Detalles de publicación
PP 013036
On the Origin of Lopsidedness in Galaxies as Determined from the Spitzer Survey of Stellar Structure in Galaxies (S4G)
1 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA; den- nis.zaritsky@gmail.com
2 Astronomy Division, Department of Physics, P.O. Box 3000, FI-90014 University of Oulu, Finland
3 Finnish Centre of Astronomy with ESO (FINCA), Univer- sity of Turku, V ̈ais ̈al ̈antie 20, FI-21500, Piikkio ̈, Finland
4 Vassar College, Dept. of Physics and Astronomy, Pough- keepsie, NY 12604, USA
5 Aix Marseille Universit ́e, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388, Marseille, France
6 Instituto de Astrof ́ısica de Canarias, V ́ıa L ́acteas 38205 La Laguna, Spain
7 Departamento de Astrof ́ısica, Universidad de La Laguna, 38206, La Laguna, Spain
8 IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598, USA
9 European Southern Observatory, Casilla 19001, Santaigo 19, Chile
10 Departamento de Astrof ́ısica, Universidad Complutense de Madrid, Madrid, Spain
11 MMT Observatory, P.O. Box 210065, Tucson, AZ 85721, USA
12 The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USA
13 ESA Fellow, European Space Agency (ESTEC), Keplerlaan 1, 2200 AG Noordwijk, The Netherlands
14 National Radio Astronomy Observatory/ NAASC, 520 Edgemont Road, Charlottesville, VA 22903, USA
15 Spitzer Science Center, 1200 East California Boulevard, Pasadena, CA 91125, USA
16 Max-Planck-Institut fu ̈r Astronomie, K ̈onigstu ̈hl 17 D- 69117, Heidelberg, Germany
17 Observatorio do Valongo, Universidade Federal de Rio de Janeiro, Ladeira Pedro Antnio, 43, Sau ́de CEP 20080-090, Rio de Janeiro-RJ-Brazil
18 California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
19 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
We study the m=1 distortions (lopsidedness) in the stellar components of 167 nearby galaxies that span a wide range of morphologies and luminosities. We confirm the previous findings of 1) a high incidence of lopsidedness in the stellar distributions, 2) increasing lopsidedness as a function of radius out to at least 3.5 exponential scale lengths, and 3) greater lopsidedness, over these radii, for galaxies of later type and lower surface brightness. Additionally, the magnitude of the lopsidedness 1) correlates with the character of the spiral arms (stronger arm patterns occur in galaxies with less lopsidedness), 2) is not correlated with the presence or absence of a bar, or the strength of the bar when one is present, 3) is inversely correlated to the stellar mass fraction, f_*, within one radial scale length, and 4) correlates directly with f_* measured within the radial range over which we measure lopsidedness. We interpret these findings to mean that lopsidedness is a generic feature of galaxies and does not, generally, depend on a rare event, such as a direct accretion of a satellite galaxy onto the disk of the parent galaxy. While lopsidedness may be caused by several phenomena, moderate lopsidedness (<A_1>_i + <A_1>_o)/2 < 0.3) is likely to reflect halo asymmetries to which the disk responds or a gravitationally self-generated mode . We hypothesize that the magnitude of the stellar response depends both on how centrally concentrated the stars are with respect to the dark matter and whether there are enough stars in the region of the lopsidedness that self-gravity is dynamically important.