arXiv subjects

Massimo Gaspari

Publications and source records attributed to Massimo Gaspari.

At least 91 records · Page 5Linked to original sources

arXiv2019

The physics and astrophysics of X-ray outflows from Active Galactic Nuclei

The highly energetic outflows from Active Galactic Nuclei detected in X-rays are one of the most powerful mechanisms by which the central supermassive black hole (SMBH) interacts with the host galaxy. The last two decades of high resolution X-ray spectroscopy with XMM and Chandra have improved our understanding of the nature of these outflowing ionized absorbers and we are now poised to take the next giant leap with higher spectral resolution and higher throughput observatories to understand the physics and impact of these outflows on the host galaxy gas. The future studies on X-ray outflows not only have the potential to unravel some of the currently outstanding puzzles in astronomy, such as the physical basis behind the MBH$-σ$ relation, the cooling flow problem in intra-cluster medium (ICM), and the evolution of the quasar luminosity function across cosmic timescales, but also provide rare insights into the dynamics and nature of matter in the immediate vicinity of the SMBH. Higher spectral resolution ($\le 0.5$ eV at $1$ keV) observations will be required to identify individual absorption lines and study the asymmetries and shifts in the line profiles revealing important information about outflow structures and their impact. Higher effective area ($\ge 1000 \rm \,cm^{2}$) will be required to study the outflows in distant quasars, particularly at the quasar peak era (redshift $1\le z\le 3$) when the AGN population was the brightest. Thus, it is imperative that we develop next generation X-ray telescopes with high spectral resolution and high throughput for unveiling the properties and impact of highly energetic X-ray outflows. A simultaneous high resolution UV + X-ray mission will encompass the crucial AGN ionizing continuum, and also characterize the simultaneous detections of UV and X-ray outflows, which map different spatial scales along the line of sight.

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arXiv2019

Probing Macro-Scale Gas Motions and Turbulence in Diffuse Cosmic Plasmas

Clusters of galaxies, the largest collapsed structures in the Universe, are located at the intersection of extended filaments of baryons and dark matter. Cosmological accretion onto clusters through large scale filaments adds material at cluster outskirts. Kinetic energy in the form of bulk motions and turbulence due to this accretion provides a form of pressure support against gravity, supplemental to thermal pressure. Significant amount of non-thermal pressure support could bias cluster masses derived assuming hydrostatic equilibrium, the primary proxy for cluster cosmology studies. Sensitive measurements of Doppler broadening and shift of astrophysical lines, and the relative fluctuations in thermodynamical quantities (e.g., density, pressure, and entropy) are primary diagnostic tools. Forthcoming planned and proposed X-ray (with large etendue, throughput, and high spectral resolution) and SZ observatories will provide crucial information on the assembly and virialisation processes of clusters, involving turbulent eddies cascading at various spatial scales and larger gas bulk motions in their external regions to the depth or their potential wells.

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arXiv2019

Galaxy Winds in the Age of Hyperdimensional Astrophysics

The past decade began with the first light of ALMA and will end at the start of the new era of hyperdimensional astrophysics. Our community-wide movement toward highly multiwavelength and multidimensional datasets has enabled immense progress in each science frontier identified by the 2010 Decadal Survey, particularly with regard to black hole feedback and the cycle of baryons in galaxies. Facilities like ALMA and the next generation of integral field unit (IFU) spectrographs together enable mapping the physical conditions and kinematics of warm ionized and cold molecular gas in galaxies in unprecedented detail (Fig. 1). JWST's launch at the start of the coming decade will push this capability to the rest-frame UV at redshifts z > 6, mapping the birth of stars in the first galaxies at cosmic dawn. Understanding of their subsequent evolution, however, now awaits an ability to map the processes that transform galaxies directly, rather than the consequences of those processes in isolation. In this paper, we argue that doing so requires an equivalent revolution in spatially resolved spectroscopy for the hot plasma that pervades galaxies, the atmospheres in which they reside, and the winds that are the engines of their evolution.

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arXiv2019

On the Assembly Bias of Cool Core Clusters Traced by H$α$ Nebulae

Do cool-core (CC) and noncool-core (NCC) clusters live in different environments? We make novel use of H$α$ emission lines in the central galaxies of redMaPPer clusters as proxies to construct large (1,000's) samples of CC and NCC clusters, and measure their relative assembly bias using both clustering and weak lensing. We increase the statistical significance of the bias measurements from clustering by cross-correlating the clusters with an external galaxy redshift catalog from the Sloan Digital Sky Survey III, the LOWZ sample. Our cross-correlations can constrain assembly bias up to a statistical uncertainty of 6%. Given our H$α$ criteria for CC and NCC, we find no significant differences in their clustering amplitude. Interpreting this difference as the absence of halo assembly bias, our results rule out the possibility of having different large-scale (tens of Mpc) environments as the source of diversity observed in cluster cores. Combined with recent observations of the overall mild evolution of CC and NCC properties, such as central density and CC fraction, this would suggest that either the cooling properties of the cluster core are determined early on solely by the local (<200 kpc) gas properties at formation or that local merging leads to stochastic CC relaxation and disruption in a periodic way, preserving the average population properties over time. Studying the small-scale clustering in clusters at high redshift would help shed light on the exact scenario.

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arXiv2019

A High-resolution SZ View of the Warm-Hot Universe

The Sunyaev-Zeldovich (SZ) effect was first predicted nearly five decades ago, but has only recently become a mature tool for performing high resolution studies of the warm and hot ionized gas in and between galaxies, groups, and clusters. Galaxy groups and clusters are powerful probes of cosmology, and they also serve as hosts for roughly half of the galaxies in the Universe. In this white paper, we outline the advances in our understanding of thermodynamic and kinematic properties of the warm-hot universe that can come in the next decade through spatially and spectrally resolved measurements of the SZ effects. Many of these advances will be enabled through new/upcoming millimeter/submillimeter (mm/submm) instrumentation on existing facilities, but truly transformative advances will require construction of new facilities with larger fields of view and broad spectral coverage of the mm/submm bands.

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arXiv2019

AGN Feedback in Galaxy Group 3C 88: Cavities, Shock and Jet Reorientation

We present results from the deep Chandra observation (105 ksec), together with new Giant Metrewave Radio Telescope and Very Large Array data of the AGN outburst in the radio-loud galaxy group 3C 88. The system shows a prominent X-ray cavity on the eastern side with a diameter of $\sim$50 kpc at $\sim28$ kpc from the nucleus. The total enthalpy of the cavity is $3.8\times10^{58}$ erg and the average power required to inflate the X-ray bubble is $\sim2.0\times10^{43}$ erg s^-1. From surface brightness profiles we detect a shock with a Mach number of $M=1.4\pm0.2$, consistent with the value obtained from temperature jump. The shock energy is estimated to be $1.9\times10^{59}$ erg. The size and total enthalpy of the cavity in 3C 88 are the largest known in galaxy groups, as well as the shock energy. The eastern X-ray cavity is not aligned with the radio jet axis. This factor, combined with the radio morphology, strongly suggests jet reorientation in the last tens of million years. The bright rim and arm features surrounding the cavity show metallicity enhancement, suggesting they originated as high metallicity gas from the group center, lifted by the rising X-ray bubbles. Our Chandra study of 3C 88 also reveals that galaxy groups with powerful radio AGN can have high cavity power, although deep X-ray observations are typically required to confirm the cavities in galaxy groups.

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arXiv2019

Mass-Metallicity Relation from Cosmological Hydrodynamical Simulations and X-ray Observations of Galaxy Groups and Clusters

Recent X-ray observations of galaxy clusters show that the distribution of intra-cluster medium (ICM) metallicity is remarkably uniform in space and time. In this paper, we analyse a large sample of simulated objects, from poor groups to rich clusters, to study the dependence of the metallicity and related quantities on the mass of the systems. The simulations are performed with an improved version of the Smoothed-Particle-Hydrodynamics \texttt{GADGET-3} code and consider various astrophysical processes including radiative cooling, metal enrichment and feedback from stars and active galactic nuclei (AGN). The scaling between the metallicity and the temperature obtained in the simulations agrees well in trend and evolution with the observational results obtained from two data samples characterised by a wide range of masses and a large redshift coverage. We find that the iron abundance in the cluster core ($r<0.1R_{500}$) does not correlate with the temperature nor presents a significant evolution. The scale invariance is confirmed when the metallicity is related directly to the total mass. The slope of the best-fitting relations is shallow ($β\sim-0.1$) in the innermost regions ($r<0.5R_{500}$) and consistent with zero outside. We investigate the impact of the AGN feedback and find that it plays a key role in producing a constant value of the outskirts metallicity from groups to clusters. This finding additionally supports the picture of early enrichment.

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arXiv2018

GAMER-2: a GPU-accelerated adaptive mesh refinement code -- accuracy, performance, and scalability

We present GAMER-2, a GPU-accelerated adaptive mesh refinement (AMR) code for astrophysics. It provides a rich set of features, including adaptive time-stepping, several hydrodynamic schemes, magnetohydrodynamics, self-gravity, particles, star formation, chemistry and radiative processes with GRACKLE, data analysis with yt, and memory pool for efficient object allocation. GAMER-2 is fully bitwise reproducible. For the performance optimization, it adopts hybrid OpenMP/MPI/GPU parallelization and utilizes overlapping CPU computation, GPU computation, and CPU-GPU communication. Load balancing is achieved using a Hilbert space-filling curve on a level-by-level basis without the need to duplicate the entire AMR hierarchy on each MPI process. To provide convincing demonstrations of the accuracy and performance of GAMER-2, we directly compare with Enzo on isolated disk galaxy simulations and with FLASH on galaxy cluster merger simulations. We show that the physical results obtained by different codes are in very good agreement, and GAMER-2 outperforms Enzo and FLASH by nearly one and two orders of magnitude, respectively, on the Blue Waters supercomputers using $1-256$ nodes. More importantly, GAMER-2 exhibits similar or even better parallel scalability compared to the other two codes. We also demonstrate good weak and strong scaling using up to 4096 GPUs and 65,536 CPU cores, and achieve a uniform resolution as high as $10{,}240^3$ cells. Furthermore, GAMER-2 can be adopted as an AMR+GPUs framework and has been extensively used for the wave dark matter ($ψ$DM) simulations. GAMER-2 is open source (available at https://github.com/gamer-project/gamer) and new contributions are welcome.

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arXiv2018

A Galaxy-Scale Fountain of Cold Molecular Gas Pumped by a Black Hole

We present ALMA and MUSE observations of the Brightest Cluster Galaxy in Abell 2597, a nearby (z=0.0821) cool core cluster of galaxies. The data map the kinematics of a three billion solar mass filamentary nebula that spans the innermost 30 kpc of the galaxy's core. Its warm ionized and cold molecular components are both cospatial and comoving, consistent with the hypothesis that the optical nebula traces the warm envelopes of many cold molecular clouds that drift in the velocity field of the hot X-ray atmosphere. The clouds are not in dynamical equilibrium, and instead show evidence for inflow toward the central supermassive black hole, outflow along the jets it launches, and uplift by the buoyant hot bubbles those jets inflate. The entire scenario is therefore consistent with a galaxy-spanning "fountain", wherein cold gas clouds drain into the black hole accretion reservoir, powering jets and bubbles that uplift a cooling plume of low-entropy multiphase gas, which may stimulate additional cooling and accretion as part of a self-regulating feedback loop. All velocities are below the escape speed from the galaxy, and so these clouds should rain back toward the galaxy center from which they came, keeping the fountain long-lived. The data are consistent with major predictions of chaotic cold accretion, precipitation, and stimulated feedback models, and may trace processes fundamental to galaxy evolution at effectively all mass scales.

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arXiv2018

X-Ray Properties of AGN in Brightest Cluster Galaxies. I.A Systematic Study of the Chandra Archive in the $0.2<z<0.3$ and $0.55<z<0.75$ Redshift Range

We present a search for nuclear X-ray emission in the brightest cluster galaxies (BCGs) of a sample of groups and clusters of galaxies extracted from the Chandra archive. The exquisite angular resolution of Chandra allows us to obtain robust photometry at the position of the BCG, and to firmly identify unresolved X-ray emission when present, thanks to an accurate characterization of the extended emission at the BCG position. We consider two redshift bins (0.2<z<0.3 and 0.55<z<0.75) and analyze all the clusters observed by Chandra with exposure time larger than 20 ks. Our samples have 81 BCGs in 73 clusters and 51 BCGs in 49 clusters in the low- and high-redshift bin, respectively. X-ray emission in the soft (0.5-2 keV) or hard (2-7 keV) band is detected only in 14 and 9 BCGs ($\sim 18$% of the total samples), respectively. The X-ray photometry shows that at least half of the BCGs have a high hardness ratio, compatible with significant intrinsic absorption. This is confirmed by the spectral analysis with a power law model plus intrinsic absorption. We compute the fraction of X-ray bright BCGs above a given hard X-ray luminosity, considering only sources with positive photometry in the hard band (12/5 sources in the low/high-z sample). In the 0.2<z<0.3 interval the hard X-ray luminosity ranges from $10^{42}$ to $7 \times 10^{43}$ erg s$^{-1}$, with most sources found below $10^{43}$ erg s$^{-1}$. In the $0.55<z<0.75$ range, we find a similar distribution of luminosities below $\sim 10^{44}$ erg s$^{-1}$, plus two very bright sources of a few $10^{45}$ erg s$^{-1}$ associated with two radio galaxies. We also find that X-ray luminous BCGs tend to be hosted by cool-core clusters, despite the majority of cool cores do not host nuclear X-ray emission (Abridged).

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arXiv2018

Formation of a Malin 1 analogue in IllustrisTNG by stimulated accretion

The galaxy Malin 1 contains the largest stellar disk known but the formation mechanism of this structure has been elusive. In this paper, we report a Malin 1 analogue in the 100 Mpc IllustrisTNG simulation and describe its formation history. At redshift zero, this massive galaxy, having a maximum circular velocity $V_{\rm max}$ of 430 ${\rm km\ s^{-1}}$, contains a 100 kpc gas/stellar disk with morphology similar to Malin 1. The simulated galaxy reproduces well many observed features of Malin 1's vast disk, including its stellar ages, metallicities, and gas rotation curve. We trace the extended disk back in time and find that a large fraction of the cold gas at redshift zero originated from the cooling of hot halo gas, triggered by the merger of a pair of intruding galaxies. Our finding provides a novel way to form large galaxy disks as extreme as Malin 1 within the current galaxy formation framework.

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arXiv2018

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.

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arXiv2018

The origin of ICM enrichment in the outskirts of present-day galaxy clusters from cosmological hydrodynamical simulations

The uniformity of the intra-cluster medium (ICM) enrichment level in the outskirts of nearby galaxy clusters suggests that chemical elements were deposited and widely spread into the intergalactic medium before the cluster formation. This observational evidence is supported by numerical findings from cosmological hydrodynamical simulations, as presented in Biffi et al. (2017), including the effect of thermal feedback from active galactic nuclei. Here, we further investigate this picture, by tracing back in time the spatial origin and metallicity evolution of the gas residing at z=0 in the outskirts of simulated galaxy clusters. In these regions, we find a large distribution of iron abundances, including a component of highly-enriched gas, already present at z=2. At z>1, the gas in the present-day outskirts was distributed over tens of virial radii from the the main cluster and had been already enriched within high-redshift haloes. At z=2, about 40% of the most Fe-rich gas at z=0 was not residing in any halo more massive than 1e11 Msun/h in the region and yet its average iron abundance was already 0.4, w.r.t. the solar value by Anders & Grevesse (1989). This confirms that the in situ enrichment of the ICM in the outskirts of present-day clusters does not play a significant role, and its uniform metal abundance is rather the consequence of the accretion of both low-metallicity and pre-enriched (at z>2) gas, from the diffuse component and through merging substructures. These findings do not depend on the mass of the cluster nor on its core properties.

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arXiv2017

Physical Origins of Gas Motions in Galaxy Cluster Cores: Interpreting Hitomi Observations of the Perseus Cluster

The Hitomi X-ray satellite has provided the first direct measurements of the plasma velocity dispersion in a galaxy cluster. It finds a relatively "quiescent" gas with a line-of-sight velocity dispersion ~ 160 km/s, at 30 kpc to 60 kpc from the cluster center. This is surprising given the presence of jets and X-ray cavities that indicates on-going activity and feedback from the active galactic nucleus (AGN) at the cluster center. Using a set of mock Hitomi observations generated from a suite of state-of-the-art cosmological cluster simulations, and an isolated but higher resolution simulation of gas physics in the cluster core, including the effects of cooling and AGN feedback, we examine the likelihood of Hitomi detecting a cluster with the observed velocities. As long as the Perseus has not experienced a major merger in the last few gigayears, and AGN feedback is operating in a "gentle" mode, we reproduce the level of gas motions observed by Hitomi. The frequent mechanical AGN feedback generates net line-of-sight velocity dispersions ~100-200 km/s, bracketing the values measured in the Perseus core. The large-scale velocity shear observed across the core, on the other hand, is generated mainly by cosmic accretion such as mergers. We discuss the implications of these results for AGN feedback physics and cluster cosmology and progress that needs to be made in both simulations and observations, including a Hitomi re-flight and calorimeter-based instruments with higher spatial resolution.

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arXiv2017

Testing the Large-Scale Environments of Cool-core and Noncool-core Clusters with Clustering Bias

There are well-observed differences between cool-core (CC) and non-cool-core (NCC) clusters, but the origin of this distinction is still largely unknown. Competing theories can be divided into internal (inside-out), in which internal physical processes transform or maintain the NCC phase, and external (outside-in), in which the cluster type is determined by its initial conditions, which in turn lead to different formation histories (i.e., assembly bias). We propose a new method that uses the relative assembly bias of CC to NCC clusters, as determined via the two-point cluster-galaxy cross-correlation function (CCF), to test whether formation history plays a role in determining their nature. We apply our method to 48 ACCEPT clusters, which have well resolved central entropies, and cross-correlate with the SDSS-III/BOSS LOWZ galaxy catalog. We find that the relative bias of NCC over CC clusters is $b = 1.42 \pm 0.35$ ($1.6σ$ different from unity). Our measurement is limited by the small number of clusters with core entropy information within the BOSS footprint, 14 CC and 34 NCC. Future compilations of X-ray cluster samples, combined with deep all-sky redshift surveys, will be able to better constrain the relative assembly bias of CC and NCC clusters and determine the origin of the bimodality.

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arXiv2016

Spectral Energy Distribution Mapping of Two Elliptical Galaxies on sub-kpc scales

We use high-resolution Herschel-PACS data of 2 nearby elliptical galaxies, IC1459 & NGC2768 to characterize their dust and stellar content. IC1459 & NGC2768 have an unusually large amount of dust for elliptical galaxies (1-3 x 10^5 Msun), this dust is also not distributed along the stellar content. Using data from GALEX (ultraviolet) to PACS (far-infrared), we analyze the spectral energy distribution (SED) of these galaxies with CIGALEMC as a function of the projected position, binning images in 7.2" pixels. From this analysis, we derive maps of SED parameters, such as the metallicity, the stellar mass, the fraction of young star and the dust mass. The larger amount of dust in FIR maps seems related in our model to a larger fraction of young stars which can reach up to 4% in the dustier area. The young stellar population is fitted as a recent (~ 0.5 Gyr) short burst of star formation for both galaxies. The metallicities, which are fairly large at the center of both galaxies, decrease with the radial distance with fairly steep gradient for elliptical galaxies.

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arXiv2016

Thermal SZ fluctuations in the ICM: probing turbulence and thermodynamics in Coma cluster with ${\it Planck}$

We report the detection of thermal Sunyaev-Zeldovich effect (SZ) fluctuations in the intracluster medium (ICM) of Coma cluster observed with ${\it Planck}$. The SZ data links the maximum observable X-ray scale to the large Mpc scale, extending our knowledge of the power spectrum of ICM fluctuations. Deprojecting the 2-d SZ perturbations into 3-d pressure fluctuations, we find an amplitude spectrum which peaks at $δP/P = 33\pm 12\%$ and $74\pm19\%$ in the $15'$ and $40'$ radius region, respectively. We perform tests to ensure fluctuations are intrinsic to the cluster and not due to noise contamination. By using high-resolution hydrodynamical models, we improve the ICM turbulence constraints in Coma, finding 3-d Mach number ${\rm Ma_{3d}}= 0.8\pm0.3$ (15' region), increasing to supersonic values at larger radii (40'), and an injection scale $L_{\rm inj}\approx 500$ kpc. Such properties are consistent with driving due to mergers, in particular tied to internal galaxy groups. The large pressure fluctuations show that Coma is in adiabatic mode (mediated by sound waves), rather than isobaric mode (mediated by buoyancy waves). As predicted by turbulence models, the distribution of SZ fluctuations is log-normal with mild non-Gaussianities (heavy tails). The substantial non-thermal pressure support implies hydrostatic mass bias $b_M=-15\%$ to $-45\%$ from the core to the outskirt region, respectively. While total SZ power probes the thermal energy content, the SZ fluctuations constrain the non-thermal deviations important for precision cosmology. The proposed, novel approach can be exploited by multifrequency observations using ground based interferometers and future space CMB missions.

astro-ph.CO↗

arXiv2016

Kinetic AGN Feedback Effects on Cluster Cool Cores Simulated using SPH

We implement novel numerical models of AGN feedback in the SPH code GADGET-3, where the energy from a supermassive black hole (BH) is coupled to the surrounding gas in the kinetic form. Gas particles lying inside a bi-conical volume around the BH are imparted a one-time velocity (10,000 km/s) increment. We perform hydrodynamical simulations of isolated cluster (total mass 10^14 /h M_sun), which is initially evolved to form a dense cool core, having central T<10^6 K. A BH resides at the cluster center, and ejects energy. The feedback-driven fast wind undergoes shock with the slower-moving gas, which causes the imparted kinetic energy to be thermalized. Bipolar bubble-like outflows form propagating radially outward to a distance of a few 100 kpc. The radial profiles of median gas properties are influenced by BH feedback in the inner regions (r<20-50 kpc). BH kinetic feedback, with a large value of the feedback efficiency, depletes the inner cool gas and reduces the hot gas content, such that the initial cool core of the cluster is heated up within a time 1.9 Gyr, whereby the core median temperature rises to above 10^7 K, and the central entropy flattens. Our implementation of BH thermal feedback (using the same efficiency as kinetic), within the star-formation model, cannot do this heating, where the cool core remains. The inclusion of cold gas accretion in the simulations produces naturally a duty cycle of the AGN with a periodicity of 100 Myr.

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