Computational assesment
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School
University of New South Wales *
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Course
3160
Subject
Astronomy
Date
Dec 6, 2023
Type
docx
Pages
6
Uploaded by mbckafido
Approach
Data gathering:
Data Gathering:
GAIA Data
: Obtain data from Vasiliev & Baumgardt (2021), Table
A1. Ensure you have all 170 rows. Choose a data format that works
best with the tools or programming languages you're familiar with.
Harris Catalogue Data
: Use the provided .csv or .txt versions of
the reformatted Harris tables.
3. Data Merging:
Since you'll be working with data from two sources, you'll likely need to
merge or join them based on a common identifier, probably the cluster
name or some identifier.
4. Data Exploration:
Inspect the data for any inconsistencies, missing values, or outliers.
Generate basic statistics (like mean, median, mode) and visualize
the data to understand the distribution of the proper motions and
recession velocities.
5. Analysis:
Direction of Rotation
: By plotting the proper motions against the
positions of the clusters (from the Harris Catalogue), you should get
an idea of any general movement patterns. A trend might indicate a
preferred direction of rotation.
Amplitude of Rotation
: If a preferred direction of rotation is
observed, calculate the magnitude of this rotation.
Velocity Dispersion
: This is essentially the spread of velocities
about the mean velocity. You can calculate this using standard
deviation.
Combining Proper Motions and Recession Velocity
: You can
use vectors to represent both velocities and then combine them to
get a total velocity vector for each cluster. This will provide a
comprehensive picture of each cluster's movement in three
dimensions.
6. Interpretation and Conclusions:
Based on the analysis, draw conclusions about the rotation of the
Milky Way's globular clusters.
Discuss the implications of your findings on the formation of the
Milky Way and its globular cluster system.
7. Further Analysis:
Suggest additional tests or studies that could further elucidate the
formation scenarios of the Milky Way. For instance, studying the age
distribution of clusters might provide clues about when they formed
relative to significant events in the Milky Way's history.
8. Documentation:
Given the emphasis on clarity and the ability for someone else to follow
your logic:
Clearly comment your code to describe what each section is doing.
If possible, divide your analysis into sections or steps with headers.
Write an accompanying report or document that explains your
approach, methods, findings, and interpretations in plain language.
Include visual aids, such as graphs or plots, to support your
conclusions.
Important Aspects:
Clarity
: Your logic should be easy to follow.
Documentation
: Each step should be well-documented so that
another person could reproduce your results.
Interpretation
: The real value of this assignment is in drawing
meaningful conclusions from the data. The technical side is
important, but understanding and interpreting your findings are
crucial.
Approach:
Start with a clear plan: Understand the data sources, the tools at
your disposal, and the final objectives.
Tackle the assignment step by step, ensuring you understand and
can explain every decision and method you choose.
Document as you go, making sure everything is clear and easy to
follow.
Remember, the emphasis is on clarity and interpretation, so make sure to
prioritize those throughout the process!
I have found out that when I plotted proper motions of glob. cluster in MW
(Declination against ascension), I got a pattern of clusters that are
accumulating on the right bottom part of the graph (90%) and the rest is
spread randomly. Also most clusters point downwards, which should
indicate a consistent pattern of preferred direction of rotation. The
Magnitude of rotation is 5.11 mas/yr using the formula: sqrt(pmRA^2 +
pmDE^2). What does this mean? Next I computed the mean velocity and
the standard deviation: Mean Recession Velocity: -4.65 Velocity
Dispersion: 141.85 and plotted a graph of X,Y,Z coordinates and got the
image of all globular clusters on a 3D plot with vectors representing
recession velocities, where half of the clusters point upwards and half of
them downwards. What does this mean?
The motion of globular clusters in relation to the Milky Way galaxy
provides valuable insights into the galaxy's history, formation, and
evolution. Here's a possible interpretation of your results, keeping in mind
the data and the characteristics you've observed:
1.
Origins and Formation of Globular Clusters
: Globular clusters
are ancient structures that can predate the formation of their host
galaxies. The 50-50 split in motion suggests a bimodal distribution
of movements. This could indicate that half of the clusters
originated in the Milky Way, while the other half might have been
captured from smaller galaxies or other structures that the Milky
Way interacted with or merged with in its past.
2.
Milky Way's Evolution
: The globular clusters pointing upwards
and downwards may be influenced by the gravitational pull of the
Milky Way's central bulge and dark matter halo. Their motion can
shed light on the Milky Way's gravitational potential and the
distribution of its dark matter.
3.
Peculiar Motions & Interactions
: If certain clusters do not
conform to the observed patterns and have peculiar motions, they
might be recent captures or could have experienced interactions
with other clusters or structures in the Milky Way, which altered
their trajectories.
4.
Future of Our Galaxy
: The motions of the clusters can be
extrapolated to predict future interactions. For example, clusters
moving towards the center of the Milky Way may eventually be
absorbed by the central bulge. Conversely, clusters moving
outwards might escape the galaxy's gravitational pull if they attain
sufficient velocity.
5.
Evidence of Past Mergers
: The Milky Way has undergone several
mergers with smaller galaxies throughout its history. The motion of
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the clusters, especially those that do not conform to the general
trend, could be remnants of these smaller galaxies. Their distinct
trajectories could be the result of the gravitational dynamics from
past galactic mergers.
6.
Galactic Disk & Halo
: The split in the direction of the globular
clusters might also provide insights into the distribution of these
clusters. Those in the halo might have different characteristics than
those in the galactic disk. The motion can help differentiate between
these two populations and offer insights into their respective roles in
the galaxy's history.
In summary, the motion of globular clusters in the Milky Way serves as a
living record of our galaxy's history and evolution. Analyzing their
trajectories helps us understand past interactions, the nature of dark
matter, the formation of the Milky Way, and potential future scenarios.
Remember, these are just interpretations, and deeper analysis, coupled
with other astronomical data, would provide a clearer picture.
6. Interpretation of Results:
Preferred Direction of Rotation:
Your observation of most clusters pointing downwards does
indicate a consistent pattern of preferred direction of rotation.
The accumulation on the right bottom part suggests a
significant group of clusters has similar proper motions,
possibly indicating a shared history or origin.
Magnitude of Rotation:
The magnitude of rotation you computed (5.11 mas/yr) is a
measure of the average angular motion of the globular
clusters. It suggests that the clusters, on average, move at
this rate across the plane of the sky. It's essential to relate this
value to actual physical distances (parsecs or light-years)
using the distance of each cluster to obtain a clearer picture.
Mean Recession Velocity & Velocity Dispersion:
The negative mean recession velocity indicates that, on
average, the clusters are moving towards us. However, the
high velocity dispersion (141.85) suggests a broad distribution
of velocities, implying that while many clusters might be
moving towards us, several are also moving away at different
speeds.
The fact that half the clusters point upwards and the other half
downwards in your 3D plot could indicate that the Milky Way's
gravitational effects and historical interactions have
influenced their trajectories. The clusters' movement could
also shed light on the dynamics of the Milky Way's core and its
dark matter distribution.
7. Conclusion & Implications:
Based on your findings, you can hypothesize about the Milky Way's
formation and the origins of its globular cluster system. The
preferred direction of rotation could be evidence of a significant
event in the Milky Way's history, such as a merger with another
galaxy.
The combined motion from both proper motions and recession
velocities helps to visualize the overall dynamic environment of the
Milky Way and the complex interactions governing the globular
clusters.
The motion of globular clusters in relation to the Milky Way galaxy
provides valuable insights into the galaxy's history, formation, and
evolution. Here's a possible interpretation of your results, keeping in mind
the data and the characteristics you've observed:
1.
Origins and Formation of Globular Clusters
: Globular clusters
are ancient structures that can predate the formation of their host
galaxies. The 50-50 split in motion suggests a bimodal distribution
of movements. This could indicate that half of the clusters
originated in the Milky Way, while the other half might have been
captured from smaller galaxies or other structures that the Milky
Way interacted with or merged with in its past.
2.
Milky Way's Evolution
: The globular clusters pointing upwards
and downwards may be influenced by the gravitational pull of the
Milky Way's central bulge and dark matter halo. Their motion can
shed light on the Milky Way's gravitational potential and the
distribution of its dark matter.
3.
Peculiar Motions & Interactions
: If certain clusters do not
conform to the observed patterns and have peculiar motions, they
might be recent captures or could have experienced interactions
with other clusters or structures in the Milky Way, which altered
their trajectories.
4.
Future of Our Galaxy
: The motions of the clusters can be
extrapolated to predict future interactions. For example, clusters
moving towards the center of the Milky Way may eventually be
absorbed by the central bulge. Conversely, clusters moving
outwards might escape the galaxy's gravitational pull if they attain
sufficient velocity.
5.
Evidence of Past Mergers
: The Milky Way has undergone several
mergers with smaller galaxies throughout its history. The motion of
the clusters, especially those that do not conform to the general
trend, could be remnants of these smaller galaxies. Their distinct
trajectories could be the result of the gravitational dynamics from
past galactic mergers.
6.
Galactic Disk & Halo
: The split in the direction of the globular
clusters might also provide insights into the distribution of these
clusters. Those in the halo might have different characteristics than
those in the galactic disk. The motion can help differentiate between
these two populations and offer insights into their respective roles in
the galaxy's history.
In summary, the motion of globular clusters in the Milky Way serves as a
living record of our galaxy's history and evolution. Analyzing their
trajectories helps us understand past interactions, the nature of dark
matter, the formation of the Milky Way, and potential future scenarios.
Remember, these are just interpretations, and deeper analysis, coupled
with other astronomical data, would provide a clearer picture.
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