arXiv subjects

Mariko Nomura

Publications and source records attributed to Mariko Nomura.

At least 19 recordsLinked to original sources

arXiv2026

Radiation Pressure Instability-Driven Variability of Line-Driven Disk Winds in AGNs: Connection to Periodic Luminosity Variations and UFO Appearance

We investigated the temporal variability of line-driven disk winds induced by radiation pressure instability in accretion disks surrounding supermassive black holes. This is the first study to self-consistently couple one-dimensional hydrodynamic simulations of accretion disks with two-dimensional radiation hydrodynamic simulations of line-driven winds and to analyze their time-dependent evolution. Our results show that periodic luminosity oscillations caused by radiation pressure instability lead to corresponding changes in both the mass outflow rate and the covering factor of gas expected to be observed as ultra-fast outflows (UFOs), with a delay comparable to the viscous timescale around the wind base. The viewing angles from which UFOs are expected to be observed also change with time. Our results therefore imply that, depending on the viewing angle, UFOs may not be detected even during high-luminosity states, whereas they may be detected even at lower luminosities. These findings are consistent with observations showing that UFOs are not always detected at high luminosities and can sometimes be detected even at lower luminosities. For a black hole mass of $10^{7.4}M_\odot$, a mass accretion rate of $1.3L_{\rm Edd}/c^2$ at a radius of about 100 Schwarzschild radii, a viscosity parameter of $α=0.1$, and a viscosity prescription parameter of $μ=0.45$, the mass outflow rate shows a delay of approximately 2--5 yr relative to the luminosity variation, and the covering factor consequently reaches a maximum of $\sim 30\%$ from the high-luminosity phase through the declining phase. Our results suggest that the intermittent detection of UFOs in luminosity-variable AGNs can be explained by radiation pressure instability driven variability of the line-driven disk winds.

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arXiv2026

Resolving the Multiple Component Outflows in PG 1211+143: II. The Soft X-ray View of the Ultra Fast Outflow

The nearby quasar, PG 1211+143, has one of the prototype examples of an ultra fast outflow (UFO), as seen in several past XMM-Newton and Chandra observations. In December 2024, PG 1211+143 was observed simultaneously with XRISM Resolve and XMM-Newton, allowing both the Fe K and soft X-ray outflows to be examined at high resolution simultaneously. The Resolve spectrum revealed a forest of Fe K band absorption lines from the UFO (Mizumoto et al. 2026), comprising of up to six discrete velocity components ranging from $v/c=-0.074$ to $v/c=-0.40$. Here we present the simultaneous XMM-Newton RGS (Reflection Grating Spectrometer) spectrum, where three lower ionization counterparts of the Fe K velocity zones are observed; at $v/c=-0.074, -0.12$ and $-0.33$. The soft X-ray absorbers tend to be somewhat less ionized than their Fe K counterparts, with their opacity mainly arising from Fe L shell lines and highly ionized Oxygen. From comparing the Resolve and RGS absorbers, we show that the outflow can be parameterized with a density profile varying with radius as $r^{-5/3}$, while the lower ionization zones likely originate from denser clumps of gas. Pure electron scattering appears insufficient to provide enough thrust to power the wind, unless sufficient low ionization gas capable of radiative line driving exists outside of the line of sight. Overall, PG 1211+143 provides further evidence for the clumpy nature of accretion disk winds, as was recently revealed in the quasar PDS 456 with XRISM.

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arXiv2026

Unification Model of Active Galactic Nuclei by Photoionization Equilibrium Calculation Based on Radiative Hydrodynamic Simulations

To investigate the origin of the dependence of the covering factor on the Eddington ratio suggested by X-ray observations, we examined the angular distribution of HI and HII based on two-dimensional radiative hydrodynamic simulations. To calculate the Compton-thin covering factor $C_{22}$ and Compton-thick covering factor $C_{24}$ of HI alone, we performed one-dimensional photoionization equilibrium calculations with the XSTAR code based on radiative hydrodynamic simulations. The results obtained are as follows. (1) The Compton-thin covering factor $C_{22}$ of HI and HII is independent of the Eddington ratio and is approximately $70\%$, while $C_{22}$ of HI alone is also independent of the Eddington ratio and is approximately $30\%$. (2) The Compton-thick covering factor $C_{24}$ of HI has the same value as $C_{22}$ of HI. (3) Our $C_{24}$ is consistent with that obtained from X-ray observations. (4) Our $C_{22}$ agrees with that obtained from X-ray observations in a high Eddington ratio, while our $C_{22}$ is smaller than that from X-ray observations in a low Eddington ratio. (5) To explain the difference between $C_{22}$ obtained from theoretical calculations and that inferred from X-ray observations, a Compton-thin gas is required in regions extending at least $10~\mathrm{pc}$ beyond the current computational regions.

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arXiv2025

Resolving the Multiple Component Outflows in PG 1211+143: I. The Fe-K Absorption Structure and UFO Forest

We present the initial high-resolution X-ray spectroscopic observations of the Fe-K absorption structure in the luminous nearby quasar PG 1211+143, utilizing the X-ray Imaging and Spectroscopy Mission (XRISM). The primary objective is to characterize the Fe-K absorption features due to Ultra-Fast Outflow (UFO) in this Eddington-luminosity source. Observations were conducted with XRISM's Resolve and Xtend instruments, complemented by simultaneous data from XMM-Newton and NuSTAR. A historically bright phase was captured. The Resolve spectra clearly reveal a prominent P Cygni profile and resolves the Fe-K absorption into six distinct velocity components, ranging from $v = -0.074c$ to $-0.405c$. A similar superposition of multiple UFOs has been reported in PDS~456, suggesting that such a ``UFO forest'' structure may be a common feature of near Eddington-luminosity sources. Some UFO components exhibit narrow line widths of approximately $σ\sim 200\,\mathrm{km\,s^{-1}}$, which may indicate that the outflows have reached their terminal velocities, thereby resulting in a smaller velocity shear. The mass outflow rate is estimated to be $\dot{M}_\mathrm{out} \sim 1~M_{\odot}~\text{yr}^{-1}$, which is of the order of the Eddington accretion rate. This suggests a physically plausible scenario where the outflow is a significant channel for mass ejection.

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arXiv2024

Multiphase Gas Nature in the Sub-parsec Region of the Active Galactic Nuclei. III. Eddington Ratio Dependence on the Structures of Dusty and Dust-free Outflows

We investigated the influence of the Eddington ratio on sub-parsec-scale outflows in active galactic nuclei (AGNs) with supermassive black holes (SMBHs) masses of $10^7$ M$_{\odot}$ using two-dimensional radiation hydrodynamics simulations. When the range of Eddington ratio, $γ_{\rm Edd} > 10^{-3}$, the radiation force exceeds the gas pressure, leading to stronger outflows and larger dust sublimation radius. Although the sub-parsec-scale outflows is a time-dependence phenomena, our simulations demonstrated that the radial distributions can be well explained by the steady solutions of the spherically symmetric stellar winds. The dynamic structure of sub-parsec-scale outflows is influenced by the dust sublimation radius and the critical radii determined by the dynamical equilibrium condition. Although significantly affecting the outflow velocity, the Eddington ratio exerts minimal effects on temperature and number density distribution. Furthermore, our analytical solutions highlight the importance of the dust sublimation scale as a crucial determinant of terminal velocity and column density in dusty outflows. Through comparisons of our numerical model with the obscuring fraction observed in nearby AGNs, we revealed insights into the Eddington ratio dependence and the tendency towards the large obscuring fraction of the dusty and dust-free gases. The analytical solutions are expected to facilitate an understanding of the dynamical structure and radiation structures along the line of sight and their viewing angles from observations of ionized outflows.

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arXiv2023

Multiphase Gas Nature in the Sub-parsec Region of the Active Galactic Nuclei I: Dynamical Structures of Dusty and Dust-free Outflow

We investigated dusty and dust-free gas dynamics for a radiation-driven sub-pc scale outflow in an active galactic nucleus (AGN) associated with a supermassive black hole $10^7 M_\odot$ and bolometric luminosity $10^{44}$ erg s$^{-1}$ based on the two-dimensional radiation-hydrodynamic simulations. A radiation-driven ``lotus-like'' multi-shell outflow is launched from the inner part ($r \lesssim 0.04$ pc) of the geometrically thin disk, and it repeatedly and steadily produces shocks as mass accretion continues through the disk to the center. The shape of the dust sublimation radius is not spherical and depends on the angle ($θ$) from the disk plane, reflecting the non-spherical radiation field and nonuniform dust-free gas. Moreover, we found that the sublimation radius of $θ\sim 20$-$60$ deg varies on a timescale of several years. The ``inflow-induced outflow" contributes the obscuration of the nucleus in the sub-parsec region. The column density of the dust-free gas is $N_{\rm H} \gtrsim 10^{22}$ cm$^{-2}$ for $r \lesssim 0.04$ pc. Gases near the disk plane ($θ\lesssim 30$ degree) can be the origin of the Compton-thick component, which was suggested by the recent X-ray observations of AGNs. The dusty outflow from the sub-parsec region can be also a source of material for the radiation-driven fountain for a larger scale.

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arXiv2021

Qwind3: UV line-driven accretion disc wind models for AGN feedback

The ultraviolet (UV) bright accretion disc in active galactic nuclei (AGN) should give rise to line driving, producing a powerful wind which may play an important role in AGN feedback as well as in producing structures like the broad line region. However, coupled radiation-hydrodynamics codes are complex and expensive, so we calculate the winds instead using a non-hydrodynamical approach (the Qwind framework). The original Qwind model assumed the initial conditions in the wind, and had only simple radiation transport. Here, we present an improved version which derives the wind initial conditions and has significantly improved ray-tracing to calculate the wind absorption self consistently given the extended nature of the UV emission. We also correct the radiation flux for relativistic effects, and assess the impact of this on the wind velocity. These changes mean the model is more physical, so its predictions are more robust. We find that, even when accounting for relativistic effects, winds can regularly achieve velocities $\simeq$ (0.1-0.5) $c$, and carry mass loss rates which can be up to 30% of the accreted mass for black hole masses of $10^{7-9}$ $\mathrm{M}_\odot$, and mass accretion rates of 50% of the Eddington rate. Overall, the wind power scales as a power law with the black hole mass accretion rate, unlike the weaker scaling generally assumed in current cosmological simulations that include AGN feedback. The updated code, Qwind3, is publicly available in GitHub

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arXiv2021

Radiation hydrodynamics simulations of line-driven AGN disc winds: metallicity dependence and black hole growth

Growth of the black holes (BHs) from the seeds to supermassive BHs (SMBHs, $\sim\!10^9\,M_\odot$) is not understood, but the mass accretion must have played an important role. We performed two-dimensional radiation hydrodynamics simulations of line-driven disc winds considering the metallicity dependence in a wide range of the BH mass, and investigated the reduction of the mass accretion rate due to the wind mass loss. Our results show that denser and faster disc winds appear at higher metallicities and larger BH masses. The accretion rate is suppressed to $\sim\! 0.4$--$0.6$ times the mass supply rate to the disc for the BH mass of $M_{\rm BH}\gtrsim 10^5\,M_{\odot}$ in high-metallicity environments of $Z\gtrsim Z_\odot$, while the wind mass loss is negligible when the metallicity is sub-solar ($\sim 0.1Z_\odot$). By developing a semi-analytical model, we found that the metallicity dependence of the line force and the BH mass dependence of the surface area of the wind launch region are the cause of the metallicity dependence ($\propto\! Z^{2/3}$) and BH mass dependencies ($\propto\! M_{\rm BH}^{4/3}$ for $M_{\rm BH}\leq 10^6\,M_\odot$ and $\propto\! M_{\rm BH}$ for $M_{\rm BH}\geq 10^6\,M_\odot$) of the mass-loss rate. Our model suggests that the growth of BHs by the gas accretion effectively slows down in the regime $\gtrsim 10^{5}M_\odot$ in metal-enriched environments $\gtrsim Z_\odot$. This means that the line-driven disc winds may have an impact on late evolution of SMBHs.

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arXiv2020

UV line driven disc wind as the origin of ultrafast outflows in AGN

UltraFast Outflows (UFO) are observed in some active galactic nuclei (AGN), with blueshifted and highly ionised Fe-K absorption features. AGN typically have a UV bright accretion flow, so UV line driving is an obvious candidate for launching these winds. However this mechanism requires material with UV opacity, in apparent conflict with the observed high ionisation state of the wind. In this paper we synthesise the X-ray energy spectra resulting from different lines of sight through a state of the art radiation hydrodynamics UV line driven disc wind simulation. We demonstrate that there are some lines of sight which only intercept highly ionised and fast outflowing material. The cooler material required for the UV line driving acceleration is out of the line of sight, close to the disc, shielded from the X-rays by a failed wind. We fit these simulated wind spectra to data from the archetypal UFO source PG 1211+143 and show that they broadly reproduce the depth and velocity of the iron absorption lines seen. This directly demonstrates that UV line driving is a viable mechanism to launch even the fastest UFOs. We simulate microcalorimeter observations of this wind and show that their high energy resolution can resolve the detailed structure in the wind and recover the wind energetics when combined with models which correctly estimate the line formation radius of the wind. New data from microcalorimeters will pave the way for physical predictions of AGN wind feedback in cosmological simulations.

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arXiv2020

Line-driven disc wind in near-Eddington active galactic nuclei: decrease of mass accretion rate due to powerful outflow

Based on recent X-ray observations, ultra-fast outflows from supermassive black holes are expected to have enough energy to dramatically affect their host galaxy but their launch and acceleration mechanisms are not well understood. We perform two-dimensional radiation hydrodynamics simulations of UV line-driven disc winds in order to calculate the mass loss rates and kinetic power in these models. We develop a new iterative technique which reduces the mass accretion rate through the inner disc in response to the wind mass loss. This makes the inner disc is less UV bright, reducing the wind power compared to previous simulations which assumed a constant accretion rate with radius. The line-driven winds in our simulations are still extremely powerful, with around half the supplied mass accretion rate being ejected in the wind for black holes with mass $10^8-$$10^{10}\, M_\odot$ accreting at $L/L_{\rm Edd}=0.5-$$0.9$. Our results open up the way for estimating the growth rate of supermassive black hole and evaluating the kinetic energy ejected into the inter stellar medium (active galactic nuclei feedback) based on a physical model of line-driven disc winds.

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arXiv2020

The Fifth Candidate for an Intermediate-mass Black Hole in the Galactic Center

We report the results of high-resolution molecular line observations of the high-velocity compact cloud HCN-0.085-0.094 with the Atacama Large Millimeter/submillimeter Array. The HCN J=4-3, HCO$^+$ J=4-3, and CS J=7-6 line images reveal that HCN-0.085-0.094 consists mainly of three small clumps with extremely broad velocity widths. Each of the three clumps has a 5.5 GHz radio continuum counterpart in its periphery toward Sgr A$^*$. The positional relationship indicates that their surfaces have been ionized by ultraviolet photons from young stars in the central cluster, suggesting the clumps are in close proximity to the Galactic nucleus. One of the three clumps has a ring-like structure with a very steep velocity gradient. This kinematical structure suggests an orbit around a point-like object with a mass of $\sim 10^4$ $M_\odot$. The absence of stellar counterparts indicates that the point-like object may be a quiescent black hole. This discovery adds another intermediate-mass black hole candidate in the central region of our Galaxy.

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arXiv2019

The thermal-radiative wind in low mass X-ray binary H 1743-322; Radiation hydrodynamic simulations

Blueshifted absorption lines are seen in high inclination black hole binary systems in their disc dominated states, showing these power an equatorial disc wind. While some contribution from magnetic winds remain a possibility, thermal and thermal-radiative winds are expected to be present. We show results from radiation hydrodynamic simulations which show that the additional radiation force from atomic features (bound-free and lines) are important along with electron scattering. Together, these increase the wind velocity at high inclinations, so that they quantitatively match the observations in H 1743-322, unlike purely thermal winds which are too slow. We highlight the role played by shadowing of the outer disc from the (sub grid) inner disc Compton heated layer, and show that the increase in shadow from the higher Compton temperature after the spectral transition to the hard state leads to strong suppression of the wind. Thermal-radiative winds explain all of the spectral features (and their disappearance) in this simplest wind system and magnetic winds play only a minor role. We speculate that thermal-radiative winds can explain all the spectral features seen in the more complex (larger disc size) binaries, GRO J1655-40 and GRS 1915+105, without requiring magnetic winds.

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arXiv2019

An energetic high-velocity compact cloud: CO$-$0.31+0.11

We have discovered an energetic high-velocity compact cloud CO$-$0.31+0.11 in the central molecular zone of our Galaxy. CO$-$0.31+0.11 is located at a projected distance of $\sim 45$ pc from the Galactic nucleus Sgr A$^*$. It is characterized by its compact spatial appearance ($d\simeq4$ pc), extremely broad velocity width ($ΔV > 100$ km s$^{-1}$), and high CO $J$=3$-$2/$J$=1$-$0 intensity ratio. The total gas mass and kinetic energy are estimated as approximately $10^4$ $M_\odot$ and $10^{51}$ erg, respectively. Two expanding bubble-like structures are found in our HCN $J$=1$-$0 map obtained with the Nobeyama Radio Observatory 45 m telescope. In the longitude--velocity maps, CO$-$0.31+0.11 exhibits an asymmetric V-shape. This kinematical structure can be well fitted by Keplerian motion on an eccentric orbit around a point mass of $2\times 10^5$ $M_\odot$. The enhanced CO $J$=3$-$2/$J$=1$-$0 ratio is possibly attributed to the tidal compression during the pericenter passage. The model suggests that a huge mass is packed within a radius of $r < 0.1$ pc. The huge mass, compactness and absence of luminous stellar counterparts may correspond to a signature of an intermediate-mass black hole (IMBH) inside. We propose a formation scenario of CO$-$0.31+0.11 in which a compact cloud has gravitationally interacted with an IMBH and a bipolar molecular outflow was driven by the past activity of the putative IMBH.

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arXiv2018

Indication of Another Intermediate-mass Black Hole in the Galactic Center

We report the discovery of molecular gas streams orbiting around an invisible massive object in the central region of our Galaxy, based on the high-resolution molecular line observations with the Atacama Large Millimeter/submillimeter Array (ALMA). The morphology and kinematics of these streams can be reproduced well through two Keplerian orbits around a single point mass of $(3.2 \pm 0.6)\times 10^4 \ M_\odot$. We also found ionized gas toward the inner part of the orbiting gas, indicating dissociative shock and/or photoionization. Our results provide new circumstantial evidences for a wandering intermediate-mass black hole in the Galactic center, suggesting also that high-velocity compact clouds can be probes of quiescent black holes abound in our Galaxy.

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arXiv2018

Magnetohydrodynamic Simulations of a Plunging Black Hole into a Molecular Cloud

Using two-dimensional magnetohydrodynamic simulations, we investigated the gas dynamics around a black hole plunging into a molecular cloud. In these calculations, we assumed a parallel-magnetic-field layer in the cloud. The size of the accelerated region is far larger than the Bondi-Hoyle-Lyttleton radius, being approximately inversely proportional to the Alfvén Mach number for the plunging black hole. Our results successfully reproduce the "Y" shape in position velocity maps of the "Bullet" in the W44 molecular cloud. The size of the Bullet is also reproduced within an order of magnitude using a reasonable parameter set. This consistency supports the shooting model of the Bullet, according to which an isolated black hole plunged into a molecular cloud to form a compact broad-velocity-width feature.

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arXiv2017

Millimetre-wave Emission from an Intermediate-Mass Black Hole Candidate in the Milky Way

It is widely accepted that black holes (BHs) with masses greater than a million solar masses (Msun) lurk at the centres of massive galaxies. The origins of such `supermassive' black holes (SMBHs) remain unknown (Djorgovski et al. 1999), while those of stellar-mass BHs are well-understood. One possible scenario is that intermediate-mass black holes (IMBHs), which are formed by the runaway coalescence of stars in young compact star clusters (Portagies Zwart et al. 1999), merge at the centre of a galaxy to form an SMBH (Ebisuzaki et al. 2001). Although many candidates for IMBHs have been proposed to date, none of them are accepted as definitive. Recently we discovered a peculiar molecular cloud, CO-0.40-0.22, with an extremely broad velocity width near the centre of our Milky Way galaxy. Based on the careful analysis of gas kinematics, we concluded that a compact object with a mass of ~1E5 Msun is lurking in this cloud (Oka et al. 2016). Here we report the detection of a point-like continuum source as well as a compact gas clump near the center of CO-0.40-0.22. This point-like continuum source (CO-0.40-0.22*) has a wide-band spectrum consistent with 1/500 of the Galactic SMBH (Sgr A*) in luminosity. Numerical simulations around a point-like massive object reproduce the kinematics of dense molecular gas well, which suggests that CO-0.40-0.22* is the most promising candidate for an intermediate-mass black hole.

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arXiv2017

Discovery of Two Small High-Velocity Compact Clouds in the Central 10 Parsecs of Our Galaxy

We discovered two small high-velocity compact clouds (HVCCs) in HCN $J=4-3$ and $J=3-2$ maps of the central 20 pc of our Galaxy. Both HVCCs have broad velocity widths ($ΔV \gtrsim 40$ km s$^{-1}$) and compact sizes ($d\sim 1$ pc), and originate from the dense molecular clouds in the position-velocity space. One of them has a faint counterpart in a Paschen-$α$ image. Their spatial structure, kinematics, and absence of luminous stellar object are compatible with the notion that each of the small HVCCs is driven by the plunge of an invisible compact object into a molecular cloud. Such objects are most likely inactive, isolated black holes.

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arXiv2016

Kinematics of Ultra-High-Velocity Gas in the Expanding Molecular Shell adjacent to the W44 Supernova Remnant

We mapped the ultra-high-velocity feature (the "Bullet") detected in the expanding molecular shell associated with the W44 supernova remnant using the Nobeyama Radio Observatory 45-m telescope and the ASTE 10-m telescope. The Bullet clearly appears in the CO ${\it J}$=1-0, CO ${\it J}$=3-2, CO ${\it J}$=4-3, and HCO$^+$ ${\it J}$=1-0 maps with a compact appearance ($0.5\times 0.8$ pc$^2$) and an extremely broad velocity width ($ΔV\!\simeq\!100 \ \rm km \, s ^{-1}$). The line intensities indicate that the Bullet has a higher density and temperature than those in the expanding molecular shell. The kinetic energy of the Bullet amounts to $10^{48.0} \ {\rm erg}$ which is approximately 1.5 orders of magnitude greater than the kinetic energy shared to the small solid angle of it. Two possible formation scenarios with an inactive isolated black hole (BH) are presented.

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