.. _p1-galaxy-radii: P01: Galaxy Radii ================= Observing Goals: ^^^^^^^^^^^^^^^^ In this project you'll determine the *characteristic scales* of one or two galaxies. Useful Background and References: ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ * `EllipticalGalaxies.pdf `__ or `DiskGalaxies.pdf `__ * The Photometry lecture from the Observational Astronomy Course Observation Planning: ^^^^^^^^^^^^^^^^^^^^^ * Observation Time * You will be observing HALF a night. * Target Selection * We suggest first looking at the Messier objects to see if there's one available at the appropriate right ascension and declination. If you can't find an appropriate one, ask for help. **Group 1 should pick a spiral galaxy** and **Group 2 should pick an elliptical galaxy** (note that sometimes more than one galaxy can be observed simultaneously!). * Observations * We suggest that you take images in at least two bands: :math:`B` and :math:`R`. If you have time, also take images in the :math:`V` band. * To calibrate your data you should also observe standard star fields. Data Analysis ^^^^^^^^^^^^^ * Data Reduction Basic Steps * Visit the page :ref:`data-reduction` * Produce artifact free images from your observations * Further for this project * You need to register and combine your images together, so that you have one final image per band * You need to estimate (using the mode, rather than the mean or median) the sky background level in each band and take it off the image * Locate the center of the galaxy in the images, and estimate the radius of the galaxy * Next use and ellipse fitting program (in astropy) to fit ellipses from the center outwards, and create a surface brightness profile for the galaxy * Further Analysis for this project * Determine whether a de Vaucouleurs :math:`a^{\frac{1}{4}}` profile or an exponential :math:`\exp(a)` profile fits the surface brightness profile best * Determine the scale length of the galaxy (the effective radius in the de Vaucouleurs profile, or the scale length of an exponetial fit) Results: Can you answer these questions with your work? ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ * Q1 what is the surface brightness profile of the galaxy, which model fits best, and what is the scale length? * Q2 do the position angle and/or ellipticity of the isophotes change as a function of semi-major axis?  If so, why? * Q3 for the elliptical galaxies (only), are the galaxies boxy or disky?  Does this change with semi-major axis? Presenting your results: ^^^^^^^^^^^^^^^^^^^^^^^^ - :ref:`a1-poster` - :ref:`a2-talk`