Submillimeter follow up_of_wise_selected_hyperluminous_galaxies

Submillimeter Follow-up of WISE-Selected Hyperluminous
Galaxies

Jingwen Wu1 , Chao-Wei Tsai2 , Jack Sayers3 , Dominic Benford4 , Carrie Bridge3 , Andrew
arXiv:1208.5518v1 [astro-ph.CO] 27 Aug 2012

Blain5 , Peter R. M. Eisenhardt1 , Daniel Stern1 , Sara Petty6 , Roberto Assef1 , Shane
Bussmann7 , Julia M. Comerford 8 , Roc Cutri2 , Neal J. Evans II8 , Roger Griﬃth2 , Thomas
Jarrett2 , Sean Lake6 , Carol Lonsdale9 , Jeonghee Rho10 , S. Adam Stanford11 , Benjamin
12
Weiner , Edward L. Wright6 , Lin Yan2

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Received ; accepted

1
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr.,
Pasadena, CA 91109, USA; jingwen.wu@jpl.nasa.gov
2
Infrared Processing and Analysis Center, California Institute of Technology, Pasadena,
CA 91125, USA
3
Division of Physics, Math and Astronomy, California Institute of Technology, Pasadena,
CA 91125, USA
4
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
5
Department of Physics and Astronomy, University of Leicester, LE1 7RH Leicester, UK
6
Department of Physics and Astronomy, University of California Los Angeles, Los Ange-
les, CA 90095, USA
7
Harvard-Smithsonian Center for Astrophysics, 60 Garden St. MS78, Cambridge, MA,
02138, USA
8
Department of Astronomy, University of Texas, Austin TX 78731,USA
9
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903,
USA
10
SETI Institute, 189 BERNARDO AVE, Mountain View, CA 94043 and SOFIA Science
Center, NASA Ames Research Center, Moﬀett Field, CA 94035, USA
11
Department of Physics, University of California Davis, One Shields Ave., Davis, CA
95616, USA
12
Steward Observatory, 933 N. Cherry St., University of Arizona, Tucson, AZ 85721, USA

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ABSTRACT

We have used the Caltech Submillimeter Observatory (CSO) to follow-up
a sample of WISE-selected, hyperluminous galaxies, so called W1W2-dropout
galaxies. This is a rare (∼ 1000 all-sky) population of galaxies at high redshift
(peaks at z=2-3), that are faint or undetected by WISE at 3.4 and 4.6 µm,
yet are clearly detected at 12 and 22 µm. The optical spectra of most of these
galaxies show significant AGN activity. We observed 14 high-redshift (z > 1.7)
W1W2-dropout galaxies with SHARC-II at 350 to 850 µm, with 9 detections;
and observed 18 with Bolocam at 1.1 mm, with five detections. Warm Spitzer
follow-up of 25 targets at 3.6 and 4.5 µm, as well as optical spectra of 12 targets
are also presented in the paper. Combining WISE data with observations from
warm Spitzer and CSO, we constructed their mid-IR to millimeter spectral energy
distributions (SEDs). These SEDs have a consistent shape, showing significantly
higher mid-IR to submm ratios than other galaxy templates, suggesting a hotter
dust temperature. We estimate their dust temperatures to be 60 − 120 K using
a single-temperature model. Their infrared luminosities are well over 1013 L⊙ .
These SEDs are not well fitted with existing galaxy templates, suggesting they are
a new population with very high luminosity and hot dust. They are likely among
the most luminous galaxies in the Universe. We argue that they are extreme cases
of luminous, hot dust-obscured galaxies (DOGs), possibly representing a short
evolutionary phase during galaxy merging and evolution. A better understanding
of their long-wavelength properties needs ALMA as well as Herschel data.

Subject headings: galaxies: formation — galaxies: high-redshift — galaxies: ISM —
galaxies: starburst— infrared: galaxies

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1. Introduction

The redshift z ∼2-3 epoch stands out as a unique era for studying galaxy formation
and evolution. At this epoch, the cosmic star formation rate reaches its peak (Heavens et
al. 2004; Hopkins & Beacom 2006; Reddy et al. 2008), and ultra-luminous infrared galaxies
(ULIRGs, LIR > 1012 L⊙ , Sanders & Mirabel 1996) contribute a signiﬁcant fraction to the
infrared luminosity density (Elbaz et al. 2002, Chapman et al. 2005, Caputi et al. 2007,
Reddy et al. 2008, Magnelli et al. 2009). The cosmic quasar density also peaks around z ∼2
(Hopkins et al. 2007, Assef et al. 2011). A framework of galaxy evolution through major
mergers has been gradually built up by theorists (Barnes & Hernquist 1992, Schweizer 1998,
Jogee 2006, Hopkins et al. 2006, 2008). In one of the most popular scenarios (e.g. Hopkins
et al. 2008), the tidal torques generated by major mergers funnel gas into the center of
galaxies, leading to a central starburst and rapid growth of a supermassive black hole
(SMBH). Black hole and supernova feedback terminate further star formation, evacuating
the residual gas and dust, leaving a visible quasar and remnant spheroid. This picture
establishes the evolutionary connections between ULIRGs, quasars, and massive elliptical
galaxies.

Submillimeter galaxies (SMGs) are thought to be the analogues of local ULIRGs at
high redshift (Blain et al. 2002, Tacconi et al. 2008). SMGs are selected by their strong
cold dust emission at 850 µm (F850 >5 mJy). They are characterized by very high star
formation rates (100-1000 M⊙ yr−1 ) and infrared luminosity (LIR ∼ 8 × 1012 L⊙ , Chapman
et al. 2005, Magnelli et al 2012). Although most SMGs host growing black holes (e.g.,
Alexander et al. 2005, 2008), their luminosities are normally dominated by star formation
(Swinbank et al. 2004; Men´ndez-Delmestre et al. 2007, Younger et al. 2008, Hainline et al.
e
2011). The redshift distribution of SMGs strongly peaks at z=2-3 (Chapman et al. 2005),
and the surface density of SMGs is several hundred per square degree.

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An 850µm selected sample (SMGs) may be biased toward ULIRGs with large amounts
of dust, but miss a substantial population of ULIRGs with a smaller amount of (but
warmer) dust, which can be found by surveys at shorter wavelengths. A series of surveys
using bright Spitzer 24µm emission combined with optically faint photometry have been
carried out to probe the ULIRG population with emission from smaller and warmer dust
grains (e.g., Rigby et al. 2004, Donley et al. 2007, Yan et al. 2007, Farrah et al. 2008,
Soifer et al. 2008, Lonsdale et al. 2009, Huang et al. 2009). One of the simplest search
criteria is given as F24 > 0.3 mJy, and R − [24] > 14 (where R and [24] are Vega magnitudes
for R band and Spitzer 24 µm), or roughly F24 /FR > 1000 (Dey et al. 2008, Fiore et al.
2008), leading to a well deﬁned z ∼2 population which is referred to as Dust Obscured
Galaxies (Dey et al. 2008, hereafter D08). The most luminous DOGs have star formation
rates (500-1000 M⊙ yr−1 or more) and infrared luminosities (LIR ∼ 1013 L⊙ , Bussmann et
al 2009, Tyler et al. 2009, Melbourne et al. 2012) that are comparable to SMGs. It has
been proposed that both SMGs and DOGs are an early phase of galaxy merging, with
SMGs representing an earlier, starburst-dominant phase, while luminous DOGs are in a
transitional phase from starburst-dominated to AGN-dominated (e.g. Narayanan 2010).
The bolometric luminosities also reach their maximum during these phases, making the
most luminous galaxies in these phases also among the most luminous objects in the
Universe.

Looking for the most luminous galaxies in the Universe is one of the major goals of
NASA’s Wide-ﬁeld Infrared Survey Explorer (WISE, Wright et al. 2010). WISE surveyed
the entire sky at 3.4, 4.6, 12 and 22 µm (hereafter W1, W2, W3, W4) in 2010. The WISE
dataset is well suited to investigate the starburst-AGN phase of distant, infrared luminous
galaxies. At z ∼ 2-3, starburst- or AGN-heated hot dust can be traced by 12 and 22 µm
emission, while the rest near infrared (NIR) obscuration is sampled by 3.4 and 4.6 µm
continuum. Studies of luminous infrared galaxies with the WISE W1, W2 and W4 bands

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can take advantage of existing knowledge and techniques developed by earlier studies with
Spitzer at similar wavelengths (IRAC at 3.6 and 4.5 µm, and MIPS at 24 µm). Observing
W4 selected galaxies with WISE is similar to observing 24 µm bright galaxies with Spitzer,
but with the surveyed area enlarged from a few tens of square degrees covered by existing
DOG surveys to the entire sky.

In order to search for hyperluminous infrared galaxies (HyLIRGs, LIR > 1013 L⊙ ) from
the WISE dataset, the WISE team has explored multiple methods to select candidates.
The most productive method so far has been to search for more heavily obscured galaxies,
whose W1 (3.4 µm) and W2 (4.6 µm) flux densities become faint or undetected by WISE,
while remaining easily detectable at 12 and/or 22 µm, with typical W4 (22 µm) flux
densities > 7mJy. We call this population ”W1W2-dropouts” (Eisenhardt et al 2012) or
for brevity ”W12drops”. Follow-up spectroscopy of more than 100 W12drop galaxies at
large telescopes (this paper, Eisenhardt et al. (2012), see also Bridge et al. 2012) reveals
that a large fraction (> 65%) of these galaxies are at high redshift (z > 1.5), with the
highest at z=4.6. Most of the redshifts are between 2 and 3, suggesting they also trace the
peak epoch of cosmic star formation and QSO activity. At these redshifts, such high flux
densities at 22 µm imply extremely high luminosities. They are potentially hyperluminous
galaxies. In order to understand the dust properties and calculate the total luminosities
of these unusual galaxies, continuum measurements at longer wavelengths are crucial. As
the first high redshift examples were identified, we began follow-up 0.35-1.1 mm continuum
observations using the Caltech Submillimeter Observatory (CSO), in order to construct
their SEDs and to explore the nature of W12drop galaxies.

In this paper, we report the initial results of this follow-up study. The WISE data
are described in section 2.1, and the W12drop population followed up with the CSO and
reported here is listed in Table 1. Sections 2.2 and 2.3 describe the CSO data, while section

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2.4 describes the follow-up optical spectroscopy, which is summarized in Table 2. Section
2.5 describes Spitzer follow-up observations at 3.6 µm and 4.5 µm of the W12drops, which
were selected to be difficult to detect by WISE at W1 (3.4 µm) and W2 (4.6 µm), and
the photometry for the sources is presented in Table 3. Section 3 presents luminosity and
dust temperatures constraints from the photometry, while section 4 compares W12drop
properties to those of DOGs and SMGs, and section 5 summarizes the findings. Throughout
this paper we assume a CDM cosmology with H0 = 71 km s−1 Mpc−1 , Ωm = 0.27, and
ΩΛ = 0.73 .

2. Observations

2.1. WISE

WISE began surveying the sky a month after it launched on 2009 December 14,
completing its first coverage of the sky six months later, and continued surveying until
February 1, 2011. The WISE all-sky data release was made public on 2012 March 14, and
its content and characteristics are documented in the Explanatory Supplement1 . WISE
has achieved much better sensitivity than previous all-sky survey missions (5σ point source
sensitivities are better than 0.07, 0.1, 0.9 and 5.4 mJy in W1, W2, W3 and W4 bands
(Explanatory Supplement 1 ), and identified hundreds of millions of sources.

The selection criteria for W12drops use WISE catalog photometry, which provides
PSF-ftting (i.e. total) magnitudes and uncertainties in the Vega system. The criteria are
W1 > 17.4, and either: a) W4 <7.7 and W2−W4 > 8.2; or b) W3 < 10.6 and W2−W3
> 5.3). Additional details are given in Eisenhardt et al. (2012). This selection yields

1
http://wise2.ipac.caltech.edu/docs/release/allsky/expsup
1
Cutri et al. 2012, http://wise2.ipac.caltech.edu/docs/release/allsky/expsup/sec6 3a.html

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only about 1000 targets over the full sky. W3 and W4 flux densities and uncertainties
for the W12drops discussed in this paper are provided in Table 3, converted from catalog
magnitudes using zero-points of 29.04 and 8.284 Jy for W3 and W4 respectively (Wright et
al. 2010). No color corrections have been made to these zero-points, because the results
presented here are not sensitive to such corrections.

2.2. SHARC-II

The Submillimeter High Angular Resolution Camera II (SHARC-II) installed at the
10.4 m CSO telescope (Dowell et al. 2002) is a background-limited 350 and 450 µm facility
camera, and it is also equipped with a filter that allows 850 µm continuum observations. It
adopts a “CCD-style” bolometer array with 12 × 32 pixels, resulting in a 0.97′ × 2.59′
field of view. The FWHM beam sizes of SHARC-II at 350 µm, 450 µm, and 850 µm are
′′ ′′ ′′
8. 5, 10. , and 19. 8, respectively. We used SHARC-II to follow-up 14 high redshift W12drop
galaxies during runs in July and September of 2010, and in February and September of 2011
(See Table 1). Most of the targets were only observed at 350 µm, with a few also observed
at 450 µm and 850 µm. Examples of SHARC-II images of detected W12drop galaxies are
presented in Figure 1. Since the 350 and 450 µm atmospheric transmission is very sensitive
to the weather, we only observed targets under good weather conditions (i.e. when the
opacity at 225 GHz τ225GHz < 0.06, which occurs ∼ 20% of the time). The targets and
observing information are listed in Table 1. The Dish Surface Optimization System (DSOS,
Leong 2006) was used to correct the dish surface figure for imperfections and gravitational
deformations as the dish moved in elevation during observations.

We used the Comprehensive Reduction Utility for SHARC-II (CRUSH, Kovćs 2006),
a
version crush2.01-4, to reduce the SHARC-II data. Option “-deep” in CRUSH was applied
to optimize the signal-to-noise ratio (S/N) for faint (< 100 mJy) point sources. Planets

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Uranus and Neptune, when available, were used for flux calibration, focus correction and
pointing correction, and secondary calibrators such as K3-50 and CRL618 were used when
these planets were not available. In order to flux calibrate, we used the starlinks “astro”
package to calculate the flux density of the calibrator within the proper beam size for a
SHARC-II band, and the “show” package in CRUSH to obtain the readout flux density of
the observed calibrator. The calibration factors (peaks) were derived by dividing the real
peak flux density of the calibrator by the readout peak flux density from CRUSH within one
beam. The flux density of the target and the rms noise were then derived by applying this
calibration factor to the readout of the peak position of the target and off-peak positions
1-2 beams from the peak, using the CRUSH “show” package in the same way as for the
calibrator, and convolving with the same beam size. The statistics of the calibration factor
over all our runs indicates a calibration uncertainty of 20%. We used the sweep mode
for the SHARC-II observations, in which the telescope moves in a Lissajous pattern that
keeps the central regions of the maps fully sampled. The edges are much noisier than the
central regions, and to compensate for this, we used “imagetool” in CRUSH to eliminate
the regions of each map that had a total exposure time less than 25% of the maximum.

Pointing was checked every hour with planets and secondary calibrators. The pointing
drift was normally less than 3′′ in both the azimuth and zenith directions between
pointing checks, and a pointing correction has been applied during the data stacking. The
uncertainty on the centroid position of an object will be the quadrature sum of the pointing
uncertainty and the measurement uncertainty on the centroid, which approximately equals
to the beam FWHM divided by S/N. Given our SHARC-II detections normally have S/N
′′
of 3-4, and beam size at 350µm is 8. 5, the measurement uncertainty on the centroid for our
targets is about 2′′ -3 ′′ . Therefore, the uncertainty of offset between the SHARC-II centroids
and WISE positions should be less than 5′′ -6 ′′ , which is consistent with our SHARC-II
detections (Figure 1).

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2.3. BOLOCAM

Bolocam is a large format camera at the CSO with 144 detectors, a circular
eight-arcmin-diameter field of view (FOV), an observing band centered at 1.1 mm, and a
point-spread function with a 30 arcsec full-width at half-maximum (FWHM) (Haig et al.
2004). Eighteen W12drop galaxies were observed with Bolocam during runs in June 2010,
December 2010, Febuary 2011, and September 2011, with observing information listed in
Table 1. The observations were made by scanning the CSO in a Lissajous pattern, with
scanning parameters chosen to keep the source within the FOV 100% of the time (Sayers
et al. 2011) while scanning at an average speed of 2′ /sec in June 2010, December 2010
and February 2011 and an average speed of 4 ′ /sec in September 2011. A pointing model,
accurate to 5′′ , was created from frequent observations of bright objects within ≃ 10 degrees
of the target galaxies following the methods described in Sayers et al. (2009). The flux
calibration, in nV/Jy, was determined according to the procedure described in Laurent
et al. (2005), based on observations of Neptune and K3-50A in June 2010, IRC 10216 in
December 2010, G34.3 and NGC 2071IR in February 2011, and Uranus in September 2011
(Sandell 1994; Griffin and Orton 1993). The Uranus calibration model of Griffin and Orton
1993 was updated based on the 143 GHz Bolocam results described in Sayers et al. 2012.
We estimate the flux calibration to be accurate to ≃ 10%.

Our atmospheric noise subtraction procedure was based on the algorithms described in
Sayers et al. (2011), with the following modifications: 1) an adaptive principal component
analysis (PCA) algorithm2 was used to subtract the correlated atmospheric signal over the

2
Due to an unknown change in the electromagnetic environment of the CSO prior to
the December 2010 observations, a large fraction of the Bolocam detectors suffered from
noise in several narrow spectral bands at the high-frequency end of the signal bandwidth.
In addition to subtracting noise from atmospheric fluctuations, the adaptive PCA algorithm

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FOV (Laurent et al. 2005, Downes et al. 2012) and 2) the data were then high-pass filtered
at a characteristic frequency of 400 mHz, which corresponds to an angular scale of 5′ and
10′ for the data collected at 2′ /sec and 4′ /sec. As described in detail in Sayers et al. (2011),
the atmospheric noise subtraction also attenuated the astronomical signal. To account
for this signal attenuation, observations of the flux calibration sources were processed in
an identical way prior to determining the flux calibration. Although the adaptive PCA
algorithm is non-linear, we verified via simulation that the combination of adaptive PCA
and a 400 mHz high-pass filter results in a constant fractional amount of signal attenuation
for point-like objects with flux densities < 100 Jy, which is well above the flux density of
any of our flux calibration sources.

We estimated the noise in our images via jackknife realizations of our data following
the methods described in Sayers et al. (2011). These jackknifes involve multiplying a
randomly selected subset of half of our data by -1. By adding these jackknifes together we
preserve the noise properties of the data while removing the astronomical signal. In addition
to instrumental and atmospheric noise, some of our images also contain a non-negligible
amount of noise due to fluctuations in the astronomical (back)foregrounds. Using the
galaxy number counts model in Bethermin & Dole (2011), we estimate the confusion
noise (quantified by the RMS noise fluctuations on beam size scales) to be 0.6 mJy, which
is approximately the confusion noise measured at the same wavelength/resolution with
AzTEC (Scott et al. 2010). The total uncertainty on the flux density of a galaxy is then
given by the quadrature sum of instrument/measurement noise and confusion noise. The
noise fluctuations in the map are Gaussian within our ability to measure them. For our

was effective at subtracting this pickup noise. This problem was resolved in April 2011,
and allowed the faster scan speeds used in September 2011 (although we still used the same
adaptive PCA algorithm to remove atmospheric noise from the September 2011 data).

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non-detections we quote 95% confidence level upper limits based on the formalism given
in Feldman and Cousins (1998), who provided a rigorous method for quoting upper limits
from a measurement with Gaussian noise and a physical constraint that the true underlying
value is non-negative (which is the case for our measurements, since negative flux densities
are unphysical). Specifically, our upper limits are computed from the values given in Table
10 of Feldman and Cousins (1998).

2.4. Optical Spectroscopy

We obtained optical spectroscopy of the WISE-selected sources over the course of
four observing runs between July 2010 and February 2011. Optical spectroscopic results
for 14 sources in Table 1 are reported in Eisenhardt et al. (2012) and Bridge et al. (in
preparation), as noted in Table 1. Table 2 lists the primary observing parameters, including
telescope, instrument, observing date, and integration time, for the remaining 12 W12drop
galaxies. All of the targets were observed with multiple exposures, which were generally
dithered along the slit to improve the reduction quality. Table 2 also lists the resultant
redshifts, most of which are based on multiple features and are therefore considered secure.

Most targets were observed with the dual-beam Low Resolution Imaging Spectrometer
(LRIS; Oke et al. 1995) on the Keck I telescope. All of the LRIS observations used the
1. 5 wide longslit, the 5600 ˚ dichroic, and the 400 ℓ mm−1 grating on the red arm of the
′′
A
spectrograph (blazed at 8500 ˚; spectral resolving power R ≡ λ/∆λ ∼ 700 for objects
A
filling the slit). The July 2010 observations used the 600 ℓ mm−1 grism on the blue arm of
the spectrograph (λblaze = 4000 ˚; R ∼ 750), while the 2011 observations used the slightly
A
lower resolution 400 ℓ mm−1 blue grism (λblaze = 3400 ˚; R ∼ 600). Observations were
A
generally obtained at a position angle that placed a brighter offset star on the slit. Since
LRIS has an atmospheric dispersion corrector, there are no issues with lost light due to

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observing at non-parallactic angles.

The final 2 sources, W0220+0137 and W0116−0505, were observed with the Blue
Channel Spectrograph (BCS) on the 6.5-m MMT telescope in non-photometric conditions
on UT 2010 December 4. These observations used the 1. 5 wide longslit and the 500 ℓ mm−1
′′

grating (λblaze = 5400 ˚; R ∼ 950), and were obtained at a position angle of 47.3 deg.
A

We processed the data using standard procedures, including bias subtraction, gain
correction, cosmic ray removal, sky subtraction and stacking the 2-dimensional spectra
′′
(e.g., Stern et al. 2010). The spectra were extracted using a 1. 5 aperture and wavelength
calibrated using internal arc lamps. As a final step in the wavelength calibration, we shifted
the wavelength solution based on telluric emission and absorption lines, conservatively
providing wavelength solutions that are robust to better than 1 ˚. We flux calibrated the
A
spectra using observations of standard stars from Massey & Gronwall (1990), generally
observed on the same night as the science observations. For photometric nights, we estimate
that the flux calibration is accurate to 10%. For non-photometric data, which includes
the two sources observed with MMT, the spectrophotometry is less accurate. The final,
reduced spectra are presented in Figure 2. The sources range in redshift from z = 1.990 to
z = 3.592 and all but three of the sources (W0338+1941, W0926+4232 and W1830+6504)
are clearly AGNs as evidenced by strong, high-ionization emission lines such as O VI, C IV,
and/or C III]. One of the three outliers, W0338+1941, has an unusually broad Lyα profile,
indicating that it is also likely an AGN. Note the diversity of spectroscopic features. Most
of the source spectra are dominated by strong, narrow Lyα emission. Some of the sources
are clearly type-2 AGNs, with only narrow emission features visible (e.g., W1422+5613).

We highlight two sources with unusual spectra. W0542−2705 shows a large number
of moderate-width (∼ 2400 km s−1 ) emission features. Of particular note is the strong
Al III λ1857 emission, which is stronger than the C III] λ1909 emission (Al III/C III] ∼ 2).

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In contrast, the corresponding line ratio for the Vanden Berk et al. (2001) SDSS quasar
composite is Al III/C III = 0.02, approximately two orders of magnitude weaker. The
other unusual spectrum is W0926+4232 which does not show any emission features, though
multiple absorption features as well as a Lyman forest break clearly indicate a redshift of
z = 2.498, analogous to the the spectrum of W1814+3412 reported in Eisenhardt et al.
(2012).

2.5. Warm Spitzer Follow-up

Warm Spitzer observations at 3.6 and 4.5 µm of all the galaxies except one
(W0211−2422) in Table 1 were obtained under program 70162 between November 2010 and
July 2011. The sources were observed using five exposures of 30s in each IRAC band (IRAC
has a 5′ field of view with 1. 2 pixels), with the medium scale Reuleaux dither pattern. The
′′

′′
Spitzer pipeline post-BCD processed images, which are resampled onto 0. 6 pixels, were used
for photometry. All targets in this paper with warm Spitzer follow-up were detected in both
′′
IRAC bands. Flux densities at 3.6 and 4.5 µm were measured in 4. 8 diameter apertures
and are listed in Table 3. The aperture corrections are 1.205 and 1.221 for 3.6 and 4.5 µm,
respectively. We did not apply a color correction, since the results presented here are not
sensitive to such corrections. For W0211−2422, which was not observed by Spitzer, we list
its W1 and W2 flux densities in Table 3.

3. Results

Of the 14 high redshift W12drop galaxies observed with SHARC-II at 350 µm, nine
were detected at ∼ 3 σ or above. The relatively high detection rate of these W12drop
galaxies at 350 µm implies they are a submillimeter bright population with high infrared

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luminosity. We also observed three of the 14 targets using the SHARC-II 450 µm band,
with one detection and one marginal detection (2σ-3σ); and observed one (W0410−0913,
which has the brightest 350µm flux density) in the 850 µm band, with a detection. The
flux densities of the detections are presented in Table 3.

We used Bolocam to follow-up 18 W12drop galaxies at z>1.7 in the 1.1 mm band,
including six of the galaxies that were observed with SHARC-II. We obtained five detections,
and 13 useful upper limits. Flux densities of the detected targets and 95% confidence (2 σ)
upper limits for undetected targets are presented in Table 3. We also tabulate in Table 3
Spitzer 3.6 and 4.5 µm, and WISE 12 and 22 µm measurements. W0149+2350 was observed
with the Submillimeter Array (SMA) at 1.3 mm (Wu, Bussmann, et al. in prep). We list
this SMA measurement in the 1.1 mm column in Table 3.

3.1. SEDs

Taking the 3.6 µm to 1.1 mm measurements from Table 3, we construct the mid-IR to
millimeter SED for W12drop galaxies. Figure 3 shows SEDs for the 9 SHARC-II detected
W12drop galaxies compared with galaxy models. In the first panel we overlay a wide range
of templates at the corresponding redshift for one W12drop galaxy, normalized to the same
W4 flux densities. These templates include the starburst-dominated galaxy Arp220, the
AGN-starburst blend Mrk231, type I (unobscured), type II (obscured) AGN models (QSO 1
and QSO 2) from Polletta et al. (2007), a torus model (Polletta et al. 2006), and simulation
models of DOGs (Narayanan et al. 2010). In the remaining panels we overlay only the
Arp220 and Mark231 templates.

The most notable feature is the apparently flat SEDs extending from the mid-IR to the
submillimeter in all of these W12drop galaxies. At 3.6 and 4.5 µm, large visual extinction

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must be added to the comparison templates to match the data, suggesting they are highly
obscured. If we normalize all SEDs at their 22 µm flux densities, then the submm emission
of W12drop galaxies is much fainter than expected for any other population, indicating
their mid-IR to submm flux ratio is unusually high. Starburst models miss these SEDs by
a large margin. QSO models are better, and the closest match is from the AGN dust torus
model, but the fit is still poor. To quantitatively show the high mid-IR to submm ratio, we
compare νLν(24µm)/νLν(350µm) in W12drops to this ratio in SMGs and DOGs in Figure
4a.

Figure 5 shows the SEDs of all submm detected W12drops plotted at their rest frame
wavelength in νLν units, normalized by their total luminosity (see the next section). This
figure shows a fairly consistent SED for all the W12drop galaxies reported in this paper.
This SED has a power-law in the mid-IR (1-5 µm), a mid-IR bump that dominates the
total luminosity contribution, and becomes flat in the mid-IR to submm. The typical SED
of W12drops is quite different from any existing galaxy templates, indicating they may be a
new type of galaxy. Their SEDs apparently peak at significantly shorter wavelengths than
other galaxy templates, indicating hotter average dust temperatures.

3.2. Luminosities and Temperatures

In order to understand the nature of the W12drop galaxies, we need to estimate their
luminosities and dust temperatures. The standard method to do this is to fit several
black-body models with wavelength-dependent opacities to fit SED points along a large
range of wavelengths, to constrain both temperatures and luminosities. We already know
that W12drop galaxies have unusually high mid-IR to submm ratios, and that the major
luminosity comes from 24µm to 350µm emission (see Figure 5), so this is clearly the
key wavelength range to characterize. At redshift 2-3, the IRAC [3.6] and [4.5] bands

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(rest wavelength 0.8-1.5 µm) may be significantly affected by stellar light, and at longer
wavelengths, we see indications that these W12drop galaxies may have components in
addition to a hot-dust component (see section 4).

In many cases infrared-luminous galaxies are dominated by one major dust component,
and can be approximated by a single-temperature modified blackbody model. For example,
a single dust temperature model provides a good description of the far-IR and submm/mm
SEDs of SMGs (e.g. Magnelli et al. 2012), with typical dust temperatures of 30-40 K
(Chapman et al. 2005, Kovćs et al. 2006, Coppin et al. 2008, Wu et al. 2009, Magnelli
a
et al. 2012). Most DOGs can also be described by a single-temperature model with dust
temperatures of 20-40 K (Melbourne et al. 2012). Because the peak of the W12drop
SEDs is not well sampled in the data presented here, it is unclear whether their 24µm to
350µm emission can be well described by a single-temperature model, and we are obtaining
Herschel data to better determine this. In this paper we use a single-temperature model to
describe the bulk of the emission from W12drops.

We apply a single temperature, modified black-body model combined with a power-law
model, to fit the mid-IR to mm SEDs. At lower frequencies we use Sν ∝ ν β × Bν (T ),
where Bν (T ) is the Plank function and β is the dust emissivity index with β = 1.5,
attached smoothly to which at higher frequencies is a power-law with Sν ∝ ν −α . The two
portions are joined at the frequency when the modified black-body slope equals that of the
power-law (α). The α parameter and dust temperature T are constrained by W3, W4 and
350µm data, as well as 450µm, 850µm and 1.1 mm data when available. These data do not
absolutely determine the shape of the SED, but the combination of the α and T parameters
provide a reasonable measure of the peak frequency of the SED. In Table 4, we give the
derived dust temperatures and mid-IR power-law indexes from this model.

The derived dust temperatures of W12drops range from 60 K to 123 K, with a median

– 18 –

value of 94 K. We applied this same model to calculate dust temperatures for DOGs in
Bo¨tes field, using similar data from Melbourne et al. (2012). We used their reported
o
IRAC 8µm and MIPS 24µm data in place of W3 and W4 to calculate α, together with
their SPIRE 350 and 500 µm data to estimate the dust temperature. We obtained similar
dust temperatures to the 20-40 K reported by Melbourne et al. (2012). This confirms that
W12drop galaxies are much hotter than typical DOGs.

Our single-temperature model also provides a luminosity when α, β and T are fixed.
However this luminosity is sensitive to the data points close to the peak, which is not well
sampled here. Therefore instead, we use a simple, but conservative method to estimate
the total luminosity, which is to simply connect the data points of all the available SED
points with power-laws, and integrate the total flux densities. This method may miss
the luminosity close to the peak of the SED, so it provides a lower bound to the true
luminosity. We list the conservative total luminosity calculated between 2-1000 µm in Table
4. The derived total luminosities range from 1.7 ×1013 L⊙ (W0211−2242), to 1.8 ×1014 L⊙
(W0410−0913), confirming that these galaxies are very luminous, well above the 1013 L⊙
threshold for HyLIRGs.

4. Discussion

Our CSO follow-up observations of 26 W12drop galaxies show that their luminosities
are very high, with some over 1014 L⊙ , and a median and mean of 5.7 and 6.1 ×1013 L⊙ , all
using the conservative power-law method. This is roughly an order of magnitude brighter
than the typical SMG (with median luminosity L ∼ 8 × 1012 L⊙ , Chapman et al. 2005,
Kovćs et al. 2006), or DOG (with median and mean luminosity ∼ 6 × 1012 and 9 × 1012 L⊙ ,
a
Melbourne et al. 2012), and is comparable to the brightest known optically selected
quasars (Schneider et al. 2005). Extremely luminous infrared galaxies are often found to be

– 19 –

magnified by galaxy-galaxy lensing (Blain 1996, Eisenhardt et al. 1996, Solomon & Vanden
Bout 2005, Vieira et al. 2010, Negrello et al. 2010). An immediate concern about the
hyperluminous W12drop galaxies is whether they are lensed, too. However, high-resolution
imaging follow-up of selected W12drops does not indicate gravitational lensing (Eisenhardt
et al. 2012, Bridge et al. in prep.), so that the derived ∼ 1014 L⊙ luminosities are consistent
with being intrinsic based on the current data. Additional high-resolution follow-up
observations with Hubble Space Telescope are currently underway, and should reveal if
these W12drop galaxies are not lensed. If the lack of lensing is confirmed, these galaxies are
one of the most luminous populations in the Universe.

Their unusually high dust temperatures and extremely high luminosities make W12drop
galaxies of great interest for studying galaxy formation and evolution. How do they become
so luminous? Are they experiencing special evolutionary events? What is their relationship
to other well-established galaxy populations, such as SMGs and DOGs?

Classical SMGs are defined with strong 850µm emission (> 5mJy) which normally
indicates significant cold-dust content. Table 3 gives examples of some W12drop galaxies
that meet this criterion. Hence some W12drop galaxies would be selected as SMGs.
However, the relatively low detection rate with Bolocam at 1.1 mm implies that many
W12drop galaxies are not as bright as SMGs at longer wavelengths. This is understandable
given that W12drop galaxies are dominated by emission from hotter dust. DOGs normally
have both AGN and starburst contributions, with warmer dust grains than SMGs. In Dey
et al (2008), DOGs are defined as galaxies with F24 > 0.3 mJy, and R − [24] > 14 (in Vega
magnitudes), where the R photometry is centered at 6393 ˚. Since the W4 band at 22 µm
A
is similar to the Spitzer 24 µm band, our W4 > 7 mJy selection corresponds to much higher
flux densities at 24 µm than normal DOGs. To make a comparison between W12drops and
typical DOGs, we obtained r-band (centered at 6231 ˚) photometry from SDSS (DR8),
A

– 20 –

as listed in table 3, and used the r-W4 color to approximate the R-[24] color. Taking the
average power-law index α of 2.09 from Table 4 and extrapolating to r-band and 24 µm, the
difference between the r-W4 and R-[24] color ranges from 0.2 to 0.24 mag as R-[24] changes
from 14 to 17. All 18 targets in Table 3 that are covered by SDSS DR8 meet the r-W4 > 14
DOG criterion, with r-W4 ranging from 14.4 to 16.1 for r-band detected sources, and r-W4
> 15.3 for r-band undetected sources (using r=22.9 Vega mag as the SDSS detection limit).
In figure 6 we compare the distribution of R vs. R-[24] for these high-redshift W12drops
to DOGs in D08. Clearly all W12drop galaxies in Table 3 qualify as DOGs, with similar
colors, but are much brighter at 24 µm.

Although many and maybe most W12drop galaxies can be classified as DOGs, their
properties are quite different from normal DOGs. Comparing to the DOGs reported in D08,
W12drop galaxies have an order of magnitude higher luminosity, although their redshift
distributions are similar (Eisenhardt et al. 2012). Bussmann et al. (2009) used SHARC-II
at 350 µm to follow-up a subset of DOGs with the brightest 24 µm flux densities from
D08 (Fig 6), obtaining infrared luminosities (8-1000µm, ∼ 1013 L⊙ ) and dust temperatures
(>30-60 K), still significantly lower than for the W12drop galaxies reported here. Since the
D08 survey covered only ∼ 9 deg2 (Bo¨tes field), the DOG surface density is ∼ 320 DOGs
o
per square degree with 24 µm fluxes density greater than 0.3 mJy. The W12drop selection
requires W4 > 7 mJy, which is at the high 24 µm flux density end of the D08 sample, and
only selects ∼ 1000 targets over the whole sky. The typical DOGs are 20 times fainter than
the W12drops, but the latter are about 10000 times rarer. The high-z W12drop galaxies
are apparently extreme cases of DOGs with very high dust obscuration and hotter dust
temperatures, and appear to be hyperluminous, hot DOGs.

The very low surface density of W12drop galaxies suggests either they are intrinsically
extremely rare, or are only seen during a very short phase of galaxy evolution. DOGs

– 21 –

are thought to be the transitional phase of mergers between starburst-dominated mode
and AGN-dominated modes. Based on the mid-IR SED (3.6-24 µm), D08 classified DOGs
into two categories, those which have a distinct “bump” in their SED between 3-10 µm
attributed to the redshifted starlight from rest-frame 1.6 µm, and those whose mid-IR SED
is a power-law. Bump DOGs are thought to be dominated by starbursts (Yan et al. 2005,
Sajina et al. 2007, Farrah et al. 2008, Desai et al. 2009), and tend to have fainter 24 µm
flux densities (Dey et al. 2008), while power-law DOGs are thought to be dominated by
AGN in the mid-IR (Weedman et al. 2006, Donley et al. 2007, Yan et al. 2007, Murphy et
al. 2009), and make up most of the bright end of the 24µm flux density distribution. The
fraction of power-law DOGs increases from 10% at F24µm = 0.3 mJy to 60% at F24µm = 1
mJy in the Spitzer Deep, Wide-Field Survey (Ashby et al. 2009). The mid-IR (MIPS 24
µm) to submm (SPIRE 250 µm) flux density ratio for power-law DOGs is found to be
similar to the AGN dominated ULIRG Mrk231 (Melbourne et al. 2012). The IRAC1 to W4
SEDs of W12drops (Fig. 5) are more like the mid-IR SEDs of DOGs rather than SMGs’
(Hainline et al. 2009). They show typical power-law shapes with no obvious bumps, and
are very bright at 24 µm. Consequently, it is plausible that W12drop galaxies are also
dominated by very powerful AGNs. These powerful, highly obscured AGNs can heat the
surrounding dust cocoon to a very high temperature.

Although the SEDs of W12drops are dominated by emission from very hot dust
components (Figure 5) that are likely contributed by powerful AGNs, a hot AGN component
alone can’t explain all of the observed SED from the mid-IR to millimeter bands. It is likely
that the SEDs are composed of multiple components with different temperatures. A more
detailed model to decompose SEDs with multiple-temperature components needs a more
complete set of SED data, which will become available from our ongoing Herschel program.
But the 350µm and 1.1 mm data reported in this paper can give a useful constraint on the
coldest component, if we assume that the 350 µm to 1.1 mm SED is tracing the coldest

– 22 –

dust in these galaxies. In figure 7, we plot the modeled flux density ratios of 350 µm to
1.1 mm continuum versus the redshifts, for models with a single-temperature black-body
times a wavelength-dependent opacity, with various dust temperatures and emissivities.
W12drop galaxies with available 350 µm and 1.1mm measurements are plotted in the figure.
For comparison, models based on galaxies with significant starburst components (Arp220
and Mrk231) are also plotted. For β between 1.5 and 2.0, the 350 µm to 1.1 mm ratios
of W12drop galaxies in Figure 7 apparently favor a model with Tdust less than 50 K, in
addition to the ∼ 100 K hot dust component that dominates the mid-IR. This temperature
of colder dust is comparable to the typical dust temperature of ∼35 K associated with
starburst galaxies (such as Arp220). Considering that the very hot AGN component will
contribute more to the continuum at 350µm than at 1.1mm, the actual 350 µm to 1.1 mm
ratios that trace the coldest dust could be lower, and therefore closer to the track of Arp220
or Mrk231 in Figure 7. This may imply that the cold dust component in these galaxies is
not very different from those in starburst galaxies, and is possibly related to star formation.
For example, in the detailed study of the first discovered W12drop galaxy (W1814+3412,
Eisenhardt et al. 2012), a significant starburst is found, although only contributing a small
fraction to the overall luminosity. The cold dust properties of W12drop galaxies may also
be different from known obscured QSOs (e.g. Mart´
ınez-Sansigre et al. 2009). The ratio
of 350 µm to 1.1 mm in AMS16, a high-z obscured quasar, is lower than for w12drops, as
plotted in Figure 7. A detailed study of the long-wavelength properties for these W12drop
galaxies, for instance, to distinguish the contribution and distribution of cold dust (star
formation) and hot dust (AGN), will need observations from ALMA as well as Herschel.

The similarity between the optical to 22 µm SEDs of DOGs and W12drop galaxies,
with the latter being much brighter, suggests W12drops may be the high luminosity tail
of the DOG distribution. But the high mid-IR to submm luminosity ratio of W12drops
implies they are much hotter than typical DOGs. Are these W12drops merely luminous

– 23 –

DOGs, or a distinct population? Or do they have any evolutionary connection? Some
theoretical models for DOGs (e.g. Narayanan et al. 2010) propose that SMGs, bump DOGs,
and power-law DOGs may form an evolutionary sequence, representing the transition of
merging galaxies from a starburst-dominated phase to an AGN-dominated phase, although
direct observational support for this is still rare. In Figure 4a, we see a strong correlation
between the mid-IR flux density and the mid-IR to submm luminosity ratio that supports
such a sequence, with W12drops at the highest luminosities. The correlation is roughly
linear, suggesting the cold dust component (traced by 350µm emission which may be from
a starburst) doesn’t change significantly during this process, as clearly shown in Figure
4b, while the hot dust component (traced by 24µm) becomes stronger, possibly tracing
the growth of an embedded SMBH. In this scenario, W12drops represent a late phase of
this evolution, with more massive SMBHs and similar cold-dust components to SMGs and
DOGs. If so, the low surface density of W12drops suggests either such a phase is very
short, or not every galaxy goes through this stage. A better understanding of whether
the populations have an evolutionary connection will need a fuller study of the W12drop
population, and of the luminosity function of all these populations.

5. Summary

WISE has discovered a possibly new type of object, the W12drop galaxies. The results
of our CSO submm/mm follow-up observations for a subsample of W12drop galaxies are as
follows:

1. We observed 14 z > 1.7 W12drop galaxies with SHARC-II at 350µm, and nine were
detected. We also observed 18 with Bolocam at 1.1 mm, and five were detected.

2. The SEDs constructed from WISE, warm Spitzer and CSO data reveal consistent

– 24 –

features for W12drop galaxies. These SEDs show a power-law shape in the mid-IR, and are
apparently flat from the mid-IR to submm/mm. Their SEDs have unusually high mid-IR
to submm luminosity ratios, indicating a hotter dust temperature than other populations.
Their SEDs can not be well fit with existing galaxy templates, indicating they are likely a
new population.

3. Using power-laws to connect the SED data points, we estimate their total
luminosities to be at least 1.7 ×1013 L⊙ to 1.8 ×1014 L⊙ . Using a single-temperature
modified blackbody model with β=1.5, we estimate their dust temperatures to be 60 K to
120 K, much hotter than other infrared luminous galaxies. Besides the hot dust component,
they may also have colder dust components that are similar to starburst galaxies.

4. W12drop galaxies in this paper would also be selected as DOGs, but are at least
10 times more luminous and 10000 times rarer. They may be the extreme cases of very
luminous, hot DOGs, and may represent a short evolutionary phase during galaxy merging,
following the phase of SMG, bump DOG and power-law DOG.

J. Wu and R. Assef were supported by an appointment to the NASA Postdoctoral
Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated
Universities through a contract with NASA. N. Evans acknowledges support from NSF
Grant AST-1109116. This publication makes use of data products from the Wide-field
Infrared Survey Explorer, which is a joint project of the University of California, Los
Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by
the National Aeronautics and Space Administration. This work is based on observations
made with the Caltech Submillimeter Observatory, which is operated by the California
Institute of Technology under funding from the National Science Foundation, contract AST
90-15755. This work uses data obtained from the Spitzer Space Telescope, which is operated
by the Jet Propulsion Laboratory, California Institute of Technology under contract with

– 25 –

NASA. Some of the data presented herein were obtained at the W.M. Keck Observatory,
which is operated as a scientific partnership among Caltech, the University of California and
NASA. The Keck Observatory was made possible by the generous financial support of the
W.M. Keck Foundation. Some data reported here were obtained at the MMT Observatory,
a joint facility of the University of Arizona and the Smithsonian Institution. This paper uses
data from SDSS (DR 8). Funding for SDSS-III has been provided by the Alfred P. Sloan
Foundation, the Participating Institutions, the National Science Foundation, and the U.S.
Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/.

– 26 –

REFERENCES

Alexander, D. M., Bauer, F. E., Chapman, S. C., et al. 2005, ApJ, 632, 736

Alexander, D. M., Brandt, W. N., Smail, I., Swinbank, A. M., Bauer, F. E., Blain, A. W.,
Chapman, S. C., Coppin, K. E. K., Ivison, R. J., Men´ndez-Delmestre, K. 2008,
e
ApJ, 135, 1968

Assef, R. J., Kochanek, C. S., Ashby, M. L. N. et al. 2011, ApJ, 728, 56

Ashby, M. L. N., Stern, D., Brodwin, M., et al. 2009, ApJ, 701, 428

Barnes, J. E., Hernquist, L. 1992, Ann. Rev. Ast. & Astrophys., 30, 705

B´thermin, M. & Dole, H. 2011, arXiv:1102.1827
e

Blain, A.W. 1996, /mnras, 283, 1340

Blain, A. W., Smail, I., Ivison, R. J., Kneib, J.P., Frayer, D. T. 2002, Physics Reports, 369,
Issue 2, 111

Bridge, C. R., Blain, A., Borys, C. J. et al. 2012, arXiv:1205.4030

´
Bussmann, R. S., Dey, A., Borys, C., Desai, V., Jannuzi, B. T.,Le Floch, E., Melbourne, J.,
Sheth, K., Soifer, B. T. 2009, ApJ, 705, 184

´
Caputi, K. I., Lagache, G., Yan, L., Dole, H., Bavouzet, N., Le Floch, E., Choi, P. I., Helou,
G., Reddy, N. 2207, ApJ, 660, 97

Chapman, S. C., Blain, A. W., Smail, Ian, Ivison, R. J. 2005, ApJ, 622, 772

Coppin, K., Halpern, M., Scott, D., et al. 2008, MNRAS, 384, 1597

Cutri, R. M., Wright, E. L., Conrow, T. et al. 2012, Explanatory Supplement to the WISE
All-Sky Data Release Products

– 27 –

Desai, V., Soifer, B. T., Dey, A., et al. 2009, ApJ, 700, 1190

´
Dey, A., Soifer, B. T., Desai, V., Brand, K., Le Floch, E., Brown, M. J. I., Jannuzi, B.
T., Armus, L., Bussmann, S., Brodwin, M., Bian, C., Eisenhardt, P., Higdon, S. J.,
Weedman, D., Willner, S. P. 2008, ApJ, 677, 943

Donley, J. L., Rieke, G. H., P´rez-Gonz´lez, P. G., Rigby, J. R., Alonso-Herrero, A. 2007,
e a
ApJ, 660, 167

Dowell, C.D., et al. 2003, SPIE, 4855, 73

Downes, T. P., Welch, D. E., Scott, K., et al. 2012, MNRAS, 423, 529

Eisenhardt, P. R., Armus, L., Hogg, D. W., Soifer, B. T., Neugebauer, G., Werner, M. W.
1996, ApJ, 461, 72

Eisenhardt, P.R.M., Wu, J., Tsai, C. et al. 2012. ApJ, 755, 173

Elbaz, D., Cesarsky, C. J., Chanial, P., et al. 2002, /aap, 384, 848

Farrah, D., Lonsdale, C. J., Weedman, D. W., Spoon, H. W. W., Rowan-Robinson, M.,
Polletta, M., Oliver, S., Houck, J. R., Smith, H. E. 2008, ApJ, 677, 957

Feldman, G. J. and Cousins, R. D., 1998, Phys. Rev. D, 57, 3873

Fiore, F., Grazian, A., Santini, P., Puccetti, S., et al. 2008, ApJ, 672, 94

Griﬃn, M. J. & Orton, G. S. 1993, Icar, 105, 537

Haig, D. J., Ade, P. A. R., Aguirre, J. E. et al. 2004, SPIE, 5498, 78

Hainline, L. J., Blain, A. W., Smail, I., Frayer, D. T., Chapman, S. C., Ivison, R. J.,
Alexander, D. M. 2009, ApJ, 699, 1610

– 28 –

Hainline, L. J., Blain, A. W., Smail, I., Alexander, D. M., Armus, L., Chapman, S. C.,
Ivison, R. J. 2011, ApJ, 740, 96

Heavens, A., Panter, B., Jimenez, R., Dunlop, J., 2004, Nature, 428, 625

Hopkins, A. M. & Beacom, J. F. 2006, ApJ, 651, 142

Hopkins, P F., Hernquist, L., Cox, T. J., Di Matteo, T., Robertson, B., Springel, V. 2006,
ApJS, 163, 1

Hopkins P. F., Hernquist L., Cox T. J., Robertson B., Krause E., 2007, ApJ, 669, 45

Hopkins, P. F., Hernquist, L., Cox, T. J., Keres, D. 2008, ApJS, 175, 356

Huang J.-S et al. 2009, ApJ700, 183

Jogee, S. 2006, in Physics of Active Galactic Nuclei on All Scales, ed. D. Alloin, R. Johnson,
& P. Lira ( Berlin: Springer), 143

Laurent, G. T., Aguirre, J. E., Glenn, J. et al. 2005, ApJ, 623, 742

Leong, M., Peng, R., Houde, M. et al. 2006, SPIE, 6275, 21

Lonsdale, C. J. et al. 2009, ApJ, 692, 442

Kov´cs,A. 2006. PhD Thesis, Caltech.
a

Kov´cs,A., Chapman, S. C., Dowell, C. D., Blain, A. W., Ivison, R. J., Smail, I., Phillips,
a
T. G. 2006, ApJ, 650, 592

Magnelli, B., Elbaz, D., Chary, R. R. et al. 2009, /aap, 496, 57

Magnelli, B., Lutz, D., Santini, P. et al. 2012, A&A, 539, 155

Massey, P. & Gronwall, C. 1990, ApJ, 358, 344

– 29 –

Mart´
ınez-Sansigre, A., Karim, A., Schinnerer, E., Omont, A., Smith, D. J. B., Wu, J., Hill,
G. J., Kl¨ckner, H.-R., Lacy, M., Rawlings, S., Willott, C. J. 2009, ApJ, 706, 184
o

Melbourne, J., Soifer, B. T., Desai, V. et al. 2012, AJ, 143, 125

Men´ndez-Delmestre, K., Blain, A. W., Alexander, D. M., Smail, I., Armus, L., Chapman,
e
S. C., Frayer, D. T., Ivison, R. J., Teplitz, H. I. 2007, ApJ, 655, 65

Murphy, E. J., Chary, R.-R., Alexander, D. M., Dickinson, M., Magnelli, B., Morrison, G.,
Pope, A., Teplitz, H. I. 2009, ApJ, 698, 1380

Narayanan, D., Dey, A., Hayward, C. C., Cox, T.J., Bussmann, R. S., Brodwin, M.,
Jonsson, P., Hopkins, P. F., Groves, B., Younger, J. D., Hernquist, L. 2010, MNRAS,
407, 1701

Negrello, M., Hopwood, R., De Zotti, G., et al. 2010, Science, 330, 800

Oke, J. B. et al. 1995, PASP, 107, 375

Polletta, M., Wilkes, B. J., Siana, B. et al. 2006, ApJ, 642, 673

Polletta, M., Tajer, M., Maraschi, L. et al. 2007, ApJ, 663, 81

Rigby, J. R., Rieke, G. H., Maiolino, R. et al. 2004, ApJS, 154, 160.

Reddy, N. A., Steidel, C. C., Pettini, M., et al. 2008, ApJS, 175, 48

Sajina, A., Yan, L., Armus, L., Choi, P., Fadda, D., Helou, G., Spoon, H. 2007, ApJ, 664,
713

Sandell, G. 1994, MNRAS, 271, 75

Sanders, D. B., & Mirabel, I. F. 1996, Ann. Rev. Ast. & Astrophys., 34, 749

– 30 –

Sayers, J., Golwala, S. R., Rossinot, P.., Ade, P. A. R., Aguirre, J. E., Bock, J. J.,
Edgington, S. F., Glenn, J., Goldin, A., Haig, D., Lange, A. E., Laurent, G. T.,
Mauskopf, P. D., Nguyen, H. T. 2009, ApJ, 690, 1597

Sayers, J., Golwala, S. R., Ameglio, S., Pierpaoli, E. 2011, ApJ, 728, 39

Sayers, J., Czakon, N. G., Golwala, S. R. 2012, /apj, 744, 169

Scott, K. S., Yun, M. S., Wilson, G. W., et al. 2010, MNRAS, 405, 2260

Schneider, D. P., Hall, P. B., Richards, G. T., et al. 2005, AJ, 130, 367

Schweizer, F. 1998, in Galaxies: Interactions and Induced Star Formation, ed. R. C.
Kennicutt Jr., F. Schweizer, J. E. Barnes, D. Friedli, L. Martinet, & D. Pfenniger (
Berlin: Springer), 105

Soifer, B. T., Helou, G., Werner, M. 2008, Ann. Rev. Ast. & Astrophys., 46, 201

Solomon, P.M. & Vanden Bout, P.A. 2005, Ann. Rev. Ast. & Astrophys., 43, 677.

Stern, D., Jimenez, R., Verde, L., Stanford, S. A., Kamionkowski, M. 2010, ApJS, 188, 280

Swinbank, A. M., Smail, I., Chapman, S. C., Blain, A. W., Ivison, R. J., Keel, W. C. 2004,
ApJ, 617, 64

Tacconi, L. J., Genzel, R., Smail, I., Neri, R., Chapman, S. C., Ivison, R. J., Blain, A., Cox,
P., Omont, A., Bertoldi, F. et al. 2008, ApJ, 680, 246

Tyler, Krystal D., Le Floc’h, E., Rieke, G. H. et al. 2009, /apj, 691, 1846

Vanden Berk, D. E., Richards, G. T., Bauer, A., et al. 2001, AJ, 122, 549

Vieira, J. D., Crawford, T. M., Switzer, E. R., et al. 2010, ApJ, 719, 763

– 31 –

Weedman, D., Polletta, M., Lonsdale, C. J., Wilkes, B. J., Siana, B., Houck, J. R., Surace,
J., Shupe, D., Farrah, D., Smith, H. E. 2006, ApJ, 653, 101

Wright, E. L. et al. 2010, AJ, 140, 1868

Wu, J., Vanden Bout, P. A., Evans, N. J. II., Dunham, M. M. 2009, ApJ, 707, 988

Yan, L., Chary, R., Armus, L., Teplitz, H., Helou, G., Frayer, D., Fadda, D., Surace, J.,
Choi, P. 2005, ApJ, 628, 604

Yan, L., Sajina, A., Fadda, D., Choi, P., Armus, L., Helou, G., Teplitz, H, Frayer, D.,
Surace, J. 2007, ApJ, 658, 778

Younger et al. 2008, ApJ, 688, 59.

This manuscript was prepared with the AAS L TEX macros v5.2.
A

Table 1. Targets observed with SHARCII and Bolocam

Source R.A. Dec. Redshift Band UT date Integration τ225GHz
Name a (J2000) (J2000) (z) (hr)

W0026+2015 00:26:09.24 +20:15:56.2 1.990 350 µm 2011 Sep 9 1.0 0.045
W0116−0505 01:16:01.41 -05:05:04.1 3.173 350 µm 2011 Sep 10 1.0 0.045
1100 µm 2011 Sep 18 2.3 0.15
W0149+2350 01:49:46.16 +23:50:14.6 3.228b 350 µm 2010 Jul 28,31 2.0 0.05
450 µm 2010 Sep 12 0.7 0.04
W0211−2242 02:11:34.63 -22:42:23.4 1.746b 350 µm 2011 Sep 10 1.0 0.05
W0220+0137 02:20:52.12 +01:37:11.6 3.122 350 µm 2010 Sep 12, 2011 Sep 10 1.8 0.045
1100 µm 2011 Sep 19,20 3.7 0.16,0.07

– 32 –
W0243+4158 02:43:44.18 +41:58:09.1 2.010 b 350 µm 2011 Sep 10 0.8 0.05
W0248+2705 02:48:58.81 +27:05:29.8 2.210 350 µm 2010 Sep 13, 2011 Sep 9 2.8 0.045
1100 µm 2011 Feb 19,20,22, Sep 18-20 7.4 0.15,0.07
W0338+1941 03:38:51.33 +19:41:28.6 2.123 350 µm 2011 Sep 10 0.8 0.05
W0410−0913 04:10:10.60 -09:13:05.2 3.592 350 µm 2011 Feb 21, 2011 Sep 9 2.3 0.95, 0.045
850 µm 2011 Feb 16-18 4.3 0.12
1100 µm 2010 Dec 12-14 7.3 0.14,0.1
W0422−1028 04:22:48.82 -10:28:32.0 2.227b 1100 µm 2011 Sep 17 2.7 0.21
W0542−2705 05:42:30.90 -27:05:40.5 2.532 350 µm 2010 Sep 13 0.4 0.05
W0757+5113 07:57:25.07 +51:13:19.7 2.277 b 1100 µm 2011 Feb 18,22 4.0 0.21
W0851+3148 08:51:24.78 +31:48:56.1 2.640 1100 µm 2010 Dec 13,14 5.3 0.13,0.1
W0856+0005 08:56:28.08 +00:05:48.7 2.519 b 1100 µm 2011 Feb 20 2.7 0.20
W0859+4823 08:59:29.94 +48:23:02.3 3.245b 1100 µm 2010 Dec 13-14,2011 Feb 16-18 6.7 0.11,0.13
W0926+4232 09:26:25.44 +42:32:51.9 2.498 1100 µm 2011 Feb 19 4.0 0.28
W1146+4129 11:46:12.87 +41:29:14.3 1.772 b 1100 µm 2011 Feb 16 3.0 0.15

Table 1—Continued

Source R.A. Dec. Redshift Band UT date Integration τ225GHz
Name a (J2000) (J2000) (z) (hr)

W1316+3512 13:16:28.53 +35:12:35.1 1.956 b 1100 µm 2011 Feb 19 2.7 0.21
W1409+1335 14:09:25.56 +13:35:02.1 3.048 b 1100 µm 2011 Feb 17,22 2.3 0.1, 0.2
W1422+5613 14:22:28.86 +56:13:55.6 2.524 1100 µm 2011 Feb 18,20,21 9.0 0.2
W1603+2745 16:03:57.39 +27:45:53.3 2.633 b 350 µm 2010 Sep 13 0.5 0.04
W1814+3412 18:14:17.30 +34:12:25.0 2.452 c 350 µm 2010 Jul 13,23 2.7 0.06, 0.04
450 µm 2010 Sep 12,13 1.8 0.045
1100 µm 2010 Jun 17,18 6.0 0.1
W1830+6504 18:30:13.53 +65:04:20.5 2.653 350 µm 2011 Sep 9,10 2.7 0.05

– 33 –
W1835+4355 18:35:33.71 +43:55:49.1 2.298 b 350 µm 2010 Sep 12 1.0 0.04
450 µm 2010 Sep 13 0.6 0.04
W2207+1939 22:07:43.84 +19:39:40.3 2.022 b 1100 µm 2010 Dec 14 1.8 0.1
W2238+2653 22:38:10.20 +26:53:19.8 2.405 1100 µm 2011 Sep 20 1.7 0.075

a According to the WISE source naming convention (http : //wise2.ipac.caltech.edu/docs/release/allsky/expsup/sec1 6a.html), tar-
gets reported here have formal source designations of: WISE Jhhmmss.ss±ddmmss.s. For example, the ﬁrst target is WISE
J002609.24+201556.2. But we use a brief form of names: Whhmm±ddmm, in this table and throughout the paper.

b Spectral information will be reported in Bridge et al. in prep

c Spectral information is reported in Eisenhardt et al. 2012

– 34 –

Table 2. Optical Spectroscopy

Source Telescope/Instr. UT Date Exp. (s) z Notes

W0026+2015 Keck/LRIS 2010 Nov 08 600 + 300 1.990 Lyα, NV, CIV, HeII, [NeIV], MgII
W0116−0505 MMT/BCS 2010 Dec 04 3 × 600 3.173 Lyβ,Lyα,NV,SiIV/OIV
W0220+0137 MMT/BCS 2010 Dec 04 3 × 600 3.122 Lyβ,Lyα,NV,SiIV/OIV
W0248+2705 Keck/LRIS 2010 Nov 09 600 + 300 2.210 Lyα,CII],MgII
W0338+1941 Keck/LRIS 2011 Feb 02 2 × 900 2.123 Lyα
W0410−0910 Keck/LRIS 2010 Nov 08 2 × 600 3.592 CIV,HeII (Lyα at dichroic)
W0542−2705 Keck/LRIS 2010 Nov 08 600 + 300 2.532 CIII,OVI,Lyα,NV,...
W0851+3148 Keck/LRIS 2011 Nov 08 600 + 300 2.640 OVI,Lyα,CIV,HeII,CIIII],CII]
W0926+4232 Keck/LRIS 2011 Feb 02 2 × 900 2.498 Absorption lines only
W1422+5613 Keck/LRIS 2010 Jul 15 600 + 300 2.524 Lyα,NV,CIV
W1830+6504 Keck/LRIS 2010 Jul 13 2 × 600 2.653 Likely Lyα
W2238+2653 Keck/LRIS 2010 Nov 08 2 × 900 2.405 Lyα, NV, SiIV/OIV , CIV

– 35 –

Table 3. Photometry of Targetsa

Source SDSS r b 3.6µm 4.5µm 12µm 22µm 350µm 450µm 850µm 1100µm
(mag) (µJy) (µJy) (mJy) (mJy) (mJy) (mJy) (mJy) (mJy)

W0026+2015 22.10 40.1(2.0) 80.5(2.0) 2.77(0.13) 15.05(0.97) < 21 ... ... ...
W0116−0505 21.38 50.7(2.2) 89.4(2.3) 2.39(0.13) 12.96(1.00) 36(12) ... ... < 8.7
W0149+2350 <22.9 19.7(1.7) 34.7(1.5) 1.77(0.10) 9.18(0.76) 29(8) 35(9) ... 2(0.4)c
W0211−2242 30.5(11)d 78.0(10)d 3.31(0.11) 11.31(0.73) 56(15) ... ... ...
W0220+0137 21.84 25.2(1.8) 38.4(1.4) 1.78(0.10) 11.98(0.81) 43(9) ... ... 6.2(2.0)
W0243+4158 ... 23.1(1.7) 70.7(2.0) 2.56(0.13) 9.02(0.93) 38(13) ... ... ...
W0248+2705 ... 31.5(1.9) 52.0(1.6) 2.04(0.14) 11.11(1.05) 32(8) ... ... < 3.6
W0338+1941 12.2(1.6) 37.5(1.6) 1.97(0.14) 10.27(0.99) < 31 ... ... ...
W0410−0913 ... 26.7(1.8) 46.1(1.5) 2.45(0.14) 12.35(0.99) 118(17) ... 40(14) 13.6(2.6)
W0422−1028 ... 18.0(1.6) 55.0(1.6) 2.74(0.13) 10.70(1.02) ... ... ... < 4.9
W0542−2705 24.6(1.7) 29.2(1.2) 2.55(0.11) 14.08(0.90) < 47 ... ... ...
W0757+5113 22.27 20.0(1.7) 35.0(1.4) 1.46(0.11) 9.31(0.84) ... ... ... < 4.7
W0851+3148 21.64 41.4(2.0) 88.5(2.2) 3.51(0.16) 14.73(1.02) ... ... ... < 3.4
W0856+0005 <22.9 52.7(2.2) 74.2(2.0) 2.94(0.13) 15.06(0.96) ... ... ... < 9.4
W0859+4823 <22.9 16.4(1.6) 44.8(1.4) 2.22(0.10) 11.83(0.91) ... ... ... 6.2(1.5)
W0926+4232 <22.9 18.6(1.6) 28.6(1.2) 1.45(0.11) 7.78(0.93) ... ... ... < 5.5
W1146+4129 <22.9 23.6(1.7) 45.7(1.5) 3.90(0.13) 20.35(1.05) ... ... ... < 6.5
W1316+3512 22.56 22.0(1.7) 49.4(1.5) 3.00(0.12) 12.62(0.94) ... ... ... < 14.2
W1409+1335 <22.9 6.9(0.4) 16.4(1.0) 1.63(0.09) 9.44(0.73) ... ... ... 5.7(2.1)
W1422+5613 <22.9 28.6(1.8) 74.3(1.9) 3.07(0.09) 11.95(0.68) ... ... ... < 2.9
W1603+2745 <22.9 29.9(1.8) 47.6(1.5) 3.15(0.12) 9.53(0.87) < 56 ... ... < 27.9
W1814+3412 23.00 20.8(2.1) 26.5(1.9) 1.86(0.10) 14.38(0.86) 33(9) < 32 ... < 2.4
W1830+6504 <22.9 14.2(1.6) 41.9(1.4) 2.25(0.05) 7.56(0.34) < 31 ... ... ...
W1835+4355 ... 51.5(2.2) 142.8(3.0) 6.13(0.13) 27.05(0.87) 46(16) 31(14) ... ...
W2207+1939 <22.9 41.7(2.0) 57.8(1.7) 1.49(0.11) 10.27(0.90) ... ... ... < 8.7
W2238+2653 22.77 42.2(2.0) 58.8(1.6) 2.35(0.11) 17.15(0.98) ... ... ... 6.0(2.2)

a Photometry of 3.6 and 4.5 µm is from warm Spitzer; 12 and 22 µm data is from WISE; 350, 450 and 850 µm data
is from CSO/SHARC-II, and 1.1 mm data is from CSO/Bolocam. Numbers in parentheses are 1σ uncertainties. For
undetected targets, we give 95% (2σ) upper limits at 350, 450, 850 and 1100 µm columns.

br band magnitude from SDSS (DR8). For undetected targets, we use 22.9 mag as upper limits.

– 36 –

c Flux density at 1.3mm, obtained from the SMA (Wu, Bussmann et al. in prep)

d Data from WISE 3.4µm and 4.6µm measurements.

– 37 –

Table 4. Dust properties and luminosities for the sample
galaxies with submm data

Source Tdust α a Power-law Luminosityb
K L⊙

W0116−0505 123±8 2.42±0.15 7.4 ×1013
W0149+2350 100±5 2.05±0.10 5.7 ×1013
W0211−2242 60±5 1.73±0.10 1.7 ×1013
W0220+0137 118±6 2.50±0.15 7.1 ×1013
W0243+4158 68±5 1.81±0.20 2.0 ×1013
W0248+2705 87±8 2.28±0.10 2.8 ×1013
W0410−0913 82±5 2.16±0.10 1.8 ×1014
W1814+3412 113±7 2.89±0.10 4.0 ×1013
W1835+4355 94±10 1.96±0.10 6.5 ×1013

a The power-law index assuming in the mid-IR fν ∝ ν −α , for a single temperature,
modiﬁed black-body model combined with a power-law model. See section 3.2.

b Total luminosity (∼2-1000 µm) calculated by connecting all available SED points
with power-laws, which gives a lower bound of the total luminosity. See section 3.2.

– 38 –

W0116-0505 W0149+2350 W0211-2242 W0220+0137

350 350 350 350
W0243+4158 W0248+2705 W0410-0913 W1835+4355

350 350 350 350
W0220+0137 W0410-0913 W0859+4823 W2238+2653

1100 1100 1100 1100

Fig. 1.— Example SHARC-II and Bolocam images of detected W12drop galaxies. All
panels are 2′ × 2′ . The source name and observing band are listed in each panel. The center
of the red circle marks the target position identiﬁed from WISE, and the sizes of the red
′′
circle represents the beam-smoothed resolution (FWHM) for each image, which is 11. 7 for
350µm maps, and 42′′ for 1.1mm maps.

– 39 –

Fig. 2.— Optical spectra of the 12 WISE-selected sources. Prominent spectroscopic features
are labeled.

– 40 –

Fig. 2.— Continued.

– 41 –

Fig. 2.— Continued.

– 42 –

Fig. 3.— The SEDs for SHARCII detected W12drop galaxies with measured photometry,
overlaid on a variety of standard SED templates at their spectroscopic redshifts (Polletta et
al. 2006, 2007, Narayanan et al. 2010), normalized at 22 µm. Additional visual extinction
must be added in order to account for the extremely red mid-IR colors of the W12drop
galaxies. Black dotted lines in the ﬁgure demonstrate the method to connect SED points
with power-laws to approximate the total luminosity, as discussed in section 3.

– 43 –

Fig. 4.— a (left): The mid-IR to submm luminosity ratios (νLν) for SMGs (Magnelli et
al. 2012), bump DOGs and power-law DOGs (Melbourne et al. 2012), and W12drops (this
work). The dashed line indicates a linear correlation with a fixed slope of unity, and a fitted
νLν(24µm)
offset: log (F24µm )=log( νLν(350µm) )+0.4. b (right): The 350 µm emission is similar in all
these populations.

– 44 –

Fig. 5.— νLν units for SEDs in SHARC-II detected W12drop galaxies. The SEDs have
been normalized by their total luminosities (derived by connoting SED data points with
power-laws), and shifted to the rest frequency frame. All SEDs and galaxy templates are
normalized at their ﬂux density at rest frame 5 µm.

– 45 –

Fig. 6.— W12drop galaxies in Table 1 (red) compared to DOGs from the Bo¨tes field (Dey et
o
al. 2008) (black). A subsample of the brightest DOGs which were followed-up by SHARC-II
at 350µm are indicated in green (Bussmann et al. 2009). Circles represent targets with R
band detections and triangles denote targets with R band upper limits . We use SDSS r band
and r-W4 color to approximate R and R-[24] for W12drop galaxies, except for W1814+4512
where we use the r-band magnitude reported in Eisenhardt et al. (2012). Blue lines and
arrows demonstrate the DOG selection criteria by Dey et al. (2008) , and the red dash
line marks the lower limit of W4 flux density for the W12drop selection. W12drop galaxies
satisfy the DOG classification, but are much brighter at 24 µm.

– 46 –

Fig. 7.— Predicted flux ratio of 350µm to 1.1mm for various dust models as a function of
redshift. Upward pointing arrows show values based on 2σ limits at 1.1 mm. The 350µm
flux density for W2238+2653 is from Yan et al. (in prep.), and data for W2246−0526 is
from Tsai et al. (in prep). For W0149+2350 (brown filled circle), we convert the SMA
measurement at 1.3 mm to 1.1 mm flux density, by assuming the emissivity of β=1.5 and
β=2, then taking the average of the two. For comparison, models of Arp220 and Mrk231
are plotted, and the upper limits of a high-z obscured quasar (AMS16, Mart´
ınez-Sansigre et
al. 2009) is noted.

Submillimeter follow up_of_wise_selected_hyperluminous_galaxies

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