Multi-phase Nature of a Radiation-Driven Fountain with Nuclear Starburst in a Low-mass Active Galactic Nucleus

The structures and dynamics of molecular, atomic, and ionized gases are studied around a low-luminosity active galactic nucleus (AGN) with a small ($2\times 10^6 M_\odot$) black hole using 3D radiation hydrodynamic simulations. We studied, for the first time, the non-equilibrium chemistry for the X-ray dominated region in the "radiation-driven fountain" (Wada 2012) with supernova feedback. A double hollow cone structure is naturally formed without postulating a thick "torus" around a central source. The cone is occupied with an inhomogeneous, diffuse ionized gas and surrounded by a geometrically thick ($h/r \gtrsim 1$) atomic gas. Dense molecular gases are distributed near the equatorial plane, and energy feedback from supernovae enhances their scale height. Molecular hydrogen exists in a hot phase ( > 1000 K) as well as in a cold ( $10^3$ cm$^{-3}$) phase. The velocity dispersion of H$_2$ in the vertical direction is comparable to the rotational velocity, which is consistent with near infrared observations of nearby Seyfert galaxies. Using 3D radiation transfer calculations for the dust emission, we find polar emission in the mid-infrared band (12$\mu m$), which is associated with bipolar outflows, as suggested in recent interferometric observations of nearby AGNs. If the viewing angle for the nucleus is larger than 75 deg, the spectral energy distribution (~ 2 -- 60 $\mu m$) of this model is consistent with that of the Circinus galaxy. The multi-phase interstellar medium observed in optical/infrared and X-ray observations is also discussed.Comment: 9 pages, 5 figures. Accepted for ApJL. A movie file for Fig.5b can be downloaded from http://astrophysics.jp/Circinus

Models of the ISM in galaxy centers

Part I: M51 is observed at a wavelength of 850 mum, where most radiation is emitted by dust. We find prominent spiral arms and an underlying exponential disk. The properties of the disk and the arms are studied. Part II and III: Gas in Galaxy Centers is exposed to intense radiation from a starburst region, an Active Galactic Nucleus (AGN), or both. The OB stars in starforming regions mostly radiate in the far-ultraviolet (FUV) and accreting black holes mostly in the X-ray regime. FUV and X-ray photons lead to a totally different chemical composition of gas clouds. Therefore, molecules such as H2, CO, HCN and HCO+ emit different line intensities. In the thesis, we model the line emission of the molecules in these gas clouds with Photon Dominated Regions models (FUV: PDR) and X-ray Dominated Region models (X-rays: XDR). These models are applied to nearby active galaxies such as NGC 253 and NGC 1068.Leiden Observatory LKBFUBL - phd migration 201

Songlines from Direct Collapse Seed Black Holes: Effects of X-rays on Black Hole Growth and Stellar Populations

In the last decade, the growth of supermassive black holes (SMBHs) has been intricately linked to galaxy formation and evolution and is a key ingredient in the assembly of galaxies. To investigate the origin of SMBHs, we perform cosmological simulations that target the direct collapse black hole (DCBH) seed formation scenario in the presence of two different strong Lyman-Werner (LW) background fields. These simulations include the X-ray irradiation from a central massive black hole (MBH), $\rm{H}_2$ self-shielding and stellar feedback from metal-free and metal-enriched stars. We find in both simulations that local X-ray feedback induces metal-free star formation $\sim 0.5$ Myr after the MBH forms. The MBH accretion rate reaches a maximum of $10^{-3}$ $M_{\odot}$ yr$^{-1}$ in both simulations. However, the duty cycle differs which is derived to be $6\%$ and $50\%$ for high and low LW cases, respectively. The MBH in the high LW case grows only $\sim 6\%$ in 100 Myr compared to $16\%$ in the low LW case. We find that the maximum accretion rate is determined by the local gas thermodynamics whereas the duty cycle is determined by the large scale gas dynamics and gas reservoir. We conclude that radiative feedback from the central MBH plays an important role in star formation in the nuclear regions and stifling initial MBH growth, relative to the typical Eddington rate argument, and that initial MBH growth might be affected by the local LW radiation field.Comment: 8 pages, 6 figures. Accepted for publication in ApJ, with minor changes to submitted versio

X-ray Ionization of Heavy Elements Applied to Protoplanetary Disks

The consequences of the Auger effect on the population of heavy-element ions are analyzed for the case of relatively cool gas irradiated by keV X-rays with intended applications to the accretion disks of young stellar objects. Highly charged ions are rapidly reduced to the doubly charged state in neutral gas, so the aim here is to derive the production rates for these singly and doubly charged ions and to specify their transformation by recombination, charge transfer, and molecular reactions. The theory is illustrated by calculations of the abundance

Tracing the Physical Conditions in Active Galactic Nuclei with Time-Dependent Chemistry

We present an extension of the code ProDiMo that allows for a modeling of processes pertinent to active galactic nuclei and to an ambient chemistry that is time dependent. We present a proof-of-concept and focus on a few astrophysically relevant species, e.g., H+, H2+ and H3+; C+ and N+; C and O; CO and H2O; OH+, H2O+ and H3O+; HCN and HCO+. We find that the freeze-out of water is strongly suppressed and that this affects the bulk of the oxygen and carbon chemistry occurring in AGN. The commonly used AGN tracer HCN/HCO+ is strongly time-dependent, with ratios that vary over orders of magnitude for times longer than 10^4 years. Through ALMA observations this ratio can be used to probe how the narrow-line region evolves under large fluctuations in the SMBH accretion rate. Strong evolutionary trends, on time scales of 10^4-10^8 years, are also found in species such as H3O+, CO, and H2O. These reflect, respectively, time dependent effects in the ionization balance, the transient nature of the production of molecular gas, and the freeze-out/sublimation of water.Comment: Accepted for publication at the Journal of Physical Chemistry A "Oka Festschrift: Celebrating 45 Years of Astrochemistry

On the Detection of High Redshift Black Holes with ALMA through CO and H2 Emission

Many present-day galaxies are known to harbor supermassive, >10^6 Mo, black holes. These central black holes must have grown through accretion from less massive seeds in the early universe. The molecules CO and H2 can be used to trace this young population of accreting massive black holes through the X-ray irradiation of ambient gas. The X-rays drive a low-metallicity ion-molecule chemistry that leads to the formation and excitation of CO and H2 in 100<T<1,000 K gas. H2 traces very low metallicity gas, ~10^-3 solar or less, while some pollution by metals, ~10^-2 solar or more, must have taken place to form CO. Strong CO J>15 and H2 S(0) & S(1) emission is found that allows one to constrain ambient conditions. Comparable line strengths cannot be produced by FUV or cosmic ray irradiation. Weak, but perhaps detectable, H3+ (2,2) - (1,1) emission is found and discussed. The models predict that black hole masses larger than 10^5 Mo can be detected with ALMA, over a redshift range of 5-20, provided that the black holes radiate close to Eddington.Comment: 12 pages, 3 figures, ApJL accepted; minor typographical change

A New Raytracer for Modeling AU-Scale Imaging of Lines from Protoplanetary Disks

The material that formed the present-day solar system originated in feeding zones in the inner solar nebula located at distances within ~20 AU from the Sun, known as the planet-forming zone. Meteoritic and cometary material contain abundant evidence for the presence of a rich and active chemistry in the planet-forming zone during the gas-rich phase of solar system formation. It is a natural conjecture that analogs can be found among the zoo of protoplanetary disks around nearby young stars. The study of the chemistry and dynamics of planet formation requires: (1) tracers of dense gas at 100-1000 K and (2) imaging capabilities of such tracers with 5-100 mas (0.5-20 AU) resolution, corresponding to the planet-forming zone at the distance of the closest star-forming regions. Recognizing that the rich infrared (2-200 μm) molecular spectrum recently discovered to be common in protoplanetary disks represents such a tracer, we present a new general ray-tracing code, RADLite, that is optimized for producing infrared line spectra and images from axisymmetric structures. RADLite can consistently deal with a wide range of velocity gradients, such as those typical for the inner regions of protoplanetary disks. The code is intended as a back-end for chemical and excitation codes, and can rapidly produce spectra of thousands of lines for grids of models for comparison with observations. Such radiative transfer tools will be crucial for constraining both the structure and chemistry of planet-forming regions, including data from current infrared imaging spectrometers and extending to the Atacama Large Millimeter Array and the next generation of Extremely Large Telescopes, the James Webb Space Telescope and beyond

A Spitzer survey of mid-infrared molecular emission from protoplanetary disks I: Detection rates

We present a Spitzer InfraRed Spectrometer search for 10-36 micron molecular emission from a large sample of protoplanetary disks, including lines from H2O, OH, C2H2, HCN and CO2. This paper describes the sample and data processing and derives the detection rate of mid-infrared molecular emission as a function of stellar mass. The sample covers a range of spectral type from early M to A, and is supplemented by archival spectra of disks around A and B stars. It is drawn from a variety of nearby star forming regions, including Ophiuchus, Lupus and Chamaeleon. In total, we identify 22 T Tauri stars with strong mid-infrared H2O emission. Integrated water line luminosities, where water vapor is detected, range from 5x10^-4 to 9x10^-3 Lsun, likely making water the dominant line coolant of inner disk surfaces in classical T Tauri stars. None of the 5 transitional disks in the sample show detectable gaseous molecular emission with Spitzer upper limits at the 1% level in terms of line-to-continuum ratios (apart from H2). We find a strong dependence on detection rate with spectral type; no disks around our sample of 25 A and B stars were found to exhibit water emission, down to 1-2% line-to-continuum ratios, in the mid-infrared, while almost 2/3 of the disks around K stars show sufficiently intense water emission to be detected by Spitzer. Some Herbig Ae/Be stars show tentative H2O/OH emission features beyond 20 micron at the 1-2 level, however, and one of them shows CO2 in emission. We argue that the observed differences between T Tauri disks and Herbig Ae/Be disks is due to a difference in excitation and/or chemistry depending on spectral type and suggest that photochemistry may be playing an important role in the observable characteristics of mid-infrared molecular line emission from protoplanetary disks.Comment: 19 pages, accepted for publication in Ap