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We present constraints on a simple analytical model for hot diffuse halo gas, derived from a fit spanning two orders of magnitude in halo mass ($M_{500} \sim 10^{12.5}-10^{14.5} M_{\odot}$). The model is motivated by the observed prevalence of a precipitation limit, and its main free parameter is the central ratio of gas cooling timescale to free-fall timescale ($t_{\rm cool}/t_{\rm ff}$). We use integrated X-ray and thermal Sunyaev-Zel'dovich observations of the environments around massive galaxies, galaxy groups and clusters, averaged in halo mass bins, and obtain the best-fitting model parameters. We find $t_{\rm cool}/t_{\rm ff} \sim 50-110$, depending on the model extrapolation beyond the halo virial radius and possibly on biases present in the data-sets used in the fitting analysis. The model adequately describes the entire mass range, except for intermediate mass halos ($M_{500} \sim 10^{13.5} M_{\odot}$) which systematically fall below the model predictions. However, the best fits for $t_{\rm cool}/t_{\rm ff}$ substantially exceed the values typically derived from X-ray observations of individual systems ($t_{\rm cool}/t_{\rm ff} \sim 10-30$). We consider several explanations for those discrepancies, including X-ray selection biases and a potential anti-correlation between X-ray luminosity and the central galaxy's stellar mass., Comment: 13 pages, 5 figures, 1 table. Accepted for publication in MNRAS

We consider a model of the circumgalactic medium (CGM) in which feedback maintains a constant ratio of cooling time to freefall time throughout the halo, so that the entire CGM is marginally unstable to multiphase condensation. This 'precipitation model' is motivated by observations of multiphase gas in the cores of galaxy clusters and the halos of massive ellipticals. We derive from the model density and temperature profiles for the CGM around galaxies with masses similar to the Milky Way. After taking into consideration the geometrical position of our solar system in the Milky Way, we show that the CGM model is consistent with observed OVI, OVII, and OVIII column densities only if temperature fluctuations with a log-normal dispersion $\sigma_{\ln T} \sim 0.6$-$1.0$ are included. We show that OVI column densities observed around star-forming galaxies require systematically greater values of $\sigma_{\ln T}$ than around passive galaxies, implying a connection between star formation in the disk and the state of the CGM. Photoionization by an extra-galactic UV background does not significantly change these CGM features for galaxies like the Milky Way but has much greater and significant effects on the CGM of lower-mass galaxies., Comment: 12 pages, 10 figures, 1 table, Accepted for publication in MNRAS

X-ray emitting atmospheres of non-rotating early-type galaxies and their connection to central active galactic nuclei have been thoroughly studied over the years. However, in systems with significant angular momentum, processes of heating and cooling are likely to proceed differently. We present an analysis of the hot atmospheres of six lenticulars and a spiral galaxy to study the effects of angular momentum on the hot gas properties. We find an alignment between the hot gas and the stellar distribution, with the ellipticity of the X-ray emission generally lower than that of the optical stellar emission, consistent with theoretical predictions for rotationally-supported hot atmospheres. The entropy profiles of NGC 4382 and the massive spiral galaxy NGC 1961 are significantly shallower than the entropy distribution in other galaxies, suggesting the presence of strong heating (via outflows or compressional) in the central regions of these systems. Finally, we investigate the thermal (in)stability of the hot atmospheres via criteria such as the TI- and C-ratio, and discuss the possibility that the discs of cold gas present in these objects have condensed out of the hot atmospheres., 12 pages, 11 figures, submitted to MNRAS

We present new, deep observations of the Phoenix cluster from the Chandra X-ray Observatory, the Hubble Space Telescope, and the Karl Jansky Very Large Array. These data provide an order of magnitude improvement in depth and/or angular resolution at X-ray, optical, and radio wavelengths, yielding an unprecedented view of the core of the Phoenix cluster. We find that the one-dimensional temperature and entropy profiles are consistent with expectations for pure-cooling hydrodynamic simulations and analytic descriptions of homogeneous, steady-state cooling flow models. In the inner ~10 kpc, the cooling time is shorter by an order of magnitude than any other known cluster, while the ratio of the cooling time to freefall time approaches unity, signaling that the ICM is unable to resist multiphase condensation on kpc scales. When we consider the thermodynamic profiles in two dimensions, we find that the cooling is highly asymmetric. The bulk of the cooling in the inner ~20 kpc is confined to a low-entropy filament extending northward from the central galaxy. We detect a substantial reservoir of cool (10^4 K) gas (as traced by the [OII] doublet), which is coincident with the low-entropy filament. The bulk of this cool gas is draped around and behind a pair of X-ray cavities, presumably bubbles that have been inflated by radio jets, which are detected for the first time on kpc scales. These data support a picture in which AGN feedback is promoting the formation of a multiphase medium via a combination of ordered buoyant uplift and locally enhanced turbulence. These processes ought to counteract the tendency for buoyancy to suppress condensation, leading to rapid cooling along the jet axis. The recent mechanical outburst has sufficient energy to offset cooling, and appears to be coupling to the ICM via a cocoon shock, raising the entropy in the direction orthogonal to the radio jets., Comment: 19 pages, 17 figures. Submitted to ApJ. Comments welcome!

Star formation in the universe's most massive galaxies proceeds furiously early in time but then nearly ceases. Plenty of hot gas remains available but does not cool and condense into star-forming clouds. Active galactic nuclei (AGN) release enough energy to inhibit cooling of the hot gas, but energetic arguments alone do not explain why quenching of star formation is most effective in high-mass galaxies. In fact, optical observations show that quenching is more closely related to a galaxy's central stellar velocity dispersion ($\sigma_v$) than to any other characteristic. Here, we show that high $\sigma_v$ is critical to quenching because a deep central potential well maximizes the efficacy of AGN feedback. In order to remain quenched, a galaxy must continually sweep out the gas ejected from its aging stars. Supernova heating can accomplish this task as long as the AGN sufficiently reduces the gas pressure of the surrounding circumgalactic medium (CGM). We find that CGM pressure acts as the control knob on a valve that regulates AGN feedback and suggest that feedback power self-adjusts so that it suffices to lift the CGM out of the galaxy's potential well. Supernova heating then drives a galactic outflow that remains homogeneous if $\sigma_v \gtrsim 240 \, {\rm km \, s^{-1}}$. AGN feedback can effectively quench galaxies with a comparable velocity dispersion, but feedback in galaxies with a much lower velocity dispersion tends to result in convective circulation and accumulation of multiphase gas within the galaxy., Comment: 29 pages, 8 figures, published in ApJ

The universe's largest galaxies reside at the centers of galaxy clusters and are embedded in hot gas that, if left unchecked, would cool prodigiously and create many more new stars than are actually observed. Cooling can be regulated by feedback from accretion of cooling gas onto the central black hole, but requires an accretion rate finely tuned to the thermodynamic state of the hot gas. Theoretical models in which cold clouds precipitate out of the hot gas via thermal instability and accrete onto the black hole exhibit the necessary tuning. We have recently presented observational evidence showing that the abundance of cold gas in the central galaxy increases rapidly near the predicted threshold for instability. Here we present observations showing that this threshold extends over a large range in cluster radius, cluster mass, and cosmic time, and incorporate the precipitation threshold into a comprehensive framework of theoretical models for the thermodynamic state of hot gas in galaxy clusters. According to that framework, precipitation regulates star formation in some giant galaxies, while thermal conduction prevents star formation in others, if it can compensate for radiative cooling and shut off precipitation., Comment: Nature (submitted 3 Sep 2014, accepted 22 Dec 14, published online 4 Mar 15): http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14167.html

We investigate a crucial phase in the cooling-feedback cycle in the star forming Brightest Cluster Galaxies (BCGs) by looking at the optical emission line properties of the reheated gas that ultimately causes the cycle to repeat. We investigate the source, or the mixture of sources, of ionization of the gas. To identify the dominant ionization processes, excitation sources, morphology and kinematics of the hot gas, line ratios over the entire optical wavelength range are necessary. For this purpose, the spatially-resolved spectra over the entire optical wavelength range for eight nearby, active BCGs in X-ray luminous groups and clusters have been obtained with the Southern African Large Telescope (SALT). The BCG sample was chosen to have H$\alpha$ detections - a strong indication of star formation activity, as well as existing hot cluster data from X-ray regime available. The fundamental gas properties such as electron density, gas temperature, metallicity and several abundances were derived using the spectral features across the long wavelength range. The present optical data will be combined with the other multi-wavelength data to form a complete view of the different phases (hot and cold gas and young stars) and how they interact in the processes of star formation and feedback detected in central galaxies in cooling flow systems, as well as the influence of the surrounding intracluster medium (ICM). Here we present our preliminary results on one of those eight BCGs, Hydra A, which shows the complexity and spatial variation of the ionization mechanisms in the nucleus.

We present ALMA CO(1-0) and CO(3-2) observations of the brightest cluster galaxy (BCG) in the 2A 0335+096 galaxy cluster (z = 0.0346). The total molecular gas mass of (1.13+/-0.15) x 10^9 M_sun is divided into two components: a nuclear region and a 7 kpc long dusty filament. The central molecular gas component accounts for (3.2+/-0.4) x 10^8 M_sun of the total supply of cold gas. Instead of forming a rotationally-supported ring or disk, it is composed of two distinct, blueshifted clumps south of the nucleus and a series of low-significance redshifted clumps extending toward a nearby companion galaxy. The velocity of the redshifted clouds increases with radius to a value consistent with the companion galaxy, suggesting that an interaction between these galaxies, 21 pages, 14 figures, accepted to ApJ

We present ALMA observations of the CO(1-0) and CO(3-2) line emission tracing filaments of cold molecular gas in the central galaxy of the cluster PKS0745-191. The total molecular gas mass of 4.6 +/- 0.3 x 10^9 solar masses, assuming a Galactic X_{CO} factor, is divided roughly equally between three filaments each extending radially 3-5 kpc from the galaxy centre. The emission peak is located in the SE filament roughly 1 arcsec (2 kpc) from the nucleus. The velocities of the molecular clouds in the filaments are low, lying within +/-100 km/s of the galaxy's systemic velocity. Their FWHMs are less than 150 km/s, which is significantly below the stellar velocity dispersion. Although the molecular mass of each filament is comparable to a rich spiral galaxy, such low velocities show that the filaments are transient and the clouds would disperse on, 16 pages, 10 figures, accepted by MNRAS

We present new Chandra X-ray observations of the brightest cluster galaxy (BCG) in the cool-core cluster Abell 2597 (z= 0.0821). The data reveal an extensive kpc-scale X-ray cavity network as well as a 15-kpc filament of soft-excess gas exhibiting strong spatial correlation with archival Very Large Array radio data. In addition to several possible scenarios, multiwavelength evidence may suggest that the filament is associated with multiphase (103-107 K) gas that has been entrained and dredged-up by the propagating radio source. Stemming from a full spectral analysis, we also present profiles and 2D spectral maps of modelled X-ray temperature, entropy, pressure and metal abundance. The maps reveal an arc of hot gas which in projection borders the inner edge of a large X-ray cavity. Although limited by strong caveats, we suggest that the hot arc may be (a) due to a compressed rim of cold gas pushed outwards by the radio bubble or (b) morphologically and energetically consistent with cavity-driven active galactic nucleus heating models invoked to quench cooling flows, in which the enthalpy of a buoyant X-ray cavity is locally thermalized as ambient gas rushes to refill its wake. If confirmed, this would be the first observational evidence for this model.

New Chandra X-ray and Herschel Far-Infrared (FIR) observations enable a multiwavelength study of active galactic nucleus (AGN) heating and intracluster medium (ICM) cooling in the brightest cluster galaxy (BCG) of Abell 2597 (z= 0.0821). The new Chandra observations reveal the central ≲30 kpc X-ray cavity network to be more extensive than previously thought, and associated with enough enthalpy to theoretically inhibit the inferred classical cooling flow. Nevertheless, we present new evidence, consistent with previous results, that a moderately strong residual cooling flow is persisting at 4-8 per cent of the classically predicted rates in a spatially structured manner amid the feedback-driven excavation of the X-ray cavity network. New Herschel observations are used to estimate warm and cold dust masses, a lower limit gas-to-dust ratio and a star formation rate consistent with previous measurements. [O i] and CO(2−1) line profiles are used to constrain the kinematics of the ∼109 M⊙ reservoir of cold molecular gas. The cooling time profile of the ambient X-ray atmosphere is used to map the locations of the observational star formation entropy threshold as well as the theoretical thermal instability threshold. Both lie just outside the ≲30-kpc central region permeated by X-ray cavities, and star formation as well as ionized and molecular gas lie interior to both. The young stars are distributed in an elongated region that is aligned with the radio lobes, and their estimated ages are both younger and older than the X-ray cavity network, suggesting both jet-triggered as well as persistent star formation over the current AGN feedback episode. Bright X-ray knots that are coincident with extended Lyα and far-ultraviolet continuum filaments motivate a discussion of structured cooling from the ambient hot atmosphere along a projected axis that is perpendicular to X-ray cavity and radio axis. We conclude that the cooling ICM is the dominant contributor of the cold gas reservoir fuelling star formation and AGN activity in the Abell 2597 BCG.

We present a systematic analysis of 43 nearby galaxy groups (kT 500 = 0.7-2.7 keV or M 500 = 1013-1014 h –1 M ☉, 0.012 0.15 r 500 and are consistent with a "universal temperature profile." We present the K-T relations at six characteristic radii (30 kpc, 0.15 r 500, r 2500, r 1500, r 1000, and r 500), for 43 groups from this work and 14 clusters from the Vikhlinin et al. (2008) sample. Despite large scatter in the entropy values at 30 kpc and 0.15 r 500, the intrinsic scatter at r 2500 is much smaller and remains the same (~ 10%) to r 500. The entropy excess at r 500 is confirmed, in both groups and clusters, but the magnitude is smaller than previous ROSAT and ASCA results. We also present scaling relations for the gas fraction. It appears that the average gas fraction between r 2500 and r 500 has no temperature dependence, ~ 0.12 for 1-10 keV systems. The group gas fractions within r 2500 are generally low and have large scatter. This work shows that the difference of groups from hotter clusters stems from the difficulty of compressing group gas inside of r 2500. The large scatter of the group gas fraction within r 2500 causes large scatter in the group entropy around the center and may be responsible for the large scatter of the group luminosities. Nevertheless, the groups appear more regular and more like clusters beyond r 2500 from the results on gas fraction and entropy. Therefore, mass proxies can be extended into low-mass systems. The M 500-T 500 and M 500-Y X,500 relations derived in this work are indeed well behaved down to at least 2 ×1013 h–1 M ☉.

We present the discovery of a 40 kpc H-alpha tail and at least 29 emission-line objects downstream of a star-forming galaxy ESO 137-001 in the rich, nearby cluster A3627. The galaxy is known to possess a dramatic 70 kpc X-ray tail. The detected H-alpha tail coincides positionally with the X-ray tail. The H-alpha emission in the galaxy is sharply truncated on the front and the sides near the nucleus, indicating significant ram pressure stripping. ESO 137-001 is thus the first cluster late-type galaxy known unambiguously with both an X-ray tail and an H-alpha tail. The emission-line objects are all distributed downstream of the galaxy, with projected distance up to 39 kpc from the galaxy. From the analysis on the H-alpha_{off} frame and the estimate of the background emission-line objects, we conclude that it is very likely all 29 emission-line objects are HII regions in A3627. The high surface number density and luminosities of these HII regions (up to 10^40 ergs/s) dwarf the previously known examples of isolated HII regions in clusters. We suggest that star formation may proceed in the stripped ISM, in both the galactic halo and intracluster space. The total mass of formed stars in the stripped ISM of ESO 137-001 may approach several times 10^7 solar masses. Therefore, stripping of the ISM not only contributes to the ICM, but also adds to the intracluster stellar light through subsequent star formation. The data also imply that ESO 137-001 is in an active stage of transformation, accompanied by the build-up of a central bulge and depletion of the ISM., 16 pages, 1 table, 6 figures (4 in color), emulateapj5.sty, to appear in ApJ, December 10, 2007, v671, n1. Spectroscopic data added; minor revision and conclusions unchanged. Please read the paper with the full-resolution figures at http://www.pa.msu.edu/~sunm/eso137_001_Ha_v1.3.ps.gz

The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure, and of the scaling relations between observables and cluster mass. To improve on this situation we have started an XMM-Newton Large Programme for the in-depth study of a representative sample of 33 galaxy clusters, selected in the redshift range z=0.055 to 0.183 from the REFLEX Cluster Survey, having X-ray luminosities above 0.4 X 10^44 h_70^-2 erg s^-1 in the 0.1 - 2.4 keV band. This paper introduces the sample, compiles properties of the clusters, and provides detailed information on the sample selection function. We describe the selection of a nearby galaxy cluster sample that makes optimal use of the XMM-Newton field-of-view, and provides nearly homogeneous X-ray luminosity coverage for the full range from poor clusters to the most massive objects in the Universe. For the clusters in the sample, X-ray fluxes are derived and compared to the previously obtained fluxes from the ROSAT All-Sky Survey. We find that the fluxes and the flux errors have been reliably determined in the ROSAT All-Sky Survey analysis used for the REFLEX Survey. We use the sample selection function documented in detail in this paper to determine the X-ray luminosity function, and compare it with the luminosity function of the entire REFLEX sample. We also discuss morphological peculiarities of some of the sample members. The sample and some of the background data given in this introductory paper will be important for the application of these data in the detailed studies of cluster structure, to appear in forthcoming publications., 17 pages, 17 figures; to appear in A&A. A pdf version with full-quality figures can be found at ftp://ftp.xray.mpe.mpg.de/people/gwp/xmmlp/xmmlp.pdf

Star formation in the universe's largest galaxies---the ones at the centers of galaxy clusters---depends critically on the thermodynamic state of their hot gaseous atmospheres. Central galaxies with low-entropy, high-density atmospheres frequently contain multiphase star-forming gas, while those with high-entropy, low-density atmospheres never do. The dividing line between these two populations in central entropy, and therefore central cooling time, is amazingly sharp. Two hypotheses have been proposed to explain the dichotomy. One points out that thermal conduction can prevent radiative cooling of cluster cores above the dividing line. The other holds that cores below the dividing line are subject to thermal instability that fuels the central AGN through a cold-feedback mechanism. Here we explore those hypotheses with an analysis of the H-alpha properties of ACCEPT galaxy clusters. We find that the two hypotheses are likely to be complementary. Our results support a picture in which cold clouds inevitably precipitate out of cluster cores in which cooling outcompetes thermal conduction and rain down on the central black hole, causing AGN feedback that stabilizes the cluster core. In particular, the observed distribution of the cooling-time to freefall-time ratio is nearly identical to that seen in simulations of this cold-feedback process, implying that cold-phase accretion, and not Bondi-like accretion of hot-phase gas, is responsible for the AGN feedback that regulates star formation in large galaxies., Submitted to ApJ Letters

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 present results from detailed imaging of the centrally dominant radio elliptical galaxy in the cooling flow cluster Abell 2597, using data obtained with the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST). This object is one of the archetypal "blue-lobed" cooling flow radio elliptical galaxies, also displaying a luminous emission-line nebula, a compact radio source, and a significant dust lane and evidence of molecular gas in its center. We show that the radio source is surrounded by a complex network of emission-line filaments, some of which display a close spatial association with the outer boundary of the radio lobes. We present a detailed analysis of the physical properties of ionized and neutral gas associated with the radio lobes, and show that their properties are strongly suggestive of direct interactions between the radio plasma and ambient gas. We resolve the blue continuum emission into a series of knots and clumps, and present evidence that these are most likely due to regions of recent star formation. We investigate several possible triggering mechanisms for the star formation, including direct interactions with the radio source, filaments condensing from the cooling flow, or the result of an interaction with a gas-rich galaxy, which may also have been responsible for fueling the active nucleus. We propose that the properties of the source are plausibly explained in terms of accretion of gas by the cD during an interaction with a gas-rich galaxy, which combined with the fact that this object is located at the center of a dense, high-pressure ICM can account for the high rates of star formation and the strong confinement of the radio source., Astrophysical Journal, in press, 34 pages, includes 6 PostScript figures. Latex format, uses aaspp4.sty and epsf.sty files

Spectropolarimetry of Broad Absorption Line Quasars (BALQSO's) has demonstrated that the geometry of the absorbing material is far from spherically symmetric. Calculations of accretion disk spectra suggest that the intrinsic radiation pattern of quasars is also anisotropic. Because the quasar counts distribution is very steep, if the orientations of these two anisotropies are correlated, optical flux-limited samples would be very strongly biassed with respect to discovery of BALQSO's. In particular, currently favored models suggest that BALQSO's may be much more common than in the samples. If so, the intrinsic covering fraction of absorbing matter must be relatively large. Numerous consequences follow, including prediction of a new population of hard X-ray sources (as may have already been seen by ASCA), and a possible explanation of the anomalously strong NV~1240 lines seen in many high redshift quasars.

We investigate dusty molecular clouds on the inner edge of the torus which are exposed to the strong ionizing continuum of the active nucleus. The incident ionizing flux pressurizes the cloud and evaporates its outer layers in a wind. The dust grains are sputtered in this hot ( T ≥ 10 6 K) wind. We show that the cloud evaporation time is comparable to the radial drift time of clouds in the torus, but longer than the orbital time. The clouds produce line emission typical of highly ionized gas. Dust opacity prevents the torus line emission from overpowering the broad and narrow line regions, however the torus may be the source of the coronal lines seen in some AGN.

The dust destruction timescales in the cores of clusters of galaxies are relatively short given their high central gas densities. However, substantial mid-infrared and sub-mm emission has been detected in many brightest cluster galaxies. In this letter we present Herschel PACS and SPIRE photometry of the brightest cluster galaxy in three strong cooling flow clusters, A1068, A2597 and Zw3146. This photometry indicates that a substantial mass of cold dust is present (>3 x 10^7 Mo) at temperatures significantly lower (20-28K) than previously thought based on limited MIR and/or sub-mm results. The mass and temperature of the dust appear to match those of the cold gas traced by CO with a gas-to-dust ratio of 80-120., Accepted for A&A Herschel Special Issue, 7 pages, 3 figures

Recent measurements of the Sunyaev-Zel'dovich (SZ) angular power spectrum from the South Pole Telescope (SPT) and the Atacama Cosmology Telescope (ACT) demonstrate the importance of understanding baryon physics when using the SZ power spectrum to constrain cosmology. This is challenging since roughly half of the SZ power at l=3000 is from low-mass systems with 10^13 h^-1 M_sun < M_500 < 1.5x10^14 h^-1 M_sun, which are more difficult to study than systems of higher mass. We present a study of the thermal pressure content for a sample of local galaxy groups from Sun et al. (2009). The group Y_{sph, 500} - M_500 relation agrees with the one for clusters derived by Arnaud et al. (2010). The group median pressure profile also agrees with the universal pressure profile for clusters derived by Arnaud et al. (2010). With this in mind, we briefly discuss several ways to alleviate the tension between the measured low SZ power and the predictions from SZ templates., 5 pages, 2 color figures, ApJL in press

The question of how much gas cools in the cores of clusters of galaxies has been the focus of many, multiwavelength studies in the past 30 years. In this letter we present the first detections of the strongest atomic cooling lines, [C II], [O I] and [N I] in two strong cooling flow clusters, A1068 and A2597, using Herschel PACS. These spectra indicate that the substantial mass of cold molecular gas (>10^9 Mo) known to be present in these systems is being irradiated by intense UV radiation, most probably from young stars. The line widths of these FIR lines indicate that they share dynamics similar but not identical to other ionised and molecular gas traced by optical, near-infrared and CO lines. The relative brightness of the FIR lines compared to CO and FIR luminosity is consistent with other star-forming galaxies indicating that the properties of the molecular gas clouds in cluster cores and the stars they form are not unusual. These results provide additional evidence for a reservoir of cold gas that is fed by the cooling of gas in the cores of the most compact clusters and provide important diagnostics of the temperature and density of the dense clouds this gas resides in., Accepted for the A&A Herschel Special Issue, 5 pages, 2 figures

(Abridged) We examine the radial entropy distribution and its scaling using 31 nearby galaxy clusters from the Representative XMM-Newton Cluster Structure Survey (REXCESS). The entropy profiles are robustly measured at least out to R_1000 in all systems and out to R_500 in 13 systems. Compared to theoretical expectations, the observed distributions show a radial and mass-dependent excess entropy that is greater and extends to larger radii in lower mass systems. At R_500, the mass dependence and entropy excess are both negligible within the uncertainties. Mirroring this behaviour, the scaling of gas entropy is shallower than self-similar in the inner regions, but steepens with radius, becoming consistent with self-similar at R_500. The dispersion in scaled entropy in the inner regions is linked to the presence of cool cores and dynamical activity; at larger radii the dispersion decreases by a factor of two and the dichotomy between subsamples disappears. Parameterising the profiles with a power law plus constant model, there are two peaks in central entropy K_0; however, we cannot distinguish between a bimodal or a left-skewed distribution. The outer slopes are correlated with system temperature; their distribution is unimodal with a median value of 0.98. Renormalising the dimensionless entropy profiles by the gas mass fraction profile f_gas(< R), leads to a remarkable reduction in the scatter, implying that gas mass fraction variations with radius and mass are the cause of the observed entropy properties. We discuss a tentative scenario to explain the behaviour of the entropy and gas mass fraction in the REXCESS sample, in which extra heating and merger mixing maintains an elevated central entropy level in the majority of the population, and a smaller fraction of systems develops a cool core., 14 pages, 9 figures, A&A, in press. Final version corrects Eqn. 3 and columns 5-8 in Table 1 and has additional minor text clarifications

Infrared spectra of dusty galactic environments often contain emission features attributed to polycyclic aromatic hydrocarbons or PAHs, which can be considered to be very small grains or very large molecules. Although IR spectra of starburst galaxies almost always show these emission features, similar spectra of active galaxies are usually featureless. Even in those active galaxies that do exhibit PAH emission, the PAHs still appear to be eradicated from the nuclear region. This dichotomy suggests that PAHs are destroyed by the intense hard radiation field from an AGN. Laboratory experiments show that certain PAHs are, in fact, so effectively destroyed by individual EUV and X-ray photons that they cannot survive even at kiloparsec distances from active nuclei. Regions within active galaxies that do show PAH emission must therefore be shielded from the central X-ray source by a substantial column density of X-ray absorbing gas.

We present the discovery of spectacular double X-ray tails associated with ESO137-001 and a possibly heated X-ray tail associated with ESO137-002, both late-type galaxies in the closest rich cluster Abell 3627. A deep Chandra observation of ESO137-001 allows us for the first time to examine the spatial and spectral properties of such X-ray tails in detail. Besides the known bright tail that extends to ~ 80 kpc from ESO137-001, a fainter and narrower secondary tail with a similar length was surprisingly revealed. There is little temperature variation along both tails. We also identified six X-ray point sources as candidates of intracluster ULXs with L(0.3-10 keV) of up to 2.5x10^40 erg s^-1. Gemini spectra of intracluster HII regions downstream of ESO137-001 are also presented, as well as the velocity map of these HII regions that shows the imprint of ESO137-001's disk rotation. For the first time, we unambiguously know that active star formation can happen in the cold ISM stripped by ICM ram pressure and it may contribute a significant amount of the intracluster light. We also report the discovery of a 40 kpc X-ray tail of another late-type galaxy in A3627, ESO137-002. Its X-ray tail seems hot, ~ 2 keV (compared to ~ 0.8 keV for ESO137-001's tails). We conclude that the high pressure environment around these two galaxies is important for their bright X-ray tails and the intracluster star formation., ApJ in press, January 2010, v708, only several minor word changes, emulateapj5.sty, 24 pages, 11 color + 5 B/W figures (figure quality degraded) and 4 tables. The abstract has been abbreviated. A high-resolution PDF is available at: http://www.astro.virginia.edu/~ms4ar/eso137_p3.pdf

Current models of galaxy evolution suggest that feedback from active galactic nuclei is needed to explain the high-luminosity cutoff in the galaxy luminosity function. Exactly how an AGN outflow couples with the ambient medium and suppresses star formation remains poorly understood. However, we have recently uncovered an important clue to how that coupling might work. Observations of H-alpha emission and blue light from the universe's most luminous galaxies, which occupy the centers of galaxy clusters, show that star formation happens only if the minimum specific entropy of the intracluster gas is less than 30 keV cm^2. Here we suggest that this threshold for star formation is set by the physics of electron thermal conduction, implying that conduction is critical for channeling AGN energy input toward incipient star-forming regions and limiting the progress of star formation., Accepted to ApJ Letters, 5 pages, 4 figures

It is now generally acknowledged that gas at the centers of galaxy clusters with short central cooling times is not simply cooling, flowing toward the center, and condensing. Some sort of heat source must replenish much of the thermal energy radiated by the gas in the cores of those clusters, and the active galactic nucleus at the center of the brightest cluster galaxy seems like the likeliest source of energy. Whatever the energy source is, it must leave an imprint on the entropy structure of the intracluster medium. In search of that imprint we have measured the radial entropy profiles of some classic cooling-flow clusters and have found a remarkable degree of regularity among them. They asymptotically approach a pure-cooling profile at ∼ 100 kpc but depart from the pure-cooling profile within 10-20 kpc of the cluster center, at an entropy scale of ∼ 10 keV cm2. Any model purporting to explain why the core gas does not simply cool and condense must explain these features of the core entropy profiles. A simple episodic feedback model can account for the observed profiles with outbursts of ∼ 1045 erg s-1 occurring on a ∼100 Myr timescale. At radii < 30 kpc these outbursts would deposit heat primarily through shocks. Rising bubbles would dominate the heat deposition at larger radii.

We use hydrodynamical simulations of galaxy clusters and groups to study the effect of pre-heating on the entropy structure of the ICM. Our simulations account for non-gravitational heating of the gas either by imposing a minimum entropy floor at redshift z=3, or by considering feedback by galactic winds powered by supernova (SN) energy. In the adiabatic simulations we find that the entropy is increased out to the external regions as a consequence of the transition from clumpy to smooth accretion induced by extra heating. This result is in line with the predictions of the semi-analytical model by Voit et al. However, the introduction of radiative cooling substantially reduces this entropy amplification effect. While galactic winds of increasing strength are effective in regulating star formation, they have a negligible effect on the entropy profile of cluster-sized halos. Only in models where the action of the winds is complemented with diffuse heating corresponding to a pre-collapse entropy do we find a sizable entropy amplification out to the virial radius of the groups. Observational evidence for entropy amplification in the outskirts of galaxy clusters and groups therefore favours a scenario for feedback that distributes heating energy in a more diffuse way than predicted by the model for galactic winds from SN explosions explored here., Comment: 12 pages, 7 figures to appear in MNRAS. Full resolution preprint available at http://adlibitum.oat.ts.astro.it/clustersim/EntrAmpl/borgani_2.ps.gz

PRIME (The Primordial Explorer) is a proposed Explorer-class mission. Aimed at the “first light” in the Universe, it will carry out a deep sky survey from space in four near-infrared bands between ~1-3.5 P ,W VXUYH\V D TXDUWHU RI WKHsky to AB magnitude of ~24, which is ~600 times deeper than 2MASS and ~ five million times deeper than COBE at long wavelengths. Deeper surveys in selected sky regions are also planned. PRIME will reach an epoch during which the first quasars, galaxies and clusters of galaxies were formed in the early universe, map the large-scale structure of the dark matter, discover Type-Ia supernovae to be used in measuring the acceleration of the expanding universe, and detect thousands of brown dwarfs and even Jupiter-size planets in the vicinity of the solar system. Most of these objects are so rare that they may be identified only in large and deep surveys. PRIME will serve as the precursor for the Next Generation Space Telescope ( NGST ), supplying rare targets for its spectroscopy and deep imaging. It is more than capable of providing targets for the largest ground-based telescopes (10-30m). Combining PRIME with other surveys (SDSS, GALEX) will yield the largest astronomical database ever built. Keywords: survey, galaxy, quasar

Of the many novel coronagraphic and nulling techniques that have been suggested to improve image contrast for exoplanet detection, one of the most promising is the Quadrant Phase Mask suggested by Rouan et al. Analysis of this optical system has previously been performed by discrete Fourier transform methods, that result in systematic errors due to the implicit assumptions of the methods and mathematical singularities in the transform of the phase mask. In this paper, we describe an analytical treatment of this optical system that treats these singularities explicitly. We calculate the leakage of a Quadrant Phase Mask Coronagraph with these analytical techniques, and show that a Quadrant Phase Mask rejects all on-axis light for an unaberrated, unobscured circular aperture and is therefore a nearly perfect coronagraph. We demonstrate why the Quadrant Phase Mask coronagraph suffers degraded performance with an obscured aperture, and propose modifications to the pupil geometry to mitigate this problem.

Evolution of the cluster temperature function is extremely sensitive to the mean matter density of the universe. Current measurements based on cluster temperature surveys indicate that Omega_M ~ 0.3 with a 1-sigma statistical error ~0.1, but the systematic errors in this method are of comparable size. Many more high-z cluster temperatures will be arriving from Chandra and XMM in the near future. In preparation for future cluster temperature surveys, this paper analyses the cluster mass-temperature relation, with the intention of identifying and reducing the systematic errors it introduces into measurements of cosmological parameters. We show that the usual derivation of this relation from spherical top-hat collapse is physically inconsistent and propose a more realistic derivation based on a hierarchical merging model that more faithfully reflects the gradual ceasing of cluster evolution in a low-Omega_M universe. We also analyze the effects of current systematic uncertainties in the M-T relation and show that they introduce a systematic uncertainty of ~0.1 in the best-fitting Omega_M. Future improvements in the accuracy of the M-T relation will most likely come from comparisons of predicted cluster temperature functions with temperature functions derived directly from large-scale structure simulations., Comment: 29 pages, 5 figures, to appear in Nov 20, 2000 ApJ

The close correlation between cooling flows and emission-line nebulae in clusters of galaxies has been recognized for over a decade and a half, but the physical reason for this connection remains unclear. Here we present deep optical spectra of the nebula in Abell 2597, one of the nearest strong cooling-flow clusters. These spectra reveal the density, temperature, and metal abundances of the line-emitting gas. The abundances are roughly half-solar, and dust produces an extinction of at least a magnitude in V. The absence of [O III] 4363 emission rules out shocks as a major ionizing mechanism, and the weakness of He II 4686 rules out a hard ionizing source, such as an active galactic nucleus or cooling intracluster gas. Hot stars are therefore the best candidate for producing the ionization. However, even the hottest O stars cannot power a nebula as hot as the one we see. Some other nonionizing source of heat appears to contribute a comparable amount of power. We show that the energy flux from a confining medium can become important when the ionization level of a nebula drops to the low levels seen in cooling-flow nebulae. We suggest that this kind of phenomenon, in which energy fluxes from the surrounding medium augment photoelectric heating, might be the common feature underlying the diverse group of objects classified as LINERS., 33 Latex pages, including 16 Postscript figures, to appear in 1997 September 1 Astrophysical Journal

IR interferometers operating at 2 – 20 µm. over ∼ 100 m baselines will be ideally suited to probing the interfaces between active galactic nuclei and their host galaxies. When these devices become operational, they will tell us how quasars generate infrared light and will clarify the relationships between the powerful black-hole engines at the centers of galaxies and the surrounding bursts of star formation.

We present the analysis of a deep Chandra observation of a ~2L_* late-type galaxy, ESO 137-002, in the closest rich cluster A3627. The Chandra data reveal a long (>40 kpc) and narrow tail with a nearly constant width (~3 kpc) to the southeast of the galaxy, and a leading edge ~1.5 kpc from the galaxy center on the upstream side of the tail. The tail is most likely caused by the nearly edge-on stripping of ESO 137-002's ISM by ram pressure, compared to the nearly face-on stripping of ESO 137-001 discussed in our previous work. Spectral analysis of individual regions along the tail shows that the gas throughout it has a rather constant temperature, ~1 keV, very close to the temperature of the tails of ESO 137-001, if the same atomic database is used. The derived gas abundance is low (~0.2 solar with the single-kT model), an indication of the multiphase nature of the gas in the tail. The mass of the X-ray tail is only a small fraction (

Imaging of NGC 7469 in the J, H, & K bands shows that the starburst ‘ring’ is a tight inner spiral with arms that extend 4″ NW and SE from the nucleus, as well as distinct infrared hotspots associated with the radio continuum sources. Imaging in the 3.28 µm dust emission feature shows extended PAH emission that is roughly aligned with published 12.5 µm continuum emission (PA75°), consistent with small dust grains heated by vigorous star formation in the inner spiral.

The radial distributions of temperature, density, and gas entropy among cool-core clusters tend to be quite similar, suggesting that they have entered a quasi-steady state. If that state is regulated by a combination of thermal conduction and feedback from a central AGN, then the characteristics of those radial profiles ought to contain information about the spatial distribution of AGN heat input and the relative importance of thermal conduction. This paper addresses those topics by deriving steady-state solutions for clusters in which radiative cooling, electron thermal conduction, and thermal feedback fueled by accretion are all present, with the aim of interpreting the configurations of cool-core clusters in terms of steady-state models. It finds that the core configurations of many cool-core clusters have entropy levels just below those of conductively balanced solutions in which magnetic fields have suppressed electron thermal conduction to ~1/3 of the full Spitzer value, suggesting that AGN feedback is triggered when conduction can no longer compensate for radiative cooling. And even when feedback is necessary to heat the central ~30 kpc, conduction may still be the most important heating mechanism within a cluster's central ~100 kpc., ApJ in press, 13 pages, 5 figures

High resolution near-infrared images of the type 1 Seyfert galaxy NGC 7469 have been obtained to probe its dusty nuclear environment. Direct J, H, and K images are relatively featureless, but residual images created by subtracting a smooth model based on best-fitting elliptical isophotes reveal a tight inner spiral whose high surface-brightness portions correspond to a previously detected 3 sec (1 kpc) diameter ring of radio continuum emission. The inner infrared spiral arms extended approximately equal to 4 sec NW and SE from the nucleus, and the NW arm joins up with large-scale spiral structure visible in the R band. The residual images also show a bar-like structure aligned with the brightest infrared/radio hotspots at PA approximately equal to 50 deg. Three infrared hotspots are detected which align remarkably well with 6 cm radio continuum sources. The near-infrared ring and the hotspots are visible in the residual images, and in a high-resolution direct K-band image restored to an effective resolution of 0.65 sec (FWHM) using the Richardson-Lucy algorithm. The infrared hotspots have luminosities of nuL(sub nu) (2.2 micrometer(s)) approximately equal to 10(exp 8) solar luminosity (M(sub k) approximately equal to -16 mag), suggesting they are either giant H II regions or individual supernovae. The two brightest regions may be associated with enhanced star formation triggered by orbit crowding of gas where spiral arms emerge from an inner bar. Narrowband (delta lambda/lambda approximately 1.5%) imaging in the 3.28 micrometer(s) dust emission feature and surrounding continuum confirms the 3 sec diameter 3.28 micrometer(s) emission region detected previously using multiaperture photometry. The extended polycyclic aromatic hydrocarbon (PAH) emission is slightly elongated and aligned with published 1O III1 line emission and 12.5 micrometer(s) continuum emission, apparently tracing the starburst. The presence of approximately equal to 25% of the total 3.28 micrometer(s) PAH emission within R less than 1 sec demonstrates that a starburst within the central few hundred parsecs must supply a significant fraction of the infrared continuum from the nucleus, and there is apparently sufficient shielding material between the starburst and the active galactic nucleus (AGN) to preserve the PAHs along our line of sight to the nucleus.

In a previous comparative study by Weymann et al. of the emission line and continuum properties of radio-quiet QSOs and broad absorption-line (BAL) QSOs, a difference spectrum, in the region of the C IV λ1549 trough, comprising the mean spectrum of 34 BALQSOs and the mean spectrum of 31 non-BALQSOs, surprisingly revealed double troughs separated in velocity space by the N v λ1240-Lyα splitting of ~ 5900 km s^(-1). In this contribution we investigate the reality of these features in a spectroscopic sample of72 BALQSOs consisting of the original 34 BALQSOs and an additional 38 BALQSOs. An atlas of the C IV BALs of72 BALQSOs is presented. We find that only 22% of this sample explicitly exhibits the double trough feature. When present the double troughs are deep. A Monte Carlo simulation of the mean C IV BAL suggests that the double-trough feature is real at only the 95%-98% level (as opposed to being the result of statistical fluctuations of BAL troughs occurring over random outflow velocities in a limited sample). We describe possible scenarios for their formation, involving the line-locking of Lyα-Nv within the BAL region. We show that no simple mechanism involving radiation pressure, alone can create the deep double troughs through the shadowing of N v λ1240 by Lyα. More complicated amplification mechanisms may be necessary. If real, the double-trough signature has the following important implications to our understanding of the BAL phenomenon: (1) The occurrence of broad absorption is somehow tied to an absolute velocity frame which is the same from quasar to quasar. (2) It follows then that the outflowing material within the BAL region is accelerating. (3) If line-locking is the mechanism behind the formation of the double troughs, then radiation pressure plays an important role in the dynamics of the BAL region.

We present upper limits on the forbidden Ca II 7291 A flux from emission-line nebulae in cluster cooling flows. The observed lack of forbidden Ca II emission indicates that gas-phase calcium is underabundant in cooling-flow nebulae and is most likely depleted onto dust grains. If calcium in the line-emitting filaments is largely bound into dust, then these filaments probably did not condense out of the hot intracluster gas.

The absorption line properties of six Mg II broad absorption line quasars (BALQs) are examined using a BALQ sample of Weymann et al. (1991). It is found that Al III absorption is always stronger than Al II absorption; C IV absorption tends to be very deep and broad; and low ionization absorption tends to be narrower and lie at the low velocity end of the C IV trough. The results indicate that the outflows in Mg II BALQs are not accelerating monotonically. It is shown that a hot cloud-confining outflow can be decelerated by adding thick absorbing clouds provided the ionization parameters of these clouds are high. It is argued that the MG II BALQ phenomenon might be a manifestation of a quasar's efforts to expel a thick shroud of gas and dust.

The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H-beta in luminosity. We show how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of Ne v emission in particular will distinguish shrouded AGNs from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

The detailed predictions of a photoionization model previously outlined in Voit and Donahue (1990) to explain the optical line emission associated with cooling flows in X-ray emitting clusters of galaxies are presented. In this model, EUV/soft X-ray radiation from condensing gas photoionizes clouds that have already cooled. The energetics and specific consequences of such a model, as compared to other models put forth in the literature is discussed. Also discussed are the consequences of magnetic fields and cloud-cloud shielding. The results illustrate how varying the individual column densities of the ionized clouds can reproduce the range of line ratios observed and strongly suggest that the emission-line nebulae are self-irradiated condensing regions at the centers of cooling flows.

A fundamental physical study of grains heated transiently by X-rays is presented. The X-ray photoionization cross sections used to determine the rate of energy deposition into the grains are given. A grain model is constructed and the radiative and evaporative responses of grains into X-ray absorption are described. The basic theory of stochastic grain heating is outlined, and analytical expressions for the temperature distributions of flickering grains are provided. The resulting IR spectra due to X-ray illumination are given, and the relevance of the present work to the IR continua of active galaxies is discussed. The present model provides two observational predictions: the infrared spectra of grains, even if they are superheated, should show a cutoff between 1 and 3 microns; and X-ray-illuminated environments should exhibit no PAH emissions.

The deposition of energy by 100-10,000 eV electrons into molecular hydrogen and helium gas of cosmic abundances and fractional ionization ranging from 10 to the -12th to 0.1 is considered. In order to account for energy deposition by both discrete and continuous degradation processes, the loss spectrum, a form of the Spencer-Fano degradation spectrum particularly suited to describing electron energy deposition in a partially ionized gas is considered. The calculated excitation and ionization yields drop as the fractional ionization increases. The dependences of these yields on fractional ionization are fitted to a form suitable for swift numerical computation.

In order to explore how supernova blast waves might catalyze star formation, we investigate the stability of a slab of decelerating gas of finite thickness. We examine the early work in the field by Elmegreen and Lada and Elmegreen and Elmegreen and demonstrate that it is flawed. Contrary to their claims, blast waves can indeed accelerate the rate of star formation in the interstellar medium. Also, we demonstrate that in an incompressible fluid, the symmetric and antisymmetric modes in the case of zero acceleration transform continuously into Rayleigh-Taylor and gravity-wave modes as acceleration grows more important.

In order to study how supernova blast waves might catalyze star formation, the stability of a slab of decelerating gas of finite thickness is explored. Previous analyses are extended by applying shock-like boundary conditions to the leading edge of the slab and by studying the effects of arbitrary deceleration. Contrary to some earlier claims, it is found that blast waves can indeed accelerate the rate of star formation in the interstellar medium by compressing the interstellar gas and enabling it to cool. Also, it is demonstrated that in an incompressible fluid, the symmetric and antisymmetric modes in the case of zero acceleration transform continuously into Rayleigh-Taylor and gravity-wave modes as acceleration grows more important. The dynamical overstability of an isothermal shock wave and its implications for star formation are discussed.