scholarly journals The effect of our local motion on the Sandage–Loeb test of the cosmic expansion

2019 ◽  
Vol 72 (1) ◽  
Author(s):  
Takuya Inoue ◽  
Eiichiro Komatsu ◽  
Wako Aoki ◽  
Takeshi Chiba ◽  
Toru Misawa ◽  
...  
Keyword(s):  
Solar System ◽  
Local Group ◽  
Galactic Center ◽  
Large Magellanic Cloud ◽  
Local Motion ◽  
Microwave Background ◽  
Cosmic Expansion ◽  
M 31 ◽  
The Universe

Abstract Redshifts of an astronomical body measured at multiple epochs (e.g., separated by 10 yr) are different due to the cosmic expansion. This so-called Sandage–Loeb test offers a direct measurement of the expansion rate of the Universe. However, acceleration in the motion of the Solar System with respect to the cosmic microwave background also changes redshifts measured at multiple epochs. If not accounted for, it yields a biased cosmological inference. To address this, we calculate the acceleration of the Solar System with respect to the Local Group of galaxies to quantify the change in the measured redshift due to local motion. Our study is motivated by the recent determination of the mass of the Large Magellanic Cloud (LMC), which indicates a significant fraction of the Milky Way mass. We find that the acceleration towards the Galactic Center dominates, which gives a redshift change of 7 cm s−1 in 10 yr, while the accelerations due to the LMC and M 31 cannot be ignored, depending on lines of sight. We create all-sky maps of the expected change in redshift and the corresponding uncertainty, which can be used to correct for this effect.

scholarly journals The Motion of the Local Group of Galaxies with Respect to the Background of Galaxies

1983 ◽  
Vol 104 ◽  
pp. 255-258
Author(s):  
R. D. Davies
Keyword(s):  
Large Scale ◽  
Local Group ◽  
Microwave Background ◽  
Optical Studies ◽  
Group Motion ◽  
Gravitational Influence ◽  
Nearby Galaxies ◽  
Peculiar Motion ◽  
The Universe ◽  
Hubble Flow

A measurement of the motion of the Local Group of galaxies through the Universe provides an indication of their peculiar motion relative to the Hubble flow consequent upon the gravitational influence of the local large scale mass inhomogeneities. This motion can be measured either relative to the cosmic microwave background at z ∼ 1000 or relative to the background or nearby (z ∼ 0.01) galaxies. The interpretation of published measurements is subject to some uncertainty. As an example, the Local Group motion derived from optical studies of nearby galaxies (Rubin et al. 1976) differs from that derived from radio frequency measurements of the dipole anisotropy in the microwave background. (Boughn et al. 1981, Gorenstein & Smoot 1981).

scholarly journals Red Clump Stars – Further Improved Distance Indicator

2002 ◽  
Vol 12 ◽  
pp. 688 ◽  
Author(s):  
P.M. Garnavich ◽  
K. Stanek
Keyword(s):  
Galactic Center ◽  
Hubble Constant ◽  
Large Magellanic Cloud ◽  
Solar Neighborhood ◽  
Horizontal Branch Stars ◽  
Standard Value ◽  
Distance Indicator ◽  
Red Clump ◽  
Distance Indicators

AbstractThe ideal distance indicator would be a standard candle abundant enough to provide many examples within reach of parallax measurements and sufficiently bright to be seen out to Local Group galaxies. The red clump stars closely match this description. These are the metal rich equivalent of the better known horizontal branch stars, and their brightness dispersion is only 0.2 mag (one sigma) in the Solar neighborhood. Using Hipparcos to calibrate a large, local sample, the red clump method has been used to measure accurate distances to the Galactic center (Paczyński & Stanek 1998), M31 (Stanek & Garnavich 1998), LMC (Udalski et al. 1998; Stanek et al. 1998; Udalski 1999) and some clusters in our Galaxy (e.g. 47Tuc: Kaluzny et al. 1998). As with all the distance indicators, the main worry lies in the possible systematics of the method, in particular, the brightness dependence on the stellar metallicity and age. These dependences have come under close scrutiny and, indeed, the population effects on the red clump brightness appear small and calibratable. Perhaps the most controversial result from the red clump method is the estimation of a “short” distance to the Large Magellanic Cloud (Udalski et al. 1998; Stanek, Zaritsky & Harris 1998; Udalski 2000). This distance to the LMC is shorter by 12% than the “standard” value, and has very important implications for the Cepheid distance scale and the determination of the Hubble constant.

scholarly journals Massive extragalactic eclipsing binaries

2006 ◽  
Vol 2 (14) ◽  
pp. 198-198
Author(s):  
Alceste Z. Bonanos
Keyword(s):  
Gamma Ray ◽  
Local Group ◽  
Galactic Center ◽  
Massive Stars ◽  
Galactic Disk ◽  
Eclipsing Binaries ◽  
Stellar Clusters ◽  
Galactic Clusters ◽  
Nearby Galaxies ◽  
M 31

Masses, radii and luminosities of distant stars can only be measured accurately in eclipsing binaries. The most massive eclipsing binary currently known is WR 20a, which consists of two ~ 80 M⊙ stars in a 3.7 d orbit. Analogs of WR 20a are bound to exist both in massive stellar clusters in our Galaxy and in nearby galaxies. The nearest ones are located in the clusters near the Galactic Center: the Center, Arches, and Quintuplet clusters. The severe amount of reddening in the galactic disk makes the study of galactic clusters challenging. However, with current 8-m class telescopes, the study of massive stars in nearby galaxies is also feasible. The nearest Local Group galaxies (LMC, SMC, M 31, M 33) provide the perfect laboratory for studying massive stars and determining their properties as a function of metallicity. Such studies will constrain models, confirm the dependence of evolution on metallicity and help understand the rate and nature of supernovae and gamma-ray bursts.

scholarly journals Distribution of IRAS Galaxies

1987 ◽  
Vol 124 ◽  
pp. 229-245
Author(s):  
Michael Rowan-Robinson
Keyword(s):  
Interstellar Dust ◽  
Local Group ◽  
Big Bang ◽  
Galactic Latitude ◽  
Gravitational Acceleration ◽  
Microwave Background ◽  
High Galactic Latitude ◽  
Galaxy Surveys ◽  
Infrared Wavelengths ◽  
The Universe

Infrared wavelengths are free of several of the problems that plague optical galaxy surveys. At high galactic latitude ≥99% of 60μ sources in the IRAS Point Source Catalog, after deletion of obvious stars, are galaxies. At lower latitudes care has to be taken to avoid confusion with emission from interstellar dust (the ‘cirrus’). IRAS galaxies have been used to determined the direction of the gravitational acceleration acting on the Local Group due to galaxies and clusters within about 200 Mpc. This agrees well with the direction of the microwave background dipole. The density of matter in the universe, distributed like IRAS galaxies, needed to account for the observed velocity of the Local Group, corresponds to Ωo = 1.0 ± 0.2. In the standard hot Big Bang model, 90–95% of this matter would have to be non-baryonic.IRAS galaxies are significantly less clustered than optically selected galaxy samples.

scholarly journals The Galactic distribution of Wolf-Rayet stars: an optical and infrared approach

2003 ◽  
Vol 212 ◽  
pp. 441-450 ◽  
Author(s):  
Karel A. van der Hucht
Keyword(s):  
Surface Density ◽  
Local Group ◽  
Galactic Center ◽  
Solar Neighborhood ◽  
Galactocentric Distance ◽  
Preliminary Results ◽  
Number Ratio ◽  
Photometric Distance ◽  
Galactic Distribution

The recent VIIth Catalogue of Galactic Wolf-Rayet Stars (van der Hucht 2001), lists 227 Population I WR stars, comprising 127 WN, 87 WC, 10 WN/WC and 3 WO stars. Additional discoveries since then bring the census to ≳ 253 WR stars, including ≳ 27 WNL and 13 WCL stars within 50 pc of the Galactic Center. A re-determination of the optical photometric distances and the galactic distribution of WR stars shows in the solar neighbourhood (d < 3 kpc) a projected surface density of 2.7 WR stars per kpc2, a NWC/NWN number ratio of 1.3, and a WR binary frequency of 40%. Compared with other Local Group galaxies, the NWC/NWN number ratio in the solar neighborhood is a factor ~2 above the observed metallicity-dependent trend. This could imply that some 30 galactic WN stars in the d < 3 kpc volume are still hiding. Preliminary results of infrared photometric distance determinations are shown. The galactocentric distance (RWR) distribution per subtype shows RWN and RWC decreasing with later WN and WC subtypes. The observed trend is more indicative of WNE → WCE and WNL → WCL subtype evolution than of WNL → WNE and WCL → WCE subtype evolution.

scholarly journals Status of dark matter in the universe

2017 ◽  
Vol 26 (06) ◽  
pp. 1730012 ◽  
Author(s):  
Katherine Freese
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Gravitational Lensing ◽  
Gamma Ray ◽  
Galactic Center ◽  
Data Sets ◽  
Multiple Sources ◽  
Microwave Background ◽  
First Stars ◽  
The Universe

Over the past few decades, a consensus picture has emerged in which roughly a quarter of the universe consists of dark matter. I begin with a review of the observational evidence for the existence of dark matter: rotation curves of galaxies, gravitational lensing measurements, hot gas in clusters, galaxy formation, primordial nucleosynthesis and Cosmic Microwave Background (CMB) observations. Then, I discuss a number of anomalous signals in a variety of data sets that may point to discovery, though all of them are controversial. The annual modulation in the DAMA detector and/or the gamma-ray excess seen in the Fermi Gamma Ray Space Telescope from the Galactic Center could be due to WIMPs; a 3.5 keV X-ray line from multiple sources could be due to sterile neutrinos; or the 511 keV line in INTEGRAL data could be due to MeV dark matter. All of these would require further confirmation in other experiments or data sets to be proven correct. In addition, a new line of research on dark stars is presented, which suggests that the first stars to exist in the universe were powered by dark matter heating rather than by fusion: the observational possibility of discovering dark matter in this way is discussed.

A determination of the Ω0mh2 cosmological parameter without tension

2021 ◽  
pp. 2150157
Author(s):  
E. Benedetto ◽  
A. Feoli ◽  
A. L. Iannella
Keyword(s):  
Experimental Data ◽  
Scientific Community ◽  
Hubble Constant ◽  
Point Of View ◽  
Cosmological Parameter ◽  
Theoretical Point ◽  
Microwave Background ◽  
Local Measurements ◽  
The Universe

Measurements for the expansion rate of the universe disagree. Indeed, local measurements suggest a higher value of the Hubble constant than those performed through the cosmic microwave background. This fact led to a very interesting debate within the scientific community. The paper is not devoted to give solutions to the problem of “Hubble tension”. The aim of this paper is, on the contrary, to deduce the [Formula: see text] cosmological parameter from a theoretical point of view, using only two experimental data: the temperature of CMB today and the temperature of photons near the decoupling time.

scholarly journals Detection of Anisotropy in the Cosmic Microwave Background at Horizon and Sub-Horizon Scales with the BOOMERanG Experiment

2005 ◽  
Vol 201 ◽  
pp. 55-64
Author(s):  
P. de Bernardis ◽  
P. A. R. Ade ◽  
J. J. Bock ◽  
J. R. Bond ◽  
J. Borrill ◽  
...  
Keyword(s):  
Total Mass ◽  
Signal To Noise Ratio ◽  
Cosmological Parameters ◽  
Power Spectra ◽  
High Signal ◽  
Mass Energy ◽  
Microwave Background ◽  
Technical Advances ◽  
The Universe

BOOMERanG has recently resolved structures on the last scattering surface at redshift ˜ 1100 with high signal to noise ratio. We review the technical advances which made this possible, and we focus on the current results for maps and power spectra, with special attention to the determination of the total mass-energy density in the Universe and of other cosmological parameters.

scholarly journals Biosignatures Search in Habitable Planets

Galaxies ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 82 ◽  
Author(s):  
Riccardo Claudi ◽  
Eleonora Alei
Keyword(s):  
Chemical Composition ◽  
Solar System ◽  
Planetary Atmospheres ◽  
General Interest ◽  
Habitable Planets ◽  
Planetary Bodies ◽  
The Right ◽  
Rocky Planets ◽  
The Universe

The search for life has had a new enthusiastic restart in the last two decades thanks to the large number of new worlds discovered. The about 4100 exoplanets found so far, show a large diversity of planets, from hot giants to rocky planets orbiting small and cold stars. Most of them are very different from those of the Solar System and one of the striking case is that of the super-Earths, rocky planets with masses ranging between 1 and 10 M ⊕ with dimensions up to twice those of Earth. In the right environment, these planets could be the cradle of alien life that could modify the chemical composition of their atmospheres. So, the search for life signatures requires as the first step the knowledge of planet atmospheres, the main objective of future exoplanetary space explorations. Indeed, the quest for the determination of the chemical composition of those planetary atmospheres rises also more general interest than that given by the mere directory of the atmospheric compounds. It opens out to the more general speculation on what such detection might tell us about the presence of life on those planets. As, for now, we have only one example of life in the universe, we are bound to study terrestrial organisms to assess possibilities of life on other planets and guide our search for possible extinct or extant life on other planetary bodies. In this review, we try to answer the three questions that also in this special search, mark the beginning of every research: what? where? how?

scholarly journals Extragalactic Stellar Astronomy with the Brightest Stars in the Universe

2007 ◽  
Vol 3 (S250) ◽  
pp. 313-326
Author(s):  
Rolf Kudritzki ◽  
Miguel A. Urbaneja ◽  
Fabio Bresolin ◽  
Norbert Przybilla
Keyword(s):  
Local Group ◽  
Spectroscopic Method ◽  
Interstellar Extinction ◽  
Stellar Astronomy ◽  
Quantitative Spectral Analysis ◽  
Determination Methods ◽  
Future Work ◽  
The Universe ◽  
Visual Light

AbstractA supergiants are objects in transition from the blue to the red (and vice versa) in the uppermost HRD. They are the intrinsically brightest “normal” stars at visual light with absolute visual magnitudes up to −9. They are ideal to study young stellar populations in galaxies beyond the Local Group to determine chemical composition and evolution, interstellar extinction, reddening laws and distances. We discuss most recent results on the quantitative spectral analysis of such objects in galaxies beyond the Local Group based on medium and low resolution spectra obtained with the ESO VLT and Keck. We describe the analysis method including the determination of metallicity and metallicity gradients. A new method to measure accurate extragalactic distances based on the stellar gravities and effective temperatures is presented, the flux weighted gravity – luminosity relationship (FGLR). The FGLR is a purely spectroscopic method, which overcomes the uncertainties introduced by interstellar extinction and variations of metallicity, which plague all photometric stellar distance determination methods. We discuss the perspectives of future work using the giant ground-based telescopes of the next generation such as the TMT, the GMT and the E-ELT.

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