X-ray Isophotes in a Rapidly Rotating Elliptical Galaxy: Evidence of Inflowing Gas

We describe two-dimensional gasdynamical computations of the X-ray emitting gas in the rotating elliptical galaxy NGC 4649 that indicate an inflow of about one solar mass per year at every radius. Such a large instantaneous inflow cannot have persisted over a Hubble time. The central constant-entropy temperature peak recently observed in the innermost 150 parsecs is explained by compressive heating as gas flows toward the central massive black hole. Since the cooling time of this gas is only a few million years, NGC 4649 provides the most acutely concentrated known example of the cooling flow problem in which the time-integrated apparent mass that has flowed into the galactic core exceeds the total mass observed there. This paradox can be resolved by intermittent outflows of energy or mass driven by accretion energy released near the black hole. Inflowing gas is also required at intermediate kpc radii to explain the ellipticity of X-ray isophotes due to spin-up by mass ejected by stars that rotate with the galaxy and to explain local density and temperature profiles. We provide evidence that many luminous elliptical galaxies undergo similar inflow spin-up. A small turbulent viscosity is required in NGC 4649 to avoid forming large X-ray luminous disks that are not observed, but the turbulent pressure is small and does not interfere with mass determinations that assume hydrostatic equilibrium.Comment: 21 pages, 9 figures, accepted for publication by Ap

Hydrostatic Gas Constraints On Supermassive Black Hole Masses: Implications For Hydrostatic Equilibrium And Dynamical Modeling In A Sample Of Early-Type Galaxies

We present new mass measurements for the supermassive black holes (SMBHs) in the centers of three early-type galaxies. The gas pressure in the surrounding, hot interstellar medium (ISM) is measured through spatially resolved spectroscopy with the Chandra X-ray Observatory, allowing the SMBH mass (M(BH)) to be inferred directly under the hydrostatic approximation. This technique does not require calibration against other SMBH measurement methods and its accuracy depends only on the ISM being close to hydrostatic, which is supported by the smooth X-ray isophotes of the galaxies. Combined with results from our recent study of the elliptical galaxy NGC4649, this brings the number of galaxies with SMBHs measured in this way to four. Of these, three already have mass determinations from the kinematics of either the stars or a central gas disk, and hence join only a handful of galaxies with MBH measured by more than one technique. We find good agreement between the different methods, providing support for the assumptions implicit in both the hydrostatic and the dynamical models. The stellar mass-to-light ratios for each galaxy inferred by our technique are in agreement with the predictions of stellar population synthesis models assuming a Kroupa initial mass function (IMF). This concurrence implies that no more than similar to 10%-20% of the ISM pressure is nonthermal, unless there is a conspiracy between the shape of the IMF and nonthermal pressure. Finally, we compute Bondi accretion rates (M(bondi)), finding that the two galaxies with the highest M(bondi) exhibit little evidence of X-ray cavities, suggesting that the correlation with the active galactic nuclei jet power takes time to be established.NASA NAS5-26555, NNG04GE76G, G07-8083XAstronom

AGN Feedback in Galaxy Groups: the two interesting cases of AWM 4 and NGC 5044

We present AGN feedback in the interesting cases of two groups: AWM 4 and NGC 5044. AWM 4 is characterized by a combination of properties which seems to defy the paradigm for AGN heating in cluster cores: a flat inner temperature profile indicative of a past, major heating episode which completely erased the cool core, as testified by the high central cooling time (> 3 Gyrs) and by the high central entropy level (~ 50 keV cm^2), and yet an active central radio galaxy with extended radio lobes out to 100 kpc, revealing recent feeding of the central massive black hole. A recent Chandra observation has revealed the presence of a compact cool corona associated with the BCG, solving the puzzle of the apparent lack of low entropy gas surrounding a bright radio source, but opening the question of its origin. NGC 5044 shows in the inner 10 kpc a pair of cavities together with a set of bright filaments. The cavities are consistent with a recent AGN outburst as also indicated by the extent of dust and H_alpha emission even though the absence of extended 1.4 GHz emission remains to be explained. The soft X-ray filaments coincident with H_alpha and dust emission are cooler than those which do not correlate with optical and infrared emission, suggesting that dust-aided cooling can contribute to the overall cooling. For the first time sloshing cold fronts at the scale of a galaxy group have been observed in this object.Comment: 4 pages, 1 figure, to appear in proceedings of the conference "The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", June 2009, Madison Wisconsi

Time-dependent Circulation Flows: Iron Enrichment in Cooling Flows with Heated Return Flows

We describe a new type of dynamical model for hot gas in galaxy groups and clusters in which gas moves simultaneously in both radial directions. Circulation flows are consistent with (1) the failure to observe cooling gas in X-ray spectra, (2) multiphase gas observed near the centers of these flows and (3) the accumulation of iron in the hot gas from Type Ia supernovae in the central galaxy. Dense inflowing gas cools, producing a positive central temperature gradient, as in normal cooling flows. Bubbles of hot, buoyant gas flow outward. Circulation flows eventually cool catastrophically if the outward flowing gas transports mass but no heat; to maintain the circulation both mass and energy must be supplied to the inflowing gas over a large volume, extending to the cooling radius. The rapid radial recirculation of gas produces a flat central core in the gas iron abundance, similar to many observations. We believe the circulation flows described here are the first gasdynamic, long-term evolutionary models that are in good agreement with all essential features observed in the hot gas: little or no gas cools as required by XMM spectra, the gas temperature increases outward near the center, and the gaseous iron abundance is about solar near the center and decreases outward.Comment: 17 pages (emulateapj5) with 6 figures; accepted by The Astrophysical Journa

ALMA observations of molecular clouds in three group centered elliptical galaxies: NGC 5846, NGC 4636, and NGC 5044

We present new ALMA CO(2--1) observations of two well studied group-centered elliptical galaxies: NGC~4636 and NGC~5846. In addition, we include a revised analysis of Cycle 0 ALMA observations of the central galaxy in the NGC~5044 group that has been previously published. We find evidence that molecular gas, in the form of off-center orbiting clouds, is a common presence in bright group-centered galaxies (BGG). CO line widths are $\gtrsim 10$ times broader than Galactic molecular clouds, and using the reference Milky Way $X_{CO}$, the total molecular mass ranges from as low as $2.6\times 10^5 M_\odot$ in NGC~4636 to $6.1\times 10^7 M_\odot$ in NGC~5044. With these parameters the virial parameters of the molecular structures is $\gg 1$. Complementary observations of NGC~5846 and NGC~4636 using the ALMA Compact Array (ACA) do not exhibit any detection of a CO diffuse component at the sensitivity level achieved by current exposures. The origin of the detected molecular features is still uncertain, but these ALMA observations suggest that they are the end product of the hot gas cooling process and not the result of merger events. Some of the molecular clouds are associated with dust features as revealed by HST dust extinction maps suggesting that these clouds formed from dust-enhanced cooling. The global nonlinear condensation may be triggered via the chaotic turbulent field or buoyant uplift. The large virial parameter of the molecular structures and correlation with the warm ($10^3 - 10^5 K$)/hot ($\ge10^6$) phase velocity dispersion provide evidence that they are unbound giant molecular associations drifting in the turbulent field, consistently with numerical predictions of the chaotic cold accretion process. Alternatively, the observed large CO line widths may be generated by molecular gas flowing out from cloud surfaces due to heating by the local hot gas atmosphere.Comment: Revised version to be published in ApJ, 16 pages, 10 figures, 4 table

Ultra-Low Iron Abundances in Distant Hot Gas in Galaxy Groups

A new XMM observation of the outer regions of the galaxy group NGC 5044 indicates hot gas iron abundances of only ~0.15 solar between r=0.2 - 0.4 r_vir. While the total baryon mass within the virial radius may be close to the cosmic mean value observed in rich clusters, the ratio of total iron mass to optical light in NGC 5044 is about 3 times lower than that in rich clusters. The remarkably low iron abundance over a large volume of the intergroup gas in the outer regions of NGC 5044 cannot be easily understood in terms of the outflow of enriched gas in a group wind during its early history or by the long term enrichment by the group member galaxies that currently occupy this region. It is possible that the stars in NGC 5044 did not produce iron with the same efficiency as in clusters, or the iron resides in non-luminous clouds or stars, or the entropy of the iron-enriched gas created in early galactic starburst winds was too high to penetrate the group gas of lower entropy.Comment: 4 pages, 2 figures, To Appear in ApJ Letter

Baryonically Closed Galaxy Groups

Elliptical galaxies and their groups having the largest L_x/L_B lie close to the locus in the L_x,L_B diagram expected for closed systems with baryon fractions equal to the cosmic mean value, f_b = 0.16. The estimated baryon fractions for several of these galaxies/groups are also close to 0.16 when the gas density is extrapolated to the virial radius. Evidently they are the least massive baryonically closed systems. Gas retention in these groups implies that non-gravitational heating cannot exceed about 1 keV per particle, consistent with the heating required to produce the deviation of groups from the L_x - T correlation for more massive clusters. Isolated galaxies/groups with X-ray luminosities significantly lower than baryonically closed groups may have undermassive dark halos, overactive central AGNs, or higher star formation efficiencies. The virial mass and hot gas temperatures of nearly or completely closed groups correlate with the group X-ray luminosities and the optical luminosities of the group-centered elliptical galaxy, an expected consequence of their merging history. The ratio of halo mass to the mass of the central galaxy for X-ray luminous galaxy/groups is about 80.Comment: 7 pages; Accepted by ApJ Letter

Utilizing NVIDIA GPUs for Waveform Analysis for the Nab Experiment

GPUs are composed of a large number of small computational cores compared to CPUs which are generally just a few larger cores. While the CPU excels at linear processes, the GPU excels at parallel tasks. For this project, the goal was to find a way to use the massive parallelism of a GPU to rapidly analyze waveform data from the Nab experiment

The X-Ray Concentration-Virial Mass Relation

We present the concentration (c)-virial mass (M) relation of 39 galaxy systems ranging in mass from individual early-type galaxies up to the most massive galaxy clusters, (0.06-20) x 10^{14} M_sun. We selected for analysis the most relaxed systems possessing the highest quality data currently available in the Chandra and XMM public data archives. A power-law model fitted to the X-ray c-M relation requires at high significance (6.6 sigma) that c decreases with increasing M, which is a general feature of CDM models. The median and scatter of the c-M relation produced by the flat, concordance LCDM model (Omega_m=0.3, sigma_8=0.9) agrees with the X-ray data provided the sample is comprised of the most relaxed, early forming systems, which is consistent with our selection criteria. Holding the rest of the cosmological parameters fixed to those in the concordance model the c-M relation requires 0.76< sigma_8 <1.07 (99% conf.), assuming a 10% upward bias in the concentrations for early forming systems. The tilted, low-sigma_8 model suggested by a new WMAP analysis is rejected at 99.99% confidence, but a model with the same tilt and normalization can be reconciled with the X-ray data by increasing the dark energy equation of state parameter to w ~ -0.8. When imposing the additional constraint of the tight relation between sigma_8 and Omega_m from studies of cluster abundances, the X-ray c-M relation excludes (>99% conf.) both open CDM models and flat CDM models with Omega_m ~1. This result provides novel evidence for a flat, low-Omega_m universe with dark energy using observations only in the local (z << 1) universe. Possible systematic errors in the X-ray mass measurements of a magnitude ~10% suggested by CDM simulations do not change our conclusions.Comment: Accepted for Publication in ApJ; 13 pages, 4 figures; minor clarifications and updates; correlation coefficients corrected in Table 1 (correct values were used in the analysis in previous versions); conclusions unchange

Erosion and Repair of Unlined Spillway Chute Excavated in Rock

Discharges up to 60,000 cfs that lasted 21 days caused extensive erosion of the unlined spillway chute excavated in alternating layers of limestone and shale. An empirical model allowed to evaluate the extent of erosion anticipated for future events. Parametric calculations showed that relatively low discharges a long period of time are critical for the induced damage. It was determined that the spillway can safely pass the design discharge if weathering of rock exposed by erosion is prevented. Accordingly, the interim repair was designed to protect the rock units, especially the critical limestone layers, from weathering. Although it is expected much of the repair to be eroded during future spillway flows, it will ensure the spillway can safely pass the next discharge event