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

TL;DR

This study uses Cepheid data to estimate the radial and vertical scale parameters of the Galactic thin disk, revealing age-dependent variations and providing updated scale length and height measurements.

Contribution

It introduces new estimates of the Galactic thin disk's scale length and height using a large Cepheid sample, accounting for age-related differences and birth distributions.

Findings

Radial scale length h_R ≈ 2.3 kpc for young Cepheids

Vertical scale height h_z ≈ 75 pc for young Cepheids

Older Cepheids show larger vertical scale heights and different Sun offset

Abstract

Up-to-date data on 2214 classical Cepheids have been used. The model of an exponential matter density distribution in the Galactic thin disk has been applied. New estimates of the radial disk scale length $h_R,$ the distance of the Sun from the symmetry plane $z_\odot$, and the vertical disk scale height $h_z$ have been obtained. Based on samples of 1087 Cepheids younger than 120 Myr and 1127 Cepheids older than 120 Myr, we have found $h_R=2.30\pm0.09$ kpc and $h_R=1.96\pm0.12$ kpc, respectively. It has turned out that an unambiguous estimate of $h_R$ cannot be obtained from their overall radial distribution. However, we have constructed the radial distribution of 806 Cepheids of different ages at the time of their birth from which we have found $h_R=2.36\pm0.24$ kpc. We show that $h_z$ depends strongly on the age of stars. For example, from 705 Cepheids younger than 120 Myr with heliocentric distances $r<6$ kpc we have found $z_\odot=-17\pm4$ pc and $h_z=75\pm5$ pc. From 393 Cepheids older than 120 Myr at $r<6$ kpc, we have found $z_\odot=-39\pm11$ pc and $h_z=131\pm10$ pc.