Releases from NASA, HubbleSite, Spitzer, ESO, ESA, NASA’s Chandra X-ray Observatory, Royal Astronomical Society, Harvard-Smithsonian Center For Astrophysics, Max Planck Institute, Gemini Observatory, Subaru Telescope, W. M. Keck Observatory, JPL-Caltech, ICRAR, Webb Space Telescope, etc
To celebrate a new year, the NASA/ESA
Hubble Space Telescope has published a montage of six beautiful galaxy
mergers. Each of these merging systems was studied as part of the recent
HiPEEC survey to investigate the rate of new star formation within such
systems. These interactions are a key aspect of galaxy evolution and
are among the most spectacular events in the lifetime of a galaxy.
It
is during rare merging events that galaxies undergo dramatic changes in
their appearance and in their stellar content. These systems are
excellent laboratories to trace the formation of star clusters under
extreme physical conditions.
The Milky Way typically forms star clusters with masses
that are 10 thousand times the mass of our Sun. This doesn’t compare to
the masses of the star clusters forming in colliding galaxies, which can
reach millions of times the mass of our Sun.
These dense stellar systems are also very luminous. Even
after the collision, when the resulting galactic system begins to fade
into a more quiescent phase, these very massive star clusters will shine
throughout their host galaxy, as long-lasting witnesses of past merging
events.
By studying the six galaxy mergers shown here, the Hubble
imaging Probe of Extreme Environments and Clusters (HiPEEC) survey has
investigated how star clusters are affected during collisions by the
rapid changes that drastically increase the rate at which new stars are
formed in these galaxies. Hubble’s capabilities have made it possible to
resolve large star-forming “knots” into numerous compact young star
clusters. Hubble’s ultraviolet and near-infrared observations of these
systems have been used to derive star cluster ages, masses, and
extinctions and to analyse the star formation rate within these six
merging galaxies. The HiPEEC study reveals that the star cluster
populations undergo large and rapid variations in their properties, with
the most massive clusters formed towards the end of the merger phase.
Each of the merging systems shown here has been previously
published by Hubble, as early as 2008 and as recently as October 2020.
To celebrate it’s 18th anniversary in 2008, the Hubble Space Telescope
released a collection of 59 images of merging galaxies, which can be
explored here.
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
The HiPEEC survey was completed as part of the Hubble Space Telescope program GO 14066 (PI: A. Adamo). A repository with the study’s final data and catalogues is available here in the MAST Archive.
The international team of astronomers in this study consists of A. Adamo, K. Hollyhead, M. Messa, J. E. Ryon, V. Bajaj, A. Runholm, A. Aalto, D. Calzeti, J. S. Gallagher, M. J. Hayes, J. M. D. Kruijssen, S. König, S. S. Larsen, J. Melinder, E. Sabbi, L. J. Smith, and G. Östlin.
Although the two galaxies in NGC 3256 appear merged
when viewed in visible light, a second, bright nucleus is found hiding
among the tangle of dust lanes in the central region. By using a range
of telescopes on the ground and in space, the GOALS (Great Observatories
All-sky LIRG Survey) research team has been analyzing galaxies like NGC
3256 from X-ray through radio wavelengths. NGC 3256 has a buried active
nucleus, large-scale shocks from two powerful outflows, and a huge
number of compact, bright star clusters. Upcoming research with the
James Webb Space Telescope will help researchers learn more about the
outflows, which will allow them to better model the hot and cold gas,
and determine what implications that has for how and where stars form in
rapidly evolving galaxies.Credits: NASA, ESA, the Hubble Heritage
(STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of
Virginia, Charlottesville/NRAO/Stony Brook University). Hi-res image
When galaxies collide, it's as if all the players in a symphony have
begun a furious crescendo: As their stars and gas fall toward the
center, star formation escalates. At the same time, the galaxies' black
holes engorge themselves and light up, releasing energy and material
into the surrounding gas. These "overtures," which continue for hundreds
of millions of years, are brightest where the centers of galaxies –
called nuclei – merge, and those areas are also filled with dust. Until
now, high-resolution infrared observations from space that can pierce
through the dust weren't possible. NASA's James Webb Space Telescope's
observations will return both infrared imagery and spectra that will allow researchers to add incredible detail to our understanding of the precise mechanics at work.
A research team led by Lee Armus of the California Institute of
Technology/IPAC in Pasadena and Aaron Evans of the University of
Virginia and the National Radio Astronomy Observatory in Charlottesville
will study the centers of a class of interacting galaxies known as
merging luminous infrared galaxies. "Webb's instruments will provide
huge leaps in our abilities to resolve what is happening in these
galaxies," explained Armus. "The images and spectra will not only be 50
to 100 times more sensitive than previous infrared data, but also
significantly sharper."
These merging galaxies are often gas-rich spiral galaxies, which
means they are still forming stars before colliding. As they approach
one another and conduct a delicate "dance," gas in the galaxies loses
angular momentum and funnels toward the center. This triggers additional
star formation at an accelerated rate, up to hundreds of solar masses
per year compared to one or two per year observed in normal star-forming
galaxies like our own. While stars are forming, they heat the
surrounding dust, generating enormous amounts of energy in infrared
light.
Since
the galaxies that make up NGC 7469 are both almost face-on when viewed
from Earth, it's easier to identify the areas where a black hole may
exist. A powerful accreting supermassive black hole, surrounded by a
ring of young stars, lives at the heart of the galaxy in the upper
right. High-resolution infrared imagery from the James Webb Space
Telescope is required to determine if the stars form differently around a
central supermassive black hole compared to star formation farther out
in the galaxy's arms. Webb will also help researchers trace the gas
outflows, which will help pinpoint where and how the interstellar medium
is affected, which subsequently drives or quenches star formation. Credits: NASA, ESA, the Hubble Heritage
(STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of
Virginia, Charlottesville/NRAO/Stony Brook University).Hi-res image
Webb's high-resolution, infrared instruments will allow researchers
to resolve the central star-forming regions for the first time. "We are
aiming to observe areas as small as 150 to 300 light-years across," said
Evans. "For context, these galaxies span hundreds of millions of
light-years across. Webb will strip away all the dust and see the
activity that’s at their cores."
Pulling back the "Dusty" Curtain
Each of the team's targets is part of a much larger, multi-decade program known as GOALS, the Great Observatories All-sky LIRG Survey.
The research team has studied more than 200 merging luminous infrared
galaxies across the electromagnetic spectrum, from radio and ultraviolet
light to visible and X-ray light, building robust data sets for each.
These
merging galaxies, known as II Zw 096, are the site of a spectacular
burst of star formation that is hinted at in the red speckles near the
middle of the image. This dust-shrouded area conceals a brilliant burst
of star formation that becomes more apparent at longer wavelengths of
infrared light. The image above combines near-infrared, visible, and
far-ultraviolet observations from the Hubble Space Telescope.
Researchers using infrared data from NASA's Spitzer Space Telescope
estimated the starburst, which lives in a small red region at the center
of this image, is cranking out stars at the breakneck pace of around
100 solar masses per year. The upcoming James Webb Space Telescope will
allow researchers to penetrate the dust and search for a buried, rapidly
growing supermassive black hole. Credits: NASA/JPL-Caltech/STScI/H. Inami (SSC/Caltech).Hi-res image
The researchers carefully selected four targets – each made up of two
galaxies – to produce a far more complete view of the activity that's
occurring in these merging galaxies by adding high-resolution infrared
data. They have a range of characteristics, though all are marked by
intense star formation or an actively feeding supermassive black hole:
Two nuclei are at the center of NGC 3256, but
one is largely hidden by dark bands of dust, making infrared
observations essential to fully understand where stars are forming and
where black holes may lie – as well as how they influence one another.
Strong galactic winds emerge from both nuclei, but their properties are
largely unknown.
NGC 7469 has a starburst ring, and a central
bright active galactic nucleus with a jet. Webb's observations will help
the researchers determine how the central, active nucleus is
influencing star formation in the center of the galaxy.
Dust also shrouds one of the pair of galaxies making up VV 114.
Though it is known that widespread star formation is occurring
throughout both interacting galaxies, one shines brightly in the
infrared and the other in ultraviolet light. Webb will give us the
clearest view yet of this fascinating and complex merging pair.
II Zw 096 is unique among GOALS galaxies since the
source of its immense infrared power comes from a very compact region
not associated with the nuclei of either of the merging galaxies. This
object is producing stars nearly 100 times faster than the Milky Way,
but in a region less than one ten-thousandth the area. Webb will follow
up on observations of these galaxies by NASA’s retired Spitzer Space Telescope, allowing researchers to penetrate the dust and search for a buried, rapidly growing supermassive black hole.
To uncover the processes that cause these conditions, it's essential
to pinpoint where and how fast stars are forming, and to measure how
much gas the central black holes are accreting with Webb's infrared
observations. "All of these objects, including stars and black holes,
are competing for resources," Armus explained. "Black holes need gas to
grow, and as they grow they become energetic and drive outflows. In
turn, those outflows affect how stars form by heating and pushing away
the gas. With Webb, we will have the ability to understand what the
interplay is between all of these processes."
Discover
how telescopes make it possible to look back in time and study the
history of the universe, and how NASA’s James Webb Space Telescope will
fill in new details on galaxy evolution over time. The earliest pages of
cosmic history are blank, but Webb will allow us to look back farther
in time than ever before, helping to fill in the lost pages of the
universe’s story. Credits: NASA, ESA, CSA, and L. Hustak and D. Player (STScI).
In addition to images, Webb will gather spectra from the centers of these four merging galaxies. "The images will tell us where things are, but spectra provide the really rich information: They tell you what is there and how it may be moving," said co-investigator Vivian U of the University of California, Irvine.
To understand what's happening at the centers of these merging
galaxies, the team needs both imagery and highly detailed spectral maps
of the active regions around the nuclei – far better than spectra that
deliver an average of the entire area observed. Webb's Near Infrared Spectrograph (NIRSpec) and its Mid-Infrared Instrument (MIRI)
can do exactly this, which will allow researchers to measure not only
what is there, but also the physical conditions within the star-forming
regions at the nucleus for the first time.
"Dust lanes are beautiful until you try to find out what's happening
behind them," U continued. "In near- and mid-infrared, we will start
seeing through the dust. And by observing what's happening at small
scales for the first time, we will learn how gas and dust are affecting
star formation and the interstellar medium in these environments."
Far-reaching Research Implications
Although theoretical models of merging galaxies demonstrate how stars
form, they currently do not precisely account for how supermassive
black holes and lots of hot young stars impact their surrounding
environments, or how gas moves within galaxy mergers. The Webb data
should give researchers a clear look at the centers of merging galaxies
and inform a new generation of models that will describe how galaxies
interact and merge.
As part of this study, the team will update and deliver software, first written for Spitzer Space Telescope
data, to fit the Webb spectra and generate maps of the galaxies in
different emission lines and colors. The team will also use this
software to map the dynamics of the gas around the nuclei and study how
outflows shape their evolution.
In addition to benefiting scientists who research these or similar
objects, this program will also demonstrate Webb's capabilities in a
wide range of scientific applications, helping other scientists
effectively and efficiently use the observatory to meet their own
science goals and provide a detailed look at nearby galaxies that may
resemble young systems in the early universe.
This research is being conducted as part of a Webb Director’s Discretionary-Early Release Science
(ERS) program. This program provides time to selected projects early in
the telescope's mission, allowing researchers to quickly learn how best
to use Webb's capabilities, while also yielding robust science.
The James Webb Space Telescope will be the world's premier space
science observatory when it launches in 2021. Webb will solve mysteries
in our solar system, look beyond to distant worlds around other stars,
and probe the mysterious structures and origins of our universe and our
place in it. Webb is an international program led by NASA with its
partners, ESA (European Space Agency) and the Canadian Space Agency.
By Claire Blome
Space Telescope Science Institute, Baltimore, Md. cBlome@stsci.edu
