The First FAST detection of neutral hydrogen emission from extragalactic galaxies

The Five-hundred-meter Aperture Spherical Radio Telescope (FAST) is the largest telescope with the highest sensitivity in the world. Extragalactic neutral hydrogen detection is one of important scientific goals of FAST.

Recently, an international research team led by Dr. Cheng Cheng from Chinese Academy of Sciences South America Center for Astronomy (CASSACA), successfully detected the neutral hydrogen line emission from three local galaxies using the FAST 19-beam receiver with only five minutes of exposure. The research paper is recently published in Astronomy & Astrophysics Letter. This is the first publication on FAST observation of extragalactic neutral hydrogen.

Fig. 1. The optical color images of the four galaxies for FAST observation. The red contours are the previous CO observation by ALMA. The white spectra in each panel are the results from FAST.

Neutral hydrogen gas is the most extended baryons in galaxies, while cold gas traced by CO is more concentrated to a galaxy center (red contour in Figure 1). With dynamical measurements of neutral hydrogen and CO, we can estimate the mass distribution of galaxies at different radii. Dynamical masses of these four galaxies estimated from the newly observed the neutral hydrogen line are 10 times higher than the observed baryon masses, indicating contribution of dark matter. On the other hand, dynamical masses estimated using previous CO observations were equivalent to their observed baryon masses. Therefore, the new FAST observation illustrates its ability of studying dark matter in galaxies using the neutral hydrogen 21cm emission line.

The FAST observation of these galaxies was an important part of an international research project, the Valparaíso ALMA Line Emission Survey (VALES), led by Prof. Edo Ibar from Valparaiso University in Chile. The VALES is a project of observing star forming galaxies using first-class international facilities such as SDSS, Herschel space observatory, ALMA, APEX and VLT. This international team has been publishing a series of scientific results.

FAST with the unpreceded sensitivity provides a very unique chance to observe the extra-galactic neutral hydrogen, and therefore has been adding to the list modern astronomical facilities used by this international collaboration. The FAST observation time was awarded in the Share-risk Observing call during the FAST Commissioning Phase. The team will apply for FAST time to further study the neutral hydrogen properties of VALES galaxies.

The paper can be accessed at https://www.aanda.org/articles/aa/full_html/2020/06/aa38483-20/aa38483-20.html

The 6th “From AGN to starburst: A multi-wavelength synergy” Meeting Successfully Held in Guiyang, China

During Aug. 12-16, 2019, the 6th “From AGN to starburst: A multi-wavelength synergy” was successfully held in Guiyang, China. The meeting was organized by National Astronomy Observatory of CAS (NAOC) and CAS South American Center of Astronomy (CASSACA), along with the Purple Mountain Observatory (PMO). Over 100 participants from 13 countries and regions attended this meeting. The AGN-starburst meeting series is a well-known international galaxy physics conference and it keeps focusing on the most advanced scientific researches and challenges in galaxy formation and evolution.

Poster of the meeting

Jiasheng Huang, SOC & Y.Sophia Dai, chair of SOC/LOC, delivered welcome speeches at the meeting

Throughout five days, over fifty reports and 17 poster talks were given by experts, young researchers and students. The presentations have a wide coverage, from the latest multi-wavelength observational results across redshifts, to the state-of-art simulation and theoretical models. Recent ALMA (the Atacama Large Millimeter/submillimeter Array) results are reported in studies of outflows, gas distribution and star formation efficiency in both AGNs and starburst galaxies. As for sky surveys in optical and infrared (IR) wavelength, speakers talked about features in different types of active galaxies and observational evidences related to “galaxy quenching”. These reports gave a detailed physical view of the relationship between supermassive blackhole (SMBH) and galaxy evolution.

(Nick Scoville, Marcia Rieke, Xiaohui Fan, Erin Hicks, Matt Malkan and Lei Hao)

(John Silverman, Luis Ho, Ran Wang, Yu Gao, Jeyhan Kartaltepe and Richard Bower)

Selected photos of experts giving presentations

On Aug. 15th, participants enjoyed a fantastic visit to the FAST (Five-hundred-meter Aperture Spherical Telescope) observatory, organized by LOC members Dr. Qisheng Li and Gaofeng Pan from the FAST observatory. After the introduction report by Dr. Chao-Wei Tsai, people had heated discussion and expressed appreciation as well as intentions for future collaborations with FAST.

Participants at the FAST observatory

Besides presentations, the meeting also sets aside time every day for free discussions. Heated debates and discussions were a common scene during these discussion sessions, over evidences in the connection between AGN and starburst, challenges in linking theoretical and simulations models to observations, as well as topics on large-scale galaxy evolution.

George Rieke, David Rosario, Jiasheng Huang, Yingjie Peng, David Elbaz, Dave Sanders in discussions

The last day of the meeting, a special session was dedicated to the many different future instruments and evolutionary results the new surveys would bring us. Principle Investigators or experts from FAST, JWST (James Webb Space Telescope), EP (Einstein Probe), eXTP (enhanced X-ray Timing and Polarimetry Mission) and CSST (Chinese Space Station Telescope) and other future instruments/surveys introduced the latest progresses and future plans. Final remarks and demand for future series were given by the SOC representatives at the end of the meeting. Participants thanked the organization by the LOC and SOC and looked forward to future international collaborations and the next meeting.

Translated by: Gaoxiang Jin, Y.Sophia Dai

Photo credit: Zijian Li, Gaoxiang Jin, Xu Shao

[Reprinted] Cloaked Black Hole Discovered in Early Universe using NASA’s Chandra

NASA/CXC

Astronomers have discovered evidence for the farthest “cloaked” black hole found to date, using NASA’s Chandra X-ray Observatory. At only about 6% of the current age of the universe, this is the first indication of a black hole hidden by gas at such an early time in the history of the cosmos.

Supermassive black holes, which are millions to billions of times more massive than our Sun, typically grow by pulling in material from a disk of surrounding matter. Rapid growth generates large amounts of radiation in a very small region around the black hole. Scientists call this extremely bright, compact source a “quasar.”

According to current theories, a dense cloud of gas feeds material into the disk surrounding a supermassive black hole during its period of early growth, which “cloaks” or hides much of the quasar’s bright light from our view. As the black hole consumes material and becomes more massive, the gas in the cloud is depleted, until the black hole and its bright disk are uncovered.

“It’s extraordinarily challenging to find quasars in this cloaked phase because so much of their radiation is absorbed and cannot be detected by current instruments,” said Fabio Vito of the Pontificia Universidad Católica de Chile, in Santiago, Chile, who led the study. “Thanks to Chandra and the ability of X-rays to pierce through the obscuring cloud, we think we’ve finally succeeded.”

The new finding came from observations of a quasar called PSO167-13, which was first discovered by Pan-STARRS, an optical-light telescope in Hawaii. Optical observations from these and other surveys have detected about 180 quasars already shining brightly when the universe was less than a billion years old, or about 8 percent of its present age. These surveys were only considered effective at finding unobscured black holes, because the radiation they detect is suppressed by even thin clouds of gas and dust. Since PSO167-13 was part of those observations, this quasar was expected to be unobscured, too.

Vito’s team were able to test this idea by using Chandra to observe PSO167-13 and nine other quasars discovered with optical surveys. After 16 hours of observation, only three X-ray light particles were detected from PSO167-13, all with relatively high energies. Since low-energy X-rays are more easily absorbed than higher energy ones, the likely explanation is that the quasar is highly obscured by gas, allowing only high-energy X-rays to be detected.

“This was a complete surprise”, said co-author Niel Brandt of Penn State University in University Park, Pennsylvania. “It was like we were expecting a moth but saw a cocoon instead. None of the other nine quasars we observed were cloaked, which is what we anticipated.”

An interesting twist for PSO167-13 is that the galaxy hosting the quasar has a close companion galaxy, visible in data previously obtained with the Atacama Large Millimeter Array (ALMA) of radio dishes in Chile and NASA’s Hubble Space Telescope. Because of their close separation and the faintness of the X-ray source, the team was unable to determine whether the newly-discovered X-ray emission is associated with the quasar PSO167-13 or with the companion galaxy.

If the X-rays come from the known quasar, then astronomers need to develop an explanation for why the quasar appeared highly obscured in X-rays but not in optical light. One possibility is that there has been a large and rapid increase in cloaking of the quasar during the three years between when the optical and the X-ray observations were made.

On the other hand, if instead the X-rays arise from the companion galaxy, then it represents the detection of a new quasar in close proximity to PSO167-13. This quasar pair would be the most distant yet detected.

In either of these two cases, the quasar detected by Chandra would be the most distant cloaked one yet seen, at 850 million years after the Big Bang. The previous record holder has been observed 1.3 billion years after the Big Bang.

The authors plan to follow up with more observations to learn more.

“With a longer Chandra observation we’ll be able to get a better estimate of how obscured this black hole is,” said co-author Franz Bauer, also from the Pontificia Universidad Católica de Chile, “and make a confident identification of the X-ray source with either the known quasar or the companion galaxy.”

The authors also plan to search for more examples of highly obscured black holes.

“We suspect that the majority of supermassive black holes in the early universe are cloaked: it’s then crucial to detect and study them to understand how they could grow to masses of a billion suns so quickly,” said co-author Roberto Gilli of INAF in Bologna, Italy.

A paper describing these results is accepted for publication in Astronomy and Astrophysics and is available online. NASA’s Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science and flight operations from Cambridge, Massachusetts.
Other materials about the findings are available at:
http://chandra.si.edu

The Fifth China-Chile Bi-lateral Astronomy Science Meeting was successfully held in Kunming during Jan. 23-26, 2019

Meeting group photo

In order to promote the communication and collaboration between astronomy communities of China and Chile, sponsored by Chinese Academy of Sciences (CAS), National Natural Science Foundation of China (NSFC), National Astronomical Observatories, CAS (NAOC), the “Fifth Chile-China Bi-lateral Astronomy Science Meeting” was successfully held in Kunming during Jan. 23-26, 2019. The meeting was organized by the CAS South American Center for Astronomy (CASSACA), also known as China-Chile Joint Center for Astronomy, along with Yunnan Astronomical Observatory (YNAO).

A glance at the meeting

CASSACA is one of the overseas projects initiated by CAS to develop cooperation in science and technology with foreign countries. In February 2013, CASSACA was inaugurated at NAOC, and its Santiago office was inaugurated in October 2013 at University of Chile. The Center serves as a platform for collaboration in astronomical research and related technologies between China and South America countries. The Center helps to build international scientific teams and joint programs engaging in frontier astronomy research. The China-Chile Astronomy Workshop is a major platform to strengthen communications in astronomical research between the two countries, and has been held alternately in Chile and China. It has been proven to be successful in the past meetings of the series, prompting knowledge and information exchange between astronomers, and initiating collaborative projects and joint programs.

Hui Sun, Director of America and Oceania Department, Bureau of International Co-operation, CAS, addressing the meeting
Suijian Xue, Deputy president of NAOC, addressing the meeting
Jiasheng Huang, Chief Scientist of CASSACA, hosting the meeting
Patricio Rojo , Chairman of SOCHIAS, introducing the astronomy in Chile
Participants discussing

Around 70 participants attended this Meeting, including experts, young scientists and students, coming from more than 20 institutes of China, Chile, and other countries. Professor. Jiasheng Huang, Chief Scientist of CASSACA, and Professor Jinming Bai, president of YNAO, offered their welcome as the hosts; Hui Sun, Director of Division of America and Oceanian Affairs, Bureau of International Cooperation, CAS and Suijian Xue, Deputy Director General of NAOC, both addressed the meeting; Dr. Wei Wang, Deputy Director of CASSACA, introduced the current status and future prospects of the Center; Professor Patricio Rojo, Chairman of Astronomical Society of Chile (SOCHIAS) and other Chilean astronomers expressed high expectations for the Chile-China cooperation, and gave a lot of suggestions and comments. At this Meeting, directors or their representatives of nearly all major astronomical observatories/departments of China and Chile summarized the major research areas and current activities of their institutions, including detailed talks on recent research highlights. During the four-day workshop, astronomers from both countries communicated cordially and comprehensively, reviewing the existing ties and finding opportunities for future collaborations. The bilateral meeting is recognized as an important catalyst for Chile-China astronomy communications, and a useful model for CAS to advance international cooperation widely.

CASSACA scientist reveals the connection between radiation and shape of circum-nuclear materials around super-massive black holes

[Dr. Claudio Ricci, a CAS-CONICYT Postdoctoral Fellow in astronomy,  led an important paper inNature》on September 27th 2017, in which he reported recent major progress regarding how radiation feedback controls the shape of close environment around super-massive black holes, drawn from a multi-band survey of a sample of black holes selected in the hard X-ray band.]

A black hole is a place in space-time where gravity pulls are so strong that even light cannot get out, it is therefore “black” in any bands. The theory of general relativity predicts that a sufficiently large and dense mass would deform space -time and give birth to a black hole. Despite its invisible interior, a black hole can be indirectly inferred and investigated at various wavelengths through its interactions with the surrounding and in-falling materials.

It is known for decades that very heavy black holes inhabit the centers of galaxies (including our own galaxy, the Milky Way), but are hidden by gas and dust. Some of these black holes can “eat” materials from their environment, and emit a lot of light during this process. Most of these “luminous” black holes are surrounded by large amount of gas and dust, distributed in a doughnut-like structure. Such a structure could resemble a pantry, which guarantees that the black hole can keep eating, radiating and growing. However, it is not known where exactly this material is located, and what the relationship is between light produced by the black hole and the dusty gas.

In order to address this long-standing issue, Dr. Claudio Ricci, a postdoc fellow supported by Chinese Academy of Sciences South America Center for Astronomy (CASSACA), and his collaborators made use of observations carried out in the X-ray band, similar to what is typically used for radiographies in hospitals. With each observation performing these “space radiographies”, they could measure the amount of material around the black hole, and then study its evolution.

This project started in 2013, and it took the authors many years to create the large database used for their research, using data from space telescopes as well as ground-based observatories, such as those in Chile. The Chilean telescopes were extremely important for measuring the properties of the black holes, and in particular, for “weighing” their masses. The main X-ray instrument used was the NASA satellite Swift, but also data from the satellites XMM-Newton of ESA, Suzaku of JAXA, and another NASA telescope, Chandra, were used. In the optical band the facilities used include the Sloan Digital Sky Survey, the UK Schmidt telescope, Gemini, CTIO, DuPont and SAAO.

With this work, Ricci and collaborators discovered the process that controls the interaction between light produced by the black hole and the gas that surrounds it, and showed that most of the material around black holes is located close to it. The authors found that, when the black hole emits a lot of light, this light pushes away the material from its vicinity; in other words, the gas can “evaporate” because of the large amount of energy released by the material falling rapidly onto the black hole. This could also mean that, if the black hole “eats” too rapidly, the energy produced could destroy the “food” available for the future.

It is a major step forward to reveal a clear picture of the connection between radiation feedback and the surrounding material’s shape. “The next step will be to further understand the details of this behavior, and what happens to the material that is pushed away from the black hole”, said Dr. Ricci, the leading author of this work.

Figure 1. Artistic impression of the gas and dust surrounding an accreting supermassive black hole. Taken from NASA/JPL/Caltech.

Figure 2. Schematic representation of the material surrounding supermassive black holes for different ranges of Eddington ratio. The Eddington ratio is the ratio between the bolometric and the Eddington luminosity, where the latter is defined as the luminosity at which the radiation pressure from a source, in this case the accreting SMBH, balances the gravitational attraction. Taken from Ricci et al. (2017, Nature Letter).