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Radio Galaxies Part 3 Gas in Radio galaxies. Why gas in radio galaxies? Merger origin of radio galaxies. Evidence: mainly optical characteristics (tails,

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Presentation on theme: "Radio Galaxies Part 3 Gas in Radio galaxies. Why gas in radio galaxies? Merger origin of radio galaxies. Evidence: mainly optical characteristics (tails,"— Presentation transcript:

1 Radio Galaxies Part 3 Gas in Radio galaxies

2 Why gas in radio galaxies? Merger origin of radio galaxies. Evidence: mainly optical characteristics (tails, counter-rotating cores, dust lanes) Host galaxies  early-type: not supposed to have much gas but….  gas on small scales: connected with the environment of the AGN (e.g. tori, but also messy gas, fueling AGN?) HI, CO, ……  gas on large scales: can trace the origin of the galaxy (more tomorrow); mainly HI

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5 Why neutral hydrogen? Interaction & mergers are often invoked for the triggering of AGN providing both the gas and the instability to bring gas to the nuclear regions LARGE-SCALE HI is known to be a good tracer for merger (if detected) it can provide clues on the origin of radio galaxies.

6 Interaction between galaxies

7 Forming an elliptical galaxy from mergers

8 Hibbard (VLA) Kinematics of the interaction

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11 Is there HI in early-type galaxies?  Some elliptical galaxies have HI content and size similar to spiral galaxies  Compare to the life of a radio source 3 arcmin~ 54 kpc (1”=0.3 kpc) orbital time ~ 2x10 9 yrs

12 The ground state can undergo a hyperfine transition, reverse the spin of the electron Frequency of the transition: 1420.405752 MHz The temperature T s (spin or excitation temperature) account for the distribution of the atoms between the two states. The population of the two states is determined primarily by collisions between atoms  T s equal to the kinetics temperature (with some exceptions!) 21-cm emission line of neutral hydrogen + 1420.40575180 MHz proton electron

13 Most common element in the universe  present “everywhere”! Transparent narrow spectral line (van de Hulst) Doppler effect  kinematics! + 1420.40575180 MHz proton electron

14 where F ~ S dV Jy km/s (1 Jy = 10 -26 W/m 2 /Hz) D distance in Mpc D ~ cz/H 0 Column density of HI, number of hydrogen atoms in the in a cylinder of unit cross-section (in the low optical depth limit) atoms/cm 2 where  is beam size (arcmin) dV km/s S mJy/beam  = optical depth To derive the mass of the neutral hydrogen

15 Doppler effect Frequency  V = 0V < 0V > 0 in emission and absorption!

16 HI cloud HI emission HI absorption

17 T spin accounts for the electrons that are in the upper state (i.e. those that do not absorb) Higher T spin more electrons in the upper state higher column density Particularly common in radio galaxies given the strong underlying radio continuum Optical depth Column density cm -2 From galactic studies, typical T spin = 100 K Typical column densities: in emission ~10 21 cm -2 in a disk of a spiral galaxy in absorption from 10 19 cm -2 against the core of some radio galaxies HI detected in absorption

18  What can produce HI absorption?

19 Observations of the neutral hydrogen (line observations) Distinguish between undisturbed and interacting galaxies using the gas

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21 Example of HI observation this will be the central frequency of your band to be able to detected HI at z=0.045 The typical bandwidth of HI observation is 5, 10 or 20 MHz: 10MHz: 1354.2  1364.2 the range of velocities covered goes from 14665 to 12358 km/s  for 10MHz ~2300 km/s velocity range covered  for 20MHz ~4600 km/s velocity range covered Channel width 1 MHz  ~ 200 km/s

22 H I observation (datacube) of NGC 4414 Kinematics of the galaxies Case of an undisturbed galaxy: rotating disk

23 A messy case

24 The radio galaxy B2 0258+35


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