Multi-wavelength observations of protoplanetary disks in the sub-millimeter continuum have measured spectral indices values which are significantly lower than what is found in the diffuse interstellar medium. Under the assumption that mm-wave emission of disks is mostly optically thin, these data have been generally interpreted as evidence for the presence of mm/cm-sized pebbles in the disk outer regions. In this work we investigate the effect of possible local optically thick regions on the mm-wave emission of protoplanetary disks without mm/cm-sized grains. A significant local increase of the optical depth in the disk can be caused by the concentration of solid particles, as predicted to result from a variety of proposed physical mechanisms. We calculate the filling factors and implied overdensities these optically thick regions would need to significantly affect the millimeter fluxes of disks, and we discuss their plausibility. We find that optically thick regions characterized by relatively small filling factors can reproduce the mm-data of young disks without requesting emission from mm/cm-sized pebbles. However, these optically thick regions require dust overdensities much larger than what predicted by any of the physical processes proposed in the literature to drive the concentration of solids. We find that only for the most massive disks it is possible and plausible to imagine that the presence of optically thick regions in the disk is responsible for the low measured values of the mm spectral index. For the majority of the disk population, optically thin emission from a population of large mm-sized grains remains the most plausible explanation. The results of this analysis further strengthen the scenario for which the measured low spectral indices of protoplanetary disks at mm wavelengths are due to the presence of large mm/cm-sized pebbles in the disk outer regions.
The Asymptotic Giant Branch (AGB) is the terminal phase of red giant evolution with timescales of millions of years and a total mass lost from the star that is a significant fraction of the initial mass. Investigation of one of these stars, WISEA J173046.10-344455.5, a kpc in the direction of the center of the Galaxy, reveals a cool oxygen rich star with a dust shell of black-body temperature 1305 K.
We obtain a new set of analytical solutions for the evolution of a self-gravitating accretion disc by holding the Toomre parameter close to its threshold, and obtaining the stress parameter from the cooling rate. In agreement with the previous numerical solutions, furthermore, the accretion rate is assumed to be independent of the disc radius. Extreme situations where the entire disc is either optically thick or optically thin are studied independently and the obtained solutions can be used for exploring the early or the final phases of a protoplanetary disc evolution. Our solutions exhibit de…
Low ionization emission line regions (LINERs) are a heterogeneous collection of up to $1/3$ of galactic nuclei in the local Universe. It is unclear whether LINERs are simply the result of low accretion rates onto supermassive black holes or whether they include a large number of optically thick radiatively inefficient but super-Eddington accretion flows (RIAFs). Optically thick RIAFs are typically disks of large scale-height or quasi-spherical gas flows. These should be dense enough to trap and merge a large number of the stellar mass black holes, which we expect to exist in galactic nuclei. E…
Dark gas in the interstellar medium (ISM) is believed to not be detectable either in CO or Hi radio emission, but it is detected by other means including gamma-rays, dust emission and extinction traced outside the Galactic plane at |b|>5 degree. In these analyses, the 21-cm HI emission is usually assumed to be completely optically thin. We have reanalyzed the HI emission from the whole sky at |b|>15 degree by considering temperature stratification in the ISM inferred from the Planck/IRAS analysis of the dust properties. The results indicate that the HI emission is saturated with an optical dep…
The local interstellar medium (ISM) is suffused with "dark" gas, identified by excess infrared and gamma ray emission, yet undetected by standard ISM tracers such as neutral hydrogen (HI) or carbon monoxide emission. Based on observed dust properties from Planck, recent studies have argued that HI mixed with dust is strongly saturated and that dark gas is dominated by optically-thick HI. We test this hypothesis by reproducing this model using data from Planck and new 21 cm emission maps from GALFA-HI -- the first large-area 21cm emission survey with comparable angular resolution to Planck. We …
Optically thick winds of very massive stars suppress intermediate-mass black hole formation
Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Universität Heidelberg, Zentrum für Astronomie (ZAH), Institut für Theoretische Astrophysik（海德堡大学天体物理中心（ZAH）理论天体物理研究所）；Universität Heidelberg, Interdiszipliäres Zentrum für Wissenschaftliches Rechnen（海德堡大学跨学科科学计算中心）；Dipartimento di Fisica e Astronomia Galileo Galilei, Università di Padova（帕多瓦大学伽利略·伽利莱物理与天文学系）；INFN, Sezione di Padova（意大利国家核物理研究所帕多瓦分部）；Gran Sasso Science Institute (GSSI)（格兰萨索科学研究所）；INFN, Laboratori Nazionali del Gran Sasso（意大利国家核物理研究所格兰萨索国家实验室）；Departament de Física Quàntica i Astrofísica, Institut de Ciències del Cosmos, Universitat de Barcelona（巴塞罗那大学量子物理与天体物理学系宇宙科学研究所）
Magnetized neutron stars power at least some ultra-luminous X-ray sources. The accretion flow in these cases is interrupted at the magnetospheric radius and then reaches the surface of a neutron star following magnetic field lines. Accreting matter moving along magnetic field lines forms the accretion envelope around the central object. We show that, in case of high mass accretion rates $\gtrsim 10^{19}\,{\rm g\,s^{-1}}$ the envelope becomes closed and optically thick, which influences the dynamics of the accretion flow and the observational manifestation of the neutron star hidden behind the …
Polarized continuum emission from aligned grains in disks around young stellar objects can be used to probe the magnetic field, radiation anisotropy, or drift between dust and gas, depending on whether the non-spherical grains are aligned magnetically, radiatively or mechanically. We show that it can also be used to probe another key disk property -- the temperature gradient -- along sight lines that are optically thick, independent of the grain alignment mechanism. We first illustrate the technique analytically using a simple 1D slab model, which yields an approximate formula that relates the…
We present an analysis of the HI and CO gas in conjunction with the Planck/IRAS submillimeter/far-infrared dust properties toward the most outstanding high latitude clouds MBM 53, 54, 55 and HLCG 92-35 at b = -30 deg to -45 deg. The CO emission, dust opacity at 353 GHz (tau353), and dust temperature (Td) show generally good spatial correspondence. On the other hand, the correspondence between the HI emission and the dust properties is less clear than in CO. The integrated HI intensity WHI and tau353 show a large scatter with a correlation coefficient of ~0.6 for a Td range from 16 K to 22 K. W…
It has recently been discovered that a fraction of ultra-luminous X-ray sources (ULXs) exhibit X-ray pulsations, and are therefore powered by super-Eddington accretion onto magnetized neutron stars (NSs). For typical ULX mass accretion rates ($\gtrsim 10^{19}\,{\rm g\,s^{-1}}$), the inner parts of the accretion disc are expected to be in the supercritical regime, meaning that some material is lost in a wind launched from the disc surface, while the rest forms an optically thick envelope around the NS as it follows magnetic field lines from the inner disc radius to the magnetic poles of the sta…
In the past years, several observations of AGN and X-ray binaries have suggested the existence of a warm T around 0.5-1 keV and optically thick, τ~ 10-20, corona covering the inner parts of the accretion disk. These properties are directly derived from spectral fitting in UV to soft-X-rays using Comptonization models. However, whether such a medium can be both in radiative and hydrostatic equilibrium with an accretion disk is still uncertain. We investigate the properties of such warm, optically thick coronae and put constraints on their existence. We solve the radiative transfer equation for …
We present a deep search for HI 21-cm emission from the gaseous halo of Messier 31 as part of Project AMIGA, a large program Hubble Space Telescope program to study the circumgalactic medium of the Andromeda galaxy. Our observations with the Robert C. Byrd Green Bank Telesope target sight lines to 48 background AGNs, more than half of which have been observed in the ultraviolet with the Cosmic Origins Spectrograph, with impact parameters $25 \lesssim ρ\lesssim 330$ kpc ($0.1 \lesssim ρ/ R_{\rm vir} \lesssim 1.1$). We do not detect any 21-cm emission toward these AGNs to limits of $N({\rm HI}) …
Gas and dust properties in the Chamaeleon molecular cloud complex have been investigated with emission lines from atomic hydrogen (HI) and 12CO molecule, dust optical depth at 353 GHz ($τ_{353}$), and $J$-band infrared extinction ($A_{J}$). We have found a scatter correlation between the HI integrated intensity ($W_{\rm HI}$) and $τ_{353}$ in the Chamaeleon region. The scattering has been examined in terms of possible large optical depth in HI emission ($τ_{\rm HI}$) using a total column density ($N_{\rm H}$) model based on $τ_{353}$. A nonlinear relation of $τ_{353}$ with the $\sim$1.2 power …
Optically Thick Outflow Driven by Supercritical Accretion May Explain Little Red Dots
State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理国家重点实验室）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）；Department of Astronomy, School of Physics, Peking University（北京大学物理学院天文学系）
We report a Fermi-LAT $γ$-ray analysis for the Chamaeleon molecular-cloud complex using a total column density (NH) model based on the dust optical depth at 353 GHz ($τ_{353}$) with the Planck thermal dust emission model. Gamma rays with energy from 250 MeV to 100 GeV are fitted with the NH model as a function of $τ_{353}$, NH $\propto$ $τ_{353}^{1/α}$ ($α$ $\geq$ 1.0), to explicitly take into account a possible nonlinear $τ_{353}$/NH ratio. We found that a nonlinear relation, $α$$\sim$1.4, gives the best fit to the $γ$-ray data. This nonlinear relation may indicate dust evolution effects acro…
In this work we investigate the Principal Component Analysis (PCA) sensitivity to the velocity power spectrum in high opacity regimes of the interstellar medium (ISM). For our analysis we use synthetic Position-Position-Velocity (PPV) cubes of fractional Brownian motion (fBm) and magnetohydrodynamics (MHD) simulations, post processed to include radiative transfer effects from CO. We find that PCA analysis is very different from the tools based on the traditional power spectrum of PPV data cubes. Our major finding is that PCA is also sensitive to the phase information of PPV cubes and this allo…
