Infrared Luminosities and Aromatic Features in the 24um 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

doi:10.1088/0004-637X/723/1/895

paper

Infrared Luminosities and Aromatic Features in the 24um Flux Limited Sample of 5MUSES

arXiv:1009.1633 · doi:10.1088/0004-637X/723/1/895

Abstract

We study a 24\, $μ$ m 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 new empirical spectral templates from {\em Spitzer} data. The infrared luminosities of this sample range mostly from 10 $^{9}$ L $_{⊙}$ to $1 0^{13.5}$ L $_{⊙}$ , with 83% in the range 10 $^{10}$ L $_{⊙}$ $<$ L $_{IR}$ $< 1 0^{12}$ L $_{⊙}$ . The redshifts range from 0.008 to 4.27, with a median of 0.144. The equivalent widths of the 6.2\, $μ$ m aromatic feature have a bimodal distribution. We use the 6.2\, $μ$ m PAH EW to classify our objects as SB-dominated (44%), SB-AGN composite (22%), and AGN-dominated (34%). The high EW objects (SB-dominated) tend to have steeper mid-IR to far-IR spectral slopes and lower L $_{IR}$ and redshifts. The low EW objects (AGN-dominated) tend to have less steep spectral slopes and higher L $_{IR}$ 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(L $_{PAH7.7 μ m}$ /L $_{PAH11.3 μ m}$ ) ratios than star-forming galaxies, possibly due to preferential destruction of the smaller aromatics by the AGN. The log(L $_{PAH7.7 μ m}$ /L $_{PAH11.3 μ m}$ ) 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 5.8, 8, 14 and 24um continuum or Aromatic Feature luminosity to L $_{IR}$ for different types of objects.

accepted for publication in ApJ

Infrared Luminosities and Aromatic Features in the 24um Flux Limited Sample of 5MUSES

Abstract

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