scholarly journals Stellar Content of Local Group Galaxies - An Introduction

1999 ◽  
Vol 192 ◽  
pp. 3-16 ◽  
Author(s):  
Sidney van den Bergh
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Large Fraction ◽  
Polar Group ◽  
Stellar Content ◽  
Groups Of Galaxies ◽  
Ic 10 ◽  
Sky Survey ◽  
Group Members ◽  
Ngc 6822

In The Realm of the Nebulae, Hubble (1936) first drew attention to the fact that the Milky Way system and the Andromeda galaxy belong to a small cluster that also contains M32, M33, the Magellanic Clouds, NGC 205, NGC 6822 and IC 1613. Hubble also listed IC 10 as a possible member of what he referred to as “the Local Group”. Inspection of the prints of the Palomar Sky Survey shows (van den Bergh 1962) that a large fraction of all field galaxies are located in such small groups or clusters. Our Milky Way system therefore appears to be situated in a rather typical region of space. All of the well-established Local Group members that are listed above are at distances D ≤ 1.0 Mpc. A conservative limit D < 1.5 Mpc may therefore be used to search for new Local Group members. An additional criterion for physical membership in the Local Group is that a candidate member with solar apex distance θ and radial velocity Vr should lie close to the Vr versus cos θ relation for well-established Local Group members (Courteau & van den Bergh 1999). Finally candidates may be disqualified from membership if they appear projected on nearby groups of galaxies that are centered at distances greater than 1.5 Mpc. In particular the Local Group candidates NGC 1560, NGC 1569, UGC-A86 and Cassiopeia 1 were excluded because they appear projected on (or near) the IC 342/Maffei group. Furthermore NGC 55 and UKS 2323-326 were excluded because they appear projected on (or near) the Sculptor (= South Polar) group. Observational data on 35 probable Local Group members are given in Table 1.

Methanol Masers in the Andromeda Galaxy

2017 ◽  
Vol 13 (S336) ◽  
pp. 113-116
Author(s):  
Ylva M. Pihlström ◽  
Loránt O. Sjouwerman
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Local Group ◽  
Angular Resolution ◽  
Transverse Velocity ◽  
High Angular Resolution ◽  
Dynamic Force ◽  
Group Members ◽  
Methanol Masers ◽  
Motion Studies

AbstractIs M31 going to collide with the Milky Way, or spiral around it? Determining the gravitational potential in the Local Group has been a challenge since it requires 3D space velocities and orbits of the members, and most objects have only had line-of-sight velocities measured. Compared to the less massive group members, the transverse velocity of M31 is of great interest, as after the Milky Way, M31 is the most dominant constituent and dynamic force in the Local Group. Proper motion studies of M31 are preferentially done using masers, as continuum sources are much weaker, and are enabled through the high angular resolution provided by VLBI in the radio regime. The challenges of achieving high astrometric accuracy at high VLBI frequencies (> 20 GHz) makes observations at lower frequencies attractive, as long as sufficient angular resolution is obtained. In particular, we have discovered 6.7 GHz methanol masers in M31 using the VLA, and here we will address their feasibility as VLBI proper motion targets using a set of global VLBI observations.

scholarly journals Planetary Nebulae in Local Group Galaxies

1983 ◽  
Vol 103 ◽  
pp. 443-460
Author(s):  
Holland C. Ford
Keyword(s):  
Local Group ◽  
Planetary Nebulae ◽  
Stellar Populations ◽  
Chemical Compositions ◽  
H Ii Regions ◽  
Helium Abundance ◽  
Abundance Gradient ◽  
Star Forming ◽  
Ic 10 ◽  
Ngc 6822

Recent surveys for planetary nebulae have given the first identifications in Fornax, NGC 6822, M33, IC 10, Leo A, Sextans A, Pegasus, WLM, NGC 404, and M81, and extended the identifications in the SMC, the LMC, and M31. Observations of planetaries have established chemical compositions in old or intermediate age populations in 8 Local Group galaxies. The chemical compositions show that i) the helium abundance is higher in planetary nebulae than in H II regions in the same galaxy, and ii) nitrogen is overabundant relative to H II regions by factors of 4 to 100. Planetary nebulae are not a major source of helium in star-forming galaxies, and are a major source of nitrogen. The planetary in Fornax has a relatively high O abundance, and, together with Fornax's carbon stars, establishes the presence of at least 2 stellar populations. The abundance gradient derived from 3 planetaries in M31 is very shallow, and gives high abundances at ~ 20 kpc. By using planetary nebulae as standard candles, upper and lower distance limits have been set for 10 Local Group candidates, and a new distance estimated for M81.

scholarly journals The Orientation of Galaxies in Nearby Galaxy Groups

2004 ◽  
Vol 217 ◽  
pp. 116-117
Author(s):  
P. Flin ◽  
M. Biernacka ◽  
J. Krywult
Keyword(s):  
Statistical Analysis ◽  
Milky Way ◽  
Random Distribution ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Nearby Galaxy ◽  
Groups Of Galaxies ◽  
Galaxy Groups ◽  
Isotropic Distribution ◽  
Local Supercluster

The statistical analysis of six nearby groups of galaxies, connected with the Milky Way, M31, M81, M101, NGC5128 and NGC5236 shows an isotropic distribution of galaxy planes, similarly to galaxies within the Local Group. Also planes of galaxies in the nearby (Vr < 500 km s−1) region of the Local Supercluster exhibit random distribution, disregarding their membership to groups. The result shows that strong environmental effects observed among dwarf galaxies do not change generally random distribution of galaxy planes in this region.

scholarly journals The Massive stellar Population at the Galactic Center

2016 ◽  
Vol 12 (S329) ◽  
pp. 287-291
Author(s):  
Francisco Najarro ◽  
Diego de la Fuente ◽  
Tom R. Geballe ◽  
Don F. Figer ◽  
D. John Hillier
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Stellar Population ◽  
Milky Way ◽  
Local Group ◽  
Galactic Center ◽  
Spectroscopic Studies ◽  
Star Formation History ◽  
Stellar Content ◽  
Formation History

AbstractWe present results from our ongoing infrared spectroscopic studies of the massive stellar content at the Center of the Milky Way. This region hosts a large number of apparently isolated massive stars as well as three of the most massive resolved young clusters in the Local Group. Our survey seeks to infer the presence of a possible top-heavy recent star formation history and to test massive star formation channels: clusters vs isolation.

scholarly journals Microarcsecond astrometry in the Local Group

2007 ◽  
Vol 3 (S248) ◽  
pp. 474-480
Author(s):  
A. Brunthaler ◽  
M. J. Reid ◽  
H. Falcke ◽  
C. Henkel ◽  
K. M. Menten
Keyword(s):  
Proper Motion ◽  
Milky Way ◽  
Local Group ◽  
Statistical Error ◽  
Dark Matter Halo ◽  
Proper Motions ◽  
Angular Rotation ◽  
Vlbi Observations ◽  
Ic 10 ◽  
Motion Measurements

AbstractMeasuring the proper motions and geometric distances of galaxies within the Local Group is very important for our understanding of its history, present state and future. Currently, proper motion measurements using optical methods are limited only to the closest companions of the Milky Way. However, given that VLBI provides the best angular resolution in astronomy and phase-referencing techniques yield astrometric accuracies of ≈ 10 micro-arcseconds, measurements of proper motions and angular rotation rates of galaxies out to a distance of ~ 1 Mpc are feasible. This paper presents results of VLBI observations in regions of H2O maser activity of the Local Group galaxies M33 and IC 10. Two masing regions in M33 are on opposite sides of the galaxy. This allows a comparison of the angular rotation rate (as measured by the VLBI observations) with the known inclination and rotation speed of the Hi gas disk leading to a determination of a geometric distance of 730 ± 100 ± 135 kpc. The first error indicates the statistical error of the proper-motion measurements, while the second error is the systematic error of the rotation model. Within the errors, this distance is consistent with the most recent Cepheid distance to M33. Since all position measurements were made relative to an extragalactic background source, the proper motion of M33 has also been measured. This provides a three dimensional velocity vector of M33, showing that this galaxy is moving with a velocity of 190 ± 59 km s−1 relative to the Milky Way. For IC 10, we obtain a motion of 215 ± 42 km s−1 relative to the Milky Way. These measurements promise a new handle on dynamical models for the Local Group and the mass and dark matter halo of Andromeda and the Milky Way.

scholarly journals Planetary Nebulae as a Probe of the Local Group Galaxies Evolution

2006 ◽  
Vol 2 (S235) ◽  
pp. 215-215
Author(s):  
A. Y. Kniazev ◽  
S. A. Pustilnik ◽  
E. K. Grebel ◽  
D. B. Zucker ◽  
P. Vaisanen
Keyword(s):  
Local Group ◽  
Planetary Nebulae ◽  
Ic 10 ◽  
Irregular Galaxies ◽  
Ngc 6822 ◽  
Dwarf Irregular Galaxies

AbstractWe present the latest results from our study of PNe and HII regions in two Local Group dwarf irregular galaxies IC 10 and NGC 6822.

scholarly journals Detailed abundance analysis of globular clusters in the Local Group

2018 ◽  
Vol 613 ◽  
pp. A56 ◽  
Author(s):  
S. S. Larsen ◽  
J. P. Brodie ◽  
A. Wasserman ◽  
J. Strader
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Element Abundances ◽  
Abundance Patterns ◽  
Lack Of Information ◽  
Very Large Telescope ◽  
Ngc 6822 ◽  
Milky Way Halo

Context. Globular clusters (GCs) are emerging as powerful tracers of the chemical composition of extragalactic stellar populations. Aims. We present new abundance measurements for 11 GCs in the Local Group galaxies NGC 147, NGC 6822, and Messier 33. These are combined with previously published observations of four GCs in the Fornax and Wolf–Lundmark–Melotte (WLM) galaxies. Methods. The abundances were determined from analyses of integrated-light spectra obtained with the HIRES spectrograph on the Keck I telescope and with UVES on the Very Large Telescope (VLT). We used our analysis technique that was developed for this purpose and tested on Milky Way GCs. Results. We find that the clusters with [Fe∕H] < −1.5 are all α-enhanced at about the same level as Milky Way GCs. Their Na abundances are also generally enhanced relative to Milky Way halo stars, suggesting that these extragalactic GCs resemble their Milky Way counterparts in containing large numbers of Na-rich stars. For [Fe∕H] > −1.5, the GCs in M33 are also α-enhanced, while the GCs that belong to dwarfs (NGC 6822 SC7 and Fornax 4) have closer to solar-scaled α-element abundances. The abundance patterns in SC7 are remarkably similar to those in the Galactic GC Ruprecht 106, including significantly subsolar [Na∕Fe] and [Ni∕Fe] ratios. In NGC 147, the GCs with [Fe∕H] < −2.0 account for about 6% of the total luminosity of stars in the same metallicity range, a lower fraction than those previously found in the Fornax and WLM galaxies, but substantially higher than in the Milky Way halo. Conclusions. At low metallicities, the abundance patterns suggest that GCs in the Milky Way, dwarf galaxies, and M33 experienced similar enrichment histories and/or processes. At higher metallicities, the lower levels of α-enhancement in the GCs found in dwarf galaxies resemble the abundance patterns observed in field stars in nearby dwarfs. Constraining the presence of multiple populations in these GCs is complicated by lack of information about detailed abundances in field stars of the corresponding metallicities. We suggest that correlations such as [Na∕Fe] versus [Ni∕Fe] may prove useful for this purpose if an accuracy of ~ 0.1 dex or better can be reached for integrated-light measurements.

scholarly journals Solo dwarfs – III. Exploring the orbital origins of isolated Local Group galaxies with Gaia Data Release 2

2020 ◽  
Vol 501 (2) ◽  
pp. 2363-2377
Author(s):  
Alan W McConnachie ◽  
Clare R Higgs ◽  
Guillaume F Thomas ◽  
Kim A Venn ◽  
Patrick Côté ◽  
...  
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Proper Motions ◽  
Star Forming ◽  
Isolated Galaxies ◽  
Data Release ◽  
Red Giant ◽  
Ngc 6822 ◽  
Interaction History

ABSTRACT We measure systemic proper motions for distant dwarf galaxies in the Local Group and investigate if these isolated galaxies have ever had an interaction with the Milky Way or M31. We cross-match photometry of isolated, star-forming, dwarf galaxies in the Local Group, taken as part of the Solo survey, with astrometric measurements from Gaia Data Release 2. We find that NGC 6822, Leo A, IC 1613, and WLM have sufficient supergiants with reliable astrometry to derive proper motions. An additional three galaxies (Leo T, Eridanus 2, and Phoenix) are close enough that their proper motions have already been derived using red giant branch stars. Systematic errors in Gaia DR2 are significant for NGC 6822, IC 1613, and WLM. We explore the orbits for these galaxies, and conclude that Phoenix, Leo A, and WLM are unlikely to have interacted with the Milky Way or M31, unless these large galaxies are very massive (${\gtrsim}1.6 \times 10^{12}\, \mathrm{M}_\odot$). We rule out a past interaction of NGC 6822 with M31 at ${\sim}99.99{{\ \rm per\ cent}}$ confidence, and find there is a &lt;10 per cent chance that NGC 6822 has had an interaction with the Milky Way. We examine the likely origins of NGC 6822 in the periphery of the young Local Group, and note that a future interaction of NGC 6822 with the Milky Way or M31 in the next 4 Gyr is essentially ruled out. Our measurements indicate that future Gaia data releases will provide good constraints on the interaction history for the majority of these galaxies.

scholarly journals Magnetic fields and ionized gas in the local group irregular galaxies IC 10 and NGC 6822

2003 ◽  
Vol 405 (2) ◽  
pp. 513-524 ◽  
Author(s):  
K. T. Chyży ◽  
J. Knapik ◽  
D. J. Bomans ◽  
U. Klein ◽  
R. Beck ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Local Group ◽  
Ionized Gas ◽  
Ic 10 ◽  
Irregular Galaxies ◽  
Ngc 6822

2MASS and the Nearby Universe

2005 ◽  
Vol 216 ◽  
pp. 170-179 ◽  
Author(s):  
John Huchra ◽  
Nathalie Martimbeau ◽  
Thomas Jarrett ◽  
Roc Cutri ◽  
Michael Skrutskie ◽  
...  
Keyword(s):  
Velocity Vector ◽  
Milky Way ◽  
Local Group ◽  
Extended Source ◽  
Sky Survey ◽  
Low Latitudes ◽  
Final Data ◽  
Data Products ◽  
Baryonic Mass ◽  
The Universe

The Two Micron All-Sky Survey was conceived over a decade ago for the express purpose of mapping the Milky Way and the Universe nearby. 2MASS is now complete and the final data products, including the extended source catalog (XSC), have been released. The XSC contains nearly a million galaxies to the stated completeness goal of K=13.5. While the catalog becomes incomplete at the faintest magnitudes and lowest galactic latitudes due to confusion, at the bright end the catalog is essentially complete down to very low latitudes (b less than 5 degrees), which makes it an excellent survey for the distribution of matter in the nearby Universe. Redshift information is now nearly complete for the 24,000 galaxies brighter than K=11.25 and above |b|=5°. We now have an amazing census of galaxy (baryonic mass) concentrations over the whole sky and inside z=0.04. Several new structures are elucidated and the characteristics of the structures are described. We also examine the match between the predicted gravitational velocity vector of the Local Group and the motions determined by other experiments including the CMB dipole.

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