcher at the IAC and the ULL and a co-author
    of the article.

    Even so, according to the researchers, studies based on Gaia data entail
    many technical difficulties. In the first place, one must determine which
    of the stars in the database really belong to the satellite galaxies,
    and which to the Milky Way itself, as the latter tend to contaminate the sample. The problem is that although the data to be analysed are limited
    to the region and the angular size of the spheroidal under study, which
    is the equivalent of one quarter of the angular diameter of the Moon,
    the vast majority of the stars detected in this area belong to the Milky
    Way and therefore indeed contaminate the sample.

    In addition, the distance of the spheroidals studied, which is up to
    some half a million light-years, and the low intrinsic luminosity of
    their stars, imply that the measurements are affected by a considerable
    level of noise. For all these reasons the analysis of the data requires
    a thorough filtration and a deep analysis of the different observational parameters to be able to reach reliable conclusions.

    ========================================================================== Story Source: Materials provided by Instituto_de_Astrofi'sica_de_Canarias_(IAC). Note: Content may be edited
    for style and length.


    ========================================================================== Journal Reference:
    1. Alberto Manuel Marti'nez-Garci'a, Andre's del Pino, Antonio
    Aparicio,
    Roeland P van der Marel, Laura L Watkins. Internal rotation of
    Milky Way dwarf spheroidal satellites with Gaia Early Data Release
    3. Monthly Notices of the Royal Astronomical Society, 2021; 505
    (4): 5884 DOI: 10.1093/mnras/stab1568 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2021/07/210727121247.htm

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