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J/ApJ/683/114        IRS spectra of faint IRAS sources         (Sargsyan+, 2008)

Spitzer IRS spectra of optically faint IRAS sources. Sargsyan L., Mickaelian A., Weedman D., Houck J. <Astrophys. J., 683, 114-122 (2008)> =2008ApJ...683..114S
ADC_Keywords: Active gal. nuclei ; Equivalent widths ; Photometry, infrared ; Redshifts ; Spectra, infrared Keywords: galaxies: active - galaxies: starburst - infrared: galaxies Abstract: Extragalactic sources from the IRAS Faint Source Catalog (FSC) that have the optically faintest magnitudes (E≳18) were selected by spatial coincidence with a source in the FIRST radio survey, and 28 of these sources have been observed with the Infrared Spectrograph on Spitzer (IRS). While an infrared source is always detected with the IRS at the FIRST position, only ∼50% of the infrared sources are real FSC detections, as estimated from the number of sources for which the fv(25um) determined with the IRS is fainter than the sensitivity limit for the FSC. Sources have 0.12<z<1.0 and luminosities 43.3<log[νLν(5.5um)]<46.7erg/s, encompassing the range from local ULIRGs to the most luminous sources discovered by Spitzer at z∼2. Detectable PAH features are found in 15 of the sources (54%), and measurable silicate absorption is found in 19 sources (68%); both PAH emission and silicate absorption are present in 11 sources. PAH luminosities are used to determine the starburst fraction of bolometric luminosity, and model predictions for a dusty torus are used to determine the AGN fraction of luminosity in all sources based on vLv(5.5um). Approximately half of the sources have luminosity dominated by an AGN and approximately half by a starburst. Description: We have obtained IRS low-resolution spectra for 24 sources, and an additional 4 have been observed in other Spitzer programs. Details of the Spitzer IRS observations are in Table 1. Final spectra were boxcar-smoothed to the approximate resolution of the different IRS modules (0.2um for short low modules, SL1 and SL2 (wavelength range 5.2-14.5um), 0.3um for long low module, LL2, and 0.4um for LL1 (wavelength range 14.0-38.0um). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 70 28 IRS observations of sources table2.dat 103 28 Observed properties of sources table3.dat 59 28 Luminosities of sources
See also: II/156 : IRAS Faint Source Catalog, |b| > 10, Version 2.0 (Moshir+ 1989) VIII/71 : The FIRST Survey Catalog, Version 03Apr11 (Becker+ 2003) J/ApJ/642/673 : IR-selected obscured AGN candidates (Polletta+, 2006) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Seq Sequence running number 4- 6 A3 --- --- [FSC] 8- 17 A10 --- FSC Source name from the IRAS Faint Source Catalog (II/156) (1) 19- 36 A18 --- FIRST Coordinates for the FIRST source (2) 38- 45 I8 --- AOR Astronomical Observation Request identification number 47- 51 I5 --- Prog Program identification number 53- 55 I3 s Tsl Total integration time for IRS short-low modules 57- 59 I3 s Tll Total integration time for IRS long-low modules 61- 70 A10 "YYYY/MM/DD" Date Date of IRS observation
Note (1): Sources are <IRAS FHHMMm+DDMMA> in Simbad. 14589+2329 is a misprint for 14589+2340, corrected at CDS. Note (2): Coordinates for the FIRST source that is closest to the FSC source (, J2000)
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Seq Sequence running number 4- 8 I5 --- Id Source number 10- 14 F5.3 --- z Redshift determined from the IRS spectra 15 A1 --- r_z [fg] References for two redshifts (3) 17- 19 I3 mJy F25i IRAS-FSC flux at 25um (Cat. II/156) 21- 25 F5.1 mJy F25s Spitzer/IRS measured flux at 25um 27- 30 F4.1 mag Emag Photographic E magnitude from APS catalog (Cabanela et al., 2003PASP..115..837C) 32 A1 --- l_Jmag Limit flag on Jmag 33- 37 F5.2 mag Jmag 2MASS J magnitude 39- 43 F5.2 mJy F1.4G ? FIRST flux at 1.4GHz 45- 48 F4.2 --- q ? Ratio of infrared to radio flux (4) 50- 54 F5.2 mJy F5.5 Spitzer/IRS flux at 5.5um 56- 60 F5.1 mJy F15 Spitzer/IRS flux at 15um 62 A1 --- l_EW Limit flag on EW 63- 67 F5.3 um EW ? Equivalent width of PAH at 6.2um 69- 73 F5.3 um e_EW ? Uncertainty on EW (5) 75 A1 --- l_F6.2 Limit flag on F6.2um 76- 80 F5.2 zW/cm2 F6.2 ? Total Spitzer/IRS flux of PAH at 6.2um (5) 82- 85 F4.2 zW/cm2 e_F6.2 ? Uncertainty on F6.2 (5) 87 A1 --- l_F11.3 Limit flag on F11.3 88- 92 F5.2 zW/cm2 F11.3 ? Total Spitzer/IRS flux of PAH at 11.3um (5) 94- 97 F4.2 zW/cm2 e_F11.3 ? Uncertainty on F11.3um (5) 99-103 F5.2 --- tau τsi measure of the depth of the 9.7um absorption feature (6)
Note (3): References as follows: f = Redshift for this object, a red quasar, is the optical redshift from Urrutia et al., 2005ApJ...627...75U g = Redshift for this object, a blazar, is from Perry et al., 1978PASP...90..337P Note (4): In the observed frame, q=log[fν(25um)/fν(1.4GHz)], using fν(1.4GHz) of "peak flux" from FIRST, corresponding to an unresolved source. Note (5): Total flux of feature, fit with a single Gaussian. Uncertainties in fluxes and equivalent widths are statistical uncertainties from fitting the feature and do not include systematic uncertainties of ≲10%, which may arise from the fitting procedure chosen, as discussed in text. Note (6): Quantity defined as τsi=ln[fν(abs)/fν(cont)], for fv(abs) measured at the maximum depth of absorption and fv(cont) is the unabsorbed continuum as extrapolated in Spoon et al., 2007ApJ...654L..49S
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Seq Sequence running number 4- 8 I5 --- Id Source number 10- 13 I4 Mpc Dist Luminosity distance (7) 15- 19 F5.2 [10-7W] L5.5 Rest-frame parameter log(νLν) at 5.5um 21- 25 F5.2 [10-7W] L15 Rest-frame log(νLν) at 15um 27 A1 --- l_L6.2 Limit flag on L6.2 28- 32 F5.2 [10-7W] L6.2 ? Total luminosity of the 6.2um PAH feature, after subtracting the underlying continuum 34 A1 --- l_Ls Limit flag on Ls 35- 39 F5.2 [10-7W] Ls ? logL(6.2+11.3) 41 A1 --- l_LSB Limit flag on LSB 42- 46 F5.2 [10-7W] LSB ? Total luminosity of starburst (8) 48 A1 --- l_LAGN Limit flag on LAGN 49- 53 F5.2 [10-7W] LAGN ? Luminosity from the dusty torus of the AGN (9) 55 A1 --- l_f(SB) Limit flag on f(SB) 56- 59 F4.2 --- f(SB) ? Fraction of luminosity from starburst (10)
Note (7): Luminosity distance determined by E.L. Wright (see for H0=71km/s/Mpc, Ωm=0.27, and ΩΛ=0.73. Note (8): Total luminosity of starburst, assuming that log[LIR(SB)]=log[L(6.2)]+2.7±0.1, from Brandl et al. (2006ApJ...653.1129B) and Pope et al. (2008ApJ...675.1171P). Note (9): Total luminosity from the dusty torus of the AGN, assuming log[LIR(AGN)]=log[νLν(5.5um)]+0.33±0.06, from Polletta et al. (2008ApJ...675..960P) and assuming that all continuum luminosity vLv(5.5um) arises from an AGN. Note (10): Fraction L(SB)/[L(SB)+L(AGN)]. If a PAH feature is detected, this fraction is shown as a lower limit because some of the continuum at 5.5um, which is attributed to an AGN, actually arises from the starburst. If no PAH feature is detected, this fraction is shown as an upper limit because there is no direct evidence that a starburst is present. Source 9 is a blazar, so the parameters for determining LIR(AGN) and LIR(SB) are not applicable.
History: From electronic version of the journal
(End) Emmanuelle Perret [CDS] 26-Nov-2010
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