Outflowing gas in ultraluminous galaxies

January 9, 2017
The ultra-luminous galaxy Arp220. A study of powerful molecular gas outflows in these objects, using the far-infrared lines of the OH molecule, finds they can expel as much as a thousand solar-masses per year. Credit: NASA, ESA, and the Hubble Team

Galaxies evolve over billions of years in part through the activity of star formation and their supermassive nuclear black holes, and also by mergers with other galaxies. Some features of galaxies, in particular the strong correlations found between the mass of the central black hole and properties like galaxy velocity structure or luminosity, imply a fundamental connection between the growth of the nuclear black hole and the assembly of stars on a global scale. Feedback of some kind is therefore expected to explain these tight correlations, and astronomers have been working to identify and study it. One prominent suggestion for feedback is the presence of warm outflowing gas, powered by new stars but which would deplete the galaxy of the raw material needed for making new stars, and/or for enhancing the black hole mass.

In the 1990s, the Infrared Space Observatory (ISO) detected evidence for warm gas in luminous galaxies, the molecule OH, and the recent Herschel Space Observatory followed up those detections with velocity-resolved observations of six of the prominent OH far infrared lines. CfA astronomers Eduardo Gonzalez-Alfonso, Matt Ashby, and Howard Smith led a team of scientists reducing and modeling the four strong lines in fourteen ultra-luminous infrared (ULIRGs). The set of OH lines from ULIRGs is remarkable in that they appear sometimes in absorption, sometimes in emission, and sometimes with a bit of both depending on the particular line and velocity component. Many of these spectral features are characteristic of gas moving in an outflow, and the team has developed a radiative transfer model to deduce the geometry and kinematics of the flowing gas from the complex line shapes.

The scientists report that there are indeed powerful outflows in these ULIRGs, some with more than a thousand solar-masses per year and the power of a hundred billion Suns (a few percent of the total luminous energy of the galaxy). The typical time it would take for this gas to be blown out of the galaxy is only a few hundred million years, and the astronomers conclude that the outflows must occur erratically (not continuously), and are probably tied to the equally random flaring activity of the central black hole, which in turn can be linked to the gas motions induced by galaxy mergers.

Explore further: Under construction: Distant galaxy churning out stars at remarkable rate

More information: Molecular outflows in local ULIRGs: energetics from multi-transition OH analysis. ApJ 2017 (in press). lanl.arxiv.org/abs/1612.08181

Related Stories

Are ultra-luminous galaxies colliding?

June 27, 2014

(Phys.org) —ltra-luminous infrared galaxies ((ULIRGs) are galaxies whose luminosity exceeds that of a trillion suns, By way of comparison, our Milky Way galaxy has a typical modest luminosity of only about ten billion suns. ...

Galaxy winds

September 23, 2013

(Phys.org) —The most luminous galaxies in our universe are not particularly bright in the visible. Most of their energy output (which can be hundreds or even thousands of times more than our Milky Way's) is emitted at infrared ...

Star formation near supermassive black holes

June 22, 2015

Most if not all galaxies are thought to host a supermassive black hole in their nuclei, a finding that is both one the most important and amazing in modern astronomy. A supermassive black hole grows by accreting mass, and ...

Image: Computer simulation of a supermassive black hole

April 7, 2016

This computer-simulated image shows a supermassive black hole at the core of a galaxy. The black region in the center represents the black hole's event horizon, where no light can escape the massive object's gravitational ...

Recommended for you

Planetary waves, first found on Earth, are discovered on Sun

March 27, 2017

The same kind of large-scale planetary waves that meander through the atmosphere high above Earth's surface may also exist on the Sun, according to a new study led by a scientist at the National Center for Atmospheric Research ...

NASA spacecraft investigate clues in radiation belts

March 27, 2017

High above Earth, two giant rings of energetic particles trapped by the planet's magnetic field create a dynamic and harsh environment that holds many mysteries—and can affect spacecraft traveling around Earth. NASA's Van ...

Stars born in winds from supermassive black holes

March 27, 2017

Observations using ESO's Very Large Telescope have revealed stars forming within powerful outflows of material blasted out from supermassive black holes at the cores of galaxies. These are the first confirmed observations ...

Evidence of giant tsunami on Mars suggests an early ocean

March 27, 2017

(Phys.org)—A team of researchers with members from France, Italy and the U.S. has found what they believe is evidence of a giant tsunami occurring on Mars approximately 3 billion years ago due to an asteroid plunging into ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

geokstr
3 / 5 (2) Jan 10, 2017
some with more than a thousand solar-masses per year and the power of a hundred billion Suns (a few percent of the total luminous energy of the galaxy).


Well, where's all this mass going? Perhaps the voids between galaxies and galaxy clusters are not as empty as currently believed. It seems every other week or so very large new sources of ordinary matter are detected. Another couple decades of this and the need for the hypothesized dark matter may disappear altogether.
cantdrive85
1.6 / 5 (7) Jan 11, 2017
The scientists report that there are indeed powerful outflows in these ULIRGs,

Powerful outflows of plasma is an electric current, the higher current density is why these are ULRGs.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.