The discovery of a statistically significant clustering in the distribution of gamma-ray bursts (GRBs) has recently been reported. Given that the cluster has a characteristic size of 2000-3000Mpc and a redshift between 1.6<=z<=2.1, it has been claimed that this structure is incompatible with the cosmological principle of homogeneity and isotropy of our Universe. In this paper, we study the homogeneity of the GRB distribution using a subsample of the Greiner GRB catalogue, which contains 314 objects with redshift 0<z<2.5 (244 of them discovered by the Swift GRB mission). We try to reconcile the dilemma between the new observations and the current theory of structure formation and growth. To test the results against the possible biases in redshift determination and the incompleteness of the Greiner sample, we also apply our analysis to the 244 GRBs discovered by Swift and the subsample presented by the Swift Gamma-Ray Burst Host Galaxy Legacy Survey (SHOALS). The real space two-point correlation function (2PCF) of GRBs, {ksi}(r), is calculated using a Landy-Szalay estimator. We perform a standard least-{Chi}^2^ fit to the measured 2PCFs of GRBs. We use the best-fit 2PCF to deduce a recently defined homogeneity scale. The homogeneity scale, R_H_, is defined as the comoving radius of the sphere inside which the number of GRBs N(<r) is proportional to r^3^ within 1%, or equivalently above which the correlation dimension of the sample D^2^ is within 1% of D^2^=3.
Recent studies found a correlation with ~3{sigma} significance between the local star formation measured by GALEX in SN Ia host galaxies and the distances or dispersions derived from these SNe. We search for these effects by using data from recent cosmological analyses to greatly increase the SN Ia sample; we include 179 GALEX-imaged SN Ia hosts with distances from the Joint Light-curve Analysis (JLA) and Pan-STARRS SN Ia cosmology samples and 157 GALEX-imaged SN Ia hosts with distances from the Riess et al. (2011, J/ApJ/730/119) H_0_ measurement. We find little evidence that SNe Ia in locally star-forming environments are fainter after light curve correction than SNe Ia in locally passive environments. We find a difference of 0.000+/-0.018 (stat+sys) mag for SNe fit with SALT2 and 0.029+/-0.027 (stat+sys) mag for SNe fit with MLCS2k2 (R_V_=2.5), which suggests that proposed changes to recent measurements of H_0_ and w are not significant and numerically smaller than the parameter measurement uncertainties. We measure systematic uncertainties of ~0.01-0.02mag by performing several plausible variants of our analysis. We find the greatly reduced significance of these distance modulus differences compared to Rigault et al. (2013A&A...560A..66R) results from two improvements with fairly equal effects, our larger sample size and the use of the JLA and Riess et al. sample selection criteria. Without these improvements, we recover the results of Rigault et al. We find that both populations have similar dispersions in distance than found by Rigault et al. and Kelly et al. (2015Sci...347.1459K), with slightly smaller dispersions for locally passive (log({Sigma}_SFR_)<-2.9dex) SNe Ia fit with MLCS, the opposite of the effect seen by Rigault et al. and Kelly et al. We caution that measuring the local environments of SNe Ia in the future may require a higher resolution instrument than GALEX and that SN Ia sample selection has a significant effect on local star formation biases.
Gamma-ray bursts (GRBs) are classified into long and short categories based on their durations. Broadband studies suggest that these two categories of objects roughly correspond to two different classes of progenitor systems, i.e., compact star mergers (Type I) versus massive star core collapse (Type II). However, the duration criterion sometimes leads to mis-identification of the progenitor systems. We perform a comprehensive multi-wavelength comparative study between duration-defined long GRBs and short GRBs as well as the so-called "consensus" long GRBs and short GRBs (which are believed to be more closely related to the two types of progenitor systems). The parameters we study include two parts: the prompt emission properties including duration (T_90_), spectral peak energy (E_p_), low energy photon index ({alpha}), isotropic {gamma}-ray energy (E_{gamma},iso_), isotropic peak luminosity (L_p,iso_), and the amplitude parameters (f and f_eff_); and the host galaxy properties including stellar mass (M_*_), star formation rate, metallicity ([X/H]), half light radius (R_50_), angular and physical (R_off_) offset of the afterglow from the center of the host galaxy, the normalized offset (r_off_=R_off_/R_50_), and the brightness fraction F_light_. For most parameters, we find interesting overlapping properties between the two populations in both one-dimensional (1D) and 2D distribution plots. The three best parameters for the purpose of classification are T_90_, f_eff_, and F_light_. However, no single parameter alone is good enough to place a particular burst into the right physical category, suggesting the need for multiple criteria for physical classification.
The Low Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) is a sensitive, high-resolution 120-168MHz survey split across multiple tiers over the northern sky. The first LoTSS Deep Fields data release consists of deep radio continuum imaging at 150 MHz of the Bootes, European Large Area Infrared Space Observatory Survey-North 1 (ELAIS-N1), and Lockman Hole fields, down to rms sensitivities of ~32, 20, and 22 muJy/beam, respectively. In this paper we present consistent photometric redshift (photo-z) estimates for the optical source catalogues in all three fields - totalling over 7 million sources (~5 million after limiting to regions with the best photometric coverage). Our photo-z estimation uses a hybrid methodology that combines template fitting and machine learning and is optimised to produce the best possible performance for the radio continuum selected sources and the wider optical source population. Comparing our results with spectroscopic redshift samples, we find a robust scatter ranging from 1.6 to 2% for galaxies and 6.4 to 7% for identified optical, infrared, or X-ray selected active galactic nuclei (AGN). Our estimated outlier fractions (|z_phot-z_spec|/(1+z_spec)>0.15) for the corresponding subsets range from 1.5 to 1.8% and 18 to 22%, respectively. Replicating trends seen in analyses of previous wide-area radio surveys, we find no strong trend in photo-$z$ quality as a function of radio luminosity for a fixed redshift. We exploit the broad wavelength coverage available within each field to produce galaxy stellar mass estimates for all optical sources at z<1.5. Stellar mass functions derived for each field are used to validate our mass estimates, with the resulting estimates in good agreement between each field and with published results from the literature.
Giant radio galaxies (GRGs) are a subclass of radio galaxies, which have grown to megaparsec scales. GRGs are much rarer than normal-sized radio galaxies (<0.7Mpc) and the reason for their gigantic sizes is still debated. Here, we report on the biggest sample of GRGs identified to date. These objects were found in the LOFAR Two-metre Sky Survey (LoTSS) first data release images, which cover a 424 deg^2^ region. Of the 239 GRGs found, 225 are new discoveries. The GRGs in our sample have sizes ranging from 0.7Mpc to 3.5Mpc and have redshifts (z) between 0.1 and 2.3. Seven GRGs have sizes above 2Mpc and one has a size of ~3.5Mpc. The sample contains 40 GRGs hosted by spectroscopically confirmed quasars. Here, we present the search techniques employed and the resulting catalogue of the newly discovered large sample of GRGs along with their radio properties. In this paper, we also show for the first time that the spectral index of GRGs is similar to that of normal-sized radio galaxies, indicating that most of the GRG population is not dead or is not similar to a remnant-type radio galaxy. We find that 20 out of 239 GRGs in our sample are located at the centres of clusters and we present our analysis on their cluster environment and radio morphology.
Low-luminosity galaxies are known to outnumber the bright galaxy population in poor groups and clusters of galaxies. Yet, the investigation of low-luminosity galaxy populations outside the Local Group remains rare and the dependence on different group environments is still poorly understood. Previous investigations have uncovered the photometric scaling relations of early-type dwarfs and a strong dependence of morphology with environment. The present study aims to analyse the photometric and spectroscopic properties of the low-luminosity galaxy population in the nearby, well-evolved and early-type dominated NGC 5846 group of galaxies. It is the third most massive aggregate of early-type galaxies after the Virgo and Fornax clusters in the local universe. Photometric scaling relations and the distribution of morphological types as well as the characteristics of emission-line galaxies are investigated.
Low-mass black holes in Sy1 galaxies. II. SDSS-DR7
Short Name:
J/ApJS/235/40
Date:
21 Oct 2021
Publisher:
CDS
Description:
A new sample of 204 low-mass black holes (LMBHs) in active galactic nuclei (AGNs) is presented with black hole masses in the range of (1-20)x10^5^M_{sun}_. The AGNs are selected through a systematic search among galaxies in the Seventh Data Release (DR7) of the Sloan Digital Sky Survey (SDSS), and careful analyses of their optical spectra and precise measurement of spectral parameters. Combining them with our previous sample selected from SDSS DR4 makes it the largest LMBH sample so far, totaling over 500 objects. Some of the statistical properties of the combined LMBH AGN sample are briefly discussed in the context of exploring the low-mass end of the AGN population. Their X-ray luminosities follow the extension of the previously known correlation with the [OIII] luminosity. The effective optical-to-X-ray spectral indices {alpha}_OX_, albeit with a large scatter, are broadly consistent with the extension of the relation with the near-UV luminosity L_2500{AA}_. Interestingly, a correlation of {alpha}_OX_ with black hole mass is also found, with {alpha}OX being statistically flatter (stronger X-ray relative to optical) for lower black hole masses. Only 26 objects, mostly radio loud, were detected in radio at 20cm in the FIRST survey, giving a radio-loud fraction of 4%. The host galaxies of LMBHs have stellar masses in the range of 10^8.8^-10^12.4^M_{sun}_ and optical colors typical of Sbc spirals. They are dominated by young stellar populations that seem to have undergone continuous star formation history.
We construct a sample of low-redshift Ly{alpha} emission-line selected sources from Galaxy Evolution Explorer (GALEX) grism spectroscopy of nine deep fields to study the role of Ly{alpha} emission in galaxy populations with cosmic time. Our final sample consists of 119 (141) sources selected in the redshift interval z=0.195-0.44 (z=0.65-1.25) from the FUV (NUV) channel. We classify the Ly{alpha} sources as active galactic nuclei (AGNs) if high-ionization emission lines are present in their UV spectra and as possible star-forming galaxies otherwise. We classify additional sources as AGNs using line widths for our Ly{alpha} emitter (LAE) analysis. These classifications are broadly supported by comparisons with X-ray and optical spectroscopic observations, though the optical spectroscopy identifies a small number of additional AGNs. Defining the GALEX LAE sample in the same way as high-redshift LAE samples, we show that LAEs constitute only about 5% of NUV-continuum selected galaxies at z~0.3. We also show that they are less common at z~0.3 than they are at z~3. Finally, we confirm that the z~2 Lyman break galaxies have relatively low metallicities for their luminosities, and we find that they lie in the same metallicity range as the z~0.3 Ly{alpha} galaxies.
An analysis of the first set of low-redshift (z<0.08) Type Ia supernovae (SNe Ia) monitored by the Carnegie Supernova Project between 2004 and 2006 is presented. The data consist of well-sampled, high-precision optical (ugriBV) and near-infrared (NIR; YJHKs) light curves in a well-understood photometric system.
We use a sample of approximately 340 low surface brightness (LSB) disk galaxies with measured redshifts in combination with the Center for Astrophysics redshift survey to test the hypothesis that LSB galaxies have a deficit of nearby companion galaxies compared to high surface brightness (HSB) disk galaxies. We find a very strong statistical deficit of galaxies located within a projected radius of 0.5 Mpc and within a velocity of 500 km/s around LSB disk galaxies compared to HSB ones. Further, comparing LSB and HSB disk galaxies which are located in the same portion of the sky indicates that the average distance to the nearest neighbor is 1.7 times farther for LSB disk galaxies. A Komologorov-Smirnoff test rules out, at greater than the 99% confidence level, the hypothesis that the distribution of nearest-neighbor distances is the same for HSB and LSB disk galaxies. We speculate that LSB disk galaxies have relatively long formation time scales and therefore must form in relative isolation. In addition, the lack of tidal interactions over a Hubble time serves to suppress the overall star-formation rate as no external trigger is available to help clump the gas. The observed low surface densities of HI in combination with the low probability of tidal interactions effectively prevents these disk galaxies from evolving very rapidly.