scholarly journals Peculiar Red Giants in External Galaxies

1989 ◽  
Vol 106 ◽  
pp. 35-50 ◽  
Author(s):  
Harvey B. Richer
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Hubble Constant ◽  
Red Giants ◽  
Stellar Content ◽  
Late Type ◽  
External Galaxies ◽  
Distance Indicators ◽  
Luminosity Evolution ◽  
Local Value

AbstractStudy of the late-type stellar content in external galaxies provides numerous clues for the theory of stellar evolution, for star-formation scenarios in galaxies, and for proper models of the luminosity evolution of galaxies which are then used in cosmological studies. In addition, these late-type stars can be used as distance indicators themselves and yield a local value of the Hubble constant consistent with recent Cepheid determinations.

scholarly journals Space Distribution of Red Giants and the Galactic Structure

1984 ◽  
Vol 78 ◽  
pp. 257-260
Author(s):  
K. Ishida
Keyword(s):  
Galactic Structure ◽  
Space Distribution ◽  
Red Giants ◽  
Stellar Content ◽  
Late Type ◽  
Ir Radiation ◽  
Near Ir ◽  
The Galaxy ◽  
K Band

AbstractStellar content contributing to near IR radiation do not show radial differentiation in the Galaxy. Late-type giants and supergiants supply about 70% of the total volume emissivity at the K band, in the solar vicinity within 1 kpc, and also at the distance of several kpc in the Scutum region.

scholarly journals The Hubble Constant and the Deceleration Parameter

1974 ◽  
Vol 63 ◽  
pp. 47-59
Author(s):  
G. A. Tammann
Keyword(s):  
Velocity Field ◽  
Deceleration Parameter ◽  
Preliminary Report ◽  
Hubble Constant ◽  
Intrinsic Properties ◽  
Local Anisotropy ◽  
A Chain ◽  
Distance Indicators ◽  
Luminosity Evolution ◽  
Parent Galaxy

A preliminary report is given of recent work with A. Sandage on the Hubble constant. Through a chain of distance indicators in Sc and Ir galaxies (cepheids, brightest stars, H iiregions, and luminosity classes) the distance scale is carried beyond any possible local anisotropy of the velocity field. Special care is taken to allow for the dependence of the intrinsic properties of the distance indicators on the size of the parent galaxy, and for the effect of the Malmquist correction. H0 is found to be 55 ± 7 km s-1 Mpc-1; within the errors no systematic changes with distance were found.A formal value of the deceleration constant q0 = 1 ± 1 was recently derived by Sandage (1972a) and Sandage and Hardy (1973). The most important correction to this value is probably the luminosity evolution of galaxies, which tends to push q0 below 0.5. The ensuing evidence for an open universe is also favored by independent arguments.

scholarly journals Fraction of bolometric luminosity absorbed by dust in DustPedia galaxies

2018 ◽  
Vol 620 ◽  
pp. A112 ◽  
Author(s):  
S. Bianchi ◽  
P. De Vis ◽  
S. Viaene ◽  
A. Nersesian ◽  
A. V. Mosenkov ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Star Formation Rate ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Spectral Energy ◽  
Stellar Content ◽  
Late Type ◽  
Bolometric Luminosity ◽  
Stellar Radiation

Aims. We aim to study the fraction of stellar radiation absorbed by dust, fabs, in 814 galaxies of different morphological types. The targets constitute the vast majority (93%) of the DustPedia sample, including almost all large (optical diameter larger than 1′), nearby (v ≤ 3000 km s−1) galaxies observed with the Herschel Space Observatory. Methods. For each object, we modelled the spectral energy distribution from the ultraviolet to the sub-millimetre using the dedicated, aperture-matched DustPedia photometry and the Code Investigating GALaxy Evolution (CIGALE). The value of fabs was obtained from the total luminosity emitted by dust and from the bolometric luminosity, which are estimated by the fit. Results. On average, 19% of the stellar radiation is absorbed by dust in DustPedia galaxies. The fraction rises to 25% if only late-type galaxies are considered. The dependence of fabs on morphology, showing a peak for Sb-Sc galaxies, is weak; it reflects a stronger, yet broad, positive correlation with the bolometric luminosity, which is identified for late-type, disk-dominated, high-specific-star-formation rate, gas-rich objects. We find no variation of fabs with inclination, at odds with radiative transfer models of edge-on galaxies. These results call for a self-consistent modelling of the evolution of the dust mass and geometry along the build-up of the stellar content. We also provide template spectral energy distributions in bins of morphology and luminosity and study the variation of fabs with stellar mass and specific star-formation rate. We confirm that the local Universe is missing the high fabs, luminous and actively star-forming objects necessary to explain the energy budget in observations of the extragalactic background light.

scholarly journals The Brightest Stars in the Magellanic Clouds and Other Late-Type Galaxies

1984 ◽  
Vol 108 ◽  
pp. 145-156
Author(s):  
Roberta M. Humphreys
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Stellar Population ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Stellar Winds ◽  
Stellar Content ◽  
Late Type ◽  
Observational Astronomy ◽  
Distant Galaxies

The brightest stars always receive considerable attention in observational astronomy, but why are we so interested in these most luminous, and therefore most massive stars? These stars are our first probes for exploring the stellar content of distant galaxies. Admittedly, they are only the tip of the iceberg for the whole stellar population and very interesting processes are occurring among the less massive, older stars, but the most massive stars are our first indicators for studies of stellar evolution in other galaxies. They provide the first hint that stellar evolution may have been different in a particular galaxy because they evolve so quickly. The most luminous stars also highly influence their environments via their strong stellar winds and mass loss and eventually as supernovae.

scholarly journals Allan Sandage and the distance scale

2012 ◽  
Vol 8 (S289) ◽  
pp. 13-25 ◽  
Author(s):  
G. A. Tammann ◽  
B. Reindl
Keyword(s):  
Large Scale ◽  
Hubble Space Telescope ◽  
Hubble Constant ◽  
Distance Scale ◽  
Type Ia ◽  
The Mean ◽  
Red Giant ◽  
Ia Supernovae ◽  
Distance Indicators ◽  
Local Value

AbstractAllan Sandage returned to the distance scale and the calibration of the Hubble constant again and again during his active life, experimenting with different distance indicators. In 1952 his proof of the high luminosity of Cepheids confirmed Baade's revision of the distance scale (H0 ~ 250 km s−1 Mpc−1). During the next 25 years, he lowered the value to 75 and 55. Upon the arrival of the Hubble Space Telescope, he observed Cepheids to calibrate the mean luminosity of nearby Type Ia supernovae (SNe Ia) which, used as standard candles, led to the cosmic value of H0 = 62.3 ± 1.3 ± 5.0 km s−1 Mpc−1. Eventually he turned to the tip of the red giant branch (TRGB) as a very powerful distance indicator. A compilation of 176 TRGB distances yielded a mean, very local value of H0 = 62.9 ± 1.6 km s−1 Mpc−1 and shed light on the streaming velocities in the Local Supercluster. Moreover, TRGB distances are now available for six SNe Ia; if their mean luminosity is applied to distant SNe Ia, one obtains H0 = 64.6 ± 1.6 ± 2.0 km s−1 Mpc−1. The weighted mean of the two independent large-scale calibrations yields H0 = 64.1 km s−1 Mpc−1 within 3.6%.

scholarly journals The effects of peculiar velocities in SN Ia environments on the local H0 measurement

2020 ◽  
Vol 500 (3) ◽  
pp. 3728-3742
Author(s):  
Thomas M Sedgwick ◽  
Chris A Collins ◽  
Ivan K Baldry ◽  
Philip A James
Keyword(s):  
Hubble Constant ◽  
Density Parameter ◽  
Host Galaxies ◽  
Peculiar Velocities ◽  
Standard Candle ◽  
Modern Cosmology ◽  
Type Ia ◽  
The Difference ◽  
Ia Supernovae ◽  
Distance Indicators

ABSTRACT The discrepancy between estimates of the Hubble constant (H0) measured from local (z ≲  0.1) scales and from scales of the sound horizon is a crucial problem in modern cosmology. Peculiar velocities (vpec) of standard candle distance indicators can systematically affect local H0 measurements. We here use 2MRS galaxies to measure the local galaxy density field, finding a notable z  <  0.05 underdensity in the SGC-6dFGS region of 27  ±  2 per cent. However, no strong evidence for a ‘Local Void’ pertaining to the full 2MRS sky coverage is found. Galaxy densities are used to measure a density parameter, Δϕ+−, which we introduce as a proxy for vpec that quantifies density gradients along a supernova (SN) line of sight. Δϕ+− is found to correlate with local H0 estimates from 88 Pantheon Type Ia supernovae (SNe Ia; 0.02  <  z  <  0.05). Density structures on scales of ∼50 Mpc are found to correlate strongest with H0 estimates in both the observational data and in mock data from the MDPL2-Galacticus simulation. Using trends of H0 with Δϕ+−, we can correct for the effects of density structure on local H0 estimates, even in the presence of biased vpec. However, the difference in the inferred H0 estimate with and without the peculiar velocity correction is limited to < 0.1  per cent. We conclude that accounting for environmentally induced peculiar velocities of SN Ia host galaxies does not resolve the tension between local and CMB-derived H0 estimates.

scholarly journals STAR FORMATION AND YOUNG STELLAR CONTENT IN THE W3 GIANT MOLECULAR CLOUD

2011 ◽  
Vol 743 (1) ◽  
pp. 39 ◽  
Author(s):  
Alana Rivera-Ingraham ◽  
Peter G. Martin ◽  
Danae Polychroni ◽  
Toby J. T. Moore
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Stellar Content ◽  
Giant Molecular Cloud

scholarly journals Populations of OB-type stars in galaxies

2010 ◽  
Vol 6 (S272) ◽  
pp. 233-241
Author(s):  
Christopher J. Evans
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Spectral Synthesis ◽  
High Redshift ◽  
Young Star ◽  
Magellanic Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
External Galaxies

AbstractOne of the challenges for stellar astrophysics is to reach the point at which we can undertake reliable spectral synthesis of unresolved populations in young, star-forming galaxies at high redshift. Here I summarise recent studies of massive stars in the Galaxy and Magellanic Clouds, which span a range of metallicities commensurate with those in high-redshift systems, thus providing an excellent laboratory in which to study the role of environment on stellar evolution. I also give an overview of observations of luminous supergiants in external galaxies out to a remarkable 6.7 Mpc, in which we can exploit our understanding of stellar evolution to study the chemistry and dynamics of the host systems.

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