- ID:
- ivo://CDS.VizieR/J/ApJ/746/27
- Title:
- Magellanic Quasars Survey. II. AGNs behind LMC
- Short Name:
- J/ApJ/746/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We quadruple the number of quasars known behind the Large Magellanic Cloud (LMC) from 56 (42 in the Optical Gravitational Lensing Experiment (OGLE)-III LMC fields) to 200 by spectroscopically confirming 169 (144 new) quasars from a sample of 845 observed candidates in four ~3 deg^2^ Anglo-Australian Telescope/AAOmega fields south of the LMC center. The candidates were selected based on their Spitzer mid-infrared colors, X-ray emission, and/or optical variability properties in the database of the OGLE microlensing survey. The contaminating sources can be divided into 115 young stellar objects (YSOs), 17 planetary nebulae (PNe), 39 Be and 24 blue stars, 68 red stars, and 12 objects classed as either YSO/PN or blue star/YSO. There are also 402 targets with either featureless spectra or too low signal-to-noise ratios for source classification. Our quasar sample is 50% (30%) complete at I = 18.6 mag (19.3 mag). The newly discovered active galactic nuclei (AGNs) provide many additional reference points for proper motion studies of the LMC, and the sample includes 10 bright AGNs (I < 18 mag) that are potentially suitable for absorption line studies. Their primary use, however, is for detailed studies of quasar variability, as they all have long-term, high cadence, continuously growing light curves from the microlensing surveys of the LMC. Completing the existing Magellanic Quasars Survey fields in the LMC and Small Magellanic Cloud should yield a sample of ~700 well-monitored AGNs, and expanding it to the larger regions covered by the OGLE-IV survey should yield a sample of ~3600 AGNs.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/194/22
- Title:
- Magellanic Quasars Survey: QSOs behind SMC
- Short Name:
- J/ApJS/194/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the spectroscopic confirmation of 29 new, 12 plausible, and three previously known quasars behind the central ~1.5deg^2^ region of the Small Magellanic Cloud (SMC). These were identified in a single 2df/AAOmega observation on the Anglo-Australian Telescope of 268 candidates selected primarily based on their mid-IR colors, along with a smaller number of optically variable sources in OGLE-II close to known X-ray sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/776/114
- Title:
- MAGIICAT. I. MgII Absorber-Galaxy Catalog
- Short Name:
- J/ApJ/776/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the MgII Absorber-Galaxy Catalog, MAGIICAT, a compilation of 182 spectroscopically identified intermediate redshift (0.07<=z<=1.1) galaxies with measurements of MgII {lambda}{lambda}2796,2803 absorption from their circumgalactic medium within projected distances of 200kpc from background quasars. In this work, we present "isolated" galaxies, which are defined as having no spectroscopically identified galaxy within a projected distance of 100kpc and a line of sight velocity separation of 500km/s. We standardized all galaxy properties to the {Lambda}CDM cosmology and galaxy luminosities, absolute magnitudes, and rest-frame colors to the B- and K-band on the AB system. We present galaxy properties and rest-frame MgII equivalent width, W_r_(2796), versus galaxy redshift. The well-known anti-correlation between W_r_(2796) and quasar-galaxy impact parameter, D, is significant to the 8{sigma} level. The mean color of MAGIICAT galaxies is consistent with an Sbc galaxy for all redshifts. We also present B- and K-band luminosity functions for different W_r_(2796) and redshift subsamples: "weak absorbing" [W_r_(2796)<0.3{AA}], "strong absorbing" [W_r_(2796)>=0.3{AA}], low redshift (z{<}<z>), and high redshift (z{>=}<z>), where <z> = 0.359 is the median galaxy redshift. Rest-frame color B-K correlates with M_K_ at the 8{sigma} level for the whole sample but is driven by the strong absorbing, high-redshift subsample (6{sigma}). Using M_K_ as a proxy for stellar mass and examining the luminosity functions, we infer that in lower stellar mass galaxies, MgII absorption is preferentially detected in blue galaxies and the absorption is more likely to be weak.
- ID:
- ivo://CDS.VizieR/J/MNRAS/474/4396
- Title:
- MASIV Survey. IV. Radio AGNs variability
- Short Name:
- J/MNRAS/474/4396
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relationship between 5GHz interstellar scintillation (ISS) and 15GHz intrinsic variability of compact, radio-selected active galactic nuclei (AGNs) drawn from the Microarcsecond Scintillation-Induced Variability (MASIV) Survey and the Owens Valley Radio Observatory blazar monitoring program. We discover that the strongest scintillators at 5GHz (modulation index, m_5_>=0.02) all exhibit strong 15GHz intrinsic variability (m_15_>=0.1). This relationship can be attributed mainly to the mutual dependence of intrinsic variability and ISS amplitudes on radio core compactness at ~100{mu}s scales, and to a lesser extent, on their mutual dependences on source flux density, arcsec-scale core dominance and redshift. However, not all sources displaying strong intrinsic variations show high amplitude scintillation, since ISS is also strongly dependent on Galactic line-of-sight scattering properties. This observed relationship between intrinsic variability and ISS highlights the importance of optimizing the observing frequency, cadence, timespan and sky coverage of future radio variability surveys, such that these two effects can be better distinguished to study the underlying physics. For the full MASIV sample, we find that Fermi-detected gamma-ray loud sources exhibit significantly higher 5GHz ISS amplitudes than gamma-ray quiet sources. This relationship is weaker than the known correlation between gamma-ray loudness and the 15GHz variability amplitudes, most likely due to jet opacity effects.
- ID:
- ivo://CDS.VizieR/J/ApJ/699/800
- Title:
- Mass functions of active black holes
- Short Name:
- J/ApJ/699/800
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present mass functions of distant actively accreting supermassive black holes residing in luminous quasars discovered in the Large Bright Quasar Survey (LBQS), the Bright Quasar Survey (BQS), and the Fall Equatorial Stripe of the Sloan Digital Sky Survey (SDSS). The quasars cover a wide range of redshifts from the local universe to z=5 and were subject to different selection criteria and flux density limits. This makes these samples complementary and can help us gain additional insight on the true underlying black hole mass distribution free from selection effects and mass estimation errors through future studies. We present the relationships used to estimate the black hole mass based on the MgII emission line; the relations are calibrated to the H{beta} and CIV relations by means of several thousand high-quality SDSS spectra. Mass estimates of the individual black holes of these samples are also presented.
- ID:
- ivo://CDS.VizieR/J/MNRAS/383/1513
- Title:
- 2MASS, SDSS and FIRST fluxes of QSOs
- Short Name:
- J/MNRAS/383/1513
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Starting from a sample of Sloan Digital Sky Survey quasars appearing also in the Two-Micron All-Sky Survey, we study the continuum properties of ~1000 objects observed in eight bands, from near-infrared to ultraviolet. We construct the mean spectral energy distribution (SED) and compare and contrast the continua of radio-loud and radio-quiet quasar (RLQ and RQQ, respectively) objects. The SEDs of the two populations are significantly different, in the sense that RLQs are redder with power-law spectral indices <alpha_RLQ_>=0.55+/-0.04 and <alpha_RQQ_>=0.31+/-0.01 in the spectral range between 10^14.5^ and 10^15.35^Hz. This difference is discussed in terms of different extinctions, different disc temperatures, or slopes of the non-thermal component.
- ID:
- ivo://CDS.VizieR/J/AJ/125/2521
- Title:
- 2MASS6x survey of the Lockman Hole
- Short Name:
- J/AJ/125/2521
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a survey of the Lockman Hole covering over 24deg^2^ using the Two Micron All Sky Survey (2MASS) observing system in a special mode that reaches roughly 1mag deeper than the nominal 2MASS survey. The resultant point-source catalog reaches to approximately (J, H, Ks)<(17.8, 16.5, 16.0)mag with completeness and reliability in excess of 90%-95% at the faintest levels. These data will be useful in identifying sources in SIRTF surveys of this area. We have cataloged 69,115 objects, almost twice as many as in the nominal 2MASS survey of this region. The sample includes a large number of potential new active galaxies, as well as a T dwarf candidate.
- ID:
- ivo://CDS.VizieR/J/MNRAS/392/1539
- Title:
- Metal absorption systems in pairs of QSOs
- Short Name:
- J/MNRAS/392/1539
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first large sample of metal absorption systems in pairs of QSOs with sightlines separated by about 1Mpc at z=2. We found 690 absorption systems in the spectra of 310 QSOs in 170 pairings. Most systems show CIV or MgII absorption.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/89
- Title:
- Metallicities of damped Ly{alpha} systems
- Short Name:
- J/ApJ/755/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical abundance measurements for 47 damped Ly{alpha} (DLA) systems, 30 at z>4, observed with the Echellette Spectrograph and Imager and the High Resolution Echelle Spectrometer on the Keck telescopes. H I column densities of the DLAs are measured with Voigt profile fits to the Ly{alpha} profiles, and we find an increased number of false DLA identifications with Sloan Digital Sky Survey at z>4 due to the increased density of the Ly{alpha} forest. Ionic column densities are determined using the apparent optical depth method, and we combine our new metallicity measurements with 195 from previous surveys to determine the evolution of the cosmic metallicity of neutral gas. We find the metallicity of DLAs decreases with increasing redshift, improving the significance of the trend and extending it to higher redshifts, with a linear fit of -0.22+/-0.03 dex per unit redshift from z=0.09-5.06. The metallicity "floor" of {approx}1/600 solar continues out to z~5, despite our sensitivity for finding DLAs with much lower metallicities. However, this floor is not statistically different from a steep tail to the distribution. We also find that the intrinsic scatter of metallicity among DLAs of ~0.5dex continues out to z~5. In addition, the metallicity distribution and the {alpha}/Fe ratios of z>2 DLAs are consistent with being drawn from the same parent population with those of halo stars. It is therefore possible that the halo stars in the Milky Way formed out of gas that commonly exhibits DLA absorption at z>2.
- ID:
- ivo://CDS.VizieR/J/ApJ/770/138
- Title:
- Metallicities of Lyman limit systems and DLA
- Short Name:
- J/ApJ/770/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We assess the metal content of the cool (~10^4^K) circumgalactic medium (CGM) about galaxies at z<~1 using an H I-selected sample of 28 Lyman limit systems (LLS; defined here as absorbers with 16.2<~logN_HI_<~18.5) observed in absorption against background QSOs by the Cosmic Origins Spectrograph on board the Hubble Space Telescope. The N_HI_ selection avoids metallicity biases inherent in many previous studies of the low-redshift CGM. We compare the column densities of weakly ionized metal species (e.g., O II, Si II, Mg II) to N_HI_ in the strongest H I component of each absorber. We find that the metallicity distribution of the LLS (and hence the cool CGM) is bimodal with metal-poor and metal-rich branches peaking at [X/H]=~-1.6 and -0.3 (or about 2.5% and 50% solar metallicities). The cool CGM probed by these LLS is predominantly ionized. The metal-rich branch of the population likely traces winds, recycled outflows, and tidally stripped gas; the metal-poor branch has properties consistent with cold accretion streams thought to be a major source of fresh gas for star forming galaxies. Both branches have a nearly equal number of absorbers. Our results thus demonstrate there is a significant mass of previously undiscovered cold metal-poor gas and confirm the presence of metal enriched gas in the CGM of z<~1 galaxies.
