369 research outputs found
Tracing the Evolution of Dust Obscured Star Formation and Accretion Back to the Reionisation Epoch with SPICA
Our current knowledge of star formation and accretion luminosity at high redshift (z > 3–4), as well as the possible connections between them, relies mostly on observations in the rest-frame ultraviolet, which are strongly affected by dust obscuration. Due to the lack of sensitivity of past and current infrared instrumentation, so far it has not been possible to get a glimpse into the early phases of the dust-obscured Universe. Among the next generation of infrared observatories, SPICA, observing in the 12–350 µm range, will be the only facility that can enable us to trace the evolution of the obscured star-formation rate and black-hole accretion rate densities over cosmic time, from the peak of their activity back to the reionisation epoch (i.e., 3 < z ≲ 6–7), where its predecessors had severe limitations. Here, we discuss the potential of photometric surveys performed with the SPICA mid-infrared instrument, enabled by the very low level of impact of dust obscuration in a band centred at 34 µm. These unique unbiased photometric surveys that SPICA will perform will fully characterise the evolution of AGNs and star-forming galaxies after reionisation
Polarization fluctuations due to extragalactic sources
We have derived the relationship between polarization and intensity
fluctuations due to point sources. In the case of a Poisson distribution of a
population with uniform evolution properties and constant polarization degree,
polarization fluctuations are simply equal to intensity fluctuations times the
average polarization degree. Conservative estimates of the polarization degree
of the classes of extragalactic sources contributing to fluctuations in the
frequency ranges covered by the forthcoming space missions MAP and Planck
Surveyor indicate that extragalactic sources will not be a strong limiting
factor to measurements of the polarization of the Cosmic Microwave Background.Comment: 15 pages LaTeX file, 3 postscript figures. Uses elsart.sty and
elsart.cls Accepted for publication in New Astronom
Are z>2 Herschel galaxies proto-spheroids?
We present a backward approach for the interpretation of the evolution of the
near-infrared and the far-infrared luminosity functions across the redshift
range 0<z<3. In our method, late-type galaxies are treated by means of a
parametric phenomenological method based on PEP/HerMES data up to z~4, whereas
spheroids are described by means of a physically motivated backward model. The
spectral evolution of spheroids is modelled by means of a single-mass model,
associated to a present-day elliptical with K-band luminosity comparable to the
break of the local early-type luminosity function. The formation of
proto-spheroids is assumed to occurr across the redshift range 1< z < 5. The
key parameter is represented by the redshift z_0.5 at which half
proto-spheroids are already formed. A statistical study indicates for this
parameter values between z_0.5=1.5 and z_0.5=3. We assume as fiducial value
z_0.5~2, and show that this assumption allows us to describe accourately the
redshift distributions and the source counts. By assuming z_0.5 ~ 2 at the
far-IR flux limit of the PEP-COSMOS survey, the PEP-selected sources observed
at z>2 can be explained as progenitors of local spheroids caught during their
formation. We also test the effects of mass downsizing by dividing the
spheroids into three populations of different present-day stellar masses. The
results obtained in this case confirm the validity of our approach, i.e. that
the bulk of proto-spheroids can be modelled by means of a single model which
describes the evolution of galaxies at the break of the present-day early type
K-band LF.Comment: Accepted for publication in ApJ; 26 pages; 13 figure
CO excitation in the Seyfert galaxy NGC7130
We present a coherent multi-band modelling of the CO Spectral Energy
Distribution of the local Seyfert Galaxy NGC7130 to assess the impact of the
AGN activity on the molecular gas. We take advantage of all the available data
from X-ray to the sub-mm, including ALMA data. The high-resolution (~0.2") ALMA
CO(6-5) data constrain the spatial extension of the CO emission down to ~70 pc
scale. From the analysis of the archival CHANDRA and NuSTAR data, we infer the
presence of a buried, Compton-thick AGN of moderate luminosity, L_2-10keV ~
1.6x10^{43} ergs-1. We explore photodissociation and X-ray-dominated regions
(PDRs and XDRs) models to reproduce the CO emission. We find that PDRs can
reproduce the CO lines up to J~6, however, the higher rotational ladder
requires the presence of a separate source of excitation. We consider X-ray
heating by the AGN as a source of excitation, and find that it can reproduce
the observed CO Spectral Energy Distribution. By adopting a composite PDR+XDR
model, we derive molecular cloud properties. Our study clearly indicates the
capabilities offered by current-generation of instruments to shed light on the
properties of nearby galaxies adopting state-of-the art physical modelling.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
Microjansky sources at 1.4 GHz
We present a deep 1.4 GHz survey made with the Australia Telescope Compact
Array (ATCA), having a background RMS of 9 microJy near the image phase centre,
up to 25 microJy at the edge of a 50' field of view. Over 770 radio sources
brighter than 45 microJy have been catalogued in the field. The differential
source counts in the deep field provide tentative support for the growing
evidence that the microjansky radio population exhibits significantly higher
clustering than found at higher flux density cutoffs. The optical
identification rate on CCD images is approximately 50% to R=22.5, and the
optical counterparts of the faintest radio sources appear to be mainly single
galaxies close to this optical magnitude limit.Comment: 6 pages, 4 figures, accepted by ApJ Letters 4 May 199
The star formation rate cookbook at 1 < z < 3: Extinction-corrected relations for UV & [OII]{\lambda}3727 luminosities
We use a spectroscopic sample of 286 star-forming galaxies (SFGs) at 1<z<3
from the GMASS survey to study different star formation rate (SFR) estimators.
Infrared (IR) data are used to derive empirical calibrations to correct
ultraviolet (UV) and [OII]{\lambda}3727 luminosities for dust extinction and
dust-corrected estimates of SFR. In the selection procedure we fully exploit
the available spectroscopic information. On the basis of three continuum
indices, we are able to identify and exclude from the sample galaxies in which
old stellar populations might bring a non-negligible contribution to IR
luminosity (LIR) and continuum reddening. Using Spitzer-MIPS and Herschel-PACS
data we derive LIR for two-thirds of our sample. The LIR/LUV ratio is used as a
probe of effective attenuation (AIRX) to search for correlations with continuum
and spectroscopic features. The relation between AIRX and UV continuum slope
({\beta}) was tested for our sample and found to be broadly consistent with the
literature results at the same redshift, though with a larger dispersion with
respect to UV-selected samples. We find a correlation between the rest-frame
equivalent width (EW) of the [OII]{\lambda}3727 line and {\beta}, which is the
main result of this work. We therefore propose the [OII]{\lambda}3727 line EW
as a dust attenuation probe and calibrate it through AIRX, though the
assumption of a reddening curve is still needed to derive the actual
attenuation towards the [OII]{\lambda}3727 line. We tested the issue of
differential attenuation towards stellar continuum and nebular emission: our
results are in line with the traditional prescription of extra attenuation
towards nebular lines. A set of relations is provided that allows the recovery
of the total unattenuated SFR from UV and [OII]{\lambda}3727 luminosities.
(Abridged)Comment: Accepted for publication in A&A; 20 pages, 19 figures, 5 table
CO excitation in the Seyfert galaxy NGC 34: stars, shock or AGN driven?
We present a detailed analysis of the X-ray and molecular gas emission in the
nearby galaxy NGC 34, to constrain the properties of molecular gas, and assess
whether, and to what extent, the radiation produced by the accretion onto the
central black hole affects the CO line emission. We analyse the CO Spectral
Line Energy Distribution (SLED) as resulting mainly from Herschel and ALMA
data, along with X-ray data from NuSTAR and XMM-Newton. The X-ray data analysis
suggests the presence of a heavily obscured AGN with an intrinsic luminosity of
L erg s. ALMA high
resolution data () allows us to scan the nuclear region
down to a spatial scale of pc for the CO(6-5) transition. We
model the observed SLED using Photo-Dissociation Region (PDR), X-ray-Dominated
Region (XDR), and shock models, finding that a combination of a PDR and an XDR
provides the best fit to the observations. The PDR component, characterized by
gas density and temperature K,
reproduces the low-J CO line luminosities. The XDR is instead characterised by
a denser and warmer gas (, K), and is
necessary to fit the high-J transitions. The addition of a third component to
account for the presence of shocks has been also tested but does not improve
the fit of the CO SLED. We conclude that the AGN contribution is significant in
heating the molecular gas in NGC 34.Comment: Accepted for publication in MNRAS. 10 pages, 6 figure
Tracing the Evolution of Dust Obscured Star Formation and Accretion Back to the Reionisation Epoch with SPICA
Our current knowledge of star formation and accretion luminosity at high redshift (z > 3–4), as well as the possible connections between them, relies mostly on observations in the rest-frame ultraviolet, which are strongly affected by dust obscuration. Due to the lack of sensitivity of past and current infrared instrumentation, so far it has not been possible to get a glimpse into the early phases of the dust-obscured Universe. Among the next generation of infrared observatories, SPICA, observing in the 12–350 µm range, will be the only facility that can enable us to trace the evolution of the obscured star-formation rate and black-hole accretion rate densities over cosmic time, from the peak of their activity back to the reionisation epoch (i.e., 3 < z ≲ 6–7), where its predecessors had severe limitations. Here, we discuss the potential of photometric surveys performed with the SPICA mid-infrared instrument, enabled by the very low level of impact of dust obscuration in a band centred at 34 µm. These unique unbiased photometric surveys that SPICA will perform will fully characterise the evolution of AGNs and star-forming galaxies after reionisation
CO luminosity function from Herschel-selected galaxies and the contribution of AGN
We derive the carbon monoxide (CO) luminosity function (LF) for different rotational transitions [i.e. (1-0), (3-2), (5-4)] starting from the Herschel LF by Gruppioni et al. and using appropriate LCO-LIR conversions for different galaxy classes. Our predicted LFs fit the data so far available at z ≈ 0 and 2. We compare our results with those obtained by semi-analytical models (SAMs): while we find a good agreement over the whole range of luminosities at z ≈0, at z≈1 and z≈2, the tension between our LFs and SAMs in the faint and bright ends increases. We finally discuss the contribution of luminous active galactic nucleus (LX > 1044 erg s-1) to the bright end of the CO LF concluding that they are too rare to reproduce the actual CO LF at z ≈ 2
A New Method for ISOCAM Data Reduction - I. Application to the European Large Area ISO Survey Southern Field: Method and Results
We have developed a new data reduction technique for ISOCAM LW data and have
applied it to the European Large Area ISO Survey (ELAIS) LW3 (15 micron)
observations in the southern hemisphere (S1). This method, known as LARI
technique and based on the assumption of the existence of two different time
scales in ISOCAM transients (accounting either for fast or slow detector
response), was particularly designed for the detection of faint sources. In the
ELAIS S1 field we obtained a catalogue of 462 15 micron sources with
signal-to-noise ratio >= 5 and flux densities in the range 0.45 - 150 mJy
(filling the whole flux range between the Deep ISOCAM Surveys and the IRAS
Faint Source Survey). The completeness at different flux levels and the
photometric accuracy of this catalogue have been tested with simulations. Here
we present a detailed description of the method and discuss the results
obtained by its application to the S1 LW3 data.Comment: 20 pages, LaTeX, MNRAS style, 20 postscript figures, full catalogue
not yet available at http://boas5.bo.astro.it/~elais/catalogues/. Accepted
for publication in MNRA
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