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

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

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

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