53 research outputs found
Spectroscopic follow-up of FIRBACK-South-Marano bright galaxies
We present optical spectroscopy of the brightest 170 microns sources in the
FIRBACK South Marano (FSM) field. The survey is 90% complete at the 4 sigma
level. The spectra are compared with those of a reference sample of faint IRAS
(60 microns selected) sources observed in the same conditions . The galaxies in
both samples are characterized by a predominance of emission-line spectra and
moderate IR luminosities (10E10.5 < L_IR < 10E12 L_Sun). The fraction of AGN's
is low (about 15%) and the majority of sources are nearby (z<0.3), dusty, star
forming galaxies, with moderate star formation rates (a few 10 solar masses per
year). The infrared emission of the FSM galaxies shows also a colder spectral
energy distribution than was expected.
The galaxies in both samples (IRAS faint sources and FSM) are essentially
undistinguishable with the available data, and seem to represent a population
of closeby, cold, star forming galaxies rather neglected up to now. Although
their contribution to the far-IR background seems to be low, they deserve a
more detailed study on their own. The contribution of fainter, presumably more
distant, galaxies to the far-IR background will be discussed when we will have
completed the follow-up of the fainter part of this 170 microns survey. It
seems however already clear that the fraction of closeby, cold galaxies is much
larger than expected by the earlier models, at least down to the sensitivity
achieved by this ISO survey.Comment: 16 pages + 9 figures (Figs 1, 8 and 9 too big to be included)
Accepted in Astronomy & Astrophysic
A far-infrared spectroscopic survey of intermediate redshift (ultra) luminous infrared galaxies
We present Herschel far-IR photometry and spectroscopy as well as ground-based CO observations of an intermediate redshift (0.21 _ z _ 0.88) sample of Herschel-selected (ultra)-luminous infrared galaxies (LIR >1011.5 L_). With these measurements, we trace the dust continuum, far-IR atomic line emission, in particular [C ii] 157.7ÎŒm, as well as the molecular gas of z ⌠0.3 luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) and perform a detailed investigation of the interstellar medium of the population. We find that the majority of Herschel-selected intermediate redshift (U)LIRGs have LCii/LFIR ratios that are a factor of about 10 higher than that of local ULIRGs and comparable to that of local normal and high-z star-forming galaxies. Using our sample to bridge local and high-z [C ii] observations, we find that the majority of galaxies at all redshifts and all luminosities follow an LCiiâLFIR relation with a slope of unity, from which local ULIRGs and high-z active-galactic-nucleus-dominated sources are clear outliers.We also confirm that the strong anti-correlation between the LCii/LFIR ratio and the far-IR color L60/L100 observed in the local universe holds over a broad range of redshifts and luminosities, in the sense that warmer sources exhibit lower LC ii/LFIR at any epoch. Intermediate redshift ULIRGs are also characterized by large molecular gas reservoirs and by lower star formation efficiencies compared to that of local ULIRGs. The high LC ii/LFIR ratios, the moderate star formation efficiencies (LIR/L _COor LIR/MH2 ), and the relatively low dust temperatures of our sample (which are also common characteristics of high-z star-forming galaxies with ULIRG-like luminosities) indicate that the evolution of the physical properties of (U)LIRGs between the present day and z > 1 is already significant by z ⌠0.3
The First Measurements of Galaxy Clustering from IRAC Data of the Spitzer First Look Survey
We present the first results of the angular auto-correlation function of the
galaxies detected by the Infrared Array Camera (IRAC) instrument in the First
Look Survey (FLS) of the Spitzer Space Telescope. We detect significant signals
of galaxy clustering within the survey area. The angular auto-correlation
function of the galaxies detected in each of the four IRAC instrument channels
is consistent with a power-law form out to
\theta = 0.2\arcdeg, with the slope ranging from to 1.8. We
estimate the correlation amplitudes to be , , , and at
\theta=1\arcdeg for galaxies detected in the IRAC 3.6m, 4.5m,
5.8m, and 8.0m instrument channels, respectively. We compare our
measurements at 3.6m with the previous K-band measurements, and discuss
the implications of these results.Comment: Accepted for publication in the ApJ Supplements Spitzer Special
Issue; 12 pages including 3 figures and 1 tabl
Ultraluminous Infrared Galaxies
Ever since their discovery in the 1970's, UltraLuminous InfraRed Galaxies
(ULIRGs; classically Lir>10^12Lsun) have fascinated astronomers with their
immense luminosities, and frustrated them due to their singularly opaque
nature, almost in equal measure. Over the last decade, however, comprehensive
observations from the X-ray through to the radio have produced a consensus
picture of local ULIRGs, showing that they are mergers between gas rich
galaxies, where the interaction triggers some combination of dust-enshrouded
starburst and AGN activity, with the starburst usually dominating. Very recent
results have thrown ULIRGs even further to the fore. Originally they were
thought of as little more than a local oddity, but the latest IR surveys have
shown that ULIRGs are vastly more numerous at high redshift, and tantalizing
suggestions of physical differences between high and low redshift ULIRGs hint
at differences in their formation modes and local environment. In this review
we look at recent progress on understanding the physics and evolution of local
ULIRGs, the contribution of high redshift ULIRGs to the cosmic infrared
background and the global history of star formation, and the role of ULIRGs as
diagnostics of the formation of massive galaxies and large-scale structures.Comment: Review article, published in "Astrophysics Update 2 - topical and
timely reviews on astronomy and astrophysics". Ed. John W. Mason.
Springer/Praxis books. ISBN: 3-540-30312-X. 53 pages, 5 figures. Higher
quality figures available on reques
Mechanisms and role of microRNA deregulation in cancer onset and progression
MicroRNAs are key regulators of various fundamental biological processes and, although representing only a small portion of the genome, they regulate a much larger population of target genes. Mature microRNAs (miRNAs) are single-stranded RNA molecules of 20â23 nucleotide (nt) length that control gene expression in many cellular processes. These molecules typically reduce the stability of mRNAs, including those of genes that mediate processes in tumorigenesis, such as inflammation, cell cycle regulation, stress response, differentiation, apoptosis and invasion. MicroRNA targeting is mostly achieved through specific base-pairing interactions between the 5âČ end (âseedâ region) of the miRNA and sites within coding and untranslated regions (UTRs) of mRNAs; target sites in the 3âČ UTR diminish mRNA stability. Since miRNAs frequently target hundreds of mRNAs, miRNA regulatory pathways are complex. Calin and Croce were the first to demonstrate a connection between microRNAs and increased risk of developing cancer, and meanwhile the role of microRNAs in carcinogenesis has definitively been evidenced. It needs to be considered that the complex mechanism of gene regulation by microRNAs is profoundly influenced by variation in gene sequence (polymorphisms) of the target sites. Thus, individual variability could cause patients to present differential risks regarding several diseases. Aiming to provide a critical overview of miRNA dysregulation in cancer, this article reviews the growing number of studies that have shown the importance of these small molecules and how these microRNAs can affect or be affected by genetic and epigenetic mechanisms
Dust and star formation properties of a complete sample of local galaxies drawn from the Planck Early Release Compact Source Catalogue
We combine Planck High Frequency Instrument data at 857, 545, 353 and 217 GHz with data from Wide-field Infrared Survey Explorer (WISE), Spitzer, IRAS and Herschel to investigate the properties of a well-defined, flux-limited sample of local star-forming galaxies. A 545 GHz flux density limit was chosen so that the sample is 80 per cent complete at this frequency, and the resulting sample contains a total of 234 local, star-forming galaxies. We investigate the dust emission and star formation properties of the sample via various models and calculate the local dust mass function. Although single-component-modified blackbodies fit the dust emission longward of 80 \u3bcm very well, with a median \u3b2 = 1.83, the known degeneracy between dust temperature and \u3b2 also means that the spectral energy distributions are very well described by a dust component with dust emissivity index fixed at \u3b2 = 2 and temperature in the range 10-25 K. Although a second, warmer dust component is required to fit shorter wavelength data, and contributes approximately a third of the total infrared emission, its mass is negligible. No evidence is found for a very cold (6-10 K) dust component. The temperature of the cold dust component is strongly influenced by the ratio of the star formation rate to the total dust mass. This implies, contrary to what is often assumed, that a significant fraction of even the emission from \u2dc20 K dust is powered by ongoing star formation, whether or not the dust itself is associated with star-forming clouds or `cirrus'. There is statistical evidence of a free-free contribution to the 217 GHz flux densities of 7220 per cent. We find a median dust-to-stellar mass ratio of 0.0046; and that this ratio is anticorrelated with galaxy mass. There is good correlation between dust mass and atomic gas mass (median Md/MHI = 0.022), suggesting that galaxies that have more dust (higher values of Md/M*) have more interstellar medium in general. Our derived dust mass function implies a mean dust mass density of the local Universe (for dust within galaxies), of 7.0 \ub1 1.4
7 105 M 99 Mpc-3, significantly greater than that found in the most recent estimate using Herschel data. \ua9 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Modelling the infrared galaxy evolution using a phenomenological approach
To characterise the cosmological evolution of the sources contributing to the
infrared extragalactic background, we have developped a phenomenological model
that constrains in a simple way the galaxy luminosity function evolution with
the redshift, and fits all the existing source counts and redshift
distributions, Cosmic Infrared Background intensity and fluctuations
observations, from the mid-infrared to the submillimetre range. The model is
based on template spectra of starburst and normal galaxies, and on the local
infrared luminosity function. Although the Cosmic Infrared Background can be
modeled with very different luminosity functions as long as the radiation
production with redshift is the right one, the number counts, and the
anisotropies of the unresolved background, imply that the luminosity function
must change dramatically with redshift, with a rapid evolution of the
high-luminosity sources (L>3 10^{11} L_{\odot}) from z=0 to z=1 which then stay
rather constant up to redshift 5. The derived evolution of the IR luminosity
function may be linked to a bimodal star formation process, one associated with
the quiescent and passive phase of the galaxy evolution and one associated with
the starburst phase, trigerred by merging and interactions. The latter
dominates the infrared and submillimetre ouput energy of the Universe.
The model is intended as a convenient tool to plan further observations, as
illustrated through predictions for Herschel, Planck and ALMA observations. Our
model predictions for given wavelengths, together with some usefull routines,
are available for general use.Comment: MNRAS, in pres
A Long-Wavelength View on Galaxy Evolution from Deep Surveys by the Infrared Space Observatory
We discuss the constraints set on galaxy evolution by data from deep surveys
performed in the mid-IR and far-IR with ISO and with mm telescopes at longer
wavelengths. These reveal extremely high rates of evolution for IR galaxies.
According to our model, the deep ISO surveys at 15 micron may have already
resolved more than 50% of the CIRB intensity, hence allowing to investigate the
origin of the CIRB. From our fits to the observed optical-IR SEDs, these
objects appear to involve massive galaxies hosting luminous starbursts (SFR 100
Mo/yr). Our evolutionary scheme considers a bimodal star formation (SF),
including long-lived quiescent SF, and enhanced SF taking place during
transient events recurrently triggered by interactions and merging. We
interpret the strong observed evolution as an increase with z of the rate of
interactions between galaxies (density evolution) and an increase of their IR
luminosity due to the more abundant fuel available in the past (luminosity
evolution). Very schematically, we associate the origin of the bulk of the
optical/NIR background to the quiescent evolution, while the CIRB is
interpreted as mostly due the dusty starburst phase (the latter possibly
leading to the formation of galaxy spheroids). The large energy contents in the
CIRB and optical backgrounds are not easily explained, considering the moderate
efficiency of energy generation by stars: a top-heavy stellar IMF associated
with the starburst phase (and compared with a more standard IMF during the
quiescent SF) would alleviate the problem. IR data suggest that the strong
observed evolution to z~1 should turn over at higher z: scenarios in which a
dominant fraction of stellar formation occurs at very high-z are not supported
by our analysis.Comment: 30 pages, version with improved references, to appear in Astronomy &
Astrophysic
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
Building the cosmic infrared background brick by brick with Herschel/PEP
The cosmic infrared background (CIB) includes roughly half of the energy
radiated by all galaxies at all wavelengths across cosmic time, as observed at
the present epoch. The PACS Evolutionary Probe (PEP) survey is exploited here
to study the CIB and its redshift differential, at 70, 100 and 160 micron,
where the background peaks. Combining PACS observations of the GOODS-S,
GOODS-N, Lockman Hole and COSMOS areas, we define number counts spanning over
more than two orders of magnitude in flux: from ~1 mJy to few hundreds mJy.
Stacking of 24 micron sources and P(D) statistics extend the analysis down to
~0.2 mJy. Taking advantage of the wealth of ancillary data in PEP fields,
differential number counts and CIB are studied up to z=5. Based on these
counts, we discuss the effects of confusion on PACS blank field observations
and provide confusion limits for the three bands considered. The total CIB
surface brightness emitted above PEP 3 sigma flux limits is 4.52 +/- 1.18, 8.35
+/- 0.95 and 9.49 +/- 0.59 [nW/m2/sr] at 70, 100, and 160 micron, respectively.
These values correspond to 58 +/- 7% and 74 +/- 5% of the COBE/DIRBE CIB direct
measurements at 100 and 160 micron. Employing the P(D) analysis, these
fractions increase to ~65% and ~89%. More than half of the resolved CIB was
emitted at redshift z<=1. The 50%-light redshifts lie at z=0.58, 0.67 and 0.73
at the three PACS wavelengths. The distribution moves towards earlier epochs at
longer wavelengths: while the 70 micron CIB is mainly produced by z<=1.0
objects, the contribution of z>1.0 sources reaches 50% at 160 micron. Most of
the CIB resolved in the three PACS bands was emitted by galaxies with infrared
luminosities in the range 1e11-1e12 L(sun).Comment: Proposed for acceptance on A&
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