- ID:
- ivo://CDS.VizieR/J/ApJ/888/36
- Title:
- SDSS/FIRST dwarf galaxies with VLA high res. obs.
- Short Name:
- J/ApJ/888/36
- Date:
- 25 Oct 2021 10:17:58
- Publisher:
- CDS
- Description:
- We present a sample of nearby dwarf galaxies with radio-selected accreting massive black holes (BHs), the majority of which are non-nuclear. We observed 111 galaxies using sensitive, high-resolution observations from the Karl G. Jansky Very Large Array (VLA) in its most extended A-configuration at X band (~8-12GHz), yielding a typical angular resolution of ~0.25" and rms noise of ~15{mu}Jy. Our targets were selected by crossmatching galaxies with stellar masses M_*_<=3x10^9^M_{sun}_ and redshifts z<0.055 in the NASA-Sloan Atlas with the VLA Faint Images of the Radio Sky at Twenty centimeters Survey. With our new high-resolution VLA observations, we detect compact radio sources toward 39 galaxies and carefully evaluate possible origins for the radio emission, including thermal HII regions, supernova remnants, younger radio supernovae, background interlopers, and active galactic nuclei (AGNs) in the target galaxies. We find that 13 dwarf galaxies almost certainly host active massive BHs, despite the fact that only one object was previously identified as having optical signatures of an AGN. We also identify a candidate dual radio AGN in a more massive galaxy system. The majority of the radio-detected BHs are offset from the center of the host galaxies, with some systems showing signs of interactions/mergers. Our results indicate that massive BHs need not always live in the nuclei of dwarf galaxies, confirming predictions from simulations. Moreover, searches attempting to constrain BH seed formation using observations of dwarf galaxies need to account for such a population of "wandering" BHs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/894
- Title:
- SDSS galaxies classification
- Short Name:
- J/MNRAS/477/894
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an automated method for the detection of bar structure in optical images of galaxies using a deep convolutional neural network that is easy to use and provides good accuracy. In our study, we use a sample of 9346 galaxies in the redshift range of 0.009-0.2 from the Sloan Digital Sky Survey (SDSS), which has 3864 barred galaxies, the rest being unbarred. We reach a top precision of 94 per cent in identifying bars in galaxies using the trained network. This accuracy matches the accuracy reached by human experts on the same data without additional information about the images. Since deep convolutional neural networks can be scaled to handle large volumes of data, the method is expected to have great relevance in an era where astronomy data is rapidly increasing in terms of volume, variety, volatility, and velocity along with other V's that characterize big data. With the trained model, we have constructed a catalogue of barred galaxies from SDSS and made it available online.
- ID:
- ivo://CDS.VizieR/J/A+A/648/A122
- Title:
- SDSS galaxies morphological classification
- Short Name:
- J/A+A/648/A122
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Machine learning methods are effective tools in astronomical tasks for classifying objects by their individual features. One of the promising utilities is related to the morphological classification of galaxies at different redshifts. We use the photometry-based approach for the SDSS data (1) to exploit five supervised machine learning techniques and define the most effective among them for the automated galaxy morphological classification; (2) to test the influence of photometry data on morphology classification; (3) to discuss problem points of supervised machine learning and labeling bias; and (4) to apply the best fitting machine learning methods for revealing the unknown morphological types of galaxies from the SDSS DR9 at z<0.1. We used different galaxy classification techniques: human labeling, multi-photometry diagrams, naive Bayes, logistic regression, support-vector machine, random forest, k-nearest neighbors. We present the results of a binary automated morphological classification of galaxies conducted by human labeling, multi-photometry, and five supervised machine learning methods. We applied it to the sample of galaxies from the SDSS DR9 with redshifts of 0.02<z<0.1 and absolute stellar magnitudes of -24mag<Mr<-19.4mag. For the analysis we used absolute magnitudes Mu, Mg, Mr, Mi, Mz; color indices Mu-Mr, Mg-Mi, Mu-Mg, Mr-Mz; and the inverse concentration index to the center R50/R90. We determined the ability of each method to predict the morphological type, and verified various dependencies of the method's accuracy on redshifts, human labeling, morphological shape, and overlap of different morphological types for galaxies with the same color indices. We find that the morphology based on the supervised machine learning methods trained over photometric parameters demonstrates significantly less bias than the morphology based on citizen-science classifiers. The support-vector machine and random forest methods with Scikit-learn software machine learning library in Python provide the highest accuracy for the binary galaxy morphological classification. Specifically, the success rate is 96.4% for support-vector machine (96.1% early E and 96.9% late L types) and 95.5% for random forest (96.7% early E and 92.8% late L types). Applying the support-vector machine for the sample of 316 031 galaxies from the SDSS DR9 at z<0.1 with unknown morphological types, we found 139659 E and 176372 L types among them.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/1274
- Title:
- SDSS-II SN Ia BVRI photometry
- Short Name:
- J/MNRAS/465/1274
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analysed multiband light curves of 328 intermediate-redshift (0.05<=z<0.24) Type Ia supernovae (SNe Ia) observed by the Sloan Digital Sky Survey-II Supernova Survey. The multiband light curves were parametrized by using the multiband stretch method, which can simply parametrize light-curve shapes and peak brightness without dust extinction models. We found that most of the SNe Ia that appeared in red host galaxies (u-r>2.5) do not have a broad light-curve width and the SNe Ia that appeared in blue host galaxies (u-r<2.0) have a variety of light-curve widths. The Kolmogorov-Smirnov test shows that the colour distribution of SNe Ia appearing in red/blue host galaxies is different (a significance level of 99.9 per cent). We also investigate the extinction law of host galaxy dust. As a result, we find that the value of Rv derived from SNe Ia with medium light-curve widths is consistent with the standard Galactic value, whereas the value of Rv derived from SNe Ia that appear in red host galaxies becomes significantly smaller. These results indicate that there may be two types of SNe Ia with different intrinsic colours, and that they are obscured by host galaxy dust with two different properties.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/115
- Title:
- SDSS-II SN Survey: host-galaxy spectral data
- Short Name:
- J/ApJ/821/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the largest single-survey sample of Type Ia supernovae (SNe Ia) to date, we study the relationship between properties of SNe Ia and those of their host galaxies, focusing primarily on correlations with Hubble residuals (HRs). Our sample consists of 345 photometrically classified or spectroscopically confirmed SNe Ia discovered as part of the SDSS-II Supernova Survey (SDSS-SNS). This analysis utilizes host-galaxy spectroscopy obtained during the SDSS-I/II spectroscopic survey and from an ancillary program on the SDSS-III Baryon Oscillation Spectroscopic Survey that obtained spectra for nearly all host galaxies of SDSS-II SN candidates. In addition, we use photometric host-galaxy properties from the SDSS-SNS data release such as host stellar mass and star formation rate. We confirm the well-known relation between HR and host-galaxy mass and find a 3.6{sigma} significance of a nonzero linear slope. We also recover correlations between HR and host-galaxy gas-phase metallicity and specific star formation rate as they are reported in the literature. With our large data set, we examine correlations between HR and multiple host-galaxy properties simultaneously and find no evidence of a significant correlation. We also independently analyze our spectroscopically confirmed and photometrically classified SNe Ia and comment on the significance of similar combined data sets for future surveys.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/1831
- Title:
- SDSS-IV eBOSS ELG UgrizW photometry
- Short Name:
- J/MNRAS/465/1831
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present two wide-field catalogues of photometrically selected emission line galaxies (ELGs) at z~=0.8 covering about 2800deg^2^ over the south galactic cap. The catalogues were obtained using a Fisher discriminant technique described in a companion paper. The two catalogues differ by the imaging used to define the Fisher discriminant: the first catalogue includes imaging from the Sloan Digital Sky Survey and the Wide-field InfraredSurvey Explorer, the second also includes information from the South Galactic Cap U-band Sky Survey. Containing respectively 560045 and 615601 objects, they represent the largest ELG catalogues available today and were designed for the ELG programme of the extended Baryon Oscillation Spectroscopic Survey (eBOSS). We study potential sources of systematic variation in the angular distribution of the selected ELGs due to fluctuations of the observational parameters. We model the influence of the observational parameters using a multivariate regression and implement a weighting scheme which allows effective removal of all of the systematic errors induced by the observational parameters. We show that fluctuations in the imaging zero-points of the photometric bands have minor impact on the angular distribution of objects in our catalogues. We compute the angular clustering of both catalogues and show that our weighting procedure effectively removes spurious clustering on large scales. We fit a model to the small-scale angular clustering, showing that the selections have similar biases of 1.35/Da(z) and 1.28/Da(z). Both catalogues are publicly available.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A121
- Title:
- SDSS-IV eBOSS emission-line galaxy pilot survey
- Short Name:
- J/A+A/592/A121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Sloan Digital Sky Survey IV extended Baryonic Oscillation Spectroscopic Survey (SDSS-IV/eBOSS) will observe 195,000 emission-line galaxies (ELGs) to measure the Baryonic Acoustic Oscillation standard ruler (BAO) at redshift 0.9. To test different ELG selection algorithms, based on data from several imaging surveys, 9,000 spectra were observed with the SDSS spectrograph as a pilot survey. First, using visual inspection and redshift quality flags, we find that the automated spectroscopic redshifts assigned by the pipeline meet the quality requirements for a robust BAO measurement. Also, we show the correlations between sky emission, signal-to-noise ratio in the emission lines and redshift error. Then we provide a detailed description of each target selection algorithm tested and compare them with the requirements of the eBOSS experiment. As a result, we provide robust redshift distributions for the different target selection schemes tested. Finally, we infer two optimal target selection algorithms to be applied on DECam photometry that fulfill the eBOSS survey electronic efficiency requirements.
- ID:
- ivo://CDS.VizieR/J/ApJ/863/134
- Title:
- SDSS low-metallicity blue compact dwarf galaxies
- Short Name:
- J/ApJ/863/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a method of identifying candidate low-metallicity blue compact dwarf galaxies (BCDs) from the Sloan Digital Sky Survey (SDSS) imaging data, and present 3m Lick Observatory and 10m W.M. Keck Observatory optical spectroscopic observations of 94 new systems that have been discovered with this method. The candidate BCDs are selected from Data Release 12 (DR12) of SDSS on the basis of their photometric colors and morphologies. Using the Kast spectrometer on the 3m telescope, we confirm that the candidate low-metallicity BCDs are emission-line galaxies, and we make metallicity estimates using the empirical R and S calibration methods. Follow-up observations on a subset of the lowest-metallicity systems are made at Keck using the Low Resolution Imaging Spectrometer, which allow for a direct measurement of the oxygen abundance. We determine that 45 of the reported BCDs are low-metallicity candidates with 12+log(O/H)<=7.65, including six systems which are either confirmed or projected to be among the lowest-metallicity galaxies known, at 1/30 of the solar oxygen abundance, or 12+log(O/H)~7.20.
- ID:
- ivo://CDS.VizieR/J/MNRAS/377/787
- Title:
- SDSS Luminous Red Galaxies
- Short Name:
- J/MNRAS/377/787
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The data are taken from the Luminous Red Galaxy sample of the Sloan Digital Sky Survey Data Release 4. From the SDSS spectra we compute the five indices Hbeta, Hgamma_F_, Dn(4000), [MgFe]', [Mg1Fe]'. These are matched indices from a synthetic library of spectra containing 31000 different star formation scenarios. From this we can infer probability distributions for a number of properties, such as age, metallicity, etc. The results are presented here as the 5th, 16th, 50th (median), 86th and 95th percentiles of the relevant distribution. The 4391 LRG properties presented here are chosen from the redshift range 0.15<z<0.4 and require all 5 of the above indices to have well-measured values (i.e. no contamination from skylines, bad pixels) Also given are a number of properties that come directly from the SDSS database, such as redshift, velocity dispersion etc. For the luminosity distance calculation (and subsequent mass estimates), we assume a FRW metric, with omega_m_=0.25, omega_lambda_=0.75 and H_0_=73km/s/Mpc.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/52
- Title:
- SDSS luminous red galaxies concentrations
- Short Name:
- J/ApJ/769/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The best gravitational lenses for detecting distant galaxies are those with the largest mass concentrations and the most advantageous configurations of that mass along the line of sight. Our new method for finding such gravitational telescopes uses optical data to identify projected concentrations of luminous red galaxies (LRGs). LRGs are biased tracers of the underlying mass distribution, so lines of sight with the highest total luminosity in LRGs are likely to contain the largest total mass. We apply this selection technique to the Sloan Digital Sky Survey and identify the 200 fields with the highest total LRG luminosities projected within a 3.5' radius over the redshift range 0.1<=z<=0.7. The redshift and angular distributions of LRGs in these fields trace the concentrations of non-LRG galaxies. These fields are diverse; 22.5% contain one known galaxy cluster and 56.0% contain multiple known clusters previously identified in the literature. Thus, our results confirm that these LRGs trace massive structures and that our selection technique identifies fields with large total masses. These fields contain two to three times higher total LRG luminosities than most known strong-lensing clusters and will be among the best gravitational lensing fields for the purpose of detecting the highest redshift galaxies.
