___Lab 011 1 Template-Galactic Morphology

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Stellar & Galactic Astronomy Lab 11 — Galactic Morphology Copyright 2021, James T. Hooten, All Rights Reserved 11-1 11 Galactic Morphology Purpose The purpose of this lab is to classify several program galaxies according to the Hubble sequence used for galaxy classification. This sequence is often called the Hubble Tuning Fork. This lab is written for both face-to-face and online labs. In some cases, special instructions are included for online students only. For this lab you will utilize the following item(s): Name of Item Item Description Stellarium Night-sky simulation software Lab 11 Template-Galactic Morphology.pdf The file you are currently reading Lab 11 Data File-Galactic Morphology.xls Excel file for use by online students Lab 11 Questions-Galactic Morphology Online quiz for Follow-Up questions Excel Spreadsheet software Background Information Edwin Hubble Edwin Hubble was an American astronomer who spent his entire professional career at Mt. Wilson Observatory studying the universe and making important contributions to the field of observational astronomy. His career at Mt. Wilson began in 1917 and ended when he died in 1953. Beginning in the 1920s, Hubble used Cepheid variable stars to measure the distance to M31, the great spiral galaxy in the constellation Andromeda and our closest large galactic neighbor.

Stellar & Galactic Astronomy Lab 11 — Galactic Morphology 11-2 Copyright 2021, James T. Hooten, All Rights Reserved As you may recall from previous labs, H ubble’s wo rk with M31 made astronomers realize that galaxies are very distant and contain billions of stars. Also, Hubble and Milton Humason confirmed the prediction of the expansion of the universe made independently by Alexander Friedmann and Georges Lemaitre. The discovery of the expanding universe became the first pillar of evidence supporting the Big Bang cosmological model. The Hubble Tuning Fork Because of his close work with galaxies, Hubble devised a scheme to classify galaxies according to their physical features. This scheme became known as the Hubble sequence or the Hubble Tuning Fork. The Hubble Tuning Fork is a classification system that is based largely on galactic morphology and little else. Nevertheless, astronomers still use the Hubble classification scheme to give galaxies an initial classification. More in-depth classification systems also exist today. The Hubble Tuning Fork broadly divides galaxies into three categories: spirals, ellipticals, and irregulars. Within each of these broad categories, there are subcategories. The Hubble sequence does not represent a transition from one galaxy type to another. It would be a mistake to think of the Hubble Tuning Fork as an evolutionary track for galaxies. The galaxies are arranged in the tuning fork shape shown in Figure 11.01 for convenience of display only. Figure 11.01: Hubble Tuning Fork Diagram

Stellar & Galactic Astronomy Lab 11 — Galactic Morphology Copyright 2021, James T. Hooten, All Rights Reserved 11-3 Elliptical galaxies can be divided into groups based on the elongation of the elliptical shape of the galaxy. For example, E0 would be the classification for an elliptical galaxy with a perfectly spherical appearance; the E designates the galaxy as elliptical and the 0 indicates it is spherical. An E1 would be less spherical and more elongated. An E2 more elongated, etc. all the way until potentially E9, which is the most elongated. In practice, galaxies past E7 are exceptionally rare or may be mistaken for edge-on spirals. Spiral galaxies are divided into two broad subcategories: normal spirals (S) and barred spirals (SB). Normal spirals have a central bulge that is spherical, while in barred spirals the central bulge is elongated forming a bar shape. Both S and SB galaxies have spiral arms, but within each of these classes there is a subclass ranging from a to c, where a represents a tightly wound spiral, c represents a loosely wound spiral, and b is between these two. For example, an SBa galaxy would be a barred spiral with tightly wound arms. The final major galaxy type in the Hubble sequence is Irregular (Irr) galaxies. This category is the catch-all for every other type of galaxy. This includes those galaxies that do not fall into either of the spiral categories or the elliptical categories.

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Stellar & Galactic Astronomy Lab 11 — Galactic Morphology 11-4 Copyright 2021, James T. Hooten, All Rights Reserved The assignment of a galaxy’s Hubble type is somewhat subjective , although experienced observers closely agree on most galaxies. Since the Hubble sequence is a non- quantitative system of galaxy classification, there may be disagreement caused by a galaxy’s orientation or the degree to which observers think spiral arms are considered tightly or loosely wound. Nevertheless, the Hubble sequence is a good starting point for galaxy classification. Further investigation may result in some galaxies being reclassified. More information about Edwin Hubble and the Hubble Tuning Fork can be found online and in your textbook. What’s to Come? For this lab, you will use Stellarium to classify several galaxies according to the Hubble Tuning Fork system. NOTE: The valid classes you should use are: Irr, Sa, Sb, Sc, SBa, SBb, SBc, S0, and E0-7. Use only these designations for the classification of each galaxy.

Stellar & Galactic Astronomy Lab 11 — Galactic Morphology Copyright 2021, James T. Hooten, All Rights Reserved 11-5 Procedure Part 1: Inspecting the Galaxies Data Table 11.01 contains a list of galaxies and characteristics that may be used in classifying each. You will use Stellarium to locate and view each galaxy. 1. First familiarize yourself with Data Table 11.01. The first column contains the names of the program galaxies for this lab. The next several columns list characteristic for galaxies. You will mark the displayed characteristics by placing an X in the appropriate column. The three broad Hubble types of Spiral, Elliptical, and Irregular are shown across the top of the table. Underneath the Spiral type there are subtype characteristics of No Bar and Barred, and under each of the subtypes there is an indicator characteristic for the state of the spiral arms, if any — No Arms, Tight Arms, Mid Arms, and Loose Arms. The same applies for the Barred Spirals. Under the Elliptical type there are subtypes characteristics relating to how elliptical the galaxy appears. An elliptical galaxy that appears spherical would be Ellipsoidal 0, while an extremely elongated elliptical galaxy would be Ellipsoidal 7. Elliptical galaxies between these two extremes would display characteristics somewhere between Ellipsoidal 1-6. The Irregular type column contains no subtypes. This column should be marked only if no other characteristics are marked. The final column is the Estimated Hubble Type. After searching and finding a program galaxy using Stellarium , you will mark the characteristics you observe by placing an X in each characteristic column. Once you are finished marking the appropriate columns, then you should be able to assign a Hubble type in the right- most column of Data Table 11.01. 2. Start Stellarium and turn off the ground [G], atmosphere [A], and Stop time from advancing [K]. You should confirm that time has stopped by making sure the clock in the lower part of the Stellarium window is not advancing. 3. Use [F3] to open the Search window, be sure the Object tab is selected. Type the Galaxy Name listed in the first column of Data Table 11.01 into the Search window and press enter. The program galaxy should center itself in the screen. If the program galaxy is not centered, then press the spacebar to center the selected object.

Stellar & Galactic Astronomy Lab 11 — Galactic Morphology 11-6 Copyright 2021, James T. Hooten, All Rights Reserved 4. Once the program galaxy is centered, zoom in using either the center mouse wheel, Page Up/Down, or Ctrl+Up/Down Arrows. You should see the galaxy selected. 5. Based upon what you observe in the galaxy image, place marks (X) in Data Table 11.01 for each characteristic of the galaxy. For example, the first galaxy in Data Table 11.01 is the Large Magellanic Cloud (LMC). Zooming on the LMC reveals the image shown in Figure 11.02 shown below. Figure 11.02: The Large Magellanic Cloud Inspection of the LMC galaxy in Figure 11.01 shows there are no spiral features present, nor are there any elliptical galaxy features present. This implies that the LMC is an Irregular galaxy. A mark of X should be placed in the Irregular column of Data Table 11.01. 6. Using the marks you placed in Data Table 11.01 as a guide, estimate the Hubble Type of each program galaxy. Record your estimate in the right-most column of the data table. For the example galaxy, the Estimated Hubble Type should be entered as “Irr.” NOTE: The valid types are: Irr, Sa, Sb, Sc, SBa, SBb, SBc, S0, and E0-7. Use only these designations for the Estimated Hubble Type of each program galaxy.

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Stellar & Galactic Astronomy Lab 11 — Galactic Morphology Copyright 2021, James T. Hooten, All Rights Reserved 11-7 7. Repeat the above steps for all program galaxies in Data Table 11.01. Submit Your Findings 8. Complete this lab by submitting your data file and answering the Follow-Up questions. ONLINE STUDENTS: To receive credit for this lab, you must upload your completed Excel data file and provide answers to the Follow Up questions through the online quiz named in the table at the beginning of this lab.

Stellar & Galactic Astronomy Lab 11 — Galactic Morphology 11-8 Copyright 2021, James T. Hooten, All Rights Reserved Data Presentation ONLINE STUDENTS: To get credit for the lab you must submit all entries online in the data file named in the table at the beginning of this lab. Data Table 11.01: Hubble Tuning Fork Classification System

Stellar & Galactic Astronomy Lab 11 — Galactic Morphology Copyright 2021, James T. Hooten, All Rights Reserved 11-9 Follow-Up ONLINE STUDENTS: To receive credit, your answers to Follow-Up questions should be entered in the online quiz named in the table at the beginning of this lab. Q11.1. Based upon what you have learned about different types of galaxies, which of the types of galaxies is most likely to be oldest? Q11.2. Which of the types of galaxies would you most likely find at the center of a large cluster of galaxies? Q11.3. Which of the galaxy types would be least likely to contain an ionization nebula like the Orion Nebula? Q11.4. Besides the shape, what are some other distinguishing characteristics of elliptical galaxies? Q11.5. Besides the shape, what are some other distinguishing characteristics of spiral galaxies?

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