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Observing the epoch of galaxy formation

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Significant observational progress in addressing the question of the origin and early evolution of galaxies has been made in the past few years, allowing for direct comparison of the epoch when most of the stars in the universe were forming to prevailing theoretical models. There is currently broad consistency between theoretical expectations and the observations, but rapid improvement in the data will provide much more critical tests of theory in the coming years.

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... Иллюстрация метода многоцветной фотометрии, используемого при поиске далеких галактик. Показано изменение наблюдаемого спектра за счет красного смещения [18] Корреляция между активностью галактик и их взаимодействием и слияниями также является сейчас уже хорошо установленным наблюдательным фактом [6,19,11]. Малая концентрация квазаров и радиогалактик позволяет возникать им даже за счет очень редких соударений или слияний. ...
... При таких наблюдениях используется метод многоцветной фотометрии в полях глубоких обзоров космического телескопа Хаббла и крупнейших наземных телескопов [1,2]. Принцип легко понять из рисунка, заимствованного из обзора [18] одного из авторов этого метода (Рис.1). Благодаря большому красному смещению, изображения далеких галактик исчезают в ультрафиолетовых и оптических фильтрах, и галактика видна только в красной или даже в ИК-области спектра (Рис. ...
... в разных фильтрах при использовании метода многоцветной фотометрии [18] 2.2. ЭВОЛЮЦИЯ КОНЦЕНТРАЦИИ НЕЙТРАЛЬНОГО ВОДОРОДА Другим эффектом, свидетельствующим о появлении звезд и галактик на больших красных смещениях, служит наблюдение вызываемой ими вторичной ионизации водорода. ...
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1 Институт радиофизики и электроники НАН Украины, Харьков; 2 Радиоастрономический институт НАН Украины, Харьков; 3 Харьковский национальный университет им. В.Н. Каразина, Харьков E-mail: ak_04@rambler.ru, vkont@ri.kharkov.ua Быстрая эволюция числа массивных галактик при красном смещении z =6, обнаруженная в последние годы при анализе сверхглубокого поля Хаббла и Субару, может быть объяснена взрывным характером про-цесса слияния галактик. 1. ВВЕДЕНИЕ Сообщение [1,2] об обнаружении в сверхглубо-ких полях Хаббла и Субару "внезапного" появления массивных галактик при красном смещении z=6 (см. также [3]), а также сообщение о наблюдении заклю-чительной стадии процесса вторичной ионизации в этот же период [4] (см. литературу и обсуждение в обзоре [5]) может свидетельствовать, по нашему мнению, так же как и эпоха возникновения квазаров [6], о взрывном характере эволюции галактик в ре-зультате слияний [7, 8]. Долгое время считалось, что после своего обра-зования в результате развития гравитационной не-устойчивости (из газового протогалактического об-лака), галактики эволюционируют сугубо индивиду-ально. Наблюдательные данные последних трех де-сятилетий, в особенности данные космического те-лескопа Хаббла и крупнейших наземных телеско-пов, дают убедительные доказательства опреде-ляющей роли слияний в космогонии галактик. Об-стоятельный обзор Кенникута, Швейцера и Барнса [9], посвященный взаимодействию и слиянию га-лактик и вызванному им индуцированному звездо-образованию (около 1000 ссылок и более 200 иллю-страций!) позволяет опустить здесь подробное опи-сание соответствующей библиографии и наблюда-тельных аргументов. Процессы слияний происходят в темной холодной материи (CDM), джинсова длина в которой мала, не-смотря на то, что эволюция происходит в горячей Вселенной. Первоначально возникшие флуктуации малых масс, порядка массы шаровых скоплений в эпоху рекомбинации водорода, сливаясь (и скучива-ясь) образуют за космологическое время массивные объекты – галактики (и их скопления). При этом све-тящееся барионное вещество представляет собой ма-лую примесь к темной материи в галактиках. ___________________________________________________________ ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2010. № 4. Серия: Плазменная электроника и новые методы ускорения (7), с.137-142. 137 В работах римской и харьковской групп в 90-е годы [7,8,10-14] показана возможность кинетиче-ского «фазового перехода» [15-17] в системе галак-тик, проявляющегося в самоускоряющемся процессе образования массивных галактик за счет слияний галактик малых масс – «эпоха» возникновения га-лактик. То есть процесс слияний при гравитацион-ном взаимодействии носит «взрывной характер». Взрывное поведение слияний существенно связано с зависимостью вероятности слияния от масс галак-тик. А именно, к взрывной эволюции и фазовому переходу приводит рост вероятности более быст-рый, чем первая степень массы [8, 10]. В современ-ных космологических теориях это обстоятельство либо игнорируется, либо учитывается недостаточно детально. "Внезапное" появление галактик при z = 6 можно пытаться рассматривать как наблюдательное свидетельство "взрывной" эволюции, чему и посвя-щена данная работа.
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We use a semi-analytic model of galaxy formation in hierarchical clustering theories to interpret recent data on galaxy formation and evolution, focussing primarily on the recently discovered population of Lyman-break galaxies at $z\simeq 3$. For a variety of cold dark matter (CDM) cosmologies we construct mock galaxy catalogues subject to identical selection criteria to those applied to the real data. We find that the expected number of Lyman-break galaxies is very sensitive to the assumed stellar initial mass function and to the normalization of the primordial power spectrum. For reasonable choices of these and other model parameters, it is possible to reproduce the observed abundance of Lyman-break galaxies in CDM models with $\Omega_0=1$ and with $\Omega_0<1$. These galaxies generally form from rare peaks at high redshift and, as a result, their spatial distribution is strongly biased, with a typical bias parameter, $b\simeq 4$, and a comoving correlation length, $r_0\simeq 4 \mpc$. The typical sizes of these galaxies, $\sim 0.5\kpc$, are substantially smaller than those of present day bright galaxies. In combination with data at lower redshifts, the Lyman-break galaxies can be used to trace the cosmic star formation history. Most galaxies (in our models and in the data) never experience star formation rates in excess of a few solar masses per year. Our models predict that even at $z=5$, the integrated star formation rate is similar to that measured locally, although less than 1% of all the stars have formed prior to this redshift. These galaxies mark the onset of the epoch of galaxy formation that continues into the present day. The basic ingredients of a consistent picture of galaxy formation may well be now in place. Comment: Minor revisions to match version published in May 10 ApJ. 1998, ApJ, 498, 504-521. Uses emulateapj.sty. Also available at http://star-www.dur.ac.uk/~cmb/galform2.html
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A population of distant dusty galaxies emitting in the submillimetre waveband has recently been detected using the Submillimetre Common-User Bolometer Array (SCUBA) camera on the James Clerk Maxwell Telescope (JCMT). This population can be used to trace the amount of high-redshift star formation activity that is obscured from view in the optical waveband by dust, and so is missing from existing inventories of star formation in the distant Universe. By including this population we can construct a complete and consistent picture of the history of star formation. The evolution of obscured star formation at redshifts less than unity is constrained by mid- and far-infrared counts of dusty galaxies. Activity increases with redshift z as (1 + z)(gamma) with gamma similar to 4, consistent with the form of evolution found in the optical waveband by the Canada-France Redshift Survey (CFRS) to z less than or similar to 1. The form of evolution at higher redshifts is constrained by both faint SCUBA counts and the intensity of background radiation in the millimetre/submillimetre waveband. We find that the total amount of energy emitted by dusty galaxies is about four times greater than that inferred from rest frame ultraviolet observations, and that a larger fraction of this energy is emitted at high redshifts. The simplest explanation for these results is that a large population of luminous, strongly obscured sources at redshifts z less than or similar to 5 is missing from optical surveys. We discuss the possible contribution of obscured active galactic nuclei to the submillimetre-wave background and counts. More accurate constraints on the history of star formation will be provided by determinations of the counts in several submillimetre wavebands and crucially by a reliable redshift distribution of the detected galaxies.
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The discovery of a population of young galaxies at an epoch when the universe was about one tenth of its current age has shed new light on the question of when and how galaxies formed. Within the context of popular models this is the population of primeval galaxies that built themselves up to the size of present--day galaxies through the process of repeated mergers. But the recent detection of a large concentration of these primeval galaxies (Steidel et al. 1997) appears to be incompatible with hierarchical clustering models, which generally predict that clusters of this size are fully formed later in time. Here we use a combination of two powerful theoretical techniques --semi-analytic modelling and N-body simulations-- to show that such large concentrations should be quite common in a universe dominated by cold dark matter, and that they are the progenitors of the rich galaxy clusters seen today. We predict the clustering properties of primeval galaxies which should, when compared with data that will be collected in the near future, test our understanding of galaxy formation within the framework of a universe dominated by cold dark matter. Comment: To appear on Nature, Latex +postscript plots, b/w version. (2 jpeg files also included). Version with high resolution colour plots available at http://star-www.dur.ac.uk:80/~fabio/
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Large-scale simulations of a universe dominated by cold dark matter (CDM) are tested against two fundamental properties of clusters of galaxies: the cluster mass function and the cluster correlation function. We find that standard biased CDM models are inconsistent with these observations for any bias parameter b. A low-density, low-bias CDM-type model, with or without a cosmological constant, appears to be consistent with both the cluster mass function and the cluster correlations. The low-density model agrees well with the observed correlation function of the Abell, Automatic Plate Measuring Facility (APM), and Edinburgh-Durham cluster catalogs. The model is in excellent agreement with the observed dependence of the correlation strength on cluster mean separation, reproducing the measured universal dimensionless cluster correlation. The low-density model is also consistent with other large-scale structure observations, including the APM angular galaxy-correlations, and for lambda = 1-Omega with the COBE results of the microwave background radiation fluctuations.
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More than a dozen papers analyzing the COBE data have now appeared. We review the different techniques and compare them to a "brute force" likelihood analysis where we invert the full 4038 Theta 4038 Galaxy-cut pixel covariance matrix. This method is optimal in the sense of producing minimal error bars, and is a useful reference point for comparing other analysis techniques. Our maximum-likelihood estimate of the spectral index and normalization are n 1:15(0:95) and Q 18:2(21:3) K including (excluding) the quadrupole. Marginalizing over the normalization C 9 , we obtain n 1:10 Sigma 0:29 (n 0:90 Sigma 0:32). When we compare these results with those of the various techniques that involve a linear "compression" of the data, we find that the latter are all consistent with the brute-force analysis and have error bars that are nearly as small as the minimal error bars. We therefore conclude that the data compressions involved in these techniques do indeed retain most of the useful cosmological information. 1 Published in ApJ, 455, 1-6, December 10, 1995. Submitted December 5, 1994. 1
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We present the results of spectroscopic studies with the LRIS spectrograph on Keck of two of the Hawaii deep survey fields. The 393 objects observed cover a 26.2 arcmin(2) area and constitute a nearly complete sample down to K=20, I=23, and B=24.5. The rest-frame K-band luminosity function and its evolution with redshift are described. Comparisons are made with other optically selected (B and I) samples in the literature, and the corresponding rest-frame B-band luminosity function evolution is presented. The B-band counts at B similar to 24 are shown to be a mixture of normal galaxies at modest redshifts and galaxies undergoing rapid star formation, which have a wide range of masses and which are spread over the redshift interval from z=0.2 to beyond z=1.7. The luminosity functions, number counts, and color distributions at optical and IR wavelengths are discussed in terms of a consistent picture of the star-forming history of the galaxy sample. [O II] emission-line diagnostics or rest-frame ultraviolet-infrared color information are used in combination with rest-frame absolute K magnitudes to construct a ''fundamental plane'' in which the evolution of the global star-formation rate with redshift can be shown, and we find that the maximum rest-frame K luminosity of galaxies undergoing rapid star formation has been declining smoothly with decreasing redshift from a value near L(x) at z>1. This smooth decrease in the characteristic luminosity of galaxies dominated by star formation can simultaneously account for the high B-band galaxy counts at faint magnitudes and the redshift distribution at z<1 in both the B- and K-selected samples. Finally, the overall K-band light density evolution is discussed as a tracer of the baryonic mass in stars and compared with the overall rates of star formation inferred from the rest-frame ultraviolet light density as a function of redshift. (C) 1996 American Astronomical Society.
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Galaxies represent the visible fabric of the Universe and there has been considerable progress recently in both observational and theoretical studies. The underlying goal is to understand the present-day diversity of galaxy forms, masses and luminosities. Popular models predict the bulk of the population assembled recently, in apparent agreement with optical observations. However, numerous uncertainties remain, including the role that dust might play in obscuring star-forming systems. Astronomers now seek more detailed tests to verify that the Hubble sequence of types arises from transformations driven by the dynamical assembly of smaller systems. Multi-wavelength surveys and studies of the resolved internal properties of distant galaxies promise answers to these fundamental questions.
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Galaxies at very high redshift (z~3 or greater) are now accessible to wholesale observation, making possible for the first time a robust statistical assessment of their spatial distribution at lookback times approaching ~90% of the age of the Universe. This paper summarizes recent progress in understanding the nature of these early galaxies, concentrating in particular on the clustering properties of photometrically selected ``Lyman break'' galaxies. Direct comparison of the data to predictions and physical insights provided by galaxy and structure formation models is particularly straightforward at these early epochs, and results in critical tests of the ``biased'', hierarchical galaxy formation paradigm. Comment: Presented at Royal Society Discussion Meeting, March 1998, "Large Scale Structure in the Universe", 14 pages LaTeX, 7 ps figures, uses rspublic.sty (included)
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The physical properties of the faint blue galaxy population are reviewed in the context of observational progress made via deep spectroscopic surveys and Hubble Space Telescope imaging of field galaxies at various limits, and theoretical models for the integrated star formation history of the Universe. Notwithstanding uncertainties in the properties of the local population of galaxies, convincing evidence has emerged from several independent studies for a rapid decline in the volume-averaged star formation rate of field galaxies since a redshift z~1. Together with the small angular sizes and modest mean redshift of the faintest detectable sources, these results can be understood in hierarchical models where the bulk of the star formation occurred at redshifts between z~1-2. The physical processes responsible for the subsequent demise of the faint blue galaxy population remains unclear. Considerable progress will be possible when the evolutionary trends can be monitored in the context of independent physical parameters such as the underlying galactic mass. Comment: 42 pages with 10 embedded figures available in gzipped postscript from ftp://ftp.ast.cam.ac.uk/pub/rse/annrev97.ps.gz To appear in Annual Reviews Astron. Astrophys. Vol 35, (1997)
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The Universidad Complutense de Madrid (UCM) Survey is a long-term project aiming at finding and analysing star-forming galaxies detected by their H$\alpha$ emission in Schmidt objective-prism plates. The instrumental set-up limits the volume of the Universe surveyed to a redshift $z\lesssim0.045$. So far we have discovered several hundred emission-line galaxies (ELGs) undergoing star formation at a wide range of levels. Analyzing a complete sample of ELGs from the UCM survey we have computed the H$\alpha$ luminosity function for the star-forming galaxies in the surveyed volume of the Universe. A Schechter function provides a good fit to the H$\alpha$ luminosity function with the following parameters: $\alpha = -1.3\pm0.2$; $L^*({\rm H}\alpha) = 10^{42.15\pm0.08} $erg$ $s$^{-1}$ and $\phi^*=10^{-3.2\pm0.2} $Mpc$^{-3}$ for $H_0 = 50 $km$ $s$^{-1} $Mpc$^{-1}$. Integrating over the full range of luminosities, we obtain an H$\alpha$ luminosity density of $10^{39.1\pm0.2} $erg$ $s$^{-1} $Mpc$^{-3}$. Using the H$\alpha$ emission as a star formation rate (SFR) estimator, this translates into a SFR density for the Local Universe of $0.013^{+0.007}_{-0.005} M_{\odot} $yr$^{-1} $Mpc$^{-3}$ in star-forming galaxies with $EW($H$\alpha+$[NII]$)>10$\AA and $z\lesssim0.045$, for a Scalo Initial Mass Function. This is the first observational determination of this quantity, which will provide a direct test of current galaxy formation and evolution models. Comment: 16 pages, PS file, 1 table and 1 figure. Accepted in ApJL
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