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

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

Download Full-text

Nearby Blue Compact Dwarf Galaxy NGC 6789

Symposium - International Astronomical Union ◽

10.1017/s0074180900204191 ◽

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.

Download Full-text

Rotating Halos and Heavy Disks: The Case of NGC 2915

Symposium - International Astronomical Union ◽

10.1017/s007418090018341x ◽

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

Download Full-text

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

The Astrophysical Journal ◽

10.3847/2041-8213/aada48 ◽

2018 ◽

Vol 864 (1) ◽

pp. L14 ◽

Cited By ~ 1

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

Download Full-text

Gas-rich LSB Galaxies – Progenitors of Blue Compact Dwarfs?

International Astronomical Union Colloquium ◽

10.1017/s0252921100054415 ◽

1999 ◽

Vol 171 ◽

pp. 253-260 ◽

Cited By ~ 1

Author(s):

John J. Salzer ◽

Stuart A. Norton

Keyword(s):

Star Formation ◽

Surface Brightness ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Mass Density ◽

Central Mass ◽

Galaxy Distribution ◽

Low Surface Brightness ◽

Central Regions ◽

Lsb Galaxies

AbstractWe analyze deep CCD images of nearby Blue Compact Dwarf (BCD) galaxies in an attempt to understand the nature of the progenitors which are hosting the current burst of star formation. In particular, we ask whether BCDs are hosted by normal or low-surface-brightness dI galaxies. We conclude that BCDs are in fact hosted by gas-rich galaxies which populate the extreme high-central-mass-density end of the dwarf galaxy distribution. Such galaxies are predisposed to having numerous strong bursts of star formation in their central regions. In this picture, BCDs can only occur in the minority of dwarf galaxies, rather than being a common phase experienced by all gas-rich dwarfs.

Download Full-text

Star Formation Thresholds in Low Surface Brightness Dwarf Galaxies

International Astronomical Union Colloquium ◽

10.1017/s0252921100054440 ◽

1999 ◽

Vol 171 ◽

pp. 274-281

Author(s):

Liese van Zee

Keyword(s):

Star Formation ◽

Comparative Study ◽

Column Density ◽

Surface Brightness ◽

Dwarf Galaxies ◽

Critical Threshold ◽

Active Star ◽

Comparison Sample ◽

Active Star Formation ◽

Low Surface Brightness

AbstractThe results of a comparative study of star formation thresholds in gas-rich, low surface brightness, dwarf galaxies are presented. Approximately half the galaxies in the study were “high MH/LB” galaxies, which appear to have inefficient star formation properties. The comparison sample comprised of otherwise “normal” dwarf galaxies, with moderate current star formation rates. In all systems, sites of active star formation were associated with local peaks in the HI column density. For both types of galaxies, the azimuthally averaged gas column density is low. Similar to other LSB systems, the global gas densities are well below the critical threshold for star formation throughout the system. Thus, star formation is inhibited globally, but occurs locally in these gas-rich dwarf galaxies.

Download Full-text

VLA HI Imaging of the Low Surface Brightness Dwarf Galaxy DDO 47

International Astronomical Union Colloquium ◽

10.1017/s0252921100054373 ◽

1999 ◽

Vol 171 ◽

pp. 224-227 ◽

Cited By ~ 2

Author(s):

F. Walter ◽

E. Brinks

Keyword(s):

Surface Brightness ◽

Dwarf Galaxy ◽

Dynamical Analysis ◽

Stellar Winds ◽

Mass Model ◽

Dynamical Mass ◽

Systemic Velocity ◽

Low Surface Brightness ◽

Simple Mass ◽

Hi Shells

AbstractWe present high resolution VLA-observations of the nearby Low Surface Brightness Dwarf Galaxy DDO 47. This object shows many hole-like structures in its neutral interstellar medium. The majority of the detected H I-shells are found to be expanding. Their origin is therefore believed to be due to stellar winds of the most massive stars and their subsequent supernova (SN type II) explosions within regions of recent star formation (SF). Current SF in DDO 47 is predominantly present on the rims of the HI-shells suggesting propagating SF. At a projected distance of 20 kpc (adopting a distance to DDO 47 of 4 Mpc), a companion galaxy was detected at almost the same systemic velocity (DDO 47 B). A search for an optical identification suggests that CGCG 087-033 is the optical counterpart of the companion. A preliminary dynamical analysis based on DDO 47’s rotation curve yields that it is dark matter dominated (about 80% of its dynamical mass is in some non-visible form). A simple mass model suggests that DDO 47 is one of the ‘thickest’ dwarf galaxies studied so far.

Download Full-text

Probing the low surface brightness dwarf galaxy population of the virgo cluster

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stv2719 ◽

2015 ◽

Vol 456 (2) ◽

pp. 1607-1617 ◽

Cited By ~ 20

Author(s):

J. I. Davies ◽

L. J. M. Davies ◽

O. C. Keenan

Keyword(s):

Surface Brightness ◽

Dwarf Galaxy ◽

Virgo Cluster ◽

Low Surface Brightness ◽

Galaxy Population

Download Full-text

Stellar Over-Densities in the Outer Halo of the Milky Way

Publications of the Astronomical Society of Australia ◽

10.1071/as09037 ◽

2010 ◽

Vol 27 (1) ◽

pp. 45-55 ◽

Cited By ~ 9

Author(s):

Stefan C. Keller

Keyword(s):

Surface Brightness ◽

Dwarf Galaxy ◽

Local Density ◽

Spatial Scales ◽

Sloan Digital Sky Survey ◽

Tidal Disruption ◽

Giant Stars ◽

Sky Survey ◽

Low Surface Brightness ◽

Model Predictions

AbstractThis study presents a tomographic survey of a subset of the outer halo (10–40 kpc) drawn from the Sloan Digital Sky Survey Data Release 6. Halo substructure on spatial scales of >3 degrees is revealed as an excess in the local density of sub-giant stars. With an appropriate assumption of a model stellar isochrone it is possible for us to then derive distances to the sub-giant population. We describe three new candidate halo substructures; the 160- and 180-degree over-densities (at distances of 17 and 19 kpc respectively and radii of 1.3 and 1.5 kpc respectively) and an extended feature at 28 kpc that covers at least 162 deg2, the Virgo Equatorial Stream. In addition, we recover the Sagittarius dwarf galaxy (Sgr) leading-arm material and the Virgo Over-Density.The derived distances, together with the number of sub-giant stars associated with each substructure, enables us to derive the integrated luminosity for the features. The tenuous, low surface brightness of the features strongly suggests an origin from the tidal disruption of an accreted galaxy or galaxies. Given the dominance of the tidal debris of Sgr in this region of the sky we investigate if our observations can be accommodated by tidal disruption models for Sgr. The clear discordance between observations and model predictions for known Sgr features means it is difficult to tell unambiguously if the new substructures are related to Sgr or not. Radial velocities in the stellar over-densities will be critical in establishing their origins.

Download Full-text