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Radio Galaxies Part 3

Radio Galaxies Part 3. Gas in Radio galaxies. Why gas in radio galaxies?. 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,

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Radio Galaxies Part 3

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  1. Radio Galaxies Part 3 Gas in Radio galaxies

  2. Why gas in radio galaxies? 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 Merger origin of radio galaxies. Evidence: mainly optical characteristics (tails, counter-rotating cores, dust lanes)

  3. LARGE-SCALE HI is known to be a good tracer for merger (if detected) it can provide clues on the origin of radio galaxies. 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

  4. Interaction between galaxies

  5. Forming an elliptical galaxy from mergers

  6. Kinematics of the interaction Hibbard (VLA)

  7. Kinematics of the interaction

  8. Is there HI in early-type galaxies? 3 arcmin~ 54 kpc (1”=0.3 kpc) orbital time ~ 2x109 yrs • Some elliptical galaxies have HI content and size similar to spiral galaxies • Compare to the life of a radio source

  9. + 1420.40575180 MHz proton electron proton electron 21-cm emission line of neutral hydrogen The ground state can undergo a hyperfine transition, reverse the spin of the electron Frequency of the transition: 1420.405752 MHz The temperature Ts (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  Ts equal to the kinetics temperature (with some exceptions!)

  10. + 1420.40575180 MHz proton electron proton electron • narrow spectral line (van de Hulst) Doppler effect  kinematics! • Most common element in the universe  present “everywhere”! • Transparent

  11.  = optical depth Column density of HI, number of hydrogen atoms in the in a cylinder of unit cross-section (in the low optical depth limit) atoms/cm2 where is beam size (arcmin) dVkm/s S mJy/beam To derive the mass of the neutral hydrogen where F ~ S dV Jy km/s (1 Jy = 10-26 W/m2/Hz) D distance in Mpc D ~ cz/H0

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

  13. HI absorption HI cloud HI emission

  14. Optical depth Column density cm-2 HI detected in absorption Particularly common in radio galaxies given the strong underlying radio continuum Tspin accounts for the electrons that are in the upper state (i.e. those that do not absorb) Higher Tspin more electrons in the upper state higher column density From galactic studies, typicalTspin= 100 K Typical column densities: in emission ~1021 cm-2 in a disk of a spiral galaxy in absorption from 1019 cm-2 againstthe core of some radio galaxies

  15. What can produce HI absorption?

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

  17. 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 • for10MHz ~2300 km/s velocity range covered • for20MHz ~4600 km/s velocity range covered Channel width 1 MHz  ~ 200 km/s

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

  19. A messy case

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