Dust and gas power spectrum in M 33 (HERM33ES)^⋆

¹ Observatoire de Paris, LERMA & CNRS: UMR8112, 61 Av. de l’Observatoire, 75014 Paris, France
e-mail: francoise.combes@obspm.fr
² Laboratoire d’Astrophysique de Marseille – LAM, Université d’Aix-Marseille & CNRS, UMR7326, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
³ Instituto Radioastronomia Milimetrica, Av. Divina Pastora 7, Nucleo Central, 18012 Granada, Spain
⁴ Institute of Astronomy and Astrophysics, National Observatory of Athens, P. Penteli, 15236 Athens, Greece
⁵ Argelander Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
⁶ Laboratoire d’Astrophysique de Bordeaux, Université Bordeaux 1, Observatoire de Bordeaux, OASU, UMR 5804, CNRS/INSU, BP 89, 33270 Floirac, France
⁷ University of Massachusetts, Department of Astronomy, LGRT-B 619E, Amherst, MA 01003, USA
⁸ IRAM-Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin d’Hères, France
⁹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁰ ATNF, CSIRO, PO Box 76, Epping, NSW 1710, Australia
¹¹ IPAC, MS 100-22 California Institute of Technology, Pasadena, CA 91125, USA
¹² Dept. Física Teórica y del Cosmos, Universidad de Granada, Spain
¹³ KOSMA, I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
¹⁴ Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
¹⁵ Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁶ JAC, 660 North A’ohoku Place, University Park, Hilo, HI 96720, USA
¹⁷ SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands

Received: 16 October 2011
Accepted: 17 January 2012

Abstract

Power spectra of deprojected images of late-type galaxies in gas or dust emission are very useful diagnostics of the dynamics and stability of their interstellar medium. Previous studies have shown that the power spectra can be approximated as two power laws, a shallow one on large scales (larger than 500 pc) and a steeper one on small scales, with the break between the two corresponding to the line-of-sight thickness of the galaxy disk. The break separates the 3D behavior of the interstellar medium on small scales, controlled by star formation and feedback, from the 2D behavior on large scales, driven by density waves in the disk. The break between these two regimes depends on the thickness of the plane, which is determined by the natural self-gravitating scale of the interstellar medium. We present a thorough analysis of the power spectra of the dust and gas emission at several wavelengths in the nearby galaxy M 33. In particular, we use the recently obtained images at five wavelengths by PACS and SPIRE onboard Herschel. The wide dynamical range (2–3 dex in scale) of most images allows us to clearly determine the change in slopes from  −1.5 to  −4, with some variations with wavelength. The break scale increases with wavelength from 100 pc at 24 and 100 μm to 350 pc at 500 μm, suggesting that the cool dust lies in a thicker disk than the warm dust, perhaps because of star formation that is more confined to the plane. The slope on small scales tends to be steeper at longer wavelength, meaning that the warmer dust is more concentrated in clumps. Numerical simulations of an isolated late-type galaxy, rich in gas and with no bulge, such as M 33, are carried out to better interpret these observed results. Varying the star formation and feedback parameters, it is possible to obtain a range of power spectra, with two power-law slopes and breaks, that nicelybracket the data. The small-scale power-law does indeed reflect the 3D behavior of the gas layer, steepening strongly while the feedback smoothes the structures by increasing the gas turbulence. M 33 appears to correspond to a fiducial model with an SFR of  ~ 0.7 M_⊙/yr, with 10% supernovae energy coupled to the gas kinematics.