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Thick Disks of Edge-On Galaxies Seen Through the Spitzer Survey of Stellar Structure in Galaxies (S^4G): Lair of Missing Baryons?

Comerón, Sébastien and Elmegreen, Bruce G. and Knapen, Johan H. and Salo, Heikki and Laurikainen, Eija and Laine, Jarkko and Athanassoula, E. and Bosma, Albert and Sheth, Kartik and Regan, Michael W. and Hinz, Joannah L. and Gil de Paz, Armando and Menéndez-Delmestre, Karín and Mizusawa, Trisha and Muñoz-Mateos, Juan-Carlos and Seibert, Mark and Kim, Taehyun and Elmegreen, Debra M. and Gadotti, Dimitri A. and Ho, Luis C. and Holwerda, Benne W. and Lappalainen, Jane and Schinnerer, Eva and Skibba, Ramin (2011) Thick Disks of Edge-On Galaxies Seen Through the Spitzer Survey of Stellar Structure in Galaxies (S^4G): Lair of Missing Baryons? Astrophysical Journal, 741 (1). Art. No. 28. ISSN 0004-637X.

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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 (S^4G). 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.”

Item Type:Article
Related URLs:
URLURL TypeDescription
Elmegreen, Bruce G.0000-0002-1723-6330
Sheth, Kartik0000-0002-5496-4118
Gil de Paz, Armando0000-0001-6150-2854
Menéndez-Delmestre, Karín0000-0003-3153-5123
Mizusawa, Trisha0000-0001-7182-5307
Seibert, Mark0000-0002-1143-5515
Elmegreen, Debra M.0000-0002-1392-3520
Ho, Luis C.0000-0001-6947-5846
Holwerda, Benne W.0000-0002-4884-6756
Schinnerer, Eva0000-0002-3933-7677
Additional Information:© 2011 The American Astronomical Society. Received 2011 April 8; accepted 2011 July 29; published 2011 October 12. The authors thank the entire S4G team for their efforts in this project. This work is based on observations and archival data made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. We are grateful to the dedicated staff at the Spitzer Science Center for their help and support in planning and execution of this Exploration Science program. We also gratefully acknowledge support from NASA JPL/Spitzer grant RSA 1374189 provided for the S4G project. We thank our anonymous referee for comments that helped to improve the paper. K.S., J.-C.M.M., T. Kim and T. Mizusawa acknowledge support from the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. E.A. and A.B. thank the Centre National d’Études Spatiales for financial support. We thank Peter Yoachim for kindly sharing information he used for his Yoachim & Dalcanton (2006) paper. This research has made use of observations made with the NASA/ESA Hubble Space Telescope and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA), and the Canadian Astronomy Data Centre (CADC/NRC/CSA). Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web site is This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NASA/JPL/SpitzerRSA 1374189
National Radio Astronomy ObservatoryUNSPECIFIED
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Japanese MonbukagakushoUNSPECIFIED
Max Planck SocietyUNSPECIFIED
Higher Education Funding Council for EnglandUNSPECIFIED
Subject Keywords:galaxies: photometry; galaxies: spiral; galaxies: structure
Issue or Number:1
Record Number:CaltechAUTHORS:20111206-095302073
Persistent URL:
Official Citation:Thick Disks of Edge-on Galaxies Seen through the Spitzer Survey of Stellar Structure in Galaxies (S4G): Lair of Missing Baryons? Sébastien Comerón et al. 2011 ApJ 741 28
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:28313
Deposited By: Ruth Sustaita
Deposited On:06 Dec 2011 18:20
Last Modified:09 Mar 2020 13:19

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