In this study, the authors present a comprehensive search and analysis of high-redshift galaxies using data from the James Webb Space Telescope (JWST). They focus on nine public JWST extragalactic fields taken in Cycle 1, covering a total effective search area of approximately 358 square arcminutes. Through conservative photometric selection, they identify 339 galaxies at redshifts ranging from 5 to 14. Of these identified galaxies, 109 have spectroscopic redshift measurements from the literature, including recent observations with JWST's Near-Infrared Spectrograph (NIRSpec). The authors perform a regression analysis and find that the rest-frame UV size-stellar mass relation follows a power-law scaling relation of $R_{\rm eff}\propto M_*^{0.20\pm0.03}$. This is similar to the size-stellar mass relation observed for star-forming galaxies at around redshift 3 but scaled down in size by approximately 0.7 dex. The study also investigates the evolution of galaxy sizes over the redshift range studied. The authors find that there is a much slower rate of average size evolution compared to previous studies, with an evolution rate of $R_{\rm eff}\propto(1+z)^{-0.4\pm0.2}$. This result suggests that high-redshift galaxies may not undergo significant growth in their physical sizes over time. Interestingly, a fraction (approximately 13%) of the sample consists of marginally resolved sources even in the NIRCam imaging, with sizes smaller than 100 parsecs. These compact sources deviate from the derived size-mass slope and exhibit high star formation surface densities ($\Sigma_{\rm SFR}>10\ M_\odot \ {\rm yr^{−1}\ kpc^{−2}}$). Such high density star forming regions are extremely rare in local star forming galaxies, accounting for less than 0.01% of the sample. The authors also investigate the presence of ongoing supermassive black hole accretion in the observed galaxies. For those with available NIRSpec data, no evidence of such accretion is found; however, they suggest that high shock velocities within intense star forming regions characterized by high $\Sigma_{\rm SFR}$ could explain the observed high [OIII]-to-Hbeta ratios. Additionally, they find that rest frame UV and optical sizes are comparable for their sample which is consistent with early galaxies building up their structures inside out and not yet exhibiting strong color gradients seen at lower redshifts.
- Comprehensive search and analysis of high-redshift galaxies using JWST data
- 339 galaxies identified at redshifts ranging from 5 to 14
- Regression analysis reveals a power-law scaling relation between UV size and stellar mass
- Slower rate of average size evolution compared to previous studies, suggesting limited growth in physical sizes over time
- Approximately 13% of the sample consists of marginally resolved sources with sizes smaller than 100 parsecs, exhibiting high star formation surface densities
- No evidence of ongoing supermassive black hole accretion found, but high shock velocities within intense star forming regions could explain observed ratios
- Rest frame UV and optical sizes are comparable, indicating early galaxies building up their structures inside out.
Scientists used a special telescope called JWST to look at faraway galaxies. They found 339 galaxies that are very far away, between 5 and 14 times farther than our own galaxy. They also discovered that the size of these galaxies is related to how much stars they have. The size of these galaxies doesn't change much over time, which means they don't grow very big. Some of the galaxies are really small, with high amounts of new stars being formed inside them. They didn't find any evidence of supermassive black holes, but they think intense star formation might explain what they saw. The size of these galaxies in ultraviolet light and visible light is similar, which means they are growing from the inside out."
Definitions - Comprehensive: including everything or nearly everything
- High-redshift: a measure of how far away an object is in space
- Galaxies: huge groups of stars held together by gravity
- Redshifts: a way to measure how much the light from an object has stretched as it travels through space
- Regression analysis: a way to find relationships between different things using math
- Power-law scaling relation: a pattern where one thing changes in proportion to another thing raised to a certain power
- UV size: the physical size of something when looking at it using ultraviolet light
- Stellar mass: how much matter there is in all the stars combined in a galaxy
- Evolution: how
Exploring High-Redshift Galaxies with the James Webb Space Telescope
The James Webb Space Telescope (JWST) is a powerful tool for exploring galaxies at high redshifts. In a recent study, researchers used JWST data to identify and analyze 339 galaxies at redshifts ranging from 5 to 14 in nine public extragalactic fields. Through their analysis, they were able to gain insight into the size-stellar mass relation of these galaxies as well as their evolution over time.
Photometric Selection and Redshift Measurements
The authors began by using conservative photometric selection techniques to identify 339 galaxies in the nine public JWST extragalactic fields, covering an effective search area of 358 square arcminutes. Of these identified galaxies, 109 had spectroscopic redshift measurements from the literature, including recent observations with JWST's Near-Infrared Spectrograph (NIRSpec).
Size-Stellar Mass Relation
Using regression analysis, the authors found that the rest-frame UV size-stellar mass relation follows a power law scaling relation of $R_{\rm eff}\propto M_*^{0.20\pm0.03}$. This result is similar to what has been observed for star forming galaxies around redshift 3 but scaled down in size by approximately 0.7 dex.
Evolution of Galaxy Sizes Over Time
The authors also investigated how galaxy sizes evolve over time and found that there was a much slower rate of average size evolution compared to previous studies, with an evolution rate of $R_{\rm eff}\propto(1+z)^{-0.4\pm0.2}$. This suggests that high redshift galaxies may not undergo significant growth in their physical sizes over time.
Compact Sources
Interestingly, 13% of the sample consists of marginally resolved sources even in NIRCam imaging; these compact sources have sizes smaller than 100 parsecs and exhibit high star formation surface densities ($\Sigma_{\rm SFR} > 10 \ M_\odot \ {\rm yr^{−1}\ kpc^{−2}}$). Such high density star forming regions are extremely rare in local star forming galaxies; they account for less than 0.01% of such samples typically studied at lower redshifts.
Supermassive Black Hole Accretion
The authors also looked into whether or not ongoing supermassive black hole accretion was present in any observed galaxy; however no evidence was found among those with available NIRSpec data . They suggest that this could be due to intense shock velocities within regions characterized by high $\Sigma_{\rm SFR}$.
Rest Frame UV and Optical Size Comparisons Finally , they found that rest frame UV and optical sizes were comparable for their sample , which is consistent with early galaxies building up their structures inside out rather than exhibiting strong color gradients seen at lower redshifts .
In conclusion , this study provides valuable insight into how high -redshift galaxies form and evolve over time . By analyzing data from JWST , researchers were able to identify 339 distant galaxies , investigate their size - stellar mass relations , observe slow rates of average size evolution , discover compact sources exhibiting extreme star formation surface densities , and explore potential explanations for why no evidence was found for ongoing supermassive black hole accretion .
