Atomic Hydrogen in Distant Galaxies
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Peculiar galaxy
In the preceding chapter I have discussed in considerable detail the properties of one individual galaxy – the Galaxy. In this chapter I discuss other galaxies (external galaxies) and I compare and contrast their properties with those of the Galaxy. The easiest property of a galaxy to discuss is its visual appearance. Soon after the existence of external galaxies had been established in the early 1920s it was realised that galaxies of regular shape could be divided into two main classes, spiral galaxies and elliptical galaxies. Subsequently it was realised that the spirals should be subdivided into ordinary spirals and barred spirals and that a further class known as lenticular galaxies should be introduced. In addition there were irregulars, galaxies possessing no obvious symmetry. In the 1930s Hubble introduced his classification of galactic types which, with some modifications, is still used today.
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Barred spiral galaxy
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Star formation activities dominate the evolution of galaxies. Elliptical galaxies are believed to be old galaxies in the Hubble sequence, and elliptical galaxies at different evolution epochs might have different star formation activities and/or morphologies. We investigate the connection between star formation rates and the morphology of elliptical galaxies. With the Sloan Digital Sky Survey (SDSS) and the Galaxy Zoo, we select a sample of elliptical galaxies by morphology and consider their infrared emission as an index of star formation rate to study the relation between the star formation rates and their morphological properties, such as ellipticities. In addition, we select some nearby spiral galaxies with very low MIR emission to probe the mechanisms of these red spiral galaxies. We display our preliminary results and discuss their implication on the evolution of galaxies in this poster.
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We prepare a catalog of the morphological types of 5840 galaxies within z = 0.01. We determine the morphological types by visual inspection using color images from the Sloan Digital Sky Survey (SDSS) DR7. The majority of the sample galaxies are SDSS spectroscopic target galaxies, but we add ~ 900 galaxies whose redshifts are available in the NASA Extra Galactic Database (NED). The fraction of elliptical and lenticular galaxies is ~ 0.06 while spiral galaxies comprise ~ 30% of the sample with a bar fraction of ~ 0.6. About half of sample are dwarf galaxies of which ~ 35% are dwarf elliptical-like galaxies. There is a strong correlation between the morphological types and luminosities of the galaxies, i.e., high luminosities in the early type galaxies and low luminosity in the late type galaxies. The mean luminosity of dwarf elliptical-like galaxies is similar to that of irregular galaxies.
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Dwarf spheroidal galaxy
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Invited Papers: Galaxy Types.- Morphology of Galaxies: An Overview.- The Luminosity Functions of Galaxies.- Elliptical Galaxies.- Structure and Kinematics of Spirals.- Brightest Cluster Members.- Central Regions of Early-Type Galaxies.- Stellar Content and Chemical Evolution in Spheroidal Populations.- Invited Papers: Galaxian Components.- Stellar Disks in Early-Type Galaxies.- Gaseous Disks in Elliptical Galaxies.- Formation and Maintenance of Spiral Structure.- Dark Matter in Elliptical Galaxies.- Dark Matter in Late-Type Galaxies.- Dark Matter in Dwarf Galaxies.- Elliptical Galaxies in X-Rays.- The Warm Component of the ISM of Elliptical Galaxies.- The Bar Component in Disk Galaxies.- Peculiar Kinematics.- Cold Gas in Elliptical Galaxies.- Cold Gas in Late-Type Galaxies.- Abundance Gradients and Related Properties in Galaxies.- Structure and Metallicity of Low-Luminosity Early-Type Galaxies.- Invited Papers: Environment and Systematics.- Interactions: Weak.- Interactions: Strong.- The Morphology of Binary Galaxies.- Intrinsic Shapes of Elliptical Galaxies.- On Understanding the Global Properties of Galaxies.- Galaxy Manifolds and Galaxy Formation.- Sub-Components in Elliptical Galaxies and their Formation.- Morphology and Classification of Galaxies - Where Do We Stand?.- Poster Papers.- Detailed Morphological Classification of Early-Type Galaxies in the Perseus Cluster.- Properties of Dwarf Spheroidals.- Bright Cores in Nearby Southern Galaxies.- Shell Formation and Thick Disks in Elliptical Galaxies.- The Origin of Strong Isophotal Twists in Elliptical Galaxies.- Photometric Properties of Disks in Elliptical Galaxies.- Elliptical Galaxies with Dark Matter.- Nuclear Dust-Discs in Radio Ellipticals.- Extended H? Filaments in Elliptical Galaxies.- The Origin of the Ionized Gas in S0 Galaxies.- Line-Strength Gradients in S0 Galaxies.- Ultraviolet Spectra of Early Type Galaxies.- On the Nature of the Compact Galaxies in the UGC.- Morphology of Galaxies Surrounding Compact Groups.- Mean Surface Density and Morphological Type in Disc-Galaxies.- Peculiar Kinematics in Interacting Elliptical Galaxies.- Morphology and Kinematics of Spiral Galaxies without Bar: The Importance of the Central Mass.- The Correlation between Velocity Gradients and Arm Classification in Spiral Galaxies.- Optical Line/Radio Luminosity Correlation and the Effects of the Interstellar Medium.- The Luminosity-Diameter Relation for Disk Galaxies: A Search for Environmental Effects.- Global Properties in Early Type Galaxies.- Masses and Mass-to-Light Ratios of Elliptical Galaxies.- On the Photometric Scaling Laws for Early-Type Galaxies.- Properties of Brightest Cluster Members.- The Fundamental Plane for Early-Type Galaxies.- Elliptical Galaxies and the Thickness of the Fundamental Plane.- Dissipationless Formation of Elliptical Galaxies.- The Two-Component Colour-Structure of the gE Galaxy NGC 4472.- The Velocity Dispersion Anisotropy in NGC 720.- NGC 205 and the Nature of Compact Nuclei in Dwarf Galaxies.- Light and Color Distribution in the Core of M32.- NGC 3384 and Its Saturn-Like Appearance.- Cigale Observations of NGC 3198.- Mapping the Star Formation in Nearby Galaxies: The Magellanic Irregular NGC 3109.- MM Observations of the Magellanic Clouds from Antarctica.- Seyfert Galaxies with Close Companions. A Method for Identification.- Globular Clusters as Probes of the Galactic Potential.- Relation between the Properties of Globular Cluster System and the Mass Distribution on the Galactic Disk.- Towards a Precise Definition of the Morphological Structures of Galaxies as a Basis for Their Automatic Classification.- Fourier Analysis of Barred Galaxies: A Convenient Alternative to the Component Decomposition.- Improvements of the Signal-to-Noise Ratio by Adaptive Filtering.- Index of Objects.
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Dwarf spheroidal galaxy
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We present results from two mid-infrared imaging programs of ultraluminous infrared galaxies (ULIRGs) and fine-structure elliptical galaxies. The former are known to nearly all be recent mergers between two gas-rich spiral galaxies, while the latter are also believed to be even more aged merger remnants. An examination of these two classes of objects, which may represent different stages of the same putative merger sequence, should reveal similarities in the distribution of their stellar populations and dust content consistent with that expected for time-evolution of the merger. The data reveal for the first time extended dust emission in the ULIRG galaxy bodies and along their tidal features. However, contrary to expectation, we find that the vast majority of the fine-structure elliptical galaxies lack such structured emission. This likely results from the optical selection of the elliptical sample, resulting in a population that reflects the IR-activity (or lack thereof) of optically selected interacting galaxies. Alternately, this may reflect an evolutionary process in the distribution of the dust content of the galaxy bodies.
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The positions of N galaxies in the (U-B, B-V) diagram are used together with the colors of various types of galaxies at corresponding redshifts to investigate whether the underlying galaxy components are spirals or ellipticals. It is assumed that an N galaxy consists of a reduced-luminosity quasar and a relatively normal galaxy of unknown morphological type with the quasar in its nucleus. The observed colors of 17 N galaxies are compared with predictions based on different morphological types for the underlying galaxy components. The results obtained are ambiguous in that they yield colors suggesting underlying spiral components for five of the N objects, either spiral or elliptical components for four others, elliptical components for five of them, and no fits for the remaining three. It is concluded that these results are consistent with the diverse galaxy types derived from a few detailed studies and also support the general pattern of continuity among quasars, N galaxies, and classical Seyfert galaxies.
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Blue early-type galaxies with galaxy-scale ongoing star formation are interesting targets in order to understand the stellar mass buildup in elliptical and S0 galaxies in the local Universe. We study the star-forming population of blue early-type galaxies to understand the origin of star formation in these otherwise red and dead stellar systems. The legacy survey imaging data taken with the dark energy camera in the $g$, $r$, and $z$ bands for 55 star-forming blue early-type galaxies were examined, and $g-r$ color maps were created. We identified low surface brightness features near 37 galaxies, faint-level interaction signatures near 15 galaxies, and structures indicative of recent merger activity in the optical color maps of all 55 galaxies. These features are not visible in the shallow Sloan Digital Sky Survey imaging data in which these galaxies were originally identified. Low surface brightness features found around galaxies could be remnants of recent merger events. The star-forming population of blue early-type galaxies could be post-merger systems that are expected to be the pathway for the formation of elliptical galaxies. We hypothesize that the star-forming population of blue early-type galaxies is a stage in the evolution of early-type galaxies. The merger features will eventually disappear, fuel for star formation will cease, and the galaxy will move to the passive population of normal early-type galaxies.
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Surface brightness fluctuation
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There is significant evidence suggesting that mergers of galaxies produce elliptical galaxies. To determine whether the known kinematic properties of elliptical galaxies are consistent with those of their suggested progenitors, we have examined the stellar velocity dispersion in 11 nuclear regions within starbursting infrared-luminous galaxies. All of these galaxies are in some stage of merging. The new data are presented and statistically analyzed in combination with data from the literature. We find that the kinematic and photometric properties of these galaxies suggest that they are the progenitors of low-luminosity (L < L*) elliptical galaxies. Dissipative collapse of gas followed by star formation is apparently not producing a core of high-density high-velocity dispersion stars like those found in very bright elliptical galaxies. We suggest that only the ultraluminous infrared galaxies can possibly produce L* ellipticals. We further present the results of population synthesis models that show that intermediate-age stellar populations should contribute significantly to the light of merger remnants even after the morphological signs of merging have vanished.
Peculiar galaxy
Velocity dispersion
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