Low-luminosity Galaxies Research Articles

Understanding the origin of early-type dwarfs: the spectrophotometric study of CGCG014−074

ABSTRACT Early-type dwarf galaxies constitute a prevalent population in the central regions of rich groups and clusters in the local Universe. These low-luminosity and low-mass stellar systems play a fundamental role in the assembly of the luminous galaxies observed today, according to the Lambda cold dark matter hierarchical theory. The origin of early-type dwarfs has been linked to the transformation of disc galaxies interacting with the intracluster medium, especially in dense environments. However, the existence of low-luminosity early-type galaxies in low-density environments presents a challenge to this scenario. This study presents a comprehensive photometric and spectroscopic analysis of the early-type dwarf galaxy CGCG014−074 using deep Gemini GMOS (Gemini Multi-Object Spectrograph) data, focusing on its peculiarities and evolutionary implications. CGCG014−074 exhibits distinct features, including a rotating inner disc, an extended stellar formation with a quiescent phase since about 2 Gyr ago, and the presence of boxy isophotes. From the kinematic analysis, we confirm CGCG014−074 as a nucleated early-type dwarf galaxy with embedded disc. The study of its stellar population parameters using different methods provides significant insights into the galaxy’s evolutionary history. These results show an old and metal-poor nucleus (${\sim}9.3$ Gyr and $\mathrm{[Z/H]}\sim -0.84$ dex), while the stellar disc is younger (${\sim}4.4$ Gyr) with a higher metallicity ($\mathrm{[Z/H]}\sim -0.40$ dex). These distinctive features collectively position CGCG014−074 as a likely building block galaxy that has evolved passively throughout its history.

A GMRT 610 MHz radio survey of the North Ecliptic Pole (NEP, ADF-N) / Euclid Deep Field North

Abstract This paper presents a 610 MHz radio survey covering 1.94 deg2 around the North Ecliptic Pole (NEP), which includes parts of the AKARI (ADF-N) and Euclid, Deep Fields North. The median 5σ sensitivity is 28 μJy beam−1, reaching as low as 19 μJy beam−1, with a synthesised beam of 3.6″× 4.1″. The catalogue contains 1675 radio components, with 339 grouped into multi-component sources and 284 ’isolated’ components likely part of double radio sources. Imaging, cataloguing, and source identification are presented, along with preliminary scientific results. From a non-statistical sub-set of 169 objects with multi-wavelength AKARI and other detections, luminous infrared galaxies (LIRGs) represent 66$\%$ of the sample, ultra-luminous infrared galaxies (ULIRGs) 4$\%$, and sources with LIR < 1011 L⊙ 30$\%$. In total, 56$\%$ of sources show some AGN presence, though only seven are AGN-dominated. ULIRGs require three times higher AGN contribution to produce high-quality SED fits compared to lower luminosity galaxies, and AGN presence increases with AGN fraction. The PAH mass fraction is not significant, although ULIRGs have about half the PAH strength of lower IR-luminosity galaxies. Higher luminosity galaxies show gas and stellar masses an order of magnitude larger, suggesting higher star formation rates. For LIRGs, AGN presence increases with redshift, indicating that part of the total luminosity could be contributed by AGN activity rather than star formation. Simple cross-matching revealed 13 ROSAT QSOs, 45 X-ray sources, and 61 sub-mm galaxies coincident with GMRT radio sources.

Dissecting the planetary nebula NGC 4361 with MUSE

Optical integral field spectroscopy of planetary nebulae (PNe) offers a unique tool to explore the spatial relationships between the complex mixture of the many components (neutral, low- and high-ionisation gas, dust, and the central star) and their underlying physical conditions. The optical line and continuum emission in the very-high-ionisation Galactic PN, NGC 4361, were mapped to study the distribution of ionisation, extinction, electron temperature, and density. Based on commissioning data, MUSE Wide Field (60times 60$''$) normal-mode (4750-9300\ observations of NGC 4361 were reduced. The PN is larger than a single MUSE field and only the central 1 arcmin2 of the PN was observed in good conditions. Emission images in recombination and collisionally excited lines were extracted and the line ratios provided the dust extinction, electron density and temperature, and ionic abundances using standard techniques. A family of compact low-ionisation knots (dubbed 'freckles') was discovered and techniques developed to measure their spectra, independently of the extended high-ionisation medium. The nebula is confirmed as optically thin in the H-ionising continuum, based on its very low He i emission, even to the edges of the field. The electron temperature, $T_ e $, is shown to have a large-scale spatially coherent structure, as indicated by a previous long-slit spectrum. Prior to this study, no low-ionisation emission had been positively detected, although MUSE revealed both weak extended N ii and O ii and $>$100 spatially unresolved knots. There are several linear associations of these knots, but none of them point convincingly back to the central star. They have low-to-moderate ionisation with $T_ e $ sim 11000\,K e $ sim 1500 cm$^ $ and generally exhibit a higher extinction than the extended high-ionisation nebula. Within the MUSE field, a low-redshift emission-line galaxy was serendipitously found to be hiding behind NGC 4361. The spectrum of this dwarf galaxy was carefully extracted from the bright foreground nebular emission and the galaxy's line and continuum properties were then determined. NGC 4361 is not completely optically thin, as indicated by several extended regions and many compact features of lower ionisation emission. The low-ionisation 'freckles' identified here do not clearly appear to differ in (He, N, O, S) abundance with respect to the extended high-ionisation gas. The spatial distribution and radial velocities of these features suggest that they belong to a thick disk oriented perpendicular to the large-scale nebular gas, which may perhaps be remnants of an earlier structure. The low-luminosity disk galaxy at sim 87\,Mpc has bright H ii regions with metallicity 12+log(O/H) cong 8.4 and is suggested to be a Magellanic irregular or low-mass spiral.

Constraints on the Lyman Continuum Escape from Low-mass Lensed Galaxies at 1.3 ≤ z ≤ 3.0

Low-mass galaxies can significantly contribute to reionization due to their potentially high Lyman continuum (LyC) escape fraction and relatively high space density. We present a constraint on the LyC escape fraction from low-mass galaxies at z = 1.3–3.0. We obtained rest-frame UV continuum imaging with the ACS/SBC and the WFC3/UVIS from the Hubble Space Telescope for eight strongly lensed galaxies that were identified in the Sloan Giant Arc Survey and the Cluster Lensing and Supernova survey with Hubble. The targeted galaxies were selected to be spectroscopically confirmed, highly magnified, and blue in their UV spectral shapes (β < −1.7). Our targets include intrinsically low-luminosity galaxies down to a magnification-corrected absolute UV magnitude M UV ∼ −14. We perform custom-defined aperture photometry to place the most reliable upper limits of LyC escape from our sample. From our observations, we report no significant (>2σ) detections of LyC fluxes, placing 1σ upper limits on the absolute LyC escape fractions of 3%–15%. Our observations do not support the expected increased escape fractions of LyC photons from intrinsically UV faint sources. Considering the highly anisotropic geometry of LyC escape, increasing the sample size of faint galaxies in future LyC observations is crucial.

Ly α emission strength and stellar properties of faint galaxies from 5 &amp;lt; z &amp;lt; 8.2

ABSTRACT We present a study on stellar properties of Lyman-alpha (Ly α) emitters at 5 &amp;lt; z &amp;lt; 8.2. We use 247 photometrically selected, lensed, high-redshift, low-luminosity galaxy candidates with spectroscopic follow-up. Of these, 38 are confirmed spectroscopically to be between 5 &amp;lt; z &amp;lt; 8.2 via detection of Ly α. For each galaxy and candidate, we estimate stellar mass, star formation rate, specific star formation rate, and mass-weighted age with spectral energy distribution fitting. We also measure the UV β slope and luminosity using values from photometry. We find no strong correlation between Ly α equivalent width and any of these properties, as well as no significant difference between the physical properties of Ly α emitters and candidates without Ly α detected. This lack of expected trends may be explained by a combination of the evolving opacity of the intergalactic medium at these redshifts as well as the unique phase space probed by our lensed sample. Via tests on other galaxy samples which show varying strengths of correlations, we conclude that if there exist any relationships between Ly α equivalent width and physical properties in the underlying population of faint galaxies, they are weak correlations. We also present the results of a spectroscopic search for C iii] emission in confirmed Ly α emitters at z ∼ 7, finding no C iii] detections, but putting constraints on strong active galactic nuclei activity and extreme nebular emission.

The Star Formation Efficiency during Reionization as Inferred from the Hubble Frontier Fields

A recent ultraviolet luminosity function (UVLF) analysis in the Hubble Frontier Fields, behind foreground lensing clusters, has helped solidify estimates of the faint-end of the z ∼ 5–9 UVLF at up to 5 mag fainter than in the field. These measurements provide valuable information regarding the role of low-luminosity galaxies in reionizing the universe and can help in calibrating expectations for JWST observations. We fit a semiempirical model to the lensed and previous UVLF data from Hubble. This fit constrains the average star formation efficiency (SFE) during reionization, with the lensed UVLF measurements probing halo mass scales as small as M ∼ 2 × 109 M ⊙. The implied trend of SFE with halo mass is broadly consistent with an extrapolation from previous inferences at M ≳ 1010 M ⊙, although the joint data prefer a shallower SFE. This preference, however, is partly subject to systematic uncertainties in the lensed measurements. Near z ∼ 6, we find that the SFE peaks at ∼20% between ∼1011 and 1012 M ⊙. Our best-fit model is consistent with the Planck 2020 determinations of the electron scattering optical depth, and most current reionization history measurements, provided the escape fraction of ionizing photons is f esc ∼ 10%–20%. The joint UVLF accounts for nearly 80% of the ionizing photon budget at z ∼ 8. Finally, we show that recent JWST UVLF estimates at z ≳ 11 require strong departures from the redshift evolution suggested by the Hubble data.

A versatile classification tool for galactic activity using optical and infrared colors

Context.The overwhelming majority of diagnostic tools for galactic activity are focused mainly on the classes of active galaxies. Passive or dormant galaxies are often excluded from these diagnostics, which usually employ emission-line features (e.g., forbidden emission lines). Thus, most of them focus on specific types of activity or only on one activity class, for example active galactic nucleus (AGN) galaxiesAims.In this work we used infrared and optical colors to build an all-inclusive galactic activity diagnostic tool that can discriminate between star-forming, AGN, low-ionization nuclear emission-line region, composite, and passive galaxies, and which can be used in local and low-redshift galaxies.Methods.We used the random forest algorithm to define a new activity diagnostic tool. As the ground truth for the training of the algorithm, we considered galaxies that have been classified based on their optical spectral lines. We explored classification criteria based on infrared colors from the first three WISE bands (bands 1, 2, and 3) supplemented with optical colors from theu, g, andrSDSS bands. From them, we sought the combination with the minimum number of colors that provides optimal results. Furthermore, to mitigate biases related to aperture effects, we introduced a new WISE photometric scheme that combines apertures of different sizes.Results.Using machine learning methods, we developed a diagnostic tool that accommodates both active and passive galaxies under one unified classification scheme using just three colors. We find that the combination ofW1-W2, W2-W3, and g-r colors offers a good performance, while the broad availability of these colors for a large number of galaxies ensures it can be applied to large galaxy samples. The overall accuracy is ~81%, and the achieved completeness for each class is ~81% for star-forming, ~56% for AGN, ~68% for LINER, ~65% for composite, and ~85% for passive galaxies.Conclusions.Our diagnostic represents a significant improvement over existing infrared diagnostics because it includes all types of active galaxies, as well as passive galaxies, extending their application to the local Universe. The inclusion of the optical colors improves its ability to identify low-luminosity AGN galaxies, which are generally confused with star-forming galaxies, and helps us identify cases of starbursts with extreme mid-infrared colors that mimic obscured AGN galaxies, a well-known problem for most infrared diagnostics.

The Multiwavelength Environment of Second Bologna Catalog Sources

We present the first results of the Chandra Cool Targets (CCT) survey of the Second Bologna Catalog (B2CAT) of powerful radio sources, aimed at investigating the extended X-ray emission surrounding these sources. For the first 33 sources observed in the B2CAT CCT survey, we performed both imaging and spectral X-ray analysis, producing multiband Chandra images, and compared these images with radio observations. To evaluate the presence of extended emission in the X-rays, we extracted surface flux profiles comparing them with simulated ACIS point-spread functions. We detected X-ray nuclear emission for 28 sources. In addition, we detected eight regions of increased X-ray flux originating from radio hot spots or jet knots, and a region of decreased flux, possibly associated with an X-ray cavity. We performed X-ray spectral analysis for 15 nuclei and found intrinsic absorption significantly larger than the Galactic values in four of them. We detected significant extended X-ray emission in five sources, and fitted their spectra with thermal models with gas temperatures ∼2 keV. In the case of B2.1 0742+31, the surrounding hot gas is compatible with the intracluster medium of low-luminosity clusters of galaxies, while the X-ray diffuse emission surrounding the highly disturbed wide-angle-tailed radio galaxy B2.3 2254+35 features a luminosity similar to those of relatively bright galaxy groups, although its temperature is similar to those of low-luminosity galaxy clusters. These results highlight the power of low-frequency radio selection, combined with short Chandra snapshot observations, for investigating the properties of X-ray emission from radio sources.

Examining the Properties of Low-luminosity Hosts of Type Ia Supernovae from ASAS-SN

We present a spectroscopic analysis of 44 low-luminosity host galaxies of Type Ia supernovae (SNe Ia) detected by the All-Sky Automated Survey for Supernovae (ASAS-SN), using hydrogen, oxygen, and sulfur emission lines to measure metallicities and star formation rates. We find no statistically significant evidence that the star formation activity and metallicities of the galaxies in our sample are inconsistent with galaxies of similar luminosities and masses. We identify two 3σ outlier galaxies that have high metallicities for their stellar masses, but find that their other properties are consistent with general galaxies. The overall consistency between our sample and general galaxy samples further strengthens the evidence from more luminous SN Ia host galaxy samples that SN Ia host galaxies are typical.

The nature of an ultra-faint galaxy in the cosmic dark ages seen with JWST.

In the first billion years after the Big Bang, sources of ultraviolet (UV) photons are believed to have ionized intergalactic hydrogen, rendering the Universe transparent to UV radiation. Galaxies brighter than the characteristic luminosity L*(refs.1,2) do not provide enough ionizing photons to drive this cosmic reionization. Fainter galaxies are thought to dominate the photon budget; however, they are surrounded by neutral gas that prevents the escape of the Lyman-α photons, which has been the dominant way to identify them so far. JD1 was previously identified as a triply-imaged galaxy with a magnification factor of 13 provided by the foreground cluster Abell 2744 (ref. 3), and a photometric redshift of z ≈ 10. Here we report the spectroscopic confirmation of this very low luminosity (≈0.05 L*) galaxy at z = 9.79, observed 480 Myr after the Big Bang, by means of the identification of the Lyman break and redward continuum, as well as multiple ≳4σ emission lines, with the Near-InfraRed Spectrograph (NIRSpec) and Near-InfraRed Camera (NIRCam) instruments. The combination of the James Webb Space Telescope (JWST) and gravitational lensing shows that this ultra-faint galaxy (MUV = -17.35)-with a luminosity typical of the sources responsible for cosmic reionization-has a compact (≈150 pc) and complex morphology, low stellar mass (107.19 M⊙) and subsolar (≈0.6 Z⊙) gas-phase metallicity.

Toward Accurate Modeling of Galaxy Clustering on Small Scales: Halo Model Extensions and Lingering Tension

This paper represents an effort to provide robust constraints on the galaxy–halo connection and simultaneously test the Planck ΛCDM cosmology using a fully numerical model of small-scale galaxy clustering. We explore two extensions to the standard Halo Occupation Distribution model: assembly bias, whereby halo occupation depends on both halo mass and the larger environment, and velocity bias, whereby galaxy velocities do not perfectly trace the velocity of the dark matter within the halo. Moreover, we incorporate halo mass corrections to account for the impact of baryonic physics on the halo population. We identify an optimal set of clustering measurements to constrain this “decorated” HOD model for both low- and high-luminosity galaxies in SDSS DR7. We find that, for low-luminosity galaxies, a model with both assembly bias and velocity bias provides the best fit to the clustering measurements, with no tension remaining in the fit. In this model, we find evidence for both central and satellite galaxy assembly bias at the 99% and 95% confidence levels, respectively. In addition, we find evidence for satellite galaxy velocity bias at the 99.9% confidence level. For high-luminosity galaxies, we find no evidence for either assembly bias or velocity bias, but our model exhibits significant tension with SDSS measurements. We find that all of these conclusions still stand when we include the effects of baryonic physics on the halo mass function, suggesting that the tension we find for high-luminosity galaxies may be due to a problem with our assumed cosmological model.

Inferring the intergalactic medium neutral fraction at z ∼ 6–8 with low-luminosity Lyman break galaxies

ABSTRACT We present a Bayesian inference on the neutral hydrogen fraction of the intergalactic medium (IGM), $\overline{x}_{\small HI}$, at z ∼ 6–8 using the properties of Lyman break galaxies (LBGs) during the epoch of reionization. We use large samples of LBG candidates at 5.5 ≤ z ≤ 8.2 with spectroscopy from Keck/DEIMOS and Keck/MOSFIRE. For each galaxy, we incorporate either the Lyman-α (Lyα) equivalent width (EW) for detections or the EW limit spectrum for non-detections to parametrize the EW distribution at various ultraviolet brightnesses for a given redshift. Using our reference sample of galaxy candidates from the ionized universe at z ∼ 6.0, we are able to infer $\overline{x}_{\small HI}$ at two redshifts: z ∼ 6.7 and z ∼ 7.6. This work includes intrinsically faint, gravitationally lensed galaxies at z ∼ 6.0 in order to constrain the intrinsic faint-end Lyα EW distribution and provide a comparable population of galaxies to counterparts in our sample that are at higher redshift. The inclusion of faint galaxy candidates, in addition to a more sophisticated modelling framework, allows us to better isolate effects of the interstellar medium and circumgalactic medium on the observed Lyα distribution from those of the IGM. We infer an upper limit of $\overline{x}_{\small HI}$ ≤ 0.25 (0.44) at z = 6.7 ± 0.2 and a neutral fraction of $\overline{x}_{\small HI}$ = $0.83^{+0.08}_{-0.11}$ (0.83$^{+0.11}_{-0.21}$) at z = 7.6 ± 0.6, both within 68 per cent (95 per cent) uncertainty, results that favour a moderately late and fairly rapid reionization.

LOFAR discovery of rare large FR I jets in the low-luminosity radio galaxy NGC 5322

ABSTRACT The discovery of faint Fanaroff–Riley type I (FR I) radio jets in the elliptical galaxy NGC 5322 is reported here using the 144-MHz image from Data Release 2 of the Low-Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS). The jets have an angular extent of ∼40 arcmin or a projected physical extent of ∼360 kpc. The faint jets remain well collimated and disappear in the intergalactic medium, without any detected hotspots or radio lobes. The relatively brighter jets, previously detected only up to the ∼21 kpc extent at higher frequencies, are within the optical extent of the galaxy. The jets become faint abruptly outside, where detection is made only in the LOFAR image. The total radio luminosity of the galaxy at 144 MHz is estimated to be (3.7 ± 0.4) × 1022 W Hz−1. The 144-MHz radio luminosity of the faint jets outside the optical extent is estimated to be (7.1 ± 2.0) × 1021 W Hz−1. The size of the jets is exceptionally large for the galaxy’s low radio luminosity, when compared with other radio galaxies. It makes NGC 5322 a rare radio galaxy, previously not detected in other radio surveys. A combined effect of stellar core depletion and low-density environment around the jets, which results in a weak entrainment of the material surrounding the jets, could be responsible for its large size despite a low radio luminosity.

The Pristine survey – XVI. The metallicity of 26 stellar streams around the Milky Way detected with the STREAMFINDER in Gaia EDR3

ABSTRACT We use the photometric metallicities provided by the panoramic Pristine survey to study the veracity and derive the metallicities of the numerous stellar streams found by the application of the STREAMFINDER algorithm to the Gaia Early Data Release 3 data. All 26 streams present in Pristine show a clear metallicity distribution function, which provides an independent check of the reality of these structures, supporting the reliability of STREAMFINDER in finding streams and the power of Pristine to measure precise metallicities. We further present six candidate structures with coherent phase-space and metallicity signals that are very likely streams. The majority of studied streams are very metal-poor (14 structures with [Fe/H] &amp;lt; −2.0) and include three systems with [Fe/H] &amp;lt; −2.9 (C-11, C-19, and C-20). These streams could be the closest debris of low-luminosity dwarf galaxies or may have originated from globular clusters of significantly lower metallicity than any known current Milky Way globular cluster. Our study shows that the promise of the Gaia data for Galactic Archeology studies can be substantially strengthened by quality photometric metallicities, allowing us to peer back into the earliest epochs of the formation of our Galaxy and its stellar halo constituents.

Explaining the UHECR spectrum, composition and large-scale anisotropies with radio galaxies

Radio galaxies are promising candidates as the sources of ultrahigh energy cosmic rays (UHECRs). In this work, we examine if the stringent constraints imposed by the dipole and quadropole anisotropies as well as the UHECR spectrum and composition allow that radio galaxies are the dominant extragalactic cosmic ray sources. In order to calculate the UHECR flux emitted by individual radio galaxies, we constrain their properties using information from the radio-CR correlation and a dynamical evolution model. In addition to the UHECR flux from individual, local sources, we include the diffuse flux emitted by the bulk of non-local radio galaxies based on their radio luminosity distribution. Analyzing the source parameters within a range around their expected properties, we finally determine the configurations of local sources describing well the UHECR spectrum, composition and large-scale anisotropies. We obtain a good description of all data even in the case that we include only a small number of local sources. In particular, we find that scenarios where few sources like Fornax A and Virgo A dominate the flux above the ankle, while low-luminosity radio galaxies contribute an isotropic background dominating below the ankle, provide a good fit to the data.

Z ∼ 2–9 Galaxies Magnified by the Hubble Frontier Field Clusters. I. Source Selection and Surface Density–Magnification Constraints from >2500 Galaxies

We assemble a large comprehensive sample of 2534 z ∼ 2, 3, 4, 5, 6, 7, 8, and 9 galaxies lensed by the six clusters from the Hubble Frontier Fields (HFF) program. Making use of the availability of multiple independent magnification models for each of the HFF clusters and alternatively treating one of the models as the “truth,” we show that the median magnification factors from the v4 parametric models are typically reliable to values of 30–50, and in one case to 100. Using the median magnification factor from the latest v4 models, we estimate the UV luminosities of the 2534 lensed z ∼ 2–9 galaxies, finding sources as faint as −12.4 mag at z ∼ 3 and −12.9 mag at z ∼ 7. We explicitly demonstrate the power of the surface density–magnification relations Σ(z) versus μ in the HFF clusters to constrain both distant galaxy properties and cluster lensing properties. Based on the Σ(z) versus μ relations, we show that the median magnification estimates from existing public models must be reliable predictors of the true magnification μ to μ < 15 (95% confidence). We also use the observed Σ(z) versus μ relations to derive constraints on the evolution of the luminosity function faint-end slope from z ∼ 7 to z ∼ 2, showing that faint-end slope results can be consistent with blank-field studies if, and only if, the selection efficiency shows no strong dependence on the magnification factor μ. This can only be the case if very low-luminosity galaxies are very small, being unresolved in deep lensing probes.

Resolving the H I in damped Lyman α systems that power star formation.

Reservoirs of dense atomic gas (primarily hydrogen) contain approximately 90 per cent of the neutral gas at a redshift of 3, and contribute to between 2 and 3 per cent of the total baryons in the Universe1-4. These 'damped Lyman α systems'-so called because they absorb Lyman α photons within and from background sources-have been studied for decades, but only through absorption lines present in the spectra of background quasars and γ-ray bursts5-10. Such pencil beams do not constrain the physical extent of the systems. Here we report integral-field spectroscopy of a bright, gravitationally lensed galaxy at a redshift of 2.7 with two foreground damped Lyman α systems. These systems are greater than 238 kiloparsecs squared in extent, with column densities of neutral hydrogen varying by more than an order of magnitude on scales of less than 3 kiloparsecs. The mean column densities are between 1020.46 and 1020.84 centimetres squared and the total masses are greater than 5.5 × 108-1.4 × 109 times the mass of the Sun, showing that they contain the necessary fuel for the next generation of star formation, consistent with relatively massive, low-luminosity primeval galaxies at redshifts greater than 2.

Magnetic field structure in the vicinity of a supermassive black hole in low-luminosity galaxies: the case of Sgr A*

ABSTRACT Observations of $\rm Sgr A^{*}$ have provided a lot of insight on low-luminosity accretion, with a handful of bright flares accompanied with orbital motion close to the horizon. It has been proposed that gas supply comes from stellar winds in the neighborhood of the supermassive black hole. We here argue that the flow at the vicinity of the black hole has a low magnetization and a structure of alternating polarity, totally dictated by the well-studied and long-ago proposed MRI turbulent process. This can be the case, provided that in larger distances from the black hole magnetic diffusivity is dominant, and thus, the magnetic field will never reach equipartition values. For $\rm Sgr A^{*}$, we show the immediate consequences of this specific magnetic field geometry, which are: (i) an intermittent flow that passes from quiescent states to flaring activity, (ii) no quasi-steady-state jet, (iii) no possibility of a magnetically arrested configuration. Moreover, a further distinctive feature of this geometry is the intense magnetic reconnection events, occurring as layers of opposite magnetic polarity, accreted in the vicinity of the black hole. Finally, we argue that the absence of a jet structure in such case will be a smoking gun in 43 and 86 GHz observations.

The eROSITA Final Equatorial-Depth Survey (eFEDS)

Context.Scaling relations link the physical properties of clusters at cosmic scales. They are used to probe the evolution of large-scale structure, estimate observables of clusters, and constrain cosmological parameters through cluster counts.Aims.We investigate the scaling relations between X-ray observables of the clusters detected in the eFEDS field using Spectrum-Roentgen-Gamma/eROSITA observations taking into account the selection effects and the distributions of observables with cosmic time.Methods.We extract X-ray observables (LX,Lbol,T,Mgas,YX) withinR500for the sample of 542 clusters in the eFEDS field. By applying detection and extent likelihood cuts, we construct a subsample of 265 clusters with a contamination level of &lt;10% (including AGNs and spurious fluctuations) to be used in our scaling relations analysis. The selection function based on the state-of-the-art simulations of the eROSITA sky is fully accounted for in our work.Results.We provide the X-ray observables in the core-included &lt;R500and core-excised 0.15R500-R500apertures for 542 galaxy clusters and groups detected in the eFEDS field. Additionally, we present our best-fit results for the normalization, slope, redshift evolution, and intrinsic scatter parameters of the X-ray scaling relations betweenLX-T,LX-Mgas,LX-YX,Lbol-T,Lbol-Mgas,Lbol-YX, andMgas-T. We find that the best-fit slopes significantly deviate from the self-similar model at a &gt;4σ confidence level, but our results are nevertheless in good agreement with the simulations including non-gravitational physics, and the recent results that take into account selection effects.Conclusions.The strong deviations we find from the self-similar scenario indicate that the non-gravitational effects play an important role in shaping the observed physical state of clusters. This work extends the scaling relations to the low-mass, low-luminosity galaxy cluster and group regime using eFEDS observations, demonstrating the ability of eROSITA to measure emission from the intracluster medium out toR500with survey-depth exposures and constrain the scaling relations in a wide mass-luminosity-redshift range.

Revisiting the relation between the number of globular clusters and galaxy mass for low-mass galaxies

ABSTRACT Using a new method to estimate total galaxy mass (MT) and two samples of low-luminosity galaxies containing measurements of the number of globular clusters (GCs) per galaxy (NGC), we revisit the NGC–MT relation using a total of 203 galaxies, 157 of which have MT ≤ 1010 M⊙. We find that the relation is nearly linear, NGC ∝ MT0.92 ± 0.08 down to at least MT ∼ 108.75 M⊙. Because the relationship extends to galaxies that average less than one GC per galaxy and to a mass range in which mergers are relatively rare, the relationship cannot be solely an emergent property of hierarchical galaxy formation. The character of the radial GC distribution in low-mass galaxies, and the lack of mergers at these galaxy masses, also appears to challenge models in which the GCs form in central, dissipatively concentrated high-density, high-pressure regions and are then scattered to large radius. The slight difference between the fitted power-law exponent and a value of one leaves room for a shallow MT-dependent variation in the mean mass per GC that would allow the relation between total mass in GCs and MT to be linear.