G. R. Tremblay

A 1010 Solar Mass Flow of Molecular Gas in the A1835 Brightest Cluster Galaxy

We report ALMA Early Science observations of the A1835 brightest cluster galaxy (BCG) in the CO (3-2) and CO (1-0) emission lines. We detect 5 × 1010 M ☉ of molecular gas within 10 kpc of the BCG. Its ensemble velocity profile width of ~130 km s–1 FWHM is too narrow for the molecular clouds to be supported in the galaxy by dynamic pressure. The gas may instead be supported in a rotating, turbulent disk oriented nearly face-on. Roughly 1010 M ☉ of molecular gas is projected 3-10 kpc to the northwest and to the east of the nucleus with line-of-sight velocities lying between –250 km s–1 and +480 km s–1 with respect to the systemic velocity. The high-velocity gas may be either inflowing or outflowing. However, the absence of high-velocity gas toward the nucleus that would be expected in a steady inflow, and its bipolar distribution on either side of the nucleus, are more naturally explained as outflow. Star formation and radiation from the active galactic nucleus (AGN) are both incapable of driving an outflow of this magnitude. The location of the high-velocity gas projected behind buoyantly rising X-ray cavities and favorable energetics suggest an outflow driven by the radio AGN. If so, the molecular outflow may be associated with a hot outflow on larger scales reported by Kirkpatrick and colleagues. The molecular gas flow rate of approximately 200 M ☉ yr–1 is comparable to the star formation rate of 100-180 M ☉ yr–1 in the central disk. How radio bubbles would lift dense molecular gas in their updrafts, how much gas will be lost to the BCG, and how much will return to fuel future star formation and AGN activity are poorly understood. Our results imply that radio-mechanical (radio-mode) feedback not only heats hot atmospheres surrounding elliptical galaxies and BCGs, but it is able to sweep higher density molecular gas away from their centers.We report ALMA Early Science observations of the Abell 1835 brightest cluster galaxy (BCG) in the CO (3-2) and CO (1-0) emission lines. We detect 5E10 solar masses of molecular gas within 10 kpc of the BCG. Its velocity width of ~130 km/s FWHM is too narrow to be supported by dynamical pressure. The gas may instead be supported in a rotating, turbulent disk oriented nearly face-on. The disk is forming stars at a rate of 100-180 solar masses per year. Roughly 1E10 solar masses of molecular gas is projected 3-10 kpc to the north-west and to the east of the nucleus with line of sight velocities lying between -250 km/s to +480 km/s with respect to the systemic velocity. Although inflow cannot be ruled out, the rising velocity gradient with radius is consistent with a broad, bipolar outflow driven by radio jets or buoyantly rising X-ray cavities. The molecular outflow may be associated with an outflow of hot gas in Abell 1835 seen on larger scales. Molecular gas is flowing out of the BCG at a rate of approximately 200 solar masses per year, which is comparable to its star formation rate. How radio bubbles lift dense molecular gas in their updrafts, how much gas will be lost to the BCG, and how much will return to fuel future star formation and AGN activity are poorly understood. Our results imply that radio-mechanical (radio mode) feedback not only heats hot atmospheres surrounding elliptical galaxies and BCGs, it is able to sweep higher density molecular gas away from their centers.

MASSIVE MOLECULAR GAS FLOWS IN THE A1664 BRIGHTEST CLUSTER GALAXY

We report ALMA Early Science CO(1-0) and CO(3-2) observations of the brightest cluster galaxy (BCG) in A1664. The BCG contains 1.1 × 1010 M ☉ of molecular gas divided roughly equally between two distinct velocity systems: one from –250 to +250 km s–1 centered on the BCGs systemic velocity and a high-velocity system blueshifted by 570 km s–1 with respect to the systemic velocity. The BCGs systemic component shows a smooth velocity gradient across the BCG center, suggestive of rotation about the nucleus. However, the mass and velocity structure are highly asymmetric and there is little star formation coincident with a putative disk. It may be an inflow of gas that will settle into a disk over several 108 yr. The high-velocity system consists of two gas clumps, each ~2 kpc across, located to the north and southeast of the nucleus. Each has a line of sight velocity spread of 250-300 km s–1. The velocity of the gas in the high-velocity system increases toward the BCG center and may be a massive flow into the nucleus. However, the velocity gradient is not smooth. These structures are also coincident with low optical-ultraviolet surface brightness regions, which could indicate dust extinction associated with each clump. The structure is complex, making a clear interpretation difficult, but if the dusty, molecular gas lies predominantly in front of the BCG, the blueshifted velocities would indicate an outflow. Based on the energy requirements, such a massive outflow would most likely be driven by the active galactic nucleus. A merger origin is unlikely but cannot be ruled out.

Herschel observations of the Centaurus cluster - the dynamics of cold gas in a cool core

Brightest cluster galaxies (BCGs) in the cores of galaxy clusters have distinctly different properties from other low-redshift massive ellipticals. The majority of the BCGs in coolcore clusters show signs of active star formation. We present observations of NGC 4696, the BCG of the Centaurus galaxy cluster, at far-infrared (FIR) wavelengths with the Herschel space telescope. Using the PACS spectrometer, we detect the two strongest coolants of the interstellar medium, [C II] at 157.74 μm and [O I] at 63.18 μm, and in addition [N II] at 121.90 μm. The [C II] emission is extended over a region of 7 kpc with a similar spatial morphology and kinematics to the optical Hα emission. This has the profound implication that the optical hydrogen recombination line, Hα, the optical forbidden lines, [N II] λ6583 A, the soft X-ray filaments and the FIR [C II] line all have the same energy source. We also detect dust emission using the PACS and SPIRE photometers at all six wavebands. We perform a detailed spectral energy distribution fitting using a two-component modified

Chandra Observations of 3C Radio Sources with z < 0.3: Nuclei, Diffuse Emission, Jets, and Hotspots

We report on our Chandra Cycle 9 program to observe half of the 60 (unobserved by Chandra) 3C radio sources at z < 0.3 for 8 ks each. Here we give the basic data: the X-ray intensity of the nuclei and any features associated with radio structures such as hotspots and knots in jets. We have measured fluxes in soft, medium, and hard bands and are thus able to isolate sources with significant intrinsic column density. For the stronger nuclei, we have applied the standard spectral analysis which provides the best-fit values of X-ray spectral index and column density. We find evidence for intrinsic absorption exceeding a column density of 10(22) cm(-2) for one-third of our sources.

Herschel observations of extended atomic gas in the core of the Perseus cluster

We present Herschel observations of the core of the Perseus cluster of galaxies. Especially intriguing is the network of filaments that surround the brightest cluster galaxy, NGC 1275, previously imaged extensively in H and CO. In this work, we report detections of farinfrared (FIR) lines, in particular, [Cii] 158 m, [Oi] 63 m, [Nii] 122 m, [Oib] 145 m and [Oiii] 88 m, with Herschel. All lines are spatially extended, except [Oiii], with the [Cii] line emission extending up to 25 kpc from the core. [Cii] emission is found to be cospatial with H and CO. Furthermore, [Cii] shows a similar velocity distribution to CO, which has been shown in previous studies to display a close association with the H kinematics. The spatial and kinematical correlation among [Cii], H and CO gives us confidence to model the di erent components of the gas with a common heating model. With the help of FIR continuum Herschel measurements, together with a suite of coeval radio, submm and infrared data from other observatories, we performed a spectral energy distribution fitting of NGC 1275 using a model that contains contributions from dust emission as well as synchrotron AGN emission. This has allowed us to accurately estimate the dust parameters. The data indicate a low dust emissivity index, 1, a total dust mass close to 10 7 M , a cold dust component with temperature 38 2 K and a warm dust component with temperature of 116 9 K. The FIR-derived star formation rate (SFR) is 24 1 M yr 1 , which is in agreement with the FUV-derived SFR in the core, determined after applying corrections for both Galactic and internal reddening. The total infrared luminosity in the range 8 m to 1000 m is inferred to be 1:5 10 11 L , making NGC 1275 a luminous infrared galaxy (LIRG). We investigated in detail the source of the Herschel FIR and H emissions emerging from a core region 4 kpc in radius. Based on simulations conducted using the radiative transfer code, cloudy, a heating model comprising old and young stellar populations is su cient to explain these observations. The optical line ratios indicate that there may be a need for a second heating component. However, stellar photoionization seems to be the dominant mechanism. We have also detected [Cii] in three well-studied regions of the filaments. Herschel, with its superior sensitivity to FIR emission, can detect far colder atomic gas than previous studies. We find a [Oi]/[Cii] ratio about 1 dex smaller than predicted by the otherwise functional Ferland (2009) model. That study considered optically thin emission from a small cell of gas and by design did not consider the e ects of reasonable column densities. The line ratio suggests that the lines are optically thick, as is typical of galactic PDRs, and implies that there is a large reservoir of cold atomic gas. This was not included in previous inventories of the filament mass and may represent a significant component.

Cold Gas Dynamics in Hydra-A: Evidence for a Rotating Disc

We present multifrequency observations of the radio galaxy Hydra-A (3C218) located in the core of a massive, X-ray luminous galaxy cluster. Integral field unit spectroscopy is used to trace the kinematics of the ionized and warm molecular hydrogen which are consistent with an ∼5 kpc rotating disc. Broad, double-peaked lines of CO(2–1), [C II] 157µm and [O I ]6 3µ ma re detected. We estimate the mass of the cold gas within the disc to beMgas = 2.3 ± 0.3 × 10 9 M� . These observations demonstrate that the complex line profiles found in the cold atomic and molecular gas are related to the rotating disc or ring of gas. Finally, a Hubble Space Telescope image of the galaxy shows that this gas disc contains a substantial mass of dust. The large gas mass, star formation rate and kinematics are consistent with the levels of gas cooling from the intracluster medium (ICM). We conclude that the cold gas originates from the continual quiescent accumulation of cooled ICM gas. The rotation is in a plane perpendicular to the projected orientation of the radio jets and ICM cavities hinting at a possible connection between the kpc-scale cooling gas and the accretion of material on to the black hole. We discuss the implications of these observations for models of cold accretion, AGN feedback and cooling flows.

Isophotal Structure and Dust Distribution in Radio-loud Elliptical Galaxies

We investigate isophotal properties and dust morphology in the nuclear regions of 84 radio galaxies, imaged in the optical and near-infrared as part of Hubble Space Telescope snapshot surveys. We present a sample-wide trend between host galaxy isophotal structure and the inclination of dusty circumnuclear disks at the centers of 13 of these objects. We find that galaxies containing edge-on disks are invariably seen to possess boxy isophotes, while round, face-on disks are seen exclusively in objects with round or elliptical isophotes. Dust-rich sources with disky isophotes are observed only to possess dust in the form of extended filamentary lanes, and not in settled distributions like disks. As we do not expect that edge-on and face-on disks reside in different populations of galaxies, we conclude that perceived isophotal boxiness is dependent on the angle at which the observer views the host galaxys axis of symmetry. We discuss our results in the context of dissipative merger scenarios, and infer that dusty disks primarily reside in old, boxy remnants of gas-poor galaxy mergers, whereas filamentary dust lanes reside in younger disky remnants of gas-rich mergers.

HST/ACS EMISSION LINE IMAGING OF LOW-REDSHIFT 3CR RADIO GALAXIES. I. THE DATA ∗

We present 19 nearby (z < 0.3) 3CR radio galaxies imaged at low and high excitation as part of a Cycle 15 Hubble Space Telescope (HST) snapshot survey with the Advanced Camera for Surveys (ACS). These images consist of exposures of the H alpha (6563 angstrom, plus [N II] contamination) and [O III]lambda 5007 emission lines using narrowband linear ramp filters adjusted according to the redshift of the target. To facilitate continuum subtraction, a single-pointing 60 s line-free exposure was taken with a mediumband filter appropriate for the targets redshift. We discuss the steps taken to reduce these images independently of the automated recalibration pipeline so as to use more recent ACS flat-field data as well as to better reject cosmic rays. We describe the method used to produce continuum-free (pure line-emission) images, and present these images along with qualitative descriptions of the narrow-line region morphologies we observe. We present H alpha+[N II] and [O III] line fluxes from aperture photometry, finding the values to fall expectedly on the redshift-luminosity trend from a past HST/WFPC2 emission line study of a larger, generally higher redshift subset of the 3CR. We also find expected trends between emission line luminosity and total radio power, as well as a positive correlation between the size of the emission line region and redshift. We discuss the associated interpretation of these results, and conclude with a summary of future work enabled by this data set.

Feedback, scatter and structure in the core of the PKS 0745−191 galaxy cluster

We present Chandra X-ray Observatory observations of the core of the galaxy cluster PKS 0745-191. Its centre shows X-ray cavities caused by AGN feedback and cold fronts with an associated spiral structure. The cavity energetics imply they are powerful enough to compensate for cooling. Despite the evidence for AGN feedback, the Chandra and XMM-RGS X-ray spectra are consistent with a few hundred solar masses per year cooling out of the X-ray phase, sufficient to power the emission line nebula. The coolest X-ray emitting gas and brightest nebula emission is offset by around 5 kpc from the radio and X-ray nucleus. Although the cluster has a regular appearance, its core shows density, temperature and pressure deviations over the inner 100 kpc, likely associated with the cold fronts. After correcting for ellipticity and projection effects, we estimate density fluctuations of ~4 per cent, while temperature, pressure and entropy have variations of 10-12 per cent. We describe a new code, MBPROJ, able to accurately obtain thermodynamical cluster profiles, under the assumptions of hydrostatic equilibrium and spherical symmetry. The forward-fitting code compares model to observed profiles using Markov Chain Monte Carlo and is applicable to surveys, operating on 1000 or fewer counts. In PKS0745 a very low gravitational acceleration is preferred within 40 kpc radius from the core, indicating a lack of hydrostatic equilibrium, deviations from spherical symmetry or non-thermal sources of pressure.

The Warped Nuclear Disk of Radio Galaxy 3C 449

This work was based on observations with the NASA/ESA Hubble Space Telescope, obtained in collaboration with the Space Telescope Science Institute (STScI), operated by AURA for NASA. Support for this work was provided by NASA/STScI through grant HSTGO- 10173. G. R. T. and A. C. Q. acknowledge support in part by NSF awards AST-0406823, PHY-0242483, and NASA/STScI grant HST-GO-10173.09-A. This research has made extensive use of the NASA Astrophysics Data System (ADS) and the NASA/IPAC Extragalactic Database (NED), operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.