THICK DISKS OF EDGE-ON GALAXIES SEEN THROUGH THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S4G): LAIR OF MISSING BARYONS?

By S. Comer'on, Bruce G. Elmegreen, Johan H. Knapen, Heikki Salo, E. Laurikainen, J. Laine, E. Athanassoula, A. Bosma, K. Sheth, M. Regan and 14 more. 2011

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Most, if not all, disk galaxies have a thin (classical) disk and a thick disk. In most models thick disks are thought to be a necessary consequence of the disk formation and/or evolution of the galaxy. We present the results of a study of the thick disk properties in a sample of carefully selected edge-on galaxies with types ranging from T = 3 to T = 8. We fitted one-dimensional luminosity profiles with physically motivated functions—the solutions of two stellar and one gaseous isothermal coupled disks in equilibrium—which are likely to yield more accurate results than other functions used in previous studies. The images used for the fits come from the Spitzer Survey of Stellar Structure in Galaxies (S4G). We found that thick disks are on average more massive than previously reported, mostly due to the selected fitting function. Typically, the thin and thick disks have similar masses. We also found that thick disks do not flare significantly within the observed range in galactocentric radii and that the ratio of thick-to-thin disk scale heights is higher for galaxies of earlier types. Our results tend to favor an in situ origin for most of the stars in the thick disk. In addition, the thick disk may contain a significant amount of stars coming from satellites accreted after the initial buildup of the galaxy and an extra fraction of stars coming from the secular heating of the thin disk by its own overdensities. Assigning thick disk light to the thin disk component may lead to an underestimate of the overall stellar mass in galaxies because of different mass-to-light ratios in the two disk components. On the basis of our new results, we estimate that disk stellar masses are between 10% and 50% higher than previously thought and we suggest that thick disks are a reservoir of “local missing baryons.”

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

Yule-Simpson’s paradox in Galactic Archaeology (2019, background): “These ”nested flares” constitute a geometric thick disk which does not flare, or in which the flaring is strongly reduced, consistent with the lack of disk flaring found in the observations of external galaxies (van der Kruit & Searle 1982; de Grijs 1998; Comerón et al. 2011).”
A CLASSICAL MORPHOLOGICAL ANALYSIS OF GALAXIES IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S4G) (2015, background): “…tidal debris (S. Laine et al. 2014; Kim et al. 2012), the properties of thick disks seen in edge-on galaxies of types Sb to Sdm and profile breaks (Comerón et al. 2011a,b,c; 2012), mid-IR flocculent and grand design spiral structure and star-forming regions (Elmegreen et al. 2011, 2014),…”
A DIVERSITY OF PROGENITORS AND HISTORIES FOR ISOLATED SPIRAL GALAXIES (2012, methodology): “The fact that the edges of thick disks are not flared (see for instance Comerón et al. 2011) was used by Bournaud et al. (2009) to show that they most likely did not form because of minor mergers, but rather are the relics of gas-rich clumpy disks at high redshift.”
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).”
A RADIAL AGE GRADIENT IN THE GEOMETRICALLY THICK DISK OF THE MILKY WAY (2016, background): “…(or morphologically), based on decomposition of vertical density profiles (Gilmore & Reid 1983; Yoachim & Dalcanton 2006; Jurić et al. 2008; Comerón et al. 2011), or at a fixed height above the disk midplane (Yoachim & Dalcanton 2008a; Rejkuba et al. 2009; Cheng et al. 2012a); (2)…”
Constraining the Milky Way assembly history with Galactic Archaeology (2016, background): “Additionally, while no flaring is observed in external edge-on discs (Comerón et al., 2011; de Grijs, 1998; van der Kruit & Searle, 1982), numerical simulations suggest that flaring cannot be avoided due to a range of different dynamical effects.”
Estimating stellar birth radii and the time evolution of Milky Way’s ISM metallicity gradient (2018, background): “These ”nested flares” constitute a geometric thick disk, which does not flare, or in which the flaring is strongly reduced, consistent with the lack of disk flaring found in the observations of external galaxies (van der Kruit & Searle 1982; de Grijs 1998; Comerón et al. 2011).”
The age structure of stellar populations in the solar vicinity Clues of a two-phase formation history of the Milky Way disk (2013, background): “…parameters may give us a hint of the existence of such a population in the Milky Way (Gilmore & Reid 1983) as well as in external galaxies (Burstein 1979; Dalcanton & Bernstein 2002; Pohlen et al. 2004; Comerón et al. 2011), but no clue as to its origin or to its link to the other populations.”
Radial migration does little for Galactic disc thickening (2012, background): “Most local galaxies are observed to host a thick disc component (e.g., Comerón et al. 2011), including our Milky Way (MW), as first proposed by Gilmore and Reid (1983).”
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).”