When NASA’s James Webb Space Telescope begins scientific operations in 2022, one of its first tasks will be an ambitious program to map the earliest structures in the universe. This broad and deep survey of half a million galaxies, called COSMOS-Webb, is the largest project Webb will undertake in the first year.
The COSMOS-Webb survey maps 0.6 square degrees of the sky – roughly the area of three full moons – using the James Webb Space Telescope’s Near Infrared Camera (NIRCam), while at the same time a smaller 0.2 square degrees with the Mid Infrared Instrument (MIRI). The jagged edges of the outline of the Hubble field are due to the separate images that make up the survey field.
Credits: Jeyhan Kartaltepe (RIT); Caitlin Casey (UT Austin); and Anton Koekemoer (STScI) graphic design Credit: Alyssa Pagan (STScI)
With more than 200 hours of observation time, COSMOS-Webb will measure a large part of the sky (0.6 square degrees) with the near-infrared camera (NIRCam). That is the size of three full moons. It will simultaneously map a smaller area with the Mid-Infrared Instrument (MIRI).
It’s a big piece of heaven that is quite unique to the COSMOS-Webb program. Most Webb programs go very deep, like pencil-ray surveys that examine tiny patches of sky, ”said Caitlin Casey, assistant professor at the University of Texas at Austin and co-director of the COSMOS-Webb program. “Because we cover such a large area, we can look at large-scale structures at the beginning of the galaxy formation. We will also look for some of the rarest galaxies that existed early on, as well as map the large-scale distribution of dark matter from galaxies to the very early ages. “
(Dark matter does not absorb, reflect, or emit light so it cannot be seen directly. We know that dark matter exists because of its effect on objects that we can observe.)
COSMOS-Webb will study half a million galaxies with high resolution multiband imaging in the near infrared and an unprecedented 32,000 galaxies in the mid infrared. With the data released quickly to the public, this survey will become a primary legacy Webb dataset for scientists worldwide studying galaxies beyond the Milky Way.
Building on Hubble’s accomplishments
The COSMOS survey began in 2002 as a Hubble program to map a much larger patch of sky, roughly the area of 10 full moons. From then on, the collaboration grew to include most of the world’s largest telescopes on earth and in space. Now COSMOS is a multi-wavelength survey that covers the entire spectrum from x-rays to radio.
This galaxy sea is the complete, original COSMOS field of the Advanced Camera for Surveys (ACS) of the Hubble Space Telescope. The full mosaic consists of 575 separate ACS images, with each ACS image being approximately one-tenth the diameter of the full moon. The jagged edges of the outline are due to the separate images that make up the survey field.
Credits: Anton Koekemoer (STScI) and Nick Scoville (Caltech)
More than 13 billion years ago, during the era of reionization, the universe was a very different place. The gas between the galaxies was largely impermeable to high-energy light, which made it difficult to observe young galaxies. What enabled the universe to become fully ionized, or transparent, which eventually led to the “clear” conditions that are found in much of the universe today? The James Webb Space Telescope will look deep into space to gather more information about objects that existed during the era of reionization to help us understand this important transition in the history of the universe.
Credits: NASA, ESA, Joyce Kang (STScI)
Because of its location in the sky, the COSMOS field is accessible to observatories around the world. It is located at the celestial equator and can be explored from both the northern and southern hemispheres, resulting in a rich and diverse treasure trove of data.
“COSMOS has become the survey that many extragalactic scientists take to do their analysis because the data products are so widespread and cover such a large area of the sky,” said Jeyhan Kartaltepe, Rochester Institute of Technology, assistant professor of physics and science Co-leader of the COSMOS-Webb program. “COSMOS-Webb is the next part of where we use Webb to expand our coverage in the near and mid-infrared of the spectrum, thereby broadening our horizons of how far we are able to see.”
The ambitious COSMOS-Webb program will build on previous discoveries to advance three specific areas of study, including: revolutionizing our understanding of the reionization era; looking for early, fully developed galaxies; and learn how dark matter evolved with the stellar content of galaxies.
Goal 1: Revolutionize our understanding of the era of reionization
Shortly after the Big Bang, the universe was completely dark. Stars and galaxies that bathe the cosmos in light had not yet formed. Instead, the universe consisted of a primordial soup of neutral hydrogen and helium atoms and invisible dark matter. This is called the cosmic dark age.
After several hundred million years, the first stars and galaxies formed and provided energy to reionize the early universe. This energy tore apart the hydrogen atoms that filled the universe, giving them an electrical charge and ending the cosmic dark age. This new era in which the universe was flooded with light is called the era of reionization.
The first goal of COSMOS-Webb focuses on this era of reionization, which occurred 400,000 to 1 billion years after the Big Bang. The reionization probably happened in small bags, not all at once. COSMOS-Webb will look for bubbles that show where the first pockets of the early universe were reionized. The team’s goal is to map the extent of these reionization bubbles.
“Hubble did a great job finding a handful of these galaxies back in the early days, but we need thousands more galaxies to understand the reionization process,” said Casey.
Scientists don’t even know what kind of galaxies ushered in the age of reionization, whether they are very massive or relatively low-mass systems. COSMOS-Webb will have the unique ability to find very massive, rare galaxies and see their distribution in large-scale structures. So do the galaxies responsible for reionization live in the equivalent of a cosmic metropolis or are they mostly evenly distributed over space? Only a survey the size of COSMOS-Webb can help scientists answer this question.
Objective 2: In search of early, fully developed galaxies
COSMOS-Webb will be looking for very early, fully developed galaxies that will halt star formation in the first 2 billion years after the Big Bang. Hubble has found a handful of these galaxies that challenge existing models of how the universe was formed. Scientists are struggling to explain how these galaxies can have old stars and avoid new stars so early in the history of the universe.
With a large survey like COSMOS-Webb, the team will find many of these rare galaxies. They are planning detailed studies of these galaxies to understand how they evolved so quickly and turned off star formation so early.
Goal 3: Use the stellar content of galaxies to learn how dark matter evolved
COSMOS-Webb will give scientists insights into how dark matter in galaxies with the stellar content of the galaxies has evolved over the lifetime of the universe.
Galaxies are made up of two types of matter: normal, luminous matter, which we see in stars and other objects, and invisible dark matter, which is often more massive than the galaxy and can surround it in an extensive halo. These two types of matter are intertwined in the formation and evolution of galaxies. However, currently there is not much knowledge about how the mass of dark matter formed in the halos of galaxies and how this dark matter affects the formation of the galaxies.
COSMOS-Webb will shed light on this process by allowing scientists to measure these halos of dark matter directly through “weak lenses”. Gravity of any type of mass – dark or glowing – can act as a lens to “bend” the light we see from galaxies further away. A weak lens effect distorts the apparent shape of background galaxies. So if a halo is in front of other galaxies, scientists can measure the mass of the halo’s dark matter directly.
“For the first time we will be able to trace the relationship between the mass of dark matter and the luminous mass of galaxies back to the first 2 billion years of cosmic time,” says team member Anton Koekemoer, research astronomer at the Space Telescope Science Institute in Baltimore who helped develop the program’s observation strategy and is responsible for creating all of the program’s images. “This is a crucial era for us to understand how the mass of galaxies was first created and how this is powered by the halos of dark matter. And that can then flow indirectly into our understanding of the formation of galaxies. “
Share data quickly with the community
COSMOS-Webb is a treasury program that, by definition, is designed to produce records of lasting scientific value. Treasury programs seek to solve multiple scientific problems with a single, coherent set of data. Data collected through a treasury program usually does not have an exclusive access period, which allows for immediate analysis by other researchers.
“As a treasury program, you commit to quickly releasing your data and your data products to the community,” said Kartaltepe. “We will create this community resource and make it publicly available so that the rest of the community can use it for their scientific analysis.”
Koekemoer added, “A treasury program is committed to making all of these scientific products publicly available so that everyone in the community, even in very small institutions, can have the same and equal access to the data products and then simply do the science. “
COSMOS-Webb is a program for general observers of the 1st cycle. General Observers’ programs were competitively selected using a dual anonymous review system, the same system used to allocate time on Hubble.
The James Webb Space Telescope will be the world’s leading space science observatory when it launches in 2021. Webb will solve secrets in our solar system, peer into distant worlds around other stars and investigate the mysterious structures and origins of our universe and our place within. Webb is an international program led by NASA with its partners ESA (European Space Agency) and the Canadian Space Agency.
More information about Webb can be found at www.nasa.gov/webb