Volume-limited Sample Research Articles

ZTF SN Ia DR2: Overview

We present the first homogeneous release of several thousand spectroscopically classified type Ia supernovae (SNe Ia) with spectroscopic redshifts. This release, named “DR2,” contains 3628 nearby ($z<0.3$) SNe Ia discovered, followed, and classified by the Zwicky Transient Facility survey between March 2018 and December 2020. Of these, 3000 have good-to-excellent sampling and 2667 pass standard cosmology light curve quality cuts. This release is thus the largest SN Ia release to date, increasing by an order of magnitude the number of well-characterized low-redshift objects. With DR2, we also provide a volume-limited ($z<0.06$) sample of nearly a thousand SNe Ia. With such a large, homogeneous, and well-controlled dataset, we are studying key current questions on SN cosmology, such as the linearity SNe Ia standardization, the SN and host dependencies, the diversity of the SN Ia population, and the accuracy of current light curve modeling. These, and more, are studied in detail in a series of articles associated with this release. Alongside the SN Ia parameters, we publish our forced-photometry gri -band light curves, 5138 spectra, local and global host properties, observing logs, and a Python tool to facilitate the use and access of these data. The photometric accuracy of DR2 is not yet suited for cosmological parameter inference, which will follow as the “DR2.5” release. We nonetheless demonstrate that our Hubble diagram of several thousands of SNe Ia has a typical 0.15 mag scatter.

WTP 19aalnxx: Discovery of a Bright Mid-infrared Transient in the Emerging Class of Low-luminosity Supernovae Revealed by Delayed Circumstellar Interaction

While core-collapse supernovae (SNe) often show early and consistent signs of circumstellar medium (CSM) interaction, some exhibit delayed signatures due to interaction with distant material around the progenitor star. Here we present the discovery in NEOWISE data of WTP 19aalnxx, a luminous mid-infrared (MIR) transient in the outskirts of the galaxy KUG 0022-007 at ≈190 Mpc. First detected in 2018, WTP 19aalnxx reaches a peak absolute (Vega) magnitude of ≈−22 at 4.6 μm in ≈3 yr, comparable to the most luminous interacting SNe. Archival data reveal a ≳5× fainter optical counterpart detected since 2015, while follow-up near-infrared observations in 2022 reveal an extremely red (Ks − W2 ≈ 3.7 mag) active transient. Deep optical spectroscopy confirm strong CSM interaction signatures via intermediate-width Balmer emission lines and coronal metal lines. Modeling the broadband spectral energy distribution, we estimate the presence of ≳10−2 M ⊙ of warm dust, likely formed in the cold dense shell. Together with the lack of nebular Fe emission, we suggest that WTP 19aalnxx is a missed, low (optical) luminosity SN in an emerging family of core-collapse SNe distinguished by their CSM-interaction-powered MIR emission that outshines the optical bands. Investigating the Zwicky Transient Facility sample of SNe with NEOWISE data, we find 16 core-collapse SNe (≳3% in a volume-limited sample) without early signs of CSM interaction that exhibit delayed IR brightening, suggestive of dense CSM shells at ≲1017 cm. We suggest that synoptic IR surveys offer a new route to revealing late-time CSM interaction and the prevalence of intense terminal mass loss in massive stars.

Euclid preparation. LVII. Observational expectations for redshift z<7 active galactic nuclei in the Euclid Wide and Deep surveys

We forecast the expected population of active galactic nuclei (AGN) observable in the Euclid Wide Survey (EWS) and Euclid Deep Survey (EDS). Starting from an X-ray luminosity function (XLF), we generated volume-limited samples of the AGN expected in the survey footprints. Each AGN was assigned a spectral energy distribution (SED) appropriate for its X-ray luminosity and redshift, with perturbations sampled from empirical distributions. The photometric detectability of each AGN was assessed via mock observations of the assigned SED. We estimate 40 million AGN will be detectable in at least one band in the EWS and 0.24 million in the EDS, corresponding to surface densities of $ and $. The relative uncertainty on our expectation for detectable AGN is 6.7<!PCT!> for the EWS and 12.5<!PCT!> for the EDS, driven by the uncertainty of the XLF. Employing colour selection criteria on our simulated data we select a sample of $) AGN in the EWS and $) in the EDS, amounting to 10<!PCT!> and 8<!PCT!> of the AGN detectable in the EWS and EDS. Including ancillary Rubin/LSST bands improves the completeness and purity of AGN selection. These data roughly double the total number of selected AGN to comprise 21<!PCT!> and 15<!PCT!> of the detectable AGN in the EWS and EDS. The total expected sample of colour-selected AGN contains 6.0\,times \,106 (74<!PCT!>) unobscured AGN and 2.1\,times \,106 (26<!PCT!>) obscured AGN, covering $0.02 z 5.2$ and $43 (L_ bol erg s 47$. With these simple colour cuts expected surface densities are already comparable to the yield of modern X-ray and mid-infrared surveys of similar area. The EWS sample is most comparable to the WISE C75 AGN selection and the EDS sample is most similar to the yield of the collated Spitzer cryogenic surveys when considering bands alone, or the XXL-3XLSS survey AGN sample when also considering selection with ancillary optical bands We project that 15<!PCT!> (7.6<!PCT!>) of the total detectable population in the EWS (EDS) will exhibit X-ray fluxes that could be detected in the XMM-COSMOS survey, showing that the vast majority of AGN would not be detectable in modern medium-depth X-ray surveys.

ZTF SN Ia DR2: The spectral diversity of Type Ia supernovae in a volume-limited sample

More than 3000 spectroscopically confirmed Type Ia supernovae (SNe Ia) are presented in the second data release (DR2) of the Zwicky Transient Facility survey. In this paper we detail the spectral properties of 482 SNe Ia near maximum light, up to a redshift limit of z leq 0.06. We measured the velocities and pseudo-equivalent widths (pEW) of key spectral features ( and and investigated the relation between the properties of the spectral features and the photometric properties from the SALT2 light-curve parameters as a function of spectroscopic sub-class. We discuss the non-negligible impact of host galaxy contamination on SN Ia spectral classifications, and we investigate the accuracy of spectral template matching of the DR2 sample. We define a new subclass of underluminous SNe Ia (04gs-like) that lie spectroscopically between normal SNe Ia and transitional 86G-like SNe Ia (stronger than normal SNe Ia, but significantly weaker features than 86G-like SNe). We model these 04gs-like SN Ia spectra using the radiative-transfer spectral synthesis code tardis and show that cooler temperatures alone are unable to explain their spectra; some changes in elemental abundances are also required. However, the broad continuity in spectral properties seen from bright (91T-like) to faint normal SN Ia, including the transitional and 91bg-like SNe Ia, suggests that variations within a single explosion model may be able to explain their behaviour.

A Micro-Flow Liquid Chromatography-Mass Spectrometry Method for the Quantification of Oxylipins in Volume-Limited Human Plasma.

Oxylipins are well-known lipid mediators in various inflammatory conditions. Their endogenous concentrations range from low picomolar to nanomolar, and there are growing demands to determine their concentrations in low-volume matrices for pathological studies, including blood, cerebrospinal fluids from animal disease models, infants, and microsampling devices. Most of the published quantification methods for comprehensive profiling of oxylipins still require more than 50µL plasma as a starting volume to detect these low levels. The aim of our study is to develop a sensitive and reliable method for the quantification of oxylipins in volume-limited human plasma samples. We established and validated a micro-liquid chromatography (LC)-mass spectrometry (MS)/MS method that requires only 5µL of human plasma for the determination of 66 oxylipins. The optimized micro-LC-MS/MS method utilized a flow rate of 4µL/min with a 0.3-mm inner diameter column. With an injection volume of 3µL, our method provides limits of detection in the range from 0.1 to 91.9pM, and limits of quantification range from 0.3 to 306.2pM. The sensitivity enhancement compared to conventional flow ranged from 1.4 to 180.7 times for 51 compounds depending on their physical-chemical properties. After validation, the method was applied to analyze 40 plasma samples from a healthy aging study to demonstrate robustness and sensitivity.

Towards a complete census of luminous Compton-thick active galactic nuclei in the Local Universe

X-ray surveys provide the most efficient means for the detection of active galactic nuclei (AGNs). However, they do face difficulties in detecting the most heavily obscured Compton-thick AGNs. The BAT detector on board the mission, operating in the very hard 14-195 keV band, has provided the largest samples of Compton-thick AGN in the Local Universe. However, even these flux-limited samples may miss the most obscured sources among the Compton-thick AGN population. A robust way to find these local sources is to systematically study volume-limited AGN samples detected in the IR or the optical part of the spectrum. Here, we utilise a local sample (<100 Mpc) of mid-IR-selected AGNs, unbiased against obscuration, to determine the fraction of Compton-thick sources in the Local Universe. When available, we acquired X-ray spectral information for the sources in our sample from previously published studies. In addition, to maximise the X-ray spectral information for the sources in our sample, we analysed eleven unexplored and observations, for the first time. In this way, we identified four new Compton-thick sources. Our results reveal an increased fraction of Compton-thick AGNs among the sources that have not been detected by BAT of 44 <!PCT!>. Overall, we have estimated a 25-30<!PCT!> share of Compton-thick sources in the Local Universe among mid-IR-selected AGNs. We find no evidence for any evolution of the AGN Compton-thick fraction with luminosity.

Microfluidics in Assessing Platelet Function.

Microfluidics incorporate physiologically relevant substrates and flows that mimic the vasculature and are, therefore, a valuable tool for studying aspects of thrombosis and hemostasis. At high-shear environments simulating arterial flow, a microfluidic assay facilitates the study of platelet function, as platelet-rich thrombi form in a localized stenotic region of a flow channel. Utilizing devices that allow for small sample volume can additionally aid in evaluating platelet function under flow from volume-limited patient samples or animal models. Studying trauma patient samples or samples following platelet product transfusion may aid in directing therapeutic strategies for patient populations in which platelet function is critical. Effects of platelet inhibition via pharmacological agents can also be studied in this model. The objective of this protocol is to establish a microfluidic platform that incorporates physiologic flow, biological surfaces, and relevant hemostatic mechanisms to assess platelet function with implications for the study of trauma induced coagulopathy and transfusion medicine.

Bar Presence in Local Galaxies: Dependence on Morphology in Field Galaxies

We analyzed the fractions of barred galaxies in the local Universe using a volume-limited sample of galaxies from the Sloan Digital Sky Survey Data Release 3. We examined 116 field galaxies with redshifts between 0.0207 and 0.030, using r and z-band images. Overall, the bar fraction was 26% in the r-band and 19% in the z-band. For distinct morphological groups, barred spiral galaxies had fractions of 33% in the r-band and 22% in the z-band, while barred lenticular galaxies had 25% in the r-band and 12% in the z-band. We observed that the bar fraction in spiral galaxies increases for stellar masses log (M */M ⊙) > 10.5 and for galaxies with red colors (u − r) > 2.0. Additionally, most barred galaxies have a bulge-to-total ratio B/T ≤ 0.2. Our results indicate that the bar fraction is more dependent on internal morphology than on the galaxy environment.

Host Galaxy Properties of Gamma-Ray Bursts Involving Neutron Star Binary Mergers and Their Impact on Kilonovae Rates

In the upcoming gravitational-wave (GW) observing runs, identifying host galaxies is crucial as it provides essential redshift information and enables the use of GW events as standard sirens. However, pinpointing host galaxies remains challenging due to the large localization uncertainties and the rapidly fading nature of their optical counterparts. Analyzing the host galaxies of short gamma-ray bursts (sGRBs) offers an alternative approach to deepen our understanding of the environments where binary neutron stars (BNS) primarily merge. This study compiles archival photometric data for the host galaxies of 76 sGRBs and four hybrid GRBs that are long GRBs accompanied by kilonova-like signals. We use this data to evaluate their physical properties through spectral energy distribution fitting. To assess the characteristics of the host galaxies, we utilized a volume-limited sample (z < 0.5) from the COSMOS field as a control group. Contrary to expectations that the BNS merger rate is proportional to host stellar mass, the short and hybrid GRB population appears less massive than the mass-weighted distribution of the control sample. Instead, we propose a formulation for the expected BNS merger rate from a galaxy as log(nBNSGyr-1)=0.86×log(M*/M⊙) + 0.44×log(sSFRyr-1)+0.857 , which optimally explains the deviation between the stellar mass distributions of the GRB host galaxies and the control sample. These insights provide a strategic framework for targeted GW follow-ups and enhance our ability to identify potential host galaxies for future GW events.

Younger age for the oldest magnetic white dwarfs

Abstract Sufficiently old white dwarfs cool down through a convective envelope that directly couples their degenerate cores to the surface. Magnetic fields may inhibit this convection by stiffening the criterion for convective instability. We consistently implemented the modified criterion in the stellar evolution code mesa, and computed the cooling of white dwarfs as a function of their mass and magnetic field B. In contrast to previous estimates, we find that magnetic fields can significantly change the cooling time t even if they are relatively weak $B^2\ll 8\pi P$, where P is the pressure at the edge of the degenerate core. Fields B ≳ 1 MG open a radiative window that decouples the core from the convective envelope, effectively lowering the luminosity to that of a fully radiative white dwarf. We identified a population of observed white dwarfs that are younger by Δt ∼ Gyr than currently thought due to this magnetic inhibition of convective energy transfer – comparable to the cooling delay due to carbon–oxygen phase separation. In volume-limited samples, the frequency and strength of magnetic fields increase with age. Accounting for magnetic inhibition is therefore essential for accurate cooling models for cosmic chronology and for determining the origin of the magnetic fields.

Rapid Screening of Biomarkers in KYSE-150 Cells Exposed to Polycyclic Aromatic Hydrocarbons via Inkjet Printing Single-Cell Mass Spectrometry.

Single-cell analysis by mass spectrometry (MS) is emerging as a powerful tool that not only contributes to cellular heterogeneity but also offers an unprecedented opportunity to predict pathology onset and facilitates novel biomarker discovery. However, the development of single-cell MS analysis techniques with a focus on sample extraction, separation, and ionization methods for volume-limited samples and complexity of cellular samples are still a big challenge. In this study, we present a high-throughput approach to inkjet drop on demand printing single-cell MS for rapid screening of biomarkers of polycyclic aromatic hydrocarbon (PAH) exposure at the KYSE-150 cell, aiming to elucidate the pathogenesis of PAH-induced esophageal cancer. With an analytical bulk KYSE-150 cell throughput of up to 51 cells per minute, the method provides a new opportunity for simultaneous single-cell analysis of multiple biomarkers. We screened 930 characteristic ions from 3,683 detected peak signals and identified 91 distinctive molecules that exhibited significant differences under various concentrations of PAH exposure. These molecules have potential as clinical diagnostic biomarkers. Additionally, the current study identifies specific biomarkers that behave completely opposite in single-cell and multicell lipidomics as the concentration of PAH changes. These biomarkers potentially subdivide KYSE-150 cells into PAH-sensitive and PAH-insensitive types, providing a basis for revealing PAH toxicity and disease pathogenesis from the heterogeneity of cellular metabolism.

Early Results from the HUMDRUM Survey: A Small, Earth-mass Planet Orbits TOI-1450A

M-dwarf stars provide us with an ideal opportunity to study nearby small planets. The HUnting for M Dwarf Rocky planets Using MAROON-X (HUMDRUM) survey uses the MAROON-X spectrograph, which is ideally suited to studying these stars, to measure precise masses of a volume-limited (<30 pc) sample of transiting M-dwarf planets. TOI-1450 is a nearby (22.5 pc) binary system containing a M3 dwarf with a roughly 3000 K companion. Its primary star, TOI-1450A, was identified by the Transiting Exoplanet Survey Satellite (TESS) to have a 2.04 days transit signal, and is included in the HUMDRUM sample. In this paper, we present MAROON-X radial velocities (RVs) which confirm the planetary nature of this signal and measure its mass at nearly 10% precision. The 2.04 days planet, TOI-1450A b, has R b = 1.13 ± 0.04 R ⊕ and M b = 1.26 ± 0.13 M ⊕. It is the second-lowest-mass transiting planet with a high-precision RV mass measurement. With this mass and radius, the planet’s mean density is compatible with an Earth-like composition. Given its short orbital period and slightly sub-Earth density, it may be amenable to JWST follow-up to test whether the planet has retained an atmosphere despite extreme heating from the nearby star. We also discover a nontransiting planet in the system with a period of 5.07 days and a Msinic=1.53±0.18M⊕ . We also find a 2.01 days signal present in the systems’s TESS photometry that likely corresponds to the rotation period of TOI-1450A’s binary companion, TOI-1450B. TOI-1450A, meanwhile, appears to have a rotation period of approximately 40 days, which is in line with our expectations for a mid-M dwarf.

Galaxy Zoo DESI: large-scale bars as a secular mechanism for triggering AGNs

ABSTRACT Despite the evidence that supermassive black holes (SMBHs) co-evolve with their host galaxy, and that most of the growth of these SMBHs occurs via merger-free processes, the underlying mechanisms which drive this secular co-evolution are poorly understood. We investigate the role that both strong and weak large-scale galactic bars play in mediating this relationship. Using 48 871 disc galaxies in a volume-limited sample from Galaxy Zoo DESI, we analyse the active galactic nucleus (AGN) fraction in strongly barred, weakly barred, and unbarred galaxies up to $z = 0.1$ over a range of stellar masses and colours. After controlling for stellar mass and colour, we find that the optically selected AGN fraction is $31.6 \pm 0.9$ per cent in strongly barred galaxies, $23.3 \pm 0.8$ per cent in weakly barred galaxies, and $14.2 \pm 0.6$ per cent in unbarred disc galaxies. These are highly statistically robust results, strengthening the tantalizing results in earlier works. Strongly barred galaxies have a higher fraction of AGNs than weakly barred galaxies, which in turn have a higher fraction than unbarred galaxies. Thus, while bars are not required in order to grow an SMBH in a disc galaxy, large-scale galactic bars appear to facilitate AGN fuelling, and the presence of a strong bar makes a disc galaxy more than twice as likely to host an AGN than an unbarred galaxy at all galaxy stellar masses and colours.

Mass calibration of DES Year-3 clusters via SPT-3G CMB cluster lensing

We measure the stacked lensing signal in the direction of galaxy clusters in the Dark Energy Survey Year 3 (DES Y3) redMaPPer sample, using cosmic microwave background (CMB) temperature data from SPT-3G, the third-generation CMB camera on the South Pole Telescope (SPT). Here, we estimate the lensing signal using temperature maps constructed from the initial 2 years of data from the SPT-3G 'Main' survey, covering 1500 deg2 of the Southern sky. We then use this lensing signal as a proxy for the mean cluster mass of the DES sample. The thermal Sunyaev-Zel'dovich (tSZ) signal, which can contaminate the lensing signal if not addressed, is isolated and removed from the data before obtaining the mass measurement. In this work, we employ three versions of the redMaPPer catalogue: a Flux-Limited sample containing 8865 clusters, a Volume-Limited sample with 5391 clusters, and a Volume&Redshift-Limited sample with 4450 clusters. For the three samples, we detect the CMB lensing signal at a significance of 12.4σ, 10.5σ and 10.2σ and find the mean cluster masses to be M 200m = 1.66±0.13 [stat.]± 0.03 [sys.], 1.97±0.18 [stat.]± 0.05 [sys.], and 2.11±0.20 [stat.]± 0.05 [sys.]×1014 M⊙, respectively. This is a factor of ∼ 2 improvement relative to the precision of measurements with previous generations of SPT surveys and the most constraining cluster mass measurements using CMB cluster lensing to date. Overall, we find no significant tensions between our results and masses given by redMaPPer mass-richness scaling relations of previous works, which were calibrated using CMB cluster lensing, optical weak lensing, and velocity dispersion measurements from various combinations of DES, SDSS and Planck data. We then divide our sample into 3 redshift and 3 richness bins, finding no significant discrepancies with optical weak-lensing calibrated masses in these bins. We forecast a 5.7% constraint on the mean cluster mass of the DES Y3 sample with the complete SPT-3G surveys when using both temperature and polarization data and including an additional ∼ 1400 deg2 of observations from the 'Extended' SPT-3G survey.

Magnetic field breakout in ultramassive crystallizing white dwarfs

ABSTRACT Ultramassive white dwarfs with masses $M\gtrsim 1.1\, {\rm M}_{\odot }$ probe extreme physics near the Chandrasekhar limit. Despite the rapid increase in observations, it is still unclear how many harbour carbon–oxygen (CO) versus oxygen–neon (ONe) cores. The origin of these white dwarfs and their strong magnetic fields – single stellar evolution or a stellar merger – is another open question. The steep mass–radius relation of the relativistic ultramassive white dwarfs shortens their crystallization time $t_{\rm cryst}$, such that the recently proposed crystallization dynamo mechanism may present an alternative to mergers in explaining the early appearance of magnetism in the observed population. However, the magnetic diffusion time from the convective dynamo to the white dwarf’s surface delays the magnetic field’s breakout time $t_{\rm break}\gt t_{\rm cryst}$. We compute $t_{\rm break}(M)$ for CO and ONe ultramassive white dwarfs and compare it to the local 40 pc volume-limited sample. We find that the breakout time from CO cores is too long to account for the observations. ONe crystallization dynamos remain a viable option, but their surrounding non-convective envelopes comprise only a few per cent of the total mass, such that $t_{\rm break}$ is highly sensitive to the details of stellar evolution.

The SRG/eROSITA All-Sky Survey

Context. The spatial distribution of galaxy clusters provides a reliable tracer of the large-scale distribution of matter in the Universe. The clustering signal depends on intrinsic cluster properties and cosmological parameters. Aims. The ability of eROSITA on board Spectrum-Roentgen-Gamma (SRG) to discover galaxy clusters allows the association of extended X-ray emission with dark matter haloes to be probed. We measured the projected two-point correlation function to study the occupation of dark matter haloes by clusters and groups detected by the first eROSITA all-sky survey (eRASS1). Methods. We created five volume-limited samples probing clusters with different redshifts and X-ray luminosity values. We interpreted the correlation function with halo occupation distribution (HOD) and halo abundance matching (HAM) models. We simultaneously fit the cosmological parameters and halo bias of a flux-limited sample of 6493 clusters with purity &gt; 96%. Results. We obtained a detailed view of the halo occupation for eRASS1 clusters. The fainter population at low redshift (S0: L̄X = 4.63 × 1043 erg s−1, 0.1 &lt; z &lt; 0.2) is the least biased compared to dark matter, with b = 2.95 ± 0.21. The brightest clusters up to higher redshift (S4: L̄X = 1.77 × 1044 erg s−1, 0.1 &lt; z &lt; 0.6) exhibit a higher bias b = 4.34 ± 0.62. Satellite groups are rare, with a satellite fraction &lt; 14.9% (8.1) for the S0 (S4) sample. We combined the HOD prediction with a HAM procedure to constrain the scaling relation between LX and mass in a new way, and find a scatter of ⟨σLx⟩ = 0.36. We obtain cosmological constraints for the physical cold dark matter density ωc = 0.12−0.02+0.03 and an average halo bias b = 3.63−0.85+1.02. Conclusions. We modelled the clustering of galaxy clusters with a HOD approach for the first time, paving the way for future studies combining eROSITA with 4MOST, SDSS, Euclid, Rubin, and DESI to unravel the cluster distribution in the Universe.

A Volume-limited Sample of Ultracool Dwarfs. II. The Substellar Age and Mass Functions in the Solar Neighborhood

We present the most precise constraints to date for the mass and age distributions of single ultracool dwarfs in the solar neighborhood, based on an updated volume-limited sample of 504 L, T, and Y dwarfs within 25 pc. We develop a Monte Carlo approach using the 〈V/Vmax〉 statistic to correct for incompleteness and obtain a space density of (1.83−0.15+0.16)×10−2 pc−3 for spectral types L0–Y2. We calculate bolometric luminosities for our sample, using an updated “super-magnitude” method for the faintest objects. We use our resulting luminosity function and a likelihood-based population synthesis approach to simultaneously constrain the mass and age distributions. We employ the fraction of young L0–L7 dwarfs as a novel input for this analysis that is crucial for constraining the age distribution. For a power-law mass function dNdM∝M−α , we find α=0.58−0.20+0.16 , indicating an increase in numbers toward lower masses, consistent with measurements in nearby star-forming regions. For an exponential age distribution b(t) ∝ e −β t we find β = −0.44 ± 0.14, i.e., a population with fewer old objects than often assumed, which may reflect dynamical heating of the Galactic plane as much as the historical brown dwarf birthrate. We compare our analysis to that of Kirkpatrick et al., who used a similar volume-limited sample. Although our mass function measurements are numerically consistent, their assumption of a flat age distribution is disfavored by our analysis, and we identify several important methodological differences between our two studies. Our calculation of the age distribution of solar neighborhood brown dwarfs is the first based on a volume-limited sample.

Halo Asymmetry in the Modeling of Galaxy Clustering

Conventional studies of galaxy clustering within the framework of halo models typically assume that the density profile of all dark matter halos can be approximated by the Navarro–Frenk–White (NFW) spherically symmetric profile. However, both modern N-body simulations and observational data suggest that most halos are either oblate or prolate, and almost never spherical. In this paper we present a modified model of the galaxy correlation function. In addition to the five “classical” halo occupation distribution (HOD) parameters proposed by Zheng et al., it includes an additional free parameter ϕ in the modified NFW density profile describing the asymmetry of the host dark matter halo. Using a subhalo abundance matching model, we populate galaxies within BolshoiP N-body simulations. We compute the projected two-point correlation function w p (r p ) for six stellar-mass volume-limited galaxy samples. We fit our model to the results and then compare the best-fit asymmetry parameter ϕ (and other halo parameters) to the asymmetry of dark matter halos measured directly from the simulations and find that they agree within 1σ. We then fit our model to the w p (r p ) results from Zehavi et al. and compare halo parameters. We show that our model accurately retrieves the halo asymmetry and other halo parameters. Additionally, we find 2%–6% differences between the halo masses ( logMmin and logM 1) estimated by our model and those estimated by “classical” HOD models. The model proposed in this paper can serve as an alternative to multiparameter HOD models, since it can be used for relatively small samples of galaxies.

A 500 pc volume-limited sample of hot subluminous stars. I. Space density, scale height, and population properties

We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from the Gaia space mission data release 3 (DR3). The sample comprises a total of 397 members, with 305 ($ 77&lt;!PCT!&gt;$) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 ($ are hydrogen-rich sdBs, 65 are sdOBs ($ 21&lt;!PCT!&gt;$), 32 are sdOs ($ 11&lt;!PCT!&gt;$), and 30 are He-sdO/Bs ($ 10&lt;!PCT!&gt;$). Among them, 48 ($ 16&lt;!PCT!&gt;$) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90&lt;!PCT!&gt; complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in the Gaia colour-magnitude diagram (CMD). The remaining sources in the sample include cataclysmic variables (CVs), blue horizontal branch stars (BHBs), hot white dwarfs (WDs), and MS stars. We derived the mid-plane density $ $ and scale height $ h z $ for the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech$^2$). The best-fit values are $ $ stars/pc3 and $ h z 62$ pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases to $ $ stars/pc3. This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates.

Identification of new nearby white dwarfs using Gaia DR3

Context. A volume-complete sample of white dwarfs is essential for statistical studies of the white dwarf population. The sample of nearby white dwarfs is the only one that allows the faint end of the luminosity function to be probed and thus is the only one that covers the entire range of white dwarf ages. However, due to their intrinsic faintness, even nearby white dwarfs are difficult to identify. Aims. Our work focuses on improving the completeness and purity of the white dwarf census within 50 pc of the Sun. To accomplish this, we used Gaia Data Release 3 (Gaia DR3) to identify and characterise new and previously overlooked white dwarfs in the solar neighbourhood. We also identify objects with spurious astrometric solutions in Gaia DR3 but claimed as high-confidence white dwarfs in the Gaia Catalogue of White Dwarfs (GCWD21) by Gentile Fusillo et al. (2021, MNRAS, 508, 3877). Methods. Based on the astrometry and photometry in Gaia DR3, we identified new nearby white dwarfs and validated those that had been missed from recent white dwarf catalogues despite being previously documented. To ensure the reliability of their astrometric solutions, we used a cut on just two parameters from Gaia DR3: the amplitude of the image parameter determination goodness-of-fit and the parallax-over-error ratio. In addition, we imposed photometric signal-to-noise requirements to ensure the reliable identification of white dwarfs when using the colour-magnitude diagram. Results. We have identified nine previously unreported white dwarfs within the local population of 50 pc, and validated 21 previously reported white dwarfs missing from the GCWD21 and other recent volume-limited white dwarf samples. A few of these objects belong to the rare class of ultra-cool white dwarfs. Four white dwarfs in our sample have an effective temperature of Teff ≤ 4000 K within the 1σ interval, and two of them have an absolute magnitude of MG &gt; 16.0 mag. The identified white dwarfs are predominantly located in crowded fields, such as near the Galactic plane or in the foreground of the Large Magellanic Cloud. We also find that 20 of these white dwarfs have common proper motion companions with angular separations ranging from 1.1″ to 7.1″ and brightness differences between the components of up to 9.8 magnitudes. One of these systems is a triple system consisting of a white dwarf and two K dwarfs, while another is a double white dwarf system. The identified white dwarfs represent a 1.3% improvement in the completeness of the 50 pc sample, resulting in a new total of 2265 known white dwarfs located within 50 pc of the Sun. We have identified 103 contaminants among the 2338 high-confidence white dwarfs in the 50 pc subsample of the GCWD21 and have found that their astrometric solutions in Gaia DR3 are spurious, improving the purity by 4.4%.