Past and recent observations have revealed unexpected variations in the FIR-mm dust emissivity. In the Herschel spectral range, those are often referred to as a 500μm emission excess. Several dust emission models have been developed to interpret astrophysical data in the FIR-mm domain. However, these are commonly unable to fully reconcile theoretical predictions with observations. In contrast, the recently revised two level system (TLS) model seems to provide a promising way of interpreting the existing data. The newly available Herschel Hi-GAL data which covers most of the inner Milky-Way offers a unique opportunity to investigate possible variations in the dust emission properties both with wavelength and environment. By combining the IRIS 100 μm with the Hi-GAL 160, 250, 350 and 500 μm data, we model the dust emission spectra in each pixel of the Hi-GAL maps, using both the TLS model and, for comparison, a single modified black-body fit. The effect of temperature mixing along the line of sight is investigated. We find a slight decrease in the dust temperature with distance from the Galactic center. We also report the detection of a significant 500 μm emissivity excess in the peripheral regions of the plane (35\circ<|l|<70\circ) of about 13-15% of the emissivity, that can reach up to 20% in some HII regions. We present the spatial distribution of the best-fit values for the two main parameters of the TLS model, i.e. the charge correlation length, lc, used to characterize the disordered charge distribution (DCD) part of the model, and the amplitude A of the TLS processes, with respect to the DCD effect. They highlight the plausible existence of an overall gradient with distance to the Galactic center. A comparison with previous findings in the solar neighborhood shows that the local value of the excess is less than expected from the Galactic gradient observed here.
Variations in the dust emissivity are critical for gas mass determinations derived from far-infrared observations, but also for separating dust foreground emission from the Cosmic Microwave Background (CMB). Hi-GAL observations allow us for the first time to study the dust emissivity variations in the inner regions of the Galactic plane at resolution below 1 degree. We present maps of the emissivity spectral index derived from the combined Herschel PACS 160 μm, SPIRE 250 μm, 350 μm, and 500 μm data, and the IRIS 100 μm data, and we analyze the spatial variations of the spectral index as a func…
Many studies of anomalous microwave emission (AME) have computed an AME emissivity to compare the strength of the AME detected in different regions. Such a value is usually defined as the ratio between the intensity of the AME at 1 cm and the thermal dust emission at 100 μm. However, as studies of Galactic dust emission have shown, the intensity of the thermal dust emission at 100 μm is strongly dependent on the dust temperature, which has severe implications for the AME emissivity defined in this way. In this work, we illustrate and quantify this effect and find that the AME emissivity decrea…
Synchrotron emission pervades the Galactic plane at low radio frequencies, originating from cosmic ray electrons interacting with the Galactic magnetic field. Using a low-frequency radio telescope, the Murchison Widefield Array (MWA), we measure the free-free absorption of this Galactic synchrotron emission by intervening HII regions along the line of sight. These absorption measurements allow us to calculate the Galactic cosmic-ray electron emissivity behind and in front of 47 detected HII regions in the region $250^\circ < l < 355^\circ$, $|b| < 2^\circ$. We find that all average emissivitie…
Cosmic rays (CRs) and magnetic fields are dynamically important components in the Galaxy, and their energy densities are comparable to that of the turbulent interstellar gas. The interaction of CRs and Galactic magnetic fields produces synchrotron radiation clearly visible in the radio regime. Detailed measurements of synchrotron radiation averaged over the line-of-sight (LOS), so-called synchrotron emissivities, can be used as a tracer of the CR density and Galactic magnetic field (GMF) strength. Our aim is to model the synchrotron emissivity in the Milky Way using a 3 dimensional dataset ins…
Context: The far-infrared (FIR) and sub-millimeter (submm) emissivity of the Milky Way (MW) cirrus is an important benchmark for dust grain models. Dust masses in other galaxies are generally derived from the FIR/submm using the emission properties of these MW-calibrated models. Aims: We seek to derive the FIR/submm emissivity in nine nearby spiral galaxies to check its compatibility with MW cirrus measurements. Methods: We obtained values of the emissivity at 70 to 500 um, using maps of dust emission from the Herschel satellite and of gas surface density from the THINGS and HERACLES surveys o…
Dust properties appear to vary according to the environment in which the dust evolves. Previous observational indications of these variations in the FIR and submm spectral range are scarce and limited to specific regions of the sky. To determine whether these results can be generalised to larger scales, we study the evolution in dust emissivities from the FIR to mm wavelengths, in the atomic and molecular ISM, along the Galactic plane towards the outer Galaxy. We correlate the dust FIR to mm emission with the HI and CO emission. The study is carried out using the DIRBE data from 100 to 240 mic…
In this paper we present a dust emission map of the starless core TMC-1C taken at 2100 microns. Along with maps at 160, 450, 850 and 1200 microns, we study the dust emissivity spectral index from the (sub)millimeter spectral energy distribution, and find that it is close to the typically assumed value of beta = 2. We also map the dust temperature and column density in TMC-1C, and find that at the position of the dust peak (A_V ~ 50), the line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo modeling, we show that the data are consistent with a constant value for the emissivi…
We study the unresolved X-ray emission in three Local Group dwarf elliptical galaxies (NGC 147, NGC 185 and NGC 205) using XMM-Newton observations, which most likely originates from a collection of weak X-ray sources, mainly cataclysmic variables and coronally active binaries. Precise knowledge of this stellar X-ray emission is crucial not only for understanding the relevant stellar astrophysics but also for disentangling and quantifying the thermal emission from diffuse hot gas in nearby galaxies.We find that the integrated X-ray emissivities of the individual dwarf ellipticals agree well wit…
Aims: We compare the far-infrared to sub-millimetre dust emission properties measured in high Galactic latitude cirrus with those determined in a sample of 204 late-type DustPedia galaxies. The aim is to verify if it is appropriate to use Milky Way dust properties to derive dust masses in external galaxies. Methods: We used Herschel observations and atomic and molecular gas masses to estimate the disc-averaged dust emissivity at 250 micrometres, and from this, the absorption cross section per H atom and per dust mass. The emissivity requires one assumption, which is the CO-to-H_2 conversion fa…
Over the past decade, studies of dust in the Andromeda galaxy (M31) have shown radial variations in the dust emissivity index ($β$). Understanding the astrophysical reasons behind these radial variations may give clues about the chemical composition of dust grains, their physical structure, and the evolution of dust. We use $^{12}$CO(J=1-0) observations taken by the Combined Array for Research in Millimeter Astronomy (CARMA) and dust maps derived from \textit{Herschel} images, both with an angular resolution of 8" and spatial resolution of 30 pc, to study variations in $β$ across an area of $\…
We derive the synchrotron distribution in the Milky Way disk from HII region absorption observations over -40° < l < 40° at six frequencies of 76.2, 83.8, 91.5, 99.2, 106.9, and 114.6 MHz with the GaLactic and Extragalactic All-sky Murchison widefield array survey (GLEAM). We develop a new method of emissivity calculation by taking advantage of the Haslam et al., (1981) map and known spectral indices, which enable us to simultaneously derive the emissivity and the optical depth of HII regions at each frequency. We show our derived synchrotron emissivities based on 152 absorption features of HI…
Localized Deviations from the CO-PAH Relation in PHANGS-JWST Galaxies: Faint PAH Emission or Elevated CO Emissivity?
Kavli Institute for Particle Astrophysics & Cosmology (KIPAC), Stanford University（斯坦福大学卡弗里粒子天体物理与宇宙学研究所）；Department of Astronomy, The Ohio State University（俄亥俄州立大学天文学系）；Center for Cosmology and Astroparticle Physics (CCAPP)（宇宙学与高能物理中心）；Department of Astronomy & Astrophysics, University of California, San Diego（加州大学圣地亚哥分校天文与天体物理系）；Sterrenkundig Observatorium, Universiteit Gent（根特大学天文台）；Department of Astronomy, University of Maryland（马里兰大学天文学系）；Observatorio Astronómico Nacional (IGN)（国家天文台（西班牙国家地理研究所））；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Department of Physics, Stanford University（斯坦福大学物理系）
We present CO J=4-3 line and 3 mm dust continuum observations of a 100 kpc-scale filamentary Lyα nebula (SSA22 LAB18) at z=3.1 using the Atacama Large Millimeter/submillimeter Array (ALMA). We detected the CO J=4-3 line at a systemic z(CO)=3.093 {\pm} 0.001 at 11 σ from one of the ALMA continuum sources associated with the Lyα filament. We estimated the CO J=4-3 luminosity of L'CO(4-3)=(2.3\pm0.2)x10^9 K km s^{-1} pc^2 for this CO source, which is one order of magnitude smaller than those of typical z>1 dusty star-forming galaxies (DSFGs) of similar far-infrared luminosity L(IR)~10^{12} Lsun. …
The observed interaction product of Cosmic Rays (CRs) and Galactic magnetic fields (GMF) is the Galactic synchrotron emission integrated over the line-of-sight (LOS). The GMF strength and morphology and the CR density can be probed by comparing this tracer to simulations using existing GMF models and CR density models. Our aim is to provide insight into these parameters by exploring and explaining the differences between simulations and observations of synchrotron intensity. At low radio frequencies HII regions become opaque due to free-free absorption. Using these HII regions we can measure t…
Physically motivated AGN emissivity profiles and their effects on quasar microlensing signatures. 1. Multi-epoch accretion disc size inference
IFPU - Institute for Fundamental Physics of the Universe（基础物理宇宙研究所）；SISSA - International School for Advanced Studies（国际高等研究院）；INAF - Osservatorio Astronomico di Trieste（的里雅斯特天文台）；Center for Astrophysics and Cosmology, University of Nova Gorica（新戈里察大学天体物理学与宇宙学中心）
We show that a one-component variable-emissivity-spectral-index model (the free-α model) provides more physically motivated estimates of dust temperature at the Galactic polar caps than one- or two-component fixed-emissivity-spectral-index models (fixed-α models) for interstellar dust thermal emission at far-infrared and millimeter wavelengths. For the comparison we have fit all-sky one-component dust models with fixed or variable emissivity spectral index to a new and improved version of the 210-channel dust spectra from the COBE-FIRAS, the 100 - 240 μm maps from the COBE-DIRBE and the 94 GHz…
We present a new 3.3 mm continuum map of the OMC-2/3 region. When paired with previously published maps of 1.2mm continuum and NH3-derived temperature, we derive the emissivity spectral index of dust emission in this region, tracking its changes across the filament and cores. We find that the median value of the emissivity spectral index is 0.9, much shallower than previous estimates in other nearby molecular clouds. We find no significant difference between the emissivity spectral index of dust in the OMC-2/3 filament and the starless or protostellar cores. Furthermore, the temperature and em…
Using 1 cm and 3 mm CARMA and 2 mm GISMO observations, we follow up the first extragalactic detection of anomalous microwave emission (AME) reported by Murphy et al. 2010 in an extranuclear region (Enuc. 4) of the nearby face-on spiral galaxy NGC 6946. We find the spectral shape and peak frequency of AME in this region to be consistent with models of spinning dust emission. However, the strength of the emission far exceeds the Galactic AME emissivity given the abundance of polycyclic aromatic hydrocarbons (PAHs) in that region. Using our galaxy-wide 1 cm map (21" resolution), we identify a tot…
We used a data set from AKARI and Herschel images at wavelengths from 7 $μ$m to 500 $μ$m to catch the evidence of dust processing in galactic winds in NGC 1569. Images show a diffuse infrared (IR) emission extending from the galactic disk into the halo region. The most prominent filamentary structure seen in the diffuse IR emission is spatially in good agreement with the western H$α$ filament (western arm). The spatial distribution of the $F_\mathrm{350}/F_\mathrm{500}$ map shows high values in regions around the super-star clusters (SSCs) and towards the western arm, which are not found in th…
Anomalous microwave emission (AME) is an important Galactic foreground of Cosmic Microwave Background (CMB) radiation. It is believed that the AME arises from rotational emission by spinning polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium (ISM). In this paper, we assume that a population of ultrasmall silicate grains may exist in the ISM, and quantify rotational emissivity from these tiny particles and its polarization spectrum. We found that spinning silicate nanoparticles can produce strong rotational emission when those small grains follow a log-normal size distribution. …
Studies of the diffuse Galactic radio emission are interesting both for better understanding the physical conditions in our Galaxy and for minimising the contamination in cosmological measurements. Motivated by this we present Cosmic Background Imager 31 GHz observations of the Galactic regions NGC 6357, NGC 6334, W51 and W40 at $\sim$4$'$.5 resolution and conduct an investigation of the spectral emission process in the regions at 4$'$.5 and 1$^{\circ}$ resolution. We find that most of the emission in the regions is due to optically thin free-free. For 2 sub-regions of NGC 6334 and for a sub-r…
Recent results have suggested that active galactic nuclei (AGN) could provide enough photons to reionise the Universe. We assess the viability of this scenario using a semi-numerical framework for modeling reionisation, to which we add a quasar contribution by constructing a Quasar Halo Occupation Distribution (QHOD) based on Giallongo et al. observations. Assuming a constant QHOD, we find that an AGN-only model cannot simultaneously match observations of the optical depth $τ_e$, neutral fraction, and ionising emissivity. Such a model predicts $τ_e$ too low by $\sim 2σ$ relative to Planck cons…
We present Atacama Large Millimetre Array (ALMA) 2mm continuum observations of a complete and unbiased sample of 99 870micron-selected sub-millimeter galaxies (SMGs) in the Extended Chandra Deep Field South (ALESS). Our observations of each SMG reach average sensitivities of 53 microJy/beam. We measure the flux densities for 70 sources, for which we obtain a typical 870micron-to-2mm flux ratio of 14 +/- 5. We do not find a redshift dependence of this flux ratio, which would be expected if the dust emission properties of our SMGs were the same at all redshifts. By combining our ALMA measurement…
Physical conditions of the interstellar medium in galaxies are closely linked to the ambient radiation field and the heating of dust grains. In order to characterize dust properties in galaxies over a wide range of physical conditions, we present here the radial surface brightness profiles of the entire sample of 61 galaxies from Key Insights into Nearby Galaxies: Far-Infrared Survey with Herschel (KINGFISH). The main goal of our work is the characterization of the grain emissivities, dust temperatures, and interstellar radiation fields responsible for heating the dust. After fitting the dust …
We use high resolution simulations of the formation of the local group post-processed by a radiative transfer code for UV photons, to investigate the reionization of the satellite populations of an isolated Milky Way-M31 galaxy pair in a variety of scenarios. We use an improved version of ATON which includes a simple recipe for radiative feedback. In our baseline models, reionization is initiated by low mass, radiatively regulated haloes at high redshift, until more massive haloes appear, which then dominate and complete the reionization process. We investigate the relation between reionizatio…
The dust properties in the Large and Small Magellanic Clouds are studied using the HERITAGE Herschel Key Project photometric data in five bands from 100 to 500 micron. Three simple models of dust emission were fit to the observations: a single temperature blackbody modified by a power- law emissivity (SMBB), a single temperature blackbody modified by a broken power-law emissivity (BEMBB), and two blackbodies with different temperatures, both modified by the same power-law emissivity (TTMBB). Using these models we investigate the origin of the submm excess; defined as the submillimeter (submm) …
We present infrared (IR) spectral energy distributions (SEDs) of individual star-forming regions in four extremely metal poor (EMP) galaxies with metallicity Z around Zsun/10 as observed by the Herschel Space Observatory. With the good wavelength coverage of the SED, it is found that these EMP star-forming regions show distinct SED shapes as compared to those of grand design Spirals and higher metallicity dwarfs: they have on average much higher f70um/f160um ratios at a given f160um/f250um ratio; single modified black-body (MBB) fittings to the SED at λ>= 100 um still reveal higher dust temper…
The C-Band All-Sky Survey (C-BASS) has observed the Galaxy at 4.76GHz with an angular resolution of $0.73^\circ$ full-width half-maximum, and detected Galactic synchrotron emission with high signal-to-noise ratio over the entire northern sky ($δ> -15^{\circ}$). We present the results of a spatial correlation analysis of Galactic foregrounds at mid-to-high ($b > 10^\circ$) Galactic latitudes using a preliminary version of the C-BASS intensity map. We jointly fit for synchrotron, dust, and free-free components between $20$ and $1000$GHz and look for differences in the Galactic synchrotron spectr…
We have performed a comprehensive investigation of the global integrated flux density of M33 from radio to ultraviolet wavelengths, finding that the data between $\sim$100 GHz and 3 THz are accurately described by a single modified blackbody curve with a dust temperature of $T_\mathrm{dust}$ = 21.67$\pm$0.30 K and an effective dust emissivity index of $β_\mathrm{eff}$ = 1.35$\pm$0.10, with no indication of an excess of emission at millimeter/sub-millimeter wavelengths. However, sub-dividing M33 into three radial annuli, we found that the global emission curve is highly degenerate with the cons…
Cosmic dust particles effectively attenuate starlight. Their absorption of starlight produces emission spectra from the near- to far-infrared, which depends on the sizes and properties of the dust grains, and spectrum of the heating radiation field. The near- to mid-infrared is dominated by the emissions by very small grains. Modeling the absorption of starlight by these particles is, however, computationally expensive and a significant bottleneck for self-consistent radiation transport codes treating the heating of dust by stars. In this paper, we summarize the formalism for computing the sto…
The distribution of various interstellar gas components and the pressure in the interstellar medium (ISM) is a result of the interplay of different dynamical mechanisms and energy sources on the gas in the Milky Way. The scale heights of the different gas tracers, such as HI and CO, are a measure of these processes. The scale height of [CII] emission in the Galactic plane is important for understanding those ISM components not traced by CO or HI. We determine the average distribution of [CII] perpendicular to the plane in the inner Galactic disk and compare it to the distributions of other key…
We search for far-infrared (FIR) counterparts of known supernova remnants (SNRs) in the Galactic plane (10 deg <| l |< 60 deg) at 70-500 micron using the Herschel Infrared Galactic Plane Survey (Hi-GAL). Of 71 sources studied, we find that 29 (41 per cent) SNRs have a clear FIR detection of dust emission associated with the SNR. Dust from 8 of these is in the central region, and 4 indicate pulsar wind nebulae (PWNe) heated ejecta dust. A further 23 have dust emission in the outer shell structures which is potentially related to swept up material. Many Galactic SNe have dust signatures but we a…
We have created synthetic neutral hydrogen (HI) Galactic Plane Survey data cubes covering 90 degrees < l < 180 degrees, using a model spiral galaxy from SPH simulations and the radiative transfer code TORUS. The density, temperature and other physical parameters are fed from the SPH simulation into TORUS, where the HI emissivity and opacity are calculated before the 21-cm line emission profile is determined. Our main focus is the observation of Outer Galaxy `Perseus Arm' HI, with a view to tracing atomic gas as it encounters shock motions as it enters a spiral arm interface, an early step in t…
We study the wavelength dependence of the dust emission as a function of position and environment across the disk of M33 at a linear resolution of 160 pc using Spitzer and Herschel photometric data. Expressing the emissivity of the dust as a power law, the power-law exponent (beta) is estimated from two independent approaches designed to properly treat the degeneracy between beta and the dust temperature. Both beta and the dust temperature are higher in the inner disk than in the outer disk, contrary to reported beta-T anti-correlations found in other sources. In the cold + warm dust model, th…
We model the infrared to submillimeter spectral energy distribution of 11 nearby galaxies of the KINGFISH sample using Spitzer and Herschel data and compare model extrapolations at 870um (using different fitting techniques) with LABOCA 870um observations. We investigate how the differences between predictions and observations vary with model assumptions or environment. At global scales, we find that modified blackbody models using realistic cold emissivity indices (beta_c=2 or 1.5) are able to reproduce the 870um observed emission within the uncertainties for most of the sample. Low values (be…
A sample of large northern Spitzer Infrared Nearby Galaxies Survey (SINGS) galaxies was recently observed with the Westerbork Synthesis Radio Telescope (WSRT) at 1300-1760 MHz. In Paper II of this series, we described sensitive observations of the linearly polarized radio continuum emission in this WSRT-SINGS galaxy sample. Here we explore the systematic patterns of azimuthal modulation of both the Faraday depth and the polarized intensity and their variation with galaxy inclination. A self-consistent and fully general model for both the locations of net polarized emissivity at 1-2 GHz frequen…
[abridged] At the end of the Spitzer cryogenic mission and the onset of the Herschel era, we review our current knowledge on galaxy evolution at IR wavelengths. We also develop new tools for the analysis of background fluctuations to constrain source counts in regimes of high confusion. We analyse a large variety of new data on galaxy evolution and high-z source populations from Spitzer surveys, as well as complementary data from sub-mm (BLAST) and millimetric ground-based observations. These data confirm earlier indications about a very rapid increase of galaxy volume emissivity up to z~1. Th…
