scholarly journals A New HI Ring: LGG 138

1999 ◽  
Vol 16 (1) ◽  
pp. 77-83 ◽  
Author(s):  
David G. Barnes
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Density Wave ◽  
Radial Distance ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
Radial Velocities ◽  
Complete Ring ◽  
Distinct Colour ◽  
Colour Break

AbstractA complete ring of neutral hydrogen gas (HI) in the LGG 138 group of galaxies has been found. The HI mass of the ring is greater than 109, and the gas appears to be rotating with a projected circular speed of ∼200 km s−1. Two bright galaxies are enclosed by the ring, both having radial velocities consistent with membership of the group. Faint stellar emission extends to the radial distance of the HI ring, where a small but distinct colour discontinuity of between 0·05 and 0·20 magnitudes is detected. Three simple models for the formation of the system are briefly described, the most likely appearing to be a past gas-sweeping collision between one of the two bright galaxies and an outside intruder, with the colour break being partly due to an expanding density wave that is triggering star formation, and partly to a different stellar population that has been collected from the outskirts of the intruder.

scholarly journals The Nearby Young Dwarf Galaxy SBS 0335-052: Primordial Gas and Lyman-Alpha Emission

1998 ◽  
Vol 11 (1) ◽  
pp. 115-116
Author(s):  
Trinh Xuan Thuan ◽  
Yuri I. Izotov
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Dwarf Galaxy ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
Gas Content ◽  
Ionized Gas ◽  
Filamentary Structure ◽  
A Chain ◽  
Super Star Clusters

Ever since their discovery, blue compact dwarf (BCD) galaxies have been thought of as excellent candidates for being young galaxies, i.e. systems presently undergoing one of their very first bursts of star formation. This is mainly because BCDs are very metal-deficient, the metallicities of their ionized gas ranging between Zʘ/50 and Zʘ/3, which makes them the least chemically evolved galaxies in the Universe. Other evidence, such as the very high fractional neutral hydrogen gas content and the lack of an evident underlying old stellar population on optical images, also point to the relative youth of some BCDs. Thuan, Izotov h Lipovetsky (1997) have argued SBS 0335-052 to be a young galaxy on the basis of the following evidence: 1) HST imaging of the BCD shows its underlying extended low surface brightness component to have an irregular and filamentary structure, suggesting that a significant part of the emission (~1/3) comes not from an underlying stellar population, but from ionized gas. Any underlying stellar population must be younger than ~108yr. Propagating star formation occurs in a chain of 6 super-star clusters with ages ranging between 4 and 30 Myr. 2) The underlying component shows unusually blue colors consistent with gaseous emission, in contrast to most BCDs which possess an underlying red component. 3) VLA 21 cm observations show the BCD to be embedded in an extraordinarily large HI cloud with dimensions some 64 × 24 kpc (the typical size of HI envelopes around BCDs is more like a few kpc in each dimension).

scholarly journals Stellar population gradients in GASS

2012 ◽  
Vol 8 (S295) ◽  
pp. 304-307
Author(s):  
Jonas Johansson ◽  
Guinevere Kauffmann ◽  
Sean Moran
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Stellar Population ◽  
Neutral Hydrogen ◽  
Stellar Populations ◽  
Element Abundance ◽  
Molecular Gas ◽  
Massive Galaxies ◽  
Additional Formation ◽  
Inside Out

AbstractWe study relationships between the stellar populations and interstellar medium in massive galaxies using the Galex Arecibo SDSS Survey (GASS). The sample consists of HI-observations (~1000 galaxies) and complementary H2-observations (330 galaxies) and long-slit spectroscopy (230 galaxies). Luminosity-weighted stellar population ages, metallicitites and element abundance ratios, are derived by fitting stellar population models of absorption line indices. We find that the ages correlate more strongly with molecular gas fraction (MH2/M*) than with neutral Hydrogen fraction (MHI/M*). This result strengthens the theory that H2 is a better tracer of star-formation than HI. The sample is dominated by negative metallicity-gradients and flat Mg/Fe-gradients. Galaxies with high MH2/M*-ratios show in general flat or weakly negative age-gradients. For low MH2/M*-ratios the age-gradients are overall negative. These results are in agreement with the inside-out galaxy formation scenario. For galaxies with high r90/r50-ratios, a sub-population show positive age-gradients indicating additional formation channels. Furthermore, for galaxies with high MH2/M*-ratios more massive systems have older stellar populations in their centers, suggesting downsizing within the inside-out formation scenario.

scholarly journals UVIT observations of the star-forming ring in NGC 7252: Evidence of possible AGN feedback suppressing central star formation

2018 ◽  
Vol 613 ◽  
pp. L9 ◽  
Author(s):  
K. George ◽  
P. Joseph ◽  
C. Mondal ◽  
A. Devaraj ◽  
A. Subramaniam ◽  
...  
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Central Region ◽  
Stellar Population ◽  
Central Star ◽  
Hydrogen Gas ◽  
Gas Reservoir ◽  
Massive Black Hole ◽  
Star Forming ◽  
Younger Age

Context. Some post-merger galaxies are known to undergo a starburst phase that quickly depletes the gas reservoir and turns it into a red-sequence galaxy, though the details are still unclear. Aims. Here we explore the pattern of recent star formation in the central region of the post-merger galaxy NGC 7252 using high-resolution ultraviolet (UV) images from the UVIT on ASTROSAT. Methods. The UVIT images with 1.2 and 1.4 arcsec resolution in the FUV and NUV are used to construct a FUV-NUV colour map of the central region. Results. The FUV-NUV pixel colour map for this canonical post-merger galaxy reveals a blue circumnuclear ring of diameter ~10′′ (3.2 kpc) with bluer patches located over the ring. Based on a comparison to single stellar population models, we show that the ring is comprised of stellar populations with ages ≲300 Myr, with embedded star-forming clumps of younger age (≲150Myr). Conclusions. The suppressed star formation in the central region, along with the recent finding of a large amount of ionised gas, leads us to speculate that this ring may be connected to past feedback from a central super-massive black hole that has ionised the hydrogen gas in the central ~4′′ ~1.3 kpc.

HI in the Small Magellanic Cloud Re-examined

1981 ◽  
Vol 4 (2) ◽  
pp. 189-195 ◽  
Author(s):  
R. X. McGee ◽  
Lynette M. Newton
Keyword(s):  
Radial Velocity ◽  
Neutral Hydrogen ◽  
Total Content ◽  
Hii Regions ◽  
Magellanic Cloud ◽  
Hydrogen Gas ◽  
Radial Velocities ◽  
Line Of Sight ◽  
Small Magellanic Cloud

Our re-examination of the neutral hydrogen gas in the Small Magellan Cloud has led to four important results. Firstly, we find that Hindman’s (1967) total content HI map is a satisfactory representation of the gas in the line of sight. Secondly, we find that the HI gas in the SMC exists in four distinct large masses separated from one another in radial velocity by 20 to 30 km s−1. Thirdly, having made this division of the gas we show that there is good correlation between the radial velocities of HII regions, supergiant stars and HI. Finally, we believe that our observations reveal that the SMC is associated with an extremely large trailing halo of HI gas which forms the major component of the inter-cloud bridge region.

scholarly journals Neutral hydrogen gas, past and future star formation in galaxies in and around the ‘Sausage’ merging galaxy cluster

2015 ◽  
Vol 452 (3) ◽  
pp. 2731-2744 ◽  
Author(s):  
Andra Stroe ◽  
Tom Oosterloo ◽  
Huub J. A. Röttgering ◽  
David Sobral ◽  
Reinout van Weeren ◽  
...  
Keyword(s):  
Star Formation ◽  
Neutral Hydrogen ◽  
Galaxy Cluster ◽  
Hydrogen Gas ◽  
Star Formation In Galaxies

scholarly journals Neutral hydrogen in the Large Magellanic Cloud

1964 ◽  
Vol 20 ◽  
pp. 289-294 ◽  
Author(s):  
R. X. McGee ◽  
Janice A. Milton
Keyword(s):  
Neutral Hydrogen ◽  
Large Magellanic Cloud ◽  
Progress Report ◽  
Magellanic Cloud ◽  
Hydrogen Gas ◽  
Radial Velocities

The neutral hydrogen gas in the Large Magellanic Cloud has been observed with the 14′.5 beam of the Parkes 210-foot telescope and the 48-channel H-line receiver. We wish to present a progress report based on computer reductions of integrated brightness and median radial velocities for some 4200 profiles. The survey is incomplete for some of the southern regions below dec. −73°. Assisting in the observations were our colleagues, M. W. Sinclair, C. J. Ohlston, and G. H. Trent and the staff at ANRAO, Parkes.

scholarly journals Triggered star formation in spiral arms

2006 ◽  
Vol 2 (S237) ◽  
pp. 445-445
Author(s):  
Eric E. Martínez-García ◽  
Rosa Amelia González-Lópezlira ◽  
Gustavo Bruzual-A.
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Rotational Velocity ◽  
Density Wave ◽  
Physical Parameters ◽  
Spiral Pattern ◽  
Spiral Arms ◽  
Dust Lane ◽  
Q Model ◽  
Pattern Speeds

AbstractWe present preliminary results for six spiral galaxies from a sample of 25, where we have used the method developed by González & Graham (1996) to search for and analyze azimuthal color gradients across spiral arms. The six galaxies analyzed here are NGC 1703 (SBrb), NGC 3001 (SABrsbc), NGC 3059 (SBrsbc), NGC 3513 (SBrsc), NGC 4593 (RSBrsb), and NGC 4603 (SAsc).NGC 1703: We found one azimuthal color gradient in NGC 1703. Star formation was traced with the reddening free parameter Q, and the dust lane was located with the (g – J) color. This gradient lies at a distance of 1.45 kpc from the center of the galaxy. In order to get some physical parameters of the star formation processes that are taking place in the spiral arms of the galaxies in our sample, we compared the observed Q profiles with the stellar population synthesis models of Bruzual & Charlot (2003). The fitted Q model is shown in figure 1. If one assumes that stars form in the site of the shock, and that they age as they move away from this birthsite, then distance from the dust lane (at constant radius) parameterizes stellar age. In fact, stretching the model Q to the fit the data fixes the ratio between the distance and the age of the stellar population. If, in addition, the rotational velocity is known, it is possible to find the angular velocity of the spiral pattern. The spiral pattern speeds derived from the gradients (under the assumption that star formation is triggered by the density wave) yield theoretical resonance positions that are coincident with the observed spiral end points, in 3 out of 6 spirals. It would be hard to avoid the conclusion that disk dynamics and star formation are fundamentally related in these objects.

scholarly journals 21 cm Hydrogen-line Survey of the Large Magellanic Cloud. I. Stellar, Nebular, and Neutral Hydrogen Radial Velocities

1964 ◽  
Vol 17 (4) ◽  
pp. 515 ◽  
Author(s):  
RX McGee
Keyword(s):  
Neutral Hydrogen ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Hydrogen Gas ◽  
Radial Velocities ◽  
Recent Survey ◽  
Hydrogen Line ◽  
Line Survey

A recent survey of the neutral hydrogen in the Large Magellanic Cloud with a 14'�5 beam and the 48�channel H�line receiver has afforded an opportunity to compare the radial velocities of a number of optical objects with the radial velocities of the hydrogen gas in their directions.

scholarly journals The Local Universe: Galaxies in 3D

2014 ◽  
Vol 10 (S309) ◽  
pp. 39-46
Author(s):  
Bärbel S. Koribalski
Keyword(s):  
Star Formation ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
Local Universe ◽  
Galaxy Surveys ◽  
Spatially Resolved ◽  
The Galaxy ◽  
Multi Wavelength ◽  
Large Survey ◽  
Individual Galaxy

AbstractHere I present results from individual galaxy studies and galaxy surveys in the Local Universe with particular emphasis on the spatially resolved properties of neutral hydrogen gas. The 3D nature of the data allows detailed studies of the galaxy morphology and kinematics, their relation to local and global star formation as well as galaxy environments. I use new 3D visualisation tools to present multi-wavelength data, aided by tilted-ring models of the warped galaxy disks. Many of the algorithms and tools currently under development are essential for the exploration of upcoming large survey data, but are also highly beneficial for the analysis of current galaxy surveys.

scholarly journals A Sky Survey of Neutral Hydrogen at l 21 cm. III. Gas at Higher Radial Velocities

1964 ◽  
Vol 17 (1) ◽  
pp. 128 ◽  
Author(s):  
RX McGee ◽  
Janice A Milton
Keyword(s):  
Radial Velocity ◽  
Atomic Hydrogen ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
Radial Velocities ◽  
Channel Spacing ◽  
Sky Survey ◽  
Half Power

Information is presented concerning the distributions of the intensity and radial velocity of atomic hydrogen gas at radial velocities away from zero. The observations were made with an aerial beam of 2?2 between half-power points and a multichannel H-line receiver of channel spacing equivalent to 7 km/s and bandwidth 38 kc/s ( 8 km/s).

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