Infrared luminosities and aromatic features in the 24μm flux-limited sample of 5muses

Yanling Wu, George Helou, Lee Armus, Diane Cormier, Yong Shi, Daniel Dale, Kalliopi Dasyra, J. D. Smith, Casey Papovich, Bruce Draine, Nurur Rahman, Sabrina Stierwalt, Dario Fadda, G. Lagache, Edward L. Wright

Research output: Contribution to journalArticlepeer-review

48 Scopus citations

Abstract

We study a 24 μm selected sample of 330 galaxies observed with the infrared spectrograph for the 5 mJy Unbiased Spitzer Extragalactic Survey. We estimate accurate total infrared luminosities by combining mid-IR spectroscopy and mid-to-far infrared photometry, and by utilizing newempirical spectral templates from Spitzer data. The infrared luminosities of this sample range mostly from 109 L⊙ to 1013.5 L⊙,with 83% in the range 1010 L⊙ < LIR < 1012 L⊙. The redshifts range from 0.008 to 4.27, with a median of 0.144. The equivalentwidths of the 6.2μm aromatic feature have a bimodal distribution,probably related to selection effects. We use the 6.2μm polycyclic aromatic hydrocarbon equivalent width (PAH EW) to classify our objects as starburst (SB)-dominated (44%), SB-AGN composite (22%), and active galactic nucleus (AGN)-dominated (34%). The high EWobjects (SB-dominated) tend to have steeper mid-IR to far-IR spectral slopes and lower LIR and redshifts. The low EW objects (AGN-dominated) tend to have less steep spectral slopes and higher LIR and redshifts. This dichotomy leads to a gross correlation between EW and slope, which does not hold within either group. AGN-dominated sources tend to have lower log(LPAH7.7 μm/LPAH11.3 μm) ratios than star-forming galaxies, possibly due to preferential destruction of the smaller aromatics by the AGN. The log(LPAH7.7 μm/L PAH11.3 μm) ratios for star-forming galaxies are lower in our sample than the ratios measured from the nuclear spectra of nearby normal galaxies, most probably indicating a difference in the ionization state or grain size distribution between the nuclear regions and the entire galaxy. Finally, we provide a calibration relating the monochromatic continuum or aromatic feature luminosity to LIR for different types of objects.

Original languageEnglish (US)
Pages (from-to)895-914
Number of pages20
JournalAstrophysical Journal
Volume723
Issue number1
DOIs
StatePublished - Nov 1 2010

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Galaxies: Active
  • Galaxies: Starburst
  • Infrared: Galaxies
  • Surveys

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