Earlier this week, the Space Telescope Science Institute (STScI) introduced the science targets for the fourth cycle of the James Webb House Telescope’s (JWST) Basic Observations program – aka. Cycle 4 GO. This newest cycle consists of 274 applications that can make up the JWST’s fourth yr of operations, amounting to eight,500 hours of prime observing time. These applications are damaged down into eight classes that embody Webb’s capabilities.
This consists of exoplanet research and characterization, the research of the earliest galaxies within the Universe, stellar populations and formation, and Photo voltaic System Astronomy. As we addressed within the earlier installment, Cycle 4 consists of many applications that can leverage Webb’s excessive sensitivity and superior devices to watch exoplanets, characterize their atmospheres, and measure their potential habitability.
In line with Webb’s main science targets, lots of the Cycle 4 applications can even concentrate on learning the earliest stars and galaxies within the Universe. These applications will construct on earlier efforts to watch high-redshift galaxies (people who shaped shortly after the Massive Bang), the primary inhabitants of stars within the Universe (Inhabitants III), and look at the function Darkish Matter (DM) performed of their formation.
Central to that is the cosmological interval often called the “Cosmic Dark Ages,” which occurred between 370,000 and 1 billion years after the Massive Bang. Throughout this time, the Universe was permeated by impartial hydrogen, and there have been solely two essential sources of photons: the relic radiation left over from the Massive Bang – the Cosmic Microwave Background (CMB) – and people sometimes launched by impartial hydrogen atoms.
This era can be when the primary stars and galaxies are believed to have shaped (ca. 13.6 billion years in the past). This led to the gradual ionization of the clouds of impartial hydrogen, which led to the “Epoch of Reionization,” which led to the Universe changing into “clear” (seen to trendy devices). Cosmologists confer with the interval the place the primary galaxies emerged from the Darkish Ages as “Cosmic Dawn.”
Earlier devices lacked the decision or sensitivity to seize gentle from this epoch, which is shifted into elements of the infrared spectrum which are very troublesome to watch. Nonetheless, Webb’s sensitivity and infrared optics enable astronomers to lastly pierce the veil of the “Darkish Ages.”
Excessive Redshift Galaxies
The earliest galaxies within the Universe are designated “excessive redshift,” which refers to how the wavelength of their gentle has change into elongated because of the enlargement of the Universe ((aka. the Hubble-Lemaitre Fixed). This causes the sunshine to change into “shifted” in the direction of the crimson finish of the spectrum. Gentle from galaxies that existed through the early Universe (greater than 13 billion years in the past) is redshifted to the purpose the place it is just seen within the infrared spectrum.
That is the aim of the GO 7208 program, titled “THRIFTY: The Excessive-RedshIft FronTier surveY.” This statement marketing campaign will construct on JWST’s detection of a number of luminous galaxies with redshift values better than 9 (z>9). This corresponds to galaxies that existed as much as 13.5 billion years in the past, one among Webb’s biggest discoveries up to now. The abundance of galaxies this early within the Universe and their obvious brightness was a shock to astronomers and has led to a revision of theories on early galaxy formation.
Doable explanations embody modifications to the Lambda Cold Dark Matter (LCDM) mannequin of cosmology, the likelihood that SMBHs might have been super-luminous on this interval, the speedy formation of stars from ample chilly gasoline clouds, feedback-free starbursts, and extra. Nonetheless, affirmation of those theories requires extra direct proof, which the THRIFTY program hopes to handle.
This system’s PI is Romain Meyer, a postdoctoral researcher on the College of Geneva (UNIGE). As he and his staff described of their GO 7208 program proposal, “THRIFTY will decide the true quantity density of ultra-luminous galaxies at z>9 by focusing on a pattern of 123 candidates chosen from >1 million sources over a complete of 0.3 sq. levels (out of the Galactic airplane) from all present prime and pure-parallel JWST imaging surveys.”
Considered one of Webb’s earliest discoveries from Cycle 1 was of a inhabitants of small, red-tinted galaxies through the early Universe that will have contained rising SMBHs. These “Little Purple Dots” (LRDs), as they had been nicknamed, had been considered Energetic Galactic Nuclei (AGNs), or quasars, however many astronomers. Whereas they had been declared one of many greatest discoveries in physics in 2023, there may be nonetheless no consensus on what they really are.
Enter the GO 7404 program, titled “How I’m wondering what you might be — do JWST’s Little Purple Dots twinkle? Testing broad-line and continuum variability on week, month, and six-month.” Rohan Naidu, a NASA Hubble Fellow and the Pappalardo Fellow in Physics on the Massachusetts Institute of Expertise (MIT), is that this program’s Principal Investigator (PI). Utilizing Webb’s Near-Infrared Camera (NIRCam), they may conduct the primary longwave systematic LRD monitoring marketing campaign to find out their actual nature.
Subsequent, there’s the GO 7814 program, titled “MINERVA: Unlocking the Hidden Gems of the Distant Universe and Finishing HST and JWST’s Imaging Legacy with Medium Bands.” This program, led by PI Dr. Adam Muzzin of York College, will construct on the deep imaging surveys carried out with the JWST Close to-Infrared Digicam (NIRCam). Whereas revolutionary, these surveys had been restricted to broad-band observations with low spectral decision.
For his or her program, they may use Webb’s Mid-Infrared Instrument (MIRI) to look at the first fields noticed by the Hubble Space Telescope (HST) and the JWST. Within the course of, they plan to extend the surveyed space practically by an element of 10 in comparison with present medium-band applications, resulting in the invention of uncommon and beforehand undetected populations in present deep-field catalogs. These observations, they state, will enable them to:
“1) effectively determine and characterize galaxies with uncommon SEDs together with z>12 candidates, high-redshift Balmer breaks, metal-poor excessive emission line galaxies, and intensely crimson/dusty sources, 2) enhance stellar mass and star-formation price density measurements at 2 < z < 10 by elements of 2-4, and three) create resolved maps of stellar mass and star formation throughout 10 Gyr of cosmic time to mannequin galaxy progress in two dimensions.”
Epoch of Reionization
Along with the earliest galaxies, one among Webb’s greatest targets is the detection of the primary stars within the Universe. These Inhabitants III stars are believed to have been ultra-hot, huge, and short-lived, remaining of their essential sequence section for just a few dozen million years. Additionally they emitted super quantities of ultraviolet radiation, which led to the “Epoch of Reionization” (EoR). Till the deployment of the JWST, this inhabitants of stars remained completely theoretical.
That is the explanation for applications like GO 7677, “Pushing the Faintest Limits: Extraordinarily Low-Luminosity and Pop III-like Star-Forming Complexes within the Early Universe.” Utilizing the JWST’s NIRSpec integral discipline unit (IFU), the staff – led by Eros Vanzella, a First Researcher of the INAF Astrophysics and Space Science Observatory in Bologna – will observe two stars at z=5.663 and z=4.194, similar to distances of 11.7 billion and 11.425 billion light-years away. As they state of their proposal:
“This research will enable us to measure the metallicity of each sources and assess the presence of huge stars in such elusive methods by evaluating their ionizing photon manufacturing effectivity. These observations will broaden (at the very least double) the pattern of ultra-faint sources with these measurements which solely JWST can carry out, pushing the frontier of understanding towards Inhabitants III-like star formation situations. The lucky angular proximity of the 2 targets permits for simultaneous statement throughout the identical IFU discipline of views.”
There’s additionally the GO 7436 program, “The Final Impartial Islands on the Finish of Reionization? Characterizing the Nature of the Longest Darkish Gaps in IGM Transmission at z~5.3.” Throughout this cosmic epoch, ionized areas steadily grew and overlapped within the intergalactic medium. Nonetheless, how and when it happened remains to be unknown, and putting correct estimates is essential to learning the formation of galaxies within the early Universe. It’s led by PI Xiangyu Jin, a graduate pupil with the Stewart Observatory on the College of Arizona.
He and his staff plan to make use of the JWST to watch galaxies with redshifts of round z=5.5, similar to distances of about 12.4 billion light-years away. At this level, roughly 1.4 billion years after the Massive Bang, the intergalactic medium (IGM) seems extremely ionized to trendy devices, however “darkish gaps” have nonetheless been noticed. “These lengthy darkish gaps could possibly be the final remaining impartial islands within the IGM on the finish of a extremely inhomogeneous reionization course of,” they suggest. “If confirmed, it is going to have a profound affect on the physics of reionization.”
To this finish, they suggest observations utilizing the W. M. Keck Observatory and Webb’s NIRCam. Whereas the Keck observations will probe the Lyman-alpha emissions from roughly 230 galaxies (about 75 within the “darkish hole” areas), NIRCam Wide Field Slitless Spectroscopy (WFSS) will conduct redshift measurements of those galaxies. “We can even characterize the galaxy density discipline round lengthy darkish gaps,” they added. “This joint program will enable us to instantly check the ultra-late reionization mannequin and to put strong constraints on the topology of reionization and the character of inhomogeneous reionization.”
Then there’s GO 8018, titled “DIVER: Deep Insights into UV Spectroscopy on the Epoch of Reionization.” Led by PI Xiaojing Lin, a graduate pupil with the University of Arizona Steward Observatory. , this program will construct on Webb’s early observations of the EoR. These revealed onerous radiation fields and bursts of star formation that had been generally accompanied by the detection of utmost situations within the interstellar medium (ISM) and weird chemical abundance.
In accordance with Lin and her colleagues, high-quality rest-frame UV spectroscopy of galaxies throughout this era is urgently wanted. The staff proposes conducting a deep spectroscopic survey of over 140 galaxies within the Great Observatories Origins Deep Survey North (GOODS-N) discipline at redshifts of z=5 to 9 (12.469 to 13.11 billion gentle years away). Because the staff wrote, it will set up the most important and deepest UV spectral database for EoR galaxies:
“DIVER will instantly (1) clock the star formation historical past by figuring out the distribution and redshift evolution of carbon abundance and (2) probe the prevalence of extraordinarily excessive electron density and its connection to bursty star formation and chemical peculiarity. DIVER can even result in numerous high-profile science, together with the UV demographics of AGNs and large stellar populations, and constraining the reionization historical past via LyA. With nice legacy values, DIVER will advance our understanding of star formation and chemical enrichment historical past within the early Universe, offering an important basis for research of z>10 galaxies.”
Darkish Matter Halos
In accordance with the Normal Mannequin of Cosmology – the Lambda Cold Dark Matter (LCDM) mannequin – Darkish Matter (DM) performed a significant function within the formation of galaxies within the early Universe. In principle, DM halos (DMHs) shaped from the gravitational collapse of density perturbations after the Massive Bang and offered the gravitational “wells” that allowed clouds of gasoline to type Inhabitants III stars and the primary galaxies. Like many different features of the early Universe, this course of has remained completely theoretical till this level.
The aim behind the GO 7519 program, “How do darkish matter halos join with supermassive black holes and their host galaxies?” is to handle the function these performed in galaxy formation. Earlier observations with Webb have performed an essential function in measuring the mass of DMHs in high-redshift quasars, however these measurements had been restricted to vibrant quasars. Per their proposal, the staff will depend on NIRCam WFSS observations to determine emission traces from doubly ionized oxygen (O III) round 12 faint quasars at distances of about 12.716 billion light-years.
“On this new effort, we are going to measure the typical DMH mass from the cross-correlation evaluation of quasars and surrounding [O III] emitters and consider the DMH mass chance density perform for particular person quasars based mostly on cosmological simulations. This program will enable us, for the primary time, to acquire a quasar pattern through which the black gap mass, stellar mass, and halo mass are all measured concurrently. This pattern will reveal their lifetime and the scaling relations within the early universe, underlying the SMBH progress of SMBHs over cosmic time.”
For many years, astronomers, astrophysicists, and cosmologists have needed to take care of limitations on what they might see throughout the cosmos. Due to the Hubble Space Telescope, they had been capable of observe galaxies that existed about 1 billion years after the Massive Bang. Due to missions just like the COsmic microwave Background Explorer (COBE), the Wilkinson Microwave Anisotropy Probe (WMAP), and Planck, they had been capable of measure the earliest gentle within the Universe.
Due to the JWST, scientists are actually capable of get a have a look at what got here in between. By observing galaxies and cosmic buildings as they existed shortly after the Massive Bang, we might sometime be capable to chart cosmic evolution all the way in which again to the start of time.
Additional Studying: STScI
