62 research outputs found
Detections of CO Molecular Gas in 24um-Bright ULIRGs at z~2 in the Spitzer First Look Survey
We present CO observations of 9 ULIRGs at z~2 with S(24\mu m)>1mJy,
previously confirmed with the mid-IR spectra in the Spitzer First Look Survey.
All targets are required to have accurate redshifts from Keck/GEMINI near-IR
spectra. Using the Plateau de Bure millimeter-wave Interferometer (PdBI) at
IRAM, we detect CO J(3-2) [7 objects] or J(2-1) [1 object] line emission from 8
sources with integrated intensities Ic ~(5-9)sigma. The CO detected sources
have a variety of mid-IR spectra, including strong PAH, deep silicate
absorption and power-law continuum, implying that these molecular gas rich
objects at z~2 could be either starbursts or dust obscured AGNs. The measured
line luminosity L'[CO] is (1.28-3.77)e+10[K km/s pc^2]. The averaged molecular
gas mass M(H2) is 1.7e+10Msun, assuming CO-to-H2 conversion factor of
0.8Msun/[K km/s pc^2]. Three sources (33%) -- MIPS506, MIPS16144 & MIPS8342 --
have double peak velocity profiles. The CO double peaks in MIPS506 and
MIPS16144 show spatial separations of 45kpc and 10.9kpc, allowing the estimates
of the dynamical masses of 3.2e+11*sin^(-2)(i)Msun and 5.4e+11*sin^{-2}(i)Msun
respectively. The implied gas fraction, M(gas)/M(dyn), is 3% and 4%, assuming
an average inclination angle. Finally, the analysis of the HST/NIC2 images,
mid-IR spectra and IR SED revealed that most of our sources are mergers,
containing dust obscured AGNs dominating the luminosities at (3-6)um. Together,
these results provide some evidence suggesting SMGs, bright 24um z~2 ULIRGs and
QSOs could represent three different stages of a single evolutionary sequence,
however, a complete physical model would require much more data, especially
high spatial resolution spectroscopy.Comment: 15 pages, 8 figures, accepted for publication in ApJ
A Deep 1.2 mm Map of the Lockman Hole North Field
We present deep 1.2 mm continuum mapping of a 566 arcmin^2 area within the
Lockman Hole North field, previously a target of the Spitzer Wide-area Infrared
Extragalactic (SWIRE) survey and extremely deep 20 cm mapping with the Very
Large Array, which we have obtained using the Max-Planck millimeter bolometer
(MAMBO) array on the IRAM 30 m telescope. After filtering, our full map has an
RMS sensitivity ranging from 0.45 to 1.5 mJy/beam, with an average of 0.75
mJy/beam. Using the pixel flux distribution in a map made from our best data,
we determine the shape, normalization, and approximate flux density cutoff for
1.2 mm number counts well below our nominal sensitivity and confusion limits.
After validating our full dataset through comparison with this map, we
successfully detect 41 1.2 mm sources with S/N > 4.0 and S(1.2 mm)\simeq 2-5
mJy. We use the most significant of these detections to directly determine the
integral number counts down to 1.8 mJy, which are consistent with the results
of the pixel flux distribution analysis. 93% of our 41 individual detections
have 20 cm counterparts, 49% have Spitzer/MIPS 24 micron counterparts, and one
may have a significant Chandra X-ray counterpart. We resolve \simeq 3% of the
cosmic infrared background (CIB) at 1.2 mm into significant detections, and
directly estimate a 0.05 mJy faint-end cutoff for the counts that is consistent
with the full intensity of the 1.2 mm CIB. The median redshift of our 17
detections with spectroscopic or robust photometric redshifts is z(median)=2.3,
and rises to z(median)=2.9 when we include redshifts estimated from the
radio/far-infrared spectral index. By using a nearest neighbor and angular
correlation function analysis, we find evidence that our S/N>4.0 detections are
clustered at the 95% confidence level.Comment: 40 pages, 25 figures, accepted for publication in Ap
Far-Infrared Properties of Spitzer-selected Luminous Starbursts
We present SHARC-2 350 micron data on 20 luminous z ~ 2 starbursts with
S(1.2mm) > 2 mJy from the Spitzer-selected samples of Lonsdale et al. and
Fiolet et al. All the sources were detected, with S(350um) > 25 mJy for 18 of
them. With the data, we determine precise dust temperatures and luminosities
for these galaxies using both single-temperature fits and models with power-law
mass--temperature distributions. We derive appropriate formulae to use when
optical depths are non-negligible. Our models provide an excellent fit to the
6um--2mm measurements of local starbursts. We find characteristic
single-component temperatures T1 ~ 35.5+-2.2 K and integrated infrared (IR)
luminosities around 10^(12.9+-0.1) Lsun for the SWIRE-selected sources.
Molecular gas masses are estimated at 4 x 10^(10) Msun, assuming
kappa(850um)=0.15 m^2/kg and a submillimeter-selected galaxy (SMG)-like
gas-to-dust mass ratio. The best-fit models imply >~2 kpc emission scales. We
also note a tight correlation between rest-frame 1.4 GHz radio and IR
luminosities confirming star formation as the predominant power source. The
far-IR properties of our sample are indistinguishable from the purely
submillimeter-selected populations from current surveys. We therefore conclude
that our original selection criteria, based on mid-IR colors and 24 um flux
densities, provides an effective means for the study of SMGs at z ~ 1.5--2.5.Comment: 13 pages, 4 figures, edited to match published version in ApJ 717,
29-39 (2010
A 158 Micron [CII] Line Survey of Galaxies at z ~ 1 to 2: An Indicator of Star Formation in the Early Universe
We have detected the 158 {\mu}m [CII] line from 12 galaxies at z~1-2. This is
the first survey of this important starformation tracer at redshifts covering
the epoch of maximum star-formation in the Universe and quadruples the number
of reported high z [CII] detections. The line is very luminous, between
<0.024-0.65% of the far-infrared continuum luminosity of our sources, and
arises from PDRs on molecular cloud surfaces. An exception is PKS 0215+015,
where half of the [CII] emission could arise from XDRs near the central AGN.
The L[CII] /LFIR ratio in our star-formation-dominated systems is ~8 times
larger than that of our AGN-dominated systems. Therefore this ratio selects for
star-formation-dominated systems. Furthermore, the L[CII]/LFIR and
L[CII]/L(CO(1-0)) ratios in our starforming galaxies and nearby starburst
galaxies are the same, so that luminous starforming galaxies at earlier epochs
(z~1-2) appear to be scaled up versions of local starbursts entailing
kilo-parsec-scale starbursts. Most of the FIR and [CII] radiation from our
AGN-dominated sample (excepting PKS 0215+015) also arises from kpc scale
starformation, but with far-UV radiation fields ~8 times more intense than in
our star-formation-dominated sample. We speculate that the onset of AGN
activity stimulates large-scale star-formation activity within AGN-dominated
systems. This idea is supported by the relatively strong [OIII] line emission,
indicating very young stars, that was recently observed in high z composite
AGN/starburst systems. Our results confirm the utility of the [CII] line, and
in particular, the L[CII]/L(FIR) and L[CII]/LCO(1-0) ratios as a tracers of
star-formation in galaxies at high redshifts.Comment: 33 pages, 5 figure
The Herschel Multi-tiered Extragalactic Survey: HerMES
The Herschel Multi-tiered Extragalactic Survey, HerMES, is a legacy program
designed to map a set of nested fields totalling ~380 deg^2. Fields range in
size from 0.01 to ~20 deg^2, using Herschel-SPIRE (at 250, 350 and 500 \mu m),
and Herschel-PACS (at 100 and 160 \mu m), with an additional wider component of
270 deg^2 with SPIRE alone. These bands cover the peak of the redshifted
thermal spectral energy distribution from interstellar dust and thus capture
the re-processed optical and ultra-violet radiation from star formation that
has been absorbed by dust, and are critical for forming a complete
multi-wavelength understanding of galaxy formation and evolution.
The survey will detect of order 100,000 galaxies at 5\sigma in some of the
best studied fields in the sky. Additionally, HerMES is closely coordinated
with the PACS Evolutionary Probe survey. Making maximum use of the full
spectrum of ancillary data, from radio to X-ray wavelengths, it is designed to:
facilitate redshift determination; rapidly identify unusual objects; and
understand the relationships between thermal emission from dust and other
processes. Scientific questions HerMES will be used to answer include: the
total infrared emission of galaxies; the evolution of the luminosity function;
the clustering properties of dusty galaxies; and the properties of populations
of galaxies which lie below the confusion limit through lensing and statistical
techniques.
This paper defines the survey observations and data products, outlines the
primary scientific goals of the HerMES team, and reviews some of the early
results.Comment: 23 pages, 17 figures, 9 Tables, MNRAS accepte
Polycyclic aromatic hydrocarbon emission in powerful high-redshift radio galaxies
We present the mid-infrared (IR) spectra of seven of the most powerful radio-galaxies known to exist at 1.5 < z < 2.6. The radio emission of these sources is dominated by the AGN with 500 MHz luminosities in the range 10^(27.8)–10^(29.1) W Hz^(−1). The AGN signature is clearly evident in the mid-IR spectra; however, we also detect polycyclic aromatic hydrocarbon emission, indicative of prodigious star formation at a rate of up to ∼1000 M_⊙ yr^(−1). Interestingly, we observe no significant correlation between AGN power and star formation in the host galaxy. We also find most of these radio galaxies to have weak 9.7 μm silicate absorption features (τ_(9.7 μm) < 0.8) which implies that their mid-IR obscuration is predominantly due to the dusty torus that surrounds the central engine, rather than the host galaxy. The tori are likely to have an inhomogeneous distribution with the obscuring structure consisting of individual clouds. We estimate that these radio galaxies have already formed the bulk of their stellar mass and appear to lie at a stage in their evolution where the obscured AGN dominates the energy output of the system but star formation is also prevalent
A Millimetre Survey of Starburst Dominated Ultraluminous Infrared Galaxies at z~2
We present millimetre observations of a sample of 12 high redshift
ultraluminous infrared galaxies (ULIRGs) in the Extended Growth Strip (EGS).
These objects were initially selected on the basis of their observed mid--IR
colours (0.0 < [3.6]-[4.5] < 0.4 and -0.7 < [3.6]-[8.0] < 0.5) to lie at high
redshift 1.5 < z < 3, and subsequent 20-38 micron mid-IR spectroscopy confirms
that they lie in a narrow redshift window centered on z=2. We detect 9/12 of
the objects in our sample at high significance (>3 sigma) with a mean
1200\micron flux of = 1.6+/-0.1 mJy. Our millimetre photometry,
combined with existing far-IR photometry from the Far-IR Deep Extragalactic
Legacy (FIDEL) Survey and accurate spectroscopic redshifts, places constraints
both sides of the thermal dust peak. This allows us to estimate the dust
properties, including the far--IR luminosity, dust temperature, and dust mass.
We find that our sample is similar to other high-z and intermediate-z ULIRGs,
and local systems, but has a different dust selection function than
submillimeter-selected galaxies. Finally, we use existing 20cm radio continuum
imaging to test the far-IR/radio correlation at high redshift. We find that our
sample is consistent with the local relation, implying little evolution.
Furthermore, this suggests that our sample selection method is efficient at
identifying ultraluminous, starburst--dominated systems within a very narrow
redshift range centered at z~2.Comment: 11 pages, 10 figures, resubmitted to MNRAS with minor revision
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