S–PASS view of polarized Galactic synchrotron at 2.3 GHz as a contaminant to CMB observations

We have analyzed the southern sky emission in linear polarization at 2.3 GHz as observed by the S -band Polarization All Sky Survey (S-PASS). Our purpose is to study the properties of the diffuse Galactic polarized synchrotron as a contaminant to B-mode observations of the cosmic microwave background (CMB) polarization. We studied the angular distribution of the S-PASS signal at intermediate and high Galactic latitudes by means of the polarization angular power spectra. The power spectra, computed in the multipole interval 20 ≤ ℓ ≤ 1000, show a decay of the spectral amplitude as a function of multipole for ℓ ≲ 200, typical of the diffuse emission. At smaller angular scales, power spectra are dominated by the radio point source radiation. We find that, at low multipoles, spectra can be approximated by a power law CℓEE,BB ∝ ℓα, with α ≃ −3, and characterized by a B-to-E ratio of about 0.5. We measured the polarized synchrotron spectral energy distribution (SED) in harmonic space, by combining S-PASS power spectra with low frequency WMAP and Planck ones, and by fitting their frequency dependence in six multipole bins, in the range 20 ≤ ℓ ≤ 140. Results show that the recovered SED, in the frequency range 2.3–33 GHz, is compatible with a power law with βs = −3.22 ± 0.08, which appears to be constant over the considered multipole range and in the different Galactic cuts. Combining the S-PASS total polarized intensity maps with those coming from WMAP and Planck we derived a map of the synchrotron spectral index βs at angular resolution of 2° on about 30% of the sky. The recovered βs distribution peaks at the value around −3.2. It exibits an angular power spectrum which can be approximated with a power law Cℓ ∝ ℓγ with γ ≃ −2.6. We also measured a significant spatial correlation between synchrotron and thermal dust signals, as traced by the Planck 353 GHz channel. This correlation reaches about 40% on the larger angular scales, decaying considerably at the degree scales. Finally, we used the S-PASS maps to assess the polarized synchrotron contamination to CMB observations of the B-modes at higher frequencies. We divided the sky in small patches (with fsky ≃ 1%) and find that, at 90 GHz, the minimal contamination, in the cleanest regions of the sky, is at the level of an equivalent tensor-to-scalar ratio rsynch ≃ 10−3. Moreover, by combining S-PASS data with Planck 353 GHz observations, we recover a map of the minimum level of total polarized foreground contamination to B-modes, finding that there is no region of the sky, at any frequency, where this contamination lies below equivalent tenor-to-scalar ratio rFG ≃ 10−3. This result confirms the importance of observing both high and low frequency foregrounds in CMB B-mode measurements.

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Planck intermediate results

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629164 ◽

2017 ◽

Vol 599 ◽

pp. A51 ◽

Cited By ~ 28

Author(s):

◽

N. Aghanim ◽

M. Ashdown ◽

J. Aumont ◽

C. Baccigalupi ◽

...

Keyword(s):

Spectral Energy Distribution ◽

Dust Emission ◽

Power Spectra ◽

Spectral Energy ◽

Polarization Angle ◽

Galactic Latitude ◽

Correlation Ratio ◽

Microwave Background

The characterization of the Galactic foregrounds has been shown to be the main obstacle in thechallenging quest to detect primordial B-modes in the polarized microwave sky. We make use of the Planck-HFI 2015 data release at high frequencies to place new constraints on the properties of the polarized thermal dust emission at high Galactic latitudes. Here, we specifically study the spatial variability of the dust polarized spectral energy distribution (SED), and its potential impact on the determination of the tensor-to-scalar ratio, r. We use the correlation ratio of the CBBℓ angular power spectra between the 217 and 353 GHz channels as a tracer of these potential variations, computed on different high Galactic latitude regions, ranging from 80% to 20% of the sky. The new insight from Planck data is a departure of the correlation ratio from unity that cannot be attributed to a spurious decorrelation due to the cosmic microwave background, instrumental noise, or instrumental systematics. The effect is marginally detected on each region, but the statistical combination of all the regions gives more than 99% confidence for this variation in polarized dust properties. In addition, we show that the decorrelation increases when there is a decrease in the mean column density of the region of the sky being considered, and we propose a simple power-law empirical model for this dependence, which matches what is seen in the Planck data. We explore the effect that this measured decorrelation has on simulations of the BICEP2-Keck Array/Planck analysis and show that the 2015 constraints from these data still allow a decorrelation between the dust at 150 and 353 GHz that is compatible with our measured value. Finally, using simplified models, we show that either spatial variation of the dust SED or of the dust polarization angle are able to produce decorrelations between 217 and 353 GHz data similar to the values we observe in the data.

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The challenging SED of AP Librae

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312009532 ◽

2011 ◽

Vol 7 (S284) ◽

pp. 411-413 ◽

Cited By ~ 3

Author(s):

David Sanchez ◽

Berrie Giebels ◽

Pascal Fortin ◽

Keyword(s):

Spectral Energy Distribution ◽

Broad Band ◽

Low Frequency ◽

Theoretical Models ◽

Intermediate Frequency ◽

High Energy ◽

Spectral Energy ◽

Broad Band Emission ◽

Band Emission ◽

Bl Lac

AbstractMatching the broad-band emission of active galaxies with the predictions of theoretical models can be used to derive constraints on the properties of the emitting region and to probe the physical processes involved. AP Librae is the third low frequency peaked BL Lac (LBL) detected at very high energy (VHE, E>100GeV) by an Atmospheric Cherenkov Telescope; most VHE BL Lacs (34 out of 39) belong to the high-frequency and intermediate-frequency BL Lac classes (HBL and IBL). LBL objects tend to have a higher luminosity with lower peak frequencies than HBLs or IBLs. The characterization of their time-averaged spectral energy distribution is challenging for emission models such as synchrotron self-Compton (SSC) models.

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Far-infrared photometry of OJ 287 with the Herschel Space Observatory

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732142 ◽

2018 ◽

Vol 610 ◽

pp. A74

Author(s):

Mark Kidger ◽

Staszek Zola ◽

Mauri Valtonen ◽

Anne Lähteenmäki ◽

Emilia Järvelä ◽

...

Keyword(s):

Energy Distribution ◽

Light Curve ◽

Spectral Index ◽

Spectral Energy Distribution ◽

Low Frequency ◽

Far Infrared ◽

Small Degree ◽

Spectral Energy ◽

Space Observatory ◽

Near Ir

Context. The blazar OJ 287 has shown a ≈12 year quasi-periodicity over more than a century, in addition to the common properties of violent variability in all frequency ranges. It is the strongest known candidate to have a binary singularity in its central engine. Aim. We aim to better understand the different emission components by searching for correlated variability in the flux over four decades of frequency measurements. Methods. We combined data at frequencies from the millimetric to the visible to characterise the multifrequency light curve in April and May 2010. This includes the only photometric observations of OJ 287 made with the Herschel Space Observatory: five epochs of data obtained over 33 days at 250, 350, and 500 μm with Herschel-SPIRE. Results. Although we find that the variability at 37 GHz on timescales of a few weeks correlates with the visible to near-IR spectral energy distribution, there is a small degree of reddening in the continuum at lower flux levels that is revealed by the decreasing rate of decline in the light curve at lower frequencies. However, we see no clear evidence that a rapid flare detected in the light curve during our monitoring in the visible to near-IR light curve is seen either in the Herschel data or at 37 GHz, suggesting a low-frequency cut-off in the spectrum of such flares. Conclusions.We see only marginal evidence of variability in the observations with Herschel over a month, although this may be principally due to the poor sampling. The spectral energy distribution between 37 GHz and the visible can be characterised by two components of approximately constant spectral index: a visible to far-IR component of spectral index α = −0.95, and a far-IR to millimetric spectral index of α = −0.43. There is no evidence of an excess of emission that would be consistent with the 60 μmdust bump found in many active galactic nuclei.

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Making maps of cosmic microwave background polarization for B-mode studies: the POLARBEAR example

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629467 ◽

2017 ◽

Vol 600 ◽

pp. A60 ◽

Cited By ~ 6

Author(s):

Davide Poletti ◽

Giulio Fabbian ◽

Maude Le Jeune ◽

Julien Peloton ◽

Kam Arnold ◽

...

Keyword(s):

Cosmic Microwave Background ◽

Time Domain ◽

Power Spectra ◽

Low Frequency ◽

Frequency Noise ◽

Spectrum Estimation ◽

Microwave Background ◽

Polarization Studies ◽

Ordered Data ◽

The Impact

Analysis of cosmic microwave background (CMB) datasets typically requires some filtering of the raw time-ordered data. For instance, in the context of ground-based observations, filtering is frequently used to minimize the impact of low frequency noise, atmospheric contributions and/or scan synchronous signals on the resulting maps. In this work we have explicitly constructed a general filtering operator, which can unambiguously remove any set of unwanted modes in the data, and then amend the map-making procedure in order to incorporate and correct for it. We show that such an approach is mathematically equivalent to the solution of a problem in which the sky signal and unwanted modes are estimated simultaneously and the latter are marginalized over. We investigated the conditions under which this amended map-making procedure can render an unbiased estimate of the sky signal in realistic circumstances. We then discuss the potential implications of these observations on the choice of map-making and power spectrum estimation approaches in the context of B-mode polarization studies. Specifically, we have studied the effects of time-domain filtering on the noise correlation structure in the map domain, as well as impact it may haveon the performance of the popular pseudo-spectrum estimators. We conclude that although maps produced by the proposed estimators arguably provide the most faithful representation of the sky possible given the data, they may not straightforwardly lead to the best constraints on the power spectra of the underlying sky signal and special care may need to be taken to ensure this is the case. By contrast, simplified map-makers which do not explicitly correct for time-domain filtering, but leave it to subsequent steps in the data analysis, may perform equally well and be easier and faster to implement. We focused on polarization-sensitive measurements targeting the B-mode component of the CMB signal and apply the proposed methods to realistic simulations based on characteristics of an actual CMB polarization experiment, POLARBEAR. Our analysis and conclusions are however more generally applicable.

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The Optical/Near-IR Colours of Red Quasars

Publications of the Astronomical Society of Australia ◽

10.1071/as00056 ◽

2000 ◽

Vol 17 (1) ◽

pp. 56-71 ◽

Cited By ~ 58

Author(s):

Paul J. Francis ◽

Matthew T. Whiting ◽

Rachel L. Webster

Keyword(s):

Power Law ◽

High Redshift ◽

Sloan Digital Sky Survey ◽

Spectral Energy ◽

Spectral Energy Distributions ◽

Energy Distributions ◽

Red Power ◽

Near Ir ◽

Sky Survey ◽

Ir Photometry

AbstractWe present quasi-simultaneous multi-colour optical/near-IR photometry for 157 radio selected quasars, forming an unbiassed sub-sample of the Parkes Flat-Spectrum Sample. Data are also presented for 12 optically selected QSOs, drawn from the Large Bright QSO Survey. The spectral energy distributions of the radio- and optically-selected sources are quite different. The optically selected QSOs are all very similar: they have blue spectral energy distributions curving downwards at shorter wavelengths. Roughly 90% of the radio-selected quasars have roughly power-law spectral energy distributions, with slopes ranging from Fv∝v0 to Fv∝v−2. The remaining 10% have spectral energy distributions showing sharp peaks: these are radio galaxies and highly reddened quasars. Four radio sources were not detected down to magnitude limits of H ∼ 19·6. These are probably high redshift (z > 3) galaxies or quasars. We show that the colours of our red quasars lie close to the stellar locus in the optical: they will be hard to identify in surveys such as the Sloan Digital Sky Survey. If near-IR photometry is added, however, the red power-law sources can be clearly separated from the stellar locus: IR surveys such as 2MASS should be capable of finding these sources on the basis of their excess flux in the K-band.

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Chemical abundances of Seyfert 2 AGNs – II. N2 metallicity calibration based on SDSS

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa193 ◽

2020 ◽

Vol 492 (4) ◽

pp. 5675-5683 ◽

Cited By ~ 3

Author(s):

S P Carvalho ◽

O L Dors ◽

M V Cardaci ◽

G F Hägele ◽

A C Krabbe ◽

...

Keyword(s):

Spectral Energy Distribution ◽

Sloan Digital Sky Survey ◽

Spectral Energy ◽

Chemical Abundances ◽

Data Set ◽

Line Intensity Ratio ◽

Sky Survey ◽

Empirical Calibration ◽

Semi Empirical ◽

Photoionization Model

ABSTRACT We present a semi-empirical calibration between the metallicity (Z) of Seyfert 2 active galactic nuclei and the N2 = log([N ii]λ6584/H α) emission-line intensity ratio. This calibration was derived through the [O iii]λ5007/[O ii]λ3727 versus N2 diagram containing observational data and photoionization model results obtained with the cloudy code. The observational sample consists of 463 confirmed Seyfert 2 nuclei (redshift $z \: \lesssim 0.4$) taken from the Sloan Digital Sky Survey DR7 data set. The obtained Z–N2 relation is valid for the range $0.3 \: \lesssim \: (Z/{\rm Z}_{\odot }) \: \lesssim \: 2.0$ that corresponds to $-0.7 \: \lesssim \: ({\rm N}2) \: \lesssim \: 0.6$. The effects of varying the ionization parameter (U), electron density and the slope of the spectral energy distribution on the Z estimations are of the order of the uncertainty produced by the error measurements of N2. This result indicates the large reliability of our Z –N2 calibration. A relation between U and the [O iii]/[O ii] line ratio, almost independent of other nebular parameter, was obtained.

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Systematic effects in LOFAR data: A unified calibration strategy

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833867 ◽

2019 ◽

Vol 622 ◽

pp. A5 ◽

Cited By ~ 33

Author(s):

F. de Gasperin ◽

T. J. Dijkema ◽

A. Drabent ◽

M. Mevius ◽

D. Rafferty ◽

...

Keyword(s):

Spectral Energy Distribution ◽

Low Frequency ◽

Reduction Process ◽

Spectral Energy ◽

Ionospheric Scintillation ◽

Source Population ◽

Full Data ◽

Low Frequencies ◽

Beam Shape ◽

Systematic Effects

Context. New generation low-frequency telescopes are exploring a new parameter space in terms of depth and resolution. The data taken with these interferometers, for example with the LOw Frequency ARray (LOFAR), are often calibrated in a low signal-to-noise ratio regime and the removal of critical systematic effects is challenging. The process requires an understanding of their origin and properties. Aim. In this paper we describe the major systematic effects inherent to next generation low-frequency telescopes, such as LOFAR. With this knowledge, we introduce a data processing pipeline that is able to isolate and correct these systematic effects. The pipeline will be used to calibrate calibrator observations as the first step of a full data reduction process. Methods. We processed two LOFAR observations of the calibrator 3C 196: the first using the Low Band Antenna (LBA) system at 42–66 MHz and the second using the High Band Antenna (HBA) system at 115–189 MHz. Results. We were able to isolate and correct for the effects of clock drift, polarisation misalignment, ionospheric delay, Faraday rotation, ionospheric scintillation, beam shape, and bandpass. The designed calibration strategy produced the deepest image to date at 54 MHz. The image has been used to confirm that the spectral energy distribution of the average radio source population tends to flatten at low frequencies. Conclusions. We prove that LOFAR systematic effects can be described by a relatively small number of parameters. Furthermore, the identification of these parameters is fundamental to reducing the degrees of freedom when the calibration is carried out on fields that are not dominated by a strong calibrator.

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USco1621 B and USco1556 B: Two wide companions at the deuterium-burning mass limit in Upper Scorpius

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936130 ◽

2020 ◽

Vol 633 ◽

pp. A152 ◽

Cited By ~ 3

Author(s):

Patricia Chinchilla ◽

Víctor J. S. Béjar ◽

Nicolas Lodieu ◽

Bartosz Gauza ◽

Maria Rosa Zapatero Osorio ◽

...

Keyword(s):

Adaptive Optics ◽

Near Infrared ◽

Spectral Energy Distribution ◽

Spectral Energy ◽

Infrared Telescope ◽

The United Kingdom ◽

Sky Survey ◽

Substellar Objects ◽

Galactic Clusters ◽

M Stars

Aims. Our objective is to identify analogues of gas giant planets, but located as companions at wide separations of very young stars. The main purpose is to characterise the binarity frequency and the properties of these substellar objects, and to elucidate their early evolutionary stages. Methods. To identify these objects, we cross correlated the Visible and Infrared Survey Telescope for Astronomy Hemisphere Survey and the United Kingdom Infrared Telescope Infrared Deep Sky Survey Galactic Clusters Survey catalogues to search for common proper motion companions to 1195 already known members of Upper Scorpius (USco; age ~5–10 Myr, distance ~145 pc). We present the discovery and spectroscopic characterisation of two very wide substellar companions of two early-M stars in Upper Scorpius: USco1621 B and USco1556 B. We obtained optical and near-infrared low-resolution spectroscopy of the candidates to characterise their spectral energy distribution and confirm their youth and membership to the association. We also acquired adaptive optics images of the primaries and secondaries to search for signs of binarity and close companions. Results. By comparison with field dwarfs and other young members of USco, we determined a spectral type of M8.5 in the optical for both companions, along with L0 and L0.5 in the near-infrared for USco1621 B and USco1556 B, respectively. The spectra of the two companions show evident markers of youth, such as weak alkaline Na I and K I lines, along with the triangular shape of the H-band. The comparison with theoretical evolutionary models gives estimated masses of 0.015 ± 0.002 and 0.014 ± 0.002 M⊙, with temperatures of 2270 ± 90 and 2240 ± 100 K, respectively. The physical separations between the components of both systems are 2880 ± 20 and 3500 ± 40 AU for USco1621 and USco1556 systems, respectively. We did not find any additional close companion in the adaptive optics images. The probability that the two secondaries are physically bound to their respective primaries, and not chance alignments of USco members, is 86%, and the probability that none of them are physically related is 1.0%.

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The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of highly star-forming galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834002 ◽

2019 ◽

Vol 621 ◽

pp. A139 ◽

Cited By ~ 12

Author(s):

K. Tisanić ◽

V. Smolčić ◽

J. Delhaize ◽

M. Novak ◽

H. Intema ◽

...

Keyword(s):

Survival Analysis ◽

Energy Distribution ◽

Power Law ◽

Rest Frame ◽

Spectral Energy Distribution ◽

Spectral Energy ◽

Radio Luminosity ◽

Star Forming ◽

The Impact ◽

Frame Frequency

We construct the average radio spectral energy distribution (SED) of highly star-forming galaxies (HSFGs) up to z ∼ 4. Infrared and radio luminosities are bound by a tight correlation that is defined by the so-called q parameter. This infrared–radio correlation provides the basis for the use of radio luminosity as a star-formation tracer. Recent stacking and survival analysis studies find q to be decreasing with increasing redshift. It was pointed out that a possible cause of the redshift trend could be the computation of rest-frame radio luminosity via a single power-law assumption of the star-forming galaxies’ (SFGs) SED. To test this, we constrained the shape of the radio SED of a sample of HSFGs. To achieve a broad rest-frame frequency range, we combined previously published Very Large Array observations of the COSMOS field at 1.4 GHz and 3 GHz with unpublished Giant Meterwave Radio Telescope (GMRT) observations at 325 MHz and 610 MHz by employing survival analysis to account for non-detections in the GMRT maps. We selected a sample of HSFGs in a broad redshift range (z ∈ [0.3, 4], SFR ≥ 100 M⊙ yr−1) and constructed the average radio SED. By fitting a broken power-law, we find that the spectral index changes from α1 = 0.42 ± 0.06 below a rest-frame frequency of 4.3 GHz to α2 = 0.94 ± 0.06 above 4.3 GHz. Our results are in line with previous low-redshift studies of HSFGs ( SFR > 10 M⊙ yr−1) that show the SED of HSFGs to differ from the SED found for normal SFGs ( SFR < 10 M⊙ yr−1). The difference is mainly in a steeper spectrum around 10 GHz, which could indicate a smaller fraction of thermal free–free emission. Finally, we also discuss the impact of applying this broken power-law SED in place of a simple power-law in K-corrections of HSFGs and a typical radio SED for normal SFGs drawn from the literature. We find that the shape of the radio SED is unlikely to be the root cause of the q − z trend in SFGs.

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Angular clustering of point sources at 150 MHz in the TGSS survey

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz831 ◽

2019 ◽

Vol 485 (4) ◽

pp. 5891-5896 ◽

Cited By ~ 4

Author(s):

Sandeep Rana ◽

Jasjeet S Bagla

Keyword(s):

Correlation Function ◽

Power Law ◽

Low Frequency ◽

Point Sources ◽

Radio Sources ◽

Redshift Distribution ◽

Intensity Mapping ◽

Flux Limit ◽

Sky Survey ◽

Angular Correlation Function

Abstract We study the angular clustering of point sources in The GMRT (Giant Metrewave Radio Telescope) Sky Survey (TGSS). The survey at 150 MHz with δ > −53.5° has a sky coverage of 3.6π steradians, i.e. $90{{\ \rm per\ cent}}$ of the whole sky. We created subsamples by applying different total flux thresholds limit (Sflux ≫ 5σ) for good completeness and measured the angular correlation function ω(θ) of point sources at large scales (≥1°). We find that the amplitude of angular clustering is higher for brighter subsamples; this indicates that higher threshold flux samples are hosted by massive haloes and cluster strongly: this conclusion is based on the assumption that the redshift distribution of sources does not change with flux and this is supported by models of radio sources. We compare our results with other low-frequency studies of clustering of point sources and verify that the amplitude of clustering varies with the flux limit. We quantify this variation as a power-law dependence of the amplitude of correlation function with the flux limit. This dependence can be used to estimate foreground contamination due to clustering of point sources for low-frequency H i intensity mapping surveys for studying the epoch of reionization.

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