arXiv subjects

Ran Wang

Publications and source records attributed to Ran Wang.

At least 145 records · Page 8Linked to original sources

arXiv2020

Discovery of an Enormous Ly$α$ nebula in a massive galaxy overdensity at $z=2.3$

Enormous Ly$α$ Nebulae (ELANe), unique tracers of galaxy density peaks, are predicted to lie at the nodes and intersections of cosmic filamentary structures. Previous successful searches for ELANe have focused on wide-field narrowband surveys, or have targeted known sources such as ultraluminous quasi-stellar-objects (QSOs) or radio galaxies. Utilizing groups of coherently strong Ly$α$ absorptions (CoSLAs), we have developed a new method to identify high-redshift galaxy overdensities and have identified an extremely massive overdensity, BOSS1441, at $z=2-3$ (Cai et al. 2016a). In its density peak, we discover an ELAN that is associated with a relatively faint continuum. To date, this object has the highest diffuse Ly$α$ nebular luminosity of $L_{\rm{nebula}}=5.1\pm0.1\times10^{44}$ erg s$^{-1}$. Above the 2$σ$ surface brightness limit of SB$_{\rm{Lyα}}= 4.8\times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$, this nebula has an end-to-end spatial extent of 442 kpc. This radio-quiet source also has extended \civ\ $\lambda1549$ and \heii\ $\lambda1640$ emission on $\gtrsim30$ kpc scales. Note that the Ly$α$, \heii\ and \civ\ emission all have double-peaked line profiles. Each velocity component has a full-width-half-maximum (FWHM) of $\approx700 - 1000$ km s$^{-1}$. We argue that this Ly$α$ nebula could be powered by shocks due to an AGN-driven outflow or/and photoionization by a strongly obscured source.

astro-ph.GA↗

arXiv2020

The Magellan M2FS Spectroscopic Survey of High-Redshift Galaxies: A Sample of 260 Ly$α$ Emitters at Redshift $z\approx5.7$

We present a spectroscopic survey of Ly$α$ emitters (LAEs) at $z\approx5.7$ using the multi-object spectrograph M2FS on the Magellan Clay telescope. This is part of a high-redshift galaxy survey carried out in several well-studied deep fields. These fields have deep images in multiple UV/optical bands, including a narrow NB816 band that has allowed an efficient selection of LAE candidates at $z\approx5.7$. Our sample consists of 260 LAEs and covers a total effective area of more than two square degrees on the sky. This is so far the largest (spectroscopically confirmed) sample of LAEs at this redshift. We use the secure redshifts and narrowband photometry to measure Ly$α$ luminosities. We find that these LAEs span a Ly$α$ luminosity range of $\sim 2\times10^{42} - 5\times10^{43}$ erg s$^{-1}$, and include some of the most luminous galaxies known at $z \ge 5.7$ in terms of Ly$α$ luminosity. Most of them have rest-frame equivalent widths between 20 and 300 Å, and more luminous Ly$α$ emission lines tend to have broader line widths. We detect a clear offset of $\sim20$ Å between the observed Ly$α$ wavelength distribution and the NB816 filter transmission curve, which can be explained by the intergalactic medium absorption of continua blueward of Ly$α$ in the high-redshift spectra. This sample is being used to study the Ly$α$ luminosity function and galaxy properties at $z\approx5.7$.

astro-ph.GA↗

arXiv2020

SCUBA2 High Redshift Bright Quasar Survey: Far-infrared Properties and Weak-line Features

We present a submillimetre continuum survey ('SCUBA2 High rEdshift bRight quasaR surveY', hereafter SHERRY) of 54 high redshift quasars at $5.6 3.5σ$). The new SHERRY detections indicate far-infrared (FIR) luminosities of $\rm 3.5\times10^{12}$ to $\rm 1.4\times10^{13}$ $L_{\odot}$, implying extreme star formation rates of 90 to 1060 $M_{\odot}$ yr$^{-1}$ in the quasar host galaxies. Compared with $z =$ 2$-$5 samples, the FIR luminous quasars ($L_{\rm FIR} > 10^{13}\,L_{\odot}$) are more rare at $z \sim 6$. The optical/near-infrared (NIR) spectra of these objects show 11% (6/54) of the sources have weak Ly$α$, emission line features, which may relate to different sub-phases of the central active galactic nuclei (AGNs). Our SCUBA2 survey confirms the trend reported in the literature that quasars with submillimeter detections tend to have weaker ultraviolet (UV) emission lines compared to quasars with nondetections. The connection between weak UV quasar line emission and bright dust continuum emission powered by massive star formation may suggest an early phase of AGN-galaxy evolution, in which the broad line region is starting to develop slowly or is shielded from the central ionization source, and has unusual properties such as weak line features or bright FIR emission.

astro-ph.GA↗

arXiv2020

Ionized and atomic interstellar medium in the z = 6.003 quasar SDSS J2310+1855

Observing the interstellar medium (ISM) in $z \gtrsim 6$ quasars host galaxies is essential for understanding the co-evolution between the supermassive black holes and their hosts. To probe the gas physical conditions and search for imprints of Active Galactic Nuclei (AGN) on the ISM, we report ALMA observations of the $\rm [N\ II]_{122 μm}$ and $\rm [O\ I]_{146 μm}$ lines and the underlying continuum from the $z=6.003$ quasar SDSS J231038.88+185519.7. Together with previous $\rm [C\ II]_{158 μm}$ and $\rm [O\ III]_{88 μm}$ observations, we use the ratios of these fine-structure lines to probe the ISM properties. Similar to other high-$z$ systems, this object exhibits a $\rm [C\ II]_{158 μm}$/$\rm [O\ I]_{146 μm}$ ratio comparable to the lowest values found in local (Ultra) luminous infrared galaxies, suggesting a "warmer" and "denser" gas component compared to typical local systems. The $\rm [O\ III]_{88 μm}$/$\rm [O\ I]_{146 μm}$ ratio is lower than that of other local and high-$z$ systems, indicating a smaller ionized gas fraction in this quasar. The $\rm [O\ III]_{88 μm}$/$\rm [N\ II]_{122 μm}$ ratio is comparable to that of local systems, and suggests a metallicity of $Z/Z_{\odot}$=1.5$-$2.1. Based on the $\rm [N\ II]_{122 μm}$ detection, we estimate that $17\%$ of the $\rm [C\ II]_{158 μm}$ emission is associated with ionized gas. The $\rm [N\ II]_{122 μm}$ line shows a "flux deficit" comparable to local systems. The $\rm [O\ I]_{146 μm}$ line, with a $\rm [O\ I]_{146 μm}$/FIR ratio $\ge 2\times$ than expected from the local relation, indicates no $\rm [O\ I]_{\rm 146 μm}$ deficit. The low $\rm [C\ II]_{158 μm}$/$\rm [O\ I]_{146 μm}$ ratio, together with the high $\rm [O\ I]_{146 μm}$/FIR ratio in J2310+1855, reveals that the warm and dense gas is likely a result of AGN heating to the ISM.

astro-ph.GA↗

arXiv2020

AGN Feedback and Star Formation of Quasar Host Galaxies: Insights from the Molecular Gas

The molecular gas serves as a key probe of the complex interplay between black hole accretion and star formation in the host galaxies of active galactic nuclei (AGNs). We use CO(2-1) observations from a new ALMA survey, in conjunction with literature measurements, to investigate the molecular gas properties of a representative sample of 40 z<0.3 Palomar-Green quasars, the largest and most sensitive study of molecular gas emission to date for nearby quasars. We find that the AGN luminosity correlates with both the CO luminosity and black hole mass, suggesting that AGN activity is loosely coupled to the cold gas reservoir of the host. The observed strong correlation between host galaxy total infrared luminosity and AGN luminosity arises from their common dependence on the molecular gas. We argue that the total infrared luminosity, at least for low-redshift quasars, can be used to derive reliable star formation rates for the host galaxy. The host galaxies of low-redshift quasars have molecular gas content similar to that of star-forming galaxies of comparable stellar mass. Moreover, they share similar gas kinematics, as evidenced by their CO Tully-Fisher relation and the absence of detectable molecular outflows down to sensitive limits. There is no sign that AGN feedback quenches star formation for the quasars in our sample. On the contrary, the abundant gas supply forms stars prodigiously, at a rate that places most of them above the star-forming main sequence and with an efficiency that rivals that of starburst systems.

astro-ph.GA↗

arXiv2020

Radio activity of supermassive black holes with extremely high accretion rates

Radio emission from the high- and super-Eddington accreting active galactic nuclei (AGNs) has various origins: a persistent jet, the magnetized corona and the wind-like outflows. It is now still unclear which is the leading mechanism responsible for the observed radio emission and how the radio emission is related to other characteristic parameters such as the Eddington ratio and black hole mass. In this paper, we present the 5 GHz Very Large Array (VLA) observational results of a sample of 25 extremely high Eddington accreting supermassive black holes (EESBHs, the Eddington ratio close to or above one) from narrow-line Seyfert 1 galaxies, among which 22 sources are detected. Most of EESBHs show a compact radio structure from a few hundred parsecs to one-kiloparsec scale. We estimated the lowest star formation rate surface density required for producing the observed radio emission, and found it is higher than the largest value previously detected in circumnuclear starburst galaxies, implying that the radio emission is from the AGN activity. Along with a comparison sample, we find an overall inverse radio loudness and Eddington ratio correlation ranging from sub- to super-Eddington ratios. The high-Eddington and mildly super-Eddington AGNs (-0.5 ~0.6) have a flatter radio spectrum, along with its low radio luminosity: L_R/L_X~10^-5, their radio emission is likely dominated by a magnetized corona, and a radiation pressure caused jet is also proposed in this paper.

astro-ph.HE↗

arXiv2020

Catching butterflies in the sky: Extended catalog of winged or X-shaped radio sources from the latest FIRST data release

We present a catalog of 290 "winged" or X-shaped radio galaxies (XRGs) extracted from the latest (2014 December 17) data release of the "Very Large Array Faint Images of the Radio Sky at Twenty centimeter." We have combined these radio images with their counterparts in the TIFR GMRT sky survey at 150 MHz, in an attempt to identify any low surface brightness radio emission present in these sources. This has enabled us to assemble a sample of 106 "strong" XRG candidates and 184 "probable" XRG candidates whose XRG designation needs to be verified by further observations. The present sample of 290 XRG candidates is almost twice as large as the number of XRGs currently known. Twenty-five of our 290 XRG candidates (9 "strong" and 16 "probable") are identified as quasars. Double-peaked narrow emission lines are seen in the optical spectra of three of the XRG candidates (two "strong" and one "probable"). Nearly 90% of the sample is located in the FR II domain of the Owen-Ledlow diagram. A few of the strong XRG candidates have a rather flat radio spectrum (spectral index alpha flatter than -0.3) between 150 MHz and 1.4 GHz, or between 1.4 and 5 GHz. Since this is not expected for lobe-dominated extragalactic radio sources (like nearly all known XRGs), these sources are particularly suited for follow-up radio imaging and near-simultaneous measurement of the radio spectrum.

astro-ph.HE↗

arXiv2020

Distributed Energy Trading and Scheduling among Microgrids via Multiagent Reinforcement Learning

The development of renewable energy generation empowers microgrids to generate electricity to supply itself and to trade the surplus on energy markets. To minimize the overall cost, a microgrid must determine how to schedule its energy resources and electrical loads and how to trade with others. The control decisions are influenced by various factors, such as energy storage, renewable energy yield, electrical load, and competition from other microgrids. Making the optimal control decision is challenging, due to the complexity of the interconnected microgrids, the uncertainty of renewable energy generation and consumption, and the interplay among microgrids. The previous works mainly adopted the modeling-based approaches for deriving the control decision, yet they relied on the precise information of future system dynamics, which can be hard to obtain in a complex environment. This work provides a new perspective of obtaining the optimal control policy for distributed energy trading and scheduling by directly interacting with the environment, and proposes a multiagent deep reinforcement learning approach for learning the optimal control policy. Each microgrid is modeled as an agent, and different agents learn collaboratively for maximizing their rewards. The agent of each microgrid can make the local scheduling decision without knowing others' information, which can well maintain the autonomy of each microgrid. We evaluate the performances of our proposed method using real-world datasets. The experimental results show that our method can significantly reduce the cost of the microgrids compared with the baseline methods.

eess.SY↗

arXiv2020

Observations by GMRT at 323 MHz of radio-loud quasars at $z>5$

We present Giant Metrewave Radio Telescope (GMRT) 323 MHz radio continuum observations toward 13 radio-loud quasars at $z>5$, sampling the low-frequency synchrotron emission from these objects. Among the 12 targets successfully observed, we detected 10 above $4σ$ significance, while 2 remain undetected. All of the detected sources appear as point sources. Combined with previous radio continuum detections from the literature, 9 quasars have power-law spectral energy distributions throughout the radio range; for some the flux density drops with increasing frequency while it increases for others. Two of these sources appear to have spectral turnover. For the power-law-like sources, the power-law indices have a positive range between 0.18 and 0.67 and a negative values between $-0.90$ and $-0.27$. For the turnover sources, the radio peaks around $\sim1$ and $\sim10$ GHz in the rest frame, the optically thin indices are $-0.58$ and $-0.90$, and the optically thick indices are 0.50 and 1.20. A magnetic field and spectral age analysis of SDSS J114657.59+403708.6 at $z=5.01$ may indicate that the turnover is not caused by synchrotron self-absorption, but rather by free-free absorption by the high-density medium in the nuclear region. Alternatively, the apparent turnover may be an artifact of source variability. Finally, we calculated the radio loudness $R_{2500\rm\, Å}$ for our sample, which spans a very wide range from 12$^{+13}_{-13}$ to 4982$^{+279}_{-254}$.

astro-ph.GA↗

arXiv2020

Discovery of a [CI]-faint, CO-bright Galaxy: ALMA Observations of the Merging Galaxy NGC 6052

We report sensitive [\ion{C}{1}]~$^3P_1$--$^3P_0$ and $^{12}$CO~$J$=4--3 observations of the nearby merging galaxy NGC 6052 using the Morita (Atacama Compact) Array of ALMA. We detect $^{12}$CO~$J$=4--3 toward the northern part of NGC 6052, but [\ion{C}{1}]~$^3P_1$--$^3P_0$ is not detected with a [\ion{C}{1}]~$^3P_1$--$^3P_0$ to $^{12}$CO~$J$=4--3 line luminosity ratio of$~\lesssim0.07$. According to models of photodissociation regions, the unusual weakness of [\ion{C}{1}]~$^3P_1$--$^3P_0$ relative to $^{12}$CO~$J$=4--3 can be explained if the interstellar medium has a hydrogen density larger than $10^5\,{\rm cm}^{-3}$, conditions that might arise naturally in the ongoing merging process in NGC 6052. Its [\ion{C}{1}]~$^3P_1$--$^3P_0$ emission is also weaker than expected given the molecular gas mass inferred from previous measurements of $^{12}$CO~$J$=1--0 and $^{12}$CO~$J$=2--1. This suggests that [\ion{C}{1}]~$^3P_1$--$^3P_0$ may not be a reliable tracer of molecular gas mass in this galaxy. NGC 6052 is a unique laboratory to investigate how the merger process impacts the molecular gas distribution.

astro-ph.GA↗

arXiv2020

CIV emission line properties and uncertainties in black hole mass estimates of z ~ 3.5 quasars

Using a high luminosity ($L_{\rm bol} \sim 10^{47.5} - 10^{48.3}$ erg s$^{-1}$), high redshift ($3.2 < z < 3.8$) quasar sample of 19 quasars with optical and near-infrared spectroscopy, we investigate the reliability of the CIV-based black hole mass estimates ($M_{\rm BH}$). The median logarithm of the CIV- and H$β$-based $M_{\rm BH}$ ratios is 0.110 dex with the scatter of 0.647 dex. The CIV-to-H$β$ BH mass differences are significantly correlated with the CIV FWHMs, blueshifts and asymmetries. Corrections of the CIV FWHM using the blueshift and asymmetry reduce the scatter of the mass differences by $\sim$ 0.04-0.2 dex. Quasars in our sample accrete at the Eddington ratio $R_{\rm EDD}>0.3$ and cover a considerable range of blueshifts, with 18/19 of the quasars showing CIV blueshifts (with the median value of 1126 km s$^{-1}$) and 14/19 of the quasars showing CIV blueshifts larger than 500 km s$^{-1}$. It suggests that not all quasars with high Eddington ratios show large blueshifts. The Baldwin effect between the CIV rest-frame equivalent width (REW) and the continuum luminosity at 1350 $\overset{\lower.5em\circ}{\mathrm{A}}$ is not seen, likely due to the limited luminosity range of our sample. We find a lack of flux in the red wing of the composite spectrum with larger CIV blueshift, and detect a higher ratio of [OIII] quasars with REW$_{\rm [OIII]}>5$ $\overset{\lower.5em\circ}{\mathrm{A}}$ in the subsample with lower CIV blueshift. It is more likely that they are caused by the combination of the Eddington ratio and the orientation effect.

astro-ph.GA↗

arXiv2020

R3: A Reading Comprehension Benchmark Requiring Reasoning Processes

Existing question answering systems can only predict answers without explicit reasoning processes, which hinder their explainability and make us overestimate their ability of understanding and reasoning over natural language. In this work, we propose a novel task of reading comprehension, in which a model is required to provide final answers and reasoning processes. To this end, we introduce a formalism for reasoning over unstructured text, namely Text Reasoning Meaning Representation (TRMR). TRMR consists of three phrases, which is expressive enough to characterize the reasoning process to answer reading comprehension questions. We develop an annotation platform to facilitate TRMR's annotation, and release the R3 dataset, a \textbf{R}eading comprehension benchmark \textbf{R}equiring \textbf{R}easoning processes. R3 contains over 60K pairs of question-answer pairs and their TRMRs. Our dataset is available at: \url{http://anonymous}.

cs.CL↗

arXiv2020

Large deviation for two-time-scale stochastic Burgers equation

A Freidlin-Wentzell type large deviation principle is established for stochastic partial differential equations with slow and fast time-scales, where the slow component is a one-dimensional stochastic Burgers equation with small noise and the fast component is a stochastic reaction-diffusion equation. Our approach is via the weak convergence criterion developed in [3].

math.PR↗

arXiv2020

Asymptotics for stochastic Burgers equation with jumps

For one-dimensional stochastic Burgers equation driven by Brownian motion and Poisson process, we study the $ψ$-uniformly exponential ergodicity with $ψ(x)=1+\|x\|$, the moderate deviation principle and the large deviation principle for the occupation measures.

math.PR↗

arXiv2020

Submillimeter Galaxy studies in the next decade: EAO Submillimetre Futures White Paper Series, 2019

Over the last two decades, the Submillimetre Common-User Bolometer Array (SCUBA) and SCUBA-2 on the James Clerk Maxwell Telescope (JCMT) achieved gread success in discovering the population of dusty starburst galaxies in the early universe. The SCUBA-2 surveys at 450 micron and 850 micron set important constraints on the obscured star formation over cosmic time, and in combination of deep optical and near-IR data, allows the study of protoclusters and structure formation. However, the current submillimeter (submm) surveys by JCMT are still limited by area of sky coverage (confusion limit mapping of only a few deg^2), which prevent a systematic study of large samples of the obscured galaxy population. In this white paper, we review the studies of the submm galaxies with current submillimeter/millimeter (submm/mm) observations, and discuss the important science with the new submm instruments in the next decade. In particular, with a 10 times faster mapping speed of the new camera, we will expect deep 850 micron surveys over 10 to 100 times larger sky area to i) largely increase the sample size of submm detections toward the highest redshift, ii) improve our knowledge of galaxy and structure formation in the early universe.

astro-ph.GA↗

arXiv2019

Probing the full CO spectral line energy distribution (SLED) in the nuclear region of a quasar-starburst system at $z=6.003$

We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO $(8-7)$, $(9-8)$, $\rm H_{2}O (2_{0,2}-1_{1,1})$ and $\rm OH^{+} (1_{1}-0_{1})$ and NOrthern Extended Millimeter Array (NOEMA) observations of CO $(5-4)$, $(6-5)$, $(12-11)$ and $(13-12)$ towards the $z = 6.003$ quasar SDSS J231038.88+185519.7, aiming to probe the physical conditions of the molecular gas content of this source. We present the best sampled CO spectral line energy distribution (SLED) at $z = 6.003$, and analyzed it with the radiative transfer code MOLPOP-CEP. Fitting the CO SLED to a one-component model indicates a kinetic temperature $T_{\rm kin} = 228 \ \rm K$, molecular gas density $log (n(\rm H_{2})/\rm cm^{-3}$ )=4.75, and CO column density $log(N(\rm CO)/\rm cm^{-2}) =17.5$, although a two-component model better fits the data. In either case, the CO SLED is dominated by a "warm" and "dense" component. Compared to samples of local (Ultra) Luminous Infrared Galaxies ((U)LIRGs), starburst galaxies and high redshift Submillimeter Galaxies (SMGs), J2310+1855 exhibits higher CO excitation at ($J \geq 8$), like other high redshift quasars. The high CO excitation, together with the enhanced $L_{\rm H_{2}O}/ L_{IR} $, $L_{\rm H_{2}O}/ L_{CO} $ and $L_{OH^{+}}/L_{\rm H_{2}O} $ ratios, suggests that besides the UV radiation from young massive stars, other mechanisms such as shocks, cosmic rays and X-rays might also be responsible for the heating and ionization of the molecular gas. In the nuclear region probed by the molecular emissions lines, any of these mechanisms might be present due to the powerful quasar and the starburst activity.

astro-ph.GA↗

arXiv2019

A note on decompositions of the stochastic convolution driven by a white-fractional Gaussian noise

Let $u = \{u(t, x); (t,x)\in \mathbb R_+\times \mathbb R\}$ be the solution to a linear stochastic heat equation driven by a Gaussian noise, which is a Brownian motion in time and a fractional Brownian motion in space with Hurst parameter $H\in(0, 1)$. For any given $x\in \mathbb R$ (resp. $t\in \mathbb R_+$), we show a decomposition of the stochastic process $t\mapsto u(t,x)$ (resp. $x\mapsto u(t,x)$) as the sum of a fractional Brownian motion with Hurst parameter $H/2$ (resp. $H$) and a stochastic process with $C^{\infty}$-continuous trajectories. Some applications of those decompositions are discussed.

math.PR↗

arXiv2019

An ALMA CO(2-1) Survey of Nearby Palomar-Green Quasars

The properties of the molecular gas can shed light on the physical conditions of quasar host galaxies and the effect of feedback from accreting supermassive black holes. We present a new CO(2-1) survey of 23 z<0.1 Palomar-Green quasars conducted with the Atacama Large Millimeter/submillimeter Array. CO emission was successfully detected in 91% (21/23) of the objects, from which we derive CO luminosities, molecular gas masses, and velocity line widths. Together with CO(1-0) measurements in the literature for 32 quasars (detection rate 53%), there are 15 quasars with both CO(1-0) and CO(2-1) measurements and in total 40 sources with CO measurements. We find that the line ratio R_21 = L'_CO(2-1)/L'_CO(1-0) is subthermal, broadly consistent with nearby galaxies and other quasars previously studied. No clear correlation is found between R_21 and the intensity of the interstellar radiation field or the luminosity of the active nucleus. As with the general galaxy population, quasar host galaxies exhibit a strong, tight, linear L_IR-L_CO relation, with a normalization consistent with that of starburst systems. We investigate the molecular-to-total gas mass fraction with the aid of total gas masses inferred from dust masses previously derived from infrared observations. Although the scatter is considerable, the current data do not suggest that the CO-to-H_2 conversion factor of quasar host galaxies significantly differs from that of normal star-forming galaxies.

astro-ph.GA↗