scholarly journals A New Age and Distance for I Zw 18, the Most Metal-Poor Galaxy in the Nearby Universe

2008 ◽  
Vol 4 (S255) ◽  
pp. 387-391
Author(s):  
A. Aloisi ◽  
G. Clementini ◽  
M. Tosi ◽  
F. Annibali ◽  
R. Contreras ◽  
...  
Keyword(s):  
High Resolution ◽  
Early Universe ◽  
Dwarf Galaxy ◽  
Hubble Space Telescope ◽  
Local Universe ◽  
Photometric Observations ◽  
The Galaxy ◽  
Cepheid Variables ◽  
History Of ◽  
Blue Compact Dwarf Galaxy

AbstractThe blue compact dwarf galaxy I Zw 18 holds the record of the lowest metallicity ever observed in the local universe. As such, it represents the closest analog to primordial galaxies in the early universe. More interestingly, it has recurrently been regarded as a genuinely young galaxy caught in the process of forming in the nearby universe. However, stars of increasingly older ages are found within I Zw 18 every time deeper high-resolution photometric observations are performed with the Hubble Space Telescope (HST): from the original few tens of Myrs to, possibly, several Gyrs. Here we summarize the history of I Zw 18 age and present an ongoing HST/ACS project which allowed us to precisely derive the galaxy distance by studying its Cepheid variables, and to firmly establish the age of its faintest resolved populations.

scholarly journals The Distance and Dynamical History of the Virgo Cluster Ultradiffuse Galaxy VCC 615

2022 ◽  
Vol 924 (2) ◽  
pp. 87
Author(s):  
J. Christopher Mihos ◽  
Patrick R. Durrell ◽  
Elisa Toloba ◽  
Patrick Côté ◽  
Laura Ferrarese ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Hubble Space Telescope ◽  
Virgo Cluster ◽  
Cluster Center ◽  
Main Body ◽  
The Galaxy ◽  
Orbit Modeling ◽  
History Of ◽  
Red Giant ◽  
Distance Estimator

Abstract We use deep Hubble Space Telescope imaging to derive a distance to the Virgo Cluster ultradiffuse galaxy (UDG) VCC 615 using the tip of the red giant branch (TRGB) distance estimator. We detect 5023 stars within the galaxy, down to a 50% completeness limit of F814W ≈ 28.0, using counts in the surrounding field to correct for contamination due to background sources and Virgo intracluster stars. We derive an extinction-corrected F814W tip magnitude of m tip , 0 = 27.19 − 0.05 + 0.07 , yielding a distance of d = 17.7 − 0.4 + 0.6 Mpc. This places VCC 615 on the far side of the Virgo Cluster (d Virgo = 16.5 Mpc), at a Virgocentric distance of 1.3 Mpc and near the virial radius of the main body of Virgo. Coupling this distance with the galaxy’s observed radial velocity, we find that VCC 615 is on an outbound trajectory, having survived a recent passage through the inner parts of the cluster. Indeed, our orbit modeling gives a 50% chance the galaxy passed inside the Virgo core (r < 620 kpc) within the past gigayear, although very close passages directly through the cluster center (r < 200 kpc) are unlikely. Given VCC 615's undisturbed morphology, we argue that the galaxy has experienced no recent and sudden transformation into a UDG due to the cluster potential, but rather is a long-lived UDG whose relatively wide orbit and large dynamical mass protect it from stripping and destruction by the Virgo cluster tides. Finally, we also describe the serendipitous discovery of a nearby Virgo dwarf galaxy projected 90″ (7.2 kpc) away from VCC 615.

scholarly journals A multi-frequency study of the Wolf-Rayet blue compact dwarf galaxy He2-10

1999 ◽  
Vol 193 ◽  
pp. 610-611
Author(s):  
David I. Méndez ◽  
César Esteban ◽  
Miroslav D. Filipović ◽  
Matthias Ehle ◽  
Prank Haberl ◽  
...  
Keyword(s):  
High Resolution ◽  
Supernova Remnants ◽  
Dwarf Galaxy ◽  
Mechanical Action ◽  
Radio Continuum ◽  
High Resolution Spectroscopy ◽  
Continuum Emission ◽  
Star Forming ◽  
The Galaxy ◽  
Blue Compact Dwarf Galaxy

We present preliminary results on multi-wavelength observations of the Wolf-Rayet Blue Compact Dwarf Galaxy He2–10. These observations include Hα and continuum imaging, high-resolution Hα spectroscopy, high-resolution radio-continuum mapping at 6.3 and 3.5 cm and X-ray mapping. The deep Hα image reveals that the galaxy consists of a complex system of different star-forming knots surrounded by kpc-scale bubble-like and filamentary structures. The most interesting structure is a bipolar superbubble centered on the most intense star-formation knot. High-resolution spectroscopy of this structure indicates that it is expanding with a velocity in the range 75–250 km s−1. This kind of outflows is likely to be produced by the mechanical action of stellar winds and supernovae explosions in the intense starbursts that the galaxy hosts. This scenario is consistent with the finding of a very steep radio spectral index in the extended radio continuum emission (α = −0.59) that confirms the presence of a large number of supernova remnants in the galaxy.

scholarly journals HERMES – An instrument of the future

2009 ◽  
Vol 5 (S262) ◽  
pp. 448-449 ◽  
Author(s):  
Elizabeth Wylie-de Boer ◽  
Kenneth Freeman
Keyword(s):  
Star Formation ◽  
High Resolution ◽  
Resolving Power ◽  
Individual Stars ◽  
Elemental Abundances ◽  
The Future ◽  
The Galaxy ◽  
History Of ◽  
High Resolution Spectrometer ◽  
Resolution Spectrometer

AbstractHERMES is a new, multi-object high resolution spectrometer for the 3.9m Anglo Australian Telescope, using the existing 2dF positioner. The primary goal of the HERMES survey is to unravel the history of the Galaxy from detailed elemental abundances for about 1.2 million individual stars. The HERMES chemical tagging survey concentrates on the 5000 to 8000 Å window at a resolving power of 30,000 in order to identify dissolved star formation aggregates and ascertain the importance of mergers throughout the history of the Galaxy.

scholarly journals The Dark Blue Compact Dwarf Galaxy NGC 2915

1997 ◽  
Vol 14 (1) ◽  
pp. 77-80 ◽  
Author(s):  
Gerhardt R. Meurer
Keyword(s):  
Dark Matter ◽  
Mass Distribution ◽  
Dwarf Galaxy ◽  
Dark Matter Halo ◽  
High Mass ◽  
Mass Star ◽  
Normal Galaxies ◽  
The Galaxy ◽  
Dark Blue ◽  
Blue Compact Dwarf Galaxy

AbstractRecent results on NGC 2915, the first blue compact dwarf galaxy to have its mass distribution modelled, are summarised. NGC 2915 is shown to have HI well beyond its detected optical extent. Its rotation curve is well determined and fit with maximum disk mass models. The dark matter halo dominates the mass distribution at nearly all radii, and has a very dense core compared to those of normal galaxies. High-mass star formation energises the HI in the centre of the galaxy, but appears to be maintained in viriai equilibrium with the dark matter halo. The implications of these results are briefly discussed.

scholarly journals Origin of the galaxy morphology

2003 ◽  
Vol 208 ◽  
pp. 431-432
Author(s):  
N. Nakasato
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
High Resolution ◽  
Cold Dark Matter ◽  
Star Formation History ◽  
The Galaxy ◽  
Particle Hydrodynamics ◽  
History Of ◽  
Analytic Models ◽  
Galaxy Morphology

In the current most plausible Cold Dark Matter (CDM) cosmology, larger halos increase their mass by the progressive mergers of smaller clumps. Due to these progressive merger events, galaxies have formed and evolved. Such merger events could trigger star bursts depending on mass of a merging object. In other words, star formation history reflects the strength of the interaction between a galaxy and merging objects. Also, a several merger events strongly affect the development of the morphology of galaxies as assumed in semi-analytic models. In the most advanced semi-analytic models, N-body simulations of dark matter particles are used to obtain the merging history of halos. By combining the description of radiative cooling, hydrodynamics and star formation with the obtained merging history, such models successfully have explained the various qualitative predictions. Here, we show the results of similar approach but using a fullly numerical model. In contrast to the semi-analytic models, we use our high resolution Smoothed Particle Hydrodynamics (SPH) models. With our SPH code, we try to tackle the problem of the galaxy morphology. We have done a several handful high-resolution SPH simulations and analyzed the merging history of such models. Accordingly, we can see the relation between the obtained morphology and the merging history or other physical properties of the model.

scholarly journals Haro15: Is it actually a low metallicity galaxy?

2009 ◽  
Vol 5 (S265) ◽  
pp. 243-244
Author(s):  
Verónica Firpo ◽  
Guillermo Bosch ◽  
Guillermo Hägele ◽  
Ángeles I. Díaz ◽  
Nidia Morrell
Keyword(s):  
Dwarf Galaxy ◽  
Empirical Methods ◽  
Chemical Abundances ◽  
Physical Conditions ◽  
Ionization Structure ◽  
The Galaxy ◽  
Low Metallicity ◽  
Echelle Spectroscopy ◽  
Abundance Determination ◽  
Blue Compact Dwarf Galaxy

AbstractWe present a detailed study of the physical properties of the nebular material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study the physical conditions (electron density and temperature), ionic and total chemical abundances of several atoms, reddening and ionization structure. The latter was derived by comparing the oxygen and sulphur ionic ratios to their corresponding observed emission line ratios (the η and η' plots) in different regions of the galaxy. Applying direct and empirical methods for abundance determination, we perform a comparative analysis between these regions.

scholarly journals The Evolutionary History of the Milky Way

1996 ◽  
Vol 171 ◽  
pp. 3-10
Author(s):  
K.C. Freeman
Keyword(s):  
Evolutionary History ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Galactic Disk ◽  
Small Satellite ◽  
Galactic Bulge ◽  
The Galaxy ◽  
History Of ◽  
Satellite Galaxies

The accretion of small satellite galaxies appears to have been important in the formation of the metal-poor halo of the Galaxy. The disrupting Sgr dwarf galaxy and the recent discovery of a young, metal-poor component of the halo indicate that this is a continuing process. The evolution of the galactic disk, and some consequences of the bar-like nature of the galactic bulge are briefly discussed.

scholarly journals Nearby Blue Compact Dwarf Galaxy NGC 6789

1999 ◽  
Vol 192 ◽  
pp. 253-258
Author(s):  
I. Drozdovsky ◽  
N. Tikhonov
Keyword(s):  
Surface Brightness ◽  
Dwarf Galaxy ◽  
High Surface ◽  
Low Surface Brightness ◽  
The Galaxy ◽  
Metal Abundance ◽  
The Mean ◽  
Red Giant ◽  
Halo Population ◽  
Blue Compact Dwarf Galaxy

We present the results of a detailed BVRI and Hα study of the isolated nearby blue compact dwarf (BCD) galaxy NGC 6789. Judging from the literature the observed galaxy has not yet been resolved into stars up to now. On CCD frames obtained with 6m BTA telescope and 2.5m Nordic telescope the galaxy is well resolved. Its colour-magnitude diagram confirms the two component (core-halo) galaxy morphology, which consists of two stellar populations distinct in structure and colour: an inner high surface-brightness young population within 150 pc from the center of the galaxy, and a relatively low surface-brightness intermediate-age population extending out to at least 600 pc. The distance to the galaxy, estimated from the tip of the red giant branch (TRGB) is 2.1 Mpc which places NGC 6789 close to the Local Group. From the mean colour of the RGB, the mean metal abundance of the halo population is estimated as [Fe/H] ≃ −1 dex.

NIHAO-UHD: High-resolution Simulations of MW mass galaxies

2017 ◽  
Vol 13 (S334) ◽  
pp. 209-212
Author(s):  
Tobias Buck ◽  
Andrea Macciò ◽  
Melissa Ness ◽  
Aura Obreja ◽  
Aaron Dutton
Keyword(s):  
High Resolution ◽  
Milky Way ◽  
Satellite System ◽  
The Galaxy ◽  
First Results ◽  
History Of ◽  
Galaxy Center ◽  
Hydrodynamical Simulations ◽  
Very High ◽  
Disc Galaxies

AbstractHigh resolution cosmological and hydrodynamical simulations have reached a resolution able to resolve in a self consistent way the disc of our galaxy, the galaxy center and the satellites orbiting around it. We present first results from the NIHAO-UHD project, a set of very high-resolution baryonic zoom-in simulations of Milky Way mass disc galaxies. These simulations model the full cosmological assembly history of the galaxies and their satellite system using the same, well tested physics as the NIHAO project. We show that these simulations can self-consistently reproduce the observed kinematical and morphological features of the X-shaped bulge observed in our own Milky Way.

scholarly journals Optical and Ultraviolet Spectral Morphology of Luminous OB Stars in the Galaxy and the Magellanic Clouds

1986 ◽  
Vol 116 ◽  
pp. 185-198 ◽  
Author(s):  
Nolan R. Walborn
Keyword(s):  
High Resolution ◽  
Hubble Space Telescope ◽  
Optical Data ◽  
High Resolution Data ◽  
Ob Stars ◽  
Central Cluster ◽  
Distant Galaxies ◽  
The Galaxy ◽  
H Ii Region ◽  
30 Doradus

Three areas of current progress relevant to the theme of this Symposium will be discussed. (1) New spectroscopic observations of the 30 Doradus central cluster, obtained independently by the author and by J. Melnick, confirm the presence of numerous very early O-type members, including several of type O3. In combination with sophisticated new direct imagery of the luminous central object R136 by A. Walker and by G. Weigelt, these results have evident implications for understanding the ionization of the supergiant H II region, as well as for the interpretation of R136 itself and of the apparently similar regions seen in more distant galaxies. In particular, no evidence remains for a supermassive object in 30 Doradus, but its central cluster is revealed as a spectacular grouping of very massive hot stars. (2) A further member of the Ofpe/WN9 category in the LMC has been identified, bringing their number to seven, with no exact spectroscopic counterparts yet known in the Galaxy. One of these objects is currently in a state of outburst and has been interpreted by O. Stahl et al. as the hottest known Hubble-Sandage variable. (3) An extensive survey of IUE high-resolution data has revealed a strong correlation between the ultraviolet stellar wind features and the optical spectral classifications for the majority of normal O stars. These results are relevant to future studies with the High Resolution Spectrograph on the Hubble Space Telescope, which may observe restricted UV wavelength ranges in faint extragalactic OB stars lacking optical data of comparable quality.

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