arXiv subjects

Konstantina Boutsia

Publications and source records attributed to Konstantina Boutsia.

At least 19 recordsLinked to original sources

arXiv2026

Mode Switching in Two Blue Large Amplitude Pulsators observed by OGLE, KMTNet and DREAMS

Blue large-amplitude pulsators (BLAPs) are rare, hot, short-period pulsating stars whose rapid oscillations provide a unique probe of stellar interiors and atmospheres. In this paper, we study two short-period BLAPs in the Galactic bulge, OGLE-BLAP-142 ($P \approx 6.6$ min) and OGLE-BLAP-148 ($P \approx 7.5$ min), by combining light curves from the OGLE, KMTNet, and DREAMS surveys, spanning 17 years with cadences ranging from minutes to hours to days. We perform Generalized Lomb-Scargle periodogram analyses of their light curves and identify, for each BLAP, three closely spaced pulsation modes separated by $\sim 1\%$. The dominant mode can switch within timescales of order a year, accompanied by a likely blueward color shift ($\sim 0.1$--$0.2$ mag). The yearly period excursions of the resolved mode families imply apparent $|\dot{P}/P|$ values of order $10^{-6}$--$10^{-4}\,\mathrm{yr^{-1}}$, large enough to mimic or exceed smooth evolutionary period changes. One mode family in OGLE-BLAP-148 shows a coherent decade-long drift at the $\sim10^{-5}\,\mathrm{yr^{-1}}$ level, but its failure to extrapolate to the earliest and latest epochs suggests a transient mode-family drift rather than secular evolution. Such close-spaced multiple pulsations and mode switching may be common among BLAPs with periods shorter than 10 min, and their physical origin remains unclear.

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arXiv2026

The extreme Disturbed Galaxy Cluster Sample (eDGeS): Spectroscopy and Dynamical Analysis of the eROSITA-Selected Merging Galaxy Cluster Candidate 1eRASS J025859.4-193727

Addressing open questions such as the effect of galaxy cluster mergers on the evolution of galaxies and the self-interaction cross-section of dark matter requires the construction of a large, diverse sample of disturbed galaxy clusters. One contribution to such a sample is the extreme Disturbed Galaxy Cluster Sample (eDGeS), an ongoing spectroscopic study of massive disturbed and merging galaxy clusters selected from complementary surveys. Here, we present our first results from the eROSITA-selected subsample (eDGeS-eROSITA): a dynamical state analysis for the merging cluster candidate 1eRASS J025859.4-193727. We present the first spectroscopic redshift measurements for 76 galaxies in the direction of the cluster, confirming 51 as cluster members. The cluster displays a line-of-sight velocity dispersion of $σ_{\rm{cl}}=808^{+59}_{-66}~\rm{km~s^{-1}}$ and a dynamical mass of $M_{200}=4.47^{+0.94}_{-0.93} \times 10^{14}~M_{\rm{Sun}}$. While the cluster shows no evidence for substructure along the line of sight, the projected distribution of member galaxies reveals three subclusters, only one of which appears associated with the cluster's X-ray contours. Phase-space analysis reveals a large fraction of recently infallen member galaxies. Together, this evidence suggests a cluster merger along the plane of the sky. Assuming that the two most massive subclusters are on outgoing (incoming) trajectories after their first pericentric passage, a two-body Monte Carlo model predicts that the two subclusters collided $0.50^{+0.20}_{-0.22}~\rm{Gyr}$ ($1.24^{+0.96}_{-0.38}~\rm{Gyr}$) ago.

astro-ph.GA↗

arXiv2026

KMT-2026-BLG-0083L: A Two-Jovian-Planet System Orbiting an M Dwarf Discovered by Microlensing

We present the analysis of the microlensing event KMT-2026-BLG-0083, which was independently detected by the KMTNet, OGLE, and PRIME surveys and also monitored by the DREAMS survey. The combined data provide dense coverage of two distinct short-duration anomalies in the light curve that cannot be reproduced by a standard binary-lens model. Independent analyses of the two anomalies indicate that each is produced by a planetary companion to the lens, motivating a triple-lens interpretation. The modeling yields two pairs of degenerate solutions arising from the well-known inner--outer degeneracy, with each pair exhibiting two local solutions depending on whether the source passes above or below the distant planetary companion. The preferred model indicates two giant planets with mass ratios $q_2=(5.25\pm 0.08)\times 10^{-3}$ and $q_3=(3.04\pm 0.24)\times10^{-3}$ orbiting a common host. Bayesian analysis indicates that the host is an M-dwarf star with a mass of $0.48^{+0.36}_{-0.28}~M_\odot$, hosting two giant planets with masses of $2.65^{+1.96}_{-1.55}~M_{\rm J}$ and $1.54^{+1.14}_{-0.90}~M_{\rm J}$. The projected planet--host separations are $10.6^{+1.7}_{-2.2}$~au and $1.7^{+0.3}_{-0.3}$~au, placing the inner planet near the host's snow line and the outer planet at a substantially larger separation. Thus, KMT-2026-BLG-0083L becomes the seventh confirmed multiple-planet system discovered through gravitational microlensing, providing another example of a cold giant planetary system orbiting a subsolar-mass star.

astro-ph.EP↗

arXiv2026

Spec-S5: A Next-Generation All-Sky Spectroscopic Facility Enabling Large-Scale Surveys for Cosmology and Astrophysics

The Stage-5 Spectroscopic Experiment (Spec-S5) is a next-generation, all-sky spectroscopic facility designed to address fundamental questions in cosmology and astrophysics. Building on the legacy of the Dark Energy Spectroscopic Instrument (DESI), Spec-S5 will upgrade two existing 4-m telescopes into 6-m, wide-field observatories, each equipped with a highly multiplexed spectrograph capable of measuring 13,000 spectra simultaneously. This overview paper summarizes the science motivation, system architecture, and integration strategy of the project. Spec-S5 will deliver a more than tenfold increase in spectroscopic capability, enabling transformative surveys in the post-Rubin, post-DESI era and advancing our understanding of dark matter, dark energy, and cosmic structure formation.

astro-ph.IM↗

arXiv2026

A Minute-Cadence Deep Bulge Survey: First Data Release of DREAMS

The DECam Rogue Earths and Mars Survey (DREAMS), a NOIRLab survey program, has been conducting a three-year survey covering a 5 deg$^2$ area in the Galactic bulge (roughly spanning $-1.2^\circ \lesssim \ell \lesssim +2.1^\circ$ and $-2.8^\circ \lesssim b \lesssim -0.6^\circ$) since 2025 June. Its primary science goal is to detect low-mass free-floating planets through microlensing, while its minute-level cadence ($20-40\,\mathrm{hr}^{-1}$ in $z$ band and $4-8\,\mathrm{hr}^{-1}$ in $r$ band) also enables the detection and characterization of rapid phenomena on timescales of minutes to hours such as stellar flares and pulsating stars. The survey reaches a single-exposure depth of $z_{\rm AB}\sim 22$ mag, about two magnitudes deeper than previous bulge time-domain surveys. We present the data reduction and calibration of the DREAMS observations obtained in 2025 and introduce the first DREAMS data release (DR1). DR1 includes 1,856 $z$-band observations and 325 $r$-band observations for 59,372,789 stars. The DREAMS DR1 catalog contains about twice as many stars as previous catalog covering the same 5 deg$^2$ area. We present DREAMS light curves for a known blue large-amplitude pulsator (BLAP) and a known low-amplitude transiting system to demonstrate the survey's capabilities. We also perform a pilot search for short-duration variables over about 0.4% of the DR1 sample, identifying one new short microlensing event, two stellar flares, and 24 new short variables. This suggests that DREAMS DR1 may contain hundreds of stellar flares and thousands of previously unknown short variables.

astro-ph.SR↗

arXiv2026

Estimating the completeness of the QUBRICS Survey with 3501 QSO redshifts from Gaia DR3 spectra

QSOs are essential for investigating the structure and evolution of the Universe. Historically, their identification has been concentrated in the northern hemisphere, primarily due to the sky coverage of major astronomical surveys. The QUBRICS survey, started in 2019 to address this asymmetry, has identified more than 1300 new bright (i<19.5) high-redshift (2.5 2.5 fell within the XGB dataset footprint, of which 152 were unclassified and thus eligible for completeness testing. Similarly, 675 QSOs with z>2.5 were within the PRF dataset footprint, including 69 unclassified objects. The XGB correctly identified as candidates 136 (89%) of the 152 QSOs with z>2.5 present in its dataset as unclassified objects. The PRF correctly identified as candidates 46 (66%) of the 69 QSOs with z>2.5 present in its dataset as unclassified objects. These findings confirm the high efficiency of the QUBRICS selection methods (recall=89%) and provide the completeness estimate for spectroscopically confirmed QSOs (82%), necessary for cosmological studies using QUBRICS data. This work also provides reliable redshifts for 1223 new QSOs (median redshift z=2.1 and magnitude G=17.8), that will help improve the performance of future selections.

astro-ph.CO↗

arXiv2026

The ESPRESSO Redshift Drift Experiment III -- The Third Epoch of QSO J052915.80-435152.0

The Sandage-Loeb test probes cosmic expansion directly by measuring the redshift drift in quasar absorption features in a model-independent way. In this series of papers, we have launched an observational campaign to assess whether current instrumentation is capable of measuring this effect and what systematic effects might interfere with a detection. We report the observations and analysis of the third epoch of ESPRESSO observations of the bright quasar J052915.80-435152.0 (SB2, z=3.962), extending the temporal baseline to $\sim2$ years, and providing the tightest constraints on the redshift drift in the series so far. We acquired 9.5 hours of ESPRESSO observations, complementing the 12 hours presented in the first paper of the series, with one year of separation from the second epoch. The complete dataset was analysed and compared to spline-based Lyman-$α$ forest models calibrated on simulations, to measure the presence of any velocity drift among the spectra. The measurement was carried out with two independent methods. Both approaches give a consistent null result, $\dot{v} = -3.5 \pm 3.6 ~{\rm m s^{-1} yr^{-1}}$ (or $\dot{z} = (-5.3\pm5.6)\times 10^{-8}~{\rm yr^{-1}}$ in redshift space), in agreement with $Λ$CDM expectations, systematic effects remain subdominant at the present level of noise. By extrapolating the results from the observed sightline to the complete QUBRICS Golden Sample, we show that ESPRESSO alone could detect the signal on century timescales, while a joint ESPRESSO+ANDES programme would reach first detection before 2080. A future analysis of the other quasars of the QUBRICS Golden Sample is required to improve this estimate. We show that the program would greatly benefit from a complementary effort with radio facilities targeting low-z HI 21 cm absorption lines. Such synergy could reduce the experiments' timeline by up to $\sim10$ years.

astro-ph.CO↗

arXiv2026

KMT-2025-BLG-1616Lb: First Microlensing Bound Planet From DREAMS

We present observations and analysis of the bound planetary microlensing event KMT-2025-BLG-1616. The planetary signal was captured by the Korea Microlensing Telescope Network (KMTNet) and the DECam Rogue Earths and Mars Survey (DREAMS). DREAMS's minute-cadence observations break the central/resonant degeneracy in the binary-lens models. The color of the faint source star ($I=22$) is measured from the DREAMS's $r - z$ color. The planetary system has a planet-host mass ratio of $q \sim 5 \times 10^{-4}$. A Bayesian analysis yields a host-star mass of $\sim 0.3\,M_\odot$, a planetary mass of $\sim 40\,M_{\oplus}$, a projected planet-host separation of $\sim 1.6~\mathrm{au}$, and a lens distance of $\sim 7.5~\mathrm{kpc}$. Based on the photometric precision achieved by DREAMS for this event, we simulate free-floating planet (FFP) detections and find that DREAMS is sensitive to Mars-mass FFPs in the Galactic bulge and Moon-mass FFPs in the Galactic disk.

astro-ph.EP↗

arXiv2025

Shocks and complex chemodynamics in the metal-poor starburst galaxy CGCG 007-025 revealed through high-resolution echelle spectroscopy

We use Magellan/MIKE echelle spectroscopy to conduct an in-depth chemodynamical analysis of the most luminous star-forming region within the metal-poor starburst dwarf galaxy CGCG 007-025. Leveraging the exceptional high resolution (R$\sim$50,000) and broad wavelength coverage, we apply Bayesian inference to simultaneously model the fluxes of 30 emission lines spanning the wavelength range 3400-9200Å. Employing a two-region ionisation model, we characterise various gas properties including electron temperature, electron density, and chemical abundances across different elements. Our direct-method inferred metallicity yields $\rm 12+\log(O/H)=7.77\pm0.03$, placing the galaxy in the metal-poor regime. Furthermore, Metal-to-Oxygen ratios such as log(S/O), log(Ne/O) or log(Ar/O) are in full agreement with the values derived for the Milky Way, consistent with expectations from stellar evolutionary models. The brightest emission lines are kinematically complex, with modelling requiring up to four distinct components. The exceptional resolution and signal-to-noise ratio of the data unveil asymmetric and wide ($σ_{HeII} \approx$ 35km/s) HeII$λ$4686 emission. The flux ratio of this nebular line, together with the absence of other high ionisation species such as [NeV]$λ$3426, indicates the presence of fast radiative shocks. This dataset underscores the capability of echelle spectroscopy in delivering comprehensive chemodynamical analyses of starbursts in the Local Volume.

astro-ph.GA↗

arXiv2025

The ESPRESSO Redshift Drift Experiment I -- High-resolution spectra of the Lyman-$α$ forest of QSO J052915.80-435152.0

The measurement of the temporal evolution in the redshift of distant objects, the redshift drift, is a probe of universal expansion and cosmology. We perform the first steps towards a measurement of such effect using the Lyman-$α$ forest in the spectra of bright quasars as a tracer of cosmological expansion. Our goal is to determine to which precision a velocity shift measurement can be carried out with the signal-to-noise (S/N) level currently available and whether this precision aligns with previous theoretical expectations. A precise assessment of the achievable measurement precision is fundamental for estimating the time required to carry out the whole project. We acquire 12 hours of ESPRESSO observations distributed over 0.875 years of the brightest quasar known, J052915.80-435152.0 (z=3.962), to obtain high-resolution spectra of the Lyman-$α$ forest, with median S/N of ~86 per 1 km/s pixel at the continuum. We divide the observations into two epochs and analyse them using both a pixel-by-pixel method and a model-based approach. This comparison allows us to estimate the velocity shift between the epochs, as well as the velocity precision that can be achieved at this S/N. The model-based method is calibrated using high-resolution simulations of the intergalactic medium, and it provides greater accuracy compared to the pixel-by-pixel approach. We measure a velocity drift of the Lyman-$α$ forest consistent with zero: $Δv = -1.25\pm 4.45 {\rm ms^{-1}}$, equivalent to a cosmological drift of $\dot{v}=-1.43\pm 5.09 {\rm ms^{-1}yr^{-1}}$ or $\dot{z}= (-2.19\pm7.77) \times 10^{-8}{\rm yr^{-1}}$. The measurement uncertainties are on par with the expected precision. We estimate that reaching a 99% detection of the cosmic drift requires a monitoring campaign of 5400 hours of integration time over 54 years with an ELT and an ANDES-like high-resolution spectrograph.

astro-ph.CO↗

arXiv2025

The Spectroscopic Stage-5 Experiment

The existence, properties, and dynamics of the dark sectors of our universe pose fundamental challenges to our current model of physics, and large-scale astronomical surveys may be our only hope to unravel these long-standing mysteries. In this white paper, we describe the science motivation, instrumentation, and survey plan for the next-generation spectroscopic observatory, the Stage-5 Spectroscopic Experiment (Spec-S5). Spec-S5 is a new all-sky spectroscopic instrument optimized to efficiently carry out cosmological surveys of unprecedented scale and precision. The baseline plan for Spec-S5 involves upgrading two existing 4-m telescopes to new 6-m wide-field facilities, each with a highly multiplexed spectroscopic instrument capable of simultaneously measuring the spectra of 13,000 astronomical targets. Spec-S5, which builds and improves on the hardware used for previous cosmology experiments, represents a cost-effective and rapid approach to realizing a more than 10$\times$ gain in spectroscopic capability compared to the current state-of-the-art represented by the Dark Energy Spectroscopic Instrument project (DESI). Spec-S5 will provide a critical scientific capability in the post-Rubin and post-DESI era for advancing cosmology, fundamental physics, and astrophysics in the 2030s.

astro-ph.CO↗

arXiv2024

What are the Pillars of Reionization? Revising the AGN Luminosity Function at z~5

In the past, high-z AGNs were given a minor role as possible drivers of reionization, despite initial evidences in favor of their large space densities at low luminosities by Chandra and HST. Recent observations from JWST are finding relatively large numbers of faint AGNs at z>4, convincingly confirming these early results. We present a sample of z~5 AGNs (both from wide, shallow ground-based surveys and from deep, pencil-beam observations from JWST), allowing to estimate their space densities with unprecedented accuracy. The bright end (M1450<-26) of the z~5 AGN luminosity function is well constrained, with a rather steep slope. The faint end (M1450>-22) indicates a high space density, the scatter is significant and the knee (M1450~-24) is mostly undetermined. Comparisons with state-of-the-art models find reasonable agreement with the observed AGN luminosity function at z=5, while the predicted space density evolution at higher redshifts appears to be too fast with respect to observational constraints. Given the large variance at the faint end, we consider different options in fitting the luminosity functions and deriving the ionizing emissivity. Even in the most conservative scenario, the photo-ionization rate produced by z~5 AGNs is consistent with the UV background measurements. A slow evolution of the space density of faint AGNs is observed, indicating that active SMBHs are probably producing large amounts of ionizing photons at z>6, well into the epoch of reionization. This is an important indication that high-z AGNs could be the major contributors to the reionization of the Universe.

astro-ph.CO↗

arXiv2023

Boost recall in QSO selection from highly imbalanced photometric datasets

Context. The identification of bright QSOs is of great importance to probe the intergalactic medium and address open questions in cosmology. Several approaches have been adopted to find such sources in currently available photometric surveys, including machine learning methods. However, the rarity of bright QSOs at high redshifts compared to contaminating sources (such as stars and galaxies) makes the selection of reliable candidates a difficult task, especially when high completeness is required. Aims. We present a novel technique to boost recall (i.e., completeness within the considered sample) in the selection of QSOs from photometric datasets dominated by stars, galaxies, and low-z QSOs (imbalanced datasets). Methods. Our method operates by iteratively removing sources whose probability of belonging to a noninteresting class exceeds a user-defined threshold, until the remaining dataset contains mainly high-z QSOs. Any existing machine learning method can be used as underlying classifier, provided it allows for a classification probability to be estimated. We applied the method to a dataset obtained by cross-matching PanSTARRS1, Gaia, and WISE, and identified the high-z QSO candidates using both our method and its direct multi-label counterpart. Results. We ran several tests by randomly choosing the training and test datasets, and achieved significant improvements in recall which increased from 50% to 85% for QSOs with z>2.5, and from 70% to 90% for QSOs with z>3. Also, we identified a sample of 3098 new QSO candidates on a sample of 2.6x10^6 sources with no known classification. We obtained follow-up spectroscopy for 121 candidates, confirming 107 new QSOs with z>2.5. Finally, a comparison of our candidates with those selected by an independent method shows that the two samples overlap by more than 90% and that both methods are capable of achieving a high level of completeness.

astro-ph.IM↗

arXiv2023

A possible surviving companion of the SN Ia in the Galactic SNR G272.2-3.2

We use the {\it Gaia} EDR3 to explore the Galactic supernova remnant SNR G272.2-3.2, produced by the explosion of a Type Ia supernova (SNIa), about 7,500 years ago, to search for a surviving companion. From the abundances in the SNR ejecta, G272.2-3.2 is a normal SN Ia. The {\it Gaia} parallaxes allow to select the stars located within the estimated distance range of the SNR, and the {\it Gaia} proper motions to study their kinematics. From the {\it Gaia} EDR3 photometry, we construct the HR diagram of the selected sample, which we compare with the theoretical predictions for the evolution of possible star companions of SNIa. We can discard several proposed types of companions by combining kinematics and photometry. We can also discard hypervelocity stars. We focus our study on the kinematically most peculiar star, {\it Gaia} EDR3 5323900215411075328 (hereafter MV-G272), a 8.9 $σ$ outlier in proper motion. It is of M1-M2 stellar type. Its trajectory on the sky locates it at the center of the SNR, 6,000--8,000 years ago, a unique characteristic among the the sample. Spectra allow a stellar parameters determination and a chemical abundance analysis. In conclusion, we have a candidate to be the surviving companion of the SN Ia that resulted in SNR G272.2-3.2. It is supported by its kinematical characteristics and its trajectory within the SNR. This opens the possibility of a single-degenerate scenario for a SN Ia with an M-type dwarf companion.

astro-ph.SR↗

arXiv2023

Searching for Intragroup Light in Deep U-band Imaging of the COSMOS Field

We present the results of deep, ground based U-band imaging with the Large Binocular Telescope of the Cosmic Evolution Survey (COSMOS) field as part of the near-UV imaging program, UVCANDELS. We utilize a seeing sorted stacking method along with night-to-night relative transparency corrections to create optimal depth and optimal resolution mosaics in the U-band, which are capable of reaching point source magnitudes of AB 26.5 mag at 3 sigma. These ground based mosaics bridge the wavelength gap between the HST WFC3 F27W and ACS F435W images and are necessary to understand galaxy assembly in the last 9-10 Gyr. We use the depth of these mosaics to search for the presence of U-band intragroup light (IGrL) beyond the local Universe. Regardless of how groups are scaled and stacked, we do not detect any U-band IGrL to unprecedented U-band depths of 29.1-29.6 mag/arcsec2, which corresponds to an IGrL fraction of less than 1% of the total group light. This stringent upper limit suggests that IGrL does not contribute significantly to the Extragalactic Background Light at short wavelengths. Furthermore, the lack of UV IGrL observed in these stacks suggests that the atomic gas observed in the intragroup medium (IGrM) is likely not dense enough to trigger star formation on large scales. Future studies may detect IGrL by creating similar stacks at longer wavelengths or by pre-selecting groups which are older and/or more dynamically evolved similar to past IGrL observations of compact groups and loose groups with signs of gravitational interactions.

astro-ph.GA↗

arXiv2023

Spectroscopy of QUBRICS quasar candidates: 1672 new redshifts and a Golden Sample for the Sandage Test of the Redshift Drift

The QUBRICS (QUasars as BRIght beacons for Cosmology in the Southern hemisphere) survey aims at constructing a sample of the brightest quasars with z>~2.5, observable with facilities in the Southern Hemisphere. QUBRICS makes use of the available optical and IR wide-field surveys in the South and of Machine Learning techniques to produce thousands of bright quasar candidates of which only a few hundred have been confirmed with follow-up spectroscopy. Taking advantage of the recent Gaia Data Release 3, which contains 220 million low-resolution spectra, and of a newly developed spectral energy distribution fitting technique, designed to combine the photometric information with the Gaia spectroscopy, it has been possible to measure 1672 new secure redshifts of QUBRICS candidates, with a typical uncertainty $σ_z = 0.02$. This significant progress of QUBRICS brings it closer to (one of) its primary goals: providing a sample of bright quasars at redshift 2.5 < z < 5 to perform the Sandage test of the cosmological redshift drift. A Golden Sample of seven quasars is presented that makes it possible to carry out this experiment in about 1500 hours of observation in 25 years, using the ANDES spectrograph at the 39m ELT, a significant improvement with respect to previous estimates.

astro-ph.CO↗

arXiv2023

Eddington accreting Black Holes in the Epoch of Reionization

The evolution of the luminosity function (LF) of Active Galactic Nuclei (AGNs) at $z \gtrsim 5$ represents a key constraint to understand their contribution to the ionizing photon budget necessary to trigger the last phase transition in the Universe, i.e. the epoch of Reionization. Recent searches for bright high-z AGNs suggest that the space densities of this population at $z>4$ has to be revised upwards, and sparks new questions about their evolutionary paths. Gas accretion is the key physical mechanism to understand both the distribution of luminous sources and the growth of central Super-Massive Black Holes (SMBHs). In this work, we model the high-z AGN-LF assuming that high-z luminous AGN shine at their Eddington limit: we derive the expected evolution as a function of the ``duty-cycle'' ($f_{\rm dc}$), i.e. the fraction of life-time that a given SMBH spends accreting at the Eddington rate. Our results show that intermediate values ($f_{\rm dc} \simeq 0.1$) predict the best agreement with the ionizing background and photoionization rate, but do not provide enough ionizing photons to account for the observed evolution of the hydrogen neutral fraction. Smaller values ($f_{\rm dc} \lesssim 0.05$) are required for AGNs to be the dominant population responsible for Hydrogen reionization in the Early Universe. We then show that this low-$f_{\rm dc}$ evolution can be reconciled with the current constraints on Helium reionization, although it implies a relatively large number of inactive SMBHs at $z\gtrsim5$, in tension with SMBH growth models based on heavy seeding.

astro-ph.CO↗

arXiv2022

The probabilistic random forest applied to the QUBRICS survey: improving the selection of high-redshift quasars with synthetic data

Several recent works have focused on the search for bright, high-z quasars (QSOs) in the South. Among them, the QUasars as BRIght beacons for Cosmology in the Southern hemisphere (QUBRICS) survey has now delivered hundreds of new spectroscopically confirmed QSOs selected by means of machine learning algorithms. Building upon the results obtained by introducing the probabilistic random forest (PRF) for the QUBRICS selection, we explore in this work the feasibility of training the algorithm on synthetic data to improve the completeness in the higher redshift bins. We also compare the performances of the algorithm if colours are used as primary features instead of magnitudes. We generate synthetic data based on a composite QSO spectral energy distribution. We first train the PRF to identify QSOs among stars and galaxies, then separate high-z quasar from low-z contaminants. We apply the algorithm on an updated dataset, based on SkyMapper DR3, combined with Gaia eDR3, 2MASS and WISE magnitudes. We find that employing colours as features slightly improves the results with respect to the algorithm trained on magnitude data. Adding synthetic data to the training set provides significantly better results with respect to the PRF trained only on spectroscopically confirmed QSOs. We estimate, on a testing dataset, a completeness of ~86% and a contamination of ~36%. Finally, 207 PRF-selected candidates were observed: 149/207 turned out to be genuine QSOs with z > 2.5, 41 with z < 2.5, 3 galaxies and 14 stars. The result confirms the ability of the PRF to select high-z quasars in large datasets.

astro-ph.IM↗