Photometry: Imaging Galaxies

• Surface brightness
• Sky brightness, e.g., at Mauna Kea
  sources include: zodiacal light (sources here and here) from interplanetary dust, airglow, more airglow, anthropogenic emission (sources here and here emission)
• Projection effects

Spiral Dynamics and Dark Matter

• Rotation curves
  • the pioneer: Vera Rubin
  • geometry of the problem
  • M31: optical, with 21-cm rotation curve from Carignan et al (2006)
  • M33 rotation curve
  • NGC 2997: optical global and zoom (sources here and here); hot off the slit spectrograph
  • typical rotation curves examples, by galaxy type
• Global velocity profiles:
  21-cm data
  the Tully-Fisher relation

Dark Matter Candidate: Cold Gas

• cold gas as dark matter
• quantum atoms: hydrogen energy levels
• testing for cold gas: absorption lines from atoms
  as seen in disk sightlines towards nearby stars (Sonneborn et al 2002)

Spiral Structure

• Spiral arms
  
  • Milky Way: H I gas (21 cm), stars (near IR) (source here)
  • grand design: M74 visible, UV, near-IR H-alpha; NGC 2997 visible (sources here, here, here)
  • flocculent: NGC 4414, source here
  • multiwavelength Andromeda (M31) NGC 1512, M81, M104,
• Leading vs trailing arms
• The winding problem
• The Lin-Shu hypothesis
  Spiral density waves
  spiral pattern from nonradial (oval) orbits