Spitzer IRS spectra of optically faint infrared sources with weak spectral features

D. W. Weedman, B. T. Soifer, Lei Hao, J. L. Higdon, S. J U Higdon, J. R. Houck, E. Le Floc'h, M. J I Brown, A. Dey, Buell Tomasson Jannuzi, Marcia J Rieke, V. Desai, C. Bian, D. Thompson, L. Armus, H. Teplitz, P. Eisenhardt, S. P. Willner

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Abstract

Spectra have been obtained with the low-resolution modules of the Infrared Spectrograph (IRS) on the Spitzer Space Telescope (Spitzer) for 58 sources having fν(24 μm) > 0.75 mJy. Sources were chosen from a survey of 8.2 deg2 within the NOAO Deep Wide-Field Survey region in Boötes (NDWFS) using the Multiband Imaging Photometer (MIPS) on Spitzer. Most sources are optically very faint (I > 24 mag). Redshifts have previously been determined for 34 sources, based primarily on the presence of a deep 9.7 μm silicate absorption feature, with a median z of 2.2. Spectra are presented for the remaining 24 sources for which we were previously unable to determine a confident redshift because the IRS spectra show no strong features. Optical photometry from the NDWFS and infrared photometry with MIPS and the Infrared Array Camera on Spitzer (IRAC) are given, with K photometry from the Keck I telescope for some objects. The sources without strong spectral features have overall spectral energy distributions (SEDs) and distributions among optical and infrared fluxes that are similar to those for the sources with strong absorption features. Nine of the 24 sources are found to have feasible redshift determinations based on fits of a weak silicate absorption feature. Results confirm that the "1 mJy" population of 24 μm Spitzer sources that are optically faint is dominated by dusty sources with spectroscopic indicators of an obscured AGN rather than a starburst. There remain 14 of the 58 sources observed in Boötes for which no redshift could be estimated, and 5 of these sources are invisible at all optical wavelengths.

Original languageEnglish (US)
Pages (from-to)101-112
Number of pages12
JournalAstrophysical Journal
Volume651
Issue number1 I
DOIs
StatePublished - Nov 1 2006

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spectrographs
field survey
silicate
photometer
wavelength
photometry
energy
silicates
infrared photometry
Space Infrared Telescope Facility
distribution
spectral energy distribution
photometers
modules
cameras
telescopes
indicator

Keywords

  • Dust, extinction
  • Galaxies: active
  • Galaxies: high-redshift
  • Galaxies: starburst
  • Infrared: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Weedman, D. W., Soifer, B. T., Hao, L., Higdon, J. L., Higdon, S. J. U., Houck, J. R., ... Willner, S. P. (2006). Spitzer IRS spectra of optically faint infrared sources with weak spectral features. Astrophysical Journal, 651(1 I), 101-112. https://doi.org/10.1086/507322

Spitzer IRS spectra of optically faint infrared sources with weak spectral features. / Weedman, D. W.; Soifer, B. T.; Hao, Lei; Higdon, J. L.; Higdon, S. J U; Houck, J. R.; Le Floc'h, E.; Brown, M. J I; Dey, A.; Jannuzi, Buell Tomasson; Rieke, Marcia J; Desai, V.; Bian, C.; Thompson, D.; Armus, L.; Teplitz, H.; Eisenhardt, P.; Willner, S. P.

In: Astrophysical Journal, Vol. 651, No. 1 I, 01.11.2006, p. 101-112.

Research output: Contribution to journalArticle

Weedman, DW, Soifer, BT, Hao, L, Higdon, JL, Higdon, SJU, Houck, JR, Le Floc'h, E, Brown, MJI, Dey, A, Jannuzi, BT, Rieke, MJ, Desai, V, Bian, C, Thompson, D, Armus, L, Teplitz, H, Eisenhardt, P & Willner, SP 2006, 'Spitzer IRS spectra of optically faint infrared sources with weak spectral features', Astrophysical Journal, vol. 651, no. 1 I, pp. 101-112. https://doi.org/10.1086/507322
Weedman DW, Soifer BT, Hao L, Higdon JL, Higdon SJU, Houck JR et al. Spitzer IRS spectra of optically faint infrared sources with weak spectral features. Astrophysical Journal. 2006 Nov 1;651(1 I):101-112. https://doi.org/10.1086/507322
Weedman, D. W. ; Soifer, B. T. ; Hao, Lei ; Higdon, J. L. ; Higdon, S. J U ; Houck, J. R. ; Le Floc'h, E. ; Brown, M. J I ; Dey, A. ; Jannuzi, Buell Tomasson ; Rieke, Marcia J ; Desai, V. ; Bian, C. ; Thompson, D. ; Armus, L. ; Teplitz, H. ; Eisenhardt, P. ; Willner, S. P. / Spitzer IRS spectra of optically faint infrared sources with weak spectral features. In: Astrophysical Journal. 2006 ; Vol. 651, No. 1 I. pp. 101-112.
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AU - Weedman, D. W.

AU - Soifer, B. T.

AU - Hao, Lei

AU - Higdon, J. L.

AU - Higdon, S. J U

AU - Houck, J. R.

AU - Le Floc'h, E.

AU - Brown, M. J I

AU - Dey, A.

AU - Jannuzi, Buell Tomasson

AU - Rieke, Marcia J

AU - Desai, V.

AU - Bian, C.

AU - Thompson, D.

AU - Armus, L.

AU - Teplitz, H.

AU - Eisenhardt, P.

AU - Willner, S. P.

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N2 - Spectra have been obtained with the low-resolution modules of the Infrared Spectrograph (IRS) on the Spitzer Space Telescope (Spitzer) for 58 sources having fν(24 μm) > 0.75 mJy. Sources were chosen from a survey of 8.2 deg2 within the NOAO Deep Wide-Field Survey region in Boötes (NDWFS) using the Multiband Imaging Photometer (MIPS) on Spitzer. Most sources are optically very faint (I > 24 mag). Redshifts have previously been determined for 34 sources, based primarily on the presence of a deep 9.7 μm silicate absorption feature, with a median z of 2.2. Spectra are presented for the remaining 24 sources for which we were previously unable to determine a confident redshift because the IRS spectra show no strong features. Optical photometry from the NDWFS and infrared photometry with MIPS and the Infrared Array Camera on Spitzer (IRAC) are given, with K photometry from the Keck I telescope for some objects. The sources without strong spectral features have overall spectral energy distributions (SEDs) and distributions among optical and infrared fluxes that are similar to those for the sources with strong absorption features. Nine of the 24 sources are found to have feasible redshift determinations based on fits of a weak silicate absorption feature. Results confirm that the "1 mJy" population of 24 μm Spitzer sources that are optically faint is dominated by dusty sources with spectroscopic indicators of an obscured AGN rather than a starburst. There remain 14 of the 58 sources observed in Boötes for which no redshift could be estimated, and 5 of these sources are invisible at all optical wavelengths.

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