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

2020 ◽  
Vol 492 (4) ◽  
pp. 5675-5683 ◽  
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.

scholarly journals Chemical abundances of Seyfert 2 AGNs – I. Comparing oxygen abundances from distinct methods using SDSS

2019 ◽  
Vol 492 (1) ◽  
pp. 468-479 ◽  
Author(s):  
O L Dors ◽  
P Freitas-Lemes ◽  
E B Amôres ◽  
E Pérez-Montero ◽  
M V Cardaci ◽  
...  
Keyword(s):  
Sloan Digital Sky Survey ◽  
Strong Line ◽  
Host Galaxies ◽  
Chemical Abundances ◽  
Oxygen Abundance ◽  
Line Intensities ◽  
Sky Survey ◽  
Direct Measurements ◽  
Low Metallicity ◽  
Semi Empirical

ABSTRACT We compare the oxygen abundance (O/H) of the narrow-line regions (NLRs) of Seyfert 2 AGNs obtained through strong-line methods and from direct measurements of the electron temperature (Te-method). The aim of this study is to explore the effects of the use of distinct methods on the range of metallicity and on the mass–metallicity relation of active galactic nuclei (AGNs) at low redshifts (z ≲ 0.4). We used the Sloan Digital Sky Survey (SDSS) and NASA/IPAC Extragalactic Database (NED) to selected optical (3000 < λ(Å) < 7000) emission line intensities of 463 confirmed Seyfert 2 AGNs. The oxygen abundances of the NLRs were estimated using the theoretical Storchi-Bergmann et al. calibrations, the semi-empirical N2O2 calibration, the Bayesian H  ii-Chi-mistry code and the Te-method. We found that the oxygen abundance estimations via the strong-line methods differ from each other up to ∼0.8 dex, with the largest discrepancies in the low-metallicity regime ($\rm 12+\log (O/H) \: \lesssim \: 8.5$). We confirmed that the Te-method underestimates the oxygen abundance in NLRs, producing unreal subsolar values. We did not find any correlation between the stellar mass of the host galaxies and the metallicity of their AGNs. This result is independent of the method used to estimate Z.

scholarly journals Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk

2018 ◽  
Vol 617 ◽  
pp. L2 ◽  
Author(s):  
A. Müller ◽  
M. Keppler ◽  
Th. Henning ◽  
M. Samland ◽  
G. Chauvin ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Near Infrared ◽  
Direct Detection ◽  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Infrared Range ◽  
Data Set ◽  
Cloud Properties ◽  
Spectrophotometric Data ◽  
First Time

Context. The observation of planets in their formation stage is a crucial but very challenging step in understanding when, how, and where planets form. PDS 70 is a young pre-main sequence star surrounded by a transition disk, in the gap of which a planetary-mass companion has recently been discovered. This discovery represents the first robust direct detection of such a young planet, possibly still at the stage of formation. Aims. We aim to characterize the orbital and atmospheric properties of PDS 70 b, which was first identified on May 2015 in the course of the SHINE survey with SPHERE, the extreme adaptive-optics instrument at the VLT. Methods. We obtained new deep SPHERE/IRDIS imaging and SPHERE/IFS spectroscopic observations of PDS 70 b. The astrometric baseline now covers 6 yr, which allowed us to perform an orbital analysis. For the first time, we present spectrophotometry of the young planet which covers almost the entire near-infrared range (0.96–3.8 μm). We use different atmospheric models covering a large parameter space in temperature, log g, chemical composition, and cloud properties to characterize the properties of the atmosphere of PDS 70 b. Results. PDS 70 b is most likely orbiting the star on a circular and disk coplanar orbit at ~22 au inside the gap of the disk. We find a range of models that can describe the spectrophotometric data reasonably well in the temperature range 1000–1600 K and log g no larger than 3.5 dex. The planet radius covers a relatively large range between 1.4 and 3.7 RJ with the larger radii being higher than expected from planet evolution models for the age of the planet of 5.4 Myr. Conclusions. This study provides a comprehensive data set on the orbital motion of PDS 70 b, indicating a circular orbit and a motion coplanar with the disk. The first detailed spectral energy distribution of PDS 70 b indicates a temperature typical of young giant planets. The detailed atmospheric analysis indicates that a circumplanetary disk may contribute to the total planetflux.

scholarly journals The Optical/Near-IR Colours of Red Quasars

2000 ◽  
Vol 17 (1) ◽  
pp. 56-71 ◽  
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.

scholarly journals Surrogate modelling the Baryonic Universe – I. The colour of star formation

2020 ◽  
Vol 495 (2) ◽  
pp. 2088-2104
Author(s):  
Jonás Chaves-Montero ◽  
Andrew Hearin
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
Principal Component ◽  
Major Axis ◽  
Sloan Digital Sky Survey ◽  
Star Formation History ◽  
Spectral Energy ◽  
Colour Space

ABSTRACT The spectral energy distribution of a galaxy emerges from the complex interplay of many physical ingredients, including its star formation history (SFH), metallicity evolution, and dust properties. Using galaxpy, a new galaxy spectral prediction tool, and SFHs predicted by the empirical model universemachine and the cosmological hydrodynamical simulation IllustrisTNG, we isolate the influence of SFH on optical and near-infrared colours from 320 to 1080 Å at z = 0. By carrying out a principal component analysis, we show that physically motivated SFH variations modify galaxy colours along a single direction in colour space: the SFH-direction. We find that the projection of a galaxy’s present-day colours on to the SFH-direction is almost completely regulated by the fraction of stellar mass that the galaxy formed over the last billion years. Together with cosmic downsizing, this results in galaxies becoming redder as their host halo mass increases. We additionally study the change in galaxy colours due to variations in metallicity, dust attenuation, and nebular emission lines, finding that these properties vary broad-band colours along distinct directions in colour space relative to the SFH-direction. Finally, we show that the colours of low-redshift Sloan Digital Sky Survey galaxies span an ellipsoid with significant extent along two independent dimensions, and that the SFH-direction is well-aligned with the major axis of this ellipsoid. Our analysis supports the conclusion that variations in SFH are the dominant influence on present-day galaxy colours, and that the nature of this influence is strikingly simple.

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

2020 ◽  
Vol 633 ◽  
pp. A152 ◽  
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%.

scholarly journals Morpho-photometric redshifts

2019 ◽  
Vol 489 (4) ◽  
pp. 4802-4808 ◽  
Author(s):  
Kristen Menou
Keyword(s):  
Poor Performance ◽  
Sloan Digital Sky Survey ◽  
Gradient Boosting ◽  
Learning Tools ◽  
Multi Layer Perceptron ◽  
Comparable Data ◽  
Photometric Redshifts ◽  
Data Set ◽  
Photometric Redshift ◽  
Sky Survey

ABSTRACT Machine learning (ML) is one of two standard approaches (together with SED fitting) for estimating the redshifts of galaxies when only photometric information is available. ML photo-z solutions have traditionally ignored the morphological information available in galaxy images or partly included it in the form of hand-crafted features, with mixed results. We train a morphology-aware photometric redshift machine using modern deep learning tools. It uses a custom architecture that jointly trains on galaxy fluxes, colours, and images. Galaxy-integrated quantities are fed to a Multi-Layer Perceptron (MLP) branch, while images are fed to a convolutional (convnet) branch that can learn relevant morphological features. This split MLP-convnet architecture, which aims to disentangle strong photometric features from comparatively weak morphological ones, proves important for strong performance: a regular convnet-only architecture, while exposed to all available photometric information in images, delivers comparatively poor performance. We present a cross-validated MLP-convnet model trained on 130 000 SDSS-DR12 (Sloan Digital Sky Survey – Data Release 12) galaxies that outperforms a hyperoptimized Gradient Boosting solution (hyperopt+XGBoost), as well as the equivalent MLP-only architecture, on the redshift bias metric. The fourfold cross-validated MLP-convnet model achieves a bias δz/(1 + z) = −0.70 ± 1 × 10−3, approaching the performance of a reference ANNZ2 ensemble of 100 distinct models trained on a comparable data set. The relative performance of the morphology-aware and morphology-blind models indicates that galaxy morphology does improve ML-based photometric redshift estimation.

scholarly journals The Spectral Energy Distribution of the Earliest Phases of Massive Star Formation

2015 ◽  
Vol 12 (S316) ◽  
pp. 151-152
Author(s):  
Randolf Klein ◽  
Jennifer Cooper ◽  
Leslie Looney ◽  
Thomas Henning ◽  
Sukanya Chakrabarti ◽  
...  
Keyword(s):  
Star Formation ◽  
Energy Distribution ◽  
Massive Star ◽  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Status Report ◽  
Massive Star Formation ◽  
Data Set ◽  
Good Spatial Resolution ◽  
Early Phases

AbstractWe have selected cold and massive (M > 100M⊙) cores as candidates for early phases of star formation from millimeter continuum surveys without associations at short wavelengths. We compared the millimeter continuum peak positions with IR and radio catalogs and excluded cores that had sources associated with the cores’ peaks. We compiled a list of 173 cores in over 117 regions that are candidates for very early phases of Massive Star Formation (MSF). Now with the Spitzer and Herschel archives, these cores can be characterized further. We are compiling this data set to construct the complete spectral energy distribution (SED) in the mid- and far-infrared with good spatial resolution and broad spectral coverage. This allow us to disentangle the complex regions and model the SED of the deeply embedded protostars/clusters. We present a status report of our efforts: a preview of the IR properties of all cores and their embedded source inferred from a grey body fit to the compiled SEDs.

scholarly journals Stellar Populations in M31 from Broad-band Photometry

2010 ◽  
Vol 6 (S277) ◽  
pp. 199-202
Author(s):  
Antti Tamm ◽  
Elmo Tempel ◽  
Peeter Tenjes ◽  
Taavi Tuvikene
Keyword(s):  
Complex Structure ◽  
Broad Band ◽  
Far Infrared ◽  
Stellar Populations ◽  
Sloan Digital Sky Survey ◽  
Spectral Energy ◽  
3 Dimensional ◽  
Sky Survey ◽  
The Galaxy ◽  
M 31

AbstractDue to its proximity, size, complex structure and high inclination angle, M31 offers an excellent opportunity for studying galactic structures outside the Milky Way and for drawing implications for their cosmological origin. We have studied the stellar populations of M 31 using the Sloan Digital Sky Survey (SDSS) photometry and the Spitzer far-infrared (FIR) mappings of dust. Combining these data, we have constructed a 3-dimensional model of the galaxy, laying constraints on the intrinsic (dust-free) properties of the galaxy and its stellar populations: their apparent and intrinsic luminosities, luminosity distributions, colours, shapes and sizes. We have interpreted the derived spectral energy distributions with synthetic stellar populations created with the Starburst99 software, in order to constrain the ages and masses of the stellar components.

scholarly journals SFR Relation with Galaxy Environment and Colour at z between 0.03 and 0.1

2006 ◽  
Vol 2 (S235) ◽  
pp. 234-235
Author(s):  
Premana W. Premadi ◽  
A. Sitti Maryam
Keyword(s):  
Galaxy Evolution ◽  
Sloan Digital Sky Survey ◽  
Emission Lines ◽  
Limited Sample ◽  
Data Set ◽  
Star Forming ◽  
Diagnostic Diagram ◽  
Sky Survey ◽  
Data Release ◽  
Galaxy Environment

This work is a preliminary result of our attempt to examine the use of SFR in the study of galaxy evolution. For this purpose we use the Sloan Digital Sky Survey Data Release 2 (SDSS DR2) Abazajian et al. (2004) and the SFR Catalogue generated from this data set by Brinchmann et al. (2004) and Kaufmann et al. (2003). Following Kewley et al. (2001) we use the Diagnostic Diagram, log ([OIII]/Hβ) vs log ([NII]/Hα), to separate the star forming galaxies from other emission lines sources such as AGN. Choosing only those with S/N > 3 out of the Brinchmann et al. (2004) catalogue, we arrive at about 200 thousand galaxies as our starting SFR subsample. With 0.05 < z < 0.22 and limit at r = 17.77, the subsample can be used to reconstruct the properties of a volume limited sample of galaxies with M* = 6 1010Modot. We benefit from the fact that Brinchmann et al. (2004) SFR Catalogue has already been aperture-corrected using the likelihood distribution P(SFR/Li/colour) scheme. For the environment, we use the data generated by Kaufmann et al. (2003), and arrive at about 40 thousand target galaxies. In this work the environment is characterised by the number (N=0-30) of neighbouring galaxies within a projected radius of 2 Mpc and velocity di.erence of 500km/s from each target galaxy, and the magnitude limit is 14.5 < r < 17.77.

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