Fewer galaxies in the early Universe

How many faint galaxies can we observe? It’s a tricky question that sought to answer a group of researchers at Michigan State University (MSU) through a series of numerical simulations conducted with supercomputers. Their findings, published in the Astrophysical Journal Letters, suggest that the origins of the universe might be a little crowded place, implying that the number of more distant galaxies, and weakest, is 10 to 100 times lower.


Credit: Brian W. O’Shea (Michigan State University), John H. Wise (Georgia Tech); Michael Norman and Hao Xu (UC San Diego)

According to a recent study led by researchers at Michigan State University (MSU), there may be fewer galaxies in the Universe than we can imagine. The findings, to be published in Astrophysical Journal Letters, suggest that the estimated number of more distant galaxies, and weakest, is 10 to 100 times lower.
Over the years, the Hubble Space Telescope has allowed astronomers to observe the most remote regions of the Universe. Thanks to its high power exploration, the space telescope has revealed a number of hypotheses about the existence of numerous faint and distant galaxies. “Our work indicates that there are fewer weak galaxies more than we think,” says Brian O’Shea’s, associate professor of physics and astronomy at MSU and lead author of the study. “Previous estimates suggest that the number of weak primordial galaxies is of the order of hundreds or thousands of times higher than the few bright galaxies that we can observe with the Hubble Space Telescope.”
O’Shea and colleagues used supercomputer Blue Waters of the National Science Foundation (NSF) to carry out a series of numerical simulations, called Renaissance Simulations, in order to examine the formation of galaxies in the early Universe. John Wise, Dunn Family Assistant Professor in Georgia Tech’s School of Physics, has worked on the code. In addition, the group of Wise has prepared the data in anticipation of future observations that will be realized in the second half of 2018 by the James Webb Space Telescope (JWST), used in this case as “calibrator” simulations so to enter the correct parameters.
The researchers simulated thousands of galaxies at a time, including the processes of the gravitational interaction and radiated. The simulations were consistent with the real distant galaxies, at least with those that have been discovered and confirmed. Moreover, the calculations did not reveal an exponential increase in the number of faint galaxies, as well as had been previously expected. “The number of fainter galaxies remains constant and does not increase significantly,” says O’Shea. “This flattening of the distribution of galaxies at successively lower brightness is the most important result of this study and significant because it provides valuable insights on the period of reionization of the Universe, that is, when the gas goes from one state to the more neutral to a state more ionized, “adds Wise.
The term “reionized” is used to indicate that the Universe was ionized immediately after the Big Bang. At that time, ordinary matter was constituted only by hydrogen atoms whose protons (having positive charge) were deprived by the electrons (which have negative charge). Subsequently, the universe cooled enough to allow electrons to join the proton, forming atoms of neutral hydrogen. They, however, did not produce any radiation or ultraviolet and optical light without that astrophysicists are not able to “see” through telescopes those clues related to cosmic evolution of the so-called “Dark Ages”. The light emerged when he began the era of reionization. In another previous work (preprint) other simulations conducted by two researchers, who participated in this study, they concluded that about 300 million years after the Big Bang the universe was ionized at 20%, after 550 million years It was ionized to 50% in order to become fully ionized 880 million years after its creation.
Thus, these simulations will be tested by the JWST telescope. The technology will have a successor to Hubble will allow astronomers to observe objects with details still better than those that have so far characterized the images provided by Hubble. “We could say that the Hubble Space Telescope is seeing only the tip of the iceberg of the most remote galaxies,” said Michael Norman, director of the San Diego Supercomputer Center at the University of California and co-author of the study. “One of the key questions to be answered is: how many galaxies are so weak that we are still able to observe? Thanks to the analysis of these new and super detailed simulations, what we find is that there are 10 to 100 times less galaxies with respect to what would predict a simple extrapolation ‘.
Despite the James Webb Space Telescope will improve the observation of distant galaxies, but its field of view is relatively small. For this reason, astronomers will have to take account of the so-called cosmic variance, that is, the statistical variation in the number of galaxies which depends on the region of space in which they are distributed. “Even if we do advances in technology, this important work makes our simulations. Perhaps, it will require a more thorough theoretical understanding to interpret correctly what you are watching, such as the data that will be produced from the survey at high redshift, “concluded O’Shea.

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