Pierre Guillard

JET-POWERED MOLECULAR HYDROGEN EMISSION FROM RADIO GALAXIES

H2 pure-rotational emission lines are detected from warm (100–1500 K) molecular gas in 17/55 (31% of) radio galaxies at redshift z< 0.22 observed with the Spitzer IR Spectrograph. The summed H2 0–0 S(0)–S(3) line luminosities are L(H2) = 7 × 10 38 –2 × 10 42 erg s −1 , yielding warm H2 masses up to 2 × 10 10 M� . These radio galaxies, of both FR radio morphological types, help to firmly establish the new class of radio-selected molecular hydrogen emission galaxies (radio MOHEGs). MOHEGs have extremely large H2 to 7.7 μm polycyclic aromatic hydrocarbon (PAH) emission ratios: L(H2)/L(PAH7.7) = 0.04–4, up to a factor 300 greater than the median value for normal star-forming galaxies. In spite of large H2 masses, MOHEGs appear to be inefficient at forming stars, perhaps because the molecular gas is kinematically unsettled and turbulent. Low-luminosity mid-IR continuum emission together with low-ionization emission line spectra indicates low-luminosity active galactic nuclei (AGNs) in all but three radio MOHEGs. The AGN X-ray emission measured with Chandra is not luminous enough to power the H2 emission from MOHEGs. Nearly all radio MOHEGs belong to clusters or close pairs, including four cool-core clusters (Perseus, Hydra, A2052, and A2199). We suggest that the H2 in radio MOHEGs is delivered in galaxy collisions or cooling flows, then heated by radio-jet feedback in the form of kinetic energy dissipation by shocks or cosmic rays.

STRONG MOLECULAR HYDROGEN EMISSION AND KINEMATICS OF THE MULTIPHASE GAS IN RADIO GALAXIES WITH FAST JET-DRIVEN OUTFLOWS

Observations of ionized and neutral gas outflows in radio galaxies (RGs) suggest that active galactic nucleus (AGN) radio jet feedback has a galaxy-scale impact on the host interstellar medium, but it is still unclear how the molecular gas is affected. Thus, it is crucial to determine the physical conditions of the molecular gas in powerful RGs to understandhowradiosourcesmayregulatethestarformationintheirhostgalaxies.WepresentdeepSpitzerInfrared Spectrograph (IRS) high-resolution spectroscopy of eight nearby RGs that show fast Hi outflows. Strikingly, all of these Hi-outflow RGs have bright H2 mid-IR lines that cannot be accounted for by UV or X-ray heating. This strongly suggests that the radio jet, which drives the Hi outflow, is also responsible for the shock excitation of the warm H2 gas. In addition, the warm H2 gas does not share the kinematics of the ionized/neutral gas. The mid-IR-ionized gas lines (with FWHM up to 1250 km s −1 for [Neii]12.8 μm) are systematically broader than the H2 lines, which are resolved by the IRS in ≈60% of the detected lines (with FWHM up to 900 km s −1 ). In five sources, 3C 236, 3C 293, 3C 459, 4C 12.50, and PKS 1549-79, the [Neii]12.8 μm line, and to a lesser extent the [Neiii]15.5 μm and [Nev]14.3 μm lines, clearly exhibits blueshifted wings (up to −900 km s −1 with respect to the systemic velocity) that match well the kinematics of the outflowing Hi or ionized gas. The H2 lines do not show these broad wings, except tentative detections in 4C 12.50, 3C 459, and PKS 1549-79. This shows that, contrary to the Hi gas, the H2 gas is inefficiently coupled to the AGN jet-driven outflow of ionized gas. While the dissipation of a small fraction (<10%) of the jet kinetic power can explain the turbulent heating of the molecular gas, our data show that the bulk of the warm molecular gas is not expelled from these galaxies.

SHOCK-ENHANCED C+ EMISSION AND THE DETECTION OF H2O FROM THE STEPHAN'S QUINTET GROUP-WIDE SHOCK USING HERSCHEL

We present the first Herschel spectroscopic detections of the [OI]63µm and [CII]158µm fine-structure transitions, and a single para-H_2O line from the 35 x 15 kpc^2 shocked intergalactic filament in Stephans Quintet. The filament is believed to have been formed when a high-speed intruder to the group collided with clumpy intergroup gas. Observations with the PACS spectrometer provide evidence for broad (> 1000 km s^(-1)) luminous [CII] line profiles, as well as fainter [OI]63µm emission. SPIRE FTS observations reveal water emission from the p-H_2O (1_(11)-0_(00)) transition at several positions in the filament, but no other molecular lines. The H_2O line is narrow, and may be associated with denser intermediate-velocity gas experiencing the strongest shock-heating. The [CII]/PAH_(tot) and [CII]/FIR ratios are too large to be explained by normal photo-electric heating in PDRs. HII region excitation or X-ray/Cosmic Ray heating can also be ruled out. The observations lead to the conclusion that a large fraction the molecular gas is diffuse and warm. We propose that the [CII], [OI] and warm H_2 line emission is powered by a turbulent cascade in which kinetic energy from the galaxy collision with the IGM is dissipated to small scales and low-velocities, via shocks and turbulent eddies. Low-velocity magnetic shocks can help explain both the [CII]/[OI] ratio, and the relatively high [CII]/H_2 ratios observed. The discovery that [CII] emission can be enhanced, in large-scale turbulent regions in collisional environments has implications for the interpretation of [CII] emission in high-z galaxies.

Turbulent Molecular Gas and Star Formation in the Shocked Intergalactic Medium of Stephan's Quintet

We report on single-dish radio CO observations towards the inter-galactic medium (IGM) of the Stephans Quintet (hereafter SQ) compact group of galaxies. Extremely bright mid-IR H2 rotational line emission (L(H2) ≈ 10 35 W) from warm (10 2-3 K) molecular gas has been detected by the Spitzer satellite in the kpc- scale shock created by a collision between a galaxy, NGC 7318b, and NGC 7319s tidal arm. We detect in the IGM CO(1-0), (2-1) and (3-2) line emission with complex profi les, spanning a velocity range of ≈ 1000 km s -1 . Assuming a Galactic CO(1-0) emission to H2 mass conversion factor, a total H2 mass of ≈ 5× 10 9 M⊙ is de- tected in the shock. Note that this mass could be lower by a factor of a few because of the large uncertainties on the CO to H2 conversion factor. The molecular gas carries a large fracti on of the gas kinetic energy involved in the collision, meaning that this energy has not been thermalized yet. The kinetic energy of the H2 gas derived from CO observations is comparable to that of the warm H2 gas derived from Spitzer IRS observations. The turbulent kinetic energy of the H2 gas is at least a factor of 5 greater than the thermal energy of the hot plasma heated by the collision. The spectra exhibit the pre-shock r ecession velocities of the two colliding gas systems (5700 and 6700 km s -1 ), but also intermediate velocities. This shows that some of the molecular gas originates from the cooling of post-shock gas, which had time to cool and be accelerated by the shock. CO emission is also detected in a bridge feature that connects the shock to t he Seyfert member of the group, NGC 7319, and in the northern star forming region, SQ-A, where a new velocity component is identified at 6900 km s -1 , in ad- dition to the two velocity components already known. Spitzer IRS mid-IR spectral mapping is used to estimate the warm H2 masses and excitation at the positions observed in radio. The ratio between the warm H2 mass and the H2 mass derived from CO fluxes is 0.23± 0.07 in the IGM of SQ, which is 10- 100 times higher than in star-forming galaxies. We suggest that the dissipation o f turbulent kinetic energy maintain a high heating rate within the H2 gas. This interpretation implies that the velocity dispers ion on the scale of giant molecular clouds in SQ is an order of magnitude larger than the Galactic value. This may explain why this gas is not forming stars efficiently. Subject headings:Galaxies: clusters: individual: Stephans Quintet - galax ies: interactions - galaxies: ISM - intergalactic medium

Low-velocity shocks: signatures of turbulent dissipationin diffuse irradiated gas

Context. Large-scale motions in galaxies (supernovae explosions, galaxy collisions, galactic shear etc.) generate turbulence, which allows a fraction of the available kinetic energy to cascade down to small scales before it is dissipated. Aims. We establish and quantify the diagnostics of turbulent dissipation in mildly irradiated diffuse gas in the specific context of shock structures. Methods. We incorporated the basic physics of photon-dominated regions into a state-of-the-art steady-state shock code. We examined the chemical and emission properties of mildly irradiated (G_0 = 1) magnetised shocks in diffuse media (n_H = 10^2 to 10^4 cm^(-3)) at low- to moderate velocities (from 3 to 40 km s^(-1)). Results. The formation of some molecules relies on endoergic reactions. Their abundances in J-type shocks are enhanced by several orders of magnitude for shock velocities as low as 7 km s^(-1). Otherwise most chemical properties of J-type shocks vary over less than an order of magnitude between velocities from about 7 to about 30 km s^(-1), where H_2 dissociation sets in. C-type shocks display a more gradual molecular enhancement with increasing shock velocity. We quantified the energy flux budget (fluxes of kinetic, radiated and magnetic energies) with emphasis on the main cooling lines of the cold interstellar medium. Their sensitivity to shock velocity is such that it allows observations to constrain statistical distributions of shock velocities. We fitted various probability distribution functions (PDFs) of shock velocities to spectroscopic observations of the galaxy-wide shock in Stephan’s Quintet and of a Galactic line of sight which samples diffuse molecular gas in Chamaeleon. In both cases, low velocities bear the greatest statistical weight and the PDF is consistent with a bimodal distribution. In the very low velocity shocks (below 5 km s^(-1)), dissipation is due to ion-neutral friction and it powers H_2 low-energy transitions and atomic lines. In moderate velocity shocks (20 km s^(-1) and above), the dissipation is due to viscous heating and accounts for most of the molecular emission. In our interpretation a significant fraction of the gas in the line of sight is shocked (from 4% to 66%). For example, C^+ emission may trace shocks in UV irradiated gas where C^+ is the dominant carbon species. Conclusions. Low- and moderate velocity shocks are important in shaping the chemical composition and excitation state of the interstellar gas. This allows one to probe the statistical distribution of shock velocities in interstellar turbulence.

Exceptional AGN-driven turbulence inhibits star formation in the 3C 326N radio galaxy

We detect bright [CII]158

DETECTION OF POWERFUL MID-IR H2 EMISSION IN THE BRIDGE BETWEEN THE TAFFY GALAXIES

\mu

Dense gas without star formation: the kpc-sized turbulent molecular disk in 3C326 N

m line emission from the radio galaxy 3C 326N at z=0.09, which shows weak star formation (

Observations and modeling of the dust emission from the H2-bright galaxy-wide shock in Stephan's Quintet

SFR<0.07

CO in Hickson compact group galaxies with enhanced warm H_2 emission: Evidence for galaxy evolution?

M