Efficient identification of broad absorption line quasars using dimensionality reduction and machine learning

Broad absorption line (BAL) quasars are characterized by gas clouds that absorb flux at the wavelength of common quasar spectral features, although blueshifted by velocities that can exceed $0.1c$. BAL features are interesting as signatures of significant feedback, yet they can also compromise cosmological studies with quasars by distorting the shape of the most prominent quasar emission lines, impacting redshift accuracy and measurements of the matter density distribution traced by the Lyman $\alpha$ forest. We present a catalogue of BAL quasars discovered in the Dark Energy Spectroscopic Instrument (DESI) survey Early Data Release, which were observed as part of DESI Survey Validation, as well as the first two months of the main survey. We describe our method to automatically identify BAL quasars in DESI data, the quantities we measure for each BAL, and investigate the completeness and purity of this method with mock DESI observations. We mask the wavelengths of the BAL features and re-evaluate each BAL quasar redshift, finding new redshifts which are $243\, {\rm km}\, {\rm s}^{-1}$ smaller on average for the BAL quasar sample. These new, more accurate redshifts are important to obtain the best measurements of quasar clustering, especially at small scales. Finally, we present some spectra of rarer classes of BALs that illustrate the potential of DESI data to identify such populations for further study.

We investigate the optical colors and radio morphologies of 214 broad absorption line (BAL) quasars with FIRST detections in the redshift range 1.68≤z≤4.93 drawn from the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) quasar catalog. The radio-detected SDSS BAL quasars are found to have Δ(g−i) colors significantly redder than their non-BAL counterparts, with a mean color difference of 0.52 mag, in good agreement with the O–E (roughly B–R) color difference between radio-selected BAL and non-BAL quasars in the FIRST Bright Quasar Survey (FBQS). The vast majority (∼90 %) of the radio-detected BAL quasars are found to be core-only sources, most of which show compact radio morphologies, consistent with the morphological results for the FBQS sample. Moreover, within the FIRST-detected SDSS sample, BAL quasars with GB6 detections are found to span a wide range in radio spectral indices, indistinguishable from that of non-BAL quasars, indicating no special line of sight for the presence of BALs. The properties of the present SDSS sample are more consistent with the evolutionary model, in which BALs are at an early evolutionary stage of quasars.

We present the quasar catalog from Data Releases 10 to 12 of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Quasar Survey, comprising quasars observed between 2021 September and 2024 June. We robustly identified 11,346 quasars, of which 5386 are newly discovered objects not present in the Million Quasars catalog. This release brings the total number of quasars identified by the 12 yr LAMOST survey to 67,521, of which 29,513 are newly discovered. While the absolute flux calibration for LAMOST quasar spectra from Data Releases 6 to 9 was previously performed using the Sloan Digital Sky Survey (SDSS)/PanSTARRS1 multiband photometric data, the inherent variability of quasars can affect the flux accuracy. To address this limitation, we recalibrated the LAMOST spectra using (quasi-)simultaneous photometric data from Zwicky Transient Facility, which has conducted high-cadence sky monitoring since 2018 March. Based on the recalibrated single-epoch spectra, we estimated the emission-line fluxes, continuum fluxes, and virial black hole masses. These improved spectra facilitate direct comparison with the spectra of common quasars from SDSS, enabling searches for rare quasars, such as changing-look quasars exhibiting the appearance or disappearance of broad emission lines and broad absorption line quasars. The combined dataset of photometry and multiepoch spectra will enhance the detections of active galactic nucleus–related transients, such as Bowen fluorescence flares and extreme variability quasars, thereby improving our understanding of quasar variability.

We present 13 broad absorption line (BAL) quasars, including 12 new objects, identi—ed in the Sloan Digital Sky Survey (SDSS) and matched within 2A to sources in the FIRST radio survey catalog. The surface density of this sample of radio-detected BAL quasars is 4.5 ^ 1.2 per 100 deg2, i.e., approximately 4 times as high as previously found by the shallower FIRST Bright Quasar Survey (FBQS). A majority of these radio-detected BAL quasars are moderately radio-loud objects. The fraction of BAL quasars in the entire radio quasar sample, 4.8% ^ 1.3%, is comparable to the fraction of BAL quasars among the SDSS optical quasar sample (ignoring selection eUects). We estimate that the true fraction of BAL quasars (mostly ii HiBALs ˇˇ) in the radio sample is 9.2% ^ 2.6%, once selection eUects are accounted for. We caution that the absorption troughs of four of the 13 radio-detected quasars considered do not strictly satisfy the standard BALnicity criteria. One or possibly two of the new radio-detected BAL quasars are of the rare ii FeLoBAL ˇˇ type. BAL quasars are generally redder than the median SDSS quasar at the same redshift. ”

We have compiled the largest sample of multiwavelength spectral energy distributions (SEDs) of broad absorption line (BAL) quasars to date, from the radio to the X-ray. We present new Spitzer MIPS (24, 70, and 160 ?m) observations of 38 BAL quasars in addition to data from the literature and public archives. In general, the mid-infrared properties of BAL quasars are consistent with those of non-BAL quasars of comparable luminosity. In particular, the optical to mid-infrared luminosity ratios of the two populations are indistinguishable. We also measure or place upper limits on the contribution of star formation to the far-infrared power. Of 22 (57%) upper limits, seven quasars have sufficiently sensitive constraints to conclude that star formation likely contributes little (<20%) to their far-infrared power. The 17 BAL quasars (45%) with detected excess far-infrared emission likely host hyperluminous starbursts with LFIR, SF = 1013-1014 L?. Mid-infrared through X-ray composite BAL quasar SEDs are presented, incorporating all of the available photometry. Overall, we find no compelling evidence for inherent differences between the SEDs of BAL versus non-BAL quasars of comparable luminosity. Therefore a cocoon picture of a typical BAL quasar outflow whereby the wind covers a large fraction of the sky is not supported by the mid-infrared SED comparison with normal quasars, and the disk-wind paradigm with a typical radio-quiet quasar hosting a BAL region remains viable.

We present results on a survey to find extremely dust-reddened Type-1 Quasars. Combining the FIRST radio survey, the 2MASS Infrared Survey and the Sloan Digital Sky Survey, we have selected a candidate list of 122 potential red quasars. With more than 80% spectroscopically identified objects, well over 50% are classified as dust-reddened Type 1 quasars, whose reddenings (E(B-V)) range from approximately 0.1 to 1.5 magnitudes. They lie well off the color selection windows usually used to detect quasars and many fall within the stellar locus, which would have made it impossible to find these objects with traditional color selection techniques. The reddenings found are much more consistent with obscuration happening in the host galaxy rather than stemming from the dust torus. We find an unusually high fraction of Broad Absorption Line (BAL) quasars at high redshift, all but one of them belonging to the Low Ionization BAL (LoBAL) class and many also showing absorption the metastable FeII line (FeLoBAL). The discovery of further examples of dust-reddened LoBAL quasars provides more support for the hypothesis that BAL quasars (at least LoBAL quasars) represent an early stage in the lifetime of the quasar. The fact that we see such a high fraction of BALs could indicate that the quasar is in a young phase in which quasar feedback from the BAL winds is suppressing star formation in the host galaxy.

Context. Broad absorption line (BAL) quasars exhibit significant outflows, offering insights into active galactic nucleus (AGN) feedback. While typically associated with high Eddington ratios, BAL quasars also occur in low Eddington ratio regimes, which remain poorly understood. The aim of this study is to compare BAL properties and variability across these regimes. Aims. We investigate the occurrence rates, absorption characteristics, and variability of BAL quasars at low and high Eddington ratios. Methods. Using the SDSS DR16 quasar catalog, we selected a redshift-matched control sample to compare low and high Eddington ratio BAL quasar sources. We first examined the BAL fraction as a function of Eddington ratio. Key absorption parameters (equivalent width, absorption line width, velocity range, and depth) were analyzed, and a multi-epoch variability study was conducted using repeat spectra, followed by a comparison of parameter distributions between the two samples. Results. For the first time, we report an increase in the BAL fraction toward low Eddington ratios, in addition to the previously known trend of high BAL fraction at high Eddington ratios. While high Eddington sources show extreme absorption features, overall distributions are statistically similar except for maximum outflow velocity. No significant variability differences were observed. The correlation between outflow velocity, Eddington ratio, and luminosity supports the role of radiation pressure in driving quasar outflows. For low Eddington ratios, additional mechanisms, such as softer SEDs, larger outflow distances, and thickened accretion disks from radiatively inefficient processes, likely drive outflow formation.

X-ray observations are presented of gravitationally lensed (GL) quasars with redshifts ranging between 1 and 4. The large magnification factors of GL systems allow us to investigate the properties of quasars with X-ray luminosities that are substantially lower than those of unlensed ones and also provide an independent means of estimating the contribution of faint quasars to the hard X-ray component of the cosmic X-ray background. Spectral indices have been estimated in the rest-frame energy bands 0.5-1 keV (soft), 1-4 keV (mid), and 4-20 keV (hard). Our spectral analysis indicates a flattening of the spectral index in the hard band for two radio-loud quasars in the GL quasar sample for which the data have moderate signal-to-noise ratio. These results are consistent with the reported spectral properties of nonlensed radio-loud quasars; however, there are no indications of spectral hardening toward fainter X-ray fluxes. We have identified a large fraction of broad absorption line (BAL) quasars among the GL quasar population. We find that approximately 35% of radio-quiet GL quasars contain BAL features, which is significantly larger than the 10% fraction of BAL quasars presently found in optically selected flux-limited quasar samples. We present a simple model that estimates the effects of attenuation and lens magnification on the luminosity function of quasars and that explains the observed fraction of GL BAL quasars. These observations suggest that a large fraction of BAL quasars are missed from flux-limited optical surveys. Modeling of several X-ray observations of the GL BAL quasar PG 1115+080 suggests that the observed large X-ray variability may be caused in part by a variable intrinsic absorber consistent with previously observed variability of the BAL troughs in the UV band. The observed large X-ray flux variations in PG 1115+080 offer the prospect of considerably reducing errors in determining the time delay with future X-ray monitoring of this system and hence constraining the Hubble constant H0.

Broad absorption lines (BALs) in the spectra of quasi-stellar objects (QSOs) are thought to arise from outflowing winds along our line of sight; winds, in turn, are thought to originate from the accretion disk, in the very surroundings of the central supermassive black hole (SMBH), and they likely affect the accretion process onto the SMBH, as well as galaxy evolution. BALs can exhibit variability on timescales typically ranging from months to years. We analyze such variability and, in particular, BAL disappearance, with the aim of investigating QSO physics and structure. We search for disappearing C {\scriptsize{IV}} BALs in the spectra of 1319 QSOs from different programs from the Sloan Digital Sky Survey (SDSS); the analyzed time span covers $0.28-4.9$ yr (rest frame), and the source redshifts are in the range $1.68-4.27$. This is to date the largest sample ever used for such a study. We find 67 sources ($5.1_{-0.6}^{+0.7}$\% of the sample) with 73 disappearing BALs in total ($3.9_{-0.5}^{+0.5}$\% of the total number of C {\scriptsize{IV}} BALs detected; \textbf{some sources have more than one BAL that disappears}). We compare the sample of disappearing BALs to the whole sample of BALs, and investigate the correlation in the variability of multiple troughs in the same spectrum. We also derive estimates of the average lifetime of a BAL trough and of the BAL phase along our line of sight.

view Abstract Citations (89) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Emission-Line Regions in Broad Absorption Line Quasars Hartig, G. F. ; Baldwin, J. A. Abstract The properties of the emission-line regions in 16 broad absorption line (BAL) quasars are compared to those of non-BAL quasars. It is found that about half the BAL quasars, those having detached BALs, are significantly different from the comparison samples of normal quasars. They have large Al III/semiforbidden C III intensity ratios, strong Fe II emission, and unusually weak C IV emission lines whose profiles do not agree well with those of the lower ionization emission lines. New spectra of the Mg II 2798 A region in 13 of these BAL quasars show a few cases of possible weak Mg II BAL absorption, but no unambiguously strong cases. Thus, it is concluded that strong BAL absorption in Mg II is rare. The quasar H0335 -336 has very narrow emission lines (1000 km/s), and thus may offer a rare opportunity to measure many weak or normally blended emission lines which can give information about physical conditions in the emission-line gas. Publication: The Astrophysical Journal Pub Date: March 1986 DOI: 10.1086/163974 Bibcode: 1986ApJ...302...64H Keywords: Astronomical Spectroscopy; Emission Spectra; Quasars; Spectral Energy Distribution; Spectral Line Width; Abundance; Aluminum; Carbon; Iron; Spectrum Analysis; Astrophysics; QUASARS full text sources ADS | data products SIMBAD (18) NED (17)

Aims. We present the white dwarf catalog derived from the third data release of the Javalambre Photometric Local Universe Survey (J-PLUS DR3), which covers 3284 deg2 using 12 optical filters. A particular focus is given to the classification of outlier sources, those largely incompatible with the theoretical models used in the analysis, through dimensionality reduction techniques. Methods. We applied a Bayesian fitting process to the 12-band J-PLUS photometry of white dwarf candidates from Gaia EDR3. The derived parameters were effective temperature, surface gravity, and parallax. We used theoretical models from H- and He-dominated atmospheres, with priors applied to parallax and spectral type. From the posteriors, we derived the probability of an H-dominated atmosphere and of calcium absorption for each source. Outliers were identified as sources withχ2 ≥ 23.2, indicating significant deviations from the best-fitting model. We analyzed the residuals from the fits using the uniform manifold approximation and projection (UMAP) technique, which enables the classification of outliers into distinct categories. Results. The catalog includes 14 844 white dwarfs with r ≤ 20 mag and 1 ≤ ϖ &lt; 100 mas, with 72% of the sources lacking spectroscopic (R ≳ 500) classification. The application of UMAP to the residuals identified three main types of outliers: random measurement fluctuations (391 sources), metal-polluted white dwarfs (98 sources), and two-component systems (282 sources). The last category also includes white dwarfs with strong carbon absorption lines. We validated the reliability of J-PLUS classifications by comparison with spectroscopy from the Sloan Digital Sky Survey and the Dark Energy Spectroscopic Instrument, and with Gaia BP/RP low-resolution spectra, confirming a one-to-one correspondence between J-PLUS photometric and spectroscopic classifications. Conclusions. The J-PLUS DR3 white dwarf catalog provides a robust dataset for statistical studies. The use of dimensionality reduction techniques enhances the identification of peculiar objects, making this catalog a valuable resource for the selection of interesting targets such as metal-polluted white dwarfs or binary systems.

Broad absorption line quasars (BALQs) present a large diversity in their broad absorption line (BAL) profiles. To investigate what physical parameters underlie this diversity, we construct a sample of BALQs which covers lambda_rest ~ 800-3000 {\AA}, based on the Sloan Digital Sky Survey DR7 quasar catalogue. The average BAL properties are evaluated by taking the ratios of average BALQ spectra to the average spectra of matched samples of non-BALQs, where the matching is based on various emission properties. We find the following properties. (i) There is no detectable Lyman edge associated with the BAL absorbing gas (tau<0.1). (ii) The known increase of average absorption depth with the ionization potential extends to the higher ionization N V and O VI BALs. We also find that the C IV BAL profile is controlled by two parameters. (i) The He II emission EW, which controls the typical velocity of the C IV BAL, but does not affect the absorption depth. (ii) The spectral slope in the 1700-3000 {\AA} range (alpha_UVl), which controls the C IV peak absorption depth, but does not affect the typical velocity. The He II EW and alpha_UVl also control the observed fraction of quasars that are BALQs. We suggest that a lower He II EW may indicate a weaker ionizing continuum, which allows the outflow to reach higher velocities before being overionized, possibly without a need to invoke a shielding gas. A redder continuum may indicate a more inclined system, and a larger covering factor and larger column of the outflow along the line of sight.

In this study, we present the construction of a new proper-motion catalog utilizing the photometric data from the Sloan Digital Sky Survey (SDSS) and Dark Energy Spectroscopic Instrument (DESI) imaging surveys, with a median time baseline of about 13 yr. To mitigate systematic errors, the DESI galaxy positions are employed to establish a reference frame and to correct the position-, magnitude-, and color-dependent discrepancies between the SDSS and DESI imaging data sets. Spanning 12,589 deg2, the catalog encompasses about 223.7 million non-Gaia objects down to m r ∼ 23. Based on 734,000 quasars, the assessment of the global systematic errors in the DESI−SDSS proper-motion catalog yields values of 0.06 mas yr−1 for μ α * and 0.12 mas yr−1 for μ δ . The catalog exhibits precision surpassing 3.4 mas yr−1, albeit varying with position, color, and magnitude. An additional evaluation employing approximately 2644 distant star samples yields an overall precision of approximately 2.5 and 2.9 mas yr−1 for μ α * and μ δ , respectively. Further comparisons with proper motions from SDSS Stripe 82 reveal a strong consistency between the two data sets. As a practical application, we utilize fainter non-Gaia objects in our catalog to update the proper motions of 15 star clusters. The resulting proper motions for these clusters exhibit excellent consistency with those derived from Gaia data. Our proper-motion measurements, characterized by a deeper limiting magnitude, stand as a valuable complement to the Gaia data set.

It was recently shown that there is a significant difference in the radio spectral index distributions of broad absorption line (BAL) quasars and unabsorbed quasars, with an overabundance of BAL quasars with steeper radio spectra. This result suggests that source orientation does play into the presence or absence of BAL features. In this paper we provide more quantitative analysis of this result based on Monte-Carlo simulations. While the relationship between viewing angle and spectral index does indeed contain a lot of scatter, the spectral index distributions are different enough to overcome that intrinsic variation. Utilizing two different models of the relationship between spectral index and viewing angle, the simulations indicate that the difference in spectral index distributions can be explained by allowing BAL quasar viewing angles to extend about 10 degrees farther from the radio jet axis than non-BAL sources, though both can be seen at small angles. These results show that orientation cannot be the only factor determining whether BAL features are present, but it does play a role.

Chapter 19 - Dimensionality Reduction and Latent Variable Modeling