University of Louisville ThinkIR: The University of Louisville's Institutional Repository Faculty Scholarship 2-2014 Unveiling the structure of barred galaxies at 3.6 μm with the Spitzer Survey of Stellar Structure in Galaxies (S4G). I. Disk breaks. Taehyun Kim National Radio Astronomy Observatory Dimitri A. Gadotti European Southern Observatory Kartik Sheth National Radio Astronomy Observatory E. Athanassoula Aix Marseille Universite Albert Bosma Aix Marseille Universite See next page for additional authors Follow this and additional works at: https://ir.library.louisville.edu/faculty Part of the Astrophysics and Astronomy Commons Original Publication Information Kim, Taehyun, et al. "Unveiling the Structure of Barred Galaxies at 3.6 μm with the Spitzer Survey of Stellar Structure in Galaxies (S4G). I. Disk Breaks." 2014. The Astrophysical Journal 782(2): 19 pp. This Article is brought to you for free and open access by ThinkIR: The University of Louisville's Institutional Repository. It has been accepted for inclusion in Faculty Scholarship by an authorized administrator of ThinkIR: The University of Louisville's Institutional Repository. For more information, please contact [email protected]. Authors Taehyun Kim, Dimitri A. Gadotti, Kartik Sheth, E. Athanassoula, Albert Bosma, Myung Gyoon Lee, Barry F. Madore, Bruce G. Elmegreen, Johan H. Knapen, Dennis Zaritsky, Luis C. Ho, Sebastien Comeron, Benne W. Holwerda, Joannah L. Hinz, Juan Carlos Munoz-Mateos, Mauricio Cisternas, Santiago Erroz-Ferrer, Ron Buta, Eija Laurikainen, Heikki Salo, Jarkko Laine, Karin Menendez-Delmestre, Michael W. Regan, Bonita de Swardt, Armando Gil de Paz, Mark Seibert, and Trisha Mizusawa This article is available at ThinkIR: The University of Louisville's Institutional Repository: https://ir.library.louisville.edu/ faculty/203 The Astrophysical Journal, 782:64 (19pp), 2014 February 20 doi:10.1088/0004-637X/782/2/64 C 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A. UNVEILING THE STRUCTURE OF BARRED GALAXIES AT 3.6 μm WITH THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S4G). I. DISK BREAKS Taehyun Kim1,2,3,4, Dimitri A. Gadotti2, Kartik Sheth3, E. Athanassoula5, Albert Bosma5, Myung Gyoon Lee1, Barry F. Madore4, Bruce Elmegreen6, Johan H. Knapen7,8, Dennis Zaritsky9, Luis C. Ho4,10,Sebastien´ Comeron´ 11,12, Benne Holwerda13, Joannah L. Hinz14, Juan-Carlos Munoz-Mateos˜ 2,3, Mauricio Cisternas7,8, Santiago Erroz-Ferrer7,8, Ron Buta15, Eija Laurikainen11,12, Heikki Salo11, Jarkko Laine11, Kar´ın Menendez-Delmestre´ 16, Michael W. Regan17, Bonita de Swardt18, Armando Gil de Paz19, Mark Seibert4, and Trisha Mizusawa3,20 1 Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-742, Korea 2 European Southern Observatory, Casilla 19001, Santiago 19, Chile 3 National Radio Astronomy Observatory/NAASC, 520 Edgemont Road, Charlottesville, VA 22903, USA 4 The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA 5 Aix Marseille Universite,´ CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388 Marseille, France 6 IBM Research Division, T.J. Watson Research Center, Yorktown Heights, NY 10598, USA 7 Instituto de Astrof´ısica de Canarias, E-38200 La Laguna, Tenerife, Spain 8 Departamento de Astrof´ısica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain 9 University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA 10 Kavli Institute for Astronomy & Astrophysics and Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871, China 11 Division of Astronomy, Department of Physical Sciences, University of Oulu, Oulu, FIN-90014, Finland 12 Finnish Centre of Astronomy with ESO (FINCA), University of Turku, Vais¨ al¨ antie¨ 20, FI-21500, Piikkio,¨ Finland 13 European Space Agency, ESTEC, Keplerlaan 1, 2200-AG, Noordwijk, The Netherlands 14 MMTO, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA 15 Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487, USA 16 Universidade Federal do Rio de Janeiro, Observatorio´ do Valongo, Ladeira Pedro Antonio,ˆ 43, CEP 20080-090, Rio de Janeiro, Brazil 17 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 18 South African Astronomical Observatory, Observatory, 7935 Cape Town, South Africa 19 Departamento de Astrof´ısica, Universidad Complutense de Madrid, Madrid 28040, Spain 20 Florida Institute of Technology, Melbourne, FL 32901, USA Received 2013 September 4; accepted 2013 December 9; published 2014 January 28 ABSTRACT We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies with B/T 0.1, the break radius to bar radius, rbr/Rbar, varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad resonance of the bar and thus moves outward as the bar grows. For galaxies with small bulges, B/T < 0.1, rbr/Rbar spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds. Key words: galaxies: evolution – galaxies: formation – galaxies: fundamental parameters – galaxies: photometry – galaxies: spiral – galaxies: structure Online-only material: color figures, figure set, machine-readable tables 1. INTRODUCTION studies of face-on galaxies (Pohlen et al. 2002; Erwin et al. 2005, 2008; Pohlen & Trujillo 2006;Gutierrez´ et al. 2011; Maltby The structural components of a galaxy evolve over cosmic et al. 2012a;Munoz-Mateos˜ et al. 2013) and edge-on galaxies time. Their present-day properties provide important clues to (Comeron´ et al. 2012;Mart´ın-Navarro et al. 2012) have found their formation and evolutionary history and provide strong that instead of a sharp truncation there is a change in the slope constraints for cosmological simulations seeking to reproduce of the radial surface brightness profile; the light profile is better realistic galaxy disks. One key tool in quantifying the structure modeled with two components—an inner and outer disk with of disks is its radial surface brightness profile. Typically galaxy different scale lengths. The transition between the two profiles disks have been modeled with a single exponential function is often referred to as the “break” in the profile. Galaxies with (Type I, Freeman 1970). However, van der Kruit (1979) found a down-bending light profile with a shallower inner disk and that some edge-on galaxies showed sharp edges in their radial a steeper outer disk are referred to as Type II, and those with surface brightness profile with a truncation radius of a few disk an up-bending profile with a steeper inner disk and a shallower scale lengths (van der Kruit & Searle 1981). A number of recent outer disk are referred to as Type III (see, e.g., Pohlen et al. 1 The Astrophysical Journal, 782:64 (19pp), 2014 February 20 Kim et al. 2002; Erwin et al. 2005; Hunter & Elmegreen 2006; Pohlen & that in outer disks, where the average gas column density is Trujillo 2006). below the critical threshold, stars may still form from turbulent For NGC 4244 and NGC 7793, breaks are found in all compression and other dynamical processes. Thus, even in a stellar populations at the same position (de Jong et al. 2007; galaxy with a single exponential gas distribution the different Radburn-Smith et al. 2012), though changes in the slope at the star formation modes can lead to a double exponential with a break are different among stellar populations, with a milder shallower inner disk and a steeper outer disk. Using N-body transition in older stellar populations (Radburn-Smith et al. simulations, Debattista et al. (2006) proposed that breaks can 2012). Indeed, numerical simulations (Roskarˇ et al. 2008; occur as a result of angular momentum redistribution induced Sanchez-Bl´ azquez´ et al. 2009) expect that through radial stellar by non-axisymmetric structures such as bars. Foyle et al. migrations older stars will show shallower radial profiles, (2008) built galaxy models using an N-body/smoothed particle because older populations are subject to scattering for longer. hydrodynamics code and let them evolve without any interaction This explains the U-shaped color profile, with a minimum at or gas accretion. They showed that, as a result of angular the break radius, found in face-on Type II galaxies (Bakos et al. momentum redistribution, purely exponential disks evolved to 2008). However, Mart´ın-Navarro et al. (2012) could not confirm develop a break. In their simulations the density profiles of inner this kind of color profile in edge-on galaxies, presumably disks evolved remarkably, while the density profile of outer disks because of the increased role of dust extinction in edge-on remained relatively stable over time. galaxies. For the up-bending (Type III) disk profiles Laurikainen & A significant fraction of disks have double exponential Salo (2001) demonstrated that galaxies encountering a less profiles. Gutierrez´ et al. (2011) gathered data from two studies massive companion (e.g., M51-like systems) developed an up- (Pohlen & Trujillo 2006; Erwin et al.