A 10 10 Solar Mass Flow of Molecular Gas in the Abell 1835 Brightest Cluster Galaxy
B. R. McNamara, H.R. Russell, P. E. J. Nulsen, A. C. Edge, N. W. Murray, R. A. Main, A. N. Vantyghem, F. Combes, A. C. Fabian, P. Salome, C.C. Kirkpatrick, S. A. Baum, J. N. Bregman, M. Donahue, E. Egami, S. Hamer, C. P. O'Dea, J.B.R. Oonk, G. Tremblay, G.M. Voit
DD RAFT VERSION S EPTEMBER
17, 2018
Preprint typeset using L A TEX style emulateapj v. 08/13/06
A 10 SOLAR MASS FLOW OF MOLECULAR GAS IN THE ABELL 1835 BRIGHTEST CLUSTER GALAXY
B. R. M C N AMARA , , H.R. R
USSELL , P. E. J. N ULSEN A. C. E
DGE , N. W. M URRAY , R. A. M AIN , A. N. V ANTYGHEM , F.C OMBES , A. C. F ABIAN , P. S ALOME , C.C. K IRKPATRICK , S. A. B AUM , J. N. B REGMAN , M. D ONAHUE , E. E GAMI , S.H AMER , C. P. O’D EA , J.B.R. O ONK , G. T REMBLAY , G.M. V OIT
University of Waterloo, Department of Physics & Astronomy, Waterloo, Canada Perimeter Institute for Theoretical Physics, Waterloo, Canada Harvard-Smithsonian Center for Astrophysics Department of Physics, Durham University, Durham, DH1 3LE, UK L’Observatoire de Paris, 61 Av. deL’Observatoire, F-75 014 Paris, France Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK Canadian Institute for TheoreticalAstrophysics, University of Toronto, 60 St. George St., Toronto, M5S 3H8, Ontario, Canada School of Physics & Astronomy, Rochester Institute ofTechnology, Rochester, NY 14623 USA Department of Astronomy, University of Michigan, 500 Church St. Ann Arbor, MI 48109 USA Department ofPhysics & Astronomy, Michigan State University, 567 Wilson Rd., East Lansing, MI 48824 USA Steward Observatory, University of Arizona, 933 N. CherryAvenue, Tucson, AZ 85721 USA Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands European SouthernObservatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
Draft version September 17, 2018
ABSTRACTWe 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 5 × M (cid:12) of molecular gas within 10 kpc of the BCG.Its ensemble velocity profile width of ∼
130 km s − FWHM is too narrow for the molecular clouds to besupported in the galaxy by dynamic pressure. The gas may instead be supported in a rotating, turbulent diskoriented nearly face-on. Roughly 10 M (cid:12) of molecular gas is projected 3 −
10 kpc to the north-west and tothe east of the nucleus with line of sight velocities lying between −
250 km s − to +
480 km s − with respect tothe systemic velocity. The high velocity gas may be either inflowing or outflowing. However, the absence ofhigh velocity gas toward the nucleus that would be expected in a steady inflow, and its bipolar distribution oneither side of the nucleus, are more naturally explained as outflow. Star formation and radiation from the AGNare both incapable of driving an outflow of this magnitude. The location of the high velocity gas projectedbehind buoyantly rising X-ray cavities and favorable energetics suggest an outflow driven by the radio AGN.If so, the molecular outflow may be associated a hot outflow on larger scales reported by Kirkpatrick andcolleagues. The molecular gas flow rate of approximately 200 M (cid:12) yr − is comparable to the star formationrate of 100 −
180 M (cid:12) yr − in the central disk. How radio bubbles would lift dense molecular gas in theirupdrafts, how much gas will be lost to the BCG, and how much will return to fuel future star formation andAGN activity are poorly understood. Our results imply that radio-mechanical (radio mode) feedback not onlyheats hot atmospheres surrounding elliptical galaxies and BCGs, it is able to sweep higher density moleculargas away from their centers. Subject headings: galaxies: clusters: general – galaxies: cooling flows – Active Galactic Nuclei INTRODUCTION
Brightest cluster galaxies (BCGs) are the largest and mostluminous galaxies in the universe. Like normal ellipticalgalaxies, their stellar populations are usually old and dor-mant. BCGs residing in cooling flow clusters are exceptional(Fabian 1994). Fueled by unusually large reservoirs of coldmolecular clouds (Edge et al. 2001, Salome & Combes 2003),many form stars at rates of several to several tens of solarmasses per year (O’Dea et al. 2008). Extreme objects, suchas the Phoenix and the Abell 1835 BCGs, are forming stars atrates upward of 100 M (cid:12) yr − (McDonald et al. 2012, McNa-mara et al. 2006, hereafter M06).The origin of star formation in a population of normally“red and dead" galaxies is not entirely clear. In some in-stances, BCGs may be rejuvenated by collisions with gas-richgalaxies. However, wet mergers must be uncommon in BCGsdue to a dearth of gas-rich donor galaxies in cluster cores.A wealth of data suggests that molecular clouds and youngstars forming in BCGs are usually fueled instead by gas cool-ing from hot atmospheres. For example, bright nebular emis-sion and young stars are observed preferentially when the cen-tral cooling time of a cluster atmosphere falls below ∼ ∼ × yr (Raffertyet al. 2008, Cavagnolo et al. 2008). Voit and others haveattributed this threshold to cooling instabilities and thermalconduction in hot atmospheres (Voit et al. 2008, Voit 2011,Gaspari et al. 2012, Guo & Mathews 2013).Despite strong indications that cold clouds are condensingout of hot atmospheres, only a few percent of the mass ex-pected to cool actually does so (Peterson & Fabian 2006).Feedback from active galactic nuclei (AGN) is almost cer-tainly suppressing cooling below the levels expected in anunimpeded cooling flow (reviewed by McNamara & Nulsen2007, 2012, Fabian 2013). So-called radio-mode or radio-mechanical feedback operates primarily on the hot, volume-filling atmosphere. The energy released by radio AGN in-creases the entropy of the hot gas (O’Neill & Jones 2010) anddrives the most rapidly cooling gas outward, thereby regulat-ing the cooling rate, the star formation rate, and the poweroutput of the AGN itself.Despite the widely held view that radio-mechanical feed-back maintains BCGs and giant elliptical galaxies in dor-mancy, little is known of its effect on molecular gas. Thisis potentially significant issue because the rate of cold accre-tion onto AGN may be a crucial element of an operationalfeedback loop (Pizzolato & Soker 2010, Gaspari et al. 2013).Radio jets are known to interact with nebular gas surrounding a r X i v : . [ a s t r o - ph . GA ] M a r them (eg. Villar-Martín et al. 2006, Nesvadba et al. 2006),which are likely to be the ionized skins of molecular clouds(Wilman et al. 2006, Emonts et al. 2013). Furthermore,blueshifted absorption lines of neutral atomic hydrogen havebeen observed toward several radio galaxies (Morganti et al.2005, 2013), indicating that radio jets couple effectively tocold clouds and are able to drive them out at high speed. NGC1275 in the Perseus cluster is a striking example of radio lobesinteracting with molecular clouds (Salome et al. 2006, 2011).Both inflow and outflow are observed in what appears to be amolecular "fountain" (Lim et al. 2008). Abell 1835, discussedhere, may be similar to Perseus.Here we examine the effects of feedback on the molec-ular gas located near the nucleus of the Abell 1835 BCG.The BCG contains upward of (cid:39) × M (cid:12) of molecu-lar gas (Edge 2001) and star formation proceeding at a rateof between 100 −
180 M (cid:12) yr − (M06). The AGN launcheda pair of cavities into its hot atmosphere a few 10 yr ago,each of which is 20 kpc in diameter and projected roughly20 kpc from the nucleus. The AGN’s radio synchrotron lu-minosity, 3 . × erg s − , is dwarfed by its mechanicalpower, L mec (cid:39) ergs − (M06), which is typical of radioAGN (Birzan et al. 2008). Abell 1835 is an archetypal cool-ing flow regulated by radio-mode feedback. The ALMA EarlyScience observations reported here and in a companion paperon Abell 1664 (Russell et al. 2013), explore for the first timeat high resolution, the relationships between molecular gas,star formation, and radio AGN feedback. At the emission lineredshift z = 0.252 (Crawford et al. 1999), 1 arcsec = 3.9 kpc. OBSERVATIONS
We obtained Early Science observations of the BCG withALMA at 92 GHz (band 3) and 276 GHz (band 7). At thecluster’s redshift the bands are sensitive to the carbon monox-ide molecule’s J = 1,0 and J = 3,2 rotational transitions, re-spectively. The exposures, totaling 60 minutes in band 3 and60 minutes in band 7, were made between 2012 March 27and 2012, April 24. The extended array available for Cycle 0included on average twenty 12 metre dishes, which provideda spatial resolution of 0.5 arcsec in the CO (3-2) transitionand 1.5 arcsec at the CO (1-0) transition. Baselines extendedto ∼
400 m. This combination yielded a sharp image of themolecular gas near the nucleus at CO (3-2), and sensitivity onlarger spatial scales at CO (1-0). A bandwidth of 1 .
875 GHzper spectral window and two spectral windows per sidebandprovided a total frequency range of ∼ .
488 MHz per channel. Channels werebinned together to improve the S/N ratio, yielding a final res-olution of 20 km s − . The quasar 3C 279 was observed forbandpass calibration and observations of Mars and Titan pro-vided absolute flux calibration. Observations switched fromAbell 1835 to the nearby phase calibrator J1332+0200 every ∼
10 minutes.The observations were calibrated using the
CASA software(version 3.3) following the detailed processing scripts pro-vided by the ALMA science support team. The continuum-subtracted images were reconstructed using the
CASA task
CLEAN assuming Briggs weighting with a robustness param-eter of 0.5 and with a simple polygon mask applied to eachchannel. This provided a synthesized beam of 1 . (cid:48)(cid:48) × . (cid:48)(cid:48) at a PA of − . ◦ at CO(1-0) and 0 . (cid:48)(cid:48) × . (cid:48)(cid:48) at a PA of − . ◦ at CO(3-2). The rms noise in the line free channelswas 0 . / beam at CO(1-0) and 1 . / beam at CO(3-2). Images of the continuum emission were also produced with CLEAN by averaging channels free of any line emission.A central continuum source is detected in both bands at posi-tion 14 01 02 . +
02 52 42 .
649 with fluxes 1 . ± .
03 mJyin band 3 and 0 . ± . of spectral index α ∝ .
84 (Hogan et al. inprep). ANALYSIS
Spectra
The total CO (3-2) and CO (1-0) spectra are presented inFig. 1. CO emission is centered within ∼
100 km s − of thenebular emission line redshift (Crawford et al. 1999). Eachspectral profile was fitted with a single gaussian after the con-tinuum was subtracted. The emission integral at CO (1-0) is3 . ± . − . The molecular gas mass was calculatedas, M mol = 1 . × X CO (cid:18) + z (cid:19) (cid:18) S CO ∆ v Jy km s − (cid:19) (cid:18) D L Mpc (cid:19) M (cid:12) . (1)This expression yields a total molecular gas mass of 4 . ± . × M (cid:12) . The conversion factor between CO and molec-ular gas, X CO = 2 × cm − (K km s − ) − , is the averageGalactic value (Bolatto et al. 2013, Narayanan et al 2012).The primary line at zero velocity has a gaussian profile fullwidth at half maximum FWHM = 130 ± − , after cor-recting for instrumental broadening. This width is 5 − ∼ −
300 km s − . Molecular gas movingwith a nearly isotropic velocity pattern cannot be supportedagainst collapse at such low speeds. The gas may be sup-ported instead by rotation in a disk projected nearly face-on.The observed velocity width would then represent gas speedsout of the disk’s plane (Sec. 4.4). Central Molecular Gas and Star Formation
R-band and Far UV images taken with the Hubble SpaceTelescope (O’Dea et al. 2010) are presented in Fig. 2. TheR-band image shows the BCG in relation to its molecular gas,hot atmosphere, and other neighboring galaxies. The box su-perposed on the image indicates the scale of the UV and CO(3-2) images presented in Fig. 2. A Chandra X-ray imagewith a similar box superposed is shown in Fig. 2. Most of themolecular gas lies within one arcsec (4 kpc) of the nucleus.The UV continuum emission is emerging from the sites of starformation proceeding at a rate upward of 100 −
180 M (cid:12) yr − (M06, Egami et al. 2006, Donahue et al. 2011). No brightUV or X-ray point source is associated with a nuclear AGN.The CO (3-2) gas coincident with the UV emission is pre-sumably fueling star formation. The CO and UV emissionare straddled by two bright and presumably rapidly coolingX-ray emission regions oriented to the NE and SW of the nu-cleus. No CO emission is detected toward the most rapidlycooling gas. Two X-ray cavities are located a few arcsec tothe NW and SE of the CO (3-2) emission.Roughly half of the CO (3-2) flux is emerging from theinner half arcsec radius of the BCG and is unresolved. As- For the convention f ν ∝ ν − α suming half of the central molecular gas mass and star for-mation lie within the same region, we find the surface den-sities of star formation and molecular gas to be log Σ SFR =0 .
87 M (cid:12) yr − kpc − and log µ CO = 3 . (cid:12) pc − , respectively.Based on these values, the BCG lies with normal, circum-nuclear starburst galaxies on the Schmidt-Kennicutt relation(Kennicutt 1998). Velocity Field of the Molecular Gas
We present a grid of CO (3-2) emission spectra correspond-ing to the grid projected onto the CO (3-2) image in Fig. 3.The mean line of sight velocities measured with gaussian pro-file fits are indicated in each grid box. The size of each gridbox corresponds approximately to the FWHM of the synthe-sized beam. Velocity differences of a few to a few tens ofkm s − are observed across the central structure. No clear ev-idence for rotation is observed. If the CO (3-2) structure isa rotating disk, the small velocity gradients and narrow linewidth are consistent with it being nearly face-on.Fig. 4 is similar to Fig. 3, but with a coarser grid intended toincrease the signal in the outer region of the central structure.The mean line of sight velocities of the emission features areindicated where significant CO (3-2) is detected in emission.The tongue of gas located 1.5 arcsec to the north has a broadline profile with velocities of −
15 to −
60 km s − . Likewise,the tongue extending to the west is traveling at a velocity of −
70 km s − with respect to the bulk of the gas. The gas in theE-SE (bottom left) grid boxes has velocities similar in magni-tude but opposite in sign (redshifted) with respect to the cen-tral emission. The N and W tongues of blueshifted gas areoriented roughly toward the NW X-ray cavity. The redshiftedgas to the SE is oriented roughly toward the SE X-ray cav-ity. The tongues of gas appear to be dynamically decoupledfrom the central structure. Below we relate this gas to moreextended molecular gas seen in CO (1-0).We examine the molecular gas velocities on larger scalesusing the grid of spectra in CO (1-0) presented in Fig. 5,which matches the resolution of the telescope configuration.The sky grid corresponds to spectra shown in the right panel.The contours represent CO emission and their colors corre-spond to the color coded velocity stripes superposed on thespectra. A two dimensional gaussian profile has been fittedto and subtracted from each channel in order to remove thecentral emission from the contour map.The CO (1-0) map reveals tongues of emission projectingroughly 10 kpc to the N-NW and SE of the nucleus. Their ori-entations are similar to the smaller, tongue-like features seenin the CO (3-2) image. Molecular gas traveling at +
480 km s − in the eastern box is redshifted with respect to the systemicvelocity. A narrower, blueshifted gas velocity componentis seen in the N and NW boxes extending to velocities of −
200 km s − . The redshifted gas contour north of the nucleusis significant only at the 2 − σ level. Present as a small bumpin the nuclear spectrum at a velocity of 300 km s − , it is ofmarginal significance and will not be discussed further.In summary: blueshifted gas lies exclusively to the N-NW,while redshifted gas lies primarily to the E-SE. No signifi-cant high velocity gas is observed in the NE, SW, and W gridboxes, nor is it observed toward the nucleus. This pattern isconsistent with a broad, bipolar flow of molecular gas, whichwe discuss in greater detail in Sec. 4.3. While this interpre-tation accounts best for the data in hand , it is not unique.The gas may in principle have accreted with some net angularmomentum that placed it on nearly circular rather than radial orbits, so that the gas is in nearly ordered motion about theBCG.The integrated flux under the redshifted and blueshiftedemission profile wings are 0 . ± . . ± .
09 Jy km s − ,respectively, giving a total flux integral of 0 . ± . − .They correspond to a molecular hydrogen mass of 1 . ± . × M (cid:12) . The accuracy of the integrated fluxes are sensitiveto the continuum, particularly in the redshifted emission wing.A slightly higher mass is found in the redshifted componentcompared to the blueshifted component, indicating an asym-metric flow. DISCUSSION
Bipolar Outflow or Inflow of Molecular Gas?
The high speed molecular gas is observed in emission, sothe ALMA observations alone are unable to discriminate be-tween inflow and outflow. An inflow of molecular gas fromthe cooling flow would be a natural but problematical inter-pretation. Gas cooling from a steady accretion flow wouldfall inward reaching its highest speeds in the nucleus (Lim etal. 2008). This is not observed. Instead, the high velocity gasis projected away from the nucleus. Assuming the CO (3-2)and CO (1-0) lines track the same gas, higher line-of-sight ve-locities are observed 5 −
10 kpc toward the NW and SE of thenucleus. The gas to the N-NW is blueshifted from velocitiesof a few tens of km s − at radii of ∼ ∼
250 km s − at a radius of ∼
10 kpc. Likewise, the gas to the E-SE isredshifted with velocities of ∼ −
60 km s − at ∼ >
300 km s − at ∼
10 kpc. The yellow wing in thenuclear spectrum at +
250 km s − strengthens as it is redshiftedto higher velocities in the eastern grid box, indicating highergas masses traveling at higher speeds.Let us assume the gas projected 10 kpc from the nucleuswith radial speeds lying between 250 −
480 km s − began itsdescent at rest and fell radially to its current location. Weestimate its initial radius using a Hernquist law by adopting anenclosed mass within a 20 kpc radius of 1 . × M (cid:12) (Mainet al. in preparation), and an effective radius of ∼
10 kpc.We find that this molecular gas would have achieved its radialspeed had it fallen from an altitude of ∼ −
30 kpc. If gasis flowing steadily onto the disk, we would expect to observegas velocities toward the disk and nucleus lying between 600 −
800 km s − , but we don’t. Molecular gas that began its journeywith a significant initial velocity (imparted by turbulence or adonor galaxy) would be traveling faster. In principle, dragfrom the ICM might slow infalling clouds more effectivelycloser to the cluster center. However, cloud parameters mustthen be finely tuned to allow the clouds to free fall at largeradii while giving them terminal speeds of order 10 km s − atsmaller radii.We are then left with the following two scenarios: the high-speed molecular gas cooled recently from the hot atmospherein the past 10 Myr or so and has not yet arrived in the disk, orthat it arrived provenance unknown and is supported againstgravity by orbiting with a large velocity in the plane of thesky. The former interpretation implies an X-ray cooling rateof ∼ (cid:12) yr − which is inconsistent with an upper limitfrom X-ray spectroscopy of <
140 M (cid:12) yr − (Sanders et al.2010). Neither scenario can be ruled out using the data athand. However, the velocity patterns and flow rates impliedby the CO (3-2) and CO (1-0) emission are inconsistent withsteady inflow, and are more naturally interpreted in the con-text of a bipolar outflow of molecular gas. Driving a Molecular Outflow by Radiation Pressure orSupernovae
Molecular outflows are common in ULIRGs, QSOs, andstarburst galaxies (reviewed by Veilleux et al. 2005 andFabian 2013). Driving mechanisms include radiation pres-sure on dust and mechanical winds powered by supernovae.Radiation from hot stars and AGN will drive out gas when dM / dt × v CO ∼ < L UV / c . The left hand side is the product ofthe outflow rate and the gas velocity. The right hand side isthe sum of the UV luminosity from the AGN and stars di-vided by the speed of light. The far UV image shown in Fig.2 reveals no UV point source associated with the AGN. Starsare producing all of the UV flux. For a stellar UV luminos-ity L FUV = 1 . × erg s − (O’Dea et al. 2010), radia-tion pressure would be too feeble to drive an outflow rate of200 M (cid:12) yr − by more than 3 orders of magnitude.The power input by core collapse supernovae, 4 × erg s − (M06), is comparable to the kinetic power of theoutflow, E K (cid:39) erg, t out (cid:39) × yr, P K ∼ erg s − ,and is therefore energetically significant. However, in or-der to power the flow by supernova explosions, most of theirmechanical energy must couple to molecular gas driving bulkmotion rather than thermal motion, which would be hard tounderstand. Furthermore their spherical blast patterns and thework against gravity and the surrounding gas pressure wouldhinder a sustained and substantial bipolar flow over such largedistances. Instead of driving a flow, supernova explosionsmay be thickening the disk, and perhaps increasing the crosssection between the molecular gas and the radio AGN, whichcan easily power the flow (Sec. 4.4). A Radio-AGN Driving a Molecular Outflow
The mechanical power of the jet estimated from the X-raycavities, P cav (cid:39) erg s − , is by far the most potent powersource. Although the jet momentum is insufficient to lift thegas, the kinetic energy of the cold flows is only ∼
1% of the to-tal energy output of the AGN. The molecular gas is projectedalong and behind the rising bubbles, providing circumstantialevidence connecting the bubbles to the molecular flow. More-over, the molecular flow speeds are consistent with buoyancyspeeds of cavities, which rise at a substantial fraction of theatmosphere’s sound speed (Churazov et al. 2001). The atmo-spheric sound speed in Abell 1835 is ∼ − .This interpretation has its own problems. Despite ampleAGN power, the bubbles must couple to the molecular gasand lift it out of the galaxy. By Archimedes principle, theywould be unable to lift more molecular gas than hot gas theydisplace, which is ∼ × M (cid:12) . In addition to displacingthe hot plasma, rising X-ray bubbles draw metal-enriched X-ray plasma out from cluster centers at rates of tens to hundredsof solar masses per year (Simionescu et al. 2008, Werner etal. 2010, Kirkpatrick et al. 2009, 2011). Abell 1835’s AGNis lifting ∼ × M (cid:12) of hot gas out along the bubble axis(Kirkpatrick in preparation), a value that is a few times largerthan the mass of the molecular outflow and close to our es-timate of the amount of gas displaced by the bubbles. Theseestimates are uncomfortably close to the outflowing molecu-lar gas mass, and would imply surprisingly efficient couplingbetween the radio bubbles and both the hot, ∼ × K, ten-uous, 0 . − , volume-filling plasma and the ∼
30 K molec-ular gas.How the molecular gas couples to the bubbles is unclear.Ram pressure associated with simulated high Eddington ra- tio, hydrodynamic jets is able to sweep away both the coldand warm phases of the interstellar medium (e.g., Wagner,Bicknell, & Umemura 2012). Whether the molecular cloudsin Abell 1835 are being accelerated by jets or are being liftedin the updraft of the X-ray bubbles (e.g., Pope et al. 2010)is unclear. Observation suggests the latter. Molecular gas ismore readily coupled to the hot gas when the density contrastis low. In section 4.4, the density in the molecular disk is esti-mated to be ∼ ∼
100 km s − , if the dynamical pres-sure of the molecular gas matched the pressure of the hot gas,it would only be 50 times as dense. The high level of tur-bulence maintained by rapid ongoing star formation may thenhelp to explain how the tenuous hot gas is able to lift molecu-lar gas.The bubbles would be able to lift the mass more easily if themolecular hydrogen cooled out of hotter gas as it rises in thebubbles’ wake (see for example Revaz et al. 2008). The meanplasma density and temperature in the central 20 kpc of thecluster is 0 . − and T = 2 . .
25 cm − . Its coolingtime would be only 2 × yr, which is comparable to the risetimes of both the bubbles and molecular gas. Therefore, the ∼ < ∼ < − × yr. They imply an out-flow rate of ∼ −
300 M (cid:12) yr − , which is comparable tothe BCG’s mean star formation rate. The center of the galaxywould then be swept of its molecular gas in only a few hun-dred million years, starving the black hole and starburst ofneeded fuel. However, the fate of most of the gas is unclear.The one dimensional outflow speeds are somewhat larger thanthe circular speed of the stars. If the molecular gas is flowingballistically, most of it should return unless it evaporates intothe hot atmosphere. If the molecular gas is coupled to therising bubbles or continues to be accelerated by the AGN, itcould travel further. However, if the molecular gas formedbehind the bubbles in a cooling wake, it is unlikely to evap-orate into the hot medium, and would return in a circulationflow or "fountain" of molecular gas, similar to that inferredin NGC 1275 (Lim et al. 2008, Salome et al. 2006, 2011).The impact of a molecular fountain on the star formation andAGN histories of BCGs and normal elliptical galaxies is notunderstood. Dynamics of the Central Molecular Gas
The dynamical state and high average density of the molec-ular gas in the central kiloparsec of the BCG have significantimplications for this system. The lack of evidence for rotationin the molecular gas implies that, if the gas is rotationally sup-ported, its rotation axis must be very close to our line of sight.At the same time, the full velocity width at half maximum forthe molecular gas in this region is 130 km s − , correspondingto a line of sight velocity dispersion of σ los (cid:39)
55 km s − anda one-dimensional turbulent velocity v T = σ los . This suggeststhe gas lies in a face-on disk.This high turbulent velocity is consistent with the disk beingmarginally gravitationally unstable; the Toomre Q parameteris Q = v c v T π Gr Σ g ( r ) ≈ . (cid:16) v c
400 km s − (cid:17) (cid:16) v T
55 km s − (cid:17)(cid:18) R e (cid:19) − (cid:18) Σ g ( R e )0 . − (cid:19) − , (2)where we have scaled to the radius R e enclosing half the CO(3-2) flux, which we assume to enclose half the mass. Basedon Abell 1835’s mass profile (Main et al. in preparation, seeSec. 4.1), the circular speed at 10 kpc lies between 300 −
420 km s − .We have therefore scaled the circular velocity at 2 kpc to aconservative value of 400 km s − . The circular velocity wouldhave to exceed 940 km s − to stabilize the gas disk, so theToomre criterion is easily met. We noted in Section 3.2 thatthe BCG lies with starburst galaxies on the Schmidt-Kennicuttrelation; galaxies on that relation have Q ∼ <
1. Furthermore,Abell 1835’s disk has similar properties to those observed invigorously star forming galaxies at z ∼ Σ g =1600 M (cid:12) pc − ) corresponds to an A v ≈ p dyn = π G Σ g ≈ . × − dyne cm − . (3)This is substantially higher than the thermal pressure of thehot gas.Being marginally gravitationally stable implies that the diskscale height H = ( v T / v c ) r , or about 275 pc at R e = 2 kpc.The mean density at that radius is then ¯ ρ c = Σ g / (2 H ) ≈ . × − g cm − , or n H ≈ M T = H Σ g (cid:39) . × M (cid:12) . The turbulent pressure of thecold gas is p turb = ¯ ρ c v T ≈ . × − dyne cm − , (4)i.e., the turbulent motions provide enough pressure to supportthe disk in a marginally stable state.Turbulence is believed to decay on a dynamical time. Main-taining the turbulence in A1835 would then require a turbulentpower of P turb = 3 M g v T R e / v c (cid:39) × erg s − . This is similar to the total luminosity supplied by super-novae, if the star formation rate is ∼
200 M (cid:12) yr − , L Sne =6 × ( ˙ M ∗ /
200 M (cid:12) yr − ) erg s − , if the supernovae are wellcoupled to the molecular gas, and if they do not radiate more than ∼
50% of their energy away. We observe that Q ≈ Origin of the Molecular Gas
Molecular gas associated with starburst galaxies, ULIRGS,and QSOs is often attributed to wet mergers. The center ofa rich cluster with a large velocity dispersion and a dearthof gas-rich donor galaxies is an unlikely location for a wetmerger. Ram pressure experienced by a plunging, gas-richdonor galaxy would strip most of its atomic gas and muchof its molecular gas before it reaches the BCG (Combes2004, Roediger & Brüggen 2007, Kirkpatrick et al. 2009,Ruszkowski et al. 2012). Being dense and centrally concen-trated, molecular gas is tightly bound and more resilient tostripping than atomic gas. Therefore, short of a direct colli-sion, a plunging galaxy should retain much of its moleculargas (Young et al. 2011). Finally, the BCG’s molecular gasmass exceeds by large factors that of most galaxies in clus-ters at its epoch. The likelihood that such a galaxy, if present,would hit the BCG directly and deposit its molecular gas atthe low speeds observed seems remote.The molecular gas in Abell 1835 probably cooled fromthe hot atmosphere and settled into the BCG. Molecular gasmasses of 10 − M (cid:12) are prevalent in BCGs, but only thosecentered in hot atmospheres whose central cooling times liebelow ∼ yr (Edge 2001, Salome & Combes 2003). BCGsin Coma-like clusters with long central cooling times are notgas rich. Abell 1835 is an extreme example of this class ofBCGs. Its cooling rate of ∼ <
140 M (cid:12) yr − (Sanders et al. 2010)would supply the molecular gas in a few hundred Myr, whichis comparable to the age of the starburst (M06). CONCLUSIONS
We have shown that the BCG in Abell 1835 containsroughly 5 × M (cid:12) of molecular gas, most of which is as-sociated with stars forming at a rate of 100 −
180 M (cid:12) yr − ,in a thick, turbulent disk projected face-on. We discov-ered a ∼ M (cid:12) bipolar molecular flow traveling between −
250 and +
480 km s − that we suggest is being acceler-ated outward by mechanical energy associated with rising X-ray bubbles. Whether the bubbles accelerated the molecularclouds themselves, or whether the molecular clouds cooledout of the hot plasma in the updraft behind the bubbles isunclear. We highlight the difficulty lifting dense moleculargas out of the central disk and we propose that the moleculargas in the flow may have cooled in the updraft of hot plasmabehind the bubbles. The problem would be mitigated if theoutflowing mass were lower than we have estimated, for ex-ample, if the X CO parameter were lower than the value weassumed.Our result has broader implications. Molecular gas abun-dance is a sharply declining function of a galaxy’s stellarmass. Above 3 × M (cid:12) most are elliptical galaxies. Ofthese, only ∼
22% contain molecular gas, and only at levelsbetween 10 − M (cid:12) (Young et al. 2011). On the otherhand, radio power is a steeply increasing function of stellarmass (Best et al. 2005, Best & Heckman 2012). Their radiodetection fraction rises from 0 .
01% at 3 × M (cid:12) to upwardof 30% at 5 × M (cid:12) (Best et al. 2005). Therefore, molecu-lar gas mass must also be a declining function of radio power.While a number of environmental factors may be contributingto this decline (Young et al. 2011), the radio source itself mayplay a role, albeit a complex one. Radio synchrotron powerrepresents only a small fraction of a radio AGN’s total me-chanical power (Birzan et al. 2008). Therefore, relatively lowpower radio synchrotron sources can be mechanically potent.Mechanical heating of hot atmospheres in elliptical galaxiesby radio mode feedback is likely to be the primary mechanismmaintaining “red and dead" elliptical galaxies (e.g., Bower etal. 2006, Croton et al. 2006). However, radio AGN are likelyfed by cold clouds. A feedback loop may be difficult to sus-tain unless the radio jets are also affecting the rate of cold gasaccretion by driving it away from the nucleus. The relativelyefficient coupling between the molecular gas and radio bub-bles inferred here in Abell 1835 and in other radio galaxies(eg., Morganti, Tadhunter, & Oosterloo 2005) suggests thatradio mode feedback may also be regulating the amount ofmolecular gas reaching the centers of galaxies.BRM thanks Tom Jones and Christine Jones for helpfulcomments. HRR and BRM acknowledge generous finan- cial support from the Canadian Space Agency Space Sci-ence Enhancement Program. BRM, RAM, HRR, and ANVacknowledge support from the Natural Sciences and Engi-neering Research Council of Canada. ACE acknowledgessupport from STFC grant ST/I001573/1 PEJN is supportedby NASA grant NAS8-03060. We thank the ALMA sci-entific support staff members Adam Leroy and StéphaneLeon. The paper makes use of the following ALMAdata: ADS/JAO.ALMA APPENDIX
THE CO TO H2 CONVERSION FACTORCO traces traces molecular hydrogen which, lacking a permanent electric dipole moment, radiates inefficiently. The value ofthe CO to molecular gas conversion factor, commonly referred to as X CO , is the prime uncertainty in our mass estimates. Absentan alternative, most investigators adopt the value for the Milky Way Galaxy and other local disk galaxies, where the CO (1-0)emission feature is usually optically thick. However, the true value depends on environmental factors, such as the gas phase metalabundance, which may depart from the average Galactic value. A lower gas phase metal abundance gives a higher mass ratio ofhydrogen to CO. Therefore, applying the Galactic X CO to low metal abundance gas would underestimate of the total moleculargas mass. On the other hand, if the molecular gas optically thin or nearly so, as it may be in turbulent flows and massive starburstgalaxies, the Galactic X CO would over estimate the molecular gas mass. Other factors that affect X CO including, the temperature,density, and dynamics of the gas, which in most situations are poorly understood (Bolatto et al. 2013).The metallicity of the cooling X-ray plasma in Abell 1835 lies between 0.5-0.8 times the Solar metallicity within 20 kpc ofthe nucleus. This alone would indicate that adopting the Galactic X CO as we have done should provide a reasonable if not aconservative underestimate of the molecular gas mass. However, Abell 1835 is a starburst galaxy. There are indications thatX CO in starburst galaxies may be depressed below the Galactic value. The central gas density, ∼ M (cid:12) pc − , lies midwaybetween normal spirals and starbursts. The gas density of the outflow, away from the bulk of star formation, has a surface densityof ∼ M (cid:12) pc − , which is comparable to normal spiral galaxies and to the Milky Way (Bolatto et al. 2013). It is thereforepossible that the X CO value for the molecular gas located near the nucleus may be suppressed by a small factor with respect tothe molecular gas in the outflow. On the other hand, indications are that X CO may be suppressed in turbulent winds, where themolecular gas becomes optically thin (Bolatto 2013). Abell 1835’s outflow velocity is lower than those in quasars (e.g., Maiolinoet al. 2012, Feruglio et al. 2010). Taken together, we have no reason to expect X CO to depart significantly from the Galactic valuein this system. Nevertheless, should X CO lie a factor of several below the Galactic value, the flow would still exceed 10 M (cid:12) .This would not qualitatively alter our result. ReferencesBest, P. N., Kauffmann, G., Heckman, T. M., et al. 2005, MNRAS, 362, 25Best, P. N., & Heckman, T. M. 2012, MNRAS, 421, 1569Bîrzan, L., McNamara, B. R., Nulsen, P. E. J., Carilli, C. L., & Wise, M. W. 2008, ApJ, 686, 859Bower, R. G., Benson, A. J., Malbon, R., et al. 2006, MNRAS, 370, 645Bolatto, A. D., Wolfire, M., & Leroy, A. K. 2013, ARAA, 51, 207Cavagnolo, K. W., Donahue, M., Voit, G. M., & Sun, M. 2008, ApJ, 683, L107Churazov, E., Brüggen, M., Kaiser, C. R., Böhringer, H., & Forman, W. 2001, ApJ, 554, 261Combes, F. 2004, Recycling Intergalactic and Interstellar Matter, 217, 440Crawford, C. S., Allen, S. W., Ebeling, H., Edge, A. C., & Fabian, A. C. 1999, MNRAS, 306, 857Croton, D.J. et al. 2006, MNRAS, 365, 11Donahue, M., de Messières, G. E., O’Connell, R. W., et al. 2011, ApJ, 732, 40Edge, A. C. 2001, MNRAS, 328, 762Egami, E., Misselt, K. A., Rieke, G. H., et al. 2006, ApJ, 647, 922Elmegreen, B. G., & Elmegreen, D. M. 2006, ApJ, 650, 644Emonts, B. H. C., Norris, R. P., Feain, I., et al. 2013, arXiv:1312.4785Fabian, A. C. 1994, ARA&A, 32, 277Fabian, A.C. 2013, ARA&A, 50, 455Feruglio, C., Maiolino, R., Piconcelli, E., et al. 2010, A&A, 518, L155Gaspari, M., Ruszkowski, M., & Sharma, P. 2012, ApJ, 746, 94Gaspari, M., Ruszkowski, M., & Oh, S. P. 2013, MNRAS, 432, 3401Guo, F., & Mathews, W. G. 2013, arXiv:1305.2958Heckman, T. M. 1981, ApJ, 250, L59Hopkins, P. F. & Quataert, E. 2010, MNRAS, 407, 1529Hopkins, P. F. & Quataert, E. 2011, MNRAS, 415, 1027Hu, E. M., Cowie, L. L., & Wang, Z. 1985, ApJS, 59, 447Kennicutt, R. C., Jr. 1998, ApJ, 498, 541Kirkpatrick, C. C., McNamara, B. R., & Cavagnolo, K. W. 2011, ApJ, 731, L23Kirkpatrick, C. C., Gitti, M., Cavagnolo, K. W., et al. 2009, ApJ, 707, L69Lim, J., Ao, Y., & Dinh-V-Trung 2008, ApJ, 672, 252Maiolino, R., Gallerani, S., Neri, R., et al. 2012, MNRAS, 425, L66McDonald, M., Bayliss, M., Benson, B. A., et al. 2012, Nature, 488, 349McNamara, B. R., & Nulsen, P. E. J. 2007, ARA&A, 45, 117McNamara, B.R., Nulsen, P.E.J., 2012, NJP, 14, 055023McNamara, B. R., Rafferty, D. A., Bîrzan, L., et al. 2006, ApJ, 648, 164Morganti, R., Tadhunter, C. N., & Oosterloo, T. A. 2005, A&A, 444, L9Morganti, R., Fogasy, J., Paragi, Z., Oosterloo, T., & Orienti, M. 2013, Science, 341, 1082Narayanan, D., Krumholz, M. R., Ostriker, E. C., & Hernquist, L. 2012, MNRAS, 421, 3127Nesvadba, N. P. H., Lehnert, M. D., Eisenhauer, F., et al. 2006, ApJ, 650, 693Newman, S. F., Shapiro Griffin, K., Genzel, R., et al. 2012, ApJ, 752, 111O’Dea, C. P., Baum, S. A., Privon, G., et al. 2008, ApJ, 681, 1035O’Dea, K. P., Quillen, A. C., O’Dea, C. P., et al. 2010, ApJ, 719, 1619O’Neill, S. M., & Jones, T. W. 2010, ApJ, 710, 180 Peterson, J. R., & Fabian, A. C. 2006, Phys. Rep., 427, 1Peterson, J. R., Kahn, S. M., Paerels, F. B. S., et al. 2003, ApJ, 590, 207Pizzolato, F. & Soker, N. 2010, MNRAS, 408, 961Pope, E. C. D., Babul, A., Pavlovski, G., Bower, R. G., & Dotter, A. 2010, MNRAS, 406, 2023Rafferty, D. A., McNamara, B. R., & Nulsen, P. E. J. 2008, ApJ, 687, 899Revaz, Y., Combes, F., & Salomé, P. 2008, A&A, 477, L33Roediger, E., & Brüggen, M. 2007, MNRAS, 380, 1399Russell, H. R., McNamara, B. R., Edge, A. C., et al. 2014, ApJ, 784, 78Ruszkowski, M., Bruggen, M., Lee, D., & Shin, M.-S. 2012, arXiv:1203.1343Sanders, J. S., Fabian, A. C., Smith, R. K., & Peterson, J. R. 2010, MNRAS, 402, L11Salome, P., & Combes, F. 2003, A& A, 412, 657Salomé, P., Combes, F., Edge, A. C., et al. 2006, A&A, 454, 437Salomé, P., Combes, F., Revaz, Y., et al. 2011, A&A, 531, A85Simionescu, A., Werner, N., Finoguenov, A., Böhringer, H., & Brüggen, M. 2008, A&A, 482, 97Veilleux, S., Cecil, G., & Bland-Hawthorn, J. 2005, ARA&A, 43, 769Villar-Martín, M., Sánchez, S. F., De Breuck, C., et al. 2006, MNRAS, 366, L1Voit, G. M. 2011, ApJ, 740, 28Voit, G. M., Cavagnolo, K. W., Donahue, M., et al. 2008, ApJ, 681, L5Wagner, A. Y., Bicknell, G. V., & Umemura, M. 2012, ApJ, 757, 136Werner, N., Simionescu, A., Million, E. T., et al. 2010, MNRAS, 407, 2063Wilman, R. J., Edge, A. C., & Swinbank, A. M. 2006, MNRAS, 371, 93Young, L. M., Bureau, M., Davis, T. A., et al. 2011, MNRAS, 414, 940 F IG . A1.— CO (1-0) and CO (3-2) spectra on the left and right, respectively. The spectra were extracted from regions measuring 6 × F IG . A2.— Upper left:
Hubble Space Telescope F702W WFPC2 image of the BCG and surrounding galaxies in Abell 1835. The red box indicates the scaleof the CO (3-2) image at lower left. The image is sensitive to both the old and young stellar populations and accompanying line emission.
Upper right:
ChandraX-ray image of the hot atmosphere surrounding the BCG. A smooth X-ray background has been subtracted. The blue box indicates the location and scale of theCO (3-2) and UV images in the lower panels. X-ray cavities inflated by the radio AGN (M06) are seen to the northwest and southeast near the edges of the box.The bright regions to the northeast and southwest of center are the locations of gas with the shortest cooling time where the atmosphere is cooling rapidly.
Lowerleft:
CO (3-2) image. The oval at lower left indicates the beam size, shape, and scale in arcseconds and kiloparsecs. The contours represent − , + , + , + ... σ . Lower right:
Far ultraviolet continuum image through filter F165LP ACS Solar Blind Channel. Note the absence of a nuclear point source associated with anAGN. Essentially all of the continuum is from the young stars. F IG . A3.— CO (3-2) images with a grid of apertures corresponding to the spectra shown in the right panel. The extractions are 0.6 arcsec on a side,corresponding to the resolution of the synthesized beam. The velocity centroids and their errors are indicated in each box.F IG . A4.— Similar to Fig. 3 but with 1 arcsec extraction apertures that extend into the fainter outer reaches of the central gas structure. The red box correspondsto the outer edge of the grid region shown in the CO (1-0) map in Fig. 5 F IG . A5.— Left panel shows a colorscale image of CO (1-0) emission with color contours divided into separate velocity bins. The contours are integratedintensity in particular velocity ranges with + σ , 3 σ , 4 σ . dark blue ( −
210 to −
150 km s − ), cyan ( −
150 to −
110 km s − ), yellow (70 to 270 km s − ), red(270 to 470 km s − ). A two dimensional gaussian profile has been fitted to and subtracted from each channel in order to remove the central emission from thecontour map. Right panel shows spectral extractions 1 ..
110 km s − ), yellow (70 to 270 km s − ), red(270 to 470 km s − ). A two dimensional gaussian profile has been fitted to and subtracted from each channel in order to remove the central emission from thecontour map. Right panel shows spectral extractions 1 .. × ..