Photometric Colors Research Articles

Exploring Filament Galaxies Using AstroSat/UVIT

Abstract We present results from our deep far-ultraviolet (FUV) survey using AstroSat/UVIT of a filamentary structure at z ∼0.072. A total of four filaments comprising 58 galaxies were probed in our study. We detect 18 filament galaxies in our FUV observation. All filament galaxies are further classified based on their photometric color, nuclear activity, and morphology. The filaments contain galaxies with mixed stellar population types and structures. We do not detect galaxies in our UVIT survey up to a distance of 0.4 Mpc h −1 from the filament axis, implying a lack of recent star formation in the inner region of filaments. The FUV star formation rate (SFR) for star-forming galaxies agrees well with the SFR144MHz calculated using Low-Frequency Array radio-continuum observations. We witness an increase in the FUV specific-SFR (sSFR) of filament galaxies with increasing distance from the filament spine (D fil). The intermediate-to-high stellar mass filament galaxies were more star-forming than cluster galaxies in a fixed stellar mass bin. The FUV morphology of some filament galaxies detected in the filament outskirts (D fil ≳ 0.7 Mpc h −1) is comparable to or slightly extended than their optical counterpart. The mass assembly of galaxies examined by estimating (FUV − r) color gradients shows that more “red-cored’ galaxies reside in the outer region of the filaments. Our results prove that the likelihood of merger interaction and gas starvation increases when approaching the filament spine. We report a definitive and inhomogeneous impact of filaments on the galaxies residing inside them.

The Effect of Age and Stellar Model Choice on Globular Cluster Color-to-metallicity Conversions

The photometric colors of globular clusters (GCs) act as effective proxies for metallicity, since all normally used optical/IR color indices exhibit a nonlinear but monotonic relation between their integrated color and their metallicity. One color index, (g − z) or (F475W–F850LP), has been spectroscopically calibrated in several studies, providing leverage to define color-to-metallicity conversions for other indices. In this paper, building on the work of Hartman et al., we study the GC color-metallicity relation in more detail by testing the dependence of the relations on different suites of stellar models and different assumed GC ages. Though noticeable differences between models exist, we find that the net effect on the derived GCS metallicity distributions is small.

A Census of Photometrically Selected Little Red Dots at 4 < z < 9 in JWST Blank Fields

Observations with the James Webb Space Telescope (JWST) have uncovered numerous faint active galactic nuclei (AGN) at z ∼ 5 and beyond. These objects are key to our understanding of the formation of supermassive black holes (SMBHs), their coevolution with host galaxies, as well as the role of AGN in cosmic reionization. Using photometric colors and size measurements, we perform a search for compact red objects in an array of blank deep JWST/NIRCam fields totaling ∼640 arcmin2. Our careful selection yields 260 reddened AGN candidates at 4 < z phot < 9, dominated by a point-source-like central component (〈r eff〉 < 130 pc) and displaying a dichotomy in their rest-frame colors (blue UV and red optical slopes). Quasar model fitting reveals our objects to be moderately dust-extincted (A V ∼ 1.6), which is reflected in their inferred bolometric luminosities of L bol = 1044–47 erg s−1 and fainter UV magnitudes M UV ≃ −17 to −22. Thanks to the large areas explored, we extend the existing dusty AGN luminosity functions to both fainter and brighter magnitudes, estimating their number densities to be ×100 higher than for UV-selected quasars of similar magnitudes. At the same time, they constitute only a small fraction of all UV-selected galaxies at similar redshifts, but this percentage rises to ∼10% for M UV ∼ − 22 at z ∼ 7. Finally, assuming a conservative case of accretion at the Eddington rate, we place a lower limit on the SMBH mass function at z ∼ 5, finding it to be consistent with both theory and previous JWST observations.

Cosmic Dragons: A Two-Component Mixture Model of COSMOS Galaxies

Using the photometric population prediction method {}, we characterize the Red Sequence (RS) and Blue Cloud (BC) of DES galaxies in the COSMOS field. Red Dragon (RD) uses a redshift-evolving, error-corrected Gaussian mixture model to detail the distribution of photometric colors, smoothly parameterizing the two populations with relative weights, mean colors, intrinsic scatters, and inter-color correlations. This resulting fit of RS and BC yields RS membership probabilities for each galaxy. Even when training on only DES main bands griz, RD selects the quiescent population (defined here as galaxies with ) with ≳90% balanced accuracy out to z=2; augmenting with extended photometry from VIRCAM improves this accuracy to ∼95% out to z=3. We measure redshift evolution of sSFR and galactic age in several stellar mass bins, finding that the BC is consistently more star-forming (by ) and typically younger (by ) than the RS (up to z∼1.4). This characterization of both RS and BC as functions of redshift and stellar mass improves our understanding of both populations and opens the door to more precise galaxy population characterization in future deep optical and IR systems.

Stellar Atmospheric Parameters for Cool Dwarfs in Gaia Data Release 3

We provide a catalog of atmospheric parameters for 1,806,921 cool dwarfs from Gaia Data Release 3 (DR3) that lie within the range covered by LAMOST cool dwarf spectroscopic parameters: 3200 K < T eff < 4300 K, −0.8 < [M/H] < 0.2 dex, and 4.5 < log g < 5.5 dex. Our values are derived based on machine-learning models trained with multiband photometry corrected for dust. The photometric data comprise optical data from the Sloan Digital Sky Survey r, i, and z bands, near-infrared data from the Two Micron All Sky Survey J, H, and K bands, and mid-infrared data from the ALLWISE W1 and W2 bands. We used both random forest and light gradient boosting machine machine-learning models and found similar results from both, with an error dispersion of 68 K, 0.22 dex, and 0.05 dex for T eff, [M/H], and log g, respectively. Assessment of the relative feature importance of different photometric colors indicated W1 − W2 as most sensitive to both T eff and log g, with J − H being most sensitive to [M/H]. We find that our values show a good agreement with the Apache Point Observatory Galactic Evolution Experiment, but are significantly different to those provided as part of Gaia DR3.

Euclid preparation

The technique of photometric redshifts has become essential for the exploitation of multi-band extragalactic surveys. While the requirements on photometric redshifts for the study of galaxy evolution mostly pertain to the precision and to the fraction of outliers, the most stringent requirement in their use in cosmology is on the accuracy, with a level of bias at the sub-percent level for the Euclid cosmology mission. A separate, and challenging, calibration process is needed to control the bias at this level of accuracy. The bias in photometric redshifts has several distinct origins that may not always be easily overcome. We identify here one source of bias linked to the spatial or time variability of the passbands used to determine the photometric colours of galaxies. We first quantified the effect as observed on several well-known photometric cameras, and found in particular that, due to the properties of optical filters, the redshifts of off-axis sources are usually overestimated. We show using simple simulations that the detailed and complex changes in the shape can be mostly ignored and that it is sufficient to know the mean wavelength of the passbands of each photometric observation to correct almost exactly for this bias; the key point is that this mean wavelength is independent of the spectral energy distribution of the source. We use this property to propose a correction that can be computationally efficiently implemented in some photometric-redshift algorithms, in particular template-fitting. We verified that our algorithm, implemented in the new photometric-redshift code Phosphoros, can effectively reduce the bias in photometric redshifts on real data using the CFHTLS T007 survey, with an average measured bias Δz over the redshift range 0.4 ≤ z ≤ 0.7 decreasing by about 0.02, specifically from Δz ≃ 0.04 to Δz ≃ 0.02 around z = 0.5. Our algorithm is also able to produce corrected photometry for other applications.

Maintaining high‐triglyceride content and reducing free fatty acids in distillers corn oil: A catalyst‐free multivariate strategy

AbstractDistillers corn oil (DCO), a byproduct of corn ethanol production, offers an alternative glyceride source for biodiesel production. Nonetheless, its higher free fatty acids (FFA) content compared to other vegetable oils hampers its direct conversion into fatty acid methyl esters (FAME) due to soap formation, catalysts' activity decreasing, and emulsions generation (thus reducing FAME yield), which compromise the quality and stability of the biodiesel produced. Thus, pretreatment steps such as esterification may reduce the FFA to mitigate these issues. In this context, by utilizing glycerine, a solution emerges: esterifying these high‐acidity oils to convert FFA into triglycerides (TAG) before transesterification. However, little is known about how integrated reaction conditions can affect the process in a catalyst‐free system. Thus, our study was guided by a clear‐cut objective: transforming DCO into a raw material ideally suited for biodiesel production, which involved a dramatic reduction in FFA content, reducing it from 18% to a mere 2% while preserving a high concentration of TAG. For that, we systematically employed a response surface methodology with a three‐factorial central composite design to investigate the complex interactions among key parameters: temperature, vacuum pressure, and the glycerol/oil mass ratio. Elevated temperatures and a 2:1 glycerol/oil mass ratio were beneficial for FFA reduction, increased TAG content, and improved oil color. Interaction analysis identified synergistic temperature and vacuum pressure effects on FFA reduction, TAG production, and photometric color index reduction, revealing optimal conditions. Hence, the statistical model highlights DCO as a viable oil for future transesterification processes, laying the foundation for an eco‐friendly and economically efficient biodiesel production network.

The First Y Dwarf Data from JWST Show that Dynamic and Diabatic Processes Regulate Cold Brown Dwarf Atmospheres

The James Webb Space Telescope (JWST) is now observing Y dwarfs, the coldest known brown dwarfs, with effective temperatures T eff ≲ 475 K. The first published observations provide important information: not only is the atmospheric chemistry out of equilibrium, as previously known, but the pressure–temperature profile is not in the standard adiabatic form. The rapid rotation of these Jupiter-size, isolated, brown dwarfs dominates the atmospheric dynamics, and thermal and compositional changes disrupt convection. These processes produce a colder lower atmosphere, and a warmer upper atmosphere, compared to a standard adiabatic profile. Leggett et al. presented empirical models where the pressure–temperature profile was adjusted so that synthetic spectra reproduced the 1 ≲ λ (μm) ≲ 20 spectral energy distributions of brown dwarfs with 260 ≤ T eff (K) ≤ 540. We show that spectra generated by these models fit the first JWST Y dwarf spectrum better than standard-adiabat models. Unexpectedly, there is no 4.3 μm PH3 feature in the JWST spectrum and atmospheres without phosphorus better reproduce the 4 μm flux peak. Our analysis of new JWST photometry indicates that the recently discovered faint secondary of the WISE J033605.05-014350AB system has T eff ≈ 295 K, making it the first dwarf in the significant luminosity gap between the 260 K WISE J085510.83-071442.5, and all other known Y dwarfs. The adiabat-adjusted disequilibrium-chemistry models are recommended for analyses of all brown dwarfs cooler than 600 K, and a grid is publicly available. Photometric color transformations are provided in an appendix.

Probabilistic classification of infrared-selected targets for SPHEREx mission: in search of young stellar objects

ABSTRACT We apply machine learning algorithms to classify infrared (IR)-selected targets for NASA’s upcoming Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) mission. In particular, we are interested in classifying young stellar objects (YSOs), which are essential for understanding the star formation process. Our approach differs from previous works, which have relied heavily on broad-band colour criteria to classify IR-bright objects, and are typically implemented in colour–colour and colour–magnitude diagrams. However, these methods do not state the confidence associated with the classification and the results from these methods are quite ambiguous due to the overlap of different source types in these diagrams. Here, we utilize photometric colours and magnitudes from seven near- and mid-IR bands simultaneously and employ machine and deep learning algorithms to carry out probabilistic classification of YSOs, asymptotic giant branch (AGB) stars, active galactic nuclei (AGNs), and main-sequence (MS) stars. Our approach also subclassifies YSOs into Class I, II, III, and flat spectrum YSOs, and AGB stars into carbon-rich and oxygen-rich AGB stars. We apply our methods to IR-selected targets compiled in preparation for SPHEREx which are likely to include YSOs and other classes of objects. Our classification indicates that out of 8308 384 sources, 1966 340 have class prediction with probability exceeding 90 per cent, amongst which $\sim 1.7~{{\ \rm per\ cent}}$ are YSOs, $\sim 58.2~{{\ \rm per\ cent}}$ are AGB stars, $\sim 40~{{\ \rm per\ cent}}$ are (reddened) MS stars, and $\sim 0.1~{{\ \rm per\ cent}}$ are AGNs whose red broad-band colours mimic YSOs. We validate our classification using the spatial distributions of predicted YSOs towards the Cygnus-X star-forming complex, as well as AGB stars across the Galactic plane.

Post-outburst Evolution of Bona Fide FU Ori-type V2493 Cygnus: A Spectro-photometric Monitoring

We present here the results of 8 yr of our near-simultaneous optical–near-infrared spectro-photometric monitoring of the bona fide FU Ori (FUor)-type candidate V2493 Cygnus (V2493 Cyg) starting from 2013 September to 2021 June. During our optical monitoring period (between 2015 October 16 and 2019 December 30), the V2493 Cyg is slowly dimming with an average dimming rate of ∼26.6 ± 5.6 mmag yr−1 in the V band. Our optical photometric colors show a significant reddening of the source post the second outburst pointing toward a gradual expansion of the emitting region post the second outburst. The mid-infrared colors, on the contrary, exhibit a blueing trend, which can be attributed to the brightening of the disk due to the outburst. Our spectroscopic monitoring shows a dramatic variation of the Hα line as it transitioned from absorption feature to the emission feature and back. Such transition can possibly be explained by the variation in the wind structure in combination with accretion. Combining our time evolution spectra of the Ca ii infrared triplet lines with the previously published spectra of V2493 Cyg, we find that the accretion region has stabilized compared to the early days of the outburst. The evolution of the O i λ7773 Å line also points toward the stabilization of the circumstellar disk post the second outburst.

Neonatal Face and Facial Landmark Detection from Video Recordings.

This paper explores automated face and facial landmark detection of neonates, which is an important first step in many video-based neonatal health applications, such as vital sign estimation, pain assessment, sleep-wake classification, and jaundice detection. Utilising three publicly available datasets of neonates in the clinical environment, 366 images (258 subjects) and 89 (66 subjects) were annotated for training and testing, respectively. Transfer learning was applied to two YOLO-based models, with input training images augmented with random horizontal flipping, photo-metric colour distortion, translation and scaling during each training epoch. Additionally, the re-orientation of input images and fusion of trained deep learning models was explored. Our proposed model based on YOLOv7Face outperformed existing methods with a mean average precision of 84.8% for face detection, and a normalised mean error of 0.072 for facial landmark detection. Overall, this will assist in the development of fully automated neonatal health assessment algorithms.Clinical relevance- Accurate face and facial landmark detection provides an automated and non-contact option to assist in video-based neonatal health applications.

Applied Machine-Learning Models to Identify Spectral Sub-Types of M Dwarfs from Photometric Surveys

M dwarfs are the most abundant stars in the Solar Neighborhood and they are prime targets for searching for rocky planets in habitable zones. Consequently, a detailed characterization of these stars is in demand. The spectral sub-type is one of the parameters that is used for the characterization and it is traditionally derived from the observed spectra. However, obtaining the spectra of M dwarfs is expensive in terms of observation time and resources due to their intrinsic faintness. We study the performance of four machine-learning (ML) models—K-Nearest Neighbor (KNN), Random Forest (RF), Probabilistic Random Forest (PRF), and Multilayer Perceptron (MLP)—in identifying the spectral sub-types of M dwarfs at a grand scale by deploying broadband photometry in the optical and near-infrared. We trained the ML models by using the spectroscopically identified M dwarfs from the Sloan Digital Sky Survey (SDSS) Data Release (DR) 7, together with their photometric colors that were derived from the SDSS, Two-Micron All-Sky Survey, and Wide-field Infrared Survey Explorer. We found that the RF, PRF, and MLP give a comparable prediction accuracy, 74%, while the KNN provides slightly lower accuracy, 71%. We also found that these models can predict the spectral sub-type of M dwarfs with ∼99% accuracy within ±1 sub-type. The five most useful features for the prediction are r − z, r − i, r − J, r − H , and g − z, and hence lacking data in all SDSS bands substantially reduces the prediction accuracy. However, we can achieve an accuracy of over 70% when the r and i magnitudes are available. Since the stars in this study are nearby (d ≲ 1300 pc for 95% of the stars), the dust extinction can reduce the prediction accuracy by only 3%. Finally, we used our optimized RF models to predict the spectral sub-types of M dwarfs from the Catalog of Cool Dwarf Targets for the Transiting Exoplanet Survey Satellite, and we provide the optimized RF models for public use.

On the impact of spectral template uncertainties in synthetic stellar populations

ABSTRACTUncertainties in stellar population models, both in terms of stellar evolution and stellar spectra, translate into uncertainties in our interpretation of stellar populations in galaxies, since stars are the source of most of the light we receive from them. Observations by JWST are revealing high-redshift galaxies in great detail, which must then be compared to models. One significant source of uncertainty is in the stellar spectra used to generate composite spectra of stellar populations, which are then compared to data. Confidence in theoretical models is important to enable reliable determination of the properties of these galaxies such as their ages and star formation history. Here, we present a comparison of spectral synthesis carried out with six different stellar spectral libraries using the Binary Population and Spectral Synthesis framework. In photometric colours, the differences between theoretical libraries are relatively small (&amp;lt;0.10 mag), similar to typical observational uncertainties on individual galaxy observations. Differences become more pronounced when detailed spectroscopic properties are examined. Predictions for spectral line indices can vary significantly, with equivalent widths differing by a factor of 2 in some cases. With these index strengths, some of the libraries yield predictions of ages and metallicities which are unphysical. Many spectral libraries lack wavelength coverage in the ultraviolet, which is of growing importance in the era of JWST observations of distant galaxies, whose flux is dominated by hot, young stars.

The JWST Early-release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 μm Spectrum of the Planetary-mass Companion VHS 1256–1257 b

We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b is a <20 M Jup widely separated (∼8″, a = 150 au), young, planetary-mass companion that shares photometric colors and spectroscopic features with the directly imaged exoplanets HR 8799c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color–magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256 b with JWST's NIRSpec IFU and MIRI MRS modes for coverage from 1 to 20 μm at resolutions of ∼1000–3700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the JWST spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion.

Synthesis and luminescence properties of Ca3Ga4O9:Eu3+: An efficient red-emitter for WLEDs

Herein we report, an efficient red-emitting phosphor Ca3Ga4O9:Eu3+ (Eu3+: CGO) was synthesized via a conventional solid-state reaction technique. The physicochemical properties of the given oxide phosphors were investigated in terms of structural, elemental, compositional, and optical characteristics. The XRD study indicates that the compound CGO and Eu3+: CGO have been crystallized in an orthorhombic crystal system with the space group of Cmm2. The nature of the oxidative state of the elements and their compositional ratios were demonstrated by the XPS and EDS studies. The SEM analysis of the phosphor samples reveals micro flakes embedded in rod-like morphology. UV–Visible diffuse reflectance studies were performed to study the optical properties of the oxide phosphors. The optical energy gap value has been calculated using Kubelka-Munk equations and the values have a reducing trend due to the addition of the Eu3+ ion. The photo-emissive properties of the Eu3+ doped samples were illustrated by the PL analysis with the excitations of 465 nm and 394 nm (7F0 -5D2 and 7F0-5L6) respectively. The photometric (color coordinates, color purity, and correlated color temperature) parameters were also calculated. The Eu3+ doped samples show a high color purity within the range of 96.75–98.71%. The correlated color temperature (CCT) was also computed from the calculations which have the values from 1819 K to 1898 K. These results depict that the prepared Eu3+ ions doped oxide phosphor will be an efficient red-emitting candidate for white LED application.

Applying unsupervised learning to resolve evolutionary histories and explore the galaxy--halo connection in IllustrisTNG

ABSTRACT We examine the effectiveness of identifying distinct evolutionary histories in IllustrisTNG-100 galaxies using unsupervised machine learning with Gaussian mixture models. We focus on how clustering compressed metallicity histories and star formation histories produces sub-population of galaxies with distinct evolutionary properties (for both halo mass assembly and merger histories). By contrast, clustering with photometric colours fails to resolve such histories. We identify several populations of interest that reflect a variety of evolutionary scenarios supported by the literature. Notably, we identify a population of galaxies inhabiting the upper red sequence, M* &amp;gt; 1010 M⊙, that has a significantly higher ex-situ merger mass fraction present at fixed masses and a star formation history that has yet to fully quench, in contrast to an overlapping, satellite-dominated population along the red sequence, which is distinctly quiescent. Extending the clustering to study four clusters instead of three further divides quiescent galaxies, whereas star-forming ones are mostly contained in a single cluster, demonstrating a variety of supported pathways to quenching. In addition to these populations, we identify a handful of populations from our other clusters that are readily applicable to observational surveys, including a population related to post-starburst galaxies, allowing for possible extensions of this work in an observational context, and to corroborate results within the IllustrisTNG ecosystem.

Improvement in Frying Stability of Safflower Oil by Blending with Refined Olive Pomace Oil during Deep Fat Frying.

The objective of the present study was to increase the frying stability of refined safflower oil (RSO) by blending it with refined olive pomace oil (ROPO) during deep fat frying. For this purpose; RSO, ROPO and their blends were utilized for frying of potato sticks at 180°C for 3 consecutive days. The frying stability of the oils was monitored by analyzing them for their free fatty acids, peroxide values, total polar contents, ultraviolet spectrophotometric indices at 232 and 270 nm, fatty acid profiles, p-anisidine values, α-tocopherol contents and photometric color indices. 3-monochloropropane-1,2-diol (3-MCPD) and glycidyl ester (GE) levels of oils before and after frying were measured as well. The results have shown that thermooxidative degradation products increased as the frying progressed for all oils, however the decomposition rate was found to slow down in blend oils by stabilizing with ROPO. Blending RSO with ROPO decreased linoleic and linolenic; but increased the oleic and palmitic acid percentages of the blends. C18:2/C16:0 ratio was found to decrease by frying for RSO and the blend oils, however ROPO was not affected significantly. 3-MCPD-E levels of the blends increased as the ratio of ROPO increased. Principal component analysis enabled a clear discrimination between oils with different composition throughout the frying process.

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

Context. Low-surface-brightness galaxies (LSBs) contribute to a significant fraction of all the galaxies in the Universe. Ultra-diffuse galaxies (UDGs) form a subclass of LSBs that has attracted a lot of attention in recent years (although its definition may vary between studies). Although UDGs are found in large numbers in galaxy clusters, groups, and in the field, their formation and evolution are still very much debated. Aims. Using a comprehensive set of multiwavelength data from the NGVS (optical), VESTIGE (Hα narrowband), and GUViCS (UV) surveys, we studied a sample of 64 diffuse galaxies and UDGs in the Virgo cluster to investigate their formation history. Methods. We analyzed the photometric colors and surface-brightness profiles of these galaxies and then compared them to models of galaxy evolution, including ram-pressure stripping (RPS) events to infer any possible strong interactions with the hot cluster gas in the past. Results. While our sample consists mainly of red LSBs, which is typical in cluster environments, we found evidence of a color variation with the cluster-centric distance. Blue, H I-bearing, star-forming diffuse galaxies are found at larger distances from the cluster center than the rest of the sample. The comparison of our models with multifrequency observations suggests that most of the galaxies of the sample might have undergone a strong RPS event in their lifetime, on average 1.6 Gyr ago (with a large dispersion, and RPS still ongoing for some of them). This process resulted in the transformation of initially gas-rich diffuse blue galaxies into gas-poor and red ones that form the dominant population now, the more extreme UDGs having undergone the process in a more distant past on average. Conclusions. The RPS in dense environments could be one of the major mechanisms for the formation of the large number of quiescent UDGs we observe in galaxy clusters.

A study of globular clusters in a lenticular galaxy in Hydra I from deep HST/ACS photometry

Aims. We take advantage of exquisitely deep optical imaging data from the Hubble Space Telescope’s Advanced Camera for Surveys (HST/ACS) in the F475W (gF475W) and F606W (VF606W) bands to study the properties of the globular cluster (GC) population in the intermediate-mass lenticular galaxy PGC 087327in the Hydra I galaxy cluster. Methods. We inspected the photometric (magnitudes and colour) and morphometric (compactness, elongation, etc.) properties of sources lying in an area of ∼19 × 19 kpc centred on PGC 087327 and compared them with four neighbouring fields over the same HST/ACS mosaic. This allowed us to identify a list of GC candidates and to inspect their properties using a background decontamination method. Results. Relative to four comparison fields, PGC 087327 shows a robust overdensity of GCs, NGC = 82 ± 9. At the estimated magnitude of the galaxy, this number implies a specific frequency of SN = 1.8 ± 0.7. In spite of the short wavelength interval available with the gF475W and VF606W passbands, the colour distribution shows a clear bimodality with a blue peak at ⟨gF475W − VF606W⟩ = 0.47 ± 0.05 mag and a red peak at ⟨gF475W − VF606W⟩ = 0.62 ± 0.03 mag. We also observe the typical steeper slope of the radial distribution of red GCs relative to blue ones. Thanks to the unique depth of the available data, we characterise the GC luminosity function (GCLF) well beyond the expected GCLF turnover. We find gTOMF475W = 26.54 ± 0.10 mag and VTOMF606W = 26.08 ± 0.09 mag, which after calibration yields a distance of DGCLF = 56.7 ± 4.3(statistical) ± 5.2(systematic) Mpc.

The family pictures of our neighbours: investigating the mass function and dynamical parameters of nearby open clusters

ABSTRACT We determine the mass functions (MFs) and the dynamical parameters of 15 nearby open clusters (OCs), using the unprecedented data set of the Gaia Early Data Release 3. We select the members of each cluster by combining the photometric (colour and magnitude) and astrometric (parallax and proper motions) parameters of stars, minimizing the contamination from Galactic field interlopers. By comparing the observed distribution of stars along the cluster main sequence with the best-fitting synthetic population, we find the present-day MF and the binary fraction of the OCs, along with their dynamical parameters like mass, half-mass radius, and half-mass relaxation time. We found that the global present-day MF of OCs are consistent with a single power-law function, F(m) ∝ mα, with slopes −3 &amp;lt; α &amp;lt; −0.6 including both subsolar, 0.2 &amp;lt; m/M⊙ &amp;lt; 1, and supersolar mass regimes. A significant correlation between the MF slope and the ratio of age to half-mass relaxation time is evidenced, similarly to the same conclusion already observed among Galactic globular clusters. However, OCs evolve along different tracks in comparison with the globular clusters, possibly indicating primordial differences in their initial mass function (IMF). The comparison with Monte Carlo simulations suggests that all the analysed OCs could be born with an IMF with slope αIMF &amp;lt; −2.3. We also show that the less evolved OCs have an MF consistent with that of the solar neighbourhood, indicating a possible connection between the dissolution of OCs and the formation of the Galactic disc.