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 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.

scholarly journals The Halos and Environments of Nearby Galaxies (HERON) Survey

2016 ◽  
Vol 11 (S321) ◽  
pp. 186-189 ◽  
Author(s):  
R. Michael Rich ◽  
Noah Brosch ◽  
James Bullock ◽  
Andreas Burkert ◽  
Michelle Collins ◽  
...  
Keyword(s):  
Star Formation ◽  
Surface Brightness ◽  
Spiral Galaxies ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
General Survey ◽  
Tidal Disruption ◽  
Local Volume ◽  
Low Surface Brightness ◽  
Nearby Galaxies

AbstractWe have used dedicated 0.7m telescopes in California and Israel to image the halos of ~ 200 galaxies in the Local Volume to 29 mag/sq arcsec, the sample mainly drawn from the 2MASS Large Galaxy Atlas (LGA). We supplement the LGA sample with dwarf galaxies and more distant giant ellipticals. Low surface brightness halos exceeding 50 kpc in diameter are found only in galaxies more luminous than L*, and classic interaction signatures are relatively infrequent. Halo diameter is correlated with total galaxy luminosity. Extended low surface brightness halos are present even in galaxies as faint as MV = - 18. Edge-on galaxies with boxy bulges tend to lack extended spheroidal halos, while those with large classical bulges exhibit extended round halos, supporting the notions that boxy or barlike bulges originate from disks. Most face-on spiral galaxies present features that appear to be irregular extensions of spiral arms, although rare cases show smooth boundaries with no sign of star formation. Although we serendipitously discovered a dwarf galaxy undergoing tidal disruption in the halo of NGC 4449, we found no comparable examples in our general survey. A search for similar examples in the Local Volume identified hcc087, a tidally disrupting dwarf galaxy in the Hercules Cluster, but we do not confirm an anomalously large half-light radius reported for the dwarf VCC 1661.

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 The dwarf galaxy population as revealed by ALFALFA

2018 ◽  
Vol 14 (S344) ◽  
pp. 464-467
Author(s):  
Elizabeth A. K. Adams ◽  
Catherine Ball ◽  
John M. Cannon ◽  
Martha P. Haynes ◽  
Alec Hirschauer ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Optical Counterpart ◽  
Star Forming ◽  
Large Numbers ◽  
Low Surface Brightness ◽  
Low Mass ◽  
Galaxy Population ◽  
Optical Surveys

AbstractThe combination of sensitivity and large sky coverage of the ALFALFA HI survey has enabled the detection of difficult to observe low mass galaxies in large numbers, including dwarf galaxies overlooked in optical surveys. Three different, but connected, studies of dwarf galaxies from the ALFALFA survey are of particular interest: SHIELD (Survey of HI in Extremely Low-mass Dwarfs), candidate gas-rich ultra-faint dwarf galaxies, and the (Almost) Dark population. SHIELD is a systematic multiwavelength study of all dwarf galaxies from ALFALFA with MHI < 107.2M⊙ and clear optical counterparts. Candidate gas-rich ultra-faint dwarf galaxies extend the dwarf galaxy population to even lower masses. These galaxies are identified as isolated HI clouds with no discernible optical counterpart but subsequent observations reveal that some are extremely faint, gas-dominated galaxies. Leo P, discovered first as an HI detection, and then found to be an actively star-forming galaxy, bridges the gap between these candidate galaxies and the SHIELD sample. The (Almost) Dark sample consists of galaxies whose optical counterparts are overlooked in current optical surveys but which are clear detections in ALFALFA. This sample includes field gas-rich ultra-diffuse galaxies. Coma P, with a peak surface brightness of only ∼26.4 mag arcsec−2 in g’, demonstrates the sort of extreme low surface brightness galaxy that can be discovered in an HI survey.

scholarly journals Abundance of dwarf galaxies around low-mass spiral galaxies in the Local Volume

2020 ◽  
Vol 644 ◽  
pp. A91
Author(s):  
Oliver Müller ◽  
Helmut Jerjen
Keyword(s):  
Surface Brightness ◽  
Spiral Galaxies ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Current Model ◽  
Host Galaxies ◽  
Local Volume ◽  
Satellite Problem ◽  
Low Mass ◽  
Crucial Test

The abundance of satellite dwarf galaxies has long been considered a crucial test for the current model of cosmology leading to the well-known missing satellite problem. Recent advances in simulations and observations have allowed the study of dwarf galaxies around host galaxies in more detail. Using the Dark Energy Camera we surveyed a 72 deg2 area of the nearby Sculptor group, also encompassing the two low-mass Local Volume galaxies NGC 24 and NGC 45 residing behind the group, to search for as yet undetected dwarf galaxies. Apart from the previously known dwarf galaxies we found only two new candidates down to a 3σ surface brightness detection limit of 27.4 r mag arcsec−2. Both systems are in projection close to NGC 24. However, one of these candidates could be an ultra-diffuse galaxy associated with a background galaxy. We compared the number of known dwarf galaxy candidates around NGC 24, NGC 45, and five other well-studied low-mass spiral galaxies (NGC 1156, NGC 2403, NGC 5023, M 33, and the LMC) with predictions from cosmological simulations, and found that for the stellar-to-halo mass models considered, the observed satellite numbers tend to be on the lower end of the expected range. This could mean either that there is an overprediction of luminous subhalos in ΛCDM or that we are missing some of the satellite members due to observational biases.

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

1999 ◽  
Vol 171 ◽  
pp. 253-260 ◽  
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.

The Hi Neighborhoods Around STARBIRDS

2018 ◽  
Vol 14 (S344) ◽  
pp. 280-282
Author(s):  
Megan C. Johnson ◽  
Kristen B. W. McQuinn ◽  
John Cannon ◽  
Charlotte Martinkus ◽  
Evan Skillman ◽  
...  
Keyword(s):  
Star Formation ◽  
Surface Brightness ◽  
Spiral Galaxies ◽  
Dwarf Galaxies ◽  
Neutral Hydrogen ◽  
Tidal Interactions ◽  
Low Surface Brightness ◽  
The Galaxy ◽  
Green Bank Telescope ◽  
Intense Star Formation

AbstractStarbursts are finite periods of intense star formation (SF) that can dramatically impact the evolutionary state of a galaxy. Recent results suggest that starbursts in dwarf galaxies last longer and are distributed over more of the galaxy than previously thought, with star formation efficiencies (SFEs) comparable to spiral galaxies, much higher than those typical of non-bursting dwarfs. This difference might be explainable if the starburst mode is externally triggered by gravitational interactions with other nearby systems. We present new, sensitive neutral hydrogen observations of 18 starburst dwarf galaxies, which are part of the STARburst IRregular Dwarf Survey (STARBIRDS) and each were mapped with the Green Bank Telescope (GBT) and/or Parkes Telescope in order to study the low surface brightness gas distributions, a common tracer for tidal interactions.

Dwarf Galaxies and Cluster Environments

2018 ◽  
Vol 14 (S344) ◽  
pp. 373-376
Author(s):  
Yasuhiro Hashimoto ◽  
J. Patrick Henry ◽  
Hans Böhringer
Keyword(s):  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Detection Algorithm ◽  
Diffuse Light ◽  
X Ray ◽  
Optical Images ◽  
Highly Sensitive ◽  
The Galaxy ◽  
Galaxy Populations ◽  
Selection Of

AbstractWe report an investigation of the properties of dwarf galaxies (Mr < -15) inside 26 clusters at z = 0.15 – 0.25, using the X-ray data from the Chandra archive, and optical images taken with Subaru Suprime-Cam. Our results include: 1. Investigation of the dwarf galaxy density distribution is sensitive to the background galaxies and the choice of colour selection of galaxies. 2. Cluster-centric dwarf-to-giant ratio is highly sensitive to the level of subtracted background galaxies. 3. A certain fraction of faint galaxies always remain undetected by the detection algorithm near the center of clusters, even after carefully treating the halo or extra diffuse light created by bright galaxies. The number of ‘undetected’ faint galaxies varies significantly from cluster to cluster, and even from pointing to pointing. 4. Dwarf galaxies extend up to 2 Mpc from the center in most clusters. Meanwhile, the distribution of blue dwarf galaxies extends more to the outside. 5. For a given colour, the spatial distributions of dwarf galaxies and giant galaxies become similar. Namely, the most of the radial distribution comes from the colour, rather than the size, of galaxies. 6. Relative to the NFW profile, all of the galaxy populations are showing a deficit near the cluster core (r < 0.3 Mpc). 7. The dwarf-to-giant ratio shows no variation against cluster measures such as the richness and X-ray luminosity, as well as various cluster X-ray characteristics related to possible dynamical status of clusters.

scholarly journals Dissecting star formation in the “Atoms-for-Peace” galaxy

2018 ◽  
Vol 614 ◽  
pp. A130 ◽  
Author(s):  
K. George ◽  
P Joseph ◽  
P. Côté ◽  
S. K. Ghosh ◽  
J. B. Hutchings ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Dwarf Galaxy ◽  
Main Body ◽  
Star Forming ◽  
Uv Imaging ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Tidal Tails

Context. The tidal tails of post-merger galaxies exhibit ongoing star formation far from their disks. The study of such systems can be useful for our understanding of gas condensation in diverse environments. Aims. The ongoing star formation in the tidal tails of post-merger galaxies can be directly studied from ultraviolet (UV) imaging observations. Methods. The post merger galaxy NGC7252 (“Atoms-for-Peace” galaxy) is observed with the Astrosat UV imaging telescope (UVIT) in broadband NUV and FUV filters to isolate the star-forming regions in the tidal tails and study the spatial variation in star formation rates. Results. Based on ultraviolet imaging observations, we discuss star-forming regions of ages <200 Myr in the tidal tails. We measure star formation rates in these regions and in the main body of the galaxy. The integrated star formation rate (SFR) of NGC7252 (i.e., that in the galaxy and tidal tails combined) without correcting for extinction is found to be 0.81 ± 0.01 M⊙ yr−1. We show that the integrated SFR can change by an order of magnitude if the extinction correction used in SFR derived from other proxies are taken into consideration. The star formation rates in the associated tidal dwarf galaxies (NGC7252E, SFR = 0.02 M⊙ yr−1 and NGC7252NW, SFR = 0.03 M⊙ yr−1) are typical of dwarf galaxies in the local Universe. The spatial resolution of the UV images reveals a gradient in star formation within the tidal dwarf galaxy. The star formation rates show a dependence on the distance from the centre of the galaxy. This can be due to the different initial conditions responsible for the triggering of star formation in the gas reservoir that was expelled during the recent merger in NGC7252.

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