| |
EI2GYB > ASTRO 19.09.21 09:47z 108 Lines 6248 Bytes #999 (0) @ WW
BID : 14765_EI2GYB
Read: GUEST
Subj: Three dwarf spheroidal galaxies found to rotate
Path: HB9ON<IW2OHX<UA6ADV<I0OJJ<GB7CIP<EI2GYB
Sent: 210919/0943Z @:EI2GYB.DGL.IRL.EURO #:14765 BPQ6.0.22
_ _ _ _
/ \ ___| |_ _ __ ___ | \ | | _____ _____
/ _ \ / __| __| '__/ _ \ | \| |/ _ \ \ /\ / / __|
/ ___ \\__ \ |_| | | (_) | | |\ | __/\ V V /\__ \
/_/ \_\___/\__|_| \___/ |_| \_|\___| \_/\_/ |___/
Three dwarf spheroidal galaxies found to rotate
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.
An international team of astrophysicists from the Instituto de Astrof¡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 Mart¡nez-Garc¡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
Andr‚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.
____ __ ____ ___ _ _ ____ ____ ____ ____
( __)( )(___ \ / __)( \/ )( _ \ ( _ \( _ \/ ___)
) _) )( / __/( (_ \ ) / ) _ ( ) _ ( ) _ (\___ \
(____)(__)(____) \___/(__/ (____/ (____/(____/(____/
PART OF THE DONEGAL PACKET RADIO NETWORK
Packet: EI2GYB@EI2GYB.DGL.IRL.EURO
Email: EI2GYB@GMAIL.COM
+------------------------------------------------------------------------------+
Read previous mail | Read next mail
| |
