Cold Clouds in Cool Cores

Transcription

1 Becky Canning NGC 1275, Perseus Cluster Cold Clouds in Cool Cores 1 Snowcluster 2015

2 Cold Clouds in Cool Cores Excitation mechanisms of the multi-phase cool/cold gas Why should we care? Heard that X-ray gas can cool from the hot halo + Heard that radio mode feedback interacts with multiphase gas and can pull it out of the galaxy Extended cool/cold gas BCG/BGG/GE Can be very massive - up to solar masses Very cold gas - but in many cases not forming stars 2

3 Cold Clouds in Cool Cores Excitation mechanisms of this multi-phase gas Why should we care? Heard that X-ray gas can cool from the hot halo + Heard that radio mode feedback interacts with multiphase gas and can pull it out of the galaxy Extended cool/cold gas BCG/BGG/GE Can be very massive - up to solar masses Very cold gas - but in many cases not forming stars Paul showed us yesterday stellar mass not increased substantially by RM feedback - also from simulations and observations of massive galaxy colours and luminosity function Bubble timescales, cooling timescales, filament lifetimes ~ years. Warm/Cold molecular gas few years 3

4 Cold Clouds in Cool Cores Excitation mechanisms of this multi-phase gas Why should we care? Heard that X-ray gas can cool from the hot halo + 4 Heard that radio mode feedback interacts with multiphase gas and can pull it out of the galaxy Some process prevents gas cooling Prevents SF Motivation: Understand how AGN feedback Extended cool/cold gas affects (or perhaps BCG/BGG/GE why does not affect) majority of GE galaxy evolution Can be very massive - up to solar masses Very cold gas - but in many cases not forming stars Bubble timescales, cooling timescales ~ years. Warm/Cold molecular gas few years

5 Cool ionised gas properties Ionised gas diverse but can be filamentary and extended All 8 galaxies have similar X-ray gas mass, stellar mass, SFR Werner et al Ha 10,000 K gas

6 2298 Cold gas properties N. Werner et al. Cold gas morphology and kinematics similar to ionised gas [C II] < 100 K gas [O I] / [C II] <~1 6 Werner et al. 2014

7 What do we need in an excitation mechanism? 1. Excitation mechanism should link warm and cold phases Model needs to be able to deal with a range of temperature and density `cloudlets and reproduce line ratios from gas of 10,000k-10k. 2. Diversity in filament properties - not all surrounded by bubbles, some are more extended than others (from 0.5 kpc to >50 kpc), but emission line ratios are not greatly affected by distance from nucleus or SF regions. Source of excitation should not have to be `local (mechanism should work wherever filaments are in galaxy). 7

8 Outline Properties of cold clouds exposed to energetic electrons 1. Brief outline of the model and some key observational tests of model 2. Predictions to test excitation mechanisms and physical properties of multiphase filaments 8

9 Cold clouds exposed to energetic electrons e - e - Some mechanism by which high energy secondary electrons are produced in the gas. Electrons can directly ionise/excite gas e - Non-maxwellian distribution of particle energies in cool/ cold gas - no single kinetic temperature for gas e - Partially ionised regions within atomic or molecular gas Some level of ionisation exists at all densities and temperatures Sources: X-rays produce high-e photoelectrons? Hot ions in X-ray atmosphere or cosmic rays? Particles generated in situ by magnetic reconnection? All sources which don t have strong spatial dependence 9 Ferland et al. 2009

10 Cold clouds exposed to energetic electrons 1. Simulate physical conditions and emission from cloudlets with a range of ionising particle fluxes and densities Contour of constant pressure cm 3 K 2. Remove freedom: Assume constant pressure, and only one free parameter - alpha 10 4π j i= j 4π j i (n i ) n α 1 i n i i=0 / i= j i=0 3. Find emissivity as a function of temperature/density. Apply weighting function and integrate to get total emissivity. n α 1 i n i, Ferland et al. 2009

11 Successes 1. [O III] ~ 35 ev weaker at low T than [Ne III] ~ 41 ev High level of ionisation -> H 0 abundant -> Charge transfer recombination: O ++ + H 0 = O + + H + (FAST) Ne ++ + H 0 = Ne + + H + (SLOW) 2. Warm H strong (upper E level -> dissociation energy of the molecule) relative to HI 3. Can reproduce all strong emission lines in optical and near-ir within factor of 2 but Ha+[N II] 70 kpc H 2 Lim et al

12 Failures Problem in far-ir: Simple model predicts [O I]/[C II]~20 Observations show [O I]/[C II]~<1 Observations show [CII]/Ha is roughly constant so excitation mechanism should account for both are the assumptions valid for cold clouds? 12

13 Cold clouds exposed to energetic electrons Model free parameter fit from 10,000K-1,000K and extrapolated to low temperatures species. 1. Assumed power law may be wrong 2. The model assumes lines are optically thin 3. No turbulence or magnetic fields are included in the model 13 Canning et al. 2015

14 Cold clouds exposed to energetic electrons More cold gas clouds? Optically thick emission lines? 14 Canning et al. 2015

15 Cold clouds exposed to energetic electrons Turbulence and magnetic fields could give a density dependent pressure. Model predicts lower density gas and velocities of ~2 kmps. SF will be inhibited naturally due to the lower gas density. 15 Canning et al. 2015

16 Can we make testable predictions? CO ladder above CO J(3-2) 0.8 mm are the most robust tests of the model Ion-molecule chemistry over a large column density leads to larger column density of warmer gas and can excite higher J CO transitions than if the heating is by softer ionising sources. 16

17 Can we make testable predictions? High density lines should be weak. ALMA can measure turbulent pressure support - can infer magnetic pressure required for equilibrium with hot gas. 17

18 Summary Cold gas appears to be stable for long timescales in extended filaments. Excitation by energetic particles can account for the behaviour of the optical, near-ir and far-ir emission lines with the inclusion of modest turbulence (2 kmps). Star formation might be delayed/inhibited in massive galaxies by the presence of the X-ray halo. ALMA is a powerful tool for constraining filament excitation and therefore understanding how massive X-ray bright galaxies evolve. 18