ASTRONOMY 3303   HW #8     due Wed Nov 29, 2017

This is a very short assignment, intended to prepare you for the last two lectures of the semester and the discussions we will have during them. Please do Part 1 before class on Monday, but you don't have to hand it in until Wednesday.

Part 1:   Dwarf galaxies as cosmological probes

On Monday, Nov 27, we will talk about how dwarf galaxies play an important role in constraining cosmology. So that you have a better idea of what such objects look like in terms of more typical galaxies, follow these links to SDSS images and the NED database. Then answer the questions about them below.

Draco   = UGC 10822     260.0512, 57.9153     DR14Navi     NED1.0

Leo I     = UGC   5470     152.1167, 12.3064     DR14Navi     NED1.0

Leo T   = AGC 198305     143.7225, 17.0514     DR14Navi     NED1.0

Leo P     = AGC 208583     155.4379, 18.0881     DR14Navi    NED1.0

DDO 126   = UGC   7559     186.7715, 37.1426     DR14Navi     NED1.0

VCC 2062   = AGC 221026     191.9996, 10.9708     DR14Navi     NED1.0

a.   Surface brightness, to first order, is independent of distance. Which object has the highest optical surface brightness? Which has the lowest?

b.   Which galaxies appear to be forming stars? Explain how you arrive at your answer.

c.   Come up with 3 substantive questions that you have about these objects (either individually or as a group/subset) as dwarf galaxies. Anything goes here as long as the questions don't have trivial answers (i.e. answers you can find in NED or doing a quick search on the web; e.g. position on the sky, measured redshift, etc).

Part 2:   Exploring the Early Universe with CCAT-p

David has been reporting on studies of the Sunyaev-Zel'dovich Effect with the CCAT-p telescope, and Ruixin has told us about using the redshift HI 21 cm line to map the topography of the neutral gas from the Dark Ages through the Epoch of Reionization. During the last class, we'll discuss the planned CCAT-p science programs focusing on the early universe, including the intensity mapping experiment using the redshifted 158 μm line of ionized carbon. To help you prepare for the discussion, answer the questions below.

a.   Compare the ionization potential of H and C. For the simple case of a spherical HII region around a single O star, comment (qualitatively) where you would expect to see emission from ionized carbon.

b.   Why is [CII] written with brackets while HII is written without them?

c.   CCAT-p will have an angular resolution of about 40 arcsec at λ ~ 850 μm. Adopting the default parameters for a flat universe given at the Cosmology Calculator (see HW #4), what linear size corresponds to that resolution at z = 7?

d.   It should be clear from your answer to the last question that confusion will still influence the ability of CCAT-p to resolve individual galaxies at high redshifts. Explain in your own words why this is not an issue for the [CII] intensity mapping experiments.

e.   Review Wayne Hu's tutorial on Polarization Intro and his animations of Polarization and EB Modes. Other pages on the same site are also very interesting. You don't have to write anything for the homework, but please try to understand what the polarization of the CMB can teach us.

The final paper is due Wed Dec 6 at 4:30 pm. Please email it to both Dominik ( and Martha ( by the deadline. A few guidelines:
  • The paper should be written with your Astro 3303 peers as the audience. Be sure to explain terminology, jargon, symbols, unfamiliar units, mathematical equations, etc so that they could follow your reasoning.
  • The paper should have a title, an introduction, a conclusion and a reference list plus, of course, middle sections which discuss the instrument/facility and the science topic.
  • Figures, tables, etc can be included when they aid in conveying the content of the paper. Be sure to mention each figure/table explicitly in the text. In most cases, you should also include the "take-away message": what point are you trying to make through the figure/table?
  • Be sure that you explain all symbols including ones used to label axes in the figures.
  • Each figure should have a caption that explains what it shows, as well as an explicit citation. Since you should be including the full citation in your reference list, you can put in the figure caption "From Smith+ 2013", and then write out the bibliographic citation for the Smith+ paper in the reference list.
  • Tables from other sources can also be included with the same guidelines as figures (be sure to convey what the contents of the table are and give the citation).
  • Be sure the references are specific enough that we can find any statement/fact/figure you cite.
  • If you have questions about how to do references or style the paper, please ask us. We are pretty flexible about the exact formatting, but we expect consistency and thoroughness.