We present new KAT-7 observations of the neutral hydrogen (HI) spectral line, and polarized radio continuum emission, in the grand design spiral M83. These observations provide a sensitive probe of the outer disk structure and kinematics, revealing a vast and massive neutral gas distribution that appears to be tightly coupled to the interaction of the galaxy with the environment. We present a new rotation curve extending out to a radius of 50 kpc. Based on our new HI dataset and comparison with multiwavelength data from the literature we consider the impact of mergers on the outer disk and discuss the evolution of M83. We also study the periphery of the HI distribution and reveal a sharp edge to the gaseous disk that is consistent with photoionization or ram pressure from the intergalactic medium (IGM). The radio continuum emission is not nearly as extended as the HI and is restricted to the main optical disk. Despite the relatively low angular resolution we are able to draw broad conclusions about the large-scale magnetic field topology. We show that the magnetic field of M83 is similar in form to other nearby star forming galaxies, and suggest that the disk-halo interface may host a large-scale regular magnetic field.
Context. Pisces A & Pisces B are the only two galaxies found via optical imaging and spectroscopy out of 22 HI clouds identified in the GALFAHI survey as dwarf galaxy candidates. Aims. Derive the HI content and kinematics of Pisces A & B. Methods. Aperture synthesis HI observations using the seven dish Karoo Array Telescope (KAT-7), which is a pathfinder instrument for MeerKAT, the South African precursor to the mid-frequency Square Kilometre Array (SKA-MID). Results. The small rotation velocities detected of ~5 km/sec and ~10 km/sec in Pisces A & B respectively, and their HI content show that…
We present high sensitivity HI observations of NGC 6822, obtained with the Karoo Array Telescope (KAT-7). We study the kinematics, the mass distribution, and the star formation thresholds. The KAT-7 short baselines and low system temperature make it sensitive to large-scale, low surface brightness emission. The observations detected $\sim$ 23$\%$ more flux than previous ATCA observations. We fit a tilted ring model to the HI velocity field to derive the rotation curve (RC). The KAT-7 observations allow the measurement of the rotation curve of NGC 6822 out to 5.8 kpc, $\sim$ 1 kpc further than …
The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries that will be 50 times more sensitive than any existing radio facility. Most of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from a few hundred MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is a technology demonstrator aimed in the mid-frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phased-array feed systems on parabolic reflector…
We map the Hi distribution of galaxies in a $\sim 1.5^\circ \times 2.5^\circ$ region located at the virial radius south of the Virgo cluster using the KAT$-$7 and the WSRT interferometers. Because of the different beam sizes of the two telescopes, a similar column density sensitivity of $\rm N_{Hi} \sim 10^{18}\,cm^{-2}$ was reached with the two observations over 16.5 km/s. We pioneer a new approach to combine the observations and take advantage of their sensitivity to both the large and small scale structures. Out to an unprecedented extent, we detect an Hi tail of $\sim 60$ kpc being strippe…
HI observations of the Local Group dwarf irregular galaxies Sextans A and B, obtained with the Karoo Array Telescope (KAT-7) are presented. The KAT-7 wide field of view and excellent surface brightness sensitivity allows us to verify the true HI extent of the galaxies. We derive HI extends of 30$^{\prime}$ and 20$^{\prime}$ and total HI fluxes of 181 $\pm$ 2.0 Jy.km.s$^{-1}$ and 105 $\pm$ 1.4 Jy.km.s$^{-1}$ for Sextans A and B respectively. This result shows clearly the overestimate of the HI extent and total flux of 54$^{\prime}$ and 264 Jy.km.s$^{-1}$ reported for Sextans A using the Effelsb…
HI 21-cm absorption spectroscopy provides a unique probe of the cold neutral gas in normal and active galaxies from redshift z > 6 to the present day. We describe the status of HI absorption studies, the plans for pathfinders/precursors, the expected breakthroughs that will be possible with SKA1, and some limitations set by the current design.
We present HI observations of the Sculptor Group starburst spiral galaxy NGC 253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for the SKA precursor MeerKAT, under construction. The short baselines and low system temperature of the telescope make it very sensitive to large scale, low surface brightness emission. The KAT-7 observations detected 33% more flux than previous VLA observations, mainly in the outer parts and in the halo for a total HI mass of $2.1 \pm 0.1$ $\times 10^{9}$ M$_{\odot}$. HI can be found at large distances perpendicular to the plane out to proje…
We present detailed science cases that a large fraction of the Indian AGN community is interested in pursuing with the upcoming Square Kilometre Array (SKA). These interests range from understanding low luminosity active galactic nuclei in the nearby Universe to powerful radio galaxies at high redshifts. Important unresolved science questions in AGN physics are discussed. Ongoing low-frequency surveys with the SKA pathfinder telescope GMRT, are highlighted.
The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no longer sustained, but lobes can be detected for a period of time before they fade away due to radiative and dynamical energy losses. The time-scale of the remnant phase and AGN duty cycle are vital to understanding the evolution of radio galaxies. In this paper, we report new band-3 observations with the upgraded Giant Meterwave Radio Telescope (uGMRT) for five remnant radio galaxies. Our uGMRT observations reveal emission of low-surface-brightness in all five remnants with 400 MHz surface brightn…
We present the first detection of OH absorption in diffuse gas at $z>0$, along with another eight stringent limits on OH column densities for cold atomic gas in galaxies at $0<z<0.4$. The absorbing gas detected towards Q0248+430 ($z_q$=1.313) originates from a tidal tail emanating from a highly star forming galaxy G0248+430 ($z_g$=0.0519) at an impact parameter of 15 kpc. The measured column density is $N$(OH) = (6.3$\pm$0.8)$\times$10$^{13}$($\frac{T_{\rm ex}}{3.5}$)($\frac{1.0}{f_c^{\rm OH}}$) cm$^{-2}$, where $f_c^{\rm OH}$ and $T_{\rm ex}$ are the covering factor and the excitation tempera…
The seven-dish KAT-7 array was built as an engineering test-bed for the 64-dish Karoo Array Telescope, known as MeerKAT, which is the South African precursor of the Square Kilometre Array (SKA). KAT-7 and MeerKAT are located close to the South African SKA core site in the Northern Cape's Karoo desert region. Construction of the KAT-7 array was completed in December 2010. The short baselines (26 to 185 m) and low system temperature (T$_{\rm sys} \sim$ 26 K) of the telescope make it very sensitive to large-scale, low-surface-brightness emission, which is one of the HI science drivers for MeerKAT…
Hydroxyl ($\rm OH$) is known to form efficiently in cold gas ($T\sim 100$K) along with the molecule $\rm H_2$ and can be used as an efficient tracer of the diffuse molecular gas in the interstellar medium (ISM). Using a simple formalism describing the $\rm H\,I/H_2$ transition and a reduced network of major chemical reactions, we present a semi-analytical prescription to estimate the abundances of O-bearing molecules in the diffuse ISM. We show that predictions based on our prescription are in good agreement with the estimates obtained using the MEUDON PDR code which utilizes the full reaction…
Carbon chain diversity in L1544 and IRAS 16293-2422: an astrochemical pathfinder study for the SKAO
INAF, Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所，阿切尔西天文台）；National Radio Astronomy Observatory（美国国家射电天文台）；Univ. Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，行星与地球物理学研究所）；European Southern Observatory（欧洲南方天文台）；Dipartimento di Chimica, Biologia e Biotecnologie（化学、生物与生物技术系）；Department of Chemistry, University of Virginia（弗吉尼亚大学化学系）；Department of Astronomy, University of Virginia（弗吉尼亚大学天文学系）；Université du Rennes, CNRS, IPR (Institut de Physique de Rennes)UMR 6251（雷恩大学，法国国家科学研究中心，雷恩物理研究所）
One of the key science drivers for the development of the SKA is to observe the neutral hydrogen, HI, in galaxies as a means to probe galaxy evolution across a range of environments over cosmic time. Over the past decade, much progress has been made in theoretical simulations and observations of HI in galaxies. However, recent HI surveys on both single dish radio telescopes and interferometers, while providing detailed information on global HI properties, the dark matter distribution in galaxies, as well as insight into the relationship between star formation and the interstellar medium, have …
The SKA and its pathfinders will enable studies of HI emission at higher redshifts than ever before. In moving beyond the local Universe, this will require the use of cosmologically appropriate formulae that have traditionally been simplified to their low-redshift approximations. In this paper, we summarise some of the most important relations for tracing HI emission in the SKA era, and present an online calculator to assist in the planning and analysis of observations (hifi.icrar.org).
Measuring radio source counts is critical for characterizing new extragalactic populations, brings a wealth of science within reach and will inform forecasts for SKA and its pathfinders. Yet there is currently great debate (and few measurements) about the behaviour of the 1.4-GHz counts in the microJy regime. One way to push the counts to these levels is via 'stacking', the covariance of a map with a catalogue at higher resolution and (often) a different wavelength. For the first time, we cast stacking in a fully bayesian framework, applying it to (i) the SKADS simulation and (ii) VLA data sta…
The Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) is a next-generation survey of neutral hydrogen (HI) in the Local Universe. It uses the widefield, high-resolution capability of the Australian Square Kilometer Array Pathfinder (ASKAP), a radio interferometer consisting of 36 x 12-m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radio-quiet zone in Western Australia. WALLABY aims to survey three-quarters of the sky (-90 degr < Dec < +30 degr) to a redshift of z < 0.26, and generate spectral line image cubes at ~30 arcsec resolution and ~1.6 mJy/beam per …
The substantial decrease in star formation density from z=1 to the present day is curious given the relatively constant neutral gas density over the same epoch. Future radio astronomy facilities, including the SKA and pathfinder telescopes, will provide pioneering measures of both the gas content of galaxies and star formation activity over cosmological timescales. Here we investigate the commensalities between neutral atomic gas (HI) and radio continuum observations, as well as the complementarity of the data products. We start with the proposed HI and continuum surveys to be undertaken with …
A key ingredient in the evolution of galaxies is the star formation cycle. Recent progress in the study of magnetic fields is revealing the close connection between star formation and its effect on the small-scale structure in the magnetized interstellar medium (ISM). In this contribution we describe how the modern generation of radio telescopes is being used to probe the physics of the ISM through sensitive multiwavelength surveys of gas and magnetic fields, from the inner star forming disk and outward into the galaxy outskirts where large-scale magnetic fields may also play a key role. We hi…
Unlocking the Full Potential of SKAO Extra-galactic Science with High-multiplex Optical Spectroscopy
University of Edinburgh（爱丁堡大学）；University of Bristol（布里斯托大学）；University of Hertfordshire（赫特福德大学）；University of Oxford（牛津大学）；North-West University（西北大学）；ASTRON, the Netherlands Institute for Radio Astronomy（荷兰射电天文研究所(ASTRON)）；University of Groningen（格罗宁根大学）；University Catholic of Lyon（里昂天主教大学）
The Australian SKA Pathfinder (ASKAP) telescope has started to localize Fast Radio Bursts (FRBs) to arcsecond accuracy from the detection of a single pulse, allowing their host galaxies to be reliably identified. We discuss the global properties of the host galaxies of the first four FRBs localized by ASKAP, which lie in the redshift range $0.11<z<0.48$. All four are massive galaxies (log( $M_{*}/ M_{\odot}$) $\sim 9.4 -10.4$) with modest star-formation rates of up to $2M_{\odot}$yr$^{-1}$ -- very different to the host galaxy of the first repeating FRB 121102, which is a dwarf galaxy with a hi…
University of Alberta（阿尔伯塔大学）；Ludwig Maximilian University of Munich (LMU)（慕尼黑大学）；The University of Western Australia（西澳大学）；University of the Witwatersrand（威特沃特斯兰德大学）；NASA Ames Research Center（美国国家航空航天局艾姆斯研究中心）；Cardiff University（卡迪夫大学）；University Catholic of Lyon（里昂天主教大学）
The Road to Identifying the Earliest Radio-Powerful AGN with the SKA
University of Tasmania（塔斯马尼亚大学）；Institute for Research in Fundamental Sciences (IPM)（伊朗基础科学研究所）；Leiden University（莱顿大学）；International Centre for Radio Astronomy Research, Curtin University（伊萨珀斯库珀廷大学国际射电天文研究中心）；INAF - Institute of Radio Astronomy（意大利国家天体物理研究所射电天文台）；Midnapore City College（米德纳波尔市学院）；Macquarie University（麦考瑞大学）
The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as diverse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and Dark Matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor t…
HI observations of the Magellanic-type spiral NGC 3109, obtained with the seven dish Karoo Array Telescope (KAT-7), are used to analyze its mass distribution. Our results are compared to what is obtained using VLA data. KAT-7 is the precursor of the SKA pathfinder MeerKAT, which is under construction. The short baselines and low system temperature of the telescope make it sensitive to large scale low surface brightness emission. The new observations with KAT-7 allow the measurement of the rotation curve of NGC 3109 out to 32', doubling the angular extent of existing measurements. A total HI ma…
We present early observations of 20 galaxies in the MHONGOOSE survey galaxies using KAT-7, the GBT, and MeerKAT. We present the best calibrators for five of the MHONGOOSE galaxies observed with the KAT-7, and search for signs of gas accretion in the GBT data, down to $3σ$ column density levels of $\rm 2.2\times10^{18}\, cm^{-2}$ over a $\rm 20\, km\, s^{-1}$ linewidth, but identify none. Using the KAT-7 and MeerKAT data, we have derived rotation curves and mass models for NGC 3621 and NGC 7424 out to an unprecedented extent. As a precursor to the SKA, the MeerKAT telescope combines both a high…
Strong evidence exists for a highly significant correlation between the radio flux density and gamma-ray energy flux in blazars revealed by Fermi. However, there are central issues that need to be clarified in this field: what are the counterparts of the about 30% of gamma-ray sources that are as yet unidentified? Are they just blazars in disguise or they are something more exotic, possibly associated with dark matter? How would they fit in the radio-gamma ray connection studied so far? With their superb sensitivity, SKA1-MID and SKA1-SUR will help to resolve all of these questions. Even more,…
Unravelling Turbulence and Magnetic Fields in Galaxy Clusters with SKA and XRISM
Mizusawa VLBI Observatory, National Astronomical Observatory of Japan（水泽VLBI观测站，日本国立天文台）；Research School of Astronomy and Astrophysics, Australian National University（天文学与天体物理学院，澳大利亚国立大学）；Department of Physics, Nagoya University（物理学系，名古屋大学）
One of the major science goals of the Square Kilometre Array (SKA) is to understand the role played by atomic hydrogen (HI) gas in the evolution of galaxies throughout cosmic time. The hyperfine transition line of the hydrogen atom at 21-cm is one of the best tools to detect and study the properties of HI gas associated with galaxies. In this article, we review our current understanding of HI gas and its relationship with galaxies through observations of the 21-cm line both in emission and absorption. In addition, we provide an overview of the HI science that will be possible with SKA and its …
Low-Frequency Recombination Lines from Galaxies and AGN over Cosmic Time
Ioffe Institute（约费研究所）；Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne University, University Paris Cité（巴黎高等师范学院物理实验室，ENS，巴黎文理研究大学，法国国家科学研究中心，索邦大学，巴黎西岱大学）；Inter-University Centre for Astronomy and Astrophysics（大学天文学与天体物理学中心）；Chalmers University of Technology, Onsala Space Observatory（查尔姆斯理工大学，翁萨拉太空观测站）；Sydney Institute for Astronomy, School of Physics A28, University of Sydney（悉尼天文研究所，A28物理学院，悉尼大学）；University of Maryland（马里兰大学）；University of Virginia（弗吉尼亚大学）
External galaxies often intervene in front of background radio sources such as quasars and radio galaxies. Linear polarization of the background emission is depolarized by Faraday rotation of inhomogeneous magnetized plasma of the intervening galaxies. Exploring the depolarizing intervening galaxies (DINGs) can be a powerful tool to investigate the cosmological evolution of the galactic magnetic field. In this paper, we investigate the effects of DINGs on background radio emission using theoretical DING models. We find that complex structures of galaxy result in complicated depolarization feat…
Rhodes University（罗德斯大学）；Queen’s University（女王大学）；Arthur B. McDonald Canadian Astroparticle Physics Research Institute, Queen’s University（亚瑟·B·麦克唐纳加拿大高能粒子物理研究所，女王大学）；IFPU – Institute for Fundamental Physics of the Universe（宇宙基础物理研究所 (IFPU)）；Seoul National University（首尔大学）；The University of Western Australia（西澳大学）
We present a catalogue of a large sample of extended radio sources in the SCORPIO field, observed and resolved by the Australia Telescope Compact Array. SCORPIO, a pathfinder project for addressing the early operations of the Australia SKA Pathfinder, is a survey of ~5 square degrees between 1.4 and 3.1 GHz, centered at l=343.5°, b=0.75° and with an angular resolution of about 10 arcsec. It is aimed at understanding the scientific and technical challenges to be faced by future Galactic surveys. With a mean sensitivity around 100 $μ$Jy/beam and the possibility to recover angular scales at least…
Here I present a brief review of interacting galaxy systems with extended low surface brightness (LSB) hydrogen tails and similar structures. Typically found in merging pairs, galaxy groups and clusters, HI features in galaxy surroundings can span many hundreds of kpc, tracing gravitational interactions between galaxies and ram pressure forces moving through the intra-group/cluster medium. Upcoming large HI surveys, e.g., with the wide-field (FOV = 30 square degrees) Phased Array Feeds on the Australian SKA Pathfinder (ASKAP), will provide a census of LSB structures in the Local Universe. By r…
The Galactic Faraday depth sky is a tracer for both the Galactic magnetic field and the thermal electron distribution. It has been previously reconstructed from polarimetric measurements of extra-galactic point sources. Here, we improve on these works by using an updated inference algorithm as well as by taking into account the free-free emission measure map from the Planck survey. In the future, the data situation will improve drastically with the next generation Faraday rotation measurements from SKA and its pathfinders. Anticipating this, the aim of this paper is to update the map reconstru…
Here I briefly highlight our studies of the gas content, kinematics and star formation in nearby dwarf galaxies (D < 10 Mpc) based on the `Local Volume HI Survey' (LVHIS, Koribalski et al. 2018), which was conducted with the Australia Telescope Compact Array (ATCA). The LVHIS sample consists of nearly 100 galaxies, including new discoveries, spanning a large diversity in size, shape, mass and degree of peculiarity. The hydrogen properties of dwarf galaxies in two nearby groups, Sculptor and CenA / M83, are analysed and compared with many rather isolated dwarf galaxies. Around 10% of LVHIS gala…
High-resolution 21-cm HI deep fields provide spatially and kinematically resolved neutral gas maps at different redshifts, which are key to understanding galaxy evolution across cosmic time and testing predictions of cosmological simulations. Here we present results from a pilot for the COSMOS HI Large Extragalactic Survey (CHILES) done with the Karl G. Jansky Very Large Array (VLA). We take advantage of the newly expanded capabilities of the telescope to probe the redshift interval 0<z<0.193 in one observation. We observe the COSMOS field for 50 hours, which contains 413 galaxies with optical…
MEDUSA I. Tracing magnetic field structures in tidal arms of the dwarf-dwarf merger NGC 1487
Ruhr Astroparticle and Plasma Physics Center (RAPP Center)（鲁尔高能粒子与等离子体物理中心）；CSIRO Space and Astronomy（澳大利亚联邦科学与工业研究组织空间与天文部门）；Thüringer Landessternwarte（图林根州立天文台）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；Ruhr University Bochum, Faculty for Physics & Astronomy, Theoretical Physics IV: Plasma Astroparticle Physics（波鸿鲁尔大学物理与天文学学院理论物理学第四系：等离子体高能天体物理学）；SKA Observatory, SKA-Low Science Operations Centre（平方公里阵列射电望远镜天文台，SKA低频科学运行中心）；INAF – Osservatorio Astronomico di Cagliari（意大利国家天体物理研究所卡利亚里天文台）；Astronomical Observatory of the Jagiellonian University（雅盖隆大学天文台）
We present an assessment of the accuracy of common operations performed in $21$-cm spectral line stacking experiments. To this end, we generate mock interferometric data surveying the 21-cm emission at frequency $1310<ν<1420$ MHz ($0.005<z<0.084$) and covering an area $\sim 6$ deg$^2$ of the sky, mimicking the observational characteristics of real MeerKAT observations. We find that the primary beam correction accounts for just few per cent ($\sim8\%$ at 0 primary beam power, $\sim 3\%$ at 0.6 primary beam power) deviations from the true $M_{\rm HI}$ signal, and that weighting schemes based on …
