arXiv subjects

B. R. McNamara

Publications and source records attributed to B. R. McNamara.

At least 19 recordsLinked to original sources

arXiv2026

Gas Motions in Hydra-A: XRISM Constraints on ICM Kinematics Across Jet-Inflated Cavities

We report on two deep XRISM observations of the central and northern regions of Hydra-A's X-ray atmosphere covering the bubbles inflated by jets from the central galaxy's active galactic nucleus (AGN). We use spatial-spectral mixing that combines Chandra's high spatial resolution with XRISM's high spectral resolution to investigate atmospheric kinematics. The atmospheric velocity dispersion in the northern region, $σ_v = 140^{+30}_{-20}$ km s$^{-1}$, is comparable to that in the central region ($σ_v = 162 \pm 10$ km s$^{-1}$). We show that the motion of the large-scale cocoon shock front could be responsible for the large dispersion toward the north. The velocity dispersion in the northeast quarter of the central pointing, $σ_v = 260 \pm 50$ km s$^{-1}$, is among the highest dispersions measured. This region contains an X-ray-bright feature previously identified as metal-rich, possibly consisting of gas uplifted in the wake of previous-generation cavities. The dispersions in all other quarter regions are low ($σ_v \leq 120$ km s$^{-1}$) and consistent with previous XRISM results from other objects. The kinetic energy at the center is comparable to the enthalpies of the cavities, while in the north, it is roughly an order of magnitude smaller. The jet thus drives gas motion efficiently at smaller scales ($r < 95$ kpc) and inefficiently at larger scales ($95-317$ kpc toward the north along the jet). A bulk flow toward our line of sight of $-100 \pm 30$ km s$^{-1}$ in the southwest quarter of the central pointing is also observed, possibly due to sloshing.

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arXiv2026

Star Formation Histories and Stellar Dynamics in the Central Galaxies of RX J0820.9+0752, A1835, and PKS 0745-191

We present Keck Cosmic Web Imager observations of stellar populations in three galaxies lying at the centers of cooling flow clusters. All three host rich molecular gas reservoirs and show prominent Balmer absorption from $30-100$ Myr-old stars consistent with long lasting star formation. Two systems, A1835 and PKS 0745$-$191, have spatially extended young stellar populations in their centers with recent star formation rates of 100 M$_{\odot}$ yr$^{-1}$ and 8 M$_{\odot}$ yr$^{-1}$, respectively. In A1835 we uncover a blueshifted clump of young stars moving at high speed with respect to the gas and central galaxy. We suggest these stars formed in a gaseous outflow and have since detached from their natal gas and are now falling inward. This result indicates that star formation is proceeding in a dynamically complex environment shaped by the central galaxy's motion relative to cooling clouds and the feedback from radio jets. In RX J0820.9+0752 intermediate-age stars are found in a filament outside the nucleus with no discernible star formation at the center of the galaxy. All projected galaxies consist of old stellar populations with deep D4000 breaks and lack detectable warm gas. While they may interact gravitationally with the central galaxy, they cannot have donated the upward of $10^{10}~ M_{\odot}$ of molecular gas found in these systems. These results highlight the importance of analyzing spatially resolved stellar kinematics and star formation histories in brightest cluster galaxies, an approach that remains relatively understudied.

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arXiv2026

XRISM detection of the 6.4 keV Fe K$α$ line in the radio galaxy Cygnus A

We detail the spectral analysis of a 170 ks XRISM Resolve observation of the core of Cygnus A. The high spectral resolution of Resolve have enabled us to probe the inner accretion region of Cygnus A by analyzing the 6.4 keV Fe K$α$ line complex. We find that it consists of two Keplerian broadened components. (1) A broad component with a velocity dispersion of $3400^{+800}_{-600}$ km s$^{-1}$ and (2) a narrow component of $440^{+60}_{-50}$ km s$^{-1}$. For an inclination of $50^{\circ}-85^{\circ}$, constrained by VLBI, we find that the broad component arises from a distance of $\sim 0.1-0.17$ pc ($800-1400$ gravitational radii) and the narrow component from $\sim 6-10$ pc ($50,000-80,000$ gravitational radii) from the central black hole depending on the inclination angle. Our result suggests that the origin of the broad component is consistent with the broad line region and the narrow component from the torus of Cygnus A. We also find a potential emission line possibly from intermediate ionized Fe XVII with a very low dispersion ($<80$ km s$^{-1}$) that originates from either the outer edge of the torus or the narrow line region. Finally, we find that the Fe K edge is redshifted compared to the Fe K$α$ line components, suggesting a line of sight bulk velocity of $470 \pm 100$ km s$^{-1}$. Such a shift may be due to an inflowing wind or relative motion between the two components originating from the near and far side of an inflowing torus, respectively.

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arXiv2026

High-resolution X-ray spectroscopy with XRISM/Resolve reveals super-Solar abundance ratios in Virgo/M87

The chemical composition of the intracluster medium (ICM) provides key insights into the enrichment history of galaxy clusters. However, high-resolution abundance measurements with X-ray microcalorimeters remain available for only a few systems. While most cool-core clusters exhibit near-Solar elemental abundance ratios relative to Fe, previous studies of the Virgo cluster suggested super-Solar ratios in its core. We investigate the chemical properties of the Virgo cluster core using XRISM/Resolve observations, focusing on precise measurements of Si, S, Ar, Ca, Cr, Fe, and Ni abundances. We aim to determine whether Virgo displays abundance patterns distinct from other nearby cool-core clusters and to explore the origin of any differences. We analysed XRISM/Resolve spectra in four regions of the Virgo core (center, east, northwest, and southwest) in the 1.7-11 keV band. Single-temperature, multi-temperature, and multi-abundance models were applied to characterize the thermal structure and derive elemental abundances. The resulting abundance ratios were compared between pointings, with previous studies of Virgo/M87, and with recent XRISM measurements of other clusters. All four pointings exhibit systematically super-Solar X/Fe ratios, although the northwest region shows values closer to Solar. Multi-abundance modeling of the eastern and southwestern regions reveals that cool, metal-rich gas uplifted by the AGN coexists with a hotter, more chemically homogeneous ambient ICM. The super-Solar ratios are robust against variations in bandpass and temperature structure. We interpret these enhanced ratios as reflecting the enrichment history of the old stellar population in M87 combined with a limited cold gas reservoir. The Virgo core exhibits spatially resolved chemical enrichment that differs from the abundance patterns observed in other cool-core clusters.

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arXiv2026

Are X-ray Atmospheres Heated by Turbulent Dissipation? XRISM Constraints

We evaluate whether dissipation of turbulence injected into hot cluster atmospheres by jets and bubbles can offset radiative cooling flows. No trends are found between atmospheric velocity dispersion, $σ_v$, and either the ratio of kinetic to thermal energy or jet power over nearly four decades of jet power. Apparently, jets disperse their energy gently at roughly constant energy per gram of gas. Assuming the velocity dispersions at the centers of Perseus, Virgo, and Hydra A reflect jetted turbulence, up to roughly half the bubble enthalpy could be dissipated by turbulent motion. A model is presented that balances radiation losses and turbulent power injected by radio bubbles rising at their terminal speeds. The model is anchored by XRISM measurements of $σ_v$ and is governed by the ratio of the bubble's terminal speed to the atmospheric sound speed. Bubbles must rise close to the sound speed and impart energy with a broad range of injection scales to heat the entire cooling volume. The level of turbulence in the powerful Hydra A system may offset cooling over some of the cooling volume. However, turbulent dissipation would struggle and probably fail to balance cooling in Perseus and Virgo, except perhaps in their inner regions. Several factors including, low velocity dispersions, small injection scales, short duty cycles, anisotropic turbulence injection, and long turbulent diffusion timescales present severe challenges for jetted turbulence heating models. A larger sample of spatially resolved cluster atmospheres is needed to reach a definitive conclusion.

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arXiv2026

The splash beneath the largest radio bubble in a cluster core

We present a 100 ks XRISM Resolve observation of the Ophiuchus cluster that measures turbulence and bulk motion in the wake of the largest radio bubble on the sky. We detect a significant velocity shift of $-80\pm20$ km/s from the cluster centre to the bubble's wake and a clear increase in velocity dispersion from $135\pm10$ km/s to $210\pm20$ km/s. The measured bulk velocity in the wake is low and suggests that the bubble's trajectory is inclined with respect to the line of sight. If we subdivide the bubble's wake, fitting spectra simultaneously with cross-region responses, we find that the velocity shift and dispersion increase are primarily detected in the very centre of the wake. This is consistent with the expected updraft, or `splash', found beneath buoyantly rising radio bubbles. In the cluster's cool core, the turbulent kinetic energy is only 1% of the thermal energy radiated over a cooling timescale of 7 Gyr, and even falls short, by a factor of 5, of the thermal energy radiated over the bubble's rise time. Whilst turbulent energy generated in the large wake region may provide additional heating, this propagates too slowly to prevent rapid cooling across the core. The turbulent-dissipation heating rate is a factor of ~3 below the cooling luminosity. Despite the vast power of the giant radio bubble in the Ophiuchus cluster, the gas motions in the wake are remarkably modest and turbulent-dissipation appears unable to prevent rapid cooling.

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arXiv2026

Dynamics of AGN feedback in the X-ray bright East and Southwest arms of M87, mapped by XRISM

As the central galaxy in the nearest cluster, M87 provides the best spatial resolution for disentangling the complex interactions between AGN jets and the surrounding environment. We investigate the velocity structure of the multitemperature X-ray gas in M87, particularly in the eastern and southwestern arms associated with past AGN outbursts, using high-resolution spectroscopy from XRISM/Resolve. We analyze a mosaic of XRISM/Resolve observations covering the core of M87, fitting single- and multi-temperature models to spectra extracted from different regions and energy bands. We assess the line-of-sight velocities and velocity dispersions of the hotter ambient and cooler uplifted gas phases, and evaluate systematic uncertainties related to instrumental gain calibration. The hotter ICM phase, traced by Fe He-$α$ emission, shows velocity dispersions below $\sim100$ km/s, and no significant velocity shifts between the arms and a relaxed offset region, suggesting limited dynamical impact from older AGN lobes. In contrast, the cooler gas phase appears to exhibit larger line of sight velocity gradients up to several hundred km/s as well as a higher velocity dispersion than the ambient hot phase, although these conclusions remain tentative pending improvements in the robustness of the gain calibration at lower energies. The first microcalorimeter-resolved map of gas dynamics in M87 supports the uplift scenario for the X-ray arms, with the cooler gas in the east and southwest seemingly moving in opposite directions along the line of sight. The kinetic energy is a small fraction of the gravitational potential energy associated with the gas uplift, and XRISM further suggests that AGN-driven motions may be short-lived in the hot ambient ICM. These constraints provide important input towards shaping future models of AGN feedback.

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arXiv2025

Spectrally Resolved Gas Kinematics in Cygnus A: XRISM Detects AGN Jet-induced Velocity Dispersion in Multi-temperature Gas

We report spectral analysis on a 170 ks XRISM \textit{Resolve} exposure of the core of Cygnus A. Analyzing the full field of view spectrum in the $1.7-12.0$ keV band, we find evidence for two-temperature cluster gas. The hotter ($kT = 5.53 \pm 0.13$ keV) gas has a velocity dispersion of $261 \pm 13$ km s$^{-1}$ and a bulk velocity of $120 \pm 20$ km s$^{-1}$ with respect to the central galaxy. The cooler gas ($kT = 2.0^{+0.4}_{-0.3}$ keV) has an even broader velocity dispersion of $440 \pm 130$ km s$^{-1}$, with a systematic uncertainty of $120$ km s$^{-1}$. The relative line-of-sight velocity between the hotter and cooler gas can be as high as $450 \pm 140$ km s$^{-1}$. We interpret the high velocity dispersions as a combination of turbulence and bulk motion due to the cocoon shock. The upper limit on the non-thermal pressure fraction for the hotter gas is $7.7 \pm 0.7\%$. We associate the cooler gas with the central region ($<35$ kpc) and the hotter phase with the gas surrounding it ($35-100$ kpc). The total energy due to the kinetic motion is $5.1 \times 10^{60}$ erg, consistent with the energy associated with the central radio source. The kinetic energy injection rate is $6.9 \times 10^{44}-7.4 \times 10^{45}$ erg s$^{-1}$ under varying assumptions of injection timescales. The range of injection power is higher than the cooling luminosity, and thus the heating and cooling rates in Cygnus A are unbalanced.

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arXiv2025

Hidden (absorbed) Cooling Flows V: Groups and Galaxies including Spirals

Cooling flows are observed in X-ray studies of the centres of cool core clusters, galaxy groups and individual elliptical galaxies. They are partly hidden from direct view by embedded cold gas so have been called Hidden Cooling Flows. X-ray spectra from the XMM RGS reveal emission from hot gas modified by photoelectric absorption by cold gas intrinsic to the flow. Here we present the spectral analysis of 6 more low redshift galaxy groups ranging from the nearest fossil group to 2 groups hosting bright radio sources. All reveal absorbed cooling flows. AGN feedback is ineffective in heating the inner cooling gas in groups and elliptical galaxies. We have extended the analysis to include 3 nearby spiral galaxies (the Sombrero, Whirlpool and Sculptor galaxies). They have similar absorbed soft X-ray spectra to elliptical galaxies and may also host cooling flows of 0.3 to 1.1\Msun/yr in their CircumGalactic Medium.

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arXiv2025

A XRISM Observation of the Archetypal Radio-Mode Feedback System Hydra-A: Measurements of Atmospheric Motion and Constraints on Turbulent Dissipation

We present XRISM Resolve observations centered on Hydra-A, a redshift z = 0.054 brightest cluster galaxy which hosts one of the largest and most powerful FR-I radio sources in the nearby Universe. We examine the effects of its high jet power on the velocity structure of the cluster's hot atmosphere. Hydra-A's central radio jets have inflated X-ray cavities with energies upward of $10^{61}$ erg. They reach altitudes of 225 kpc from the cluster center, well beyond the atmosphere's central cooling region. Resolve's $3\times3$ arcmin field-of-view covers $190\times190$ kpc, which encompasses most of the cooling volume. We find a one dimensional atmospheric velocity dispersion across the volume of $164\pm10$ km/s. The fraction in isotropic turbulence or unresolved bulk velocity is unknown. Assuming pure isotropic turbulence, the turbulent kinetic energy is $2.5 \%$ of the thermal energy radiated away over the cooling timescale, implying that kinetic energy must be supplied continually to offset cooling. While Hydra-A's radio jets are powerful enough to supply kinetic energy to the atmosphere at the observed level, turbulent dissipation alone would struggle to offset cooling throughout the cooling volume. The central galaxy's radial velocity is similar to the atmospheric velocity, with an offset of $-37 \pm 23$ km/s.

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arXiv2025

Velocity Structure Correlations between the Nebular, Molecular, and Atmospheric Gases in the Cores of Four Cool Core Clusters

We investigate the velocity structure of nebular gas in the central galaxies of four clusters: Abell 1835, PKS 0745-191, Abell 262, and RXJ0820.9+0752, using data from the Keck Cosmic Web Imager (KCWI). Velocity structure functions (VSFs) of the [OII] emission line are compared to VSFs of molecular clouds observed with the Atacama Large Millimeter/submillimeter Array (ALMA). Apart from Abell 262 where the gas is located in a circumnuclear disk, the nebular gas in the remaining galaxies lies in off-nuclear filamentary structures with VSFs steeper than the Kolmogorov slope. This steepening may be plausibly attributed to gravity although other factors, such as magnetic stresses and bulk motion,} may be significant. The VSFs of CO and [OII] emission are similar in RXJ0820 and Abell 262, indicating close coupling of the nebular and molecular gases. In contrast, the nebular and molecular gases are differentiated on most scales in PKS 0745 and Abell 1835. This discrepancy is likely due to the radio-AGN churning the gas. We compare the scale-dependent velocity amplitudes of the hot atmospheres constrained by X-ray surface brightness fluctuation analysis using Chandra observations to the nebular VSFs. The large-scale consistency in Abell 1835 and RXJ0820 is consistent with condensation from the hot atmospheres. {We explore substantial systematic biases, including projection effects, windowing, and smoothing effects when comparing VSFs using different telescopes and instruments.

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arXiv2025

Gas Perturbations in Hot Smooth Atmospheres X-ray Surface Brightness Fluctuations in Smooth Galaxy Cluster Atmospheres

We measure surface brightness fluctuations in Chandra X-ray images of the cores of the galaxy clusters Abell 2029, Abell 2151, Abell 2107, RBS0533, and RBS0540. Their relatively structureless X-ray atmospheres exhibit the thermodynamic properties of cool cores including short central cooling times and low entropy. However, unlike typical cool-core clusters, molecular gas, star formation, and bubbles associated with radio jets are faint or absent near their central galaxies. Four clusters show typical gas density fluctuation amplitudes of $\sim$ 10 per cent on the scales probed, apart from RBS0540, which exhibits lower amplitudes, suggesting that its gas is mildly disturbed. Under the assumption that gas density fluctuations are indicative of random gas velocities, we estimate scale-dependent velocity amplitudes of gas motions across all studied clusters, which range from 100 km/s to 200 km/s in Abell 2029, Abell 2151, and Abell 2107. These velocity estimates are comparable to the atmospheric velocity dispersion in the Perseus cluster measured by the Hitomi X-ray Observatory. The turbulent heating rates implied by our measurements are of the same order as the radiative cooling rates. Our results suggest that atmospheric sloshing and perhaps turbulent motion may aid radio jets in stabilizing atmospheric cooling.

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arXiv2024

Cocoon shock, X-ray cavities and extended Inverse Compton emission in Hercules A: clues from Chandra observations

We present a detailed analysis of jet activity in the radio galaxy 3C348 at the center of the galaxy cluster Hercules A. We use archival Chandra data to investigate the jet-driven shock front, the radio-faint X-ray cavities, the eastern jet, and the presence of extended Inverse Compton (IC) X-ray emission from the radio lobes. We detect two pairs of shocks: one in the north-south direction at 150 kpc from the center, and another in the east-west direction at 280 kpc. These shocks have Mach numbers of $\mathcal{M} = 1.65\pm0.05$ and $\mathcal{M} = 1.9\pm0.3$, respectively. Together, they form a complete cocoon around the large radio lobes. Based on the distance of the shocks from the center, we estimate that the corresponding jet outburst is 90-150 Myr old. We confirm the presence of two radio-faint cavities within the cocoon, misaligned from the lobes, each $\sim$100 kpc wide and 40-60 Myr old. A backflow from the radio lobes might explain why the cavities are dynamically younger than the cocoon shock front. We also detect non-thermal X-ray emission from the eastern jet and from the large radio lobes. The X-ray emission from the jet is visible at 80 kpc from the AGN and can be accounted for by an IC model with a mild Doppler boosting ($δ\sim2.7$). A synchrotron model could explain the radio-to-X-ray spectrum only for very high Lorentz factors $γ\geq10^{8}$ of the electrons in the jet. For the large radio lobes, we argue that the X-ray emission has an IC origin, with a 1 keV flux density of $21.7\pm1.4\text{(statistical)}\pm1.3\text{(systematic)}$ nJy. A thermal model is unlikely, as it would require unrealistically high gas temperature, density, and pressure, along with a strong depolarization of the radio lobes, which are instead highly polarized. The IC detection, combined with the synchrotron flux density, suggests a magnetic field of $12\pm3μ$G in the lobes.

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arXiv2024

Hidden Cooling Flows IV: More Details on Centaurus and the Efficiency of AGN Feedback in Clusters

Cooling flows are common in galaxy clusters which have cool cores. The soft X-ray emission below 1 keV from the flows is mostly absorbed by cold dusty gas within the central cooling sites. Further evidence for this process is presented here through a more detailed analysis of the nearby Centaurus cluster and some additional clusters. Predictions of JWST near and mid-infrared spectra from cooling gas are presented. [NeVI] emission at 7.65 micron should be an important diagnostic of gas cooling between 6 and 1.5 times 10^5 K. The emerging overall picture of hidden cooling flows is explored. The efficiency of AGN feedback in reducing the total cooling rate in cool cores is shown to be above 50 percent for many clusters but is rarely above 90 per cent. The reduction is mostly in outer gas. Cooling dominates in elliptical galaxies and galaxy groups which have mass flow rates below about 15M/yr and in some massive clusters where rates can exceed 1000M/yr.

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arXiv2024

Complex Velocity Structure of Nebular Gas in Active Galaxies Centred in Cooling X-ray Atmospheres

[OII] emission maps obtained with the Keck Cosmic Web Imager (KCWI) are presented for four galaxies centered in cooling X-ray cluster atmospheres. Nebular emission extending tens of kpc is found in systems covering a broad range of atmospheric cooling rates, cluster masses, and dynamical states. Abell 262's central galaxy hosts a kpc-scale disk. The nebular gas in RXJ0820.9+0752 is offset and redshifted with respect to the central galaxy by $10-20$ kpc and 150 km s$^{-1}$, respectively. The nebular gases in PKS 0745-191 and Abell 1835 are being churned to higher velocity dispersion by X-ray bubbles and jets. The churned gas is enveloped by larger scale, lower velocity dispersion (quiescent) nebular emission. The mean line-of-sight speeds of the churned gas, quiescent gas, and the central galaxy each differ by up to $\sim 150$ km s$^{-1}$; nebular speeds upward of $800$ km s$^{-1}$ are found. Gases with outwardly-rising speeds upward of several hundred km s$^{-1}$ are consistent with being advected behind and being lifted by the rising bubbles. The peculiar motion between the galaxy, nebular gas, and perhaps the hot atmosphere from which it presumably condensed is affecting the bubble dynamics, and may strongly affect thermally unstable cooling, the dispersal of jet energy, and the angular momentum of gas accreting onto the galaxies and their nuclear black holes.

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arXiv2024

Consequences of a low-mass, high-pressure, star formation mode in early galaxies

High resolution X-ray spectra reveal hidden cooling flows depositing cold gas at the centres of massive nearby early-type galaxies with little sign of normal star formation. Optical observations are revealing that a bottom-heavy Initial Mass Function is common within the inner kpc of similar galaxies. We revive the possibility that a low-mass star formation mode is operating due to the high thermal pressure in the cooling flow, thus explaining the accumulation of low-mass stars. We further explore whether such a mode operated in early, high-redshift galaxies and has sporadically continued to the present day. The idea links observed distant galaxies with black holes which are ultramassive for their stellar mass, nearby red nuggets and massive early-type galaxies. Nearby elliptical galaxies may be red but they are not dead.

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arXiv2024

Two distinct molecular cloud populations detected in massive galaxies

We present new ALMA observations of CO, CN, CS, HCN and HCO$^{+}$ absorption seen against the bright and compact radio continuum sources of eight massive galaxies. Combined with archival observations, they reveal two distinct populations of molecular clouds, which we identify by combining CO emission and absorption profiles to unambiguously reveal each cloud's direction of motion and likely location. In galaxy disks, we see clouds with low velocity dispersions, low line of sight velocities and a lack of any systemic inflow or outflow. In galactic cores, we find high velocity dispersion clouds inflowing at up to 550 km/s. This provides observational evidence in favour of cold accretion onto galactic centres, which likely contributes to the fuelling of active galactic nuclei. We also see a wide range in the CO(2-1)/CO(1-0) ratios of the absorption lines. This is likely the combined effect of hierarchical substructure within the molecular clouds and continuum sources which vary in size with frequency.

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arXiv2024

A massive multiphase plume of gas in Abell 2390's brightest cluster galaxy

We present new ALMA CO(2-1) observations tracing $2.2 \times 10^{10}$ solar masses of molecular gas in Abell 2390's brightest cluster galaxy, where half the gas is located in a one-sided plume extending 15 kpc out from the galaxy centre. This molecular gas has a smooth and positive velocity gradient, and is receding 250 km/s faster at its farthest point than at the galaxy centre. To constrain the plume's origin, we analyse our new observations alongside existing X-ray, optical and radio data. We consider the possibility that the plume is a jet-driven outflow with lifting aided by jet inflated X-ray bubbles, is a trail of gas stripped from the main galaxy by ram pressure, or is formed of more recently cooled and infalling gas. The galaxy's star formation and gas cooling rate suggest the lifespan of its molecular gas may be low compared with the plume's age -- which would favour a recently cooled plume. Molecular gas in close proximity to the active galactic nucleus is also indicated by 250 km/s wide CO(2-1) absorption against the radio core, as well as previously detected CO(1-0) and HI absorption. This absorption is optically thick and has a line of sight velocity towards the galaxy centre of 200 km/s. We discuss simple models to explain its origin.

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