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J/ApJ/658/778       Spitzer mid-IR spectroscopy of z∼2 ULIRGs       (Yan+, 2007)
Spitzer mid-infrared spectroscopy of infrared luminous galaxies at z ∼ 2.
I. The spectra.
    Yan L., Sajina A., Fadda D., Choi P., Armus L., Helou G., Teplitz H.,
    Frayer D., Surace J.
   <Astrophys. J. 658, 778-793 (2007)>
   =2007ApJ...658..778Y
ADC_Keywords: Galaxies, IR ; Redshifts ; Spectroscopy ; Active gal. nuclei ;
              Photometry, infrared
Keywords: galaxies: evolution - galaxies: high-redshift - galaxies: starburst
          infrared: galaxies

Abstract:
    We present the mid-infrared spectra obtained with the Spitzer IRS for
    52 sources, selected as infrared luminous, z≳1 candidates in the
    Extragalactic First Look Survey (XFLS). The sample selection criteria
    are F24um≳0.9mJy, vFv(24um)/vFv(8um)≳3.16, and
    vFv(24um)/vFv(0.7um)≳10. Of the 52 spectra, 47 (90%) produced
    measurable redshifts based solely on the mid-IR spectral features,
    with 35/47 (74%) at 1.5≲z≲3.2. Keck spectroscopy of a subsample
    (17/47) agrees with the mid-IR redshift measurements. The observed
    spectra fall into three categories: (1) 33% (17/52) have strong PAH
    emission and are probably powered by star formation with total IR
    luminosity roughly a factor of 5 higher than the local starburst
    ULIRGs; (2) 33% (17/52) have only deep silicate absorption at 9.8um,
    indicating deeply embedded dusty systems -these data alone cannot
    determine the energetic nature of the heating sources in these
    systems; and (3) the remaining 34% are mid-IR continuum-dominated
    systems with weak PAH emission and/or silicate absorption. This
    subsample is probably AGNs.

Description:
    All observations were taken using IRS Staring mode, with nearby bright
    stars as peak-up targets to accurately center the slit on the science
    targets.

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table1.dat        83       52   IRS Low-Resolution spectroscopy observation log
table2.dat        63       52   The measured redshifts and types for our sample
table3.dat        99       17   The Keck spectroscopy of the IRS sample


See also:
   J/AJ/125/2411 : SIRTF First-Look Survey (Condon+, 2003)
   J/AJ/131/250  : Spitzer 70 and 160um observations in xFLS (Frayer+, 2006)
   J/AJ/131/2859 : Extragalactic First Look Survey: 24µm data (Fadda+, 2006)
   J/A+A/467/565 : z=1-3 ULIRGs from the Spitzer SWIRE survey (Berta+, 2007)
  http://ssc.spitzer.caltech.edu/fls/extragal/ : Extragalactic First Look Survey


Byte-by-byte Description of file: table1.dat

   Bytes Format Units   Label     Explanations

   1-  4  A4    ---     ---       [MIPS]
   6- 10  I5    ---     MIPS      MIPS identification number
  12- 16  A5    ---     ---       [SST24]
  18- 36  A19   ---     SST24     SST24 identification (JHHMMSS.ss+DDMMSS.s)
  38- 45  F8.3  mJy     F24um     Flux at 24um
  47- 53  F7.3  uJy     F8um      Flux at 8um
  55- 59  F5.3  uJy     FR        Flux at R-band (or 2σ limit)
  61- 67  A7    s       SL1       IRS Short-Low first order resolution (7.4-14.5um)
  69- 75  A7    s       LL2       IRS Long-Low second order resolution (14-21.3um)
  77- 83  A7    s       LL1       IRS Long-Low first order resolution (19.5-38um)


Byte-by-byte Description of file: table2.dat

   Bytes Format Units     Label   Explanations

   1-  4  A4    ---       ---     [MIPS]
   6- 10  I5    ---       MIPS    MIPS identification number
  12- 15  F4.2  ---       z       ?=- Redshift (no redshift for Type=4)
  17- 20  F4.2  ---       e_z     ? Redshift uncertainty
  22- 26  F5.2  [solLum] logL5.8  ?=- Estimated rest-frame luminosity at 5.8um
  28- 31  F4.2  [solLum] e_logL5.8  ? Uncertainty in logL5.8um
      33  A1    ---       q_z     [ab-] Redshift quality flag (1)
  35- 37  F3.1  ---       Type    Spectral group classification (2)
  39- 63  A25   ---       Feat    Spectral features used for redshift
                                  measurements

Note (1): Redshift quality flag as follows:
    a = Secure identification
    b = Spectral features whose identifications are ambiguous
Note (2): Type as follows:
    1 = Systems with strong PAH emission
    2 = Sources without any evidence for PAH emission, but with a strong 9.8um
        silicate absorption feature
  1.5 = Intermediate sources between these two types, i.e., with strong Si
        absorption, as well as prominent 8um bumps, which are possibly due to
        PAH emission (occasionally supported by 6.2um features)
    3 = Sources with strong continuum plus weak PAH emission and/or silicate
        absorption features
    4 = Sources with pure power-law continua without identifiable features.
          See section 4.2 for further details.


Byte-by-byte Description of file: table3.dat

   Bytes Format Units   Label     Explanations

       1  A1    ---     Inst      [NLD] Instrument used for data (1)
   3-  6  A4    ---     ---       [MIPS]
   8- 12  I5    ---     MIPS      MIPS identification number
  14- 19  F6.4  ---     zKeck     Redshift from Keck
  21- 24  F4.2  ---     zIRS      Redshift from IRS
  26- 50  A25   ---     IRS       Source type classified from the IRS
  52- 99  A48   ---     Keck      Source type from the optical spectra

Note (1): Instrument flag as follows:
  N = NIRSPEC on the Keck Telescopes
  L = LRIS on the Keck Telescopes
  D = DEIMOS on the Keck Telescopes


History:
    From electronic version of the journal

References:
    Sajina et al. Paper II.  2007ApJ...664..713S
    Sajina et al. Paper III. 2008ApJ...683..659S
(End)                                     Emmanuelle Perret [CDS]    25-Feb-2010