- ID:
- ivo://CDS.VizieR/J/MNRAS/354/L31
- Title:
- SDSS DR2 QSO and DLA properties
- Short Name:
- J/MNRAS/354/L31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Sloan Digital Sky Survey (SDSS) Data Release 2 quasi-stellar object (QSO) spectra to constrain the dust-reddening caused by intervening damped Lyman {alpha} systems (DLAs). Comparing the spectral index distribution of a 70 sight-line DLA sample with that of a large control sample reveals no evidence for dust-reddening at z~3.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/639/766
- Title:
- SDSS-DR3 strong MgII absorbers
- Short Name:
- J/ApJ/639/766
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of two complementary investigations into the nature of strong (rest equivalent width, Wr>1.0{AA}) MgII absorption systems at high redshift. The first line of questioning examines the complete Sloan Digital Sky Survey Data Release 3 set of quasar spectra to determine the evolution of the incidence of strong MgII absorption. This search resulted in 7421 confirmed MgII systems of Wr>1.0{AA}, yielding a >95% complete statistical sample of 4835 absorbers (systems detected in S/N>7 spectral regions) spanning a redshift range 0.35<z<2.3.
- ID:
- ivo://CDS.VizieR/J/A+A/546/A122
- Title:
- SDSS extremely metal-poor emission-line galaxies
- Short Name:
- J/A+A/546/A122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 6.5-m MMT and 3.5m APO spectrophotometry of 69 HII regions in 42 low-metallicity emission-line galaxies, selected from the data release 7 of the Sloan Digital Sky Survey to have mostly [OIII]{lambda}4959/H{beta}<~1 and [NII]{lambda}6583/H{beta}<~0.1. The electron temperature-sensitive emission line [OIII]{lambda}4363 is detected in 53 HII regions allowing a direct abundance determination. The oxygen abundance in the remaining 16 HII regions is derived using a semi-empirical method. The oxygen abundance of the galaxies in our sample ranges from 12+logO/H~7.1 to ~7.9, with 14 HII regions in 7 galaxies with 12+logO/H<=7.35. In 5 of the latter galaxies, the oxygen abundance is derived here for the first time. Including other known extremely metal-deficient emission-line galaxies from the literature, e.g. SBS 0335-052W, SBS 0335-052E and I Zw 18, we have compiled a sample of the 17 most metal-deficient (with 12+logO/H<=7.35) emission-line galaxies known in the local universe. There appears to be a metallicity floor at 12+log O/H~6.9, suggesting that the matter from which dwarf emission-line galaxies formed was pre-enriched to that level by e.g. Population III stars.
- ID:
- ivo://CDS.VizieR/J/AJ/153/174
- Title:
- SDSS-III/APOGEE. II. The multi-epoch ABE sample
- Short Name:
- J/AJ/153/174
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the H-band spectral variability of classical Be stars observed over the course of the Apache Point Galactic Evolution Experiment (APOGEE), one of four subsurveys comprising SDSS-III. As described in the first paper of this series, the APOGEE B-type emission-line (ABE) star sample was culled from the large number of blue stars observed as telluric standards during APOGEE observations. In this paper, we explore the multi-epoch ABE sample, consisting of 1100 spectra for 213 stars. These "snapshots" of the circumstellar disk activity have revealed a wealth of temporal variability including, but not limited to, gradual disappearance of the line emission and vice versa over both short and long timescales. Other forms of variability include variation in emission strength, emission peak intensity ratios, and emission peak separations. We also analyze radial velocities (RVs) of the emission lines for a subsample of 162 stars with sufficiently strong features, and we discuss on a case-by-case basis whether the RV variability exhibited by some stars is caused by binary motion versus dynamical processes in the circumstellar disks. Ten systems are identified as convincing candidates for binary Be stars with as of yet undetected companions.
- ID:
- ivo://CDS.VizieR/J/A+A/547/L1
- Title:
- SDSS-III DR9 DLA catalogue
- Short Name:
- J/A+A/547/L1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the column density distribution and cosmological mass density of neutral gas from a survey of Damped Lyman-alpha systems in the Sloan Digital Sky Survey III Data Release 9.
- ID:
- ivo://CDS.VizieR/J/ApJS/221/7
- Title:
- SDSS QSOs at z<0.8. II. New spectroscopic obs.
- Short Name:
- J/ApJS/221/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new spectroscopic observations that are part of our continuing monitoring campaign of 88 quasars at z<0.7 whose broad H{beta} lines are offset from their systemic redshifts by a few thousand km/s. These quasars have been considered as candidates for hosting supermassive black hole binaries (SBHBs) by analogy with single-lined spectroscopic binary stars. We present the data and describe our improved analysis techniques, which include an extensive evaluation of uncertainties. We also present a variety of measurements from the spectra that are of general interest and will be useful in later stages of our analysis. Additionally, we take this opportunity to study the variability of the optical continuum and integrated flux of the broad H{beta} line. We compare the variability properties of the SBHB candidates to those of a sample of typical quasars with similar redshifts and luminosities observed multiple times during the Sloan Digital Sky Survey. We find that the variability properties of the two samples are similar (variability amplitudes of 10%-30% on timescales of approximately 1-7 years) and that their structure functions can be described by a common model with parameters characteristic of typical quasars. These results suggest that the broad-line regions of SBHB candidates have a similar extent as those of typical quasars. We discuss the implications of this result for the SBHB scenario and the ensuing constraints on the orbital parameters.
- ID:
- ivo://CDS.VizieR/J/MNRAS/469/323
- Title:
- SDSS quasars with PV broad absorption
- Short Name:
- J/MNRAS/469/323
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Broad absorption lines (BALs) found in a significant fraction of quasar spectra identify high-velocity outflows that might be present in all quasars and could be a major factor in feedback to galaxy evolution. Understanding the nature of these flows requires further constraints on their physical properties, including their column densities, for which well-studied BALs, such as CIV {lambda}{lambda}1548,1551, typically provide only a lower limit because of saturation effects. Low-abundance lines, such as PV {lambda}{lambda}1118,1128, indicate large column densities, implying that outflows more powerful than measurements of CIV alone would indicate. We search through a sample of 2694 BAL quasars from the Sloan Digital Sky Survey III/Baryon Oscillation Spectroscopic Survey data release 9 quasar catalogue for such absorption, and we identify 81 'definite' and 86 'probable' detections of PV broad absorption, yielding a firm lower limit of 3.0-6.2 per cent for the incidence of such absorption among BAL quasars. The PV-detected quasars tend to have stronger CIV and SiIV absorption, as well as a higher incidence of LoBAL absorption, than the overall BAL quasar population. Many of the PV-detected quasars have CIV troughs that do not reach zero intensity (at velocities where PV is detected), confirming that the outflow gas only partially covers the UV continuum source. P V appears significantly in a composite spectrum of non-PV-detected BAL quasars, indicating that P V absorption (and large column densities) is much more common than indicated by our search results. Our sample of PV detections significantly increases the number of known PV detections, providing opportunities for follow-up studies to better understand BAL outflow energetics.
- ID:
- ivo://CDS.VizieR/J/ApJ/872/21
- Title:
- SDSS RM project: <10day CIV BAL variability
- Short Name:
- J/ApJ/872/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We systematically investigate short-timescale (<10 day rest-frame) CIV broad absorption-line (BAL) variability to constrain quasar-wind properties and provide insights into BAL-variability mechanisms in quasars. We employ data taken by the Sloan Digital Sky Survey Reverberation Mapping project, as the rapid cadence of these observations provides a novel opportunity to probe BAL variability on shorter rest-frame timescales than have previously been explored. In a sample of 27 quasars with a median of 58 spectral epochs per quasar, we have identified 15 quasars (55_-14_^+18^%), 19 of 37 CIV BAL troughs (51_-12_^+15^%), and 54 of 1460 epoch pairs (3.7%+/-0.5%) that exhibit significant CIV BAL equivalent-width variability on timescales of less than 10 days in the quasar rest frame. These frequencies indicate that such variability is common among quasars and BALs, though somewhat rare among epoch pairs. Thus, models describing BALs and their behavior must account for variability on timescales down to less than a day in the quasar rest frame. We also examine a variety of spectral characteristics and find that, in some cases, BAL variability is best described by ionization-state changes, while other cases are more consistent with changes in covering fraction or column density. We adopt a simple model to constrain the density and radial distance of two outflows appearing to vary by ionization-state changes, yielding outflow density lower limits consistent with previous work.
- ID:
- ivo://CDS.VizieR/J/ApJ/758/1
- Title:
- SDSS-Spitzer AGN properties
- Short Name:
- J/ApJ/758/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study a combined sample of 264 star-forming, 51 composite, and 73 active galaxies using optical spectra from the Sloan Digital Sky Survey (SDSS) and mid-infrared (mid-IR) spectra from the Spitzer Infrared Spectrograph. We examine optical and mid-IR spectroscopic diagnostics that probe the amount of star formation and relative energetic contributions from star formation and an active galactic nucleus (AGN). Overall we find good agreement between optical and mid-IR diagnostics. Misclassifications of galaxies based on the SDSS spectra are rare despite the presence of dust obscuration. The luminosity of the [Ne II] 12.8{mu}m emission line is well correlated with the star formation rate measured from the SDSS spectra, and this holds for the star-forming, composite, and AGN-dominated systems. AGNs show a clear excess of [Ne III] 15.6{mu}m emission relative to star-forming and composite systems. We find good qualitative agreement between various parameters that probe the relative contributions of the AGN and star formation, including the mid-IR spectral slope, the ratio of the [Ne V] 14.3{mu}m to [Ne II] 12.8{mu}m fluxes, the equivalent widths of the 7.7{mu}m, 11.3{mu}m, and 17{mu}m polycyclic aromatic hydrocarbon (PAH) features, and the optical "D" parameter which measures the distance at which a source lies from the locus of star-forming galaxies in the optical BPT emission-line diagnostic diagram. We also consider the behavior of the three individual PAH features by examining how their flux ratios depend upon the degree of AGN dominance. We find that the PAH 11.3{mu}m feature is significantly suppressed in the most AGN-dominated systems.
- ID:
- ivo://CDS.VizieR/J/ApJ/825/126
- Title:
- SEAMBHs. V. The third year
- Short Name:
- J/ApJ/825/126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper reports results of the third-year campaign of monitoring super-Eddington accreting massive black holes (SEAMBHs) in active galactic nuclei (AGNs) between 2014 and 2015. Ten new targets were selected from the quasar sample of the Sloan Digital Sky Survey (SDSS), which have generally been more luminous than the SEAMBH candidates in the last two years. H{beta} lags ({tau}_H{beta}_) in five of the 10 quasars have been successfully measured in this monitoring season. We find that the lags are generally shorter, by large factors, than those of objects with same optical luminosity, in light of the well-known R_H{beta}_-L_5100_ relation. The five quasars have dimensionless accretion rates of dM/dt=10-10^3^. Combining these with measurements of the previous SEAMBHs, we find that the reduction of H{beta} lags depends tightly on accretion rates, {tau}_H{beta}_/{tau}_R-L_{propto}(dM/dt)^-0.42^, where {tau}_R-L_ is the H{beta} lag from the normal R_H{beta}_-L_5100_ relation. Fitting 63 mapped AGNs, we present a new scaling relation for the broad-line region: R_H{beta}_={alpha}_1_l_44_^{beta}1^min [1,(dM/dt)/(dM/dt)_c_)^-{gamma}1^], where l_44_=L_5100_/10^44^erg/s is the 5100{AA} continuum luminosity, and the coefficients are {alpha}_1_=29.6_-2.8_^+2.7^ lt-day, {beta}1=0.56_-0.03_^+0.03^, {gamma}1=0.52_-0.16_^+0.33^, and (dM/dt)_c_=11.19_-6.22_^+2.29^. This relation is applicable to AGNs over a wide range of accretion rates, from 10^-3^ to 10^3^. Implications of this new relation are briefly discussed.
