Estimation of the Radial Scale Length and Vertical Scale Height of the Galactic Thin Disk from Cepheids

Abstract. A 30-day incoherent scatter radar (ISR) experiment was conducted at Millstone Hill (288.5° E, 42.6° N) from 4 October to 4 November 2002. The altitude profiles of electron density Ne, ion and electron temperature (Ti and Te), and line-of-sight velocity during this experiment were processed to deduce the topside plasma scale height Hp, vertical scale height VSH, Chapman scale height Hm, ion velocity, and the relative altitude gradient of plasma temperature (dTp/dh)/Tp, as well as the F2 layer electron density (NmF2) and height (hmF2). These data are analyzed to explore the variations of the ionosphere over Millstone Hill under geomagnetically quiet and disturbed conditions. Results show that ionospheric parameters generally follow their median behavior under geomagnetically quiet conditions, while the main feature of the scale heights, as well as other parameters, deviated significantly from their median behaviors under disturbed conditions. The enhanced variability of ionospheric scale heights during the storm-times suggests that the geomagnetic activity has a major impact on the behavior of ionospheric scale heights, as well as the shape of the topside electron density profiles. Over Millstone Hill, the diurnal behaviors of the median VSH and Hm are very similar to each other and are not so tightly correlated with that of the plasma scale height Hp or the plasma temperature. The present study confirms the sensitivity of the ionospheric scale heights over Millstone Hill to thermal structure and dynamics. The values of VSH/Hp tend to decrease as (dTp/dh)/Tp becomes larger or the dynamic processes become enhanced.

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Astrometric Plate Reduction with Orthogonal Functions and Milliarcseconds Accuracy in Deep Proper Motion Surveys

Symposium - International Astronomical Union ◽

10.1017/s0074180900228519 ◽

1995 ◽

Vol 166 ◽

pp. 368-368

Author(s):

Devendra Ojha ◽

Olivier Bienaymé

Keyword(s):

Galactic Plane ◽

Structural Parameters ◽

Thin Disk ◽

Scale Height ◽

Thick Disk ◽

Sample Survey ◽

Time Base ◽

List Type ◽

Proper Motions ◽

Velocity Dispersions

We have been doing a sample survey in UBV photometry and proper motions as part of an investigation of galactic structure and evolution. The 3 fields in the direction of galactic anticentre (l = 167°, b = 47°), centre (l = 3°, b = 47°) and antirotation (l = 278°, b = 47°) have been surveyed. The high astrometric quality of the MAMA machine (CAI, Paris) gives access to micronic accuracy (leading to < 2 mas per year) on proper motions with a 35 years time base. The kinematical distribution of F and G–type stars have been probed to distances up to 2.5 kpc above the galactic plane. We have derived the constrain on the structural parameters of the thin and thick disk components of the Galaxy (Ojha et al. 1994abc): • The scale lengths of the thin and thick disks are found to be 2.6±0.1 and 3.3±0.5 kpc, respectively. The density laws for stars with 3.5≤MV≤5 as a function of distance above the plane follow a single exponential with scale height of ∼ 260 pc (thin disk) and a second exponential with scale height of ∼ 800 pc (thick disk) with a local normalization of 5–6% of the disk.• The thin disk population was found with (〈 U+W〉, 〈V〉) = (1±4, −14±2) km/s and velocity dispersions (σU+W, σV) = (35±2, 30±1) km/s. The thick disk population was found to have a rotational velocity of Vrot = 177 km/s and velocity dispersions (σU, σV, σW) = (67,51,42) km/s. No dependence with r and z distances was found in the asymmetric drift measurements of the thick disk population.

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The radial extent of the Galactic thick disk

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316008875 ◽

2016 ◽

Vol 11 (S321) ◽

pp. 3-5

Author(s):

Thomas Bensby

Keyword(s):

Milky Way ◽

Galactic Disk ◽

Thin Disk ◽

Thick Disk ◽

Stellar Disk ◽

Chemical Signatures ◽

Radial Extent ◽

Thin And Thick Disks ◽

Thick Disks ◽

Scale Length

AbstractBased on observational data from the fourth internal data release of the Gaia-ESO Survey we probe the abundance structure in the Milky Way stellar disk as a function of galactocentric radius and height above the plane. We find that the inner and outer Galactic disks have different chemical signatures. The stars in the inner Galactic disk show abundance signatures of both the thin and thick disks, while the stars in the outer Galactic disk resemble in majority the abundances seen in the thin disk. Assuming that the Galactic thick disk can be associated with the α-enriched population, this can be interpreted as that the thick disk density drops drastically beyond a galactocentric radius of about 10 kpc. This is in agreement with recent findings that the thick disk has a short scale-length, shorter than that of the the thin disk.

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Impacts of Radial Mixing on the Galactic Thick and Thin Disks

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317007517 ◽

2017 ◽

Vol 13 (S334) ◽

pp. 132-135

Author(s):

Daisuke Kawata

Keyword(s):

Thin Disk ◽

Scale Height ◽

Thick Disk ◽

The Other ◽

Galactic Disks ◽

Spiral Arms ◽

Other Hand ◽

Initial Scale ◽

Thin Disks ◽

Metallicity Distribution

AbstractUsing N-body simulations of the Galactic disks, we qualitatively study how the metallicity distributions of the thick and thin disk stars are modified by radial mixing induced by the bar and spiral arms. We show that radial mixing drives a positive vertical metallicity gradient in the mono-age disk population whose initial scale-height is constant and initial radial metallicity gradient is tight and negative. On the other hand, if the initial disk is flaring, with scale-height increasing with galactocentric radius, radial mixing leads to a negative vertical metallicity gradient, which is consistent with the current observed trend. We also discuss impacts of radial mixing on the metallicity distribution of the thick disk stars. By matching the metallicity distribution of N-body models to the SDSS/APOGEE data, we argue that the progenitor of the Milky Way’s thick disk should not have a steep negative metallicity gradient.

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NIHAO-UHD: The properties of MW-like stellar disks in high resolution cosmological simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3241 ◽

2019 ◽

Cited By ~ 11

Author(s):

Tobias Buck ◽

Aura Obreja ◽

Andrea V Macciò ◽

Ivan Minchev ◽

Aaron A Dutton ◽

...

Keyword(s):

Milky Way ◽

General Structure ◽

Stellar Mass ◽

Scale Height ◽

Stellar Disk ◽

Galactic Disks ◽

Cosmological Simulations ◽

Hydrodynamical Simulations ◽

Single Exponential ◽

Scale Length

Abstract Simulating thin and extended galactic disks has long been a challenge in computational astrophysics. We introduce the NIHAO-UHD suite of cosmological hydrodynamical simulations of Milky Way mass galaxies and study stellar disk properties such as stellar mass, size and rotation velocity which agree well with observations of the Milky Way and local galaxies. In particular, the simulations reproduce the age-velocity dispersion relation and a multi-component stellar disk as observed for the Milky Way. Half of our galaxies show a double exponential vertical profile, while the others are well described by a single exponential model which we link to the disk merger history. In all cases, mono-age populations follow a single exponential whose scale height varies monotonically with stellar age and radius. The scale length decreases with stellar age while the scale height increases. The general structure of the stellar disks is already set at time of birth as a result of the inside-out and upside-down formation. Subsequent evolution modifies this structure by increasing both the scale length and height of all mono-age populations. Thus, our results put tight constraints on how much dynamical memory stellar disks can retain over cosmological timescales. Our simulations demonstrate that it is possible to form thin galactic disks in cosmological simulations provided there are no significant stellar mergers at low redshifts. Most of the stellar mass is formed in-situ with only a few percent ($\lesssim 5\%$) brought in by merging satellites at early times. Redshift zero snapshots and halo catalogues are publicly available.

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H i scale height in spiral galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2959 ◽

2020 ◽

Vol 499 (2) ◽

pp. 2063-2075

Author(s):

Narendra Nath Patra

Keyword(s):

Boltzmann Equation ◽

Spiral Galaxies ◽

Axial Ratio ◽

Scale Height ◽

Vertical Scale ◽

Ngc 6946 ◽

Component Systems ◽

Poisson Boltzmann ◽

Poisson Boltzmann Equation ◽

Set Up

ABSTRACT We model the galactic discs of seven nearby large spiral galaxies as three-component systems consist of stars, molecular gas, and atomic gas in vertical hydrostatic equilibrium. We set up the corresponding joint Poisson–Boltzmann equation and solve it numerically to estimate the 3D distribution of H i in these galaxies. While solving the Poisson–Boltzmann equation, we do not consider a constant H i velocity dispersion (σHI); rather, we develop an iterative method to self-consistently estimate the σHI profile in a galaxy by using the observed second-moment profile of the H i spectral cube. Using the density solutions, we determine the H i vertical scale height in our galaxies. We find that the H i discs flare in a linear fashion as a function of radius. H i scale height in our galaxies is found to vary between a few hundred parsecs at the centre to ∼1–2 kpc at the outskirts. We estimate the axial ratio of the H i discs in our sample galaxies and find a median ratio of 0.1, which is much lower than what is found for dwarf galaxies, indicating much thinner H i discs in spiral galaxies. Very low axial ratios in three of our sample galaxies (NGC 5055, NGC 6946, and NGC 7331) suggest them to be potential superthin galaxies. Using the H i distribution and the H i hole sizes in NGC 6946, we find that most of the H i holes in this galaxy are broken out into the circumgalactic medium and this breaking out is more effective in the inner radii as compared to the outer radii.

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Scale length of the galactic thin disk

Journal of Astrophysics and Astronomy ◽

10.1007/bf02702262 ◽

2000 ◽

Vol 21 (1-2) ◽

pp. 53-59

Author(s):

D. K. Ojha

Keyword(s):

Thin Disk ◽

Scale Length

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The Structure of the Superthin Spiral Galaxy UGC7321

International Astronomical Union Colloquium ◽

10.1017/s0252921100054336 ◽

1999 ◽

Vol 171 ◽

pp. 207-209

Author(s):

L.D. Matthews ◽

J.S. Gallagher ◽

W. van Driel

Keyword(s):

Star Formation ◽

Spiral Galaxy ◽

Surface Brightness ◽

Scale Height ◽

Vertical Scale ◽

Low Surface Brightness ◽

Galaxy Disk ◽

Color Gradients

AbstractUGC 7321 is an edge-on low surface brightness (LSB) spiral galaxy with a number of extraordinary properties. Its vertical scale height (~70 pc) is one of the smallest ever measured for a galaxy disk. Its disk also exhibits strong vertical and radial color gradients. UGC 7321 appears to be an extremely unevolved galaxy in both a dynamical and in a star-formation sense.

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