NASA/IPAC Extragalactic Database Research Articles

Estimating the evolution and the content fractions of baryonic gas for Luminous Infrared Galaxies

ABSTRACT Luminous Infrared Galaxies (LIRGs) play a crucial role in understanding of galaxy evolution. The present study examined 82 LIRGs, using data taken from the Sloan Digital Sky Survey (SDSS), NASA/IPAC Extragalactic Database (NED), and HyperLEDA to explore their gas fractions and optical properties. The analysis of data highlights the relationship between molecular-to-atomic mass of hydrogen gas ratio $M_{\text{H}_2}/M_{\rm{H {}{\small I}}}$ and morphological types, gas mass fractions, and galaxy characteristics such as color and luminosity. The results showed that the regressions between $M_{\text{dust}} - M^{*,V}$ and $M_{\text{dust}} - \text{SFR}$ are not quite flat (when correlation coefficient > 0.5), which indicates a decrease in the dust-to-stellar content ratio as the gas is consumed and transformed into stars, and also a relatively flat trend for $M_{\text{dust}} - M^{*,V}$ and $f_{\text{dust,bar}} - M^{*,V}$. Moreover, as the star’s mass declines, the total gas mass fraction ($f_{\text{gas}}$) increases quickly, with a high negative correlation coefficient of –0.7 and a regression of –0.85. Therefore, it can be inferred that galaxies with a high gas fraction ($f_{\text{gas}}$) are either accreting gas at a rate sufficient to meet their energy requirements for star formation or converting gas into stars less effectively. According to the findings, the gas exhaustion time in these galaxies quickly reduces as the stellar mass increases, with a significant negative correlation coefficient of –0.7 and a regression that is a nearly linear regression of –0.9. On the other hand, when the baryonic gas mass fraction grows, which makes up the majority of the baryonic gas, grows, the gas depletion time increases quickly.

Comparison of the Physical Trace of Global Luminosity Emission at Multiwavelength and Star Formation Rates of Luminous Infrared Galaxies Using Extragalactic Distance Scale Techniques

This paper aims to study the rate of star formation (SFR) in luminous infrared galaxies at different wavelengths using distance measurement techniques (dl, dm) and to know which methods are the most accurate to determine the rate of star formation as we present through this research the results of the statistical analysis (descriptive statistics) for a sample of luminous infrared galaxies. The data used in this research were collected from the NASA Extragalactic Database (NED) and HYPERLEDA, then used to calculate the star formation rate and indicate the accuracy of the distance methods used (dl, dm). Two methods were tested on Hα, OII, FIR, radio continuum at 1.4 GHz, FUV, NUV, and total (FUV + FIR). The results showed that the dl measurement method has the most accuracy in calculating SFR as it depends on the redshift where the relationship between them is direct. while the other distance method (dm) depends on absolute blue magnitude (MB), it was somewhat less accurate, but the two methods are helpful for this type of calculation.

The Relationships of Dust and Total Masses of Luminous Infrared Galaxies with Their Far Infrared and Total Luminosities Using Two Methods of Distance Measurements

This research aims to determine the nature of the relationships among luminous infrared galaxies (LIRGs) by using different methods of distance measurement (distance modulus “dm” and luminosity distance “dl”). We used data from the following sources: NASA Extragalactic Database (NED) and the HYPERLEDA database, where this data was used to study the nature of the relationships and the extent to which they relate to each other. The program (statistica-win-program) was employed, which helped us know the strength of the association between the variables. The results of the statistical analysis showed that there was a strong correlation between dust mass (Mdust dm & Mdust dl) and luminous infrared (LFIRdm, LIRdm) & (LFIRdl, LIRdl), where the partial correlation coefficient was equal to (R⋍0.7) and the slope was linear. There was also a positive correlation between (LFIRdm, LFIRdl)& ( ) where the partial correlation coefficient was (R⋍0.4) with a linear slope. The relationship between (LIR)& ( ) was a positive relation in the modulus distance case (dm), where its correlation was equal to (R⋍0.4), but in another case (luminosity distance), the relation was very weak, and the correlation was (R⋍0.2). The relationship between total masses ( ) & (LFIRdm, dl­­) in both cases of distance (dm) & (dl) was good, and the partial correlation coefficient was equal to (R⋍0.4) with a linear slope. The relationship between (LIR) & ( ) in both cases of distance was also positive, and the partial correlation coefficient was equal to (R⋍0.3). There was an inverse relationship between the ratio fluxes (F100/F60) & ( ), as well as a very tight partial correlation coefficient, which was equal to (R⋍-0.9) with a slope of (-1).

Completeness of the NASA/IPAC Extragalactic Database (NED) Local Volume Sample

Abstract We introduce the NASA/IPAC Extragalactic Database (NED) Local Volume Sample (NED-LVS), a subset of ∼1.9 million objects with distances out to 1000 Mpc. We use UV and IR fluxes available in NED from all-sky surveys to derive physical properties, and estimate the completeness relative to the expected local luminosity density. The completeness relative to near-IR luminosities (which traces a galaxy’s stellar mass) is roughly 100% at D < 30 Mpc and remains moderate (70%) out to 300 Mpc. For brighter galaxies (≳L *), NED-LVS is ∼100% complete out to ∼400 Mpc. When compared to other local Universe samples (GLADE and HECATE), all three are ∼100% complete below 30 Mpc. At distances beyond ∼80 Mpc, NED-LVS is more complete than both GLADE and HECATE by ∼10%–20%. NED-LVS is the underlying sample for the NED gravitational-wave follow-up service (NED-GWF), which provides prioritized lists of host candidates for GW events within minutes of alerts issued by the LIGO–Virgo–KAGRA collaboration. We test the prioritization of galaxies in the volume of GW170817 by three physical properties, where we find that both stellar mass and inverse specific star formation rate place the correct host galaxy in the top 10. In addition, NED-LVS can be used for a wide variety of other astrophysical studies: galaxy evolution, star formation, large-scale structure, galaxy environments, and more. The data in NED are updated regularly, and NED-LVS will be updated concurrently. Consequently, NED-LVS will continue to provide an increasingly complete sample of galaxies for a multitude of astrophysical research areas for years to come.

Harnessing the Hubble Space Telescope Archives: A Catalog of 21,926 Interacting Galaxies

Mergers play a complex role in galaxy formation and evolution. Continuing to improve our understanding of these systems requires ever larger samples, which can be difficult (even impossible) to select from individual surveys. We use the new platform ESA Datalabs to assemble a catalog of interacting galaxies from the Hubble Space Telescope science archives; this catalog is larger than previously published catalogs by nearly an order of magnitude. In particular, we apply the Zoobot convolutional neural network directly to the entire public archive of HST F814W images and make probabilistic interaction predictions for 126 million sources from the Hubble Source Catalog. We employ a combination of automated visual representation and visual analysis to identify a clean sample of 21,926 interacting galaxy systems, mostly with z < 1. Sixty-five percent of these systems have no previous references in either the NASA Extragalactic Database or Simbad. In the process of removing contamination, we also discover many other objects of interest, such as gravitational lenses, edge-on protoplanetary disks, and “backlit” overlapping galaxies. We briefly investigate the basic properties of this sample, and we make our catalog publicly available for use by the community. In addition to providing a new catalog of scientifically interesting objects imaged by HST, this work also demonstrates the power of the ESA Datalabs tool to facilitate substantial archival analysis without placing a high computational or storage burden on the end user.

A 0.6 Mpc H i structure associated with Stephan’s Quintet

Stephan’s Quintet (SQ, co-moving radial distance = 85 ± 6 Mpc, taken from the NASA/IPAC Extragalactic Database (NED)1) is unique among compact groups of galaxies2–12. Observations have previously shown that interactions between multiple members, including a high-speed intruder galaxy currently colliding into the intragroup medium, have probably generated tidal debris in the form of multiple gaseous and stellar filaments6,8,13, the formation of tidal dwarfs7,14,15 and intragroup-medium starbursts16, as well as widespread intergalactic shocked gas5,10,11,17. The details and timing of the interactions and collisions remain poorly understood because of their multiple nature18,19. Here we report atomic hydrogen (H i) observations in the vicinity of SQ with a smoothed sensitivity of 1σ = 4.2 × 1016 cm−2 per channel (velocity bin-width Δv = 20 km s−1; angular resolution = 4′), which are about two orders of magnitude deeper than previous observations8,13,20,21. The data show a large H i structure (with linear scale of around 0.6 Mpc) encompassing an extended source of size approximately 0.4 Mpc associated with the debris field and a curved diffuse feature of length around 0.5 Mpc attached to the south edge of the extended source. The diffuse feature was probably produced by tidal interactions in early stages of the formation of SQ (>1 Gyr ago), although it is not clear how the low-density H i gas (NH i ≲ 1018 cm−2) can survive the ionization by the intergalactic ultraviolet background on such a long time scale. Our observations require a rethinking of properties of gas in outer parts of galaxy groups and demand complex modelling of different phases of the intragroup medium in simulations of group formation.

Constraints on extragalactic transmitters via Breakthrough Listen observations of background sources

ABSTRACT The Breakthrough Listen Initiative has embarked on a comprehensive Search for Extraterrestrial Intelligence (SETI) survey of nearby stars in the Milky Way that is vastly superior to previous efforts as measured by a wide range of different metrics. SETI surveys traditionally ignore the fact that they are sensitive to many background objects, in addition to the foreground target star. In order to better appreciate and exploit the presence of extragalactic objects in the field of view, the aladin sky atlas and NASA/IPAC Extragalactic Database (NED) were employed to make a rudimentary census of extragalactic objects that were serendipitously observed with the 100-m Green Bank Telescope observing at 1.1–1.9 GHz. For 469 target fields [assuming a full width at half-maximum (FWHM) radial field of view of 4.2 arcmin], NED identified a grand total of 143 024 extragalactic objects, including various astrophysical exotica e.g. active galactic nuclei (AGN) of various type, radio galaxies, interacting galaxies, and one confirmed gravitational lens system. Several nearby galaxies, galaxy groups, and galaxy clusters are identified, permitting the parameter space probed by SETI surveys to be significantly extended. Constraints are placed on the luminosity function of potential extraterrestrial transmitters assuming it follows a simple power law and limits on the prevalence of very powerful extraterrestrial transmitters associated with these vast stellar systems are also determined. It is demonstrated that the recent Breakthrough Listen Initiative, and indeed many previous SETI radio surveys, places stronger limits on the prevalence of extraterrestrial intelligence in the distant Universe than is often fully appreciated.

Comparing NED and SIMBAD classifications across the contents of nearby galaxies

ABSTRACT Cataloguing and classifying celestial objects is one of the fundamental activities of observational astrophysics. In this work, we compare the contents of two comprehensive data bases, the NASA Extragalactic Database (NED) and Set of Identifications, Measurements and Bibliography for Astronomical Data (SIMBAD) in the vicinity of nearby galaxies. These two data bases employ different classification schemes – one flat and one hierarchical – and our goal was to determine the compatibility of classifications for objects in common. Searching both data bases for objects within the respective isophotal radius of each of the ∼1300 individual galaxies in the Local Volume Galaxy sample, we found that, on average, NED contains about 10 times as many entries as SIMBAD and about two-thirds of SIMBAD objects are matched by position to a NED object, at 5 arcsec tolerance. These quantities do not depend strongly on the properties of the parent galaxies. We developed an algorithm to compare individual object classifications between the two data bases and found that 88 per cent of the classifications agree; we conclude that NED and SIMBAD contain consistent information for sources in common in the vicinity of nearby galaxies. Because many galaxies have numerous sources contained only in one of NED or SIMBAD, researchers seeking the most complete picture of an individual galaxy’s contents are best served by using both data bases.

Classification of Astrophysics Journal Articles with Machine Learning to Identify Data for NED

The NASA/IPAC Extragalactic Database (NED) is a comprehensive online service that combines fundamental multi-wavelength information for known objects beyond the Milky Way and provides value-added, derived quantities and tools to search and access the data. The contents and relationships between measurements in the database are continuously augmented and revised to stay current with astrophysics literature and new sky surveys. The conventional process of distilling and extracting data from the literature involves human experts to review the journal articles and determine if an article is of extragalactic nature, and if so, what types of data it contains. This is both labor intensive and unsustainable, especially given the ever-increasing number of publications each year. We present here a machine learning (ML) approach developed and integrated into the NED production pipeline to help automate the classification of journal article topics and their data content for inclusion into NED. We show that this ML application can successfully reproduce the classifications of a human expert to an accuracy of over 90% in a fraction of the time it takes a human, allowing us to focus human expertise on tasks that are more difficult to automate.

Improving NASA/IPAC Extragalactic Database Redshift Calculations

Abstract The NASA/IPAC Extragalactic Database (NED) is an impressive tool for finding near-exhaustive information on millions of astrophysical objects. Here, we outline a small systematic error that occurs in NED because a low-redshift approximation is used when making the correction from redshifts in the heliocentric frame to the cosmic microwave background (CMB) rest frame. It means that historically NED systematically misreported the values of CMB-frame redshifts by up to ∼10−3 z (about 0.001 at redshift of 1). This is a systematic error, and therefore the impact on applications requiring precise redshifts has the potential to be significant—for example, a systematic redshift error of ∼10−4 at low redshift could resolve the Hubble tension. We have consulted with the NED team and they are updating the software to remove this systematic error so these corrections are accurate at all redshifts. Here, we explain the changes and how they impact the redshift values NED currently reports.

Jellyfish galaxy candidates in MACS J0717.5+3745 and 39 other clusters of the DAFT/FADA and CLASH surveys

Context. Galaxies in clusters undergo several phenomena, such as RPS and tidal interactions, that can trigger or quench their star formation and, in some cases, lead to galaxies acquiring unusual shapes and long tails – some become jellyfish. Aims. We searched for jellyfish galaxy candidates in a sample of 40 clusters from the DAFT/FADA and CLASH surveys covering the redshift range 0.2 &lt; z &lt; 0.9. In MACS J0717.5+3745 (MACS0717), our large spatial coverage and abundant sampling of spectroscopic redshifts allowed us to pursue a detailed analysis of jellyfish galaxy candidates in this cluster and its extended filament. Methods. We retrieved galaxy spectroscopic redshifts in the NASA Extragalactic Database for galaxies in all the clusters of our sample (except for MACS0717 for which we had an extensive catalogue), looked at the Hubble Space Telescope ACS images of these objects (mainly the F606W and F814W bands), and classified them as a function of their likeliness to be jellyfish galaxies. We give catalogues of jellyfish galaxy candidates with positions, redshifts, magnitudes, and projected distance to their respective cluster centre. For MACS0717, an eight-magnitude optical and infrared catalogue covering the entire region allowed us to compute the best stellar population fits with LePhare through the GAZPAR interface. For the 31 jellyfish candidates in the other clusters belonging to the CLASH survey, we extracted up to 17 magnitudes available in the CLASH catalogues to fit their spectral energy distribution in the same way. Results. We found 81 jellyfish galaxy candidates in the extended region around MACS0717 as well as 97 in 22 other clusters. Jellyfish galaxy candidates in MACS0717 tend to avoid the densest regions of the cluster, while this does not appear to be the case in the other clusters. The best fit templates found by LePhare show that star formation is occurring. Stellar masses are in the range 109 − 1011 M⊙, and the star formation rates (SFRs) are in the 10−1 − 60 M⊙ yr−1 range for MACS0717 and in the 10−1 − 10 M⊙ yr−1 range for the other sample. Specific star formation rates (sSFRs) are notably higher in MACS0717, with more than half of the sample having values larger than 10−9 yr−1, while in the other clusters, most galaxies have sSFR &lt; 10−10 yr−1. Stellar populations appear younger in MACS0717 (more than half have an age smaller than 1.5 × 109 yrs), and, following mid-infrared criteria, two galaxies may contain an active galactic nucleus. In a SFR versus stellar mass diagram, jellyfish galaxy candidates appear to have somewhat larger SFRs than “non-jellyfish star-forming” galaxies. For MACS0717, the mean sSFR of the 79 jellyfish galaxy candidates is 3.2 times larger than that of star-forming non-jellyfish galaxies (selected with log(sSFR) ≥ − 11). Conclusions. Our jellyfish galaxy candidates are star-forming objects, with young ages and blue colours. Based on several arguments, the jellyfish candidates identified in MACS0717 seem to have fallen rather recently into the cluster. A very rough estimate of the proportions of jellyfish galaxies in the studied clusters is about 10%; this number does not seem to vary strongly with the cluster relaxation state, though this result must be confirmed with more data. Our sample of 97 galaxies in 22 clusters represents the basis of future works.

Chandra Survey of Nearby Galaxies: An Extended Catalog

Abstract She et al. (Paper I) assembled a catalog of nearby galaxies observed with the Chandra X-ray observatory, by cross-matching galaxies in the NASA Extragalactic Database within 50 Mpc and the Chandra archive. That sample has enabled searches of low-mass black holes associated with late-type, bulgeless galaxies and studies of the accretion physics related to low-luminosity active galactic nuclei (AGNs). Using a similar approach, here we construct an extended catalog up to 150 Mpc and make a cross-correlation with a catalog of nearby galaxy groups. The new catalog consists of 1964 galaxies, out of which 1692 have a redshift-independent distance, 1557 are listed in the galaxy group catalog with group properties available, and 782 are identified to be X-ray AGN candidates. Compared with the AGN sample in Paper I, the new sample is 2.5 times larger in size (782 versus 314), with ∼80% of the new members having an Eddington ratio less than 10−4. We confirm that the conclusions based on the previous sample remain. With the new sample, we compare AGN fractions between early-type and late-type galaxies, and between central and satellite galaxies in groups, and find no significant difference. This suggests that the secular process is not the dominant mechanism feeding AGNs in the local universe.

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

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 &amp;lt; λ(Å) &amp;lt; 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.

The rotational profiles of cluster galaxies

ABSTRACT We compile two samples of cluster galaxies with complimentary hydrodynamic and N-body analysis using flash code to ascertain how their differing populations drive their rotational profiles and to better understand their dynamical histories. We select our main cluster sample from the X-ray Galaxy Clusters Database (BAX), which are populated with Sloan Digital Sky Survey (SDSS) galaxies. The BAX clusters are tested for the presence of substructures, acting as proxies for core mergers, culminating in sub-samples of eight merging and 25 non-merging galaxy clusters. An additional sample of 12 galaxy clusters with known dumbbell components is procured using galaxy data from the NASA/IPAC Extragalactic Database (NED) to compare against more extreme environments. BAX clusters of each sample are stacked on to a common RA–Dec. space to produce rotational profiles within the range of 0.0–2.5 r200. Merging stacks possess stronger core rotation at ≲0.5r200 primarily contributed by a red galaxy sub-population from relaxing core mergers; this is alongside high rotational velocities from blue galaxy sub-populations, until they mix and homogenize with the red sub-populations at ∼r200, indicative of an infalling blue galaxy sub-population with interactive mixing between both sub-populations at ≳ r200. flash code is utilized to simulate the merger phase between two originally independent clusters and test the evolution of their rotational profiles. Comparisons with the dumbbell clusters leads to the inference that the peculiar core rotations of some dumbbell clusters are the result of the linear motions of core galaxies relaxing on to the potential during post second infall.

The environment of C- and S-shaped radio galaxies

We study the environment of radio galaxies with different morphological types using the Proctor sample, which was built from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey archive. Among the 15 radio galaxy types classified by Proctor, 199 C-shaped (i.e., wide- or narrow-angle tail) and 203 S-shaped (i.e., S- or Z-shaped) sources are selected in this work, which are located in the redshift range of 0.02 < z < 1, because these two subsamples are relatively larger than the other subsamples in the Proctor sample. By cross-matching these radio galaxies with the optical sources drawn from the Sloan Digital Sky Survey (SDSS) database and counting the SDSS sources with an r-band absolute magnitude brighter than −19 located within a 0.5 Mpc distance around each source (i.e., the richness), we find that the fraction of C-shaped sources with a richness above 10 is larger than that of S-shaped sources. We have also correlated the radio galaxies in our sample with the brightest cluster galaxies (BCGs) defined in the NASA/IPAC Extragalactic Database (NED), and infer that the C-shaped sources are more likely to be BCGs than the S-shaped sources. These results support the idea that C-shaped radio galaxies often reside in a richer environment than radio galaxies with other morphological types.

A New Version of the OCARS Catalog of Optical Characteristics of Astrometric Radio Sources

Abstract A new version of the Optical Characteristics of Astrometric Radio Sources (OCARS) catalog is presented. This compiled catalog includes radio sources observed in different VLBI programs and experiments that result in source position determination, their redshift, and photometry in the visible and near-infrared bands. A cross-identification table between the OCARS and other catalogs is also provided. The status of the catalog as of 2018 September 7 is described in this paper. The OCARS catalog currently contains 6432 sources, of which 3895 have redshift data and 5479 have photometric data. Compared with the previous version, the current version has been enriched with extended redshift and photometry information, and cross-identification with several catalogs in radio, optical, infrared, ultraviolet, X-ray, and gamma-ray bands. The OCARS catalog is updated every few weeks on average to incorporate new data that appear in the NASA/IPAC Extragalactic Database (NED), SIMBAD database, and in the literature.

The Redshift Completeness of Local Galaxy Catalogs

Abstract There is considerable interest in understanding the demographics of galaxies within the local universe (defined, for our purposes, as the volume within a radius of 200 Mpc or z ≤ 0.05). In this pilot paper, using supernovae (SNe) as signposts to galaxies, we investigate the redshift completeness of catalogs of nearby galaxies. In particular, type Ia SNe are bright and are good tracers of the bulk of the galaxy population, as they arise in both old and young stellar populations. Our input sample consists of SNe with redshift ≤0.05, discovered by the flux-limited ASAS-SN survey. We define the redshift completeness fraction (RCF) as the number of SN host galaxies with known redshift prior to SN discovery, determined, in this case, via the NASA Extragalactic Database, divided by the total number of newly discovered SNe. Using SNe Ia, we find % (90% confidence interval) for z &lt; 0.03. We examine the distribution of host galaxies with and without cataloged redshifts as a function of absolute magnitude and redshift, and, unsurprisingly, find that higher-z and fainter hosts are less likely to have a known redshift prior to the detection of the SN. However, surprisingly, some galaxies are also missing. We conclude with thoughts on the future improvement of RCF measurements that will be made possible from large SN samples resulting from ongoing and especially upcoming time-domain surveys.

Cost-efficient scheduling of FAST observations

A cost-efficient schedule for the Five-hundred-meter Aperture Spherical radio Telescope (FAST) requires to maximize the number of observable proposals and the overall scientific priority, and minimize the overall slew-cost generated by telescope shifting, while taking into account the constraints including the astronomical objects visibility, user-defined observable times, avoiding Radio Frequency Interference (RFI). In this contribution, first we solve the problem of maximizing the number of observable proposals and scientific priority by modeling it as a Minimum Cost Maximum Flow (MCMF) problem. The optimal schedule can be found by any MCMF solution algorithm. Then, for minimizing the slew-cost of the generated schedule, we devise a maximally-matchable edges detection-based method to reduce the problem size, and propose a backtracking algorithm to find the perfect matching with minimum slew-cost. Experiments on a real dataset from NASA/IPAC Extragalactic Database (NED) show that, the proposed scheduler can increase the usage of available times with high scientific priority and reduce the slew-cost significantly in a very short time.

Evolution of the NASA/IPAC Extragalactic Database (NED) into a Data Mining Discovery Engine. II. Current Contents and Future Plans

Recent advances have been made in evolving the NASA/IPAC Extragalactic Database (NED) into a data mining discovery engine. Infrastructure changes and data integration techniques are enabling more than a 10-fold expansion. NED will soon contain over a billion objects with their fundamental attributes (such as names, positions, redshifts, fluxes, and diameters) determined via cross-identifications among the largest sky surveys and over 100,000 smaller but scientifically important catalogs and journal articles. In addition, enhancements to the user interface, including new APIs, VO protocols, and queries involving derived physical quantities, will provide new pathways for multi-wavelength studies of large extragalactic samples.

REDSHIFT-INDEPENDENT DISTANCES IN THE NASA/IPAC EXTRAGALACTIC DATABASE: METHODOLOGY, CONTENT, AND USE OF NED-D

ABSTRACT Estimates of galaxy distances based on indicators that are independent of cosmological redshift are fundamental to astrophysics. Researchers use them to establish the extragalactic distance scale, to underpin estimates of the Hubble constant, and to study peculiar velocities induced by gravitational attractions that perturb the motions of galaxies with respect to the “Hubble flow” of universal expansion. In 2006 the NASA/IPAC Extragalactic Database (NED) began making available a comprehensive compilation of redshift-independent extragalactic distance estimates. A decade later, this compendium of distances (NED-D) now contains more than 100,000 individual estimates based on primary and secondary indicators, available for more than 28,000 galaxies, and compiled from over 2000 references in the refereed astronomical literature. This paper describes the methodology, content, and use of NED-D, and addresses challenges to be overcome in compiling such distances. Currently, 75 different distance indicators are in use. We include a figure that facilitates comparison of the indicators with significant numbers of estimates in terms of the minimum, 25th percentile, median, 75th percentile, and maximum distances spanned. Brief descriptions of the indicators, including examples of their use in the database, are given in an appendix.