11 research outputs found

    Satellites and central galaxies in SDSS: The influence of interactions on their properties

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    We use SDSS-DR14 to construct a sample of galaxy systems consisting of a central object and two satellites. We adopt projected distance and radial velocity difference criteria and impose an isolation criterion to avoid membership in larger structures. We also classify the interaction between the members of each system through a visual inspection of galaxy images, finding sim80mpercent{sim}80{{ m per cent}} of the systems lack evidence of interactions whilst the remaining sim20mpercent{sim}20{{ m per cent}} involve some kind of interaction, as inferred from their observed distorted morphology. We have considered separately, samples of satellites and central galaxies, and each of these samples were tested against suitable control sets to analyse the results. We find that central galaxies showing signs of interactions present evidence of enhanced star formation activity and younger stellar populations. As a counterpart, satellite samples show these galaxies presenting older stellar populations with a lower star formation rate than the control sample. The observed trends correlate with the stellar mass content of the galaxies and with the projected distance between the members involved in the interaction. The most massive systems are less affected since they show no star formation excess, possibly due to their more evolved stage and less gas available to form new stars. Our results suggest that it is arguably a transfer of material during interactions, with satellites acting as donors to the central galaxy. As a consequence of the interactions, satellite stellar population ages rapidly and new bursts of star formation may frequently occur in the central galaxy.Fil: Mesa, Valeria Alejandra. Universidad de La Serena; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Alonso, Sol. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; ArgentinaFil: Coldwell Lloveras, Georgina Vanesa. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Garcia Lambas, Diego Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Nilo Castellon, J. L. Universidad de La Serena; Chil

    Clash of Titans: A MUSE dynamical study of the extreme cluster merger SPT-CL J0307-6225

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    We present MUSE spectroscopy, Megacam imaging, and Chandra X-ray emission for SPT-CL J0307-6225, a z = 0.58 major merging galaxy cluster with a large BCG-SZ centroid separation and a highly disturbed X-ray morphology. The galaxy density distribution shows two main overdensities with separations of 0.144 and 0.017 arcmin to their respective BCGs. We characterize the central regions of the two colliding structures, namely 0307-6225N and 0307-6225S, finding velocity derived masses of M200, N = 2.44 ± 1.41 × 1014M⊙ and M200, S = 3.16 ± 1.88 × 1014M⊙, with a line-of-sight velocity difference of |Δv| = 342 km s-1. The total dynamically derived mass is consistent with the SZ derived mass of 7.63 h70-1 ± 1.36 × 1014M⊙. We model the merger using the Monte Carlo Merger Analysis Code, estimating a merging angle of 36+14-12 ° with respect to the plane of the sky. Comparing with simulations of a merging system with a mass ratio of 1:3, we find that the best scenario is that of an ongoing merger that began 0.96+0.31-0.18 Gyr ago. We also characterize the galaxy population using Hδand [O ii] λ3727 Å lines. We find that most of the emission-line galaxies belong to 0307-6225S, close to the X-ray peak position with a third of them corresponding to red-cluster sequence galaxies, and the rest to blue galaxies with velocities consistent with recent periods of accretion. Moreover, we suggest that 0307-6225S suffered a previous merger, evidenced through the two equally bright BCGs at the centre with a velocity difference of ∼674 km s-1

    The DECam Local Volume Exploration Survey Data Release 2

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    We present the second public data release (DR2) from the DECam Local Volume Exploration survey (DELVE). DELVE DR2 combines new DECam observations with archival DECam data from the Dark Energy Survey, the DECam Legacy Survey, and other DECam community programs. DELVE DR2 consists of similar to 160,000 exposures that cover >21,000 deg(2) of the high-Galactic-latitude ( divide b divide > 10 degrees) sky in four broadband optical/near-infrared filters (g, r, i, z). DELVE DR2 provides point-source and automatic aperture photometry for similar to 2.5 billion astronomical sources with a median 5 sigma point-source depth of g = 24.3, r = 23.9, i = 23.5, and z = 22.8 mag. A region of similar to 17,000 deg(2) has been imaged in all four filters, providing four-band photometric measurements for similar to 618 million astronomical sources. DELVE DR2 covers more than 4 times the area of the previous DELVE data release and contains roughly 5 times as many astronomical objects. DELVE DR2 is publicly available via the NOIRLab Astro Data Lab science platform

    Multi-messenger observations of a binary neutron star merger

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    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

    Photometric redshifts for the S-PLUS Survey: Is machine learning up to the task?

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    The Southern Photometric Local Universe Survey (S-PLUS) is a novel project that aims to map the Southern Hemisphere using a twelve filter system, comprising five broad-band SDSS-like filters and seven narrow-band filters optimized for important stellar features in the local universe. In this paper we use the photometry and morphological information from the first S-PLUS data release (S-PLUS DR1) cross-matched to unWISE data and spectroscopic redshifts from Sloan Digital Sky Survey DR15. We explore three different machine learning methods (Gaussian Processes with GPz and two Deep Learning models made with TensorFlow) and compare them with the currently used template-fitting method in the S-PLUS DR1 to address whether machine learning methods can take advantage of the twelve filter system for photometric redshift prediction. Using tests for accuracy for both single-point estimates such as the calculation of the scatter, bias, and outlier fraction, and probability distribution functions (PDFs) such as the Probability Integral Transform (PIT), the Continuous Ranked Probability Score (CRPS) and the Odds distribution, we conclude that a deep-learning method using a combination of a Bayesian Neural Network and a Mixture Density Network offers the most accurate photometric redshifts for the current test sample. It achieves single-point photometric redshifts with scatter (σNMAD) of 0.023, normalized bias of -0.001, and outlier fraction of 0.64% for galaxies with r_auto magnitudes between 16 and 21. © 2021 Elsevier B.V. All rights reserved.The author acknowledges the financial support given by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brazil (CAPES, grant 88887.470064/2019-00) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, grant 169181/2017-0), during the development of this research. L. S. J. acknowledges support from Brazilian agencies FAPESP (2019/10923-5) and CNPq (304819/2017-4). L. N. acknowledges the financial support provided by the São Paulo Research Foundation (FAPESP), Brazil (grant 2019/01312-2 and 2014/10566-4). M. L. B. acknowledges the financial support provided by the São Paulo Research Foundation (FAPESP), Brazil (grant 2018/09165-6 and 2019/23388-0). C. Q. acknowledges the financial support provided by the São Paulo Research Foundation, Brazil (grant 2015/11442-0 and 2019/06766-1) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brazil. F. R. H. thanks FAPESP for the financial support through the program 2018/21661-9. J. L. N. C. is grateful for the financial support received from the Southern Office of Aerospace Research and development (SOARD), grants FA9550-18-1-0018 and FA9550-22-1-0037, of the Air Force Office of the Scientific Research International Office of the United States (AFOSR/IO). M. L. L. D. acknowledges the polish NCN, Poland grant number 2019/34/E/ST9/00133. S. A. acknowledges support under the grant 5077 financed by IAASARS/NOA. Y. J-T has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 898633. Y. J-T. also acknowledges financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709).Peer reviewe

    Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-faint Dwarf Galaxy in the Constellation Pegasus

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    We report the discovery of Pegasus IV, an ultra-faint dwarf galaxy found in archival data from the Dark Energy Camera processed by the DECam Local Volume Exploration Survey. Pegasus IV is a compact, ultra-faint stellar system ( r1/2=416+8{r}_{1/2}={41}_{-6}^{+8} pc; M _V = −4.25 ± 0.2 mag) located at a heliocentric distance of 906+4kpc{90}_{-6}^{+4}\,\mathrm{kpc} . Based on spectra of seven nonvariable member stars observed with Magellan/IMACS, we confidently resolve Pegasus IV’s velocity dispersion, measuring σv=3.31.1+1.7{\sigma }_{v}={3.3}_{-1.1}^{+1.7} km s ^−1 (after excluding three velocity outliers); this implies a mass-to-light ratio of M1/2/LV,1/2=16799+224M/L{M}_{1/2}/{L}_{V,1/2}={167}_{-99}^{+224}{M}_{\odot }/{L}_{\odot } for the system. From the five stars with the highest signal-to-noise spectra, we also measure a systemic metallicity of [Fe/H] = 2.630.30+0.26-{2.63}_{-0.30}^{+0.26} dex, making Pegasus IV one of the most metal-poor ultra-faint dwarfs. We tentatively resolve a nonzero metallicity dispersion for the system. These measurements provide strong evidence that Pegasus IV is a dark-matter-dominated dwarf galaxy, rather than a star cluster. We measure Pegasus IV’s proper motion using data from Gaia Early Data Release 3, finding ( μ _α _* , μ _δ ) = (0.33 ± 0.07, −0.21 ± 0.08) mas yr ^−1 . When combined with our measured systemic velocity, this proper motion suggests that Pegasus IV is on an elliptical, retrograde orbit, and is currently near its orbital apocenter. Lastly, we identify three potential RR Lyrae variable stars within Pegasus IV, including one candidate member located more than 10 half-light radii away from the system’s centroid. The discovery of yet another ultra-faint dwarf galaxy strongly suggests that the census of Milky Way satellites is still incomplete, even within 100 kpc

    Identification of Galaxy–Galaxy Strong Lens Candidates in the DECam Local Volume Exploration Survey Using Machine Learning

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    We perform a search for galaxy–galaxy strong lens systems using a convolutional neural network (CNN) applied to imaging data from the first public data release of the DECam Local Volume Exploration Survey, which contains ∼520 million astronomical sources covering ∼4000 deg ^2 of the southern sky to a 5 σ point–source depth of g = 24.3, r = 23.9, i = 23.3, and z = 22.8 mag. Following the methodology of similar searches using Dark Energy Camera data, we apply color and magnitude cuts to select a catalog of ∼11 million extended astronomical sources. After scoring with our CNN, the highest-scoring 50,000 images were visually inspected and assigned a score on a scale from 0 (not a lens) to 3 (very probable lens). We present a list of 581 strong lens candidates, 562 of which are previously unreported. We categorize our candidates using their human-assigned scores, resulting in 55 Grade A candidates, 149 Grade B candidates, and 377 Grade C candidates. We additionally highlight eight potential quadruply lensed quasars from this sample. Due to the location of our search footprint in the northern Galactic cap ( b > 10 deg) and southern celestial hemisphere (decl. < 0 deg), our candidate list has little overlap with other existing ground-based searches. Where our search footprint does overlap with other searches, we find a significant number of high-quality candidates that were previously unidentified, indicating a degree of orthogonality in our methodology. We report properties of our candidates including apparent magnitude and Einstein radius estimated from the image separation

    Observations of the First Electromagnetic Counterpart to a Gravitational-wave Source by the TOROS Collaboration

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    We present the results of prompt optical follow-up of the electromagnetic counterpart of the gravitational-wave event GW170817 by the Transient Optical Robotic Observatory of the South Collaboration. We detected highly significant dimming in the light curves of the counterpart (Δg = 0.17 ± 0.03 mag, Δr = 0.14 ± 0.02 mag, Δi = 0.10 ± 0.03 mag) over the course of only 80 minutes of observations obtained ∼35 hr after the trigger with the T80-South telescope. A second epoch of observations, obtained ∼59 hr after the event with the EABA 1.5 m telescope, confirms the fast fading nature of the transient. The observed colors of the counterpart suggest that this event was a "blue kilonova" relatively free of lanthanides.Fil: Díaz, Mario Claudio. University of Texas; Estados UnidosFil: Macri, Lucas M.. Texas A&M University; Estados UnidosFil: Garcia Lambas, Diego Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Mendes de Oliveira, C.. Universidade de Sao Paulo; BrasilFil: Nilo Castellon, Jose Luis Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina. Universidad de La Serena; ChileFil: Ribeiro, T.. Universidade Federal de Sergipe; BrasilFil: Sánchez, Bruno Orlando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Schoenell, W.. Universidade de Sao Paulo; Brasil. Universidade Federal de Santa Catarina; BrasilFil: Abramo, L. R.. Universidade Federal de Santa Catarina; Brasil. Universidade de Sao Paulo; BrasilFil: Akras, S.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Alcaniz, J. S.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Artola, R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Beroiz, Martin Isidro Ramon. University of Texas; Estados UnidosFil: Bonoli, S.. Centro de Estudios de Física del Cosmos de Aragón; EspañaFil: Cabral, Juan Bautista. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Camuccio, R.. University of Texas; Estados UnidosFil: Castillo, M.. University of Texas; Estados UnidosFil: Chavushyan, Vahram. Instituto Nacional de Astrofísica, Óptica y Electrónica; MéxicoFil: Coelho, P.. Universidade de Sao Paulo; BrasilFil: Colazo, Juan Cruz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Costa Duarte, M. V.. Universidade de Sao Paulo; BrasilFil: Cuevas Larenas, H.. Universidad de La Serena; ChileFil: DePoy, D. L.. Texas A&M University; Estados UnidosFil: Dominguez Romero, Mariano Javier de Leon. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Dultzin, Debora. Universidad Nacional Autonoma de Mexico. Instituto de Astronomia; MéxicoFil: Fernández, D.. Pontificia Universidad Católica de Chile; ChileFil: García, J.. University of Texas; Estados UnidosFil: Girardini, C.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Goncalves Gama, Diana Renata. Universidade Federal do Rio de Janeiro; BrasilFil: Gonçalves, T. S.. Universidade Federal do Rio de Janeiro; BrasilFil: Gurovich, Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Jiménez Teja, Y.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Kanaan, A.. Universidade Federal de Santa Catarina; BrasilFil: Lares, M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Lopes de Oliveira, R.. Universidade Federal de Sergipe; Brasil. National Aeronautics and Space Administration; Estados UnidosFil: López Cruz, Omar. Instituto Nacional de Astrofísica, Óptica y Electrónica; MéxicoFil: Marshall, J. L.. Texas A&M University; Estados UnidosFil: Melia, R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Molino, A.. Universidade de Sao Paulo; BrasilFil: Padilla, Nelson. Pontificia Universidad Católica de Chile; ChileFil: Peñuela, T.. University of Texas; Estados Unidos. Ludwig Maximilian Universität Munich; AlemaniaFil: Placco, V. M.. University of Notre Dame; Estados Unidos. Center for the Evolution of the Elements. Joint Institute for Nuclear Astrophysics; Estados UnidosFil: Quiñones, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Rivera, A. Ramírez. Universidad de La Serena; ChileFil: Renzi, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Riguccini, L.. Universidade Federal do Rio de Janeiro; BrasilFil: Ríos López, Emmanuel. Instituto Nacional de Astrofísica, Óptica y Electrónica; MéxicoFil: Rodriguez, Horacio Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Sampedro, L.. Universidade de Sao Paulo; BrasilFil: Schneiter, Ernesto Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Sodré, Laerte. Universidade de Sao Paulo; BrasilFil: Starck Cuffini, Manuel Darío. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Torres Flores, S.. Universidad de La Serena; ChileFil: Tornatore, M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Zadrożny, A.. University of Texas; Estados Unido
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