Introduction

Redshifts are the lifeblood of cosmology. Until the demonstration that spiral nebulae are external galaxies, and the 1929 discovery by Hubble (Hubble 1929) that there is a correlation of the redshifts with apparent brightness, it was thought that the Universe was static. This is indeed why Einstein put a cosmological constant in his equations. After it appeared that Hubble's result was observational confirmation of the Friedmann–Lemaitre solution to Einstein's equations, it was generally accepted that the Universe is expanding.

Thus from 1930 onwards, there was a strong belief that redshifts could only be due either to Doppler motions away from the observer, as they had been found long ago in galactic stars, or if they were large and systematic they must be shifts due to the expansion of the Universe, and therefore they could be used for cosmological investigations.

Over the years considerable glamour has become attached to the study of large redshifts. This is because they are the only direct tools that give us some measure of what happened in the past, and if we can determine the rate of the expansion Ho we can get some idea of the time scale since the beginning ∼H, i.e., a time scale for the Universe. In this talk we want to give a brief survey of the way that the measurements of redshifts have gone over the last 75 years.

I have a dual role to play: As convener of this Panel Discussion and as a co-organizer of this meeting. So what I have to say is a mixture of the two.

First I wish to thank the panelists for expressing their points of view succinctly and also replying to the comments from the floor. Their differing points of view are what this meeting is about, namely a free and frank discussion of our current ideas about the origin of the Universe.

The majority view is expressed by Bertola and Blanchard, while the skeptical minority view is expressed by Disney and Burbidge. The majority view is simply that the standard model with specified parameters, having rather precisely determined values, explains all known facts of the Universe and that there is now a consensus amongst the community that this is so. Whatever remains to be understood can and should be explained only within this framework. This view is today called “precision cosmology” or “concordance cosmology.” Besides stating this premise, the view is that no other way of understanding the Universe has gone down to the same level of detail as the standard model and therefore all such alternatives cannot be compared to the standard model.

The minority view is that the successes claimed by the concordance model have been achieved at the expense of certain assumptions that have not been independently tested. These include inflation, non-baryonic dark matter, dark energy, etc. and the very high energy physics used as the basis of these ideas has not been tested in the laboratory. Further, there remain observed peculiarities, especially about redshifts, that cannot be understood by the standard model.

Abstract

The time has come to stop calling measured redshifts of extragalactic objects “anomalous” or “discordant.” Observational evidence over 38 years has made it clear that objects at the same distance from the observer can have strongly differing redshifts. Rigorous solutions of the basic mass, energy, and momentum equations show that redshift is primarily a function of the age of the matter constituting a galaxy. Reluctance to accept these results is blocking meaningful advance in physics and cosmology.

Introduction

Starting in 1966 evidence began to accumulate that high redshift quasars were physically associated with low redshift, relatively nearby galaxies. Of course the existence of even one redshift not caused primarily by recession velocity would negate the fundamental assumption on which all big-bang cosmology depends. In the ensuing 38 years a majority of extragalactic astronomers have built a complex and massively publicized edifice on the assumption that redshifts are an identical measure of distance. During these same decades a minority of astronomers have struggled to observe and report the increasingly powerful evidence that contradicts that crucial assumption.

In the present review we show only samples of this contradictory observational evidence taken from a body of evidence that is now too large for even book-sized discussions. Once the empirical rules of association are laid down the pictures and diagrams communicate at a glance more eloquently than text. As a result we will communicate here the main thread of the argument in pictorial form.

Abstract

We review evidence for the widespread occurrence of iron grains in the form of long slender whiskers of radii ∼0.01 μm and lengths in the range ∼5 μm and 1 mm in the Galaxy and in extragalactic sources. Such particles are characterized by their property of being able to thermalize starlight to much longer wavelengths than is possible with standard interstellar grains. The cosmological role of iron whiskers is briefly discussed.

Introduction

The existence of iron particles as a component of interstellar grains was first proposed by Schalén (1939), an iron composition being argued at the time by analogy with the composition of iron meteorites. Many years later we proposed that an iron component of grains may arise from the mass flows from protoplanetary nebulae, cool stars, and from the outflowing material of supernova explosions (Hoyle and Wickramasinghe 1968, 1970). Such a component was also shown to be consistent with data on the extinction curve of starlight (Wickramasinghe and Nandy 1972).

In our early models, however, the iron particles were regarded as being spherical or nearly spherical in shape, with radii typically ∼0.01 μm. Particles in the form of slender whiskers were considered only much later to account for the high grain emissivities required in certain galactic infrared sources, and also as a possible contributor to the cosmic microwave background (Wickramasinghe et al. 1975, Edmunds and Wickramasinghe 1975). The extinction properties in the visual and ultraviolet waveband for iron whiskers would be nearly identical to those of spherical particles of the same radius, provided the whiskers were in random orientation.

Introduction

Over the past decade, the observation of the galaxy distribution at large scale has made significant advances thanks to (i) the building of fiber spectrographs with a large field of view and a high multiplex gain (Lewis et al. 2002; Burles et al. 1999, Watson et al. 1998), and (ii) the dedication of large numbers of observing nights or the use of dedicated telescopes for such projects. These observations have led to extensive maps of the distribution of matter traced by the galaxies. The three major projects aimed at mapping the “local Universe” over large solid angles are:

• the 2dF Galaxy Redshift Survey, an Anglo-Australian collaboration;

• the Sloan Digital Sky Survey, a US–Japanese–German collaboration;

• the 6dF Galaxy Survey, another Anglo-Australian collaboration.

In the following, I review these surveys and the remarkable results that they have provided on the large-scale structure of the Universe. I also review the recent or undergoing surveys to higher depth.

The large solid angle surveys

The 2dF Galaxy Redshift Survey

The 2dF Galaxy Redshift Survey (2dFGRS) is now complete and covers ∼1 500 square degrees of the southern sky, distributed in two strip-like regions of 70 to 80° long in right ascension and∼10° and∼14° wide resp. in declination, plus∼80 single fields dispersed over the Southern Galactic Cap. The photometric catalog is based on the APM catalog (for “Automatic Plate Measuring machine” used to scan theUK Schmidt photographic plates; Maddox et al. 1990), which has been re-calibrated using CCD images. The limiting magnitude of the 2dFGRS is bJ = 19.45.

The feedback effects of massive stars on their galactic and intergalactic environments can dominate evolutionary processes in galaxies and affect cosmic structure in the Universe. Only the Local Group offers the spatial resolution to quantitatively study feedback processes on a variety of scales. Lyman continuum radiation from hot, luminous stars ionizes H II regions and is believed to dominate production of the warm component of the interstellar medium (ISM). Some of this radiation apparently escapes from galaxies into the intergalactic environment. Supernovae and strong stellar winds generate shell structures such as supernova remnants, stellar wind bubbles, and superbubbles around OB associations. Hot (106 K) gas is generated within these shells, and is believed to be the origin of the hot component of the ISM. Superbubble activity thus is likely to dominate the ISM structure, kinematics, and phase balance in starforming galaxies. Galactic superwinds in starburst galaxies enable the escape of mass, ionizing radiation, and heavy elements. Although many important issues remain to be resolved, there is little doubt that feedback processes plays a fundamental role in energy cycles on scales ranging from individual stars to cosmic structure. This contribution reviews studies of radiative and mechanical feedback in the Local Group.

Introduction

The Local Group is especially suited as a laboratory for studying the effects of the massive star population on the galactic environment. There are three types of massive star feedback:

1. (a) Radiative feedback, i.e., ionizing emission, which results in photoionized nebulae and diffuse, warm (104 K) ionized gas;

2. (b) Mechanical feedback, predominantly from supernovae (SNe), resulting in supernova remnants (SNRs), superbubbles, and galactic superwinds; and

3. […]

The Galaxy's extended halo contains numerous satellites which are in the process of being disrupted. This paper discusses the stages of satellite accretion onto the Galaxy with a focus on the Magellanic Clouds and Sagittarius dwarf galaxy. In particular, a possible gaseous component to the stellar stream of the Sgr dwarf is presented that has a total neutral hydrogen mass between 4–10×106 M⊙ at the distance to the stellar debris in this direction (36 kpc). This gaseous stream was most likely stripped from the main body of the dwarf 0.2–0.3 Gyr ago during its current orbit after a passage through a diffuse edge of the Galactic disk with a density > 10−4 cm−3. This gas represents the dwarf's last source of star formation fuel and explains how the galaxy was forming stars 0.5–2 Gyr ago. This is consistent with the star formation history and H I content of the other Local Group dwarf galaxies.

Introduction

Our Galaxy has built itself up by accreting satellite galaxies. This process if evident today through the satellites currently found in the extended Galactic halo. There are nine satellite galaxies within 150 kpc interacting with our Galaxy at various levels. These are in order of distance (Grebel, Gallagher, & Harbeck 2003): the Fornax dSph (138 kpc), the Carina dSph (94 kpc), the Sculptor dSph (88 kpc), the Sextans dSph (86 kpc), the Draco dSph (79 kpc), the Ursa Minor dSph (69 kpc), the Small Magellanic Cloud (63 kpc), the Large Magellanic Cloud (50 kpc), and the closest example of a recognizable accreting satellite is the Sagittarius Dwarf (28 kpc; hereafter Sgr dwarf).

There is increasing observational evidence that hot, highly ionized interstellar and intergalactic gas plays a significant role in the evolution of galaxies in the local universe. The primary spectral diagnostics of the warm-hot interstellar/intergalactic medium are ultraviolet and X-ray absorption lines of O VI and O VII. In this paper, I summarize some of the recent highlights of spectroscopic studies of hot gas in the Local Group and low-redshift universe. These highlights include investigations of the baryonic content of low-z Ovi absorbers, evidence for a hot Galactic corona or Local Group medium, and the discovery of a highly ionized high velocity cloud system around the Milky Way.

Introduction

We live in a wonderful age of discovery and exploration of the universe. As we peer farther and farther back in time, it is becoming ever more important to make sure that we observe the local universe as well as possible. Observations of galactic systems and the intergalactic medium (IGM) in the low-redshift universe are required to study the universe as it has evolved over the last ∼5 billion years. They are essential for the interpretation of higher redshift systems, and they form a framework for studies of such key topics as galactic evolution, “missing mass,” and the distribution of dark matter. Studies of hot gas and its relationship to galaxies are shedding new light on these and other astronomical topics of interest today. In this review, I summarize some basic information about the elemental species and types of observations that can be used to study hot gas.

The primordial abundances of deuterium, helium-3, helium-4, and lithium-7 probe the baryon density of the Universe only a few minutes after the Big Bang. Of these relics from the early Universe, deuterium is the baryometer of choice. After reviewing the current observational status of the relic abundances (a moving target!), the baryon density determined by big bang nucleosynthesis (BBN) is derived. The temperature fluctuation spectrum of the cosmic background radiation (CBR), established several hundred thousand years later, probes the baryon density at a completely different epoch in the evolution of the Universe. The excellent agreement between the BBN- and CBR-determined baryon densities provides impressive confirmation of the standard model of cosmology, permitting the study of extensions of the standard model. In combination with the BBN- and/or CBR-determined baryon density, the relic abundance of 4He provides an excellent chronometer, constraining those extensions of the standard model which lead to a nonstandard early-Universe expansion rate.

Introduction

As the hot, dense, early Universe rushed to expand and cool, it briefly passed through the epoch of big bang nucleosynthesis (BBN), leaving behind as relics the first complex nuclei: deuterium, helium-3, helium-4, and lithium-7. The abundances of these relic nuclides were determined by the competition between the relative densities of nucleons (baryons) and photons and, by the universal expansion rate. In particular, while deuterium is an excellent baryometer, He provides an accurate chronometer.

Our Milky Way Galaxy is a typical large spiral galaxy, representative of the most common morphological type in the local Universe. We can determine the properties of individual stars in unusual detail, and use the characteristics of the stellar populations of the Galaxy as templates in understanding more distant galaxies. The star formation history and merging history of the Galaxy is written in its stellar populations; these reveal that the Galaxy has evolved rather quietly over the last ∼10 Gyr. More detailed simulations of galaxy formation are needed, but this result apparently makes our Galaxy unusual if ∧CDM is indeed the correct cosmological paradigm for structure formation. While our Milky Way is only one galaxy, a theory in which its properties are very anomalous most probably needs to be revised. Happily, observational capabilities of next-generation facilities should, in the foreseeable future, allow the acquisition of detailed observations for all galaxies in the Local Group.

Introduction: The fossil record

The origins and evolution of galaxies such as our own MilkyWay and of their associated dark matter haloes are among the major outstanding questions of astrophysics. Detailed study of the zero-redshift Universe provides complementary constraints on models of galaxy formation to those obtained from direct study of high-redshift objects. Stars of mass similar to that of the Sun live for essentially the present age of the Universe and nearby low-mass stars can be used to trace conditions in the high-redshift Universe when they formed, perhaps even the ‘First Light’ that ended the Cosmological Dark Ages.

The spatial resolution and multiwavelength capability of the Hubble Space Telescope has advanced greatly the study of spheroidal populations of galaxies. The main sequence turnoff point of the Galactic bulge has been clearly measured and the proper motions of stars used to separate the foreground disk from the bulge. The study of bulge globular clusters by HST shows that the bulge field population is coeval with the halo. In the obscured Galactic Center, infrared imaging with NICMOS reveals a continuous star formation history. NICMOS imaging of the nucleus of M31 has settled a long standing debate about whether luminous AGB stars (possibly indicative of an intermediate age stellar population) are present. Measurements of the composition from the ground, and of the age from HST, are consistent with a scenario in which spheroidal populations formed very early. HST spectroscopy has also revealed the presence of central black holes in many bulges and spheroids. The formation of the stellar populations and black holes in spheroids was probably one of the earliest events in galaxy formation.

Introduction

The bulge populations of the Local Group are a window in the nearby Universe to some of the most important aspects of galaxy formation: The age (formation epoch) of bulge populations, their metal content, and their coevolution and connection with nuclear black holes. Spheroidal populations (including bulges) account for more than half of the stellar mass at the present epoch (Fukugita, Hogan, & Peebles 1998) and also even at redshift 0.7 (Bell et al. 2004). The connection between nearby and distant bulge populations is not a new revelation.

I review what is known about the general trends of metallicity and element abundance ratios in Local Group galaxies, and some implications of the abundance trends for chemical evolution. The Local Group spirals show radial metallicity gradients and a mean metallicity that increases with luminosity. The composition gradients steepen with decreasing galaxy luminosity, but are roughly similar when the gradients are derived per unit disk scale length. This suggests that the evolution of the metallicity gradient is closely tied to the evolution of the baryon distribution. The M31 and MilkyWay bulges appear to have similar metallicity distributions. The high [α/Fe] in Galactic bulge stars indicates that the bulge formed rapidly. Metallicity distributions for M31 and Galactic halo stars are also similar, except that M31 has more globular clusters that are metal-rich, possibly related to its larger bulge. M33 is anomalous in that its halo clusters may be significantly younger than the Galactic halo. Local Group irregular galaxies are metal-poor, and their mean metallicity correlates with galaxy luminosity. They have low effective yields, as derived from a comparison of mean metallicity with gas fraction, and the effective yield is correlated with galaxy rotation speed (or mass). This is evidence that the irregulars have lost metals to the IGM, either through galactic winds or stripping. Dwarf ellipticals in the Local Group are also metal-poor, and follow a similar metallicity-luminosity relation. The fact that the dEs have no gas also points to loss of metals as a significant factor in their evolution.

The Space Telescope Science Institute Symposium on “The Local Group as an Astrophysical Laboratory” took place during 5–8 May 2003.

The Local Group is in some sense the universe in a nutshell. The processes of galaxy mergers and interactions are the bread and butter of hierarchical structure formation. These processes can be studied in unsurpassed detail in the Local Group. Starburst regions in the LMC provide spectacular local versions of their high-redshift counterparts. While black holes are believed to reside at the centers of most galaxies, the best determination of the mass of a central black hole has been achieved in our own Galaxy (through the orbits of individual stars). In addition, the Local Group provides a rich census of star formation histories and of stellar populations. In short, before we attempt to understand the Universe, understanding our own backyard is a good start.

These proceedings represent only a part of the invited talks that were presented at the symposium. We thank the contributing authors for preparing their manuscripts.

We thank Sharon Toolan of ST ScI for her help in preparing this volume for publication.

Status quo and perspectives of standard chemical evolution models of Local Group galaxies are summarized, and what we have learned from them is discussed, as well as what we have not learned yet, and what I think will be learned in the near future. Galactic chemical evolution models have shown that: i) stringent constraints on primordial nucleosynthesis can be derived from the observed Galactic abundances of the light elements; ii) the Milky Way has been accreting external gas from early epochs to the present time; and iii) the vast majority of Galactic halo stars have formed quite rapidly at early epochs. Chemical evolution models for the closest dwarf galaxies, although still uncertain, are expected to become extremely reliable in the immediate future, thanks to the quality of new generation photometric and spectroscopic data which are currently being acquired.

Introduction

The proximity of Local Group galaxies makes them the ideal benchmarks to study galaxy formation and evolution, because they are the only systems where the accuracy and the wealth of observational data allows us to understand them in a sufficiently reliable way. In fact, to understand the evolution of galaxies, astronomers must follow two distinct and complementary approaches: on one hand they must develop theoretical models of galaxy formation, of chemical and dynamical evolution, and on the other hand, they must collect accurate observational data to constrain the models. It is of particular importance to acquire reliable data on chemical abundances, masses and kinematics of galactic components (gas, stars, dark matter), star formation (SF) regimes, and stellar initial mass function (IMF)—quantities that are best derived in nearby systems.