Newly Improved Ionization Corrections for the Neutral Interstellar Medium: Enabling Accurate Abundance Determinations in Star-forming Galaxies throughout the Universe
Svea Hernandez, Alessandra Aloisi, Bethan L. James, Gary J. Ferland, Andrew J. Fox, Monica Tosi, Jason Tumlinson
备注：
20 pages, 8 tables, 8 Figures, Accepted for Publication in ApJ
Studies measuring the chemical abundances of the neutral gas in star-forming galaxies (SFGs) require ionization correction factors (ICFs) to accurately measure their metal contents. In the work presented here we calculate newly improved ICFs for a sample of SFGs. These new corrections include both the contaminating ionized gas along the line of sight (ICF$_{\rm ionized}$) and unaccounted higher ionization stages in the neutral gas (ICF$_{\rm neutral}$). We make use of recently acquired spectroscopic observations taken with the Cosmic Origins Spectrograph (COS) on board Hubble to measure column densities for Fe II and Fe III. Using the Fe III/Fe II ratios as well as other physical properties (i.e. $\log$[L$_{\rm UV}$], $N$(H I), T, and $Z$) we generate ad-hoc photoionization models with CLOUDY to quantify the corrections required for each of the targets. We identify a luminosity threshold of $\log$[L$_{\rm UV}$]$\sim$ 40.75 erg s$^{-1}$ above which the ICF$_{\rm neutral}$ values for nitrogen are relatively higher (ICF$_{\rm neutral}=0.05$-0.7) than those for the rest of the elements (ICF$_{\rm neutral}\sim 0.01$). This behavior indicates that for the high UV luminosity objects, N II is found in non-negligible quantities in the neutral gas, making these ICF$_{\rm neutral}$ corrections critical for determining the true abundances in the interstellar medium. In addition, we calculate ICFs from a uniform grid of models covering a wide range of physical properties typically observed in studies of SFGs and extragalactic H II regions. We provide the community with tabulated ICF values for the neutral gas abundances measured from a variety of environments and applicable to chemical studies of the high redshift universe.
Gaussian analysis of new, high-angular-resolution interstellar 21-cm neutral hydrogen emission profile structure more clearly reveals the presence of the previously reported signature of the critical ionization velocity ({\it CIV}) of Helium (34 km s$^{-1}$). The present analysis includes 1496 component line widths for 178 neutral hydrogen profiles in two areas of sky at galactic latitudes around $-$50$^\circ$, well away from the galactic plane. The new data considered here allow the interstellar abundance of Helium to be calculated, and the derived value of 0.095 $\pm$ 0.020 compares extremel…
We report cosmic ray ionization rates towards ten reddened stars studied within the framework of the EDIBLES (ESO Diffuse Interstellar Bands Large Exploration Survey) program, using the VLT-UVES. For each sightline, between 2 and 10 individual rotational lines of OH$^+$ have been detected in its (0,0) and (1,0) $A^3Π-X^3Σ^-$ electronic band system. This allows constraining of OH$^+$ column densities towards different objects. Results are also presented for 28 additional sightlines for which only one or rather weak signals are found. An analysis of these data makes it possible to derive the pri…
Observations of H3+ in the Galactic diffuse interstellar medium (ISM) have led to various surprising results, including the conclusion that the cosmic-ray ionization rate (zeta_2) is about 1 order of magnitude larger than previously thought. The present survey expands the sample of diffuse cloud sight lines with H3+ observations to 50, with detections in 21 of those. Ionization rates inferred from these observations are in the range (1.7+-1.3)x10^-16 s^-1<zeta_2<(10.6+-8.2)x10^-16 s^-1 with a mean value of zeta_2=(3.5^+5.3_-3.0)x10^-16 s^-1. Upper limits (3 sigma) derived from non-detections o…
When the neutral interstellar medium is exposed to EUV and soft X ray radiation, the argon atoms in it are far more susceptible to being ionized than the hydrogen atoms. We make use of this fact to determine the level of ionization in the nearby, warm, neutral medium (WNM). By analyzing FUSE observations of ultraviolet spectra of 44 hot subdwarf stars a few hundred pc away from the Sun, we can compare column densities of Ar I to those of O I, where the relative ionization of oxygen can be used as a proxy for that of hydrogen. The measured deficiency [ Ar I/O I]= 0.427+/- 0.11dex below the expe…
We present numerical computations and analytic scaling relations for interstellar ion-molecule gas phase chemistry down to very low metallicities ($ 10^{-3} \times$ solar), and/or up to high driving ionization rates. Relevant environments include the cool interstellar medium (ISM) in low-metallicity dwarf galaxies, early enriched clouds at the reionization and Pop-II star formation era, and in dense cold gas exposed to intense X-ray or cosmic-ray sources. We focus on the behavior for H$_2$, CO, CH, OH, H$_2$O and O$_2$, at gas temperatures $\sim 100$ K, characteristic of a cooled ISM at low me…
We model the production of OH+, H2O+, and H3O+ in interstellar clouds, using a steady state photodissociation region code that treats the freeze-out of gas species, grain surface chemistry, and desorption of ices from grains. The code includes PAHs, which have important effects on the chemistry. All three ions generally have two peaks in abundance as a function of depth into the cloud, one at A_V<~1 and one at A_V~3-8, the exact values depending on the ratio of incident ultraviolet flux to gas density. For relatively low values of the incident far ultraviolet flux on the cloud (χ<~ 1000; χ= 1=…
The energy spectrum of electrons produced in molecular gas by interstellar cosmic rays (CRs) is rigorously calculated as a function of gas column density $N$ traversed by the CRs. This allows us to accurately compute the local value of the secondary ionization rate of molecular hydrogen, $ζ_{\rm sec}(N)$, as a function of the local primary ionization rate, $ζ_p(N)$. The ratio $ζ_{\rm sec}/ζ_p$ increases monotonically with $N$, and can considerably exceed the value of $\approx0.67$ commonly adopted in the literature. For sufficiently soft interstellar spectra, the dependence $ζ_{\rm sec}/ζ_p$ v…
This paper reviews recent observations of water in Galactic interstellar clouds and nearby galactic nuclei. Two results are highlighted: (1) Multi-line H$_2$O mapping of the Orion Bar shows that the water chemistry in PDRs is driven by photodissociation and -desorption, unlike in star-forming regions. (2) High-resolution spectra of H$_2$O and its ions toward 5 starburst / AGN systems reveal low ionization rates, unlike as found from higher-excitation lines. We conclude that the chemistry of water strongly depends on radiation environment, and that the ionization rates of interstellar clouds de…
A good understanding of the ionization rates of neutral species in the heliosphere is important for studies of the heliosphere and planetary atmospheres. So far, the intensities of the ionization reactions have been studied based on observations of the contributing phenomena, such as the solar spectral flux in the EUV band and the flux of the solar wind protons, alpha particles, and electrons. The results strongly depend on absolute calibration of these measurements, which, especially for the EUV measurements, is challenging. Here, we propose a novel method of determining the ionization rate o…
Using data from the Green Bank Telescope, we analyze the radio continuum (free-free) and radio recombination line (RRL) emission of the compact HII region NGC 7538 (Sharpless 158). We detect extended radio continuum and hydrogen RRL emission beyond the photodissociation region (PDR) toward the north and east, but a sharp decrease in emission toward the south and west. This indicates that a non-uniform PDR morphology is affecting the amount of radiation "leaking" through the PDR. The strongest carbon RRL emission is found in the western PDR that appears to be dense. We compute a leaking fractio…
We searched for diffuse interstellar bands (DIBs) in the 0.91$<λ<$1.33 $μ$m region by analyzing the near-infrared (NIR) high-resolution ($R=20,000$ and 28,000) spectra of 31 reddened early-type stars ($0.04<E(B-V)<4.58$) and an unreddened reference star. The spectra were collected using the WINERED spectrograph, which was mounted on the 1.3 m Araki telescope at Koyama Astronomical Observatory, Japan, in 2012--2016, and on the 3.58 m New Technology Telescope at La Silla Observatory, Chile, in 2017--2018. We detected 54 DIBs -- 25 of which are newly detected by this study -- eight DIB candidates…
We present numerical computations and analysis of atomic to molecular (HI-to-H$_2$) transitions in cool ($\sim$100 K) low-metallicity dust-free (primordial) gas, in which molecule formation occurs via cosmic-ray driven negative ion chemistry, and removal is by a combination of far-UV photodissociation and cosmic-ray ionization and dissociation. For any gas temperature, the behavior depends on the ratio of the Lyman-Werner (LW) band FUV intensity to gas density, $I_{\rm LW}/n$, and the ratio of the cosmic-ray ionization rate to the gas density, $ζ/n$. We present sets of HI-to-H$_2$ abundance pr…
We present a sample of local analogs for high-redshift galaxies selected in the Sloan Digital Sky Survey (SDSS). The physical conditions of the interstellar medium (ISM) in these local analogs resemble those in high-redshift galaxies. These galaxies are selected based on their positions in the [OIII]/H$β$ versus [NII]/H$α$ nebular emission-line diagnostic diagram. We show that these local analogs share similar physical properties with high-redshift galaxies, including high specific star formation rates (sSFRs), flat UV continuums and compact galaxy sizes. In particular, the ionization paramete…
We present a systematic study of deuterated molecular hydrogen (HD) at high redshift, detected in absorption in the spectra of quasars. We present four new identifications of HD lines associated with known $\rm H_2$-bearing Damped Lyman-$α$ systems. In addition, we measure upper limits on the $\rm HD$ column density in twelve recently identified $\rm H_2$-bearing DLAs. We find that the new $\rm HD$ detections have similar $N({\rm HD})/N(\rm H_2)$ ratios as previously found, further strengthening a marked difference with measurements through the Galaxy. This is likely due to differences in phys…
Non-linear behavior in interstellar chemical models has been recognized for 25 years now. Different mechanisms account for the possibility of multiple fixed-points at steady state, characterized by the ionization degree of the gas. Chemical oscillations are also a natural behaviour of non-linear chemical models. We study under which conditions spontaneous sustained chemical oscillations are possible, and what kind of biffurcations lead to, or quench, the occurrence of such oscillations. Methods. The well known Ordinary Differential Equations (ODE) integrator VODE is used to explore initial con…
We present a semi-analytical description of the relative HD/H2 abundance in the diffuse interstellar medium. We found three asymptotics of the relative HD/H$_2$ abundance for different parts of the medium and their dependence on the physical parameters, namely, number density, intensity of the ultraviolet field, cosmic-ray ionization rate and metallicity. Our calculations are in a good agreement with the full network calculations using Meudon PDR code. We found that in the case of low metallicity and/or higher cosmic ray ionization rate, HD formation rate is significantly enhanced, HD/H2 ratio…
Interstellar polycyclic aromatic hydrocarbons (PAHs) are expected to be strongly processed by vacuum ultraviolet photons. Here, we report experimental studies on the ionization and fragmentation of coronene (C24H12), ovalene (C32H14) and hexa-peri-hexabenzocoronene (HBC; C42H18) cations by exposure to synchrotron radiation in the range of 8--40 eV. The results show that for small PAH cations such as coronene, fragmentation (H-loss) is more important than ionization. However, as the size increases, ionization becomes more and more important and for the HBC cation, ionization dominates. These re…
The ionization fraction plays a key role in the physics and chemistry of the neutral interstellar medium, from controlling the coupling of the gas to the magnetic field to allowing fast ion-neutral reactions that drive interstellar chemistry. Most estimations of the ionization fraction have relied on deuterated species such as DCO+, whose detection is limited to dense cores representing an extremely small fraction of the volume of the giant molecular clouds they are part of. As large field-of-view hyperspectral maps become available, new tracers may be found. We search for the best observable …
We present a comprehensive survey of diffuse interstellar bands (DIBs) in $0.91-1.32μ$m with a newly-developed near-infrared (NIR) spectrograph, WINERED, mounted on the Araki 1.3 m Telescope in Japan. We obtained high-resolution ($R=28,300$) spectra of 25 early-type stars with color excesses of $0.07<E(B-V)<3.4$. In addition to the five DIBs previously detected in this wavelength range, we identified 15 new DIBs, 7 of which were reported as DIB "candidates" by Cox. We analyze the correlations among NIR DIBs, strong optical DIBs, and the reddening of the stars. Consequently, we found that all N…
We use a simple one-zone model of the thermal and chemical evolution of interstellar gas to study whether molecular hydrogen (H2) is ever an important coolant of the warm, diffuse interstellar medium (ISM). We demonstrate that at solar metallicity, H2 cooling is unimportant and the thermal evolution of the ISM is dominated by metal line cooling. At metallicities below 0.1 Z_solar, however, metal line cooling of low density gas quickly becomes unimportant and H2 can become the dominant coolant, even though its abundance in the gas remains small. We investigate the conditions required in order f…
E(A+M)PEC traces the ionization structure, cooling and emission spectra of plasmas. It is written in OpenCL, runs in NVIDIA Graphics Processor Units and can be coupled to any HD or MHD code to follow the dynamical and thermal evolution of any plasma in, e.g., the interstellar medium (ISM).
We present the first statistical sample of rest-frame far-UV spectra of star-forming galaxies at z~1. These spectra are unique in that they cover the high-ionization CIVλλ1548, 1550 doublet. We also detect low-ionization features such as SiIIλ1527, FeIIλ1608, AlIIλ1670, NiIIλλ1741, 1751 and SiIIλ1808, and intermediate-ionization features from AlIIIλλ1854, 1862. Comparing the properties of absorption lines of lower- and higher- ionization states provides a window into the multi-phase nature of circumgalactic gas. Our sample is drawn from the DEEP2 survey and spans the redshift range 1.01 < z < …
This study is motivated by recent observations on ubiquitous interstellar density filaments and guided by modern theories of compressible magnetohydrodynamic (MHD) turbulence. The interstellar turbulence shapes the observed density structures. As the fundamental dynamics of compressible MHD turbulence, perpendicular turbulent mixing of density fluctuations entails elongated density structures aligned with the local magnetic field, accounting for low-density parallel filaments seen in diffuse atomic and molecular gas. The elongation of low-density parallel filaments depends on the turbulence an…
We present results from Subaru/FMOS near-infrared (NIR) spectroscopy of 118 star-forming galaxies at $z\sim1.5$ in the Subaru Deep Field. These galaxies are selected as [OII]$λ$3727 emitters at $z\approx$ 1.47 and 1.62 from narrow-band imaging. We detect H$α$ emission line in 115 galaxies, [OIII]$λ$5007 emission line in 45 galaxies, and H$β$, [NII]$λ$6584, and [SII]$λλ$6716,6731 in 13, 16, and 6 galaxies, respectively. Including the [OII] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate physical conditions of …
The detection of CF$^+$ in interstellar clouds potentially allows astronomers to infer the elemental fluorine abundance and the ionization fraction in ultraviolet-illuminated molecular gas. Because local thermodynamic equilibrium (LTE) conditions are hardly fulfilled in the interstellar medium (ISM), the accurate determination of the CF$^+$ abundance requires one to model its non-LTE excitation via both radiative and collisional processes. Here, we report quantum calculations of rate coefficients for the rotational excitation of CF$^+$ in collisions with para- and ortho-H2 (for temperatures up…
We present new results from near-infrared spectroscopy with Keck/MOSFIRE of [OIII]-selected galaxies at $z\sim3.2$. With our $H$ and $K$-band spectra, we investigate the interstellar medium (ISM) conditions, such as ionization states and gas metallicities. [OIII] emitters at $z\sim3.2$ show a typical gas metallicity of $\mathrm{12+log(O/H) = 8.07\pm0.07}$ at $\mathrm{log(M_*/M_\odot) \sim 9.0-9.2}$ and $\mathrm{12+log(O/H) = 8.31\pm0.04}$ at $\mathrm{log(M_*/M_\odot) \sim 9.7-10.2}$ when using the empirical calibration method. We compare the [OIII] emitters at $z\sim3.2$ with UV-selected galax…
Far-ultraviolet photons from OB-type massive stars regulate the heating, ionization, and chemistry of much of the neutral interstellar gas in star-forming galaxies. The interaction of FUV radiation and interstellar matter takes place in environments broadly known as photodissociation regions (PDRs). PDR line diagnostics are the smoking gun of the radiative feedback from massive stars. Improving our understanding of stellar feedback in the ISM requires quantifying the energy budget, gas dynamics, and chemical composition of PDR environments. This goal demands astronomical instrumentation able t…
This is the first in a series of three papers describing a project with the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure abundances of the neutral interstellar medium (ISM) in a sample of 9 nearby star-forming galaxies. The goal is to assess the (in)homogeneities of the multiphase ISM in galaxies where the bulk of metals can be hidden in the neutral phase, yet the metallicity is inferred from the ionized gas in the HII regions. The sample, spanning a wide range in physical properties, is to date the best suited to investigate the metallicity behavior of the neutral gas …
We analyze interstellar absorption features in the full UV spectrum of the nearby (d = 24 pc) B8 IVn star alpha Leo (Regulus) obtained at high resolution and high S/N by the HST ASTRAL Treasury program. We derive column densities for many key atomic species and interpret their partial ionizations. The gas in front of alpha Leo exhibits two absorption components, one of which coincides in velocity with the local interstellar cloud (LIC) that surrounds the Sun. The second, smaller, component is shifted by +5.6 km/s relative to the main component, in agreement with results for other lines of sigh…
Context: Observations of small carbon-bearing molecules such as CCH, C4H, c-C3H2, and HCO in the Horsehead Nebula have shown these species to have higher abundances towards the edge of the source than towards the center. Aims: Given the determination of a wide range of values for zeta (s-1), the total ionization rate of hydrogen atoms, and the proposal of a column-dependent zeta(N_H), where N_H is the total column of hydrogen nuclei, we desire to determine if the effects of zeta(N_H) in a single object with spatial variation can be observable. We chose the Horsehead Nebula because of its geome…
We present a general parameter study, in which the abundance of interstellar argonium (ArH$^+$) is predicted using a model for the physics and chemistry of diffuse interstellar gas clouds. Results have been obtained as a function of UV radiation field, cosmic-ray ionization rate, and cloud extinction. No single set of cloud parameters provides an acceptable fit to the typical ArH$^+$, OH$^+$ and $\rm H_2O^+$ abundances observed in diffuse clouds within the Galactic disk. Instead, the observed abundances suggest that ArH$^+$ resides primarily in a separate population of small clouds of total vi…
The bulk propagation speed of GeV-energy cosmic rays is limited by frequent scattering off hydromagnetic waves. Most galaxy evolution simulations that account for this confinement assume the gas is fully ionized and cosmic rays are well-coupled to Alfvén waves; however, multiphase density inhomogeneities, frequently under-resolved in galaxy evolution simulations, induce cosmic ray collisions and ionization-dependent transport driven by cosmic ray decoupling and elevated streaming speeds in partially neutral gas. How do cosmic rays navigate and influence such a medium, and can we constrain this…
The spectral index of synchrotron emission is an important parameter in understanding the properties of cosmic ray electrons (CREs) and the interstellar medium (ISM). We determine the synchrotron spectral index ($α_{\rm nt}$) of four nearby star-forming galaxies, namely NGC 4736, NGC 5055, NGC 5236 and NGC 6946 at sub-kpc linear scales. The $α_{\rm nt}$ was determined between 0.33 and 1.4 GHz for all the galaxies. We find the spectral index to be flatter ($\gtrsim -0.7$) in regions with total neutral (atomic + molecular) gas surface density, $Σ_{\rm gas} \gtrsim \rm 50~M_\odot pc^{-2}$, typica…
High resolution X-ray absorption spectroscopy is a powerful diagnostic tool for probing chemical and physical properties of the interstellar medium (ISM) at various phases. We present detections of K transition absorption lines from the low ionization ions of OI, OII, NeI, NeII, and NeIII, and the high ionization ones of OVI, OVII, OVIII, NeIX, and MgXI, as well as details of neutral absorption edges from Mg, Ne, and O in an unprecedented high quality spectrum of the low mass X-ray binary Cyg X-2. These absorption features trace the intervening interstellar medium which is indicated by the uns…
We present an efficient heating/cooling method coupled with chemistry and ultraviolet (UV) radiative transfer, which can be applied to numerical simulations of the interstellar medium (ISM). We follow the time-dependent evolution of hydrogen species (H$_2$, H, H$^+$), assume carbon/oxygen species (C, C$^+$, CO, O, and O$^+$) are in formation-destruction balance given the non-steady hydrogen abundances, and include essential heating/cooling processes needed to capture thermodynamics of all ISM phases. UV radiation from discrete point sources and the diffuse background is followed through adapti…
New Estimate for the Cosmic Ray-Induced $\rm H_2$ Photodissociation Rate in the Interstellar Medium
Max-Planck-Institut für Extraterrestrische Physik（马克斯·普朗克地外物理研究所）；INAF – Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所 – 阿切特里天文台）；Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA UMR 7583（巴黎东克雷泰伊大学和巴黎西岱大学，法国国家科学研究中心，LISA联合研究实验室）；LUX, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université（LUX，巴黎天文台，巴黎文理研究大学，法国国家科学研究中心，索邦大学）
We analyze relative abundances and ionization conditions in a strong absorption system at z=6.84, seen in the spectrum of the z=7.54 background quasar ULAS J134208.10+092838.61. Singly ionized C, Si, Fe, Mg, and Al measurements are consistent with a warm neutral medium that is metal-poor but not chemically pristine. Firm non-detections of C IV and Si IV imply that any warm ionized phase of the IGM or CGM has not yet been enriched past the ultra-metal-poor regime (<0.001Z_{solar}), unlike lower redshift DLAs where these lines are nearly ubiquitous. Relative abundances of the heavy elements 794 …
The first detection of cosmic-ray excited H$_2$ in interstellar space
Technion - Israel Institute of Technology（以色列理工学院）；The Johns Hopkins University（约翰斯·霍普金斯大学）；Space Telescope Science Institute（太空望远镜科学研究所）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）；Università di Bologna（博洛尼亚大学）；University of Duisburg-Essen（杜伊斯堡-埃森大学）；Observatoire de Paris, Université PSL, Sorbonne Université（巴黎天文台，巴黎文理研究大学，索邦大学）；Laboratoire de Physique de l’Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris（巴黎高等师范学院物理实验室，ENS，巴黎文理研究大学，法国国家科学研究中心，索邦大学，巴黎大学）；Zhejiang Laboratory（浙江实验室）；Universität zu Köln（科隆大学）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；INAF-Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）
Inferring Interstellar Medium Density, Temperature, and Metallicity from Turbulent H II Regions
University of Chicago（芝加哥大学）；Sub-department of Astrophysics, University of Oxford（牛津大学天体物理亚系）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）；Cosmic Dawn Center (DAWN)（黎明宇宙中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）
Molecular hydrogen is the most abundant molecular species in the Universe. While no doubts exist that it is mainly formed on the interstellar dust grain surfaces, many details of this process remain poorly known. In this work, we focus on the fate of the energy released by the H$_2$ formation on the dust icy mantles, how it is partitioned between the substrate and the newly formed H$_2$, a process that has a profound impact on the interstellar medium. We carried out state-of-art \textit{ab-initio} molecular dynamics simulations of H$_2$ formation on periodic crystalline and amorphous ice surfa…
We used the multiplex capabilities of the AAOmega spectrograph at the Anglo-Australian Telescope to create a half-square-degree map of the neutral and low-ionized ISM in front of the nearby (~5 kpc), most massive Galactic globular cluster, omega Centauri. Its redshifted, metal-poor and hot horizontal branch stars probe the medium-strong Ca II K and Na I D2 line absorption, and weak absorption in the lambda5780 and lambda5797 Diffuse Interstellar Bands (DIBs), on scales around a parsec. The kinematical and thermodynamical picture emerging from these data is that we predominantly probe the warm …
Primordial black holes are a viable dark matter candidate. They decay via Hawking evaporation. Energetic particles from the Hawking radiation interact with interstellar gas, depositing their energy as heat and ionization. For a sufficiently high Hawking temperature, fast electrons produced by black holes deposit a substantial fraction of energy as heat through the Coulomb interaction. Using the dwarf galaxy Leo T, we place an upper bound on the fraction of primordial black hole dark matter. For $M < 5 \times 10^{-17} M_\odot$, our bound is competitive with or stronger than other bounds.
We study the thermal structure of the neutral atomic (H {\small I}) interstellar medium across a wide range of metallicities, from supersolar down to vanishing metallicity, and for varying UV intensities and cosmic-ray ionization rates. We calculate self-consistently the gas temperature and species abundances (with a special focus on the residual H$_2$), assuming thermal and chemical steady-state. For solar metallicity, $Z' \equiv 1$, we recover the known result that there exists a pressure range over which the gas is multiphased, with the warm ($\sim 10^4$ K, WNM) and cold ($\sim 100$ K, CNM)…
Cosmic rays are an important source of heating in the interstellar medium, in particular in dense molecular cloud cores shielded from the external ultraviolet radiation field. The limits placed on the cosmic-ray ionization rate from measurements of the gas temperature in dense clouds are unaffected by the uncertainties associated to the traditional methods based on the analysis of molecular abundances. However, high-resolution data are required to determine with sufficient accuracy the spatial temperature distribution within prestellar cores. In this contribution we illustrate in detail the ca…
Evidence of Enhanced Ionization in Protostellar Envelopes
Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）；Univ. Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学、法国国家科学研究中心、地球与行星物理学研究所）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文学研究所）；Laboratoire d’Astrophysique (AIM) Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM（巴黎萨克雷大学、巴黎西岱大学、法国原子能和替代能源委员会、法国国家科学研究中心天体分子实验室）；INAF, Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切尔天文台）
We develop the theory of radiative association of an atom and a diatomic molecule within a close-coupling framework. We apply it to the formation of H$_3^-$ after the low energy collision (below 0.5 eV) of H$_2$ with H$^-$. Using recently obtained potential energy and permanent dipole moment surfaces of H$_3^-$, we calculate the lowest rovibrational levels of the H$_3^-$ electronic ground state, and the cross section for the formation of H$_3^-$ by radiative association between H$^-$ and ortho- and para-H$_2$. We discuss the possibility for the H$_3^-$ ion to be formed and observed in the cold…
As a part of interstellar dust, polycyclic aromatic hydrocarbons (PAHs) are processed by the interaction with vacuum ultraviolet (VUV) photons that are emitted by hot young stars. This interaction leads to the emission of the well-known aromatic infrared bands but also of electrons, which can significantly contribute to the heating of the interstellar gas.Our aim is to investigate the impact of molecular size on the photoionization properties of cationic PAHs.Methods. Trapped PAH cations of sizes between 30 and 48 carbon atoms were submitted to VUV photons in the range of 9 to 20 eV from the D…
Ionization of gas-phase organic molecules such as polycyclic aromatic hydrocarbons (PAHs) requires vacuum ultraviolet photons at wavelengths shorter than 200 nm (~6-9 eV). We present here for the first time that visible photons - accessible through sunlight - can cause photoionization of trapped PAHs in cryogenic water-ice, accounting for 4.4 eV less ionization energy than in the gas phase. This finding opens up new reaction pathways involving low-energy ionization in many environments where water and organic matter coexist. This include the interstellar medium, molecular clouds, protoplanetar…
In order to find out capable chemical evolution step from astronomically created organic in interstellar space to biological organic on the earth, infrared spectrum of nitrogen substituted carbon pentagon-hexagon coupled polycyclic aromatic hydrocarbon was analyzed by the density functional theory. Ionization was modeled from neutral to tri-cation. Among one nitrogen and two nitrogen substituted NPAH, we could find good examples showing similar IR behavior with astronomically well observed one as like C8H6N1, C7H5N2, and C7H5N2. We can imagine that such ionized NPAH may be created in interstel…
XRISM spectroscopy of a crowded Galactic center region -- III. S, Ar and Ca ISM Absorption Features in the spectrum of MAXI J1744-294
Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）；Ehime University（爱媛大学）；Hasan Kalyoncu University（哈桑·卡伦库大学）；Western Michigan University（西密歇根大学）；Columbia Astrophysics Laboratory, Columbia University（哥伦比亚大学天体物理学实验室）；Kyoto University（京都大学）；Shizuoka University（静冈大学）；Nara University of Education（奈良教育大学）
