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.

Rotating Halos and Heavy Disks: the Case of NGC 2915

2004 ◽  
Vol 217 ◽  
pp. 172-173
Author(s):  
Frédéric S. Masset ◽  
Martin Bureau
Keyword(s):  
Surface Brightness ◽  
Spiral Structure ◽  
Dwarf Galaxy ◽  
Neutral Hydrogen ◽  
Dark Halo ◽  
Pattern Frequency ◽  
Spin Parameter ◽  
Low Surface Brightness ◽  
Hydrodynamical Simulations ◽  
Blue Compact Dwarf Galaxy

NGC 2915 is a blue compact dwarf galaxy embedded in an extended, low surface brightness HI disk with a bar and two-armed spiral structure. Common mechanisms are unable to explain those patterns and disk dark matter or a rotating triaxial dark halo were proposed as alternatives. Hydrodynamical simulations were run for each case and compared to observations using customized column density and kinematic constraints. The spiral structure can be accounted for by an unseen bar or triaxial halo, but the large bar mass or halo pattern frequency required make it unlikely that the spiral is driven by an external perturber. In particular, the spin parameter lambda is much higher than predicted by current CDM structure formation scenarios. Massive disk models show that when the gas surface density is scaled up by a factor of about 10, the disk develops a spiral structure matching the observed one in perturbed density as well as velocity. This suggests that the disk of NGC 2915 contains much more mass than is visible tightly linked to the neutral hydrogen. A classic (quasi-)spherical halo is nevertheless still required, as increasing the disk mass further to fit the circular velocity curve would make the disk violently unstable

scholarly journals Wolf-Rayet Populations in Dwarf Galaxies

1991 ◽  
Vol 143 ◽  
pp. 601-612
Author(s):  
Lindsey F. Smith
Keyword(s):  
Surface Brightness ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
High Surface ◽  
Hii Regions ◽  
Necessary Condition ◽  
Large Numbers ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
High Metallicity

The Wolf-Rayet (WR) feature at 4650 A is observed in about 10% of the dwarf galaxies with high surface brightness knots. The intensity of the feature implies the presence of tens to thousands of WR stars. Hbeta fluxes imply correspondingly large numbers of O stars. The easily observed intensity ratio WRbump/Hbeta is a measure of the WR/O star numbers.The metallicity of dwarf galaxies ranges from Z = Zo/30 to Zo/2, or O/H” = log(O/H)+12 = 7.4 to 8.6. WRbump/Hbeta correlates with O/H′ and O/H″ > 7.9 appears to be a necessary condition for the presence of the WR feature. Giant HII regions in ordinary galaxies extend to higher than solar metallicities and, in extreme cases, WR/O ≈ 1 are implied.The subtypes present in giant HII regions in nearby galaxies appear to be exclusively late type WN and, occasionally, early type WC. Spectra of most BCD galaxies are compatible with a similar population. However, some high metallicity giant HII regions in large galaxies appear to have stronger NIII4640 relative to HeII4686 than occurs in WN subtypes in the Galaxy and the Magellanic Clouds.The data needed for more detailed analysis of dwarf galaxy observations is collected.

scholarly journals The blue compact dwarf galaxy I Zw 18: A comparative study of its low-surface-brightness component

2002 ◽  
Vol 393 (2) ◽  
pp. 461-483 ◽  
Author(s):  
P. Papaderos ◽  
Y. I. Izotov ◽  
T. X. Thuan ◽  
K. G. Noeske ◽  
K. J. Fricke ◽  
...  
Keyword(s):  
Comparative Study ◽  
Surface Brightness ◽  
Dwarf Galaxy ◽  
Low Surface Brightness ◽  
Blue Compact Dwarf Galaxy

scholarly journals Rotating Halos and Heavy Disks: The Case of NGC 2915

2004 ◽  
Vol 220 ◽  
pp. 293-298
Author(s):  
Frédéric S. Masset ◽  
Martin Bureau
Keyword(s):  
Surface Brightness ◽  
Spiral Structure ◽  
Dwarf Galaxy ◽  
Neutral Hydrogen ◽  
Dark Halo ◽  
Pattern Frequency ◽  
Spin Parameter ◽  
Low Surface Brightness ◽  
Hydrodynamical Simulations ◽  
Blue Compact Dwarf Galaxy

NGC 2915 is a blue compact dwarf galaxy embedded in an extended, low surface brightness HI disk with a bar and two-armed spiral structure. Common mechanisms are unable to explain those patterns and disk dark matter or a rotating triaxial dark halo were proposed as alternatives. Hydrodynamical simulations were run for each case and compared to observations using customized column density and kinematic constraints. the spiral structure can be accounted for by an unseen bar or triaxial halo, but the large bar mass or halo pattern frequency required make it unlikely that the spiral is driven by an external perturber. in particular, the spin parameter lambda is much higher than predicted by current CDM structure formation scenarios. Massive disk models show that when the gas surface density is scaled up by a factor of about 10, the disk develops a spiral structure matching the observed one in perturbed density as well as velocity. This suggests that the disk of NGC 2915 contains much more mass than is visible, tightly linked to the neutral hydrogen. A classic (quasi-)spherical halo is nevertheless still required, as increasing the disk mass further to fit the circular velocity curve would make the disk violently unstable

scholarly journals The haloes and environments of nearby galaxies (HERON) – I. Imaging, sample characteristics, and envelope diameters

2019 ◽  
Vol 490 (2) ◽  
pp. 1539-1569 ◽  
Author(s):  
R Michael Rich ◽  
Aleksandr Mosenkov ◽  
Henry Lee-Saunders ◽  
Andreas Koch ◽  
John Kormendy ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Dwarf Galaxy ◽  
Sky Survey ◽  
Low Surface Brightness ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Sample Characteristics ◽  
S0 Galaxies ◽  
Red Sequence

ABSTRACT We use a dedicated 0.7-m telescope to image the haloes of 119 galaxies in the Local Volume to μr ∼ 28–30 mag arcsec−2. The sample is primarily from the Two Micron All Sky Survey Large Galaxy Atlas (Jarrett et al. 2003) and extended to include nearby dwarf galaxies and more distant giant ellipticals, and spans fully the galaxy colour–magnitude diagram including the blue cloud and red sequence. We present an initial overview, including deep images of our galaxies. Our observations reproduce previously reported low surface brightness structures, including extended plumes in M 51, and a newly discovered tidally extended dwarf galaxy in NGC 7331. Low surface brightness structures, or ‘envelopes’, exceeding 50 kpc in diameter are found mostly in galaxies with MV < −20.5, and classic interaction signatures are infrequent. Defining a halo diameter at the surface brightness 28 mag arcsec−2, we find that halo diameter is correlated with total galaxy luminosity. Extended signatures of interaction are found throughout the galaxy colour–magnitude diagram without preference for the red or blue sequences, or the green valley. Large envelopes may be found throughout the colour–magnitude diagram with some preference for the bright end of the red sequence. Spiral and S0 galaxies have broadly similar sizes, but ellipticals extend to notably greater diameters, reaching 150 kpc. We propose that the extended envelopes of disc galaxies are dominated by an extension of the disc population rather than by a classical Population II halo.

scholarly journals On the general structure of giant low surface brightness galaxy Malin 2

2012 ◽  
Vol 8 (S295) ◽  
pp. 236-236
Author(s):  
A. S. Saburova ◽  
A. V. Kasparova ◽  
I. Yu. Katkov ◽  
D. V. Bizyaev ◽  
I. V. Chilingarian
Keyword(s):  
Surface Brightness ◽  
General Structure ◽  
High Surface ◽  
Gas Pressure ◽  
Distribution Model ◽  
Dark Halo ◽  
Surface Photometry ◽  
Radial Profiles ◽  
Low Surface Brightness ◽  
The Galaxy

AbstractWe carried out the multicolor surface photometry in BVR and griz filters parallel with stellar kinematic measurements from the long slit spectra for the low surface brightness galaxy Malin 2. The use of the multicolor surface photometry as well as the available HI rotation curve allowed us to construct the mass distribution model of the galaxy. Photometrical and dynamical mass estimates agree with the dark halo mass fraction of about 70% within four disc radial scalelengths (~ 70 kpc). We used our dynamical model to obtain radial profiles of the equilibrium disc volume density and gas pressure in the galaxy midplane based on the available HI and CO data. The observed molecular gas fraction appears to be much higher than in the high surface brightness galaxies for a similar gas pressure.

scholarly journals Dwarf Elliptical Galaxies in the M81 Group: The Structure and Stellar Populations of BK5N and F8D1

1998 ◽  
Vol 11 (1) ◽  
pp. 132-133
Author(s):  
Taft E. Armandroff ◽  
Nelson Caldwell ◽  
G.S. Da Costa ◽  
Patrick Seitzer
Keyword(s):  
Surface Brightness ◽  
Local Group ◽  
Absolute Magnitude ◽  
Groups Of Galaxies ◽  
Central Surface ◽  
Luminous Matter ◽  
Total Magnitude ◽  
Metal Abundance ◽  
The Mean ◽  
Red Giant

The M81 group is one of the nearest groups of galaxies, but its properties are quite different from those of the Local Group. It has therefore provided a different environment for the evolution of its member galaxies. We have carried out a CCD survey of the M81 group to search for analogs to Local Group dwarf elliptical (dE) galaxies. All the M81 dwarfs previously identified in photographic surveys were recovered and we also discovered several new systems whose surface brightnesses fall within the range found for Local Group dE’s. We have obtained HST WFPC2 images through the F555W and F814W filters of two M81 group dE’s: BK5N and a new system, designated F8D1. The resulting color-magnitude diagrams show the upper two magnitudes of the red giant branch. The I magnitudes of the red giant branch tip in both galaxies yield distances that are consistent with membership in the M81 group. Surface brightness and total magnitude measurements indicate that BK5N and F8D1 have similar central surface brightness (24.5 and 25.4 mag arcsec-2 in V, respectively), but F8D1 is larger length scale results in it being 3 magnitudes more luminous than BK5N. BK5N lies on the relation between central surface brightness and absolute magnitude defined by Local Group dwarf ellipticals, but F8D1 does not. F8D1 is more luminous for its central surface brightness than the relation predicts, similar to the large low surface brightness dwarf galaxies found in, for example, Virgo. The mean color of the giant branch is used to establish the mean abundance of each galaxy. F8D1, the more luminous galaxy, is significantly more metal rich ([Fe/H] ≈ -1.0) than BK5N ([Fe/H] ≈ -1.7). Both BK5N and F8D1 lie on the relation between absolute magnitude and metal abundance defined by Local Group dwarf ellipticals. However, as regards the relation between central surface brightness and metal abundance, BK5N again follows the Local Group dwarfs, while F8D1 deviates significantly from this relation. This suggests that the total amount of luminous matter is more fundamental in controlling metal enrichment than the surface density of luminous matter. We have also used the color width of the giant branch compared with the photometric errors to establish abundance ranges in both galaxies, the sizes of which are comparable to those in Local Group dE’s.

scholarly journals Delayed Stellar Mass Assembly in the Low Surface Brightness Dwarf Galaxy KDG 215

2018 ◽  
Vol 864 (1) ◽  
pp. L14 ◽  
Author(s):  
John M. Cannon ◽  
Zili Shen ◽  
Kristen B. W. McQuinn ◽  
Joshua Bartz ◽  
Lilly Bralts-Kelly ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Dwarf Galaxy ◽  
Stellar Mass ◽  
Low Surface Brightness ◽  
Mass Assembly

scholarly journals The last breath of the Sagittarius dSph

2020 ◽  
Vol 497 (4) ◽  
pp. 4162-4182 ◽  
Author(s):  
Eugene Vasiliev ◽  
Vasily Belokurov
Keyword(s):  
Milky Way ◽  
Dwarf Galaxy ◽  
3D Structure ◽  
Major Axis ◽  
Final State ◽  
Tidal Forces ◽  
The Galaxy ◽  
The Mean ◽  
Red Clump ◽  
Astrometric Data

ABSTRACT We use the astrometric and photometric data from Gaia Data Release 2 and line-of-sight velocities from various other surveys to study the 3D structure and kinematics of the Sagittarius dwarf galaxy. The combination of photometric and astrometric data makes it possible to obtain a very clean separation of Sgr member stars from the Milky Way foreground; our final catalogue contains 2.6 × 105 candidate members with magnitudes G &lt; 18, more than half of them being red clump stars. We construct and analyse maps of the mean proper motion and its dispersion over the region ∼30 × 12 deg, which show a number of interesting features. The intrinsic 3D density distribution (orientation, thickness) is strongly constrained by kinematics; we find that the remnant is a prolate structure with the major axis pointing at ∼45° from the orbital velocity and extending up to ∼5 kpc, where it transitions into the stream. We perform a large suite of N-body simulations of a disrupting Sgr galaxy as it orbits the Milky Way over the past 2.5 Gyr, which are tailored to reproduce the observed properties of the remnant (not the stream). The richness of available constraints means that only a narrow range of parameters produce a final state consistent with observations. The total mass of the remnant is $\sim \!4\times 10^8\, \mathrm{M}_\odot$, of which roughly a quarter resides in stars. The galaxy is significantly out of equilibrium, and even its central density is below the limit required to withstand tidal forces. We conclude that the Sgr galaxy will likely be disrupted over the next Gyr.

scholarly journals Kinematics of Planetary Nebulae in M51's Tidal Tail

2003 ◽  
Vol 209 ◽  
pp. 633-634
Author(s):  
John J. Feldmeier ◽  
J. Christopher Mihos ◽  
Patrick R. Durrell ◽  
Robin Ciardullo ◽  
George H. Jacoby
Keyword(s):  
Surface Brightness ◽  
Numerical Models ◽  
Planetary Nebulae ◽  
Tidal Tail ◽  
Low Surface Brightness ◽  
Galaxy Interaction ◽  
Self Consistent ◽  
The Galaxy ◽  
Interacting Systems ◽  
Kinematic Properties

The galaxy pair NGC 5194/95 (M51) is one of the closest and best known interacting systems. Despite its notoriety, however, many of its features are not well studied. Extending westward from NGC 5195 is a low surface brightness tidal tail, which can only be seen in deep broadband exposures. Our previous [O III] λ5007 planetary nebulae (PN) survey of M51 recovered this tidal tail, and presented us with a opportunity to study the kinematics of a galaxy interaction in progress. We report the results of a spectroscopy survey of the PN, aimed at determining their kinematic properties. We then use these data to constrain new self-consistent numerical models of the system.

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