43 research outputs found
Distribution of Maximal Luminosity of Galaxies in the Sloan Digital Sky Survey
Extreme value statistics (EVS) is applied to the distribution of galaxy luminosities in the Sloan Digital Sky Survey (SDSS). We analyze the DR8 Main Galaxy Sample (MGS), as well as the Luminous Red Galaxies (LRG). Maximal luminosities are sampled from batches consisting of elongated pencil beams in the radial direction of sight. For the MGS, results suggest a small and positive tail index , effectively ruling out the possibility of having a finite maximum cutoff luminosity, and implying that the luminosity distribution function may decay as a power law at the high luminosity end. Assuming, however, , a non-parametric comparison of the maximal luminosities with the Fisher-Tippett-Gumbel distribution (limit distribution for variables distributed by the Schechter fit) indicates a good agreement provided uncertainties arising both from the finite batch size and from the batch size distribution are accounted for. For a volume limited sample of LRGs, results show that they can be described as being the extremes of a luminosity distribution with an exponentially decaying tail, provided the uncertainties related to batch-size distribution are taken care of
Single parameter galaxy classification: The Principal Curve through the multi-dimensional space of galaxy properties
We propose to describe the variety of galaxies from SDSS by using only one
affine parameter. To this aim, we build the Principal Curve (P-curve) passing
through the spine of the data point cloud, considering the eigenspace derived
from Principal Component Analysis of morphological, physical and photometric
galaxy properties. Thus, galaxies can be labeled, ranked and classified by a
single arc length value of the curve, measured at the unique closest projection
of the data points on the P-curve. We find that the P-curve has a "W" letter
shape with 3 turning points, defining 4 branches that represent distinct galaxy
populations. This behavior is controlled mainly by 2 properties, namely u-r and
SFR. We further present the variations of several galaxy properties as a
function of arc length. Luminosity functions variate from steep Schechter fits
at low arc length, to double power law and ending in Log-normal fits at high
arc length. Galaxy clustering shows increasing autocorrelation power at large
scales as arc length increases. PCA analysis allowed to find peculiar galaxy
populations located apart from the main cloud of data points, such as small red
galaxies dominated by a disk, of relatively high stellar mass-to-light ratio
and surface mass density. The P-curve allows not only dimensionality reduction,
but also provides supporting evidence for relevant physical models and
scenarios in extragalactic astronomy: 1) Evidence for the hierarchical merging
scenario in the formation of a selected group of red massive galaxies. These
galaxies present a log-normal r-band luminosity function, which might arise
from multiplicative processes involved in this scenario. 2) Connection between
the onset of AGN activity and star formation quenching, which appears in green
galaxies when transitioning from blue to red populations. (Full abstract in
downloadable version)Comment: Full abstract in downloadable versio
Probing Spectroscopic Variability of Galaxies & Narrow-Line Active Galactic Nuclei in the Sloan Digital Sky Survey
Under the unified model for active galactic nuclei (AGNs), narrow-line (Type
2) AGNs are, in fact, broad-line (Type 1) AGNs but each with a heavily obscured
accretion disk. We would therefore expect the optical continuum emission from
Type 2 AGN to be composed mainly of stellar light and non-variable on the
time-scales of months to years. In this work we probe the spectroscopic
variability of galaxies and narrow-line AGNs using the multi-epoch data in the
Sloan Digital Sky Survey (SDSS) Data Release 6. The sample contains 18,435
sources for which there exist pairs of spectroscopic observations (with a
maximum separation in time of ~700 days) covering a wavelength range of
3900-8900 angstrom. To obtain a reliable repeatability measurement between each
spectral pair, we consider a number of techniques for spectrophotometric
calibration resulting in an improved spectrophotometric calibration of a factor
of two. From these data we find no obvious continuum and emission-line
variability in the narrow-line AGNs on average -- the spectroscopic variability
of the continuum is 0.07+/-0.26 mag in the g band and, for the emission-line
ratios log10([NII]/Halpha) and log10([OIII]/Hbeta), the variability is
0.02+/-0.03 dex and 0.06+/-0.08 dex, respectively. From the continuum
variability measurement we set an upper limit on the ratio between the flux of
varying spectral component, presumably related to AGN activities, and that of
host galaxy to be ~30%. We provide the corresponding upper limits for other
spectral classes, including those from the BPT diagram, eClass galaxy
classification, stars and quasars.Comment: AJ accepte
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
The 16th Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17)
Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
We describe the Sloan Digital Sky Survey IV (SDSS-IV), a project encompassing three major spectroscopic programs. The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is observing hundreds of thousands of Milky Way stars at high resolution and high signal-to-noise ratios in the near-infrared. The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey is obtaining spatially resolved spectroscopy for thousands of nearby galaxies (median ). The extended Baryon Oscillation Spectroscopic Survey (eBOSS) is mapping the galaxy, quasar, and neutral gas distributions between and 3.5 to constrain cosmology using baryon acoustic oscillations, redshift space distortions, and the shape of the power spectrum. Within eBOSS, we are conducting two major subprograms: the SPectroscopic IDentification of eROSITA Sources (SPIDERS), investigating X-ray AGNs and galaxies in X-ray clusters, and the Time Domain Spectroscopic Survey (TDSS), obtaining spectra of variable sources. All programs use the 2.5 m Sloan Foundation Telescope at the Apache Point Observatory; observations there began in Summer 2014. APOGEE-2 also operates a second near-infrared spectrograph at the 2.5 m du Pont Telescope at Las Campanas Observatory, with observations beginning in early 2017. Observations at both facilities are scheduled to continue through 2020. In keeping with previous SDSS policy, SDSS-IV provides regularly scheduled public data releases; the first one, Data Release 13, was made available in 2016 July
Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
We describe the Sloan Digital Sky Survey IV (SDSS-IV), a project encompassing three major spectroscopic programs. The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is observing hundreds of thousands of Milky Way stars at high resolution and high signal-to-noise ratios in the near-infrared. The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey is obtaining spatially resolved spectroscopy for thousands of nearby galaxies (median ). The extended Baryon Oscillation Spectroscopic Survey (eBOSS) is mapping the galaxy, quasar, and neutral gas distributions between and 3.5 to constrain cosmology using baryon acoustic oscillations, redshift space distortions, and the shape of the power spectrum. Within eBOSS, we are conducting two major subprograms: the SPectroscopic IDentification of eROSITA Sources (SPIDERS), investigating X-ray AGNs and galaxies in X-ray clusters, and the Time Domain Spectroscopic Survey (TDSS), obtaining spectra of variable sources. All programs use the 2.5 m Sloan Foundation Telescope at the Apache Point Observatory; observations there began in Summer 2014. APOGEE-2 also operates a second near-infrared spectrograph at the 2.5 m du Pont Telescope at Las Campanas Observatory, with observations beginning in early 2017. Observations at both facilities are scheduled to continue through 2020. In keeping with previous SDSS policy, SDSS-IV provides regularly scheduled public data releases; the first one, Data Release 13, was made available in 2016 July
The Eighteenth Data Release of the Sloan Digital Sky Surveys: Targeting and First Spectra from SDSS-V
The eighteenth data release of the Sloan Digital Sky Surveys (SDSS) is the
first one for SDSS-V, the fifth generation of the survey. SDSS-V comprises
three primary scientific programs, or "Mappers": Milky Way Mapper (MWM), Black
Hole Mapper (BHM), and Local Volume Mapper (LVM). This data release contains
extensive targeting information for the two multi-object spectroscopy programs
(MWM and BHM), including input catalogs and selection functions for their
numerous scientific objectives. We describe the production of the targeting
databases and their calibration- and scientifically-focused components. DR18
also includes ~25,000 new SDSS spectra and supplemental information for X-ray
sources identified by eROSITA in its eFEDS field. We present updates to some of
the SDSS software pipelines and preview changes anticipated for DR19. We also
describe three value-added catalogs (VACs) based on SDSS-IV data that have been
published since DR17, and one VAC based on the SDSS-V data in the eFEDS field.Comment: Accepted to ApJ
The eighteenth data release of the Sloan Digital Sky Surveys : targeting and first spectra from SDSS-V
The eighteenth data release of the Sloan Digital Sky Surveys (SDSS) is the first one for SDSS-V, the fifth generation of the survey. SDSS-V comprises three primary scientific programs, or "Mappers": Milky Way Mapper (MWM), Black Hole Mapper (BHM), and Local Volume Mapper (LVM). This data release contains extensive targeting information for the two multi-object spectroscopy programs (MWM and BHM), including input catalogs and selection functions for their numerous scientific objectives. We describe the production of the targeting databases and their calibration- and scientifically-focused components. DR18 also includes ~25,000 new SDSS spectra and supplemental information for X-ray sources identified by eROSITA in its eFEDS field. We present updates to some of the SDSS software pipelines and preview changes anticipated for DR19. We also describe three value-added catalogs (VACs) based on SDSS-IV data that have been published since DR17, and one VAC based on the SDSS-V data in the eFEDS field.Publisher PDFPeer reviewe