Structural Parameters of Thin and Thick Disks in Edge-on Disk Galaxies

By P. Yoachim, J. J. Dalcanton. 2005

257 citations recorded by the source corpus.

We analyze the global structure of 34 late-type, edge-on, undisturbed, disk galaxies spanning a wide range of mass. We measure structural parameters for the galaxies using two-dimensional least-squares fitting to our R-band photometry. The fits require both a thick and a thin disk to adequately fit the data. The thick disks have larger scale heights and longer scale lengths than the embedded thin disks by factors of ∼2 and ∼1.25, respectively. The observed structural parameters agree well with the properties of thick and thin disks derived from star counts in the Milky Way and from resolved stellar populations in nearby galaxies. We find that massive galaxies' luminosities are dominated by the thin disk. However, in low-mass galaxies (Vc ≲ 120 km s-1) thick disk stars contribute nearly half the luminosity and dominate the stellar mass. Thus, although low-mass dwarf galaxies appear blue, the majority of their stars are probably quite old. Our data are most easily explained by a formation scenario in which the thick disk is assembled through direct accretion of stellar material from merging satellites while the thin disk is formed from accreted gas. The baryonic fraction in the thin disk therefore constrains the gas richness of the merging pregalactic fragments. If we include the mass in H I as part of the thin disk, the thick disk contains ≲10% of the baryons in high-mass galaxies and ∼25%–30% of the baryons in low-mass galaxies. Our data, therefore, indicate that the fragments were quite gas rich at the time of merging (fgas = 75%–90%). However, because low-mass galaxies have a smaller fraction of baryons in their thin disks, the pregalactic fragments from which they assembled must have been systematically more gas poor. We believe this trend results from increased outflow due to supernova-driven winds in the lower mass pregalactic fragments. We estimate that ∼60% of the total baryonic mass in these systems was lost due to outflows. Pushing the episode of significant winds to early times allows the mass-metallicity relationship for disks to be established early, before the main disk is assembled, and obviates the difficulty in driving winds from diffuse disks with low star formation efficiencies. We discuss other implications of this scenario for solving the G dwarf problem, for predicting abundance trends in thick disks, and for removing discrepancies between semianalytic galaxy formation models and the observed colors of low-mass galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/1d17799effbf03d7ceec32961ecb9d4fa658752e

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Citations in the corpus

Exploring the Milky Way stellar disk - A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood (2013, background): “Furthermor , other recent studies actually show that many, if not all, edge-on spiral galaxies appear to host dual disk systems (e.g., Yoachim & Dalcanton 2006; Comerón et al. 2011).”
From Rings to Bulges: Evidence for Rapid Secular Galaxy Evolution at z ~ 2 from Integral Field Spectroscopy in the SINS Survey (2008, background): “It is tempting to speculate that the thick, old stellar disks seen in the Milky Way and nearby galaxies (e.g., Freeman & Bland-Hawthorn 2002; Yoachim & Dalcanton 2006) are the remnants of this z 2Y3 phase of transient evolution of clumpy, turbulent disks fed by rapid cold flows.”
Dissecting simulated disc galaxies - I. The structure of mono-age populations (2014, background): “The stellar disc of the Milky Way, as well as of many nearby galaxies, is traditionally viewed as consisting of two distinct components: a thin and a thick disc (e.g., Burstein 1979; Tsikoudi 1979; Gilmore & Reid 1983; Dalcanton & Bernstein 2002; Yoachim & Dalcanton 2006; Comerón et al. 2011).”
THE SPATIAL STRUCTURE OF MONO-ABUNDANCE SUB-POPULATIONS OF THE MILKY WAY DISK (2011, background): “…found that thickerdisk components have larger scale heights and longer scale lengths than their corresponding thin disk (Robin et al. 1996; Buser et al. 1999; Chen et al. 2001; Ojha 2001; Neeser et al. 2002; Larsen & Humphreys 2003; Yoachim & Dalcanton 2006; Pohlen et al. 2007; Jurić et al. 2008).”
THE MILKY WAY HAS NO DISTINCT THICK DISK (2011, background): “…by many studies in the last two decades (e.g., Reid & Majewski 1993; Jurić et al. 2008), seems to be a generic feature of galactic disks (e.g., Yoachim & Dalcanton 2006) and has typically been described by, and often ascribed to, the presence of a “thick-disk” component, distinct from both…”
FORMING REALISTIC LATE-TYPE SPIRALS IN A ΛCDM UNIVERSE: THE ERIS SIMULATION (2011, background): “…structure of edge-on spiral galaxies finds that the scale height of their thin disk increases systematically with circular velocity as z0 = 610 (Vc/100 km s −1)0.9 pc (Yoachim & Dalcanton 2006), where z0 is the scale height of a sech2 profile, z0 ≈ 2hz at large heights above the disk plane.”
Thin disc, thick disc and halo in a simulated galaxy (2012, result): “This would be consistent with observations which indicate that thick discs are more prominent in lower mass disc galaxies (Yoachim & Dalcanton 2006).”
Observations of Thick Disks in the Hubble Space Telescope Ultra Deep Field (2006, methodology): “This ratio is 2.3± 0.7 from Figure 17, and 3.4± 1.7 for modern galaxies in Yoachim & Dalcanton (2006).”
A RADIAL AGE GRADIENT IN THE GEOMETRICALLY THICK DISK OF THE MILKY WAY (2016, background): “These geometrically thick disks are extended (they form a red envelope all around the thin disks) and have scale lengths comparable to those of thin disks (Yoachim & Dalcanton 2006; Pohlen et al. 2007; Comerón et al. 2012).”
The GALAH survey: scientific motivation (2015, background): “In addition to their defining thin discs, almost all spirals appear to have a thick disc component (Yoachim & Dalcanton 2006).”
The structure and dynamical evolution of the stellar disc of a simulated Milky Way-mass galaxy (2016, background): “Such a two-component profile is also seen in external edge-on disk galaxies (e.g. Yoachim & Dalcanton 2006; Comerón et al. 2011, 2012).”
New constraints on the chemical evolution of the solar neighbourhood and galactic disc(s) - improved astrophysical parameters for the Geneva-Copenhagen Survey (2011, background): “Observations of external edge-on galaxies show the presenc of both a thin and thick disc component (Burstein 1979; Dalcanton & Bernstein 2002; Yoachim & Dalcanton 2006).”
Mapping the Milky Way with LAMOST– III. Complicated spatial structure in the outer disc (2018, background): “The ratio of the scale length of the thick to thin disc is ∼ 1.3, in agreement with the typical ratios found in the external galaxies (Yoachim & Dalcanton 2006).”
The Milky Way Tomography with SDSS. I. Stellar Number Density Distribution (2005, result): “Quantitatively, the ratio of best-fit length scales is close to 1.4, similar (within uncertainties) to typical scale length ratios of 1.25 seen in edge-on late-type disk galaxies (Yoachim & Dalcanton 2006).”
Vertical disc heating in Milky Way-sized galaxies in a cosmological context (2015, background): “The existence of thickened stellar discs has been known since observations of the luminosity profiles of edge-on external galaxies (Burstein 1979; Tsikoudi 1979) revealed an excess of starlight at more than ∼ 1 kpc vertical distance from the mid plane (Yoachim & Dalcanton 2006; Jurić et al. 2008).”
Constraining the Milky Way assembly history with Galactic Archaeology (2016, background): “Stellar disc density decomposition into thinner and thicker components in external edge-on galaxies find that thicker disc components have larger scale-lengths than the thin discs (e.g., Comerón et al. 2012; Pohlen et al. 2007; Yoachim & Dalcanton 2006).”
Constraining the thick disc formation scenario of the Milky Way (2014, unknown): “Our thick disc has a very similar short scale length to that of the old thin disc, as is also observed in most external galaxies (Yoachim & Dalcanton 2006).”
Oxygen abundances in nearby stars - Clues to the formation and evolution of the Galactic disk (2007, background): “In a recent study of thick disks in edge-on galaxies, Yoachim & Dalcanton (2006) conclude that their observations can be explained by models in which stars form in galactic subunits before merging to form a thick disk.”
Measuring the vertical age structure of the Galactic disc using asteroseismology and SAGA (2015, background): “…of the Royal Astronomical Society at T he A ustralian N ational U niversity on A pril 10, 2016 http://m nras.oxfordjournals.org/ disc appears as a puffed-up component extending to a larger height above a sharper thin disc (e.g. Burstein 1979; van der Kruit & Searle 1981; Yoachim & Dalcanton 2006).”