Observations of line ratios in the Milky Way's warm ionized medium (WIM) suggest that photoionization is not the only heating mechanism present. For the additional heating to explain the discrepancy it would have to have a weaker dependence on the gas density than the cooling rate, $Λn_e^2$. \cite{reynolds99} suggested turbulent dissipation or magnetic field reconnection as possible heating sources. We investigate here the viability of MHD-wave mediated cosmic ray heating as a supplemental heating source. This heating rate depends on the gas density only through its linear dependence on the Alfvén speed, which goes as $n_e^{-1/2}$. We show that, scaled to appropriate values of cosmic ray energy density, cosmic ray heating can be significant. Furthermore, this heating is stable to perturbations. These results should also apply to warm ionized gas in other galaxies.
In light of evidence for a high ionization rate due to Low-Energy Cosmic Rays (LECR), in diffuse molecular gas in the solar neighbourhood, we evaluate their heat input to the Warm Ionized Medium (WIM). LECR are much more effective at heating plasma than they are at heating neutrals. We show that the upper end of the measured ionization rates corresponds to a local LECR heating rate sufficient to maintain the WIM against radiative cooling, independent of the nature of the ionizing particles or the detailed shape of their spectrum. Elsewhere in the Galaxy the LECR heating rates may be higher tha…
The X-ray spectra of active galactic nuclei (AGNs) often exhibit an excess of emission above the primary power-law at energies <~ $2$ keV. Two models for the origin of this `soft excess' are ionized relativistic reflection from the inner accretion disc and Comptonization of thermal emission in a warm corona. Here, we introduce reXcor, a new AGN X-ray ($0.3$-$100$ keV) spectral fitting model that self-consistently combines the effects of both ionized relativistic reflection and the emission from a warm corona. In this model, the accretion energy liberated in the inner disc is distributed betwee…
We discuss the role of turbulence in establishing the observed emission measures and ionization of the warm ionized medium. A Monte Carlo radiative transfer code applied to a snapshot of a simulation of a supernova-driven, multi-temperature, stratified ISM reproduces the essential observed features of the WIM.
We review the observational evidence that the warm ionized medium (WIM) is a major and physically distinct component of the Galactic interstellar medium. Although up to ~20% of the faint, high-latitude H-alpha emission in the Milky Way may be scattered light emitted in midplane H II regions, recent scattered light models do not effectively challenge the well-established properties of the WIM.
This article reviews observations and models of the diffuse ionized gas that permeates the disk and halo of our Galaxy and others. It was inspired by a series of invited talks presented during an afternoon scientific session of the 65th birthday celebration for Professor Carl Heiles held at Arecibo Observatory in August 2004. This review is in recognition of Carl's long standing interest in and advocacy for studies of the ionized as well as the neutral components of the interstellar medium.
HIFI GOT C+ Galactic plane [CII] spectral survey has detected strong emission at the spiral arm tangencies. We use the unique viewing geometry of the Scutum-Crux (S-C) tangency near i = 30degs to detect the warm ionized medium (WIM) component traced by [CII] and to study the effects of spiral density waves on Interstellar Medium (ISM) gas. We compare [CII] velocity features with ancillary HI, 12CO and 13CO data near tangent velocities at each longitude to separate the cold neutral medium and the warm neutral + ionized components in the S-C tangency, then we identify [CII] emission at the highe…
The two papers referred to in the title, claiming the detection of a large-scale massive hot gaseous halo around the Galaxy, have generated a lot of confusion and unwarranted excitement (including public news coverage). However, the papers are seriously flawed in many aspects, including problematic analysis and assumptions, as well as mis-reading and mis-interpreting earlier studies, which are inconsistent with the claim. Here we show examples of such flaws.
Ionized interstellar gas is an important component of the interstellar medium and its lifecycle. The recent evidence for a widely distributed highly ionized warm interstellar gas with a density intermediate between the warm ionized medium (WIM) and compact HII regions suggests that there is a major gap in our understanding of the interstellar gas. Here we investigate the properties of the dense warm ionized medium (D-WIM) in the Milky Way using spectrally resolved SOFIA GREAT [NII] 205 micron line emission and Green Bank Telescope hydrogen radio recombination lines (RRL) data, supplemented by …
Active Galactic Nuclei and STaR fOrmation in Nearby Galaxies AGNSTRONG. III. A Study on Ionized and Warm Molecular Gas Outflows of 6 Type-2 AGNs
Department of Astronomy, University of Science and Technology of China（中国科学技术大学天文系）；School of Astronomy and Space Science, University of Science and Technology of China（中国科学技术大学天文与空间科学学院）
Ionized nebulae have been targets of interest since the introduction of the telescope centuries ago. These isolated, "classical" H II regions gave us some of the earliest insight into the copious feedback energy that stars inject into the interstellar medium. Their unique spectra contain information about the quality and quantity of the ionizing field as well as the temperature, density, and metallicity of these discrete locations in the Galaxy. With increasing sensitivity across many spectral domains, we now know that ionized gas is not localized to massive star regions in many star-forming g…
Wu et al. (2009) suggested an empirical relation between the magnetic field strength along the line of sight (LOS) and the dispersion of Faraday rotation measure (RM) distribution in turbulent media with root-mean-square sonic Mach number $M_s \simeq 1$. In this paper, we extend the work by incorporating the Mach number dependence. Media with $\sim 0.5 < M_s < \sim 2$ are considered to cover the Mach number range of the warm ionized medium (WIM) of our Galaxy. Three-dimensional, magnetohydrodynamic isothermal turbulence simulations with solenoidal forcing are used. We suggest a new relation am…
We studied Faraday rotation measure (RM) in turbulent media with the rms Mach number of unity, using isothermal, magnetohydrodynamic turbulence simulations. Four cases with different values of initial plasma beta were considered. Our main findings are as follows. (1) There is no strong correlation between the fluctuations of magnetic field strength and gas density. So the magnetic field strength estimated with RM/DM (DM is the dispersion measure) correctly represents the true mean strength of the magnetic field along the line of sight. (2) The frequency distribution of RMs is well fitted to th…
Wisconsin H-Alpha Mapper (WHAM) observations of H-Alpha and [S II]$\lambda6716$ emission are used to trace the vertical distribution and physical conditions of the warm ionized medium (WIM) along the Sagittarius-Carina arm. CO emission, tracing cold molecular gas in the plane of the Galaxy, is used as a guide to isolate H-Alpha and [S II] emission along individual spiral arms. Exponential scale heights of electron density squared (or emission measure) are determined using H-Alpha emission above (below) the midplane to be $330 \pm 80$ pc ( $550 \pm 230$ pc) along the near Sagittarius arm, $300 …
The relationship between warm and hot gas-phase metallicity in massive elliptical galaxies and the influence of AGN feedback
Universidad de Santiago de Chile（圣地亚哥智利大学）；University of Kentucky（肯塔基大学）；NASA-Ames Research Center（美国国家航空航天局艾姆斯研究中心）；University of Nottingham（诺丁汉大学）；University of Modena & Reggio Emilia（摩德纳与雷焦艾米利亚大学）；Observatoire de Paris（巴黎天文台）；Collége de France（法兰西学院）；PSL University（巴黎文理研究大学）；Sorbonne University（索邦大学）；University of Alabama in Huntsville（阿拉巴马大学亨茨维尔分校）；Universidad de Tarapacá（塔拉帕卡大学）
We report on a systematic investigation of the cold and mildly ionized gaseous baryonic metal components of our Galaxy, through the analysis of high resolution Chandra and XMM-Newton spectra of two samples of Galactic and extragalactic sources. The comparison between lines of sight towards sources located in the disk of our Galaxy and extragalactic sources, allows us for the first time to clearly distinguish between gaseous metal components in the disk and halo of our Galaxy. We find that a Warm Ionized Metal Medium (WIMM) permeates a large volume above and below the Galaxy's disk, perhaps up …
A warm corona at the surface of an accretion disc has been proposed as a potential location for producing the soft excess commonly observed in the X-ray spectra of active galactic nuclei (AGNs). In order to fit the observed data the gas must be at temperatures of $\sim 1$ keV and have an optical depth of $τ_{\mathrm{T}}\approx 10$--$20$. We present one-dimensional calculations of the physical conditions and emitted spectra of a $τ_{\mathrm{T}}=10$ or $20$ gas layer subject to illumination from an X-ray power-law (from above), a blackbody (from below) and a variable amount of internal heating. …
We have used the Gemini Near-Infrared Integral Field Spectrograph (NIFS) in the J and K bands to map the distribution, excitation and kinematics of the ionized HII and warm molecular gas H$_2$, in the inner few 100 pc of 6 nearby active galaxies: NGC 788, Mrk 607, NGC 3227, NGC 3516, NGC 5506, NGC 5899. {For most galaxies, this is the first time that such maps have been obtained}. The ionized and H$_2$ gas show distinct kinematics: while the H$_2$ gas is mostly rotating in the galaxy plane with low velocity dispersion ($σ$), the ionized gas usually shows signatures of outflows associated with …
The metallicity of galactic gaseous halos provides insights into accretion and feedback of galaxies. The nearby edge-on galaxy NGC 891 has a multi-component gaseous halo and a background AGN (LQAC 035+042 003) projected 5 kpc above the disk near the minor axis. Against the UV continuum of this AGN, we detect lines from 13 ions associated with NGC 891 in new {\it HST}/COS spectra. Most of the absorption is from the warm ionized gas with $\log T=4.22\pm0.04$, $\log n_{\rm H}=-1.26\pm0.51$, and $\log N_{\rm H}=20.81\pm 0.20$. The metallicity of volatile elements (i.e., C, N, and S) is about half …
We present the first systematic investigation of the existence, spatial distribution, and kinematics of warm ionized gas as traced by the [O II] 3727AA emission line in 74 of the most massive galaxies in the local Universe. All of our galaxies have deep integral field spectroscopy from the volume- and magnitude-limited MASSIVE survey of early-type galaxies with stellar mass log(M_*/M_sun) > 11.5 (M_K < -25.3 mag) and distance D < 108 Mpc. Of the 74 galaxies in our sample, we detect warm ionized gas in 28, which yields a global detection fraction of 38\pm6% down to a typical [O II] equivalent w…
We present Wisconsin H-Alpha Mapper [S II] λ6716 and Hα spectroscopic maps of the warm ionized medium (WIM) in the Scutum-Centaurus Arm at Galactic longitudes 310° < l < 345°. Using extinction-corrected Hα intensities (IHαc), we measure an exponential scale height of electron density-squared in the arm of H_ne^2 = 0.30 kpc (assuming a distance of 3.5 kpc), intermediate between that observed in the inner Galaxy and in the Perseus Arm. The [S II]/Hα line ratio is enhanced at large |z| and in sightlines with faint IHαc. We find that the [S II]/Hα line ratio has a power law relationship with IHαc …
We present new XMM-Newton observations of the intriguing warm absorber in I Zwicky 1. This luminous and nearby narrow-line Seyfert 1 galaxy shows ionized absorption by two components of outflowing gas; a low and a high-ionization phase with log $ξ$~0 and log $ξ$~2 respectively. Detailed modelling of these data reveal a complex and variable multi-phase warm absorber. However, we find the changes in the ionization state of the gas not to be straightforwardly correlated with the variability of the intrinsic continuum source, in apparent contrast with photoionization equilibrium. The observed vari…
We present large-scale submm observations towards the Sgr A Complex covering ~300 arcmin2. These data were obtained in the frame of the HEXGAL Program with the Herschel-HIFI satellite and are complemented with submm observations obtained with the NANTEN2/SMART telescope as part of the NANTEN2/SMART Central Nuclear Zone Survey. The observed species are CO(4-3) observed with the NANTEN2/SMART telescope, and [CI](1-0), [CI](2-1), [NII](1-0), and [CII](3/2-1/2) observed with the Herschel-HIFI satellite. The observations are presented in a 1 km/s spectral resolution and a spatial resolution ranging…
We analyze Near-Infrared Integral Field Spectrograph (NIFS) observations of the type-2 quasar (QSO2) SDSS J094521.33+173753.2 to investigate its warm molecular and ionized gas kinematics. This QSO2 has a bolometric luminosity of 10$^{45.7}$ erg s$^{-1}$ and a redshift of z = 0.128. The K-band spectra provided by NIFS cover a range of 1.99-2.40 $μ$m where low-ionization (Pa$α$ and Br$δ$), high ionization ([S XI]$λ$1.920 $μ$m and [Si~VI]$λ$1.963 $μ$m) and warm molecular lines (from H$_2$ 1-0S(5) to 1-0S(1)) are detected, allowing us to study the multi-phase gas kinematics. Our analysis reveals g…
We present new 3D magnetohydrodynamic (MHD) simulations of a supernova-driven, stratified interstellar medium. These simulations were run using the Waagan (2009) positivity preserving scheme for ideal MHD implemented in the Flash code. The scheme is stable even for the Mach numbers approaching 100 found in this problem. We have previously shown that the density distribution arising from hydrodynamical versions of these simulations creates low-density pathways through which Lyman continuum photons can travel to heights |z| > 1 kpc. This naturally produces the warm ionized medium through photoio…
We investigate the warm ionized gas in the blue compact galaxy (BCG) Haro 14 by means of integral field spectroscopic observations taken with the MUSE/VLT. The large FoV of MUSE and its unprecedented sensitivity enable observations of the galaxy nebular emission up to large galactocentric distances. This allowed us to trace the ionized gas morphology and ionization structure up to kiloparsec scales and, for the first time, to accurately investigate the excitation mechanism operating in the outskirts of a typical BCG. The intensity and diagnostic maps reveal at least two highly distinct compone…
Constraints on the properties of warm ionized gas from low-frequency hydrogen radio recombination lines
Green Bank Observatory（格林班克天文台）；National Radio Astronomy Observatory（国家射电天文台）；Westminster College（威斯敏斯特学院）；Florida Space Institute, University of Central Florida（中佛罗里达大学佛罗里达航天研究所）；Arecibo Observatory（阿雷西博天文台）；Center for Advanced Research in Science and Engineering, University of Puerto Rico（波多黎各大学先进科学与工程研究中心）；West Virginia University（西弗吉尼亚大学）
First results from the JWST Early Release Science Program Q3D: The Warm Ionized Gas Outflow in z ~ 1.6 Quasar XID 2028 and its Impact on the Host Galaxy
The Magellanic System includes some of the nearest examples of galaxies disturbed by galaxy interactions. These interactions have redistributed much of their gas into the halos of the Milky Way and the Magellanic Clouds. We present Wisconsin H-alpha Mapper kinematically resolved observations of the warm ionized gas in the Magellanic Bridge over the velocity range of +100 to +300 km/s in the local standard-of-rest reference frame. These observations include the first full H-alpha intensity map and the corresponding intensity-weighted mean velocity map of the Magellanic Bridge across (l, b) = (2…
We present direct measures of the ionization fractions of several sulfur ions in the Galactic warm ionized medium (WIM). We obtained high resolution ultraviolet absorption line spectroscopy of post-asymptotic giant branch stars in the the globular clusters Messier 3 [(l,b)=(42.2, +78.7); d=10.2 kpc, z=10.0 kpc] and Messier 5 [(l,b)=(3.9, +46.8); d=7.5 kpc, z = +5.3 kpc] with the Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer to measure, or place limits on, the column densities of S I, S II, S III, S IV, S VI, and H I. These clusters also house millisecond pulsars, whose disp…
We report on a comparison between 21 cm rotation measure (RM) and the optically-thin atomic hydrogen column density (N_HI) measured towards unresolved extragalactic sources in the Galactic plane of the northern sky. HI column densities integrated to the Galactic edge are measured immediately surrounding each of nearly 2000 sources in 1-arcminute 21 cm line data, and are compared to RMs observed from polarized emission of each source. RM data are binned in column-density bins 4x10^20 cm^-2 wide, and one observes a strong relationship between the number of hydrogen atoms in a 1 cm^2 column throu…
We investigate the influence of High Mass X-ray Binaries on their high redshift environments. Using a one-dimensional radiative transfer code, we predict the ionization and temperature profiles surrounding a coeval stellar population, composed of main sequence stars and HMXBs, at various times after its formation. We consider both uniform density surroundings, and a cluster embedded in a 10^8 solar mass NFW halo. HMXBs in a constant density environment produce negligible enhanced ionization because of their high-energy SEDs and short lifetimes. In this case, HMXBs only marginally contribute to…
The gas-phase chemistry of water in protoplanetary disks is analyzed with a model based on X-ray heating and ionization of the disk atmosphere. Several uncertain processes appear to play critical roles in generating the column densities of warm water that are detected from disks at infrared wavelengths. The dominant factors are the reactions that form molecular hydrogen, including formation on warm grains, and the ionization and heating of the atmosphere. All of these can work together to produce a region of high water abundances in the molecular transition layer of the inner disk atmosphere, …
We have observed the Galactic Center (GC) region at 0.154 and 0.255 GHz with the GMRT. A total of 62 compact likely extragalactic sources are detected. Their scattering sizes go down linearly with increasing angular distance from the GC up to about 1 deg. The apparent scattering sizes of sources are more than an order of magnitude down than predicted earlier by the NE2001 model of Galactic electron distribution within 359.5 deg < l < 0.5 deg and -0.5 deg <b <0.5 deg (Hyperstrong scattering region) of the Galaxy. High free-free optical depths are observed towards most of the extended nonthermal…
Young radio AGN are pivotal for our understanding of many of the still-debated aspects of AGN feedback. In this paper we present a study of the interstellar medium in the compact, peaked-spectrum radio galaxy PKSB1934-63 using X-shooter observations. Most of the warm ionized gas resides within a circum-nuclear disk with a radius of about 200pc that is likely to constitute the gas reservoir from which the central black hole feeds. On the other hand, we find a biconical outflow of warm ionized gas with an estimated radius of 59+/-12pc. This matches the radial extent of the radio source and sugge…
The high-velocity cloud (HVC) Complex A is a probe of the physical conditions in the Galactic halo. The kinematics, morphology, distance, and metallicity of Complex A indicate that it represents new material that is accreting onto the Galaxy. We present Wisconsin H-alpha Mapper (WHAM) kinematically resolved observations of Complex A over the velocity range of -250 to -50 km/s in the local standard of rest reference frame. These observations include the first full H-alpha intensity map of Complex A across (l, b) = (124, 18) to (171, 53) and deep targeted observations in H-alpha, [S II]6716, [N …
Context. Cosmic ray particles that hit interstellar grains in dark molecular cores may induce whole-grain heating. The high temperature of a CR-heated grain allows energy barriers for bulk diffusion and reactions to be overcome. Additionally, ice molecules are destroyed by direct cosmic-ray induced dissociation. Aims. We provide a justified estimate of the significance of cosmic-ray induced surface-mantle diffusion, chemical reactions in ice, and dissociation of ice species in a star-forming interstellar cloud core. Methods. We considered a gas clump in a collapsing low-mass prestellar core an…
This paper investigates the neutral gas phase of galactic winds via the Na I D$λλ5890,5895$Å feature within $z \sim 0.04$ MaNGA galaxies, and directly compares their incidence and strength to the ionized winds detected within the same parent sample. We find evidence for neutral outflows in 127 galaxies ($\sim 5$ per cent of the analysed line-emitting sample). Na I D winds are preferentially seen in galaxies with dustier central regions and both wind phases are more often found in systems with elevated SFR surface densities, especially when there has been a recent upturn in the star formation a…
We investigate if and how growing super-massive black holes (SMBH) known as Active Galactic Nuclei (AGN) and gravitational interactions affect the warm molecular gas and dust of galaxies. Our analysis focuses on the morphologies and warm ISM properties of 630 galaxies at z < 0.1. We use grizy images from the Pan-STARRS survey to classify the galaxies into mergers, early mergers, and non-mergers. We use MIR spectroscopic measurements of emission from rotational H2 transitions, dust and PAH features, and silicate emission or absorption lines at 9.7 microns to study how gravitational interactions…
We report the results of analyses of galactic outflows in a sample of 45 low-redshift starburst galaxies in the COS Legacy Archive Spectroscopic SurveY (CLASSY), augmented by five additional similar starbursts with COS data. The outflows are traced by blueshifted absorption-lines of metals spanning a wide range of ionization potential. The high quality and broad spectral coverage of CLASSY data enable us to disentangle the absorption due to the static ISM from that due to outflows. We further use different line multiplets and doublets to determine the covering fraction, column density, and ion…
We reveal the importance of ongoing in-situ star formation in the Brightest Cluster Galaxy in the massive cool-core CLASH cluster MACS 1931.8-2635 at z=0.35. Using a multi-wavelength approach, we assess the stellar and warm ionized medium components, spatially resolved by the VLT-MUSE spectroscopy, and link them to the molecular gas by incorporating sub-mm ALMA observations. We measure the fluxes of strong emission lines, allowing us to determine the physical conditions of the warm ionized gas. The ionized gas flux brightness peak corresponds to the location of the supermassive black hole and …
We elaborate on the dynamics of ionized interstellar medium in the presence of hidden photon dark matter. Our main focus is the ultra-light regime, where the hidden photon mass is smaller than the plasma frequency in the Milky Way. We point out that as a result of the Galactic plasma shielding direct detection of ultra-light photons in this mass range is especially challenging. However, we demonstrate that ultra-light hidden photon dark matter provides a powerful heating source for the ionized interstellar medium. This results in a strong bound on the kinetic mixing between hidden and regular …
The molecular gas in the DR21 massive star formation region is known to be affected by the strong UV field from the central star cluster and by a fast outflow creating a bright shock. The relative contribution of both heating mechanisms is the matter of a long debate. By better sampling the excitation ladder of various tracers we provide a quantitative distinction between the different heating mechanisms. HIFI observations of mid-J transitions of CO and HCO+ isotopes allow us to bridge the gap in excitation energies between observations from the ground, characterizing the cooler gas, and exist…
Galaxy and occupies perhaps a quarter of the volume of the Galactic disk. Decoding the spectrum of the Galactic diffuse ionizing field is of fundamental interest. This can be done via direct measurements of ionization fractions of various elements. Based on current physical models for the WIM we predicted that mid-IR fine structure lines of Ne, Ar and S would be within the grasp of the Mid-Infrared Imager-Medium Resolution Spectrometer (MIRI-MRS), an Integral Field Unit (IFU) spectrograph, aboard the James Webb Space Telescope (JWST). Motivated thus we analyzed a pair of commissioning data set…
The morphological, spectroscopic and kinematical properties of the warm interstellar medium (wim) in early-type galaxies (ETGs) hold key observational constraints to nuclear activity and the buildup history of these massive, quiescent systems. High-quality integral field spectroscopy (IFS) data with a wide spectral and spatial coverage, such as those from the CALIFA survey, offer an unprecedented opportunity for advancing our understanding of the wim in ETGs. This article centers on a 2D investigation of the wim component in 32 nearby (<~150Mpc) ETGs from CALIFA, complementing a previous 1D an…
(Abridged) NGC 985 was observed by XMM-Newton twice in 2015, revealing that the source was coming out from a soft X-ray obscuration event that took place in 2013. These kinds of events are possibly recurrent since a previous XMM-Newton archival observation in 2003 also showed signatures of partial obscuration. We have analyzed the high-resolution X-ray spectra of NGC 985 obtained by the RGS in 2003, 2013, and 2015 in order to characterize the ionized absorbers superimposed to the continuum and to study their response as the ionizing flux varies. We found that up to four warm absorber (WA) comp…
Analysis of interstellar absorption lines observed in high-resolution {\em HST} spectra of nearby stars provides temperatures, turbulent velocities, and kinetic properties of warm interstellar clouds. Previous studies identified 15 warm partially ionized clouds within about 10~pc of the Sun and measured their mean thermal and kinematic properties. A new analysis of 100 interstellar velocity components reveals a wide range of temperatures and turbulent velocities within the Local Interstellar Cloud (LIC) and other nearby clouds. These variations appear to be random with Gaussian distributions. …
Based on new near-infrared spectroscopic data from the instrument EMIR on the 10.4 m Gran Telescopio Canarias (GTC) we report the presence of an ionized and warm molecular outflow in the luminous type-2 quasar J150904.22+043441.8 (z = 0.1118). The ionized outflow is faster than its molecular counterpart, although the outflow sizes that we derive for them are consistent within the errors (1.34$\pm$0.18 kpc and 1.46$\pm$0.20 kpc respectively). We use these radii, the broad emission-line luminosities and in the case of the ionized outflow, the density calculated from the trans-auroral [OII] and […
Column densities for H I, Al III, Si IV, C IV, and O VI toward 109 stars and 30 extragalactic objects have been assembled to study the extensions of these species away from the Galactic plane into the Galactic halo. H I and Al III mostly trace the warm neutral and warm ionized medium, respectively, while Si IV, C IV and O VI trace a combination of warm photoionized and collisionally ionized plasmas. The much larger object sample compared to previous studies allows us to consider and correct for the effects of the sample bias that has affected earlier but smaller surveys of the gas distribution…
The cooling transition temperature gas in the interstellar medium (ISM), traced by the high ions, Si IV, C IV, N V, and O VI, helps to constrain the flow of energy from the hot ISM with T >10^6 K to the warm ISM with T< 2x10^4 K. We investigate the properties of this gas along the lines of sight to 38 stars in the Milky Way disk using 1.5-2.7 km/s resolution spectra of Si IV, C IV, and N V absorption from the Space Telescope Imaging Spectrograph (STIS), and 15 km/s resolution spectra of O VI absorption from the Far Ultraviolet Spectroscopic Explorer (FUSE). The absorption by Si IV and C IV exh…
It has been hypothesized that photons from young, massive star clusters are responsible for maintaining the ionization of diffuse warm ionized gas seen in both the Milky Way and other disk galaxies. For a theoretical investigation of the warm ionized medium (WIM), it is crucial to solve radiation transfer equations where the ISM and clusters are modeled self-consistently. To this end, we employ a Solar neighborhood model of TIGRESS, a magnetohydrodynamic simulation of the multiphase, star-forming ISM, and post-process the simulation with an adaptive ray tracing method to transfer UV radiation …
