Astrophys. J., 692, 422-442 (2009/February-2)
MAMBO 1.2 mm observations of luminous starbursts at z ∼ 2 in the SWIRE fields.
LONSDALE C.J., POLLETTA M.DEL C., OMONT A., SHUPE D., BERTA S., ZYLKA R., SIANA B., LUTZ D., FARRAH D., SMITH H.E., LAGACHE G., DE BREUCK C., OWEN F., BEELEN A., WEEDMAN D., FRANCESCHINI A., CLEMENTS D., TACCONI L., AFONSO-LUIS A., PEREZ-FOURNON I., COX P. and BERTOLDI F.
Abstract (from CDS):
We report on-off pointed MAMBO observations at 1.2 mm of 61 Spitzer-selected star-forming galaxies from the Spitzer Wide Area Infrared Extragalactic Legacy survey (SWIRE). The sources are selected on the basis of bright 24 µm fluxes (f_24 µm_> 0.4 mJy) and of stellar dominated near-infrared spectral energy distributions in order to favor z ∼ 2 starburst galaxies. The average 1.2 mm flux for the whole sample is 1.5±0.2 mJy. Our analysis focuses on 29 sources in the Lockman Hole field where the average 1.2 mm flux (1.9 ± 0.3 mJy) is higher than in other fields (1.1±0.2 mJy). The analysis of the multiwavelength spectral energy distributions indicates that these sources are starburst galaxies with far-infrared luminosities from 1012 to 1013.3 L☉, and stellar masses of ∼0.2-6x1011 M☉. Compared to submillimeter selected galaxies (SMGs), the SWIRE-MAMBO sources are among those with the largest 24 µm/1.2 mm flux ratios. The origin of such large ratios is investigated by comparing the average mid-infrared spectra and the stacked far-infrared spectral energy distributions of the SWIRE-MAMBO sources and of SMGs. The mid-infrared spectra, available for a handful of sources, exhibit strong polycyclic aromatic hydrocarbon (PAH) features, and a warm dust continuum. The warm dust continuum contributes ∼34% of the mid-infrared emission, and is likely associated with an AGN component. This contribution is consistent with what is found in SMGs. The large 24 µm/1.2 mm flux ratios are thus not due to AGN emission, but rather to enhanced PAH emission compared to SMGs. The analysis of the stacked far-infrared fluxes yields warmer dust temperatures than typically observed in SMGs. Our selection favors warm ultraluminous infrared sources at high-z, a class of objects that is rarely found in SMG samples. Indeed SMGs are not common among bright 24 µm sources (e.g., only about 20% of SMGs have f_24 µm_> 0.4 mJy). Our sample is the largest Spitzer-selected sample detected at millimeter wavelengths currently available.
cosmology: observations - galaxies: formation - galaxies: high-redshift - galaxies: starburst - infrared: galaxies - submillimeter
VizieR on-line data:
<Available at CDS (J/ApJ/692/422): table1.dat table2.dat table4.dat>
Tables 1-4: [LPO2009] LH NN (Nos 1-29), [LPO2009] EN1 NN (Nos 1-17), [LPO2009] EN2 N (Nos 1-9), [LPO2009] XMM N (Nos 1-6).
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