HI (21cm) emissions from a nearby galaxy are detected at three locations: (C) – galaxy centre (E) – -10 arcmin to the east of the galaxy center (W) –-10 arcmin to the west of the galaxy center The emission peaks at XXXXXXXXXXcm at (C), XXXXXXXXXXcm at (W), and XXXXXXXXXXcm at (E). (a) For a Hubble constant of 70 km/sec/Mpc, how far away is this galaxy (in Mpc)? Calculate redshift: z = (obs / emit) /emit z = XXXXXXXXXX / 21.106) / XXXXXXXXXXz = XXXXXXXXXXCalculate distance d ~ cz/H0 d ~ (c * 0.0475) / 70 d ~ 203Mpc Distance is approx 203Mpc (b) How fast is the galaxy rotating? Assume that the galaxy is seen edge-on. f = c / w f(21.204cm) = 1.4138Ghz f(21.176cm) = 1.4157Ghz Width = XXXXXXXXXXv = XXXXXXXXXX / 1.4138) * c v = XXXXXXXXXXkm/s (c) Assuming the gas is on circular orbits, use Newton's law of gravity to determine the amount of mass in the galaxy interior to 10 arcmin radius. M = (v^2 * r) / G r = d * angle * (Pi/180) r = 1.8221x10^19 km M = 402^2 * 1.8221x10^19 / G M = 4.412x10^34 kg M = 22,181 M_sun (d) The peak brightness temperature at location (C) is 12K - what is the peak column density of this galaxy at this location?
HI (21cm) emissions from a nearby galaxy are detected at three locations: (C) – galaxy centre (E) – -10 arcmin to the east of the galaxy center (W) –-10 arcmin to the west of the galaxy center The emission peaks at XXXXXXXXXXcm at (C), XXXXXXXXXXcm at (W), and XXXXXXXXXXcm at (E). (a) For a Hubble constant of 70 km/sec/Mpc, how far away is this galaxy (in Mpc)? Calculate redshift: z = (obs / emit) /emit z = XXXXXXXXXX / 21.106) / 21.106 z = 0.0475 Calculate distance d ~ cz/H0 d ~ (c * 0.0475) / 70 d ~ 203Mpc Distance is approx 203Mpc (b) How fast is the galaxy rotating? Assume that the galaxy is seen edge-on. f = c / w f(21.204cm) = 1.4138Ghz f(21.176cm) = 1.4157Ghz Width = 0.0019 v = XXXXXXXXXX / 1.4138) * c v = XXXXXXXXXXkm/s (c) Assuming the gas is on circular orbits, use Newton's law of gravity to determine the amount of mass in the galaxy interior to 10 arcmin radius. M = (v^2 * r) / G r = d * angle * (Pi/180) r = 1.8221x10^19 km M = 402^2 * 1.8221x10^19 / G M = 4.412x10^34 kg M = 22,181 M_sun (d) The peak brightness temperature at location (C) is 12K - what is the peak column density of this galaxy at this location? ???
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