157 research outputs found
Microwave and radio emission of dusty star-forming galaxies: Implication for the cosmic radio background
We use the most up-to-date cosmological evolution models of star-forming (SF)
galaxies and radio sources to compute the extragalactic number counts and the
cosmic background from 408MHz to 12THz. The model of SF galaxies reproduces the
constraints obtained by Spitzer, Herschel, and ground-based submm/mm
experiments: number counts, redshift distribution of galaxies, cosmic
background intensity and anisotropies. The template SEDs of this model are
extrapolated to the radio adding synchrotron, free-free, and spinning dust
emissions. To fix the synchrotron intensity, we use the IR/radio flux ratio,
q70, and a spectral index beta=-3. For a constant q70, our model added to the
AGN contribution provides a good fit to the number counts from 12THz to 408MHz
and to the CIB. Spinning dust accounts for up to 20% of the cosmic microwave
background produced by SF galaxies, but for less than 10% of the total
background when AGN are included. The SF galaxies account for 77.5% of the
number counts at 1.4GHz for a flux of 1e-4Jy. However, the model does not
explain the CRB measured with the ARCADE2 experiment. Considering the case when
q70 decreases strongly with redshift, this still does not explain the ARCADE2
results. It also yields to an overestimate of the low-flux number counts in the
radio. Thus, we rule out a steep variation of q70 with redshift at least for
z<3.5. Adding a population of faint SF galaxies at high redshift (Lir<1e11Lsun
and 4<z<6), which would reproduce the ARCADE2 results, leads to predictions of
the CIB much higher than what is observed, ruling out this as the explanation
for the ARCADE2 results. Considering our findings and previous studies, we
conclude that if the radio emission measured by ARCADE2 is astrophysical in
origin, it has to originate in the Galaxy or in a new kind of radio sources
(with no mid- to far-IR counterparts) or emission mechanism still to be
discovered.Comment: accepted for publication by A&A, modification of one citatio
Comments on the paper "The initial conditions of isolated star formation - VI. SCUBA mapping of prestellar cores" (Kirk et al. 2005)
In their survey paper of prestellar cores with SCUBA, Kirk et al. (2005) have
discarded two of our papers on L183 (Pagani et al. 2003, 2004). However these
papers bring two important pieces of information that they cannot ignore.
Namely, the real structure of L183 and the very poor correlation between
submillimeter and far infrared (FIR) dust emission beyond \Avb 15
mag. Making the erroneous assumption that it is the same dust that we are
seeing in emission at both 200 and 850 m, they derive constant
temperatures which are only approximate, and column densities which are too
low. In fact dust temperatures do decrease inside dark clouds and the FIR
emission is only tracing the outer parts of the dark clouds (Pagani et al.
2004
Dissecting the high-z interstellar medium through intensity mapping cross-correlations
We explore the detection, with upcoming spectroscopic surveys, of
three-dimensional power spectra of emission line fluctuations produced in
different phases of the Interstellar Medium (ISM) by ionized carbon, ionized
nitrogen and neutral oxygen at redshift z>4. The emission line [CII] from
ionized carbon at 157.7 micron, and multiple emission lines from carbon
monoxide, are the main targets of planned ground-based surveys, and an
important foreground for future space-based surveys like the Primordial
Inflation Explorer (PIXIE). However, the oxygen [OI] (145.5 micron) line, and
the nitrogen [NII] (121.9 micron and 205.2 micron) lines, might be detected in
correlation with [CII] with reasonable signal-to-noise ratio (SNR). These lines
are important coolants of both the neutral and the ionized medium, and probe
multiple phases of the ISM. We compute predictions of the three-dimensional
power spectra for two surveys designed to target the [CII] line, showing that
they have the required sensitivity to detect cross-power spectra with the [OI]
line, and the [NII] lines with sufficient SNR. The importance of
cross-correlating multiple lines is twofold. On the one hand, we will have
multiple probes of the different phases of the ISM, which is key to understand
the interplay between energetic sources, the gas and dust at high redshift.
This kind of studies will be useful for a next-generation space observatory
such as the NASA Far-IR Surveyor. On the other end, emission lines from
external galaxies are an important foreground when measuring spectral
distortions of the Cosmic Microwave Background spectrum with future space-based
experiments like PIXIE; measuring fluctuations in the intensity mapping regime
will help constraining the mean amplitude of these lines, and will allow us to
better handle this important foreground.Comment: 13 pages, 2 table, 7 figures, Accepted for publication in Ap
A dynamical transition from atomic to molecular intermediate-velocity clouds
Towards the high galactic latitude sky, the far-infrared (FIR) intensity is
tightly correlated to the total hydrogen column density which is made up of
atomic (HI) and molecular hydrogen (H. Above a certain column density
threshold, atomic hydrogen turns molecular. We analyse gas and dust properties
of intermediate-velocity clouds (IVCs) in the lower galactic halo to explore
their transition from the atomic to the molecular phase. Driven by
observations, we investigate the physical processes that transform a purely
atomic IVC into a molecular one. Data from the Effelsberg-Bonn HI-Survey
(EBHIS) are correlated to FIR wavebands of the Planck satellite and IRIS.
Modified black-body emission spectra are fitted to deduce dust optical depths
and grain temperatures. We remove the contribution of atomic hydrogen to the
FIR intensity to estimate molecular hydrogen column densities. Two IVCs show
different FIR properties, despite their similarity in HI, such as narrow
spectral lines and large column densities. One FIR bright IVC is associated
with H, confirmed by CO emission; the other IVC
is FIR dim and shows no FIR excess, which indicates the absence of molecular
hydrogen. We propose that the FIR dim and bright IVCs probe the transition
between the atomic and molecular gas phase. Triggered by dynamical processes,
this transition happens during the descent of IVCs onto the galactic disk. The
most natural driver is ram pressure exerted onto the cloud by the increasing
halo density. Because of the enhanced pressure, the formation timescale of
H is reduced, allowing the formation of large amounts of H within a
few Myr.Comment: 13 pages, 14 figures, accepted for publication by A&
The [CII] 158\u3cem\u3eμ\u3c/em\u3em Line Emission in High-Redshift Galaxies
Gas is a crucial component of galaxies, providing the fuel to form stars, and it is impossible to understand the evolution of galaxies without knowing their gas properties. The [CII] fine structure transition at 158 μm is the dominant cooling line of cool interstellar gas, and is the brightest of emission lines from star forming galaxies from FIR through metre wavelengths, almost unaffected by attenuation. With the advent of ALMA and NOEMA, capable of detecting [CII]-line emission in high-redshift galaxies, there has been a growing interest in using the [CII] line as a probe of the physical conditions of the gas in galaxies, and as a star formation rate (SFR) indicator at z ≥ 4. In this paper, we have used a semi-analytical model of galaxy evolution (G.A.S.) combined with the photoionisation code CLOUDY to predict the [CII] luminosity of a large number of galaxies (25 000 at z ≃ 5) at 4 ≤ z ≤ 8. We assumed that the [CII]-line emission originates from photo-dominated regions. At such high redshift, the CMB represents a strong background and we discuss its effects on the luminosity of the [CII] line. We studied the L[CII]–SFR and L[CII]–Zg relations and show that they do not strongly evolve with redshift from z = 4 and to z = 8. Galaxies with higher [CII] luminosities tend to have higher metallicities and higher SFRs but the correlations are very broad, with a scatter of about 0.5 and 0.8 dex for L[CII]–SFR and L[CII]–Zg, respectively. Our model reproduces the L[CII]–SFR relations observed in high-redshift star-forming galaxies, with [CII] luminosities lower than expected from local L[CII]–SFR relations. Accordingly, the local observed L[CII]–SFR relation does not apply at high-z (z ≳ 5), even when CMB effects are ignored. Our model naturally produces the [CII] deficit (i.e. the decrease of L[CII]/LIR with LIR), which appears to be strongly correlated with the intensity of the radiation field in our simulated galaxies. We then predict the [CII] luminosity function, and show that it has a power law form in the range of L[ CII] probed by the model (1 × 107–2 × 109 L⊙ at z = 6) with a slope α = −1. The slope is not evolving from z = 4 to z = 8 but the number density of [CII]-emitters decreases by a factor of 20×. We discuss our predictions in the context of current observational estimates on both the differential and cumulative luminosity functions
Cross-correlation of cosmic far-infrared background anisotropies with large scale structures
We measure the cross-power spectra between luminous red galaxies (LRGs) from
the Sloan Digital Sky Survey (SDSS)-III Data Release Eight (DR8) and cosmic
infrared background (CIB) anisotropies from Planck and data from the Improved
Reprocessing (IRIS) of the Infrared Astronomical Satellite (IRAS) at 353, 545,
857, and 3000 GHz, corresponding to 850, 550, 350 and 100 micron, respectively,
in the multipole range 100<l<1000. Using approximately 6.5 10^5 photometrically
determined LRGs in 7760 deg^2 of the northern hemisphere in the redshift range
0.45 < z < 0.65, we model the far-infrared background (FIRB) anisotropies with
an extended version of the halo model. With these methods, we confirm the basic
picture obtained from recent analyses of FIRB anisotropies with Herschel and
Planck, that the most efficient halo mass at hosting star forming galaxies is
log(M_ eff/M_\odot)=12.84+/-0.15. We estimate the percentage of FIRB
anisotropies correlated with LRGs as approximately 11.8 %, 3.9 %, 1.8 %, and
1.0 % of the total at 3000, 857, 545, and 353 GHz, respectively. At redshift
z~0.55, the bias of FIRB galaxies with respect to the dark matter density field
has the value b_{FIRB}~1.45, and the mean dust temperature of FIRB galaxies is
T_d=26 K. Finally, we discuss the impact of present and upcoming
cross-correlations with far-infrared background anisotropies on the
determination of the global star formation history and the link between
galaxies and dark matter.Comment: 9 pages, 6 figures, accepted for publication in A&
IRIS: A new generation of IRAS maps
The Infrared Astronomical Satellite (IRAS) had a tremendous impact on many
areas of modern astrophysics. In particular it revealed the ubiquity of
infrared cirrus that are a spectacular manifestation of the interstellar medium
complexity but also an important foreground for observational cosmology. With
the forthcoming Planck satellite there is a need for all-sky complementary data
sets with arcminute resolution that can bring informations on specific
foreground emissions that contaminate the Cosmic Microwave Background
radiation. With its 4 arcmin resolution matching perfectly the high-frequency
bands of Planck, IRAS is a natural data set to study the variations of dust
properties at all scales. But the latest version of the images delivered by the
IRAS team (the ISSA plates) suffer from calibration, zero level and striping
problems that can preclude its use, especially at 12 and 25 micron. In this
paper we present how we proceeded to solve each of these problems and enhance
significantly the general quality of the ISSA plates in the four bands (12, 25,
60 and 100 micron). This new generation of IRAS images, called IRIS, benefits
from a better zodiacal light subtraction, from a calibration and zero level
compatible with DIRBE, and from a better destriping. At 100 micron the IRIS
product is also a significant improvement from the Schlegel et al. (1998) maps.
IRIS keeps the full ISSA resolution, it includes well calibrated point sources
and the diffuse emission calibration at scales smaller than 1 degree was
corrected for the variation of the IRAS detector responsivity with scale and
brightness. The uncertainty on the IRIS calibration and zero level are
dominated by the uncertainty on the DIRBE calibration and on the accuracy of
the zodiacal light model.Comment: 16 pages, 17 figures, accepted for publication in ApJ (Suppl). Higher
resolution version available at
http://www.cita.utoronto.ca/~mamd/IRIS/IrisTechnical.htm
Far-infrared excess emission as a tracer of disk-halo interaction
Given the current and past star-formation in the Milky Way in combination
with the limited gas supply, the re-fuelling of the reservoir of cool gas is an
important aspect of Galactic astrophysics. The infall of \ion{H}{i} halo clouds
can, among other mechanisms, contribute to solving this problem. We study the
intermediate-velocity cloud IVC135+54 and its spatially associated
high-velocity counterpart to look for signs of a past or ongoing interaction.
Using the Effelsberg-Bonn \ion{H}{i} Survey data, we investigated the interplay
of gas at different velocities. In combination with far-infrared Planck and
IRIS data, we extended this study to interstellar dust and used the correlation
of the data sets to infer information on the dark gas. The velocity structure
indicates a strong compression and deceleration of the infalling high-velocity
cloud (HVC), associated with far-infrared excess emission in the
intermediate-velocity cloud. This excess emission traces molecular hydrogen,
confirming that IVC135+54 is one of the very few molecular halo clouds. The
high dust emissivity of IVC135+54 with respect to the local gas implies that it
consists of disk material and does not, unlike the HVC, have an extragalactic
origin. Based on the velocity structure of the HVC and the dust content of the
IVC, a physical connection between them appears to be the logical conclusion.
Since this is not compatible with the distance difference between the two
objects, we conclude that this particular HVC might be much closer to us than
complex C. Alternatively, the indicators for an interaction are misleading and
have another origin.Comment: 11 pages, 10 figures, accepted for publication in A&
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