Context. A large fraction of the interstellar medium can be characterized as a multiphase medium. The neutral hydrogen gas is bistable with a cold and warm neutral medium (CNM and WNM respectively) but there is evidence for an additional phase at intermediate temperatures, a lukewarm neutral medium (LNM) that is thermally unstable. Aims. We use all sky data from the HI4PI survey to separate these neutral HI phases with the aim to determine their distribution and phase fractions in the local interstellar medium. Methods. HI4PI observations, gridded on an nside = 1024 HEALPix grid, were decomposed into Gaussian components. From the frequency distribution of the velocity dispersions we infer three separate linewidth regimes. Accordingly we extract the HI line emission corresponding to the CNM, LNM, and WNM. We generated all-sky maps of these phases in the local HI gas with -8 < v_LSR < 8 km/s. Results. Each of the HI phases shows distinct structures on all scales. The LNM never exists as a single phase but contributes on average 41% of the HI. The CNM is prominent only for 22% of the sky, contributes there on average 34% but locally up to 60% of the HI and is associated with dust at temperatures T_dust ~ 18.6 K. Embedded cold filaments show a clear anti-correlation between CNM and LNM. Also the smoothly distributed WNM is anti-correlated with the CNM. It contributes for the rest of the sky 39% with dust associated at temperatures T_dust ~ 19.4 K. Conclusions. The CNM in filaments exists on small scales. Here the observed anti-correlation between LNM and CNM implies that both, filaments and the surrounding more extended LNM, must have a common origin.
In order to investigate when and how the birth of a protostellar core occurs, we made survey observations of four well-studied dense cores in the Taurus molecular cloud using CO transitions in submillimeter bands. We report here the detection of unexpectedly warm (~ 30 - 70 K), extended (radius of ~ 2400 AU), dense (a few times 10^{5} cm^{-3}) gas at the heart of one of the dense cores, L1521F (MC27), within the cold dynamically collapsing components. We argue that the detected warm, extended, dense gas may originate from shock regions caused by collisions between the dynamically collapsing co…
We present a method to determine the spin temperature $T_{\rm S}$ and volume density $n$ of HI gas simultaneously along the tangent-point circle of galactic rotation in the Milky Way by using the least-$χ^2$ method. The best-fit $T_{\rm S}$ is shown to range either in $T_{\rm S}=100-120$ K or in $1000-3000$ K, indicating that the gas is either in cold HI phase with high density and large optical depth, or in warm HI with low density and small optical depth. Averaged values at $3\le R \le 8$ kpc are obtained to be $T_{\rm S}=106.7 \pm 16.0$ K and $n=1.53\pm 0.86$ H cm$^{-3}$ for cold HI, and $1…
Star-forming galaxies are rich reservoirs of dust, both warm and cold. But the cold dust emission is faint alongside the relatively bright and ubiquitous warm dust emission. Recently, evidence for a very cold dust component has also been revealed via millimeter/submillimeter photometry of some galaxies. This component, despite being the most massive of the three dust components in star-forming galaxies, is by virtue of its very low temperature, faint and hard to detect together with the relatively bright emission from warmer dust. Here we analyze the dust content of a carefully selected sample…
We present Herschel SPIRE-FTS intermediate-sampled mapping observations of the central ~8 kpc (~150") of M51, with a spatial resolution of 40". We detect 4 12CO transitions (J=4-3 to J=7-6) and the CI 3P2-3P1 and 3P1-3P0 transitions. We supplement these observations with ground based observations of 12CO J=1-0 to J=3-2 and perform a two-component non-LTE analysis. We find that the molecular gas in the nucleus and centre regions has a cool component (T_kin~10-20 K) with a moderate but poorly constrained density (n(H2)~10^3-10^6 cm^-3), as well as significant molecular gas in a warmer (T_kin~300…
Dust properties are very likely affected by the environment in which dust grains evolve. For instance, some analyses of cold clumps (7 K- 17 K) indicate that the aggregation process is favored in dense environments. However, studying warm (30 K-40 K) dust emission at long wavelength ($λ$$>$300 $μ$m) has been limited because it is difficult to combine far infared-to-millimeter (FIR-to-mm) spectral coverage and high angular resolution for observations of warm dust grains. Using Herschel data from 70 to 500 $μ$m, which are part of the Herschel infrared Galactic (Hi-GAL) survey combined with 1.1 m…
We use N-body simulations of dark matter haloes in cold dark matter (CDM) and a large set of different warm dark matter (WDM) cosmologies to demonstrate that the spherically averaged density profile of dark matter haloes has a shape that depends on the power spectrum of matter perturbations. Density profiles are steeper in WDM but become shallower at scales less than one percent of the virial radius. Virialization isotropizes the velocity dispersion in the inner regions of the halo but does not erase the memory of the initial conditions in phase space. The location of the observed deviations f…
We report Arecibo 21 cm absorption-emission observations to characterise the physical properties of neutral hydrogen (HI) in the proximity of five giant molecular clouds (GMCs): Taurus, California, Rosette, Mon OB1, and NGC 2264. Strong HI absorption was detected toward all 79 background continuum sources in the ~60x20 square degree region. Gaussian decompositions were performed to estimate temperatures, optical depths and column densities of the cold and warm neutral medium (CNM, WNM). The properties of individual CNM components are similar to those previously observed along random Galactic s…
During star formation, the dense gas undergoes significant chemical evolution leading to the emergence of a rich variety of molecules associated with hot cores and hot corinos. The physical and chemical conditions are poorly constrained; the early phases of emerging hot cores in particular represent an unexplored territory. We provide here a full molecular inventory of a massive protostellar core that is proposed to be a precursor of a hot core. We performed an unbiased spectral survey towards the hot core precursor associated with clump G328.2551-0.5321 between 159GHz and 374GHz. To identify …
(Abridged) Using the Arecibo Observatory we have obtained neutral hydrogen (HI) absorption and emission spectral pairs in the direction of 26 background radio continuum sources in the vicinity of the Perseus molecular cloud. Strong absorption lines were detected in all cases allowing us to estimate spin temperature (T_s) and optical depth for 107 individual Gaussian components along these lines of sight. Basic properties of individual HI clouds (spin temperature, optical depth, and the column density of the cold and warm neutral medium, CNM and WNM) in and around Perseus are very similar to th…
The physical evolution of low-mass protostars is relatively well-established, however, there are many open questions on the chemical structure of protostars. The chemical fingerprint generated in the early embedded phase of star formation may be transmitted to the later stages of star, planet and comet formation. The factors that influence the chemical fingerprint are then of interest to study, and determine whether the chemical structure is inherited from the parent cloud or product of the physical processes during star formation. Results of observations and modelling of molecules that trace …
We present deep observations of the 12CO(1-0) and (3-2) lines in the ultra-luminous infrared and radio galaxy 4C12.50, carried out with the 30m telescope of the Institut de Radioastronomie Millimetrique. Our observations reveal the cold molecular gas component of a warm molecular gas outflow that was previously known from Spitzer Space Telescope data. The 12CO(3-2) profile indicates the presence of absorption at -950 km/s from systemic velocity with a central optical depth of 0.22. Its profile is similar to that of the HI absorption that was seen in radio data of this source. A potential detec…
Using the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope, we have obtained high-resolution ultraviolet spectra of the C I absorption toward two stars behind the Local Leo Cold Cloud (LLCC). At a distance (~20 pc) that places it well inside the Local Bubble, the LLCC is the nearest example of the coldest known (T~20 K) diffuse interstellar clouds. The STIS measurements of the C I fine-structure excitation toward HD 85259 and HD 83023 indicate that the thermal gas pressure of the LLCC is much greater than that of the warm clouds in the Local Bubble. The mean LLCC …
We present the Green Bank Telescope absorption survey of cold atomic hydrogen ($\lesssim 300$K) in the inner halo of low-redshift galaxies. The survey aims to characterize the cold gas distribution and to address where condensation - the process where ionized gas accreted by galaxies condenses into cold gas within the disks of galaxies - occurs. Our sample consists of 16 galaxy-quasar pairs with impact parameters of $\le$ 20kpc. We detected an HI absorber associated with J0958+3222 (NGC 3067) and HI emission from six galaxies. We also found two \ion{Ca}{2} absorption system in the archival SDS…
Kinematically cold and warm planetary nebulae samples, HII regions and supernovae remnants in the disc of the face-on spiral galaxy NGC 628 (M74) -- The Planetary Nebulae Spectrograph with the H$α$ arm
ESO（欧洲南方天文台）；Max-Planck-Institüt fur Extraterrestrisches Physik（马克斯·普朗克地外物理研究所）；Research School of Astronomy and Astrophysics, Australia National University（澳大利亚国立大学天文学与天体物理学研究学院）；Oxford Astrophysics, University of Oxford（牛津大学牛津天体物理学）；Finnish Centre for Astronomy with ESO, (FINCA), University of Turku（图尔库大学芬兰ESO天文学中心）；Tuorla Observatory, Department of Physics and Astronomy, University of Turku（图尔库大学物理与天文学系图奥拉天文台）；Turku Collegium for Science, Medicine and Technology (TCSMT), University of Turku（图尔库大学科学、医学与技术学院）；School of Physics and Astronomy, University of Nottingham（诺丁汉大学物理与天文学院）；Universidade Federal do Rio de Janeiro, Observatório do Valongo（里约热内卢联邦大学瓦隆戈天文台）；Osservatorio Astronomico di Capodimonte, INAF（意大利国家天体物理研究所卡波迪蒙特天文台）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Department of Physics “E. Pancini”, University of Naples Federico II（那不勒斯斐迪南多二世大学“E.潘奇尼”物理学系）；Department of Physics and Astronomy, San Jose State University（圣何塞州立大学物理与天文学系）
We present two sets of grid-based hydrodynamical simulations of high-velocity clouds (HVCs) traveling through the diffuse, hot Galactic halo. These HI clouds have been suggested to provide fuel for ongoing star formation in the Galactic disk. The first set of models is best described as a wind-tunnel experiment in which the HVC is exposed to a wind of constant density and velocity. In the second set of models we follow the trajectory of the HVC on its way through an isothermal hydrostatic halo towards the disk. Thus, we cover the two extremes of possible HVC trajectories. The resulting cloud m…
We have conducted two-component, non-LTE modeling of the CO lines from J = 1-0 through J = 13-12 in 87 galaxies observed by the Herschel SPIRE Fourier Transform Spectrometer (FTS). We find the average pressure of the cold molecular gas, traced especially by CO J = 1-0, is $\sim 10^{5.0 \pm 0.5}$ K cm$^{-3}$. The mid- to high-J lines of CO trace higher-pressure gas at $10^{6.5 \pm 0.6}$ K cm$^{-3}$; this pressure is slightly correlated with LFIR. Two components are often necessary to accurately fit the Spectral Line Energy Distributions (SLEDs); a one-component fit often underestimates the flux…
Much attention has been placed on the dust distribution in protostellar envelopes, but there are still many unanswered questions regarding the structure of the gas. We aim to start identifying the factors that determine the chemical structure of protostellar regions, by studying and comparing low-mass embedded systems in key molecular tracers. The cold and warm chemical structures of two embedded Class 0 systems, IRAS16293 and VLA1623 are characterized through interferometric observations. DCO+, N2H+ and N2D+ are used to trace the spatial distribution and physics of the cold regions of the env…
The surroundings of Luminous Blue Variable (LBV) stars are excellent laboratories to study the effects of their high UV radiation, powerful winds, and strong ejection events onto the surrounding gas and dust. The LBV G79.29+0.46 powered two concentric infrared rings which may interact with the infrared dark cloud (IRDC) G79.3+0.3. The Effelsberg 100m telescope was used to observe the NH_3 (1,1), (2,2) emission surrounding G79.29+0.46 and the IRDC. In addition, we observed particular positions in the (3,3) transition toward the strongest region of the IRDC. We report here the first coherent she…
Galactic winds are crucial to the cosmic cycle of matter, transporting material out of the dense regions of galaxies. Observations show the coexistence of different temperature phases in such winds, which is not easy to explain. We present a set of 3D shock-multicloud simulations that account for radiative heating and cooling at temperatures between $10^2\,\rm K$ and $10^7\,\rm K$. The interplay between shock heating, dynamical instabilities, turbulence, and radiative heating and cooling creates a complex multi-phase flow with a rain-like morphology. Cloud gas fragments and is continuously ero…
Both absorption and emission line studies show that cold gas around galaxies is commonly outflowing at speeds of several hundred km$\,\textrm{s}^{-1}$. This observational fact poses a severe challenge to our theoretical models of galaxy evolution since most feedback mechanisms (e.g., supernovae feedback) accelerate hot gas, and the timescale it takes to accelerate a blob of cold gas via a hot wind is much larger than the time it takes to destroy the blob. We revisit this long-standing problem using three-dimensional hydrodynamical simulations with radiative cooling. Our results confirm previou…
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 …
We present Herschel SPIRE-FTS observations of the Antennae (NGC 4038/39), a well studied, nearby ($22$ Mpc) ongoing merger between two gas rich spiral galaxies. We detect 5 CO transitions ($J=4-3$ to $J=8-7$), both [CI] transitions and the [NII]$205μm$ transition across the entire system, which we supplement with ground based observations of the CO $J=1-0$, $J=2-1$ and $J=3-2$ transitions, and Herschel PACS observations of [CII] and [OI]$63μm$. Using the CO and [CI] transitions, we perform both a LTE analysis of [CI], and a non-LTE radiative transfer analysis of CO and [CI] using the radiative…
We use a pair of high resolution N-body simulations implementing two dark matter models, namely the standard cold dark matter (CDM) cosmogony and a warm dark matter (WDM) alternative where the dark matter particle is a 1.5keV thermal relic. We combine these simulations with the GALFORM semi-analytical galaxy formation model in order to explore differences between the resulting galaxy populations. We use GALFORM model variants for CDM and WDM that result in the same z=0 galaxy stellar mass function by construction. We find that most of the studied galaxy properties have the same values in these…
We study the evolving environment dependence of mass accretion by dark haloes in simulations of cold and warm dark matter (CDM and WDM) cosmologies. The latter allows us to probe the nature of halo growth at scales below the WDM half-mode mass, which form an extreme regime of nonlinear collisionless dynamics and offer an excellent test-bed for ideas relating to hierarchical growth. As environmental proxies, we use the local halo-centric matter density $δ$ and tidal anisotropy $α$, as well as large-scale halo bias $b_1$. Our analysis, while reproducing known trends for environment-dependent acc…
High levels of deuterium fractionation in gas-phase molecules are usually associated with cold regions, such as prestellar cores. Significant fractionation ratios are also observed in hot environments such as hot cores or hot corinos, where they are believed to be produced by the evaporation of the icy mantles surrounding dust grains, and thus are remnants of a previous cold (either gas-phase or grain surface) chemistry. The recent detection of DCN towards the Orion Bar, in a clump at a characteristic temperature of 70K, has shown that high deuterium fractionation can also be detected in PDRs.…
Data from the Herschel Space Observatory have revealed an unusual elliptical galaxy, NGC 4125, which has strong and extended submillimeter emission from cold dust but only very strict upper limits to its CO and HI emission. Depending on the dust emissivity, the total dust mass is 2-5x10^6 Msun. While the neutral gas-to-dust mass ratio is extremely low (< 12-30), including the ionized gas traced by [CII] emission raises this limit to < 39-100. The dust emission follows a similar r^{1/4} profile to the stellar light and the dust to stellar mass ratio is towards the high end of what is found in n…
