المؤلفون: Whittam, I. H., Prescott, M., Hale, C. L., Jarvis, M . J., Heywood, I., An, Fangxia, Glowacki, M., Maddox, N., Marchetti, L., Morabito, L. K., Adams, N. J., Bowler, R. A. A., Hatfield, P. W., Varadaraj, R. G., Collier, J., Frank, B., Taylor, A. R., Santos, M. G., Vaccari, M., Afonso, J., Ao, Y., Delhaize, J., Knowles, K., Kolwa, S., Randriamampandry, S. M., Randriamanakoto, Z., Smirnov, O., Smith, D. J. B., White, S. V.

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: In this paper we combine the Early Science radio continuum data from the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey, with optical and near-infrared data and release the cross-matched catalogues. The radio data used in this work covers $0.86$ deg$^2$ of the COSMOS field, reaches a thermal noise of $1.7$ $\mu$Jy/beam and contains $6102$ radio components. We visually inspect and cross-match the radio sample with optical and near-infrared data from the Hyper Suprime-Cam (HSC) and UltraVISTA surveys. This allows the properties of active galactic nuclei and star-forming populations of galaxies to be probed out to $z \approx 5$. Additionally, we use the likelihood ratio method to automatically cross-match the radio and optical catalogues and compare this to the visually cross-matched catalogue. We find that 94 per cent of our radio source catalogue can be matched with this method, with a reliability of $95$ per cent. We proceed to show that visual classification will still remain an essential process for the cross-matching of complex and extended radio sources. In the near future, the MIGHTEE survey will be expanded in area to cover a total of $\sim$20~deg$^2$; thus the combination of automated and visual identification will be critical. We compare redshift distribution of SFG and AGN to the SKADS and T-RECS simulations and find more AGN than predicted at $z \sim 1$.
Comment: 15 pages, 15 figures. Accepted for publication in MNRAS

URL الوصول: http://arxiv.org/abs/2310.17409

المؤلفون: Carvajal, R., Matute, I., Afonso, J., Norris, R. P., Luken, K. J., Sánchez-Sáez, P., Cunha, P. A. C., Humphrey, A., Messias, H., Amarantidis, S., Barbosa, D., Cruz, H. A., Miranda, H., Paulino-Afonso, A., Pappalardo, C.

المصدر: A&A 679, A101 (2023)

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies, Astrophysics - Instrumentation and Methods for Astrophysics

الوصف: We developed and trained a pipeline of three machine learning (ML) models than can predict which sources are more likely to be an AGN and to be detected in specific radio surveys. Also, it can estimate redshift values for predicted radio-detectable AGNs. These models, which combine predictions from tree-based and gradient-boosting algorithms, have been trained with multi-wavelength data from near-infrared-selected sources in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) Spring field. Training, testing, calibration, and validation were carried out in the HETDEX field. Further validation was performed on near-infrared-selected sources in the Stripe 82 field. In the HETDEX validation subset, our pipeline recovers 96% of the initially labelled AGNs and, from AGNs candidates, we recover 50% of previously detected radio sources. For Stripe 82, these numbers are 94% and 55%. Compared to random selection, these rates are two and four times better for HETDEX, and 1.2 and 12 times better for Stripe 82. The pipeline can also recover the redshift distribution of these sources with $\sigma_{\mathrm{NMAD}}$ = 0.07 for HETDEX ($\sigma_{\mathrm{NMAD}}$ = 0.09 for Stripe 82) and an outlier fraction of 19% (25% for Stripe 82), compatible with previous results based on broad-band photometry. Feature importance analysis stresses the relevance of near- and mid-infrared colours to select AGNs and identify their radio and redshift nature. Combining different algorithms in ML models shows an improvement in the prediction power of our pipeline over a random selection of sources. Tree-based ML models (in contrast to deep learning techniques) facilitate the analysis of the impact that features have on the predictions. This prediction can give insight into the potential physical interplay between the properties of radio AGNs (e.g. mass of black hole and accretion rate).
Comment: Accepted for publication in A&A, 24 pages and 21 figures. Updated to include information on retrieval of data and models, which can be obtained from https://zenodo.org/doi/10.5281/zenodo.10220008

URL الوصول: http://arxiv.org/abs/2309.11652

المؤلفون: Hale, C. L., Whittam, I. H., Jarvis, M. J., Best, P. N., Thomas, N. L., Heywood, I., Prescott, M., Adams, N., Afonso, J., An, Fangxia, Bowler, R. A. A., Collier, J. D., Cook, R. H. W., Davé, R., Frank, B. S., Glowacki, M., Hatfield, P. W., Lovell, S. Kolwa C. C., Maddox, N., Marchetti, L., Morabito, L. K., Murphy, E., Prandoni, I., Randriamanakoto, Z., Taylor, A. R.

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: We present deep 1.4 GHz source counts from $\sim$5 deg$^2$ of the continuum Early Science data release of the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey down to $S_{1.4\textrm{GHz}}\sim$15 $\mu$Jy. Using observations over two extragalactic fields (COSMOS and XMM-LSS), we provide a comprehensive investigation into correcting the incompleteness of the raw source counts within the survey to understand the true underlying source count population. We use a variety of simulations that account for: errors in source detection and characterisation, clustering, and variations in the assumed source model used to simulate sources within the field and characterise source count incompleteness. We present these deep source count distributions and use them to investigate the contribution of extragalactic sources to the sky background temperature at 1.4 GHz using a relatively large sky area. We then use the wealth of ancillary data covering{a subset of the COSMOS field to investigate the specific contributions from both active galactic nuclei (AGN) and star forming galaxies (SFGs) to the source counts and sky background temperature. We find, similar to previous deep studies, that we are unable to reconcile the sky temperature observed by the ARCADE 2 experiment. We show that AGN provide the majority contribution to the sky temperature contribution from radio sources, but the relative contribution of SFGs rises sharply below 1 mJy, reaching an approximate 15-25% contribution to the total sky background temperature ($T_b\sim$100 mK) at $\sim$15 $\mu$Jy.
Comment: 24 pages, 12 figures; Accepted for publication in MNRAS

URL الوصول: http://arxiv.org/abs/2211.05741

المؤلفون: Pereira, K. S., Schmidt, M. C. F., Afonso, J. C.

المصدر: Brazilian Journal of Chemical Engineering. December 2010 27(4)

مصطلحات موضوعية: Sulfur compounds, Gas chromatography, Chemiluminescence, Dual plasma

الوصف: This work describes the calibration of a gas chromatograph equipped with a sulfur chemiluminescent detector with dual plasma (GC-SCD-DP) for analysis of sulfur-containing petroleum refinery gaseous streams. A packed column in an inert tube (Sulfinert) and an inlet system resistant to reactive sulfur compounds were used. The behavior of the calibration procedure over time depended on the sulfur compound: hydrogen sulfide (H2S), carbonyl sulfide (COS), methanethiol (MeSH) and dimethylsulfide (DMS) gave constant responses, whereas SO2 presented a systematic increase and dimethyldisulfide (DMDS) showed a systematic decrease of their response factors. In all cases, the response factors were lower than the ones found in the ASTM D 5504-08 method. The GC-SCD-DP technique proved to be a suitable tool for quantification of sulfur compounds (including SO2) at µg.m-3 levels in several petroleum refinery gaseous streams.

وصف الملف: text/html

URL الوصول: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322010000400011

المؤلفون: Whittam, I. H., Jarvis, M. J., Hale, C. L., Prescott, M., Morabito, L. K., Heywood, I., Adams, N. J., Afonso, J., An, Fangxia, Ao, Y., Bowler, R. A., Collier, J. D., Deane, R. P., Delhaize, J., Frank, B., Glowacki, M., Hatfield, P. W., Maddox, N., Marchetti, L., Matthews, A. M., Prandoni, I., Randriamampandry, S., Randriamanakoto, Z., Smith, D. J. B., Taylor, A. R., Thomas, N. L., Vaccari, M.

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics

الوصف: We study the nature of the faint radio source population detected in the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Early Science data in the COSMOS field, focusing on the properties of the radio-loud active galactic nuclei (AGN). Using the extensive multi-wavelength data available in the field, we are able to classify 88 per cent of the 5223 radio sources in the field with host galaxy identifications as AGN (35 per cent) or star-forming galaxies (54 per cent). We select a sample of radio-loud AGN with redshifts out to $z \sim 6$ and radio luminosities $10^{20} < \textrm{L}_{1.4~\textrm{GHz}} / \textrm{W Hz}^{-1} < 10^{27}$ and classify them as high-excitation and low-excitation radio galaxies (HERGs and LERGs). The classification catalogue is released with this work. We find no significant difference in the host galaxy properties of the HERGs and LERGs in our sample. In contrast to previous work, we find that the HERGs and LERGs have very similar Eddington-scaled accretion rates; in particular we identify a population of very slowly accreting AGN that are formally classified as HERGs at these low radio luminosities, where separating into HERGs and LERGs possibly becomes redundant. We investigate how black hole mass affects jet power, and find that a black hole mass $\gtrsim 10^{7.8}~\textrm{M}_\odot$ is required to power a jet with mechanical power greater than the radiative luminosity of the AGN ($L_\textrm{mech}/L_\textrm{bol} > 1$). We discuss that both a high black hole mass and black hole spin may be necessary to launch and sustain a dominant radio jet.
Comment: Accepted for publication in MNRAS. The multi-wavelength source classification catalogue is released publicly with this work. 20 pages, 15 figures

URL الوصول: http://arxiv.org/abs/2207.12379

المؤلفون: Efstathiou, A., Farrah, D., Afonso, J., Clements, D. L., González-Alfonso, E., Lacy, M., Oliver, S., Lesta, V. Papadopoulou, Pearson, C., Rigopoulou, D., Rowan-Robinson, M., Spoon, H. W. W., Verma, A., Wang, L.

المصدر: 2022MNRAS.512.5183E

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: We present the ultraviolet to submillimetre spectral energy distributions (SEDs) of the HERschel Ultra Luminous Infrared Galaxy Survey (HERUS) sample of 42 local ultraluminous infrared galaxies (ULIRGs) and fit them with a Markov chain Monte Carlo (MCMC) code using the CYprus models for Galaxies and their NUclear Spectra (CYGNUS) radiative transfer models for starbursts, active galactic nucleus (AGN) tori and host galaxy. The Spitzer IRS spectroscopy data are included in the fitting. Our bayesian SED fitting method takes comparable time to popular energy balance methods but it is more physically motivated and versatile. All HERUS galaxies harbor high rates of star formation but we also find bolometrically significant AGN in all of the galaxies of the sample. We estimate the correction of the luminosities of the AGN in the ULIRGs due to the anisotropic emission of the torus and find that it could be up to a factor of $\sim10$ for nearly edge-on tori. We present a comparison of our results with the smooth torus model of Fritz et al. and the two-phase models of Siebenmorgen et al. and SKIRTOR. We find that the CYGNUS AGN torus models fit significantly better the SEDs of our sample compared to all other models. We find no evidence that strong AGN appear either at the beginning or end of a starburst episode or that starbursts and AGN affect each other. IRAS 01003-2238 and Mrk 1014 show evidence for dual AGN in their SED fits suggesting a minimum dual AGN fraction in the sample of 5%.
Comment: Published in Monthly Notices of the Royal Astronomical Society. The CYGNUS models used in this paper are available at https://arc.euc.ac.cy/cygnus/

URL الوصول: http://arxiv.org/abs/2205.00011

المؤلفون: Broderick, J. W., Drouart, G., Seymour, N., Galvin, T. J., Wright, N., Rosell, A. Carnero, Chhetri, R., Dannerbauer, H., Driver, S. P., Morgan, J. S., Moss, V. A., Prabu, S., Afonso, J. M., De Breuck, C., Emonts, B. H. C., Franzen, T. M. O., Gutiérrez, C. M., Hancock, P. J., Heald, G. H., Hurley-Walker, N., Ivison, R. J., Lehnert, M. D., Noirot, G., Read, M., Shabala, S. S., Stern, D., Sutherland, W. J., Sutorius, E., Turner, R. J., Vernet, J.

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies

الوصف: While unobscured and radio-quiet active galactic nuclei are regularly being found at redshifts $z > 6$, their obscured and radio-loud counterparts remain elusive. We build upon our successful pilot study, presenting a new sample of low-frequency-selected candidate high-redshift radio galaxies (HzRGs) over a sky area twenty times larger. We have refined our selection technique, in which we select sources with curved radio spectra between 72-231 MHz from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. In combination with the requirements that our GLEAM-selected HzRG candidates have compact radio morphologies and be undetected in near-infrared $K_{\rm s}$-band imaging from the Visible and Infrared Survey Telescope for Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, we find 51 new candidate HzRGs over a sky area of approximately 1200 deg$^2$. Our sample also includes two sources from the pilot study: the second-most distant radio galaxy currently known, at $z=5.55$, with another source potentially at $z \sim 8$. We present our refined selection technique and analyse the properties of the sample. We model the broadband radio spectra between 74 MHz and 9 GHz by supplementing the GLEAM data with both publicly available data and new observations from the Australia Telescope Compact Array at 5.5 and 9 GHz. In addition, deep $K_{\rm s}$-band imaging from the High-Acuity Widefield $K$-band Imager (HAWK-I) on the Very Large Telescope and from the Southern Herschel Astrophysical Terahertz Large Area Survey Regions $K_{\rm s}$-band Survey (SHARKS) is presented for five sources. We discuss the prospects of finding very distant radio galaxies in our sample, potentially within the epoch of reionisation at $z \gtrsim 6.5$.
Comment: 49 pages, 3 figures (one of which is a multi-page figure with 102 separate panels), 9 tables, accepted for publication in PASA

URL الوصول: http://arxiv.org/abs/2204.08490

المؤلفون: Seymour, N., Drouart, G., Noirot, G., Broderick, J. W., Turner, R. J., Shabala, S. S., Stern, D. K., Bellstedt, S., Driver, S., Davies, L., De Breuck, C. A., Afonso, J., Vernet, J. D. R., Galvin, T. J.

مصطلحات موضوعية: Astrophysics - Cosmology and Nongalactic Astrophysics

الوصف: We present Hubble Space Telescope Wide Field Camera 3 photometric and grism observations of the candidate ultra-high-redshift (z>7) radio galaxy, GLEAM J0917-0012. This radio source was selected due to the curvature in its 70-230 MHz, low-frequency Murchison Widefield Array radio spectrum and its faintness in K-band. Follow-up spectroscopic observations of this source with the VLA and ALMA were inconclusive as to its redshift. Our F105W and F0986M imaging observations detect the host of GLEAM J0917-0012 and a companion galaxy, ~one arcsec away. The G102 grism observations reveal a single weak line in each of the spectra of the host and the companion. To help identify these lines we utilised several photometric redshift techniques including template fitting to the grism spectra, fitting the UV-to-radio photometry with galaxy templates plus a synchrotron model, fitting of the UV-to-near-infrared photometry with EAZY, and fitting the radio data alone with RAiSERed. For the host of GLEAM J0917-0012 we find a line at 1.12 micron and the UV-to-radio spectral energy distribution fitting favours solutions at z~2 or z~8. While this fitting shows a weak preference for the lower redshift solution, the models from the higher redshift solution are more consistent with the strength of the spectral line. The redshift constraint by RAiSERed of z>6.5 also supports the interpretation that this line could be Lyman-alpha at z=8.21; however EAZY favours the z~2 solution. We discuss the implications of both solutions. For the companion galaxy we find a line at 0.98 micron and the spectral energy distribution fitting favours solutions at z<3 implying that the line could be the [OII]3727 doublet at z=1.63 (although the EAZY solution is z~2.6+/-0.5). Further observations are still required to unambiguously determine the redshift of this intriguing candidate ultra-high-redshift radio galaxy (abridged).
Comment: 18 pages, 7 figures, 6 tables, accepted for publication in PASA

URL الوصول: http://arxiv.org/abs/2203.01349

المؤلفون: Heywood, I., Jarvis, M. J., Hale, C. L., Whittam, I. H., Bester, H. L., Hugo, B., Kenyon, J. S., Prescott, M., Smirnov, O. M., Tasse, C., Afonso, J. M., Best, P. N., Collier, J. D., Deane, R. P., Frank, B. S., Hardcastle, M. J., Knowles, K., Maddox, N., Murphy, E. J., Prandoni, I., Randriamampandry, S. M., Santos, M. G., Sekhar, S., Tabatabaei, F., Taylor, A. R., Thorat, K.

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies, Astrophysics - Instrumentation and Methods for Astrophysics

الوصف: MIGHTEE is a galaxy evolution survey using simultaneous radio continuum, spectro-polarimetry, and spectral line observations from the South African MeerKAT telescope. When complete, the survey will image $\sim$20 deg$^{2}$ over the COSMOS, E-CDFS, ELAIS-S1, and XMM-LSS extragalactic deep fields with a central frequency of 1284 MHz. These were selected based on the extensive multiwavelength datasets from numerous existing and forthcoming observational campaigns. Here we describe and validate the data processing strategy for the total intensity continuum aspect of MIGHTEE, using a single deep pointing in COSMOS (1.6 deg$^{2}$) and a three-pointing mosaic in XMM-LSS (3.5 deg$^{2}$). The processing includes the correction of direction-dependent effects, and results in thermal noise levels below 2~$\mathrm{\mu}$Jy beam$^{-1}$ in both fields, limited in the central regions by classical confusion at $\sim$8$''$ angular resolution, and meeting the survey specifications. We also produce images at $\sim$5$''$ resolution that are $\sim$3 times shallower. The resulting image products form the basis of the Early Science continuum data release for MIGHTEE. From these images we extract catalogues containing 9,896 and 20,274 radio components in COSMOS and XMM-LSS respectively. We also process a close-packed mosaic of 14 additional pointings in COSMOS and use these in conjunction with the Early Science pointing to investigate methods for primary beam correction of broadband radio images, an analysis that is of relevance to all full-band MeerKAT continuum observations, and wide field interferometric imaging in general. A public release of the MIGHTEE Early Science continuum data products accompanies this article.
Comment: 21 pages, 13 figures, 3 tables, to be published in MNRAS

URL الوصول: http://arxiv.org/abs/2110.00347

المؤلفون: Silva, R. G.^Aff5, Araújo, M. G.^Aff6, Afonso, J. C.^Aff7, Mahler, C. F.^Aff5, Nunes, K. R. A.^Aff5

المساهمون: Jawaid, Mohammad, Series Editor^{Aff1, Aff3}, Khan, Anish, Series Editor^{Aff2, Aff4}

المصدر: Conversion of Electronic Waste in to Sustainable Products. :179-195