Point Source Catalog Research Articles

Obscured star clusters in the inner Milky Way. How many massive young clusters are still awaitingdetection

Milky Way star clusters provide important clues about the history of star formation in our Galaxy. However, the dust in the disk and in the innermost regions hides them from the observers. Our goal is twofold. First, to detect new clusters -- we have applied the newest methods of detecting clusters with the best available wide-field sky surveys in the mid-infrared because they are the least affected by extinction. Second, we address the question of cluster detection's completeness, for now limiting it to the most massive star clusters. This search is based on the mid-infrared Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), to minimize the effect of dust extinction. The search Ordering Points To Identify the Clustering Structure (OPTICS) clustering algorithm was applied to identify clusters, after excluding the bluest, presumably foreground sources, to improve the cluster-to-field contrast. The success rate for cluster identification was estimated with a semi-empirical simulation that adds clusters, based on the real objects, to the point source catalog, to be recovered later with the same search algorithm that was used in the search for new cluster candidates. As a first step, this was limited to the most massive star clusters with a total mass of sim 10$^4$\,M$_ odot$. Our automated search, combined with inspection of the color-magnitude diagrams and images, yielded 659 cluster candidates; 106 of these appear to have been previously identified, suggesting that a large hidden population of star clusters still exists in the inner Milky Way. However, the search for the simulated supermassive clusters achieves a recovery rate of 70-95\,<!PCT!>, depending on the distance and extinction toward them. The new candidates -- if confirmed -- indicate that the Milky Way still harbors a sizeable population of unknown clusters. However, they must be objects of modest richness, because our simulation indicates that there is no substantial hidden population of supermassive clusters in the central region of our Galaxy.

The MDW Hα Sky Survey: Data Release 0

The Mittelman–di Cicco–Walker (MDW) Hα Sky Survey is an autonomously operated and ongoing all-sky imaging survey in the narrowband Hα wavelength. The survey was founded by amateur astronomers and is presented here in its first stage of refinement for rigorous scientific use. Each field is exposed through an Hα filter with a 3 nm bandwidth for a total of 4 hr, with a pixel scale of 3.″2. Here, we introduce the first Data Release of the MDW Hα Survey (Data Release 0, or DR0), spanning 238 fields in the region of Orion (∼3100 deg2). DR0 includes: calibrated mean fields, star-removed mean fields, a point-source catalog matched to Data Release 1 of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) and the Isaac Newton Telescope Galactic Plane Survey (IGAPS), and mosaics. 3 3 DR0 components are available at http://mdw.astro.columbia.edu; the DR0 catalog can also be found on the AAS Journals Zenodo repository: doi:10.5281/zenodo.12747455.

A gamma-ray stacking survey of Fermi-LAT undetected globular clusters

ABSTRACT We present evidence for $\gamma$-ray emission from a stacked population of 39 high-latitude globular clusters (GCs) not detected in the Fermi Point Source Catalogue, likely attributable to populations of millisecond pulsars within them. In this work, we use 13 yr of data collected by the Large Area Telescope aboard the Fermi Gamma-Ray Space Telescope to search for a cumulative signal from undetected GCs and compared them to control fields (CFs), selected to match the celestial distribution of the target clusters so as to distinguish the $\gamma$-ray signal from background emission. The joint likelihood distribution of the GCs has a significant separation ($\sim 4\sigma$) from that of the CFs. We also investigate correlations between detected cluster luminosities and other cluster properties such as distance, the number of millisecond pulsars associated with each cluster, and stellar encounter rate but find no significant relationships.

Variability of young stellar objects in the Orion nebula

The Orion Nebula is one of the best-studied star-forming regions in our Galaxy and provides an ideal laboratory to study the early stages of star formation. Understanding the variability of young stellar objects (YSOs) can provide valuable insights into the underlying physical processes that occur during this crucial phase of stellar evolution. In this context, we have conducted a photometric survey with high temporal resolution of a six-square-degree region centered on NGC\,1980. We used two filters ($R$ and $I$) between 2012 and 2015 with the 15\,cm twin telescope RoBoTT at the Universit\"atssternwarte Bochum in Chile. Our goal is to identify and characterize the variable objects in this sample using a unique observational setup that allows us to obtain high-quality light curves with time sampling on the order of minutes. This is the first time such an intensive ground-based photometric campaign has been conducted in the Orion Nebula. After careful quality control, more than 13000 light curves were produced in either $R$ or $I$; the total number of matched light curves is 11889. The corresponding stars were subsequently matched with the 2MASS point source catalog, resulting in 8197 stars with $I < 16.5$ mag and AAA quality flags. We employed three methods -- amplitude, standard deviation, and the Stetson J index -- to identify variable objects in our sample, successfully classifying 561 stars as variables (irregular, periodic, and quasi-periodic). These stars serve as the foundation for further analysis. We confirmed 456 of these as known pre-main-sequence stars through cross-referencing with existing YSO catalogs, supported by spectroscopic and photometric data. The youth of the remaining stars was established based on their optical and infrared color signatures. The period, $P$, could be determined for 147 sources and ranges from 0.2 days to several weeks. The frequency of very short periods ($ < 1$ day) is two to four times higher than reported in previous studies. A significant population (10<!PCT!>) comes primarily from weak-line T Tauri stars, which are characterized by rotation periods of less than 1 day. These results emphasize the advantages of observations with an exceptional time sampling strategy that allows the identification of variability on scales from hours to years.

Multiple collisions in N59 bubble: sequential cloud–cloud collisions

ABSTRACT We report that the gas components in the N59 bubble suffered from sequential multiple cloud–cloud collision (CCC) processes. The molecular gas in the N59 bubble can be decomposed into four velocity components, namely Cloud A [95, 108] km s$^{-1}$, Cloud B [86, 95] km s$^{-1}$, Cloud C [79, 86] km s$^{-1}$, and Cloud D [65, 79] km s$^{-1}$. Four CCC processes occurred among these four velocity components, i.e. Cloud A versus Cloud B, Cloud A versus Cloud C, Cloud C versus Cloud D, and Cloud A versus Cloud D. Using the near- and mid-infrared photometric point source catalogues, we identified 514 young stellar object (YSO) candidates clustered in 13 YSO groups, and most of them ($\sim 60~{{\ \rm per\ cent}}$) were located at the colliding interfaces, indicating that they were mainly triggered by these four CCC processes. We also found that these four collisions occurred in a time sequential order: the earliest and most violent collision occurred between Cloud A and Cloud D about 2 Myr ago, then Cloud B collided with Cloud A about 1 Myr ago, and finally, Cloud C collided with Clouds A and D simultaneously about 0.4 Myr ago.

Stripe 82-XL: The ∼54.8 deg2 and ∼18.8 Ms Chandra and XMM-Newton Point-source Catalog and Number of Counts

We present an enhanced version of the publicly available Stripe 82X catalog (S82-XL), featuring a comprehensive set of 22,737 unique X-ray point sources identified with a significance ≳4σ. This catalog is four times larger than the original Stripe 82X catalog, by including additional archival data from the Chandra and XMM-Newton telescopes. Now covering ∼54.8 deg2 of nonoverlapping sky area, the S82-XL catalog roughly doubles the area and depth of the original catalog, with limiting fluxes (half-area fluxes) of 3.4 × 10−16 (2.4 × 10−15), 2.9 × 10−15 (1.5 × 10−14), and 1.4 × 10−15 (9.5 × 10−15) erg s−1 cm−2 across the soft (0.5–2 keV), hard (2–10 keV), and full (0.5–10 keV) bands, respectively. S82-XL occupies a unique region of flux-area parameter space compared to other X-ray surveys, identifying sources with rest-frame luminosities from 1.2 × 1038 to 1.6 × 1047 erg s−1 in the 2–10 keV band (median X-ray luminosity, 7.2 × 1043 erg s−1), and spectroscopic redshifts up to z ∼ 6. By using hardness ratios, we derived the obscuration of active galactic nuclei (AGNs), obtaining a median value of log(NH/cm−2)=21.6−1.6+1.0 and an overall, obscured fraction ( log(NH/cm−2)>22 ) of ∼36.9%. S82-XL serves as a benchmark in X-ray surveys and, with its extensive multiwavelength data, is especially valuable for comprehensive studies of luminous AGNs.

FASHI: A Search for Extragalactic OH Megamasers with FAST

The FAST All Sky H i survey (FASHI) is broader in frequency band and sky volume, and deeper in detection sensitivity than the Arecibo Legacy Fast ALFA survey. To efficiently expand the sample of OH megamasers (OHMs), whose strongest line has a rest frequency of 1667.35903 MHz, we directly matched the IRAS Point Source Catalog Redshift (PSCz) catalog with the corresponding FASHI data cube. From 145 PSCz sources already covered by FASHI, we obtained 27 OHMs with a detection rate of 18.6%, including 9 previously known and 18 new ones, within a redshift range of 0.14314 ≲ z OH ≲ 0.27656. We also measured the hyperfine ratio of nine OHMs between the 1667 and 1665 MHz lines. The ratio ranges from 1.32 to 15.22, with an average of R 1667:1665 = 4.74. In a fit to the L OH versus L FIR relation, we have logLOH=(1.57±0.10)logLFIR−(15.80±1.19) , which is almost the same as derived from previous observations. As expected, since the OHM sample was selected by cross correlation with the IRAS-selected PSCz, our detected OHMs are (ultra)luminous infrared galaxies ((U)LIRGs). However, not all (U)LIRGs have detectable OH emission, suggesting that the OH emission may be triggered within a specific stage of the merger or can only be seen in specific orientations. In general, FAST, with its 19-beam array and Ultra-Wide Bandwidth receiver, will be a powerful tool for observing more OHMs and unraveling their mystery in the future.

Probabilistic and progressive deblended far-infrared and sub-millimetre point source catalogues

Context.Single-dish far-infrared (far-IR) and sub-millimetre (sub-mm) point source catalogues and their connections with galaxy catalogues at other wavelengths are of paramount importance to studying galaxy evolution. However, due to the large mismatch in spatial resolution, cross-matching galaxies detected at different wavelengths is not straightforward.Aims.This work aims to develop the next-generation deblended far-IR and sub-mm catalogues in deep extragalactic survey fields, by extracting photometry at the positions of known sources. We present the first application of our methodology in the COSMOS field.Methods.Our progressive deblending used the Monte Carlo Markov chain (MCMC)-based Bayesian probabilistic framework known as XID+. The deblending process started from theSpitzer/MIPS 24 μm data, using an initial prior list composed of sources selected from the COSMOS2020 catalogue and radio catalogues from the VLA and the MeerKAT surveys, based on spectral energy distribution (SED) modelling which predicts fluxes of the known sources at the deblending wavelength. To speed up flux prediction, we made use of a neural network-based emulator. After deblending the 24 μm data, we proceeded to theHerschelPACS (100 and 160 μm) and SPIRE wavebands (250, 350 and 500 μm). Each time we constructed a tailor-made prior list based on the predicted fluxes of the known sources, taking into account the deblended photometry from the previous steps.Results.Using simulated far-IR and sub-mm sky, we detailed the performance of our deblending pipeline. After validation with simulations, we then deblended the real observations from 24 to 500 μm and compared with blindly extracted catalogues and previous versions of deblended catalogues. As an additional test, we deblended the SCUBA-2 850 μm map and compared our deblended fluxes with ALMA measurements, demonstrating a higher level of flux accuracy compared to previous results. We publicly release our XID+ deblended point source catalogues, including best estimates and posterior probability distribution functions. These deblended long-wavelength data, which are cross-matched with multi-band photometry by construction, are crucial for studies such as deriving the fraction of dust-obscured star formation and better separation of quiescent galaxies from dusty star-forming galaxies.

Investigating episodic mass loss in evolved massive stars

Context. Episodic mass-loss events such as giant eruptions in luminous blue variables or pre-supernova eruptions in red supergiants drastically alter the evolutionary path of a massive star, resulting in a rich and complex circumstellar environment and IR excess. However, the incidence of these events, and hence their importance in massive star evolution, remains unknown. Aims. The ASSESS project (Episodic Mass Loss in Evolved Massive Stars: Key to Understanding the Explosive early Universe) aims to determine the role of episodic mass loss in the evolution of massive stars. As a first step, we constructed a catalog of spectroscopically identified dusty, evolved massive stars in ten southern galaxies for which Spitzer point-source catalogs are available. The resulting catalog may be used to identify stars that have undergone an episodic mass-loss event. The target galaxies span a range of metallicities, Z = 0.06–1.6 Z⊙, allowing for the investigation of a potential metallicity dependence. Methods. We conducted multi-object spectroscopy of dusty massive star candidates in ten target galaxies using the Very Large Telescope. We obtained 763 spectra from WLM, NGC 55, NGC 247, NGC 253, NGC 300, NGC 1313, NGC 3109, Sextans A, M83, and NGC 7793. The targets were selected using their Spitzer photometry, by prioritizing targets with a strong IR excess, which indicates the presence of hot dust. We determined a spectral classification for each target. Additionally, we used archival images from the Hubble Space Telescope (HST), available for 150 of our targets, to provide a visual classification for 80 targets, as a star, cluster, or galaxy. Results. We provide a catalog of 541 spectroscopically classified sources that includes 185 massive stars, of which 154 are newly classified massive stars. The catalog contains 129 red supergiants, 27 blue supergiants, 10 yellow supergiants, 4 luminous blue variable candidates, 7 supergiant B[e] stars, and 8 emission-line objects. Evidence for circumstellar dust is found in 24% of these massive stars, based on their IR colors. We report a success rate of 28% for identifying massive stars from our observed spectra, while the average success rate of our priority system for selecting evolved massive stars is 36%. Additionally, the catalog contains 21 background galaxies (including active galactic nuclei and quasars), 10 carbon stars, and 99 H II regions. We measured the line ratios [N II]/Hα and [S II]/Hα for 76 H II regions and 36 other spectra with nebular emission lines, thereby identifying eight sources with shocked emission. Conclusions. We present the largest catalog of evolved massive stars and in particular of red supergiants in nearby galaxies at low Z beyond the Local Group. The brightest and reddest of these are candidates for episodic mass loss. The fraction of dusty massive stars observed with respect to the initial selection is ~30%. We expect this catalog to trigger follow-up studies and pave the way for a comprehensive study of the eruptive late stages of massive star evolution in the era of the James Webb Space Telescope and the new survey telescopes (e.g., the Euclid mission, Nancy Grace Roman Space Telescope, and Vera C. Rubin Observatory).

Frequencies of Warm Debris Disks Based on Point Source Catalogs of Spitzer, WISE, and Gaia

More than a thousand warm debris disks have been detected as infrared excess at mid-infrared wavelengths, and their frequencies have been obtained for various spectral types of stars. However, the dependence of the frequencies on spectral type is still debated because the number of stars with significant and detectable infrared excess is limited. Herein, we present the largest systematic search for infrared excess using data from Gaia, WISE, and Spitzer. We identified 373, 485, and 255-reliable infrared excesses in the mid-infrared archival data at wavelengths of 12, 22, and 24 μm for WISE/W3, W4, and Spitzer/MIPS ch1, respectively. Although we confirmed that more massive stars tend to show higher frequencies of debris disks, these disk frequencies are relatively flat for both low- and intermediate-mass stars, with a jump at 7000 K for all three wavelengths. Assuming that bright, warm debris disks have lifetimes of a few to several hundred million years, the disk frequency can be understood as the ratio between the timescale and the upper limits of the sample ages. We also found that intermediate-mass stars with infrared excess tend to be bluer and fainter along the evolutionary track than those without, implying that massive stars hosting debris disks are relatively young, with an isochronal age of approximately 500 Myr. These tendencies are reasonably explained by a standard scenario in which debris disks are likely to be produced by collisions of planetesimals in the early stages of stellar evolution, such as the Late Heavy Bombardment.

From Active Stars to Black Holes: A Discovery Tool for Galactic X-Ray Sources

Galactic X-ray sources are diverse, ranging from active M dwarfs to compact object binaries, and everything in between. The X-ray landscape of today is rich, with point source catalogs such as those from XMM-Newton, Chandra, and Swift, each with ≳105 sources and growing. Furthermore, X-ray astronomy is on the verge of being transformed through data releases from the all-sky SRG/eROSITA survey. Many X-ray sources can be associated with an optical counterpart, which in the era of Gaia, can be determined to be Galactic or extragalactic through parallax and proper motion information. Here, I present a simple diagram—the “X-ray Main Sequence,” which distinguishes between compact objects and active stars based on their optical color and X-ray-to-optical flux ratio (F X/F opt). As a proof of concept, I present optical spectroscopy of six exotic accreting WDs discovered using the X-ray Main Sequence as applied to the XMM-Newton catalog. Looking ahead to surveys of the near future, I additionally present SDSS-V optical spectroscopy of new systems discovered using the X-ray Main Sequence as applied to the SRG/eROSITA eFEDS catalog.

SMC-Last Extracted Photometry

We present point-source photometry from the Spitzer Space Telescope's final survey of the Small Magellanic Cloud (SMC). We mapped nearly 30 deg2 in two epochs in 2017, with the second extending to early 2018 at 3.6 and 4.5 μm using the Infrared Array Camera. This survey duplicates the footprint from the SAGE-SMC program in 2008. Together, these surveys cover a nearly 10 yr temporal baseline in the SMC. We performed aperture photometry on the mosaicked maps produced from the new data. We did not use any prior catalogs as inputs for the extractor in order to be sensitive to any moving objects (e.g., foreground brown dwarfs) and other transient phenomena (e.g., cataclysmic variables or FU Ori–type eruptions). We produced a point-source catalog with high-confidence sources for each epoch as well as a combined-epoch catalog. For each epoch and the combined-epoch data, we also produced a more complete archive with lower-confidence sources. All of these data products will be made available to the community at the Infrared Science Archive.

SRG/ART-XC Galactic Bulge deep survey. II. Catalogue of point sources

ABSTRACT We present a catalogue of point sources detected with the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory during a wide-field survey of the Galactic Bulge that was conducted as part of the mission’s calibration and performance verification phase in 2019. The survey consisted of nearly 18 d of consecutive scanning observations of the sky region |l| < 6 deg, |b| < 2.5 deg with the median sensitivity of 4 × 10−13 erg s−1 cm−2 in the 4–12 keV energy band, which allows the detection of sources down to a luminosity of 3 × 1033 erg s−1 near the Galactic Centre. Using a maximum-likelihood-based algorithm, 172 sources were detected. Of these, 153 are registered on the average 4–12 keV map and 18 sources are either extremely hard (detected only at energies above 7 keV) or highly variable (detected only in individual scans shorter than a day). For 121 sources, there are plausible counterparts in other X-ray source catalogues, including 43 with known classification. The remaining 51 sources are previously unknown objects, discovered by ART-XC during the Galactic Bulge survey.

A sky survey of ultraviolet sources observed through AstroSat’s UVIT: A point source catalogue

Abstract The Ultra Violet Imaging Telescope (UVIT) onboard India’s first dedicated multiwavelength satellite AstroSat observed a significant fraction of the sky in the ultraviolet with a spatial resolution of 1.4 $^{\prime\prime}$ . We present a catalogue of the point sources observed by UVIT in the far ultraviolet (FUV; 1 300–1 800 Å) and near ultraviolet (NUV; 2 000–3 000 Å). We carried out astrometry and photometry of 428 field pointings in the FUV and 54 field pointings in the NUV band, observed in 5 filter bands in each channel, respectively, covering an area of about 63 square degrees. The final catalogue contains about 102 773 sources. The limiting magnitude(AB) of the F148W band filter, that has the largest number of detections is $\sim$ $21.3$ . For the NUV channel, we find the limiting magnitude at around $\sim$ 23. We describe the final catalogue and present the results of the statistical analysis.

Exploration of faint X-ray and radio sources in the massive globular cluster M14: a UV-bright counterpart to Nova Ophiuchus 1938

ABSTRACT Using a 12 ks archival Chandra X-ray Observatory ACIS-S observation on the massive globular cluster (GC) M14, we detect a total of 7 faint X-ray sources within its half-light radius at a $0.5{\small --}7\, \mathrm{keV}$ depth of $2.5\times 10^{31}\, \mathrm{erg s^{-1}}$. We cross-match the X-ray source positions with a catalogue of the Very Large Array radio point sources and a Hubble Space Telescope (HST) UV/optical/near-IR photometry catalogue, revealing radio counterparts to 2 and HST counterparts to 6 of the X-ray sources. In addition, we also identify a radio source with the recently discovered millisecond pulsar PSR 1737−0314A. The brightest X-ray source, CX1, appears to be consistent with the nominal position of the classic nova Ophiuchi 1938 (Oph 1938), and both Oph 1938 and CX1 are consistent with a UV-bright variable HST counterpart, which we argue to be the source of the nova eruption in 1938. This makes Oph 1938 the second classic nova recovered in a Galactic GC since Nova T Scorpii in M80. CX2 is consistent with the steep-spectrum radio source VLA8, which unambiguously matches a faint blue source; the steepness of VLA8 is suggestive of a pulsar nature, possibly a transitional millisecond pulsar with a late K dwarf companion, though an active galactic nucleus (AGN) cannot be ruled out. The other counterparts to the X-ray sources are all suggestive of chromospherically active binaries or background AGNs, so their nature requires further membership information.

H i Galaxy Detections in the Zone of Avoidance with FAST

The Zone of Avoidance (ZoA) is a region of low galactic latitude that is heavily obscured by the Milky Way. Observations with radio telescopes are basically unaffected by dust extinction and can unveil the structure behind it through the Milky Way. One of the scientific goals of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) is to search for the neutral hydrogen and understand the large-scale physics to explore the origin and evolution of the universe. We take the 15,500 IRAS (the Infrared Astronomical Satellite) galaxies from PSCz (“Point Source Catalog”) survey to reconstruct the density field of the local universe, obtain the distribution of the relative density of galaxies in the ZoA region with a redshift z below 0.07, and the number of detectable galaxies with FAST is estimated by using the neutral hydrogen mass function of the ALFA (Arecibo L-band Feed Array) survey. We conclude that FAST can observe more than 2000 ZoA galaxies within a distance of 300 Mpc , and present preliminary results of the partial GPPS (the FAST Galactic Plane Pulsar Snapshot survey) data, compared with ALFA ZoA (The Arecibo L-band Feed Array Zone of Avoidance), show that FAST has a higher detection sensitivity to search for H i galaxies in the ZoA area.

Evaluation of Uncertainties in the Anthropogenic SO2 Emissions in the USA from the OMI Point Source Catalog.

Satellite remote sensing is a promising method of monitoring emissions that may be missing in inventories, but the accuracy of these estimates is often not clear. We demonstrate here a comprehensive evaluation of errors in anthropogenic sulfur dioxide (SO2) emission estimates from NASA's OMI point source catalog for the contiguous US by comparing emissions from the catalog with high-quality emission inventory data over different dimensions including size of individual sources, aggregate vs individual source errors, and potential bias in individual source estimates over time. For sources that are included in the catalog, we find that errors in aggregate (sum of error for all included sources) are relatively low. Errors for individual sources in any given year can be substantial, however, with over- or underestimates in terms of total error ranging from -80 to 110 kt (roughly 10-90th percentile). We find that these errors are not necessarily random over time and that there can be consistently positive or negative biases for individual sources. We did not find any overall statistical relationship between the degree of isolation of a source and bias, either at a 40 or 70 km scales. For a sub-set of sources where inventory emissions over a radius of 70 km around an OMI detection are larger than twice the emissions within 40 km, the OMI value is consistently overestimated. We find, as expected, that emission sources not included in the catalog are the largest aggregate source of difference between the satellite estimates and inventories, especially in more recent years where source emission magnitudes have been decreasing and note that trends in satellite detections do not necessarily track trends in total emissions. We find that the OMI-based SO2 emissions are accurate in aggregate, when summed over a number of sources, but must be interpreted more cautiously at the individual source level. Similar analyses would be valuable for other satellite emission estimates; however, in many cases, the appropriate high-quality reference data may need to be generated.

Multiscale stellar associations across the star formation hierarchy in PHANGS–HST nearby galaxies: methodology and properties

ABSTRACT We develop a method to identify and determine the physical properties of stellar associations using Hubble Space Telescope (HST) NUV−U−B−V−I imaging of nearby galaxies from the Physics at High Angular Resolution in Nearby GalaxieS with the Hubble Space Telescope (PHANGS–HST) survey. We apply a watershed algorithm to density maps constructed from point source catalogues Gaussian smoothed to multiple physical scales from 8 to 64 pc. We develop our method on two galaxies that span the distance range in the PHANGS–HST sample: NGC 3351 (10 Mpc) and NGC 1566 (18 Mpc). We test our algorithm with different parameters such as the choice of detection band for the point source catalogue (NUV or V), source density image filtering methods, and absolute magnitude limits. We characterize the properties of the resulting multiscale associations, including sizes, number of tracer stars, number of associations, and photometry, as well as ages, masses, and reddening from spectral energy distribution fitting. Our method successfully identifies structures that occupy loci in the UBVI colour–colour diagram consistent with previously published catalogues of clusters and associations. The median ages of the associations increase from log(age/yr) = 6.6 to log(age/yr) = 6.9 as the spatial scale increases from 8 to 64 pc for both galaxies. We find that the youngest stellar associations, with ages <3 Myr, indeed closely trace H ii regions in H α imaging, and that older associations are increasingly anticorrelated with the H α emission. Owing to our new method, the PHANGS–HST multiscale associations provide a far more complete census of recent star formation activity than found with previous cluster and compact association catalogues.

Multiwavelength and astrometric study of the DBS 89−90−91 embedded clusters region

Aims. Our main aims are to improve our understanding of the main properties of the radio source G316.8−0.1 (IRAS 14416−5937) where the DBS 89−90−91 embedded clusters are located, to identify the stellar population present in this region, and to study the interaction of these stars with the interstellar medium. Methods. We analyzed some characteristics of the G316.8−0.1 radio source, consulting the SUMSS to study the radio continuum emission at 843 MHz and the H I SGPS at 21 cm. We also used photometric data at the JHK bands in the region of DBS 89−90−91 clusters obtained from the VVV survey and supplemented with the 2MASS catalogue. Our investigation of possible stars associated with the H II region was complemented with an astrometric analysis using the Gaia Early Data Release 3. To study the young stellar objects (YSOs), we consulted the mid-infrared photometric information from WISE, Spitzer−GLIMPSE Surveys, and the MSX point source catalog. Results. The photometric and astrometric research carried out in the IRAS 14416−5937 region allowed us to improve our current understanding of the DBS 89−90−91 embedded clusters and their interaction with the interstellar medium. In the case of the cluster DBS 89, we identified 9 astrophotometric candidate members and 19 photometric candidate members, whereas for DBS 90−91 clusters we found 18 candidate photometric members. We obtained a distance value for DBS 89 linked to the radio source G316.8−0.1 of 2.9 ± 0.5 kpc. We also investigated 12 Class I YSO candidates, 35 Class II YSO candidates, 2 massive young stellar objects (MYSOs), and 1 compact ionized hydrogen (CHII) region distributed throughout the IRAS 14416−5937 region. Our analysis reveals that the G316.8−0.1 radio source is optically thin at frequencies ≥0.56 GHz. The H II regions G316.8−0.1−A and G316.8−0.1−B have similar radii and ionized hydrogen masses of ∼0.5 pc and ∼35 M⊙, respectively. The ionization parameter computed with the younger spectral types of adopted members of DBS 89 and DBS 90−91 clusters shows that they are able to generate the H II regions. The flux density of the H II region G316.8−0.1−B is lower than the flux density of the H II region G316.8−0.1−A. Conclusions. We carried out a photometric and astrometric study, looking for members of the DBS 89−90−91 embedded clusters. We were able to identify the earliest stars of the clusters as the main exciting sources of the G316.8−0.1 radio source and have also estimated the main physical parameters of this source. We improve the current knowledge of the stellar components present in the Sagittarius-Carina arm of our Galaxy and its interaction with the interstellar medium.

Local Group dwarf galaxy detection limit in the CSST survey

ABSTRACT We predict the dwarf galaxy detection limits for the upcoming Chinese Space Station Telescope (CSST) survey that will cover 17 500 ${\rm \, deg}^{2}$ of the sky with a wide field of view of 1.1 deg2. The point-source depth reaches 26.3 mag in the g band and 25.9 mag in the i band. Constructing mock survey data based on the designed photometric bands, we estimate the recovery rate of artificial dwarf galaxies from mock point-source photometric catalogues. The detection of these artificial dwarf galaxies is strongly dependent on their distance, magnitude, and size, in agreement with searches in current surveys. We expect CSST to enable the detection of dwarf galaxies with MV = −3.0 and μ250 = 32.0 mag arcsec−2 (surface brightness limit for a system of half-light radius rh = 250 ${\rm \, pc}$) at $400 {\rm \, kpc}$, and MV = −4.9 and μ250 = 30.5 mag arcsec−2 around the Andromeda galaxy. Beyond the Local Group, the CSST survey will achieve MV = −5.8, and μ250 = 29.7 mag arcsec−2 in the distance range of 1–2 Mpc, opening up an exciting discovery space for faint field dwarf galaxies. With its optical bands, wide survey footprint, and space resolution, CSST will undoubtedly expand our knowledge of low-mass dwarf galaxies to an unprecedented volume.