Galaxies

Table of contents:

• My galaxy zoo
• Basics of galaxies
• Observations of galaxies
  • Millimeter observations
• Simulation of galaxies
• Theoretical studies of galaxies

My galaxy zoo (back to top)

This page contains the galaxies I am interested in:

Basics of galaxies: (back to top)

• Epicyclic freuquency
• pattern speed
• Resonance: corotation, Lindblad resonance, ultraharmmonic resonance
  

Epicyclic frequency (κ) -- the frequency of periodic radial motion of gas and/or stars beside their nearly circular motion in a galaxy.
Pattern speed (Ω_p) -- the group angular speed of those large scale substructures of a galaxy, such as bars and spirals. In a barred spiral galaxy, the bar and the spirals are usually assumed to have the same pattern speed.
Resonance: there are two broad categories of resonances:
  (1)one when Ω=Ω_p with Ω being the angular speed of a star or cloud;
  (2)the other when mn(Ω-Ω_p)= +/-κ, with m being the number of spirals arms, n being any positive integer number.
    Corotation (CR) -- the first kind of the above resonances.
    Lindblad Resonance (LR) -- the special resonance when n=1 in the second case of the above resonances. The inner and outer Lindblad resonance radii (ILR and OLR) are corresponding to the + and - sign of κ on the right side of the definition equation.
    Ultraharmmonic Resonance (UHR) -- the special resonance when n>=2 in the second case of the above resonances. The inner and outer Lindblad resonance radii (iUHR and oUHR) are corresponding to the + and - sign of κ on the right side of the definition equation.

Observations of galaxies (back to top)

• Millimeter observations (back to top)
  • Koda et al. 2009ApJ...700L.132K
    Facts: They reported the highest-fidelity observations of the grand-design spiral galaxy M51 in carbon monoxide (CO), using CARMA (six 10-m and nine 6-m antenna). Sensitivity is 40mJy/beam in 5.1 km/s velocity resolution (equivalent to a mass resolution of 10^5 Msun at d=8.2 Mpc if assume a XCO = 2x10^20 cm^-2 (K.km/s)^-1). Angular resolution is 4 arcsec (160pc). Thus typical Galactic GMC (4x10^5 Msun, 40pc in size) can be detected at 4-sigma level.
    Results: More than 90% of flux is resolved out by the interferometer. Only found few GMCs associated with each previously known GMAs. High mass GMCs tend to appear in downstream regions. Smaller clouds are at the upstream sides and little emission is found in the interarm region on the downstream side.
    Conclusions: Smaller clouds coll
    Problems: They argued that the GMC can not accumulate enough mass to form from diffuse atomic gas locally. But they have assumed that the accretion gas density are low and constant, which is not true. If the arrection is fixed to some arbitratry radius, the accretion gas density should increase with time. This is clear when we imagine a gravitationally free fall sphere. Thus, they have severely overestimated the accretion time scale and they arguments do not stand.(by Jinhua He)
    (figs.: left -- CO 1-0 map at 4 arcsec resolution; middle right -- velocity fields; middle -- GMCs/GMAs; middle right -- NRAO 45m single dish map of CO 1-0 at a resolution of 22 arc; right -- 2H2/(HI+2H2).)
    
  • Egusa et al. 2011ApJ...726...85E
    Facts: They mapped CO 1-0 in one spiral arm local region of M51 with CARMA at an angular resolution of 0.7 arcsec (30 pc).
    Results: More than 90% of flux is resolved out by the interferometer. Only found few GMCs associated with each previously known GMAs. High mass GMCs tend to appear in downstream regions. Smaller clouds are at the upstream sides and little emission is found in the interarm region on the downstream side.
    Conclusions: Smaller clouds collide to form GMCs and GMAs preferentially on the downstream side.
  • Koda et al. 2012ApJ...761...41K
    Facts: They compared CO 2-1/1-0 ratio (R_2-1/1-0) map of M51 with H_alpha and FUV maps.
    Results: The ratios R_2-1/1-0 is higher mainly in the downstream side of the spiral arms which coincided with the strong emission regions of H_alpha, FUV, and 24um continum (star formation tracers).
    Conclusions: The CO 2-1/1-0 ratio is higher in star formation regions in the downstream side of spiral arms.
    (figs: left -- CO 2-1/1-0 ratio overlaid with I_CO1-0 contours; middel left -- Spitzer SINGS 24um map; middle right -- Spitzer SINGS Halpha map; right -- GalexView FUV map.)
    
  • Rebolledo et al. 2012ApJ...757..155R
    Facts: They mapped CO 1-0, 2-1 and 13CO 1-0 in a 6kpc x 6kpc region in the eastern part of the non-grand spiral galaxy NGC 6946 with CARMA at angular resolutions of 2-6 arcsec. Single dishes Nobeyama 45 m and IRAM 30 m are used to make the short base lines components.
    Results: They identified 45 CO cloud complexes in the CO(1-0) map and 64 GMCs in the CO(2-1) maps. The sizes, line widths, and luminosities of the GMCs are similar to values found in other extragalactic studies.
    Conclusions: GMCs on arms, particularly those in a specific region that shows a strong velocity gradient, have higher SF rates/efficiencies.
  • Louie et al. 2013ApJ...763...94L
    Facts: They carefully compared the geometry of gas tracers (CO and HI 21cm) and star formation tracers (Halpha and 24um) maps of M51 to investigate possible geometrical offsets among them.
    Results: They found that HI peaks are usually at the downstream side of CO peaks.
    Conclusions: (1) HI peaks trace photodissociated gas near to young stars which makes it a bad tracer of either star forming gas or forming stars. Therefore only CO (among the two tracers) is a good tracer of star forming gas. (2) the geometrical offsets depends on the chosed tracers.
  • Momose et al. 2013ApJ...772L..13M
    Facts: They performed first sub-kpc scale analysis of Kennicutt-Schmidt (K-S)law using CO 1-0, a better tracer of bulk gas than CO 2-1.
    Results: They found an index of N=1.3 for the K-S law and N becomes 1.8 when the diffuse stellar and dust background emission is subtracted from the Halpha and 24μm images.
    Conclusions: Star formation is enhanced by non-linear processes (because a linear process has N=1) in regions of high gas density, e.g., gravitational collapse and cloud–cloud collisions.

Simulation of galaxies (back to top)

Theoretical studies of galaxies (back to top)

Koda's papers:

http://adsabs.harvard.edu/abs/2013ApJ...772..107D

http://adsabs.harvard.edu/abs/2013ApJ...777...96C

http://adsabs.harvard.edu/abs/2015ApJ...800...70S

http://adsabs.harvard.edu/abs/2015A%26A...576A..33H

http://adsabs.harvard.edu/abs/2015ApJ...807L...2K

http://adsabs.harvard.edu/abs/2015ApJ...808...99R

http://adsabs.harvard.edu/abs/2015ApJ...815...59P