How many galaxies have been discovered in the universe? The true dimensions of space or how many galaxies are in the universe

Those who have a little idea about the Universe are well aware that the cosmos is constantly in motion. The universe is expanding every second, becoming larger and larger. Another thing is that on the scale of human perception of the world, it is quite difficult to understand the size of what is happening and imagine the structure of the Universe. In addition to our galaxy, in which the Sun is located and we are located, there are dozens, hundreds of other galaxies. Nobody knows the exact number of distant worlds. How many galaxies are in the Universe can only be known approximately by creating a mathematical model of the cosmos.

Therefore, given the size of the Universe, we can easily assume that tens, hundreds of billions of light years from Earth, there are worlds similar to ours.

Space and worlds that surround us

Our galaxy, which received beautiful name The Milky Way, a few centuries ago, according to many scientists, was the center of the universe. In fact, it turned out that this is only part of the Universe, and there are other galaxies various types and sizes, large and small, some further, others closer.

In space, all objects are closely interconnected, moving in in a certain order and occupy the allotted space. Planets known to us, well-known stars, black holes and our own solar system located in the Milky Way galaxy. The name is not accidental. Even ancient astronomers, observing the night sky, compared the space around us to a milk track, where thousands of stars look like drops of milk. The Milky Way Galaxy, the celestial galactic objects in our field of vision, make up the nearby cosmos. What may be beyond the visibility of telescopes became known only in the 20th century.

Subsequent discoveries, which expanded our cosmos to the size of the Metagalaxy, led scientists to the theory of the Big Bang. A grandiose cataclysm occurred almost 15 billion years ago and served as an impetus for the beginning of the processes of formation of the Universe. One stage of the substance was replaced by another. From dense clouds of hydrogen and helium, the first beginnings of the Universe began to form - protogalaxies consisting of stars. All this happened in the distant past. Light of many heavenly bodies, which we can observe in the strongest telescopes, is only a farewell greeting. Millions of stars, if not billions, that dotted our sky are located a billion light years from Earth, and have long ceased to exist.

Map of the Universe: nearest and farthest neighbors

Our Solar System and other cosmic bodies observed from Earth are relatively young structural formations and our closest neighbors in the vast Universe. For a long time Scientists believed that the closest to the Milky Way was the dwarf galaxy Large Magellanic Cloud, located only 50 kiloparsecs. Only very recently have the real neighbors of our galaxy become known. In the constellation Sagittarius and in the constellation Canis Major small dwarf galaxies are located, the mass of which is 200-300 times less than the mass of the Milky Way, and the distance to them is just over 30-40 thousand light years.

These are one of the smallest universal objects. In such galaxies the number of stars is relatively small (on the order of several billion). As a rule, dwarf galaxies gradually merge or are absorbed by larger formations. The speed of the expanding Universe, which is 20-25 km/s, will unwittingly lead neighboring galaxies to a collision. When this will happen and how it will turn out, we can only guess. The collision of galaxies is happening all this time, and due to the transience of our existence, it is not possible to observe what is happening.

Andromeda, two to three times the size of our galaxy, is one of the closest galaxies to us. It continues to be one of the most popular among astronomers and astrophysicists and is located just 2.52 million light years from Earth. Like our galaxy, Andromeda is a member of the Local Group of galaxies. The size of this giant cosmic stadium is three million light years across, and the number of galaxies present in it is about 500. However, even such a giant as Andromeda looks short in comparison with the galaxy IC 1101.

This largest spiral galaxy in the Universe is located more than a hundred million light years away and has a diameter of more than 6 million light years. Despite containing 100 trillion stars, the galaxy is primarily composed of dark matter.

Astrophysical parameters and types of galaxies

The first space explorations carried out at the beginning of the 20th century provided plenty of food for thought. The cosmic nebulae discovered through the lens of the telescope, of which more than a thousand were eventually counted, were most interesting objects in the Universe. For a long time, these bright spots in the night sky were considered to be gas accumulations that were part of the structure of our galaxy. Edwin Hubble in 1924 managed to measure the distance to a cluster of stars and nebulae and made a sensational discovery: these nebulae are nothing more than distant spiral galaxies, independently wandering across the scale of the Universe.

An American astronomer was the first to suggest that our Universe is made up of many galaxies. Space exploration in the last quarter of the 20th century, observations made using spacecraft and technology, including the famous Hubble telescope, confirmed these assumptions. Space is limitless and our Milky Way is far from the largest galaxy in the Universe and, moreover, is not its center.

Only with the advent of powerful technical means observations, the Universe began to take on clear outlines. Scientists are faced with the fact that even such huge formations as galaxies can differ in their structure and structure, shape and size.

Through the efforts of Edwin Hubble, the world received a systematic classification of galaxies, dividing them into three types:

spiral;
elliptical;
incorrect.

Elliptical and spiral galaxies are the most common types. These include our Milky Way galaxy, as well as our neighboring Andromeda galaxy and many other galaxies in the Universe.

Elliptical galaxies have the shape of an ellipse and are elongated in one direction. These objects lack sleeves and often change their shape. These objects also differ from each other in size. Unlike spiral galaxies, these cosmic monsters do not have a clearly defined center. There is no core in such structures.

According to the classification, such galaxies are designated by the Latin letter E. All currently known elliptical galaxies are divided into subgroups E0-E7. Distribution into subgroups is carried out depending on the configuration: from galaxies to almost round shape(E0, E1 and E2) to highly stretched objects with indices E6 and E7. Among the elliptical galaxies there are dwarfs and true giants with diameters of millions of light years.

There are two subtypes of spiral galaxies:

galaxies presented in the form of a crossed spiral;
normal spirals.

The first subtype is distinguished by the following features. In shape, such galaxies resemble a regular spiral, but in the center of such a spiral galaxy there is a bridge (bar), giving rise to arms. Such bridges in a galaxy are usually the result of physical centrifugal processes that divide the galactic core into two parts. There are galaxies with two nuclei, the tandem of which makes up the central disk. When the nuclei meet, the bridge disappears and the galaxy becomes normal, with one center. There is also a bridge in our Milky Way galaxy, in one of the arms of which our Solar system is located. From the Sun to the center of the galaxy, the path, according to modern estimates, is 27 thousand light years. The thickness of the Orion Cygnus arm, in which our Sun and our planet reside, is 700 thousand light years.

In accordance with the classification, spiral galaxies are designated by the Latin letters Sb. Depending on the subgroup, there are other designations for spiral galaxies: Dba, Sba and Sbc. The difference between the subgroups is determined by the length of the bar, its shape and the configuration of the sleeves.

Spiral galaxies may have various sizes, ranging from 20,000 light years and up to 100 thousand light years in diameter. Our Milky Way galaxy is in the “golden mean”, its size gravitating toward medium-sized galaxies.

The rarest type is irregular galaxies. These universal objects are large clusters of stars and nebulae that do not have a clear shape or structure. In accordance with the classification, they received the indices Im and IO. As a rule, structures of the first type do not have a disk or it is weakly expressed. Often such galaxies can be seen to have similar arms. Galaxies with IO indices are a chaotic collection of stars, clouds of gas and dark matter. Prominent representatives of this group of galaxies are the Large and Small Magellanic Clouds.

All galaxies: regular and irregular, elliptical and spiral, consist of trillions of stars. The space between stars and their planetary systems is filled with dark matter or clouds of cosmic gas and dust particles. In the spaces between these voids there are black holes, large and small, which disturb the idyll of cosmic tranquility.

Based on the existing classification and research results, we can answer with some confidence the question of how many galaxies there are in the Universe and what type they are. There are more spiral galaxies in the Universe. They constitute more than 55% of the total number of all universal objects. There are half as many elliptical galaxies - only 22% of the total number. There are only 5% of irregular galaxies similar to the Large and Small Magellanic Clouds in the Universe. Some galaxies are neighboring us and are in the field of view of the most powerful telescopes. Others are in the farthest space, where dark matter predominates and the blackness of endless space is more visible in the lens.

Galaxies up close

All galaxies belong to certain groups that are modern science are usually called clusters. The Milky Way is part of one of these clusters, which contains up to 40 more or less known galaxies. The cluster itself is part of a supercluster, a larger group of galaxies. The Earth, along with the Sun and the Milky Way, is part of the Virgo supercluster. This is our actual cosmic address. Together with our galaxy, there are more than two thousand other galaxies in the Virgo cluster, elliptical, spiral and irregular.

The map of the Universe, which astronomers rely on today, gives an idea of what the Universe looks like, what its shape and structure are. All clusters gather around voids or bubbles of dark matter. It is possible that dark matter and bubbles are also filled with some objects. Perhaps this is antimatter, which, contrary to the laws of physics, forms similar structures in a different coordinate system.

Current and future state of galaxies

Scientists believe that it is impossible to create a general portrait of the Universe. We have visual and mathematical data about the cosmos that is within our understanding. The real scale of the Universe is impossible to imagine. What we see through a telescope is starlight that has been coming to us for billions of years. Perhaps the real picture today is completely different. As a result of cosmic cataclysms, the most beautiful galaxies in the Universe could already turn into empty and ugly clouds of cosmic dust and dark matter.

It cannot be ruled out that in the distant future, our galaxy will collide with a larger neighbor in the Universe or swallow a dwarf galaxy existing next door. What will be the consequences of such universal changes remains to be seen. Despite the fact that the convergence of galaxies occurs at the speed of light, earthlings are unlikely to witness a universal catastrophe. Mathematicians have calculated that just over three billion Earth years are left before the fatal collision. Whether life will exist on our planet at that time is a question.

Other forces can also interfere with the existence of stars, clusters and galaxies. Black holes, which are still known to man, are capable of swallowing a star. Where is the guarantee that such monsters of enormous size, hiding in dark matter and in the voids of space, will not be able to swallow the galaxy entirely?

Part of the Hubble Ultra Deep Field. All you see are galaxies.

More recently, in 1920, the famous astronomer Edwin Hubble was able to prove that ours is not the only galaxy in existence. Today we are already accustomed to the fact that space is filled with thousands and millions of other galaxies, against the background of which ours looks very tiny. But exactly how many galaxies in the Universe are close to us? Today we will find the answer to this question.

It sounds incredible, but even our great-grandfathers, even the most scientists, considered our Milky Way a metagalaxy - an object covering the entire Universe. Their error was quite logically explained by the imperfection of telescopes of that time - even the best of them saw galaxies as blurry spots, which is why they were universally called nebulae. It was believed that stars and planets would eventually form from them, just as our solar system once formed. This guess was confirmed by the discovery of the first planetary nebula in 1796, in the center of which there was a star. Therefore, scientists believed that all other nebulous objects in the sky were the same clouds of dust and gas, in which stars had not yet formed.

First steps

Naturally, progress did not stand still. Already in 1845, William Parsons built the Leviathan telescope, gigantic for those times, the size of which was close to two meters. Wanting to prove that "nebulae" are actually made of stars, he brought astronomy seriously closer to modern concept galaxies. He was able for the first time to notice the spiral shape of individual galaxies, and also to detect differences in luminosity in them, corresponding to especially large and bright star clusters.

However, the debate lasted well into the 20th century. Although it was already generally accepted in the progressive scientific community that there were many other galaxies besides the Milky Way, official academic astronomy needed irrefutable evidence of this. Therefore, telescopes from all over the world are looking at the large galaxy closest to us, which was also previously mistaken for a nebula - the Andromeda Galaxy.

The first photograph of Andromeda was taken by Isaac Roberts in 1888, and additional photographs were taken throughout 1900–1910. They show both the bright galactic core and even individual clusters of stars. But the low resolution of the images allowed for errors. What was mistaken for star clusters could be nebulae, or simply several stars that “stuck together” into one during the exposure of the image. But a final solution to the issue was not far off.

Modern painting

In 1924, using the record-breaking telescope of the beginning of the century, Edwin Hubble was able to more or less accurately estimate the distance to the Andromeda galaxy. It turned out to be so huge that it completely ruled out that the object belonged to the Milky Way (despite the fact that Hubble’s estimate was three times less than the modern one). The astronomer also discovered many stars in the “nebula,” which clearly confirmed the galactic nature of Andromeda. In 1925, despite criticism from his colleagues, Hubble presented the results of his work at a conference of the American Astronomical Society.

This speech gave rise to a new period in the history of astronomy - scientists “rediscovered” nebulae, assigning them the title of galaxies, and discovered new ones. In this they were helped by the developments of Hubble itself - for example, the discovery. The number of known galaxies grew with the construction of new telescopes and the launch of new ones - for example, the widespread use of radio telescopes after World War II.

However, until the 90s of the 20th century, humanity remained in the dark about the real number of galaxies surrounding us. The Earth's atmosphere prevents even the largest telescopes from getting an accurate picture - gaseous shells distort the image and absorb starlight, blocking the horizons of the Universe from us. But scientists managed to get around these restrictions by launching a spacecraft, named after an astronomer you already know.

Thanks to this telescope, people for the first time saw the bright disks of those galaxies that previously seemed like small nebulae. And where the sky previously seemed empty, billions of new ones were discovered - and this is not an exaggeration. However, further research has shown that even the thousands of billions of stars visible to Hubble are at least a tenth of their actual number.

Final count

And yet, exactly how many galaxies are there in the Universe? Let me warn you right away that we will have to count together - such questions are usually of little interest to astronomers, since they are devoid of scientific value. Yes, they catalog and track galaxies - but only for more global purposes like studying the Universe.

However, no one undertakes to find the exact number. Firstly, our world is infinite, which is why knowledge full list galaxies is problematic and devoid of practical meaning. Secondly, to count even those galaxies that are within the visible Universe, an astronomer’s entire lifetime will not be enough. Even if he lives 80 years, starts counting galaxies from birth, and spends no more than a second on discovering and registering each galaxy, the astronomer will find only 2 trillion objects - much less than the number of galaxies that actually exist.

To determine the approximate number, let's take some of the high-precision space studies - for example, the "Ultra Deep Field" of the Hubble telescope from 2004. In an area equal to 1/13,000,000 of the entire area of the sky, the telescope was able to detect 10 thousand galaxies. Given that other in-depth studies at the time showed a similar picture, we can average the result. Therefore, within Hubble's sensitivity we see 130 billion galaxies from across the universe.

However, that's not all. After Ultra Deep Field, many other shots were taken that added new details. And not only in the visible spectrum of light, which Hubble operates, but also in infrared and x-rays. As of 2014, within a radius of 14 billion, 7 trillion 375 billion galaxies are available to us.

But this, again, is a minimum estimate. Astronomers believe that dust accumulations in intergalactic space take away 90% of the objects we observe - 7 trillion easily turns into 73 trillion. But this figure will rush even further to infinity when a telescope enters the orbit of the Sun. This device will reach in minutes where Hubble took days to reach, and will penetrate even further into the depths of the Universe.

An international team of astronomers led by Christopher J. Conselice, professor of astrophysics at the University of Nottingham, found that The Universe contains at least 2 trillion galaxies, ten times more than previously thought. The team's work, which began with a grant from the Royal Astronomical Society, was published in the Astrophysical Journal on October 14, 2016.

Astronomers have long sought to determine how many galaxies exist in the observable universe, the part of space where light from distant objects has managed to reach us. Over the past 20 years, scientists have used images from the Hubble Space Telescope to estimate that the universe we see contains about 100 to 200 billion galaxies. Current astronomical technology allows us to study only 10% of these galaxies, and the remaining 90% will only be visible once bigger and better telescopes are developed.

Professor Conselice's research is the culmination of 15 summer job, which was also partially funded by a research grant awarded to senior student Aaron Wilkinson. Aaron, currently a PhD candidate at the University of Nottingham, began by reviewing all previous galaxy counting studies, which provided the fundamental basis for establishing a larger study.

Professor Conselice's team has converted narrow images of deep space from telescopes around the world, and especially from the Hubble Telescope, into 3D maps. This allowed them to calculate the density of galaxies, as well as the volume of one small region of space after another. This painstaking research allowed the team to determine how many galaxies had been missed in earlier studies. We can say that they conducted an intergalactic archaeological excavation.

The results of this study are based on measurements of the number of observed galaxies in different eras– time slices on a galactic scale - for the entire history of the Universe. When Professor Conselice and his team from Nottingham, in collaboration with scientists from the Leiden Observatory at Leiden University in the Netherlands and the Institute of Astronomy at the University of Edinburgh, examined how many galaxies there were in each era, they found that there were more early stage development of the Universe, the number of galaxies was much greater than now.

It appears that when the universe was only a few billion years old, the number of galaxies in a given volume of space was ten times greater than in a similar volume today. Most of these galaxies were systems with light weight, i.e. with masses similar to those of the galaxies currently surrounding the Milky Way.

Professor Conselis said: "This is very surprising because we know that in the 13.7 billion years of cosmic evolution since Big Bang the size of galaxies increased due to star formation and mergers with other galaxies. Establishing the fact of existence more galaxies in the past implies that significant evolution must have occurred to reduce their number through extensive mergers of systems. We miss the vast majority of galaxies because they are very faint and distant. The number of galaxies in the Universe is a fundamental question in astronomy, and it is amazing since 90% of galaxies in space are still unexplored. Who knows what interesting properties we will find when we study these galaxies with the next generation of telescopes?”

Translation of the article “Density distribution of galaxies at Z< 8 и ее последствия». Октябрь 2016. Права на перевод принадлежат
Authors:
Christopher J. Conselice, School of Physics and Astronomy, University of Nottingham, Nottingham, England.
Aaron Wilkinson, Leiden Observatory Leiden University, The Netherlands
Kenneth Duncan, Royal Observatory, Institute of Astronomy, University of Edinburgh, Scotland

annotation

The distribution of the density of galaxies in the Universe and, consequently, the total number of galaxies is a fundamental question in astrophysics that influences the resolution of many problems in the field of cosmology. However, before the publication of this article, there had never been a similar detailed study of this important indicator, as well as the definition of a clear algorithm for finding this number. To solve this problem, we used observed galactic stellar mass functions up to $z \sim 8$ to determine how the galaxy number density varies as a function of time and the mass limit. We have shown that the increase in the total density of galaxies ($\phi_T$) more massive than $M_* = 10^6M_\odot$ decreases as $\phi_T \sim t^(-1)$, where t is the age of the Universe . We further showed that this trend reverses and rather increases with time at higher mass limits $M_* > 10^7M_\odot$. Using $M_* = 10^6M_\odot$ as a lower limit, we justified that the total number of galaxies in the Universe up to $z = 8$ is: $2.0 (+0.7\choose -0.6) \times (10^(12)) $ or just $2.0 \times (10^(12))$ (two trillion!), i.e. almost ten times more than has been seen in all sky-based surveys. We will discuss the implications of these results for understanding the process of galaxy evolution, and also compare our results with the latest models formation of galaxies. These results also indicate that cosmic background light in the optical and near-infrared region likely originates from these unobserved faint galaxies. We will also show how these results address the question of why the night sky is dark, otherwise known as .

1. Introduction

When we discover the Universe and its properties, we always want to know absolute values. For example, astronomical interest is to calculate how many stars are in our Galaxy, how many planets surround these stars (Fressin et al. 2013), the overall density of the Universe (e.g. Fukugita & Peebles 2004), among other absolutes in the properties of the Universe . Here an approximate answer to one of these questions has been given - this is the total density of the number of galaxies and, therefore, the total number of galaxies in the Universe.

This question is not just an idle curiosity, but is related to many other questions in cosmology and astronomy. The density distribution of galaxies is related to questions such as galaxy formation/evolution by number of systems formed, changing ratios of giant galaxies to dwarf galaxies, distant supernova and gamma-ray burst rates, the rate of star formation in the Universe, and how new galaxies are created/destroyed through mergers ( for example, Bridge et al. 2007; Lin et al. 2008; Jogee et al. 2009; Conselice et al. 2011; Bluck et al. 2012; Conselice 2014; Ownsworth et al. 2014). The number of galaxies in the observable Universe also reveals information about the density of matter (matter and energy) of the Universe, background light at different wavelengths, and an understanding of Olbers' paradox. However, there is still no good measurement of this fundamental quantity. Our ability to study the density distribution of galaxies using telescopes only arose with the advent of CCD cameras. Ultra-long-range exploration of distant galaxies began in the 1990s (e.g. Koo & Kron 1992; Steidel & Hamilton 1992; Djorgovski et al. 1995), and reached its current depth with Hubble Space Telescope projects, especially ( Williams et al. 1996). Subsequently, research was continued within the framework of (Williams et al., 2000), (Giavalisco et al. 2004), a survey in the infrared spectrum (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) (Grogin et al. 2011; Koekemoer et al. 2011), and culminated in the Hubble Ultra Deep Field (Beckwith et al. 2006), which remains the deepest optical and near-infrared survey of our Universe to date.
However, despite all these studies, it is still unclear how the overall number density of galaxies evolves over time. This interest Ask, since we know that the star formation rate increases and then decreases with z< 8 (например, Bouwens et al. 2009; ; Madau & Dickinson 2014), в то же время галактики становятся более крупными и менее своеобразными (например, Conselice et al. 2004; Papovich et al. 2005; Buitrago et al. 2013; Mortlock et al. 2013; Lee et al. 2013; Conselice 2014; Boada et al. 2015). Однако мы не знаем, как изменяется общее количество галактик во времени и как это связано с general education populations of galaxies as a whole.
There are several reasons why it is not easy to determine the total number of galaxies based on the results of ultra-long-range surveys. One of them is that all ultra-long-range observations are incomplete. This is due to limitations in exposure time and depth, causing some galaxies to be detected more easily than others. The result of this is an incomplete picture even in the most long-range surveys, which can be corrected but which still leaves some uncertainty. However, the more important problem is that these observations do not reach the faintest galaxies, even though we know from theory that there should be many more faint galaxies beyond the limits of what we can currently observe.
It is also important to pay attention to what we mean by the total density of galaxies in the Universe. It is not a simple quantity that can be defined as the total density that currently exists, the total density that is observable in principle, and the total density that can be observed using modern technology, are different questions with different answers. There is also the problem that we are limited to the cosmological horizon above what we can observe, and therefore there are galaxies that we cannot see beyond it. Even the number of galaxies that exist in the Universe today, that is, if we could consider the entire Universe as it is at the present moment, and not be limited by the transit time of light, represents complex issue. Galaxies in the distant universe have evolved beyond what we can currently observe due to finite nature speed of light and, apparently, will be similar to those in the visible Universe. We address all of these issues in this paper, namely how the galaxy number density varies within the current observable universe up to z ~ 8.
For comparison purposes, in the Appendix to this work, we also analyze the number of galaxies that are visible to modern telescopes at all wavelengths and that we can currently observe. We then compare this data with measurements of the total number of galaxies that could potentially be observed in the Universe based on the measured mass functions. We will also discuss how these results reveal information about the evolution of the galaxy and . We also provide information about future studies and what fraction of galaxies they will observe.
This article is divided into several sections. §2 describes the data we use in this analysis, §3 describes the results of this work, including methods for analyzing galaxy stellar mass functions to obtain the total number of galaxies in the Universe, §4 describes the implications of these results, and §5 presented summary articles. In this work we use standard cosmology: H 0 = 70 km s −1 Mpc −1 , and Ω m = 1 − Ω λ = 0.3.

2. Data

The data we use for this article comes from numerous sources and results. previous works. In the Appendix we describe how many galaxies we can currently observe in the Universe, based on the deepest observations available to date. Here in the main article, we explore the question of how many galaxies could potentially be detected in the Universe if deep imaging at all wavelengths was performed in all parts of the sky without any galactic interference or other distortion.
For much of this analysis and the results of this work, we use mass functions of galaxies from the observable Universe down to z ~ 8 to determine how the galaxy number density evolves with time and . These mass and luminosity functions are now just beginning to be measured at high redshifts, and our primary data comes from mass functions calculated using high-precision infrared and optical surveys from Hubble and ground stations.
As presented in the next section, the mass functions we use are taken from Fontana et al. ( , ), Tomczak et al. (2014), and for galaxies at z< 3. Для самых высоких значений красного смещения мы используем функции масс, опубликованные , и . Мы упорядочили все эти функции масс из каждого вышеуказанного исследования на основе для звезд от $0.1M_\odot$ до $100M_\odot$. Мы использовали плотности галактик из этих функций масс, соответствующие их объемам, в отличие от физических объемов. Это говорит о том, как количество галактик изменяется в одном и том же эффективном объеме, при этом эффекты расширения Хаббла исключаются. Эти функции масс показаны на {{ show1_MathJax ? "Закрыть":"Рисунке 1" }} до предела масс, взятых из ранее упомянутых исследований, которые также перечислены в Таблице 1.

Picture 1. The mass functions we use in this paper are plotted using All these values are taken from various studies mentioned in §2. The mass functions are presented depending on the values of , the left graph shows systems at z< 1, средний график показывает 1 < z < 3 и z >3 (far right). These mass functions are shown so that the solid colored lines are mass functions up to the limit of the corresponding data in which they are complete, and the dotted lines show our extrapolation to $M_* = 10^6 M_\odot$. The “flattest” graph of the mass function for 1< z < 3 взят из работы и для z >3 taken from work.

3. Galaxy density distribution

3.1 Introduction and Cautions

The main method we use to determine the density of galaxies in the Universe is to integrate the number of galaxies through established mass functions for a given cosmological redshift. This requires extrapolating established stellar mass functions to reach a minimum limit on the mass of the galaxy population. There are many ways this can be done, which we will discuss below. One of the most important questions is the lower limit from which we should start counting the number of galaxies as a function of mass functions. Thanks to recent publications giving stellar mass functions up to z ~ 8 (e.g. ; , we can now make this calculation for the first time. Another issue is whether it can be extrapolated below the limit of the data for which it was originally suitable. This is a question which we will explore in detail.
This complements the directly observed approach presented in the Appendix and is a more accurate way to measure the number of galaxies in the currently observable Universe if the mass functions are correctly measured and accurately parameterized. However, this method has potential pitfalls that need to be carefully considered and analyzed. This is not least due to the fact that measurements depend on much more factors than just photometry and object identification problems that are always present when simply measuring the number of galaxies. The situation here is related to other uncertainties associated with measuring stellar masses and redshifts. However, if we can account for these uncertainties, integration of the established mass functions can tell us about the densities of galaxies at a given redshift interval with some measured uncertainty.
We use this method to calculate the total density of galaxies within the currently observable Universe as a function of redshift. To do this, we do not directly integrate the observed mass functions, but use a parameterized form, given by the function Schechter (1976) to determine the total galaxy number density as a function of redshift. The form of this function is given:

$\phi(M) = b\times\phi^\ast\ln(10)^(1+\alpha)$ $\times\exp[-10^(b(M-M^\ast))] . . . . .(1)$

where b = 1 for the mass function, b = 0.4 for , which will be written in terms of absolute values. For a mass function, $M^*$ is the typical mass in logarithmic units and determines where the mass function changes slope, and $M = \log(\frac(M_*)(M_\bigodot))$ is the mass in logarithmic units. Similarly for the luminosity function, $M^*$ corresponds to a typical value. For both functions, $\phi^*$ has a normalization, and $\alpha$ determines the slope for fainter and less massive galaxies. Our method uses published values of $\phi^*$, $\alpha$ and $M^*$ to calculate the integrated number of galaxies at different redshifts.
We use the Schechter luminosity function as a tool for calculating the overall density since it generally describes well the distribution of galaxy masses at all redshifts in the ranges we study. However, we do not know at what lower mass limit it remains valid, which is one uncertainty in our analysis. Next we discuss the use of $M_*>10^6 M_\bigodot$ as a limit and the rationale for using it as our lower limit. We also discuss how our results would have changed if we had used a different value for the lower mass limit.
Since we integrate mass functions across the entire history of the universe, we must use many surveys to account for the number of galaxies at different redshifts. Different redshift ranges require studies performed at different wavelengths, and different studies sometimes find different meanings Schechter parameters. In this work, we attempt to comprehensively study mass functions that, especially at low redshift, can produce widely divergent density values and evolutionary shapes. We get almost the same results when we use Schechter's double luminosity function to calculate the mass function at low cosmological redshifts as when we use the power law () to calculate the mass function at high cosmological redshifts .

1. page 170-183 Lectures on stellar astronomy. Loktin A.V., Marsakov V.A., 2009.
2.
3.
4., a section of the NASA Extragalactic Database (NED) - the largest repository of images, photometry and spectra of galaxies obtained from sky surveys in the microwave, infrared, optical and ultraviolet (UV) ranges.
5.
6.
7.
8. This work introduced the double Schechter luminosity function. Section 4.2 on page 10.
9. Lorenzo Zaninetti. May 29, 2017. A Left and Right Truncated Schechter Luminosity Function for Quasars

In the cosmological redshift range z ~ 0 - 3 we use the established values of the mass functions and their errors from the work carried out by Fontana et al. ( , ), And . These stellar mass functions are determined by measuring the stellar masses of objects using the SED fitting() procedure. Despite the large scatter in different measurements of the Schechter function parameters, we use all this information to take into account the different measurement methods and models used, as well as cosmic dispersion (). These mass functions, parameterized by the Schechter function, are shown in Figure 1. We also convert those studies that use the initial Chabrier mass functions () - Pozzetti et al. (2007), Duncan et al. (2014), Mortlock et al. (2015) and Muzzin et al. (2013) which uses the initial Kroupa mass functions (Kroupa IMF) into the initial Salpeter mass functions (Salpeter IMF). The list of values we use in our analysis is shown in (( show2_MathJax ? "Close": "Table 1")) Note- This table lists the parameters of the given Schechter functions that we use to perform our calculations. They are all normalized to produce comparable values of the initial Salpeter mass functions (Salpeter IMF), although Pozzetti et al. (2007), Duncan et al. (2014) and Mortlock et al. (2015) used initial Chabrier mass functions (), and Muzzin et al. (2013) used Kroupa initial mass functions (Kroupa IMF).

(( show2_MathJax ? "Close": "Table 1")) .

Note that we consider only those mass functions where the parameter α changes are permitted in applicable Schechter models. If the result of the mass function is obtained from a fixed value α , then this leads to a distortion in the number of galaxies, since this value has a significant impact on the number of faint galaxies with low mass in a given volume (§3.2). Therefore, we exclude mass function results from studies using α GOODS (Great Observatories Origins Deep Survey project) as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, as well as from .
For high values of cosmological redshift, mass functions are a relatively new parameter, so in order to obtain consistent and consistent data, we also analyzed the obtained luminosity functions in the ultraviolet range, mainly at 1500˚A. To do this, we used data published in Bouwens et al. (2011), McLure et al. (2009), McLure et al. (2013), Bouwens et al. (2015) and Finkelstein et al. (2015). McLure et al. (2013) and Bouwens et al. (2015) analyze data from the most distant surveys, including the HUDF12 survey, which examined galaxies at the highest cosmological redshifts at $z = 8$ and $z = 9$.
To convert the stellar mass limit to the UV magnitude limit, we use the ratios between these two quantities calculated in Duncan et al. (2014). Duncan et al. (2014) modeled the linear relationship between mass and light in the UV and how it develops under different meanings cosmological redshift. We use these to determine the UV magnitude limit corresponding to our standard mass limit $M_* = 10^6M_\odot$. Thus, we can relate our stellar mass limit to the absolute magnitude limit in the UV. We do not use these values in our calculations, but use these luminosity functions to check the consistency of our results obtained from the stellar mass functions. We find high consistency with stellar mass functions, including using different variations of the stellar mass-to-UV luminosity conversion (e.g., Duncan et al. 2014; Song et al. 2015). Moreover, all of our mass functions for high values of cosmological redshift are more or less consistent, with the exception of Grazian et al. (2015), the results of which lead to a slightly lower value of $\phi_T$.

5. Brief summary of the study

We explored the fundamental question of the density distribution of galaxies in the Universe. We analyze this problem in several ways and discuss implications for galactic evolution and cosmology. We use recently derived mass functions for galaxies up to z ∼ 8 to determine the density distribution of galaxies in the Universe. Our main conclusion is that the density of the number of galaxies decreases over time as $\phi_T(z) \sim t^(-1)$, where t is the age of the Universe.
We next discuss the implications of this increase in galaxy density with hindsight for a variety of key astrophysical questions. By integrating the density of the number of galaxies, we calculated number of galaxies in the Universe, the value of which was $2.0 (+0.7\choose -0.6) \times (10^(12))$ for $z = 8$, which in principle can be observed. This is approximately ten times more than with direct calculation. This means that we have yet to discover a large population of faint, distant galaxies.

In terms of the astrophysical evolution of galaxies, we show that the increase in the integrable mass functions of all galaxies with redshift is explained by the merger model. We show that simple model merger is capable of reproducing a decrease in the number of galaxies with a merger time scale of $\tau=1.29 ± 0.35 Gyr$. The resulting merger rate at z = 1.5 is R ∼ 0.05 mergers $Gyr^(−1) Mpc^(−3)$, close to the value obtained from structural and pairwise analysis. Most of these convergent galaxies are lower-mass systems, increasing in galaxy number density over time from the lower limit to higher masses when calculating the total density.

Finally, we discuss the implications of our findings for future research.

In the future, as mass functions become better known through better SED modeling and deeper and broader data from JWST and Euclid/LSST, we will be able to more accurately measure the overall galaxy number density and thus obtain a better measure of this fundamental quantity.

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More recently, in 1920, the famous astronomer Edwin Hubble was able to prove that ours is not the only one in existence. Today we are already accustomed to the fact that space is filled with thousands and millions of other galaxies, against the background of which ours looks very tiny. But exactly how many galaxies are there near us? Today we will find the answer to this question.

From one to infinity

It sounds incredible, but even our great-grandfathers, even the most scientists, considered our Milky Way a metagalaxy - an object covering the entire observable Universe. Their error was quite logically explained by the imperfections of that time - even the best of them saw galaxies as blurry spots, which is why they were universally called nebulae.

It was believed that over time they were formed from them, just as ours was once formed. This guess was confirmed by the discovery of the first in 1796, in the center of which there was a star. Therefore, scientists believed that all other nebulous objects in the sky were the same, in which stars had not yet formed.

First steps

Naturally, progress did not stand still. Already in 1845, William Parsons built the Leviathan telescope, gigantic for those times, the size of which was close to two meters. Wanting to prove that “nebulae” are actually made of stars, he brought astronomy seriously closer to the modern concept of a galaxy. He was able for the first time to notice the spiral shape of individual galaxies, and also to detect differences in luminosity in them, corresponding to especially large and bright ones.

Modern painting

This speech gave rise to a new period in the history of astronomy - scientists “rediscovered” nebulae, assigning them the title of galaxies, and discovered new ones. In this they were helped by the achievements of Hubble itself - for example, the discovery of the red shift. The number of known galaxies grew with the construction of new telescopes and the launch of new ones - for example, the widespread use of radio telescopes after World War II.

However, until the 90s of the 20th century, humanity remained in the dark about the real number of galaxies surrounding us. The atmosphere prevents even the largest telescopes from getting an accurate picture - gaseous shells distort the image and absorb starlight, blocking the horizons of the Universe from us. But scientists managed to get around these restrictions by launching, named after an astronomer you already know.

Final count

However, no one undertakes to find the exact number. Firstly, our world is infinite, which makes maintaining a complete list of galaxies problematic and devoid of practical meaning. Secondly, to count even those galaxies that are within the visible Universe, an astronomer’s entire lifetime will not be enough. Even if he lives 80 years, starts counting galaxies from birth, and spends no more than a second on discovering and registering each galaxy, the astronomer will find only 2 trillion objects - much less than the number of galaxies that actually exist.

However, that's not all. After Ultra Deep Field, many other shots were taken that added new details. And not only in the visible spectrum of light, which Hubble operates, but also in infrared and x-rays. As of 2014, within a radius of 14 billion light years, 7 trillion 375 billion galaxies are available to us.

But this, again, is a minimum estimate. Astronomers believe that dust accumulations in intergalactic space take away 90% of the objects we observe - 7 trillion easily turns into 73 trillion. But this figure will rush even further to infinity when the James Webb telescope enters orbit. This device will reach in minutes where Hubble took days to reach, and will penetrate even further into the depths of the Universe.

Based on materials

Trillions of stars are distributed unevenly in outer space. Over time, they form into galaxies, as if residents settle in cities, while the spaces between them remain free. The individual stars visible in the sky belong to the spiral-shaped Milky Way galaxy, which contains approximately 200 billion stars. This is a huge rotating disk of gas and dust with a vortex of stars radiating from the central part of our Universe.

The solar system, together with planet Earth, is located on its periphery. The luminary takes more than 200 million years to complete a full revolution, and its movement occurs at a speed of 940,000 km/h. The distance between stars in the galaxy is measured in trillions of kilometers of empty space. And beyond it lies the black emptiness of space, in fact inhabited by hundreds of billions of galaxies with millions of stars that are very similar to the Sun we see. Extreme distances do not allow them to be seen as clearly as the Moon. They appear to be just tiny spots in the night sky.

Separately located galaxies and even isolated stars are clearly visible in clear weather. For example, the Andromeda nebula is the closest galaxy to us, having the same spiral shape as the Milky Way. Some galaxies are shaped like an ellipse, where the stars resemble a swarm of bees circling their hive. In such galaxies, the stars are so ancient that after billions of years they have degenerated into red giants, giving their Universes red-orange hues. There are other forms of galaxies: those resembling a doubly convex lens, a spiral figure, or shapeless (irregular) galaxies.

Existing for billions of years, galaxies resemble living beings: they are born, gas emissions occur in them, releasing incredible amounts of energy, and they gradually collide with each other, giving birth to new galaxies. Such collisions last for millions of years. The gravitational fields of two different galaxies displace stars from their orbits and change shape.

Thus, scientists suggest that famous galaxies That's exactly how they were formed. For example, two spiral ones give rise to one elliptical one. Thus, the formation of the Milky Way may have required the merger of tens or hundreds of smaller galaxies. Modern telescopes are so powerful that they can view Universes 2 million light years away from Earth. Astrophysicists now see galaxies exactly as they were many millions of years ago.