Surface Brightness Research Articles

Keck and Gemini Characterization of Hayabusa2# Rendezvous Target 1998 KY26

Abstract Near-Earth object (NEO) 1998 KY26 is a target of the Hayabusa2# spacecraft, which it will rendezvous with in 2031 July. The asteroid has been noted to rotate rapidly and has a large out-of-plane nongravitational acceleration. We present observations consisting of deep-g- and R-band imaging obtained with the Keck I/Low Resolution Imaging Spectrometer (LRIS) and visible spectroscopy from Gemini North/Gemini Multi-Object Spectrograph (GMOS) taken of 1998 KY26 on 2024 June 8–9 when the asteroid was ∼0.037 au from the Earth. The asteroid does not show evidence of a dust coma and has a surface brightness profile similar to nearby background stars in the deep images. The spectrum of 1998 KY26 from the combined LRIS and GMOS observations most closely resembles Xe-type asteroids, possessing a spectral slope of 6.71% ± 0.43% 100 nm−1, and color indices g – r = 0.63 ± 0.03, r – i = 0.15 ± 0.03, i – z = 0.05 ± 0.04, and implies a diameter of ∼10 m. From our deep image stacks, we compute a 3σ upper limit on the dust production of 1998 KY26 of <10−5 kg s−1, <10−2 kg s−1, and <10−1 kg s−1 assuming μm, mm, and cm size dust particles. In addition, we compare the orbit of 1998 KY26 and other known asteroids with large nongravitational parameters to NEO population models and find that the majority, including 1998 KY26, likely originated from the inner Main Belt, while the second most numerous group originates from the outer main belt, followed by a third group possibly originating from the Jupiter Family Comet population. Given its inner Main Belt origin, its Xe-type spectrum, and rapid rotation, we hypothesize that the nongravitational acceleration of 1998 KY26 may be caused by the shedding of large dust grains from its surface due to its rotation rather than H2O vapor outgassing.

X-Raying CAMELS: Constraining Baryonic Feedback in the Circumgalactic Medium with the CAMELS Simulations and eRASS X-Ray Observations

Abstract The circumgalactic medium (CGM) around massive galaxies plays a crucial role in regulating star formation and feedback. Using the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) suite, we develop emulators for the X-ray surface brightness profile and the X-ray luminosity–stellar mass scaling relation, to investigate how stellar and active galactic nucleus (AGN) feedback shape the X-ray properties of the hot CGM. Our analysis shows that at CGM scales (1012 ≲ M halo/M ⊙ ≲ 1013, 10 ≲ r kpc−1 ≲ 400), stellar feedback more significantly impacts the X-ray properties than AGN feedback within the parameters studied. Comparing the emulators to recent eROSITA All Sky Survey (eRASS) observations, it is found that stronger feedback than is currently implemented in the IllustrisTNG, SIMBA, and Astrid simulations is required to match the observed CGM properties. However, adopting these enhanced feedback parameters causes deviations in the stellar mass–halo mass relations from observational constraints below the group-mass scale. This tension suggests possible unaccounted-for systematics in X-ray CGM observations or inadequacies in the feedback models of cosmological simulations.

The LUNIS-AGN Catalog: Trends of Emission Line Velocity Dispersion and Surface Brightness within the Circumnuclear Regions of Seyfert Galaxies

Abstract We present the Local Universe Near-Infrared Seyfert catalog of K-band integral field unit data of 88 nearby active galactic nuclei (AGN), curated from SINFONI/Very Large Telescope and OSIRIS/Keck archival data sets. This catalog includes both type 1 and type 2 Seyfert AGN probed down to scales of tens of parsecs with z < 0.02 and spanning over 5 orders of magnitude in L 14−195 keV AGN luminosity. As part of this catalog, we make publicly available for all galaxies the processed data cubes, a central 200 pc integrated spectrum, and two-dimensional maps of flux, velocity, and velocity dispersion for H2 1-0 S(1) 2.1218 μm, [Si vi] 1.9641 μm, and Br-γ 2.1655 μm. The morphology and geometry of [Si vi], a tracer of AGN outflows, are reported for the 66% of galaxies with extended emission. We utilize this large sample to probe the behavior of molecular and ionized gas, identifying trends in the properties of the circumnuclear gas (surface brightness and velocity dispersion) with fundamental AGN properties (obscuration and X-ray luminosity). While there is significant variation in circumnuclear gas characteristics across the sample, we find molecular hydrogen to be less centrally concentrated and to exhibit lower velocity dispersion relative to ionized gas. In addition, we find elevated molecular hydrogen surface brightness and decreased [Si vi] velocity dispersion in obscured relative to unobscured AGN. The [Si vi] and Br-γ emission scale with L 14−195 keV X-ray luminosity, which, along with the elevated velocity dispersion compared to the molecular gas, verifies an association with AGN outflow processes.

Discovery of Two Ultra-diffuse Galaxies with Unusually Bright Globular Cluster Luminosity Functions via a Mark-dependently Thinned Point Process (MATHPOP)

Abstract We present MArk-dependently THinned POint Process (Mathpop), a novel method to infer the globular cluster (GC) counts in ultra-diffuse galaxies (UDGs) and low-surface brightness galaxies (LSBGs). Many known UDGs have a surprisingly high ratio of GC number to surface brightness. However, standard methods to infer GC counts in UDGs face various challenges, such as photometric measurement uncertainties, GC membership uncertainties, and assumptions about the GC luminosity functions (GCLFs). Mathpop tackles these challenges using the mark-dependent thinned point process, enabling joint inference of the spatial and magnitude distributions of GCs. In doing so, Mathpop allows us to infer and quantify the uncertainties in both GC counts and GCLFs with minimal assumptions. As a precursor to Mathpop, we also address the data uncertainties coming from the selection process of GC candidates: we obtain probabilistic GC candidates instead of the traditional binary classification based on the color–magnitude diagram. We apply Mathpop to 40 LSBGs in the Perseus cluster using GC catalogs from a Hubble Space Telescope imaging program. We then compare our results to those from an independent study using the standard method. We further calibrate and validate our approach through extensive simulations. Our approach reveals two LSBGs having GCLF turnover points much brighter than the canonical value with Bayes’ factor being ∼4.5 and ∼2.5, respectively. An additional crude maximum-likelihood estimation and simulation study show that their GCLF TO points are approximately 0.9 mag and 1.1 mag brighter than the canonical value, with p-values of ∼10−8 and ∼10−5, respectively.

MeerKAT H i Observations of Low Surface Brightness/Ultradiffuse Galaxy Candidates Projected around Two Southern Loose Groups

Abstract A large catalog of low surface brightness galaxies (LSBGs) from the Dark Energy Survey showed significant clustering around nearby galaxy groups and clusters. Using the HIPASS survey, we tried to determine the redshift of a subsample of these LSBGs and determine whether they were members of the groups they were projected near, but this was hampered by HIPASS’s high spectral rms. This Letter reports on MeerKAT H i observations to determine the redshifts of 52 LSBG candidates projected in the vicinity of two groups from our previous HIPASS study. The main goal is to investigate and ascertain whether these LSBGs are genuine group members. H i was detected with MeerKAT and redshifts were determined for only five of the 52 candidates within a velocity range of ±2500 km s−1 of their respective group velocities. All five H i detections were blue LSBGs, and two of them were confirmed to be ultradiffuse galaxies (UDGs). Both these UDGs were group members, while the other three detections were either foreground or background galaxies. In this Letter we explore scenarios that can explain the 90% nondetection. MeerKAT’s excellent sensitivity allows us to conclude that the majority of the nondetected candidates, particularly the blue galaxies, are not group members but lie at higher redshifts. However, this still leaves the open question of why Tanoglidis LSBG candidates, in particular the red ones, appear to be clustered in projection around nearby groups.

Jet-mode Feedback in NGC 5972: Insights from Resolved MUSE, GMRT, and VLA Observations

Abstract NGC 5972, a Voorwerp galaxy, features a helical-shaped extended emission-line region (EELR) with a radius >10 kpc and an S-shaped radio structure spanning about 470 kpc. We use the Very Large Telescope, Multi Unit Spectroscopic Explorer, Giant Metrewave Radio Telescope, and Very Large Array (VLA) to study the stellar and ionized gas kinematics and how the radio jet influences the gas in the galaxy. Our sensitive radio observations detect the southern jet for the first time, roughly coinciding with the southern EELR. The VLA images show a continuous inner jet connected to the outer east–west lobe, confirming the jet origin of the radio emission. Our kinematic analysis shows spatial correlations between the radio jet and the outflowing gas, supporting the jet-driven feedback mechanism. More interestingly, we observe enhanced velocity dispersion in the perpendicular direction along with a shell-like structure. Our Baldwin–Phillips–Telervich analysis shows that the [O III] emission overlapping with the radio jet is consistent with the shock+precursor model, whereas in the perpendicular region, a pure shock model fits well with the observations, indicating jet-induced shocks. Radio observations indicate episodic AGN activity characterized by surface brightness and spectral index discontinuities. Overall, based on our findings, we propose a jet-driven feedback mechanism as one of the key factors in the formation of the EELR in NGC 5972. Future high-resolution radio observations will be crucial to further investigate the origin of the EELR and quantify the extent to which the jet influences its formation and evolution.

UV LIGHTS

Ultra-deep optical imaging surveys have reached unprecedented depths (≳30 mag arcsec−2; 3σ, 10″ × 10″), thus facilitating the study of very faint galactic structures. However, the ultraviolet bands, which are key to the study of stellar populations, remain essentially unexplored at these depths. In this paper, we present a detailed surface brightness and color analysis of the outermost regions of 20 nearby galaxies in the LBT Imaging of Galactic Haloes and Tidal Structues (LIGHTS) fields observed by GALEX in the far-UV and near-UV. We adapted and applied a low surface brightness oriented methodology that has proven effective in ultra-deep optical surveys. We propose a novel approach to background subtraction for UV imaging. Instead of subtracting a constant value from the background, we subtract a Poisson distribution that transforms the background into a pseudo-Gaussian distribution centered at zero. Furthermore, the point spread function (PSF) deconvolution algorithms developed for optical data are applied to our sample, using a novel set of very extended (R = 750″) PSFs for the GALEX bands. This methodology allowed us to obtain depths ranging from 28.5 to 30 mag arcsec−2 (3σ; 10″ × 10″) with reliable surface brightness profiles up to 31 mag arcsec−2. This is about 1 mag deeper than with standard UV techniques. We used the surface brightness and color profiles to show that the application of PSF deconvolution, especially in the far-UV, effectively mitigates the excess of light present in the outer regions of certain galaxies compared to the standard GALEX pipeline. This finding is crucial for any accurate stellar population inference from the color profiles. Additionally, a qualitative analysis of the results is presented, with particular emphasis on the surface brightness and color properties of the galaxies beyond their optical edges. Our work highlights the importance of developing innovative low surface brightness methods for UV surveys.

A JVLA, GMRT, and XMM study of Abell 795: Large-scale sloshing and a candidate radio phoenix

Aims. The galaxy cluster Abell 795 (z = 0.1374) is known from previous works for the presence of extended (≈200 kpc) radio emission with a steep spectral index of an unclear origin surrounding the brightest cluster galaxy (BCG), and for the sloshing signatures visible in Chandra observations of its cool core. Our purpose is to investigate the nature of the extended radio emission and its possible link with the dynamical state of the intracluster medium (ICM) on large scales (≈1 Mpc). Methods. We used new JVLA 1.5 GHz, as well as archival GMRT 325 MHz and XMM-Newton X-ray observations to study the cluster with a thermal and nonthermal approach. Results. From the XMM surface brightness analysis, we detected an azimuthally asymmetric excess reaching around 650 kpc from the center of Abell 795. The excess appears to follow the sloshing spiral previously detected, but with the existing XMM data it is not possible to confirm its classification as a large-radius cold front in Abell 795. Furthermore, the X-ray data allowed us to detect the hot gas from a previously unknown galaxy group at a projected distance of ≈7.4′ (1 Mpc) northwest of Abell 795. Its surface brightness radial profile is well-fitted with a β model of slope β = 0.52 ± 0.17, and the spectral analysis reveals a thermal plasma of temperature kT = 1.08 ± 0.08 keV and metallicity Z = 0.13 ± 0.06 Z⊙. We discuss the possibility that this galaxy group is the perturber that initiated sloshing in Abell 795, and we show that the velocity distribution of member galaxies supports the dynamically unrelaxed nature of Abell 795. The analysis of JVLA 1.5 GHz and GMRT 325 MHz images confirms the presence of extended radio emission with the largest linear size ≈200 kpc, preferentially extended toward southwest and terminating in a sub-component (“SW blob”). We measured the spectral indices between 325 MHz and 1.5 GHz, finding αExt = −2.24 ± 0.13 for the diffuse extended emission, and αSWb = −2.10 ± 0.13 for the SW blob. These ultra-steep spectral index values, coupled with the complex morphology and cospatiality with the radio-loud active galactic nuclei (AGN) present in the BCG, suggest that this extended emission could be classified as a radio phoenix, possibly arising from adiabatic compression of an ancient AGN radio lobe due to the presence of sloshing motions.

Structure and kinematics of the interacting group NGC 5098/5096

Context. Most galaxies in the Universe are found in groups that have various morphologies and dynamical states. Studying how groups evolve is an important step for our understanding of both large-scale structure formation and galaxy evolution. Aims. We analysed a system composed of two groups at z ≃ 0.037, NGC 5098, a group dominated by a pair of elliptical galaxies, and NGC 5096, a compact system that appears to be interacting with NGC 5098. We describe its current dynamical state in order to investigate how it fits in our current cosmological framework. Methods. Our analysis is based on deep Canada-France-Hawaii Telescope (CFHT/MegaCam) g and r imaging, archival Chandra X-ray data, and publicly available data of the galaxy redshift distribution. We modelled the surface brightness of the 12 brightest galaxies in the field of view and investigated the diffuse intragroup light that we detected. With a redshift sample of 112 galaxies, we studied the dynamical states of both groups. Results. We detected low surface brightness diffuse light associated with both galaxy–galaxy interactions and a possible group–group collision. The substructure we found in velocity space indicates a past interaction between the two groups. This is further corroborated by the X-ray analysis. Conclusions. We conclude that NGC 5098 and NGC 5096 form a complex system that may have collided in the past, thus producing a sloshing observed in X-rays and a large-scale diffuse component of intragroup light as well as some important tidal debris.

Cross-correlation between soft X-rays and galaxies

This paper presents the construction and validation of complete stellar mass-selected, volume-limited galaxy samples using the Legacy Survey (data release 10) galaxy catalogs, covering ∼16 800 deg2 of extra-galactic sky and extending to redshifts of z < 0.35. We used companion mock catalogs to ensure a controlled galaxy selection. We measured the two-point correlation function of these galaxies with tiny statistical uncertainties at the percent level and systematic uncertainties up to 5%. We fitted a four-parameter halo occupation distribution (HOD) model to retrieve the population of host halos, yielding results on the stellar to halo mass relation that are consistent with the current models of galaxy formation and evolution. Using these complete galaxy samples, we measured and analyzed the cross-correlation between galaxies and all soft X-ray photons observed by SRG/eROSITA in the 0.5–2 keV band over ∼13 000 deg2. The cross-correlation measurements have an unprecedented sub-percent statistical uncertainty and 5–10% systematic uncertainty. We introduced a novel extension to the halo model to interpret the cross-correlation, decomposing contributions from X-ray point sources, hot gas, satellites, and the two-halo term. The model offers a new comprehensive view of the relation between the complete 0.5–2 keV X-ray photon field and complete sets of galaxies at low redshift and their host halos. For low stellar mass thresholds (log M*/M⊙ > 10, 10.25, 10.5), we find that the point source emission dominates the cross-correlation at small separation (r < 80 kpc). Then, in the range of 80 < r < 2 Mpc, the emission from large halos hosting satellite galaxies dominates. Finally, on scales beyond those considered here (r > 2 Mpc), the two-halo term becomes dominant. Interestingly, there is no scale at which the hot gas dominates. In the range (20 < r < 200 kpc), the hot gas contributes to more than 10% of the signal. Progressively, with the minimum stellar mass increasing, the hot gas emission increases. For the log M*/M⊙ > 10.75 sample, in the range 50–60 kpc, the three components contribute each the same surface brightness. For the log M*/M⊙ > 11 sample, the hot gas is the dominating emission source over the range of 30–200 kpc. Finally, for the log M*/M⊙ > 11.25 and (11.5) samples, the hot gas emission dominates over other components until 400 (700) kpc. We constrained the slope of the scaling relation between halo mass and X-ray luminosity (over three orders of magnitude in mass) at the 5% level, using the samples with the lowest mass threshold. We find a slope of 1.629−0.089+0.091. Additional analyses explore the energy dependence of the cross-correlation and differences between red sequence and blue cloud galaxies, revealing sensitivity to galaxy quiescent fractions and opening avenues for a more complex, unified modeling of galaxies, active galactic nuclei (AGNs), and hot gas in the optical and X-rays.

Deep Chandra observations of PLCKG287.0+32.9: A clear detection of a shock front in a heated former cool core

Context. The massive, hot galaxy cluster PSZ2 G286.98+32.90 (hereafter PLCKG287, z = 0.383) hosts a giant radio halo and two prominent radio relics that are signs of a disturbed dynamical state. Gravitational lensing analysis shows a complex cluster core with multiple components. However, despite optical and radio observations indicating a clear multiple merger, the X-ray emission of the cluster, derived from XMM-Newton observations, shows only moderate disturbance. Aims. The aim of this work is to study the X-ray properties and investigate the core heating of such a massive cluster by searching for surface brightness discontinuities and associated temperature jumps that would indicate the presence of shock waves. Methods. We present new 200 ks Chandra X-ray Observatory ACIS-I observations of PLCKG287 and perform a detailed analysis to investigate the morphological and thermodynamical properties of the region inside R500 (∼1.5 Mpc). Results. The global X-ray morphology of the cluster has a comet-like shape, oriented in the NW-SE direction, with an ∼80 kpc offset between the X-ray peak and the brightest cluster galaxy (BCG). We detect a shock front in the NW direction at a distance of ∼390 kpc from the X-ray peak, characterized by a Mach number of ℳ ∼ 1.3, as well as a cold front at a distance of ∼300 kpc from the X-ray peak, nested in the same direction as the shock in a typical configuration expected for a merger. We also find evidence for X-ray depressions to the E and W, which could be the signature of feedback from the active galactic nucleus (AGN). The radial profile of the thermodynamic quantities shows a temperature and abundance peak in the cluster’s center, where the pressure and entropy also exhibit a rapid increase. Conclusions. Based on these properties, we argue that PLCKG287 is what remains of a cool core after a heating event. We estimate that both the shock energy and the AGN feedback energy, implied by the analysis of the X-ray cavities, are sufficient to heat the core to the observed temperature of ∼17 keV in the central ≈160 kpc. We discuss the possible origin of the detected shock by investigating alternative scenarios of merger and AGN outburst, finding that they are both energetically viable. However, no single model seems able to explain all the X-ray features detected in this system. This suggests that the combined action of merger and central AGN feedback is likely necessary to explain the reheated cool core, the large-scale shock, and the cold front. The synergy of these two processes may act to shape the distribution of cool core and non-cool core clusters.

Quantifying observational projection effects with a simulation-based hot CGM model

Aims. The hot phase of the circumgalactic medium (CGM) allows us to probe the inflow and outflow of gas responsible for dictating the evolution of a galaxy's structure. Studying the hot CGM sheds light on the physical properties of the gas phase of the baryons, which is crucial to inform and constrain simulation models. With the recent advances in observational measurements probing the hot CGM in X-rays and thermal Sunyaev-Zeldovich (tSZ), we have a new avenue for widening our knowledge of gas physics and feedback. Methods. In this paper, we use the TNG300 hydrodynamical simulations to build a fully self-consistent forward model for the hot CGM. In order to do that, we construct a lightcone and generate mock X-ray observations of the large-scale structure. We quantify the main projection effects impacting CGM measurements, namely the locally correlated large-scale structure in X-rays and the effect due to satellite galaxies misclassified as centrals, which affect the measured hot CGM galactocentric profiles in stacking experiments. Results. We present an analytical model that describes the intrinsic X-ray surface brightness profiles of halos across the stellar and halo mass bins. The increasing stellar mass bins result in decreasing values of β, the exponent quantifying the slope of the intrinsic galactocentric profiles. We measure the effect of misclassified centrals in stacking experiments for three stellar mass bins 1010.5−11 M⊙, 1011−11.25 M⊙, and 1011.25−11.5 M⊙. We find that the contaminating effect of the misclassified centrals on the stacked profiles increases when the stellar mass decreases. When stacking galaxies of Milky-Way-like stellar mass, this effect is dominant already at a low level of contamination: in particular, misclassified centrals contributing 30%, 10%, or 1% of a sample dominate the measured surface brightness profile at radii ≥0.11×R500c, ≥0.24×R500c, and ≥1.04×R500c, respectively.

The Complete Spitzer Survey of Stellar Structure in Galaxies (CS4G)

Context. The Spitzer Survey of Stellar Structure in Galaxies (S4G), together with its Early Type Galaxy (ETG) extension, stands as the most extensive dataset of deep uniform mid-infrared (mid-IR; 3.6 and 4.5 μm) imaging for a sample of 2817 nearby (d < 40 Mpc) galaxies. However, the velocity criterion used to select the original sample results in an additional 422 galaxies without H I detection that should have been included in the S4G on the basis of their optical recession velocities. Aims. In order to create a complete magnitude-, size-, and volume-limited sample of nearby galaxies, we collected 3.6 μm and i-band images using archival data from different surveys and complemented it with new observations for the missing galaxies. Since most, but not all, of these galaxies have a Hubble type in Hyperleda THL > 0, we denote the sample of these additional galaxies as disc galaxy (DG) extension. We present the Complete Spitzer Survey of Stellar Structure in Galaxies (CS4G), encompassing a sample of 3239 galaxies (S4G+ETG+DG) with consistent imaging, surface brightness profiles, photometric parameters, and revised morphological classification. Methods. Following the original strategy of the S4G survey, we produced masks, surface brightness profiles, and curves of growth using masked 3.6 μm and i-band images. From these profiles, we derived the integrated quantities, including total magnitude, stellar mass, concentration parameter, and galaxy size, converting between optical i-band and 3.6 μm. We also re-measured these parameters for the S4G and ETG to create a homogenous sample. We present new morphologically revised T-types, and we showcase mid-IR scaling relations for the stellar mass, galaxy size, concentration index, and morphological type. Results. Our new masking procedure increases the number of pixels masked out by a factor of five, improving the masking of fainter regions over previous S4G data. Our photometric parameters from i-band imaging yield measurements consistent with the original sample (S4G) and its ETG extension in the 3.6 μm band. The new DG extension consists of galaxies with a wide morphological range (−5 < THL < 10) and a mass range of 6 < log(M⋆/M⊙) < 11. The galaxies in the DG sample have an average mass of log(M⋆/M⊙) = 9.21, an average galaxy isophotal radius at 25.5 mag arcsec−2 of R25.5 = 7.1 kpc, and an average concentration index of C82 = 2.92. Conclusions. We completed the S4G sample by incorporating 422 galaxies into the original dataset. The new galaxies constitute 15% of the total previous sample (S4G+ETG), but in the lower-mass range (M⋆ < 109 M⊙), and the disc galaxy extension increases the sample by 36%. The CS4G includes at least 99.94% of the complete sample of nearby galaxies, meeting the original selection criteria based on a comparison with the NED database. We make the images and surface brightness profiles available to the community together with the conjunct catalogue of the whole CS4G dataset with consistent photometric measurements for 3239 galaxies. The CS4G will enable a wide set of investigations into galaxy structure and evolution, and it will complement the optical, near-IR, and mid-IR imaging that will obtained in the coming years with Euclid, Rubin, Roman, and other research projects.

Surface brightness–colour relations of Cepheids calibrated by optical interferometry

Context. Surface brightness–colour relations (SBCRs) are widely used to determine the angular diameters of stars. They are in particular used in the Baade-Wesselink (BW) method of distance determination of Cepheids. However, the impact of the SBCR on the BW distance of Cepheids is about 8%, depending on the choice of SBCR considered in the literature. Aims. We aim to calibrate a precise SBCR dedicated to Cepheids using the best quality interferometric measurements available as well as different photometric bands, including the Gaia bands. Methods. We selected interferometric and photometric data in the literature for seven Cepheids covering different pulsation periods. From the phased photometry in the different bands (VJHKGGBP GRP) corrected from extinction and the interferometric limb-darkened angular diameters, we calculated the SBCR associated with each combination of colours. Results. We first find that the seven Cepheids have consistent SBCRs as long as the two magnitudes considered are not too close in wavelengths. For the SBCR (FV, V − K): FV = −0.1336±0.0009(V − K)0 + 3.9572±0.0015, we obtain a root mean square (RMS) of 0.0040 mag, which is three times lower than the latest estimate from 2004. Also, for the first time, we present an SBCR dedicated to Cepheids based on Gaia bands only: FGBP = −0.3001±0.0030(GBP − GRP)0 + 3.9977±0.0029, with an excellent RMS of 0.0061 mag. However, using theoretical models, we show that this SBCR is highly sensitive to metallicity. From this empirical multi-wavelength approach, we also show that the impact of the CircumStellar Environment (CSE) of Cepheids emission is not negligible and should be taken into account in the future. Conclusions. With this study, we improve the calibration and our understanding of the SBCR of Cepheids. The overall goal of this project is to provide a purely empirical SBCR version of the BW method that takes into account the metallicity and the CSE emission of Cepheids and that could be applied to individual Cepheids in the local group in the context of JWST and ELT.

Euclid: Early Release Observations – Deep anatomy of nearby galaxies

Euclid is poised to make significant advances in the study of nearby galaxies in the Local Universe. Here we present a first look at six galaxies observed for the Nearby Galaxy Showcase as part of the Euclid Early Release Observations acquired between August and November, 2023. These targets, three dwarf galaxies (Holmberg II, IC 10, and NGC 6822) and three spirals (IC 342, NGC 2403, and NGC 6744), range in distance from about 0.5 Mpc to 8.8 Mpc. We first assess the surface brightness depths in the stacked Euclid images, and confirm previous estimates in 100 arcsec2 regions for Visible Camera (VIS) of 1σ limits of 30.5 mag arcsec-2, but find deeper than previous estimates for Near-Infrared Spectrometer and Photometer (NISP) with 1σ = 29.2-29.4mag arcsec-2. By combining Euclid HE, YE, and IE into RGB images, we illustrate the large field of view (FoV) covered by a single reference observing sequence (ROS), together with exquisite detail on scales of <1-4 parsecs in these nearby galaxies. Our analysis of radial surface brightness and color profiles demonstrates that the photometric calibration of Euclid is consistent with what is expected for galaxy colors according to stellar synthesis models. We perform standard source-selection techniques for stellar photometry, and find approximately 1.3 million stars across the six galaxy fields. After subtracting foreground stars and background galaxies, and applying a color and magnitude selection, we extract stellar populations of different ages for the six galaxies. The resolved stellar photometry obtained with Euclid allows us to constrain the star-formation histories of these galaxies, which we do by disentangling the distributions of young stars and asymptotic giant branch and red giant branch stellar populations. We finally examine two galaxies individually for surrounding systems of dwarf galaxy satellites and globular cluster populations. Our analysis of the ensemble of dwarf satellites around NGC 6744 recovers all the previously known dwarf satellites within the Euclid FoV, and also confirms the satellite nature of a previously identified candidate, dw1909m6341, a nucleated dwarf spheroidal at the end of a spiral arm. Our new census of the globular clusters around NGC 2403 yields nine new star-cluster candidates, eight of which exhibit colors indicative of evolved stellar populations. In summary, our first investigation of six “showcase” galaxies demonstrates that Euclid is a powerful probe of stellar structure and stellar populations in nearby galaxies, and will provide vastly improved statistics on dwarf satellite systems and extragalactic globular clusters in the local Universe, among many other exciting results.

Euclid: Early Release Observations – Unveiling the morphology of two Milky Way globular clusters out to their periphery

As part of the Euclid Early Release Observations (ERO) programme, we analysed deep, wide-field imaging from the VIS and NISP instruments of two Milky Way globular clusters (GCs), namely NGC 6254 (M10) and NGC 6397, to look for observational evidence of their dynamical interaction with the Milky Way. We searched for such an interaction in the form of structural and morphological features in the clusters’ outermost regions, which would be suggestive of the development of tidal tails on scales larger than those sampled by the ERO data. From our multi-band photometric analysis, we obtained deep and well-behaved colour–magnitude diagrams that, in turn, enabled an accurate membership selection. The surface brightness profiles built from these samples of member stars are the deepest ever obtained for these two Milky Way GCs, reaching down to ∼30.0 mag/arcsec2, which is ∼1.5 mag/arcsec2 lower than before. The investigation of the two-dimensional density map of NGC 6254 reveals an elongated morphology of the cluster peripheries in the direction and with the amplitude predicted by N-body simulations of the cluster’s dynamical evolution, at high statistical significance. We interpret this as strong evidence for the first detection of tidally induced morphological distortion around this cluster. The density map of NGC 6397 reveals a slightly elliptical morphology, in agreement with previous studies, which requires further investigation on larger scales to be properly interpreted. This ERO project thus demonstrates the power of Euclid in studying the outer regions of GCs at an unprecedented level of detail, thanks to the combination of the large field of view, high spatial resolution, and depth enabled by the telescope. Our results highlight the future Euclid survey as the ideal dataset for investigating GC tidal tails and stellar streams.

Euclid: Early Release Observations – The intracluster light and intracluster globular clusters of the Perseus cluster

We study the intracluster light (ICL) and intracluster globular clusters (ICGCs) in the nearby Perseus cluster of galaxies using Euclid’s Early Release Observations. By modelling the isophotal and iso-density contours, we mapped the distributions and properties of the ICL and ICGCs out to radii of 200-600 kpc (up to ~ 1/3 of the virial radius, depending on the parameter) from the brightest cluster galaxy (BCG). We find that the central 500 kpc of the Perseus cluster hosts 70 000 ± 2800 globular clusters, and 1.7 × 1012 L⊙ of diffuse light from the BCG+ICL in the near-infrared HE. This accounts for 38 ± 6% of the cluster’s total stellar luminosity within this radius. The ICL and ICGCs share a coherent spatial distribution which suggests that they have a common origin or that a common potential governs their distribution. Their contours on the largest scales (>200 kpc) are not centred on the BCG’s core, but are instead offset westwards by 60 kpc towards several luminous cluster galaxies. This offset is opposite to the displacement observed in the gaseous intracluster medium. The radial surface brightness profile of the BCG+ICL is best described by a double Sérsic model, with 68 ± 4% of the HE light contained in the extended, outer component. The transition between these components occurs at ≈60 kpc, beyond which the isophotes become increasingly elliptical and off-centred. Furthermore, the radial ICGC number density profile closely follows the profile of the BCG+ICL only beyond this 60 kpc radius, where we find an average of 60-80 globular clusters per 109 M⊙ of diffuse stellar mass. The BCG+ICL colour becomes increasingly blue with radius, consistent with the stellar populations in the ICL having subsolar metallicities [Fe/H] ~ –0.6 to –1.0. The colour of the ICL, and the specific frequency and luminosity function of the ICGCs suggest that the ICL+ICGCs were tidally stripped from the outskirts of massive satellites with masses of a few ×1010 M⊙, with an increasing contribution from dwarf galaxies at large radii.

Analysis of X-Ray Surface Brightness Radial Profiles in Several Relatively Symmetric Young Supernova Remnants

Abstract Based on observations from XMM-Newton, we analyze the surface brightness radial profiles of several young supernova remnants (SNRs) with relatively symmetric structures. The surface brightness data are obtained from the MOS1, MOS2, and PN instruments. We fit these profiles using a phenomenological model combining Gaussian and β models. Our results reveal a significant difference between SNRs with bright shell edges and those with faint shell edges. SNRs with bright shell edges exhibit a surface brightness peak within a certain range. In contrast, SNRs with faint shell edges show a gradual decrease in brightness, indicating differences in the physical mechanisms driving their evolution. Subsequently, we use the Gaussian and β models to fit these profiles. The results effectively reflect their evolutionary trends and brightness distribution, indicating that the internal part of the profiles is generally expressed by the Gaussian models, while the external part is characterized by the β model. Notably, the β-values in our model closely approximate the expansion parameters of the SNRs. This intriguing similarity suggests that detailed analyses of surface brightness radial profiles may provide valuable insights into the expansion dynamics of SNRs.

Faint and Extended Galaxies as Probes for Understanding the Nature of Dark Matter Particles

This study delves into the complex nature of dark matter, a fundamental yet poorly understood component of the universe that constitutes approximately 27% of its total mass-energy content. By focusing on faint and extended galaxies specifically dwarf galaxies and low surface brightness galaxies this research aims to elucidate the properties of dark matter particles. Utilizing a comprehensive methodology that integrates observational data from reputable astronomical surveys, including the Sloan Digital Sky Survey (SDSS), the Hubble Space Telescope (HST), and the Dark Energy Survey (DES), the study investigates the relationships between the observed characteristics of these galaxies and the underlying dark matter properties. Key findings reveal that faint galaxies exhibit significantly higher mass-to-light ratios, averaging approximately M/L ≈ 20. This elevated mass-to-light ratio suggests a substantial dark matter component that is not accounted for by visible stellar matter, indicating that these galaxies possess unique structural and dynamical properties influenced by their dark matter content. The analysis of rotation curves demonstrates predominantly flat profiles across the majority of the selected galaxies, reinforcing the notion that dark matter plays a crucial role in maintaining the observed velocities of stars and gas in the outer regions of these systems. Additionally, the study derives halo mass functions that exhibit strong consistency with predictions from the cold dark matter (CDM) model, indicating that faint galaxies can effectively trace the underlying dark matter distribution in the universe. Significant correlations between galaxy morphology and dark matter density profiles were observed, with irregular galaxies showing higher dark matter concentrations. This suggests that gravitational interactions during their formation may have influenced both their structure and dark matter content. The implications of these findings extend beyond the individual characteristics of faint galaxies, emphasizing the need for a comprehensive understanding of the interplay between baryonic matter and dark matter in shaping the universe. The results challenge traditional views of galaxy formation, suggesting that faint galaxies are not merely scaled-down versions of brighter galaxies but rather possess unique properties that are essential for probing dark matter.

ExoALMA. I. Science Goals, Project Design, and Data Products

Abstract Planet formation is a hugely dynamic process requiring the transport, concentration, and assimilation of gas and dust to form the first planetesimals and cores. With access to observations with extremely high spatial and spectral resolution at unprecedented sensitivities, it is now possible to probe the planet-forming environment in detail. To this end, the exoALMA Large Program targeted 15 large protoplanetary disks, ranging between ∼1″ and ∼7″ in radius, and mapped the gas and dust distributions. 12CO J = 3–2, 13CO J = 3–2, and CS J = 7–6 molecular emission was imaged at high angular ( ∼ 0 . ″ 15 ) and spectral (∼100 m s−1) resolution, achieving a surface brightness temperature sensitivity of ∼1.5 K over a single channel, while the 330 GHz continuum emission was imaged at 90 mas resolution and achieved a point source sensitivity of ∼40 μJy beam−1. These observations constitute some of the deepest observations of protoplanetary disks to date. Extensive substructure was found in all but one disk, traced by both dust continuum and molecular line emission. In addition, the molecular emission allowed for the velocity structure of the disks to be mapped with excellent precision (uncertainties of the order of 10 m s−1), revealing a variety of kinematic perturbations across all sources. From this sample it is clear that, when observed in detail, all disks appear to exhibit physical and dynamical substructure indicative of ongoing dynamical processing due to young, embedded planets, large-scale (magneto)hydrodynamical instabilities or winds.