Comparisons of a standard galaxy model with stellar observations in five fields

Bahcall, John N.; Soneira, R. M.

doi:10.1086/190948

Cited by 160 publications

(136 citation statements)

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“…The expected contamination of our sample due to Milky Way foreground stars is negligible; generic star-count models (e.g., Bahcall & Soneira 1984), as well as direct star counts from the Hubble Deep Field and Medium Deep Fields (e.g., Santiago et al 1996;Mendez et al 1996), predict that we should expect to see less than one foreground star with I < 26 mag within the HRC field size of 0.2 arcmin 2 . Similarly, the galaxy counts from the Hubble Deep Field (Williams et al 1996) suggest we should see at most six galaxies with I < 26 mag in our field.…”

Section: Observations and Data Reductionmentioning

confidence: 85%

Two Populations of Young Massive Star Clusters in Arp 220

Wilson

Harris

Longden

et al. 2006

ApJ

103

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We present new optical observations of young massive star clusters in Arp 220, the nearest ultraluminous infrared galaxy, taken in UBVI with the Hubble Space Telescope ACS HRC camera. We find a total of 206 probable clusters whose spatial distribution is centrally concentrated toward the nucleus of Arp 220. We use model star cluster tracks to determine ages, luminosities, and masses for 14 clusters with complete UBVI indices or previously published nearinfrared data. We estimate rough masses for 24 additional clusters with I < 24 mag from BVI indices alone. The clusters with useful ages fall into two distinct groups: a ''young'' population (<10 Myr) and an intermediate-age population ('300 Myr). There are many clusters with masses clearly above 10 6 M and possibly even above 10 7 M in the most extreme instances. These masses are high enough that the clusters being formed in the Arp 220 starburst can be considered to be genuine young globular clusters. In addition, this study allows us to extend the observed correlation between global star formation rate and maximum cluster luminosity by more than 1 order of magnitude in star formation rate.

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Section: Observations and Data Reductionmentioning

confidence: 85%

Two Populations of Young Massive Star Clusters in Arp 220

Wilson

Harris

Longden

et al. 2006

ApJ

103

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“…This is certainly a reasonable assumption for small z, although there is no reason why the galactic disk should be isothermal at all. Bahcall (1984b) (but see also Bahcall 1984a;Bahcall & Soneira 1984) treated the problem assuming that non isothermality can be simulated by the superposition of more isothermal components. The observations of Kuijken & Gilmore (1989b) (Kuijken & Gilmore 1989a,c) show significant departures from isothermality at large z.…”

Section: Non-isothermal Profile Of the Galactic Disksmentioning

confidence: 99%

“…the Milky Way. A major advancement of these techniques was achieved by Bahcall & Soneira (1984) who applied the concept of stellar populations to the solar neighbourhood (see also Bahcall 1984a,b) and nowadays, more theoretically sophisticated star-count models are the standard tools to investigate the MW stellar distribution (e.g., the Besançon model, Robin et al 2003). The ultimate step toward the understanding of our Galaxy is thus represented by the extension of the concept of stellar populations to include kinematics, dynamics, photometric and chemical properties together in a global MW modelling approach (e.g., Méndez et al 2000;Vallenari et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Spiral arm kinematics for Milky Way stellar populations

Pasetto

Natale

Kawata

et al. 2016

Mon. Not. R. Astron. Soc.

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We present a new theoretical population synthesis model (the Galaxy Model) to examine and deal with large amounts of data from surveys of the Milky Way and to decipher the present and past structure and history of our own Galaxy.We assume the Galaxy to consist of a superposition of many composite stellar populations belonging to the thin and thick disks, the stellar halo and the bulge, and to be surrounded by a single dark matter halo component. A global model for the Milky Way's gravitational potential is built up self-consistently with the density profiles from the Poisson equation. In turn, these density profiles are used to generate synthetic probability distribution functions (PDFs) for the distribution of stars in colour-magnitude diagrams (CMDs). Finally, the gravitational potential is used to constrain the stellar kinematics by means of the moment method on a (perturbed)-distribution function. Spiral arms perturb the axisymmetric disk distribution functions in the linear response framework of density-wave theory where we present an analytical formula of the so-called 'reduction factor' using Hypergeometric functions.Finally, we consider an analytical non-axisymmetric model of extinction and an algorithm based on the concept of probability distribution function to handle colour magnitude diagrams with a large number of stars. A genetic algorithm is presented to investigate both the photometric and kinematic parameter space.This galaxy model represents the natural framework to reconstruct the structure of the Milky Way from the heterogeneous data set of surveys such as Gaia-ESO, SEGUE, APOGEE2, RAVE and the Gaia mission.

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“…The former group of stars includes the prominent peak associated with the giant southern stream and is roughly centered on M31's systemic velocity of À300 km s À1 ; they are therefore designated ''candidate M31 RGB stars.'' The latter group of stars occupies the radial velocity range predicted by the Institute for Advanced Study Galaxy (IASG) star-count model (RG02; Bahcall & Soneira 1984;Ratnatunga & Bahcall 1985); they are therefore designated ''candidate Galactic dwarf stars.'' We now test the validity of these designations by comparing the properties of these two groups of stars.…”

Section: Radial Velocitymentioning

confidence: 99%

Dynamics and Stellar Content of the Giant Southern Stream in M31. I. Keck Spectroscopy of Red Giant Stars

et al. 2006

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This paper presents the first results from a large spectroscopic survey of red giant branch ( RGB) stars in M31 using DEIMOS on the Keck 10 m telescope. A photometric prescreening method, based on the intermediate-width DDO51 band centered on the Mg b/MgH absorption feature, was used to select spectroscopic targets. RGB candidates were targeted in a small section of M31's giant southern tidal stream at a projected distance of 31 kpc from the galaxy's center. We isolate a clean sample of 68 RGB stars by removing contaminants (foreground Milky Way dwarf stars and background galaxies) using a combination of spectroscopic, imaging, and photometric methods: radial velocity and the surface gravity-sensitive Na i doublet are particularly useful in this regard. About 65% of the M31 stars are found to be members of the giant southern stream, while the rest appear to be members of the general spheroid population. The mean (heliocentric) radial velocity of the stream in our field is À458 km s À1 , blueshifted by À158 km s À1 relative to M31's systemic velocity, in good agreement with recent velocity measurements at other points along the stream. The intrinsic velocity dispersion of the stream is found to be 15 þ8 À15 km s À1 (90% confidence limit). A companion paper by Font and coworkers discusses possible orbits, implications of the coldness of the stream, and properties of the progenitor satellite galaxy. The kinematics, and possibly the metallicity distribution, of the general spheroid (i.e., nonstream) population in this region of M31 indicate that it is significantly different from samples drawn from other parts of the M31 spheroid; this is probably an indication of substructure in the bulge and halo. The stream appears to have a higher mean metallicity than the general spheroid, h½Fe/H i $ À0:54 versus À0.74, and a smaller metallicity spread. The relatively high metallicity of the stream implies that its progenitor must have been a luminous dwarf galaxy. The Ca ii triplet line strengths of the M31 RGB stars are generally consistent with photometric estimates of their metallicity (derived by fitting RGB fiducials in the color-magnitude diagram). There is indirect evidence of a population of intermediate-age stars in the stream.

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Comparisons of a standard galaxy model with stellar observations in five fields

Cited by 160 publications

References 0 publications

Two Populations of Young Massive Star Clusters in Arp 220

Two Populations of Young Massive Star Clusters in Arp 220

Spiral arm kinematics for Milky Way stellar populations

Dynamics and Stellar Content of the Giant Southern Stream in M31. I. Keck Spectroscopy of Red Giant Stars

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