Having to have low thermal energy, the molecular gas in galaxies is expected to settle in a thin disc near the midplane. However, contradicting this understanding, recent studies have revealed considerably thick molecular discs in nearby spiral galaxies. To understand this apparent discrepancy, we theoretically model the molecular discs in a sample of eight nearby spiral galaxies and estimate their molecular scale heights (Half Width at Half Maxima (HWHM)). We assume that the baryonic discs are in vertical hydrostatic equilibrium under their mutual gravity in the external force field of the dark matter halo. We set up the joint Poisson's-Boltzman equation of hydrostatic equilibrium and numerically solve it to obtain the three-dimensional molecular gas distribution and determine the scale heights in our sample galaxies. We find that the scale heights follow a universal exponential law with a scale length of $0.46 \pm 0.01 \ r_{25}$. The molecular scale heights in our sample galaxies are found to vary between 50-200 pc depending on the galaxy and radius. Using the density solutions, we build dynamical models of the molecular discs and produce molecular column density maps. These model maps found to match to the observed ones reasonably well. We further incline the dynamical models to an inclination of 90$^o$ to estimate the expected observed thickness of the molecular discs. Interestingly it is found that at edge-on orientation, our sample galaxies under hydrostatic assumption can easily produce a few kpc thick observable molecular disc.
The vertical halo scale height is a crucial parameter to understand the transport of cosmic-ray electrons (CRE) and their energy loss mechanisms in spiral galaxies. Until now, the radio scale height could only be determined for a few edge-on galaxies because of missing sensitivity at high resolution. We developed a sophisticated method for the scale height determination of edge-on galaxies. With this we determined the scale heights and radial scale lengths for a sample of 13 galaxies from the CHANG-ES radio continuum survey in two frequency bands. The sample average value for the radio scale h…
We model the galactic discs of seven nearby large spiral galaxies as three-component systems consist of stars, molecular gas, and atomic gas in vertical hydrostatic equilibrium. We set up the corresponding joint Poisson-Boltzmann equation and solve it numerically to estimate the three-dimensional distribution of HI in these galaxies. While solving the Poisson-Boltzmann equation, we do not consider a constant HI velocity dispersion ($σ_{\rm HI}$); rather, we develop an iterative method to self-consistently estimate the $σ_{\rm HI}$ profile in a galaxy by using the observed second-moment profile…
We use an empirical relation to measure the HI scale height of relatively HI rich galaxies using 21-cm observations. The galaxies were selected from the BLUEDISK, THINGS and VIVA surveys. We aim to compare the thickness of the HI layer of unusually HI rich with normal spiral galaxies and find any correlation between the HI scale height with other galaxies properties. We found that on average the unusually HI rich galaxies have similar HI disk thickness to the control sample and the galaxies selected from the THINGS and VIVA surveys within their uncertainties. Our result also show that the aver…
A number of giant cometary HII regions (GCH) sheathed inside molecular bow shocks (MBS) are found along spiral arms of the barred galaxy M83. The open cone structure is explained by a model of expanded HII front in a gaseous arm with steep density gradient, and the bow shock is shown to be formed by encounter of an HII region with the supersonic gas flow across the arm. It is suggested that dual-side compression of molecular gas at the bow head between the MBS and GCH enhances star formation along the spiral arms.
From our radio observations of the magnetic field strength and large-scale pattern of spiral galaxies of different Hubble types and star formation rates (SFR) we conclude that - though a high SFR in the disk increases the total magnetic field strength in the disk and the halo - the SFR does not change the global field configuration nor influence the global scale heights of the radio emission. The similar scale heights indicate that the total magnetic field regulates the galactic wind velocities. The galactic wind itself may be essential for an effective dynamo action.
We explore the development of structures in molecular gas in the Milky Way by applying the analysis of the brightness distribution function (BDF) and the brightness distribution index (BDI) in the archival data from the Boston University-Five College Radio Astronomy Observatory 13CO J=1-0 Galactic Ring Survey. The BDI measures the fractional contribution of spatially confined bright molecular emission over faint emission extended over large areas. This relative quantity is largely independent of the amount of molecular gas and of any conventional, pre-conceived structures, such as cores, clump…
We investigate the structure of the Milky Way by determining how features in a spatial map correspond to CO features in a velocity map. We examine structures including logarithmic spiral arms, a ring and a bar. We explore the available parameter space, including the pitch angle of the spiral arms, radius of a ring, and rotation curve. We show that surprisingly, a spiral arm provides a better fit to the observed molecular ring than a true ring feature. This is because both a spiral arm, and the observed feature known as the molecular ring, are curved in velocity longitude space. We find that mu…
We study the relationship between the scale-height of the molecular gas disc and the turbulent velocity dispersion of the molecular interstellar medium within a simulation of a Milky Way-like galaxy in the moving-mesh code Arepo. We find that the vertical distribution of molecular gas can be described by a Gaussian function with a uniform scale-height of ~50 pc. We investigate whether this scale-height is consistent with a state of hydrostatic balance between gravity and turbulent pressure. We find that the hydrostatic prediction using the total turbulent velocity dispersion (as one would meas…
Molecular line images of 13CO, C18O, CN, CS, CH3OH, and HNCO are obtained toward the spiral arm of M51 at a 7" times 6" resolution with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Distributions of the molecules averaged over a 300 pc scale are found to be almost similar to one another and to essentially trace the spiral arm. However, the principal component analysis shows a slight difference of distributions among molecular species particularly for CH3OH and HNCO. These two species do not correlate well with star-formation rate, implying that they are not enhanced by …
In recent years there has been a growing interest in studying giant molecular filaments (GMFs), which are extremely elongated (> 100pc in length) giant molecular clouds (GMCs). They are often seen as inter-arm features in external spiral galaxies, but have been tentatively associated with spiral arms when viewed in the Milky Way. In this paper, we study the time evolution of GMFs in a high-resolution section of a spiral galaxy simulation, and their link with spiral arm GMCs and star formation, over a period of 11Myrs. The GMFs generally survive the inter-arm passage, although they are subject …
In decomposing the HI rotation curves of disc galaxies, it is necessary to break a degeneracy between the gravitational fields of the disc and the dark halo by estimating the disc surface density. This is done by combining measurements of the vertical velocity dispersion of the disc with the disc scale height. The vertical velocity dispersion of the discs is measured from absorption lines (near the V-band) of near-face-on spiral galaxies, with the light coming from a mixed population of giants of all ages. However, the scale heights for these galaxies are estimated statistically from near-IR s…
We have investigated the dynamics of the molecular gas and the evolution of GMAs in the spiral galaxy M51 with the NRO 45-m telescope. The velocity components of the molecular gas perpendicular and parallel to the spiral arms are derived at each spiral phase from the distribution of the line-of-sight velocity of the CO gas. In addition, the shear motion in the galactic disk is determined from the velocity vectors at each spiral phase. It is revealed that the distributions of the shear strength and of GMAs are anti-correlated. GMAs exist only in the area of the weak shear strength and further o…
We present dust polarization and CO molecular line images of NGC 7538 IRS1. We combined data from the SMA, CARMA and JCMT telescopes to make images with 2.5 arcsec resolution at 230 and 345 GHz. The images show a remarkable spiral pattern in both the dust polarization and molecular outflow. These data dramatically illustrate the interplay between a high infall rate onto IRS1 and a powerful outflow disrupting the dense, clumpy medium surrounding the star. The images of the dust polarization and the CO outflow presented here provide observational evidence for the exchange of energy and angular m…
We have identified a spiral arm lying beyond the Outer Arm in the first Galactic quadrant ~15 kpc from the Galactic center. After tracing the arm in existing 21 cm surveys, we searched for molecular gas using the CfA 1.2 meter telescope and detected CO at 10 of 220 positions. The detections are distributed along the arm from l = 13 deg, v = -21 km/s to l = 55 deg, v = -84 km/s and coincide with most of the main H I concentrations. One of the detections was fully mapped to reveal a large molecular cloud with a radius of 47 pc and a molecular mass of ~50,000 Mo. At a mean distance of 21 kpc, the…
The formation of molecular clouds, which serve as stellar nurseries in galaxies, is poorly understood. A class of cloud formation models suggests that a large-scale galactic magnetic field is irrelevant at the scale of individual clouds, because the turbulence and rotation of a cloud may randomize the orientation of its magnetic field. Alternatively, galactic fields could be strong enough to impose their direction upon individual clouds, thereby regulating cloud accumulation and fragmentation, and affecting the rate and efficiency of star formation. Our location in the disk of the Galaxy makes…
The morphology of the Milky Way is still a matter of debate. In order to shed light on uncertainties surrounding the structure of the Galaxy, in this paper, we study the imprint of spiral arms on the distribution and properties of its molecular gas. To do so, we take full advantage of the SEDIGISM survey that observed a large area of the inner Galaxy in the $^{13}$CO(2-1) line at an angular resolution of 28". We analyse the influences of the spiral arms by considering the features of the molecular gas emission as a whole across the longitude-velocity map built from the full survey. Additionall…
As recent observations of the molecular discs in spiral galaxies point to the existence of a diffuse, low-density thick molecular disc along with the prominent thin one, we investigate the observational signatures of this thick disc by theoretically modelling two-component molecular discs in a sample of eight nearby spiral galaxies. Assuming a prevailing hydrostatic equilibrium, we set up and solved the joint Poisson's-Boltzmann equation to estimate the three-dimensional distribution of the molecular gas and the molecular scale height in our sample galaxies. The molecular scale height in a two…
Combined Poisson's-Boltzman equations of hydrostatic equilibrium were set up and solved numerically for different baryonic components to obtain the molecular scale height as defined by the Half Width at Half Maxima (HWHM) in the spiral galaxy NGC 7331. The scale height of the molecular gas was found to vary between $\sim 100-200$ pc depending on the radius and assumed velocity dispersion. The solutions of the hydrostatic equation and the observed rotation curve were used to produce a dynamical model and consequently a simulated column density map of the molecular disk. The modelled molecular d…
The formation and evolution of giant molecular clouds (GMCs) in spiral galaxies have been investigated in the traditional framework of the combined quasi-stationary density wave and galactic shock model. However, our understanding of the dynamics of spiral arms is changing from the traditional spiral model to a dynamically evolving spiral model. In this study, we investigate the structure and evolution of GMCs in a dynamically evolving spiral arm using a three-dimensional N-body/hydrodynamic simulation of a barred spiral galaxy at parsec-scale resolution. This simulation incorporated self-grav…
The spiral arm tangencies are ideal lines of sight in which to determine the distribution of interstellar gas components in the spiral arms and study the influence of spiral density waves on the interarm gas in the Milky Way. We present a large scale (~15deg) position-velocity map of the Galactic plane in [CII] from l = 326.6 to 341.4deg observed with Herschel HIFI. We use [CII] l-v maps along with those for Hi and 12CO to derive the average spectral line intensity profiles over the longitudinal range of each tangency. Using the VLSR of the emission features, we locate the [CII], HI, and 12CO …
From gas to stars along the spiral wave: CO, HCN, and star formation variations across the spiral arms in NGC 4321 and M51
Argelander-Institut für Astronomie, Universität Bonn（波恩大学阿根兰德天文学研究所）；European Southern Observatory（欧洲南方天文台）；Observatorio Astronómico Nacional (IGN)（国家天文观测台（西班牙国家地理研究所））；Sterrenkundig Observatorium, Universiteit Gent（根特大学天文台）；Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik（海德堡大学天文学中心理论天体物理研究所）；Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen（海德堡大学跨学科科学计算中心）
Spiral patterns in some disc galaxies have two arms in the centre, and three or more arms on the periphery. The same result is also obtained in numerical simulations of stellar and gaseous discs. We argue that such patterns may occur due to fast cooling of the gas, resulting in formation of giant molecular clouds. The timescale of this process is 50 Myr, the factor of 10 shorter than of ordinary secular instability. The giant molecular clouds give rise to multiarm spirals through the mechanism of swing amplification.
We compare vertical profiles of the extraplanar H$α$ emission to those of the UV emission for 38 nearby edge-on late-type galaxies. It is found that detection of the "diffuse" extraplanar dust (eDust), traced by the vertically extended, scattered UV starlight, always coincides with the presence of the extraplanar H$α$ emission. A strong correlation between the scale heights of the extraplanar H$α$ and UV emissions is also found; the scale height at H$α$ is found to be $\sim0.74$ of the scale height at FUV. Our results may indicate the multiphase nature of the diffuse ionized gas and dust in th…
We conduct spectral line survey observations in the 3 mm band toward a spiral arm, a bar-end, and a nuclear region of the nearby barred spiral galaxy NGC 3627 with the IRAM 30 m telescope and the Nobeyama 45 m telescope. Additional observations are performed toward the spiral arm and the bar-end in the 2 mm band. We detect 8, 11, and 9 molecular species in the spiral arm, the bar-end, and the nuclear region, respectively. Star-formation activities are different among the three regions, and in particular, the nucleus of NGC 3627 is known as a LINER/Seyfert 2 type nucleus. In spite of these phys…
Multiple molecular lines with radiative transfer modelling are a powerful tool to probe the physics of star-forming gas in galaxies. We investigate the gas properties in the centre of the spiral galaxy NGC 2903 using low-J CO lines, i.e. 12CO(1-0), 12CO(2-1), 12CO(3-2), 13CO(1-0), and HCN(1-0). We apply a nonlocal thermodynamic equilibrium radiative transfer code to derive beam-averaged molecular gas properties. We use two methods (i.e. chi-square minimizations and likelihood) to define the best model representing the observed line ratios best. The line ratio diagnostics suggest that CO gas in…
We present a study of the molecular gas properties in a sample of 98 HI - flux selected spiral galaxies within $\sim25$ Mpc, using the CO $J=3-2$ line observed with the James Clerk Maxwell Telescope. We use the technique of survival analysis to incorporate galaxies with CO upper limits into our results. Comparing the group and Virgo samples, we find a larger mean H$_{2}$ mass in the Virgo galaxies, despite their lower mean HI mass. This leads to a significantly higher H$_{2}$ to HI ratio for Virgo galaxies. Combining our data with complementary H$α$ star formation rate measurements, Virgo gala…
Sub-kpc scale gas density histograms of the nearby barred spiral galaxy M83: Multi-component molecular gas structure reflecting the galactic environment
The University of Tokyo（东京大学）；Kagoshima University（鹿儿岛大学）；Kogakuin University（工科大学）；University of Aizu（会津大学）；Osaka Electro-Communication University（大阪电波大学）；Gifu University（岐阜大学）
Shocks and torques produced by non-axisymmetric structures such as spiral arms and bars may transport gas to galaxy central regions. We test this hypothesis by studying the dependence of concentration of CO luminosity ($C_{CO}$), molecular gas ($C_{mol}$), and star formation rate ($C_{SFR}$) in central $\sim$ 2 kpc on the $strength$ of non-axisymmetric disk structure using a sample of 57 disk galaxies selected from the EDGE-CALIFA survey. $C_{mol}$ is calculated using a CO-to-H$_2$ conversion factor that decreases with higher metallicity and higher stellar surface density. We find that $C_{mol…
We analyze radial and azimuthal variations of the phase balance between the molecular and atomic ISM in the Milky Way. In particular, the azimuthal variations -- between spiral arm and interarm regions -- are analyzed without any explicit definition of spiral arm locations. We show that the molecular gas mass fraction, i.e., fmol=H2/ (HI+H2) in mass, varies predominantly in the radial direction: starting from ~100% at the center, remaining ~>50% (~>60%) to R~6kpc, and decreasing to ~10-20% (~50%) at R=8.5 kpc when averaged over the whole disk thickness (in the mid plane). Azimuthal, arm-intera…
We report molecular line and continuum observations toward one of the most massive giant molecular clouds (GMCs), GMC-16, in M33 using ALMA with an angular resolution of 0$''$44 $\times$ 0$''$27 ($\sim$2 pc $\times$ 1 pc). We have found that the GMC is composed of several filamentary structures in $^{12}$CO and $^{13}$CO ($J$ = 2-1). The typical length, width, and total mass are $\sim$50-70 pc, $\sim$5-6 pc, and $\sim$10$^{5}$ $M_{\odot}$, respectively, which are consistent with those of giant molecular filaments (GMFs) as seen in the Galactic GMCs. The elongations of the GMFs are roughly perp…
Based on two models, we investigate the molecular-to-atomic gas ratio in Virgo cluster galaxies in comparison with field galaxies. We show that the enhanced metallicity for cluster members and the ram pressure stripping of atomic gas from the disk periphery cannot fully explain the observed gas component ratios. The additional environmental factors affecting the interstellar medium and leading to an increase in the molecular gas fraction should be taken into account for cluster galaxies.
Radio continuum observations allow to reveal the magnetic field structure in the disk and halo of nearby spiral galaxies, their magnetic field strength and vertical scale heights. The spiral galaxies studied so far show a similar magnetic field pattern which is of spiral shape along the disk plane and X-shaped in the halo, sometimes accompanied by strong vertical fields above and below the central region of the disk. The strength of the halo field is comparable to that of the disk. The total and turbulent magnetic field strength is (weakly) increasing with the star formation. There are, howeve…
Recent studies of the molecular medium in nearby galaxies have provided mounting evidence that the molecular gas can exist in two phases: one that is clumpy and organized as molecular clouds and another one that is more diffuse. This last component has a higher velocity dispersion than the clumpy one. In order to investigate these two molecular components further, we compare the fluxes and line widths of CO in NGC 4736 and NGC 5055, two nearby spiral galaxies for which high-quality interferometric as well as single-dish data sets are available. Our analysis leads to two main results: 1) Employ…
Resolved molecular gas and star-formation in massive unquenched spirals : I. UGC 8179
Observatoire de Paris（巴黎天文台）；Sorbonne Université（索邦大学）；CNRS（法国国家科学研究中心）；Institut d’Astrophysique de Paris（巴黎天体物理研究所）；Université Côte d’Azur（蔚蓝海岸大学）；Observatoire de la Côte d’Azur（蔚蓝海岸天文台）；Laboratoire Lagrange（拉格朗日实验室）；Université de Strasbourg（斯特拉斯堡大学）；Universidad de Granada（格拉纳达大学）；Collège de France（法兰西公学院）；IRAM（红外毫米波联合研究所）
We present the results of $^{12}$CO($J$=1-0) and $^{13}$CO($J$=1-0) simultaneous mappings toward the nearby barred spiral galaxy NGC 4303 as a part of the CO Multi-line Imaging of Nearby Galaxies (COMING) project. Barred spiral galaxies often show lower star-formation efficiency (SFE) in their bar region compared to the spiral arms. In this paper, we examine the relation between the SFEs and the volume densities of molecular gas $n(\rm{H}_2)$ in the eight different regions within the galactic disk with CO data combined with archival far-ultraviolet and 24 $μ$m data. We confirmed that SFE in th…
We report molecular line and dust continuum observations, made with the SEST telescope, towards four young high-mass star forming regions associated with highly luminous (L> 6x10^5 Lsun) IRAS sources (15290-5546, 15502-5302, 15567-5236 and 16060-5146). Molecular emission was mapped in lines of CS (J=2-1, 3-2 and 5-4), SiO (J=2-1 and 3-2), CH3OH (Jk=3k-2k and 2k-1k), and C34S (J=3-2). In addition, single spectra at the peak position were taken in the CO, 13CO and C18O (J=1-0) lines. We find that the luminous star forming regions are associated with molecular gas and dust structures with radii o…
We explore the interplay between supernovae and the ionizing radiation of their progenitors in star forming regions. The relative contributions of these stellar feedback processes are not well understood, particularly on scales greater than a single star forming cloud. We focus predominantly on how they affect the interstellar medium. We re-simulate a 500 pc^2 region from previous work that included photoionization and add supernovae. Over the course of 10 Myr more than 500 supernovae occur in the region. The supernovae remnants cool very quickly in the absence of earlier photoionization, but …
WISDOM Project - XXVII. Giant molecular clouds of the lenticular galaxy NGC 1387: similarities with spiral galaxy clouds
European Southern Observatory（欧洲南方天文台）；Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg（海德堡大学天体物理计算研究所）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；DTU-Space, Technical University of Denmark（丹麦技术大学空间科学系）；Sub-department of Astrophysics, Department of Physics, University of Oxford（牛津大学物理系天体物理学小组）；Department of Physics and Astronomy, McMaster University（麦克马斯特大学物理与天文学系）；Cardiff Hub for Astrophysics Research & Technology, School of Physics & Astronomy, Cardiff University（卡迪夫大学物理与天文学院天体物理学研究与技术枢纽）；Trottier Space Institute and Department of Physics（特罗蒂尔太空研究所和物理系）
The escape of ultraviolet photons from the densest regions of the interstellar medium (ISM) --- Giant Molecular Clouds (GMCs) --- is a poorly constrained parameter which is vital to understanding the ionization of the ISM and the intergalactic medium. We characterize the escape fraction, f$_{\text{esc,GMC}}$, from a suite of individual GMC simulations with masses in the range 10$^{4-6}$ M$_{\odot}$ using the adaptive-mesh refinement code FLASH. We find significantly different f$_{\text{esc,GMC}}$ depending on the GMC mass which can reach $>$90% in the evolution of 5$\times$10$^4$ and 10$^{5}$ …
We use hydrodynamical simulations to construct a new coherent picture for the gas flow in the Central Molecular Zone (CMZ), the region of our Galaxy within $R\leq 500\, \mathrm{pc}$. We relate connected structures observed in $(l,b,v)$ data cubes of molecular tracers to nuclear spiral arms. These arise naturally in hydrodynamical simulations of barred galaxies, and are similar to those that can be seen in external galaxies such as NGC4303 or NGC1097. We discuss a face-on view of the CMZ including the position of several prominent molecular clouds, such as Sgr B2, the $20\,{\rm km\, s^{-1}}$ an…
We present an analysis of the radial profiles of a sample of 43 HI-flux selected spiral galaxies from the Nearby Galaxies Legacy Survey (NGLS) with resolved James Clerk Maxwell Telescope (JCMT) CO $J=3-2$ and/or Very Large Array (VLA) HI maps. Comparing the Virgo and non-Virgo populations, we confirm that the HI disks are truncated in the Virgo sample, even for these relatively HI-rich galaxies. On the other hand, the H$_{2}$ distribution is enhanced for Virgo galaxies near their centres, resulting in higher H$_{2}$ to HI ratios and steeper H$_{2}$ and total gas radial profiles. This is likely…
The formation of thick stellar disks in spiral galaxies is studied. Simulations of gas-rich young galaxies show formation of internal clumps by gravitational instabilities, clump coalescence into a bulge, and disk thickening by strong stellar scattering. The bulge and thick disks of modern galaxies may form this way. Simulations of minor mergers make thick disks too, but there is an important difference. Thick disks made by internal processes have a constant scale height with galactocentric radius, but thick disks made by mergers flare. The difference arises because in the first case, perpendi…
Molecular emission lines are essential tools to shed lights on many questions regarding star formation in galaxies. Multiple molecular lines are particularly useful to probe different phases of star-forming molecular clouds. In this study, we investigate the physical properties of giant molecular clouds (GMCs) using multiple lines of CO, i.e. CO(1-0, 2-1, 3-2) and $^{13}$CO(1-0), obtained at selected 20 positions in the disc of NGC 0628. Eleven positions were selected over the radial cut, including the centre, and remaining nine positions were selected across the southern and northern arms of …
Magnetic fields play a very important role in the evolution of galaxies through their direct impact on star formation and stellar feedback-induced turbulence. However, their co-evolution with these processes has still not been thoroughly investigated, and the possible effect of the initial conditions is largely unknown. This letter presents the first results from a series of high-resolution numerical models, aimed at deciphering the effect of the initial conditions and of stellar feedback on the evolution of the galactic magnetic field in isolated, Milky-Way-like galaxies. The models start wit…
We present the [CII] 157.7 micron map of galaxy NGC 7331 obtained with FIFI-LS on SOFIA. This map extends an existent Herschel/PACS observation of the central strip of the galaxy to encompass the entire molecular ring and much of the disk, including multiple spiral arms with intense far-IR emission. We also present Herschel archival data of the [NII] 205 micron line which covers a substantial part of the [CII] SOFIA observations and allows us to estimate the neutral fraction of the [CII] emission along the ring and disk of the galaxy. We find that the neutral fraction rises with the distance f…
We present simulations of a 500 pc$^2$ region, containing gas of mass 4 $\times$ 10$^6$ M$_\odot$, extracted from an entire spiral galaxy simulation, scaled up in resolution, including photoionising feedback from stars of mass > 18 M$_\odot$. Our region is evolved for 10 Myr and shows clustered star formation along the arm generating $\approx$ 5000 cluster sink particles $\approx$ 5% of which contain at least one of the $\approx$ 4000 stars of mass > 18 M$_\odot$. Photoionisation has a noticeable effect on the gas in the region, producing ionised cavities and leading to dense features at the e…
We use new HCN(1-0) data from the ALMOND (ACA Large-sample Mapping Of Nearby galaxies in Dense gas) survey to trace the kpc-scale molecular gas density structure and CO(2-1) data from PHANGS-ALMA to trace the bulk molecular gas across 25 nearby, star-forming galaxies. At 2.1 kpc scale, we measure the density-sensitive HCN/CO line ratio and the SFR/HCN ratio to trace the star formation efficiency in the denser molecular medium. At 150 pc scale, we measure structural and dynamical properties of the molecular gas via CO(2-1) line emission, which is linked to the lower resolution data using an int…
In this first paper in a series we present a study of the global dust emission distribution in nearby edge-on spiral galaxies. Our sample consists of 16 angularly large and 13 less spatially resolved galaxies selected from the DustPedia sample. To explore the dust emission distribution, we exploit the Herschel photometry in the range 100-500 $μ$m. We employ Sérsic and three-dimensional disc models to fit the observed two-dimensional profiles of the galaxies. Both approaches give similar results. Our analysis unequivocally states the case for the presence of extraplanar dust in between 6 to 10 …
Observations of various molecular lines toward a disk region of a nearby galaxy are now feasible, and they are being employed as diagnostic tools to study star-formation activities there. However, the spatial resolution attainable for a nearby galaxy with currently available radio telescopes is $10-1000$ pc, which is much larger than the scales of individual star-forming regions and molecular cloud cores. Hence, it is of fundamental importance to elucidate which part of an interstellar medium such spatially-unresolved observations are tracing. Here we present sensitive measurements of the H$_2…
We present high spatial resolution observations of Giant Molecular Clouds (GMCs) in the eastern part of the nearby spiral galaxy NGC 6946 obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We have observed 12CO(1-0), 12CO(2-1) and 13CO(1-0), achieving spatial resolutions of 5.4" x 5.0", 2.5" x 2.0" and 5.6" x 5.4" respectively over a region of 6 x 6 kpc. This region extends from 1.5 kpc to 8 kpc galactocentric radius, thus avoiding the intense star formation in the central kpc. We have recovered short-spacing u-v components by using single dish observations fro…
It has long been suspected that powerful radio sources may lower the efficiency with which stars form from the molecular gas in their host galaxy, but so far, alternative mechanisms, in particular related to the stellar mass distribution in the massive bulges of their host galaxies, are not ruled out. We present new ALMA CO(1-0) interferometry of cold molecular gas in the nearby (z=0.0755), massive (M_stellar=4x10^11 M_sun), isolated, late-type spiral galaxy 2MASSX J23453269-044925, which is outstanding for having two pairs of powerful, giant radio jets, and a bright X-ray halo. The molecular …
Studies of the three-dimensional (3D) structures of galactic magnetic fields are now entering a new era, with broadband, highly sensitive radio observations and new analysis methods. To reveal the magnetic field configuration from the observed value integrated along the line of sight, it is necessary to derive an appropriate model that can reproduce the observational characteristics. We aim to clarify the relationship between the radiation field and the spatial distribution of physical quantities through pseudo-observations using global 3D magnetohydrodynamics (MHD) simulation results. In part…
We present IRAM 30m observations of molecular lines of CO and its isotopologues from the massive spiral galaxy NGC 5908 selected from the CGM-MASS sample. $^{12}$CO $J=1-0$, $^{12}$CO $J=2-1$, and $^{13}$CO $J=1-0$ lines have been detected in most of the positions along the galactic disk. The total molecular gas mass of NGC 5908 is $\sim7\times10^9\rm~M_\odot$ and the total cool gas mass adding atomic hydrogen is $\sim1.3\times10^{10}\rm~M_\odot$, comparable to the upper limit of the mass of the X-ray emitting hot gas in the halo. Modeling the rotation curves constructed with all three CO line…
Cosmic-ray electrons (CREs) originating from the star-forming discs of spiral galaxies frequently form extended radio haloes that are best observable in edge-on galaxies. For the present study we selected two nearby edge-on galaxies from the CHANG-ES survey, NGC 891 and 4565, which differ largely in halo size and SFR. To figure out how such differences are related to the CRE transport in disc and halo, we use wide-band 1.5 and 6 GHz VLA observations obtained in the B, C, and D configurations, and combine the 6 GHz images with Effelsberg observations to correct for missing short spacings. We st…
We present high-resolution smoothed particle hydrodynamics simulations of a region of gas flowing in a spiral arm and identify dense gas clouds to investigate their kinematics with respect to a Milky Way model. We find that, on average, the gas in the arms can have a net radial streaming motion of $v_R \approx -9 \,\mathrm{km/s}$ and rotate $\approx 6 \,\mathrm{km/s}$ slower than the circular velocity. This translates to average peculiar motions towards the Galaxy centre and opposite to Galactic rotation. These results may be sensitive to the assumed spiral arm perturbation, which is $\approx …
