Details

Autor(en) / Beteiligte

• Desai, V
• Armus, L
• Soifer, B. T
• Weedman, D. W
• Higdon, S
• Bian, C
• Borys, C
• Spoon, H. W. W
• Charmandaris, V
• Brand, K
• Brown, M. J. I
• Dey, A
• Higdon, J
• Houck, J
• Jannuzi, B. T
• Le Floc’h, E
• Ashby, M. L. N
• Smith, H. A

Titel

IRS Spectra of Two Ultraluminous Infrared Galaxies at z = 1.3

Ist Teil von

• The Astrophysical journal, 2006-04, Vol.641 (1), p.133-139

Ort / Verlag

Chicago, IL: IOP Publishing

Erscheinungsjahr

2006

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• We present low-resolution (64 < R < 124) mid-infrared (8-38 km) spectra of two z - 1.3 ultraluminous infrared galaxies (ULIRGs) with L sub(8-1000) km - 10 super(13) L sub(z). The spectra were taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. Both objects were discovered in the NOAO Deep Wide-Field Survey (NDWFS) Bootes field. MIPS J142824.0+352619 is a bright 160 km source with a large infrared-to-optical flux density ratio. Previous authors provided evidence for a foreground lens and estimated an amplification of <10, although this factor is currently poorly constrained. The 6.2, 7.7, 11.3, and 12.8 km polycyclic aromatic hydrocarbon (PAH) emission bands in its 1RS spectrum indicate a redshift of z - 1.3. The large equivalent width of the 6.2 km PAH feature indicates that at least 50% of the mid-infrared energy is generated in a starburst, an interpretation supported by a large [Ne super(II)]/[Ne super(III)] ratio and a low upper limit on the X-ray luminosity. SST24 J142827.19+354127.71 has the brightest 24 km flux (10.55 mJy) among optically faint (R > 20) galaxies in the NDWFS. Its midinfrared spectrum lacks emission features, but the broad 9.7 km silicate absorption band places this source at z - 1.3. Optical spectroscopy confirms a redshift of z = 1.293 c 0.001. Given this redshift, SST24 J142827.19+354127.71 has among the largest rest-frame 5 km luminosities known. The similarity of its SED to those of known AGN-dominated ULIRGs and its lack of either PAH features or large amounts of cool dust indicate that the mid-infrared emission is dominated by an AGN rather than a starburst.