Gabriela Canalizo

Graduate student’s BADASS code has astronomical benefits

Anonymous — Wed, 16 Dec 2020 23:55:09 +0000

Graduate student’s BADASS code has astronomical benefits Anonymous (not verified) Wed, 12/16/2020 - 15:55 More News Iqbal Pittalwala | Inside UCR December 16, 2020

An astro-statistics course University of California, Riverside, graduate student Remington O. Sexton took three years ago taught him techniques that led him to develop free, open-source code benefiting astronomers everywhere.

Called BADASS, which stands for Bayesian AGN Decomposition Analysis for SDSS Spectra, the code in its current form fits astronomical spectra of active galactic nuclei, or AGNs, from the Sloan Digital Sky Survey, or SDSS, using advanced statistical methods.

Remington Sexton earned his doctoral degree earlier this year.

“The code is unique in that it finally provides a way for astronomers to fit the stellar motions of stars simultaneously with many other components, is written in the popular programming language Python, and is versatile enough to fit not just AGNs, but normal galaxies as well,” said Sexton, who earned his doctoral degree in physics and astronomy in September 2020.

Sexton’s breakthrough work is published in the January 2021 issue of the Monthly Notices of the Royal Astronomical Society.

AGN is the general term used to describe a supermassive black hole in the center of a galaxy that is actively accreting material, usually in the form of interstellar gas, using its strong gravitational influence. AGNs are common; but not all galaxies have them at their centers. Each galaxy’s center is believed, however, to have a supermassive black hole. Normal galaxies, such as the Milky Way, lack actively accreting black holes.

Different celestial objects produce different types of spectra. An object’s spectrum helps astronomers identify what type of object it is. Light from a celestial body with no intervening matter produces a spectrum that appears as a continuum. A challenge in astronomy has been separating the contribution of stellar light and the contribution of AGN light from each other in the galaxy’s main spectral continuum.

“The challenge is separating the two from each other, that is, isolating the stellar component from the AGN light contribution,” Sexton said. “Aside from being versatile enough to fit many kinds of astronomical objects, which many codes aren't designed for, BADASS simultaneously fits stellar kinematics simultaneously with all other components in the spectra. Codes in the past used a two-step process of fitting stellar kinematics and other components independently. But this could introduce biases or uncertainties. The best way to perform spectral decomposition is to fit all components simultaneously. This is what BADASS does.”

Sexton designed BADASS also to detect and fit ionized gas outflows typically seen in optical emission line features and is the first to incorporate a set of specific criteria for their detection. Ionized gas outflow refers to the bulk motion of interstellar gas capable of escaping the gravitational influence of its host galaxy and the blackhole.

“Ionized gas outflows have become a hot topic in the past decade and could explain how supermassive black holes and galaxies co-evolve with each other over cosmic time,” said coauthor Gabriela Canalizo, a professor of physics and astronomy at UC Riverside and Sexton’s doctoral advisor.

Currently, BADASS is only being used to fit AGN objects. Sexton emphasized, however, that the code is versatile, easy to use, and can fit other objects such as normal galaxies.

“BADASS can be used for fitting normal non-AGN host galaxies, and even individual stars,” he said. “Currently, its usage is strictly for astronomical spectra, but the statistical framework BADASS is built on can be generalized for any kind of spectroscopy. That makes it extraordinarily versatile and useful.”

One motivation Sexton had to develop BADASS was to phase out the need for proprietary software — IDL programming language — and replace it with a free open-source language such as Python.

“Now anyone can download BADASS for free and use it,” he said. “It is ready to be run as long as you can install Python and all the packages it requires. Because this code can also detect and fit ionized gas outflows in optical spectra, it could greatly assist in the heightened interest in astronomy now in studying ionized gas outflows by creating larger samples for analysis.”

Sexton and Canalizo were joined in the research by William Matzko of George Mason University in Virginia; Nicholas Darden of UCR; and Varoujan Gorjian of the Jet Propulsion Laboratory in California.

The research was supported partially by the National Science Foundation and the NASA MIRO program through the Fellowships and Internships for Extremely Large Data Sets (FIELDS) in the form of a graduate student fellowship.

The research paper is titled, “Bayesian AGN Decomposition Analysis for SDSS spectra: a correlation analysis of [O III] λ5007 outflow kinematics with AGN and host galaxy properties.”

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Black holes stunt growth of dwarf galaxies

Anonymous — Thu, 24 Oct 2019 22:42:30 +0000

Black holes stunt growth of dwarf galaxies Anonymous (not verified) Thu, 10/24/2019 - 15:42 More News IQBAL PITTALWALA | UCR News October 11, 2019 https://news.ucr.edu/articles/2019/10/11/black-holes-stunt-growth-dwarf-galaxies

Astronomers at the University of California, Riverside, have discovered that powerful winds driven by supermassive black holes in the centers of dwarf galaxies have a significant impact on the evolution of these galaxies by suppressing star formation.

Dwarf galaxies hosting active galactic nuclei that have spatially extended outflows. (SDSS)

Dwarf galaxies are small galaxies that contain between 100 million to a few billion stars. In contrast, the Milky Way has 200-400 billion stars. Dwarf galaxies are the most abundant galaxy type in the universe and often orbit larger galaxies.

The team of three astronomers was surprised by the strength of the detected winds.

“We expected we would need observations with much higher resolution and sensitivity, and we had planned on obtaining these as a follow-up to our initial observations,” said Gabriela Canalizo, a professor of physics and astronomy, who led the research team. “But we could see the signs strongly and clearly in the initial observations. The winds were stronger than we had anticipated.”

Canalizo explained that astronomers have suspected for the past couple of decades that supermassive black holes at the centers of large galaxies can have a profound influence on the way large galaxies grow and age.

“Our findings now indicate that their effect can be just as dramatic, if not more dramatic, in dwarf galaxies in the universe,” she said.

Study results appear in The Astrophysical Journal.

The researchers, who also include Laura V. Sales, an assistant professor of physics and astronomy; and Christina M. Manzano-King, a doctoral student in Canalizo’s lab, used a portion of the data from the Sloan Digital Sky Survey, which maps more than 35% of the sky, to identify 50 dwarf galaxies, 29 of which showed signs of being associated with black holes in their centers. Six of these 29 galaxies showed evidence of winds — specifically, high-velocity ionized gas outflows — emanating from their active black holes.

“Using the Keck telescopes in Hawaii, we were able to not only detect, but also measure specific properties of these winds, such as their kinematics, distribution, and power source — the first time this has been done,” Canalizo said. “We found some evidence that these winds may be changing the rate at which the galaxies are able to form stars.”

From left to right: Laura Sales, Christina Manzano-King, and Gabriela Canalizo. (UCR/Stan Lim)

Manzano-King, the first author of the research paper, explained that many unanswered questions about galaxy evolution can be understood by studying dwarf galaxies.

“Larger galaxies often form when dwarf galaxies merge together,” she said. “Dwarf galaxies are, therefore, useful in understanding how galaxies evolve. Dwarf galaxies are small because after they formed, they somehow avoided merging with other galaxies. Thus, they serve as fossils by revealing what the environment of the early universe was like. Dwarf galaxies are the smallest galaxies in which we are directly seeing winds — gas flows up to 1,000 kilometers per second — for the first time.”

Manzano-King explained that as material falls into a black hole, it heats up due to friction and strong gravitational fields and releases radiative energy. This energy pushes ambient gas outward from the center of the galaxy into intergalactic space.

“What’s interesting is that these winds are being pushed out by active black holes in the six dwarf galaxies rather than by stellar processes such as supernovae,” she said. “Typically, winds driven by stellar processes are common in dwarf galaxies and constitute the dominant process for regulating the amount of gas available in dwarf galaxies for forming stars.”

Astronomers suspect that when wind emanating from a black hole is pushed out, it compresses the gas ahead of the wind, which can increase star formation. But if all the wind gets expelled from the galaxy’s center, gas becomes unavailable and star formation could decrease. The latter appears to be what is occurring in the six dwarf galaxies the researchers identified.

“In these six cases, the wind has a negative impact on star formation,” Sales said. “Theoretical models for the formation and evolution of galaxies have not included the impact of black holes in dwarf galaxies. We are seeing evidence, however, of a suppression of star formation in these galaxies. Our findings show that galaxy formation models must include black holes as important, if not dominant, regulators of star formation in dwarf galaxies.”

Next, the researchers plan to study the mass and momentum of gas outflows in dwarf galaxies.

“This would better inform theorists who rely on such data to build models,” Manzano-King said. “These models, in turn, teach observational astronomers just how the winds affect dwarf galaxies. We also plan to do a systematic search in a larger sample of the Sloan Digital Sky Survey to identify dwarf galaxies with outflows originating in active black holes.”

The research was funded by the National Science Foundation, NASA, and the Hellman Foundation. Data was obtained at the W. M. Keck Observatory, and made possible by financial support from the W. M. Keck Foundation.