Testing Algorithms for Identifying Source Confusion in the H i-MaNGA Survey

Astronomical observations of neutral atomic hydrogen (H i) are an important tracer of several key processes of galaxy evolution, but face significant difficulties with terrestrial telescopes. Among these is source confusion, or the inability to distinguish between emission from multiple nearby sources separated by distances smaller than the telescope’s spatial resolution. Confusion can compromise the data for the primary target if the flux from the secondary galaxy is sufficient. This paper presents an assessment of the confusion-flagging methods of the H i-MaNGA survey, using higher-resolution H i data from the Westorbork Synthesis Radio Telescope-Apertif survey. We find that removing potentially confused observations using a confusion probability metric—calculated from the relationship between galaxy color, surface brightness, and H i content—successfully eliminates all significantly confused observations in our sample, although roughly half of the eliminated observations are not significantly confused.

Perceptual reality monitoring: Neural mechanisms dissociating imagination from reality

There is increasing evidence that imagination relies on similar neural mechanisms as externally triggered perception. This overlap presents a challenge for perceptual reality monitoring: deciding what is real and what is imagined. Here, we explore how perceptual reality monitoring might be implemented in the brain. We first describe sensory and cognitive factors that could dissociate imagery and perception and conclude that no single factor unambiguously signals whether an experience is internally or externally generated. We suggest that reality monitoring is implemented by higher-level cortical circuits that evaluate first-order sensory and cognitive factors to determine the source of sensory signals. According to this interpretation, perceptual reality monitoring shares core computations with metacognition. This multi-level architecture might explain several types of source confusion as well as dissociations between simply knowing whether something is real and actually experiencing it as real. We discuss avenues for future research to further our understanding of perceptual reality monitoring, an endeavor that has important implications for our understanding of clinical symptoms as well as general cognitive function.

Detection likelihood of cluster-induced CMB polarization

Nearby galaxy clusters can potentially induce sub-microkelvin polarization signals in the cosmic microwave background (CMB) at characteristic scales of a few arcminutes. We explore four such polarization signals induced in a rich nearby fiducial cluster and calculate the likelihood of their detection by a telescope project with capabilities such as those of the Simons Observatory (SO). In our feasibility analysis, we include instrumental noise, primordial CMB anisotropy, statistical thermal Sunyaev-Zeldovich (SZ) cluster signal, and point source confusion, assuming a few percent of the nominal telescope observation time of an SO-like project. Our analysis indicates that the thermal SZ intensity can be sensitively mapped in rich nearby clusters and that the kinematic SZ intensity can be measured with high statistical significance toward a fast moving nearby cluster. The detection of polarized SZ signals will be quite challenging but could still be feasible toward several very rich nearby clusters with very high SZ intensity. The polarized SZ signal from a sample of ∼20 clusters can be statistically detected at S/N ∼ 3, if observed for several months.

The C-Band All-Sky Survey (C-BASS): constraining diffuse Galactic radio emission in the North Celestial Pole region

ABSTRACT The C-Band All-Sky Survey (C-BASS) is a high sensitivity all-sky radio survey at an angular resolution of 45 arcmin and a frequency of 4.7 GHz. We present a total intensity map of the North Celestial Pole (NCP) region of sky, above declination >+80°, which is limited by source confusion at a level of ≈0.6 mK rms. We apply the template-fitting (cross-correlation) technique to WMAP and Planck data, using the C-BASS map as the synchrotron template, to investigate the contribution of diffuse foreground emission at frequencies ∼20–40 GHz. We quantify the anomalous microwave emission (AME) that is correlated with far-infrared dust emission. The AME amplitude does not change significantly (${\lt }10\, {{\ \rm per\ cent}}$) when using the higher frequency C-BASS 4.7 GHz template instead of the traditional Haslam 408 MHz map as a tracer of synchrotron radiation. We measure template coefficients of 9.93 ± 0.35 and $9.52\pm 0.34\,$ K per unit τ353 when using the Haslam and C-BASS synchrotron templates, respectively. The AME contributes $55\pm 2\, \mu$K rms at 22.8 GHz and accounts for ${\approx } 60{{\ \rm per\ cent}}$ of the total foreground emission. Our results show that a harder (flatter spectrum) component of synchrotron emission is not dominant at frequencies ≳5 GHz; the best-fitting synchrotron temperature spectral index is β = −2.91 ± 0.04 from 4.7 to 22.8 GHz and β = −2.85 ± 0.14 from 22.8 to 44.1 GHz. Free–free emission is weak, contributing ${\approx } 7\, \mu$K rms (${\approx } 7{{\ \rm per\ cent}}$) at 22.8 GHz. The best explanation for the AME is still electric dipole emission from small spinning dust grains.

Blazars in the LOFAR Two-Metre Sky Survey first data release

Historically, the blazar population has been poorly understood at low frequencies because survey sensitivity and angular resolution limitations have made it difficult to identify megahertz counterparts. We used the LOFAR Two-Metre Sky Survey (LoTSS) first data release value-added catalogue (LDR1) to study blazars in the low-frequency regime with unprecedented sensitivity and resolution. We identified radio counterparts to all 98 known sources from the Third Fermi-LAT Point Source Catalogue (3FGL) or Roma-BZCAT Multi-frequency Catalogue of Blazars (5th edition) that fall within the LDR1 footprint. Only the 3FGL unidentified γ-ray sources (UGS) could not be firmly associated with an LDR1 source; this was due to source confusion. We examined the redshift and radio luminosity distributions of our sample, finding flat-spectrum radio quasars (FSRQs) to be more distant and more luminous than BL Lacertae objects (BL Lacs) on average. Blazars are known to have flat spectra in the gigahertz regime but we found this to extend down to 144 MHz, where the radio spectral index, α, of our sample is −0.17 ± 0.14. For BL Lacs, α = −0.13 ± 0.16 and for FSRQs, α = −0.15 ± 0.17. We also investigated the radio-to-γ-ray connection for the 30 γ-ray-detected sources in our sample. We find Pearson’s correlation coefficient is 0.45 (p = 0.069). This tentative correlation and the flatness of the spectral index suggest that the beamed core emission contributes to the low-frequency flux density. We compare our sample distribution with that of the full LDR1 on colour-colour diagrams, and we use this information to identify possible radio counterparts to two of the four UGS within the LDR1 field. We will refine our results as LoTSS continues.

Extending the event-weighted pulsation search to very faint gamma-ray sources

Context. Because of the relatively broad angular resolution of current gamma-ray instruments in the MeV–GeV energy range, the photons of a given source are mixed with those coming from nearby sources or diffuse background. This source confusion seriously hampers the search for pulsation from faint sources. Aims. Statistical tests for pulsation can be made significantly more sensitive when the probability that a photon comes from the pulsar is used as a weight. However, computing this probability requires knowledge of the spectral model of all sources in the region of interest, including the pulsar itself. This is not possible for very faint pulsars that are not detected as gamma-ray sources or whose spectrum is not measured precisely enough. Extending the event-weighted pulsation search to such very faint gamma-ray sources would allow improving our knowledge of the gamma-ray pulsar population. Methods. We present two methods that overcome this limitation by scanning the spectral parameter space, while minimizing the number of trials. The first one approximates the source to background ratio yielding a simple estimate of the weight while the second one makes use of the full spatial and spectral information of the region of interest around the pulsar. Results. We tested these new methods on a sample of 144 gamma-ray pulsars already detected by the Fermi Large Area Telescope data. Both methods detect pulsation from all pulsars of the sample, including the ones for which no significant phase-averaged gamma-ray emission is detected.

Contrast sensitivities in the Gaia Data Release 2

The source detection sensitivity of Gaia is reduced near sources. To characterise this contrast sensitivity is important for understanding the completeness of the Gaia data products, in particular when evaluating source confusion in lower resolution surveys such as photometric monitoring for transits. Here, we statistically evaluate the catalogue source density to determine the Gaia Data Release 2 source detection sensitivity as a function of angular separation and brightness ratio from a bright source. The contrast sensitivity from ∼0.4″ out to 12″ ranges in ΔG = 0–14 mag. We find the derived contrast sensitivity to be robust with respect to target brightness, colour, source density, and Gaia scan coverage.

The first catalog of Fermi-LAT sources below 100 MeV

We present the first Fermi Large Area Telescope (LAT) low energy catalog (1FLE) of sources detected in the energy range 30 – 100 MeV. The imaging Compton telescope (COMPTEL) onboard NASA’s Compton Gamma-Ray Observatory detected sources below 30 MeV, while catalogs of point sources released by the Fermi-LAT and EGRET collaborations use energies above 100 MeV. Because the Fermi-LAT detects gamma rays with energies as low as 20 MeV, we create a list of sources detected in the energy range between 30 and 100 MeV, which closes a gap of point source analysis between the COMPTEL catalog and the Fermi-LAT catalogs. One of the main challenges in the analysis of point sources is the construction of the background diffuse emission model. In our analysis, we use a background-independent method to search for point-like sources based on a wavelet transform implemented in the PGWave code. The 1FLE contains 198 sources detected above 3σ significance with eight years and nine months of the Fermi-LAT data. For 187 sources in the 1FLE catalog we have found an association in the Fermi-LAT 3FGL catalog: 148 are extragalactic, 22 are Galactic, and 17 are unclassified in the 3FGL. The ratio of the number of flat spectrum radio quasars (FSRQ) to BL Lacertae (BL Lacs) in 1FLE is three to one, which can be compared with an approximately 1:1 ratio for the 3FGL or a 1:6 ratio for 3FHL. The higher ratio of the FSRQs in the 1FLE is expected due to generally softer spectra of FSRQs relative to BL Lacs. Most BL Lacs in 1FLE are of low-synchrotron peaked blazar type (18 out of 31), which have softer spectra and higher redshifts than BL Lacs on average. Correspondingly, we find that the average redshift of the BL Lacs in 1FLE is higher than in 3FGL or 3FHL. There are 11 sources that do not have associations in the 3FGL. Most of the unassociated sources either come from regions of bright diffuse emission or have several known 3FGL sources in the vicinity, which can lead to source confusion. The remaining unassociated sources have significance less than 4σ.

Incoherent Discriminative Dictionary Learning for Speech Enhancement

Speech enhancement is one of the many challenging tasks in signal processing, especially in the case of nonstationary speech-like noise. In this paper a new incoherent discriminative dictionary learning algorithm is proposed to model both speech and noise, where the cost function accounts for both “source confusion” and “source distortion” errors, with a regularization term that penalizes the coherence between speech and noise sub-dictionaries. At the enhancement stage, we use sparse coding on the learnt dictionary to find an estimate for both clean speech and noise amplitude spectrum. In the final phase, the Wiener filter is used to refine the clean speech estimate. Experiments on the Noizeus dataset, using two objective speech enhancement measures: frequency-weighted segmental SNR and Perceptual Evaluation of Speech Quality (PESQ) demonstrate that the proposed algorithm outperforms other speech enhancement methods tested.

A complete sample of LSP blazars fully described in γ-rays

Context. We study the γ-ray and broadband spectral energy distribution (SED) properties of a complete sample of 104 bright, radio-selected low-synchrotron peaked (LSP) blazars, which have well-characterized SEDs from radio to X-rays. Most of the sources have already been detected in the γ-ray band by Fermi-LAT, however almost 20% of these blazars have no counterpart in any of the Fermi catalogs published so far. Aims. Using the Fermi Science Tools, we look for γ-ray emission for those objects not yet reported in any Fermi-LAT catalog, finding new detections and associations. We then study the multifrequency SED for all sources in our sample, fitting their synchrotron (Syn) and inverse Compton (IC) components. A complete sample of LSP blazars with a full description in γ-ray is unique. We use this sample to derive the distribution of the Compton dominance (CD) along with population properties such as Syn and IC peak power, and frequency distributions. Methods. We performed a binned likelihood analysis in the 0.3–500 GeV energy band with Fermi-LAT Pass 8 data, integrating over 7.5 yr of observations. We studied γ-ray light curves and test statistic (TS) maps to validate new detections and associations, thereby building a better picture of the high-energy activity in radio-selected LSP blazars. We fit the IC component for the new detections using all data at our disposal from X-rays to GeV γ-rays, enhancing the amount of information available to study the Syn to IC peak-power correlations. Results. We deliver a unique characterization in γ-rays for a complete sample of LSP blazars. We show that three previously unidentified 3FGL sources can be associated with blazars when using improved γ-ray positions obtained from TS maps. Six previously unreported γ-ray sources are detected at TS > 20 level, while another three show TS values between 10–20. We evaluate two cases in which source confusion is likely present. In four cases there is no significant γ-ray signature when integrating over 7.5 yr. Short-lived flares at ~1 month scale, however, have been detected in these sources. Finally, we measure the log(CD) for the sample, which has a Gaussian-like distribution with median log(CD) ≈ 0.1, implying that on average the peak-power for the Syn and IC components in LSP blazars is similar.