Dominant Galaxy Research Articles

X-ray observations of Blueberry galaxies

Context. Compact star-forming galaxies were dominant galaxy types in the early Universe. Blueberry galaxies (BBs) represent their local analogues, being very compact and having intense star formation. Aims. Motivated by high X-ray emission recently found in other analogical dwarf galaxies, called Green Peas, we probed the X-ray properties of BBs to determine if their X-ray emission is consistent with the empirical laws for star-forming galaxies. Methods. We performed the first X-ray observations of a small sample of BBs with the XMM-Newton satellite. Spectral analysis for detected sources and upper limits measured via Bayesian-based analysis for very low-count measurements were used to determine the X-ray properties of our galaxy sample. Results. Clear detection was obtained for only two sources, with one source exhibiting an enhanced X-ray luminosity to the scaling relations. For the remaining five sources, only an upper limit was constrained, suggesting BBs to be rather underluminous as a whole. Our analysis shows that the large scatter cannot be easily explained by the stochasticity effects. While the bright source is above (and inconsistent with) the expected distribution at almost the 99% confidence level, the upper limits of the two sources are below the expected distribution. Conclusions. These results indicate that the empirical relations between the star formation rate, metallicity, and X-ray luminosity might not hold for BBs with uniquely high specific star formation rates. One possible explanation could be that the BBs may not be old enough to have a significant X-ray binary population. The high luminosity of the only bright source can then be caused by an additional X-ray source, such as a hidden active galactic nucleus or more extreme ultraluminous X-ray sources.

On the Kinematic Nature of Apparent Disks at High Redshifts: Local Counterparts are Not Dominated by Ordered Rotation but by Tangentially Anisotropic Random Motion

It is not straightforward to physically interpret the apparent morphology of galaxies. Recent observations by the James Webb Space Telescope (JWST) revealed a dominant galaxy population at high redshifts (z > 2) that were visually classified as disks for their flattened shapes and/or exponential light profiles. The extensively accepted interpretation is that they are dynamically cold disks supported by bulk rotation. However, it is long known that flattened shapes and exponential profiles are not exclusive for rotating disk structure. To break degeneracy and assess the rotational support of typical high-z galaxies in the JWST samples, those with active star formation and stellar masses lg(M⋆/M⊙)∼9 , we study the kinematics of their equal-mass counterparts at z = 0. While these local star-forming low-mass galaxies are photometrically similar to real dynamically cold disks, they are not supported by ordered rotation but primarily by random motion, and their flattened shapes result largely from tangential orbital anisotropy. Given the empirical and theoretical evidence that young galaxies are dynamically hotter at higher redshifts, our results suggest that the high-z JWST galaxies may not be cold disks but are dynamically warm/hot galaxies with flattened shapes driven by anisotropy. While both have low rotational support, local low-mass galaxies possess oblate shapes, contrasting the prolate shapes (i.e., cigar like) of low-mass systems at high redshifts. Such shape transition (prolate ⇒ oblate) indicates an associated change in orbital anisotropy (radial ⇒ tangential), with roots likely in the assembly of their host dark matter halos.

Fractal Architecture of the Universe Based on Primary-Centric World-View - A Post Copernican Conjecture

This paper investigates the fractal architecture of our Universe based on Primary-Centric Theoretical Formulation. Through theoretical analysis of Earth-Moon System, I arrived at the planetary satellite dynamics which was found to apply equally well to Solar and Exo-solar systems. This gave the theoretical foundation of the New Perspective of the birth and evolution of Exo-solar Systems. This was further extended to the theoretical analysis of star pairs and Neutron-Star pairs. This laid down the Primarycentric World View which I postulate as the physical process which has been shaping the evolution of the Universe and the hot-spots of the Cosmic Microwave Background Radiation right from 380,000 yrs after the Big Bang to date in top-down model resulting into Super-clusters, Clusters, Galaxies and Solar Systems. Primary-centric analysis corresponds to keplerian Analysis for negligibly small mass ratio less than 0.001. In the Copernican Framework, Kepler’s Third Law places no restriction on the orbit of the secondary component in a celestial pair. In Primary Centric Framework there is a very definite constraint on the permitted stable orbit, introduced due to periodic tidal deformations . There are two Clarke’s Orbits which are fully circularized and synchronized and hence nondissipative and equilibrium orbits called inner and outer Clarke's orbits equivalent to two geosynchronous orbits in Earth-Moon scenario. Outer Clarke’s Orbit is permissible as a stable orbit if the mass ratio of secondary to primary is greater than 0.2, Inner Clarke’s Orbit is permissible if mass ratio is less than 10-4 . If the mass ratio is between 10-4 to 0.2 then secondary spirals-out from inner Clarke’s Orbit to outer Clarke’s Orbit if it tumbles into super-synchronous orbit and spirals-in if it tumbles into sub-synchronous orbit destined to be destroyed by the primary. My conjecture states that every cosmological sub-system has a Monarch (or dominant) Primary (M_primary) Component anchoring the given sub-system and this Primary decides the stable equilibrium orbits of the secondary/secondaries. Planet-Satellite has a Planet as the M_primary, Solar System and exo-Solar Systems have a planet hosting star (PHS) as the M_primary, Galaxy has a Super-Massive Black Hole(SMBH) as the M_primary, Cluster has a cD galaxy (central dominant Galaxy) which is also known as Brightest Cluster Galaxy(BCG) as the M_primary, Super-Cluster has a massive Cluster hosting a QUASER/Blazer as the M_primary. This goes adinfinitum until a Cosmic Web is woven with Cosmic filaments. This conjecture gains a definite credence after the recent discoveries of the over-massive Black Holes in M_Galaxies namely Messier 87 in Virgo Cluster, NGC 3842 in Leo Cluster, NGC 4889 in Coma Cluster[68] and NGC 1277 in Perseus Cluster[66] which had been proposed as M_Galaxies on general considerations even before the confirmation of over-massive black holes. In 2011, a group of floating planets have been discovered. This is a transitory event and is an exception to this conjecture.

Compact groups from semi-analytical models of galaxy formation – V. Their assembly channels as a function of the environment

ABSTRACT We delved into the assembly pathways and environments of compact groups (CGs) of galaxies using mock catalogues generated from semi-analytical models (SAMs) on the Millennium simulation. We investigate the ability of SAMs to replicate the observed CG environments and whether CGs with different assembly histories tend to inhabit specific cosmic environments. We also analyse whether the environment or the assembly history is more important in tailoring CG properties. We find that about half of the CGs in SAMs are non-embedded systems, 40 per cent are inhabiting loose groups or nodes of filaments, while the rest distribute evenly in filaments and voids, in agreement with observations. We observe that early-assembled CGs preferentially inhabit large galaxy systems ($\sim 60~{{\ \rm per\ cent}}$), while around 30 per cent remain non-embedded. Conversely, lately formed CGs exhibit the opposite trend. We also obtain that lately formed CGs have lower velocity dispersions and larger crossing times than early-formed CGs, but mainly because they are preferentially non-embedded. Those lately formed CGs that inhabit large systems do not show the same features. Therefore, the environment plays a strong role in these properties for lately formed CGs. Early-formed CGs are more evolved, displaying larger velocity dispersions, shorter crossing times, and more dominant first-ranked galaxies, regardless of the environment. Finally, the difference in brightness between the two brightest members of CGs is dependent only on the assembly history and not on the environment. CGs residing in diverse environments have undergone varied assembly processes, making them suitable for studying their evolution and the interplay of nature and nurture on their traits.

A Chandra Study of the NGC 7618/UGC 12491 Major Group Merger at Apogee: Multiple Cold Fronts, Boxy Wings, Filaments, and Arc-shaped Slingshot Tails

Analyses of major group mergers are key to understanding the evolution of large-scale structure in the Universe and the microphysical properties of the hot gas in these systems. We present imaging and spectral analyses of deep Chandra observations of hot gas structures formed in the major merger of the NGC 7618 and UGC 12491 galaxy groups and compare the observed hot gas morphology, temperatures, and abundances with recent simulations. The morphology of the observed multiple cold front edges and boxy wings are consistent with those expected to be formed by Kelvin–Helmholtz instabilities and gas sloshing in inviscid gas. The arc-shaped slingshot tail morphologies seen in each galaxy suggest that the dominant galaxies are near their orbital apogee after having experienced at least one core passage at a large impact parameter.

TRACING THE ASSEMBLY HISTORIES OF GALAXY CLUSTERS IN THE NEARBY UNIVERSE

We have compiled a sample of 67 nearby (z < 0.15) clusters of galaxies, for which on average more than 150 spectroscopic members are available and, by applying different methods to detect substructures in their galaxy distribution, we have studied their assembly history. Our analysis confirms that substructures are present in 70% of our sample, having a significant dynamical impact in 57% of them. A classification of the assembly state of the clusters based on the dynamical significance of their substructures is proposed. In 19% of our clusters, the originally identified brightest cluster galaxy is not the central gravitationally dominant galaxy (CDG), but turns out to be either the second-rank, or the dominant galaxy of a substructure (a SDG, in our classification), or even a possible “fossil” galaxy in the periphery of the cluster. Moreover, no correlation was found in general between the projected offset of the CDG from the X-ray peak and its peculiar velocity.

AMUSE-Antlia. I. Nuclear X-Ray Properties of Early-type Galaxies in a Dynamically Young Galaxy Cluster

To understand the formation and growth of supermassive black holes (SMBHs) and their coevolution with host galaxies, it is essential to know the impact of environment on the activity of active galactic nuclei (AGNs). We present new Chandra X-ray observations of nuclear emission from member galaxies in the Antlia cluster, the nearest non-cool core and the nearest merging galaxy cluster, residing at D = 35.2 Mpc. Its inner region, centered on two dominant galaxies NGC 3268 and NGC 3258, has been mapped with three deep Chandra ACIS-I pointings. Nuclear X-ray sources are detected in 7/84 (8.3%) early-type galaxies (ETG) and 2/8 (25%) late-type galaxies with a median detection limit of 8 × 1038 erg s−1. All nuclear X-ray sources but one have a corresponding radio continuum source detected by MeerKAT at the L band. Nuclear X-ray sources detected in early-type galaxies are considered the genuine X-ray counterpart of low-luminosity AGN. When restricted to a detection limit of and a stellar mass of , six of 11 ETGs are found to contain an X-ray AGN in Antlia, exceeding the AGN occupation fraction of 7/39 (18.0%) and 2/12 (16.7%) in the more relaxed, cool core clusters, Virgo and Fornax, respectively, and rivaling that of the AMUSE-Field ETG of 27/49 (55.1%). Furthermore, more than half of the X-ray AGN in Antlia is hosted by its younger subcluster, centered on NGC 3258. We believe that this is because SMBH activity is enhanced in a dynamically young cluster compared to relatively relaxed clusters.

Wide-Angle-Tail (WAT) Radio Sources

We review the properties of Wide-Angle-Tail (WAT) radio sources. The WAT radio sources are powerful, bent radio sources typically associated with the dominant galaxy in a cluster or group. For the purpose of this review, we define the radio morphology properties of WATs as (1) a sudden jet-tail transition, (2) overall bending of the tails to one side, and (3) non-parallel tails. The mechanism for the rapid jet-tail transition is uncertain but it seems to occur near the transition from the host ISM to ICM. The jet-tail transition may make the jets easier to bend. The narrow range in radio luminosity can be understood if there is a minimum luminosity required to allow the jets to propagate undisturbed for tens of kpc and a maximum luminosity required to allow the jet disruption mechanism to act. WATs are typically hosted by the brightest cluster galaxies in clusters which are currently merging. Thus, WATs can be used as tracers of merging clusters. The merging produces large-scale bulk motions in the ICM which can provide sufficient ram pressure to bend the jets. We suggest that although the Lorentz force may not bend the jets in WATs, it may be relevant in other sources, e.g., protostellar jets.

Feedback in the Extremely Violent Group Merger NGC 6338

The galaxy group NGC 6338 is one of the most violent group–group mergers known to date. While the central dominant galaxies rush at each other at 1400 km s−1 along the line of sight, with dramatic gas heating and shock fronts detected, the central gas in the BCGs remains cool. There are also indications of feedback from active galactic nuclei, and neither subcluster core has been disrupted. With our deep radio uGMRT data at 383 and 650 MHz, we clearly detect a set of large, old lobes in the southern BCG coinciding with the X-ray cavities, while the northern and smaller BCG appears slightly extended in the radio. The southern BCG also hosts a smaller younger set of lobes perpendicular to the larger lobes, but also coinciding with the inner X-ray cavities and matching the jet direction in the parsec-resolution VLBA image. Our spectral analysis confirms the history of two feedback cycles. The high radio frequency analysis classifies the compact source in the southern BCG with a power law, while ruling out a significant contribution from accretion. The radio lightcurve over three decades shows a change about 10 yr ago, which might be related to ongoing feedback in the core. The southern BCG in the NGC 6338 merger remains another prominent case where the direction of jet-mode feedback between two cycles changed dramatically.

Understanding the role of morphology and environment in the dynamical evolution of isolated galaxy triplets

Context. The environments where galaxies reside affects their evolutionary histories. Galaxy triplets (systems composed of three physically bound galaxies) are one of simplest groups of galaxies, and are therefore excellent laboratories to study evolutionary mechanisms where effects of the environment are minimal. Aims. We present a statistical study of the dynamical properties of isolated galaxy triplets as a function of their local and large-scale environments. To explore the connection of the dynamical evolution on the systems with the evolution of the galaxies composing the triplets, we consider observational properties such as morphology and star formation rate (SFR). Methods. We used the SDSS-based catalogue of Isolated Triplets (SIT), which contains 315 triplets. We classified each triplet according to galaxy morphologies and defined a parameter Qtrip to quantify the total local tidal strengths in the systems. To quantify the dynamical stage of the system we used the parameters of harmonic radius RH, velocity dispersion σvr, crossing time H0tc, and virial mass Mvir. Results. Triplets composed of three early-type galaxies present the smallest RH, indicating that they are in general more compact than triplets with one or more late-type galaxies. Among triplets with low values of RH and H0tc, SIT triplets with Qtrip < −2 are relaxed systems that are more dynamically evolved, while triplets with Qtrip > −2 show compact configurations due to interactions within the system, such as ongoing mergers. Conclusions. We found that there is no dominant galaxy in triplets in terms of properties of stellar populations such as global colour and SFR. Moreover, the global SFR in isolated triplets composed of two or more early-type galaxies increases with the stellar mass ratio of the galaxies with respect to the central galaxy, therefore the system is globally ‘rejuvenated’.

The Relation between Gas-phase Metallicity and Stellar Mass Surface Density in Post-starburst E+A and E+A+ Galaxies within the Coma Cluster Observed by the SDSS-IV MaNGA Survey

We present an analysis of the Mass–Metallicity Relation (MZR) in 29 post-starburst galaxies in the Coma Cluster. Outward from the central dominant galaxy, NGC 4889, we conducted a conical survey of all galaxies observed by the Sloan Digital Sky Survey Data Release 17 (SDSS DR17) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey within a 5° radius and redshift constraints 0.013 < z < 0.033. We identified 21 E+A galaxies and 8 “E+A+ galaxies” whose spectra matched the criteria of an E+A galaxy, but contain Balmer emission lines, indicating star formation. We utilized the MaNGA data to calculate each galaxy’s star formation rate densities, gas-phase metallicity and stellar mass. We then compared the MZR between E+A galaxies and E+A+ galaxies to observe how varying star formation rates alter this relation.

On the Convergence of the Milky Way and M31 Kinematics from Cosmological Simulations

The kinematics of the Milky Way (MW) and M31, the dominant galaxies in the Local Group (LG), can be used to estimate the LG total mass. New results on the M31 proper motion have recently been used to improve that estimate. Those results are based on kinematic priors that are sometimes guided and evaluated using cosmological N-body simulations. However, the kinematic properties of simulated LG analogs could be biased due to the effective power spectrum truncation induced by the small size of the parent simulation. Here we explore the dependence of LG kinematics on the simulation box size to argue that cosmological simulations need a box size on the order of 1 Gpc in order to claim convergence on the LG kinematic properties. Using a large enough simulation, we find M31 tangential and radial velocities relative to the MW to be in the range and , respectively. This study highlights that LG kinematics derived from N-body simulations have to be carefully interpreted, taking into account the size of the parent simulation.

Study of the Very High Energy Emission of M87 through its Broadband Spectral Energy Distribution

The radio galaxy M87 is the central dominant galaxy of the Virgo Cluster. Very high-energy (VHE, ≳0.1 TeV) emission from M87 has been detected by imaging air Cherenkov telescopes. Recently, marginal evidence for VHE long-term emission has also been observed by the High Altitude Water Cherenkov Observatory, a gamma-ray and cosmic-ray detector array located in Puebla, Mexico. The mechanism that produces VHE emission in M87 remains unclear. This emission originates in its prominent jet, which has been spatially resolved from radio to X-rays. In this paper, we construct a spectral energy distribution from radio to gamma rays that is representative of the nonflaring activity of the source, and in order to explain the observed emission, we fit it with a lepto-hadronic emission model. We found that this model is able to explain nonflaring VHE emission of M87 as well as an orphan flare reported in 2005.

High-resolution, High-sensitivity, Low-frequency uGMRT View of Coma Cluster of Galaxies

We present high-resolution, high-sensitivity upgraded Giant Metrewave Radio Telescope observations of the Coma cluster (A1656) at 250–500 MHz and 550–850 MHz. At 250–500 MHz, 135 sources have extensions >0.′45 (with peak-to-local-noise ratio >4). Of these, 24 sources are associated with Coma-member galaxies. In addition, we supplement this sample of 24 galaxies with 20 ram pressure stripped (RPS) galaxies from (Chen et al. 2020, eight are included in the original extended radio source sample) and an additional five are detected and extended. We present radio morphologies, radio spectra, spectral index maps, and equipartition properties for these two samples. In general, we find the equipartition properties lie within a narrow range (e.g., = 1–3 × 10− 13 dynes cm−2). Only NGC 4874, one of the two brightest central Coma cluster galaxies, has a central energy density and pressure about five times higher and a radio source age about 50% lower than that of the other Coma galaxies. We find a diffuse tail of radio emission trailing the dominant galaxy of the merging NGC 4839 group that coincides with the slingshot tail seen in X-rays. The southwestern radio relic, B1253+275, has a large extent ≈32′ × 10′ (≃1.08 × 0.34 Mpc2). For NGC 4789, whose long radio tails merge into the relic and may be a source of its relativistic seed electrons, we find a transverse radio spectral gradient, a steepening from southwest to northeast across the width of the radio source. Finally, radio morphologies of the extended and RPS samples suggest that these galaxies are on their first infall into Coma on (predominantly) radial orbits.

The XXL Survey

Why are some galaxy groups pervaded by a hot X-ray emitting intracluster medium, whilst others have no detectable X-ray emission? Is the presence of hot gas a reliable indicator of dynamical maturity, and can some virialised groups contain little or none of it? What are the main differences between samples of groups selected in the X-ray and optical bands? We address these questions by studying 232 optical spectroscopically selected groups from the Galaxy And Mass Assembly (GAMA) survey that overlap the XXL X-ray cluster survey. X-ray aperture flux measurements combined with GAMA group data provides the largest available sample of optical groups with detailed galaxy membership information and consistently measured X-ray fluxes and upper limits. A sample of 142 of these groups is divided into three subsets based on the relative strength of X-ray and optical emission, and we see a trend in galaxy properties between these subsets: X-ray overluminous groups contain a lower fraction of both blue and star forming galaxies compared with X-ray underluminous systems. X-ray overluminous groups also have a more dominant central galaxy, with a magnitude gap between first and second ranked galaxies on average 0.22 mag larger than in underluminous groups. Moreover, the central galaxy in overluminous groups lies closer to the luminosity-weighted centre of the group. We examine a number of other structural properties of our groups, such as axis ratio, velocity dispersion, and group crossing time, and find evidence of trends with X-ray emission in some of these properties despite the high stochastic noise arising from the limited number of group galaxies. We attribute the trends we see primarily to the evolutionary state of groups, with X-ray overluminous systems being more dynamically evolved than underluminous groups. The X-ray overluminous groups have had more time to develop a luminous intragroup medium, quench member galaxies, and build the mass of the central galaxy through mergers compared to underluminous groups. However, an interesting minority of X-ray underluminous groups have properties that suggest them to be dynamically mature. We find that the lack of hot gas in these systems cannot be accounted for by high star formation efficiency, suggesting that high gas entropy resulting from feedback is the likely cause of their weak X-ray emission.

Tracing the local volume galaxy halo‐to‐stellar mass ratio with satellite kinematics

AbstractRapid advance has been made recently in accurate distance measurements for nearby ( Mpc) galaxies based on the magnitude of the tip of red giant branch stars resolved with the Hubble Space Telescope. We use observational properties of galaxies presented in the last version of Updated Nearby Galaxy Catalog to derive a halo mass of luminous galaxies via orbital motion of their companions. Our sample contains 298 assumed satellites with known radial velocities around 25 Milky Way‐like massive galaxies and 65 assumed satellites around 47 fainter dominant galaxies. The average total mass‐to‐K‐band luminosity ratio is for the luminous galaxies, increasing up to toward dwarfs. The bulge‐dominated luminous galaxies are characterized with , while the disk‐dominated spirals have . We draw attention to a particular subsample of luminous spiral galaxies with signs of declining rotation curve, which have a radial velocity dispersion of satellites less than 55 km s−1 and a poor dark matter halo with . We note that a fraction of quenched (dSph, dE) companions around Milky Way‐like galaxies decreases with their linear projected separation as .

Signatures of quenching in dwarf galaxies in local galaxy clusters

Context. The transformation of late-type galaxies has been suggested as the origin of early-type dwarf galaxies (typically M⋆ ≤ 109 M⊙) in galaxy clusters. Based on deep images, Venhola and colleagues analysed correlations between colour and surface brightness for galaxies in the Fornax cluster binned by luminosity or stellar mass. In the bins with M⋆ &lt; 108 M⊙, the authors identified a correlation of redness with fainter surface brightness and interpreted it as a consequence of the quenching of star formation by ram pressure stripping in the dwarf galaxies. Aims. This study carries out a similar analysis for the Virgo cluster. The analysis for both clusters is then used to compare the Virgo and Fornax clusters, for which the ram pressure is expected to have different strengths. The purpose of this is to scrutinise the ram pressure interpretation from the other study and search for differences between the clusters that reflect the different ram pressure efficiencies, which would either support or weaken this interpretation. Ultimately, this could help weigh the importance of ram pressure stripping relative to other transformative processes in the shaping of the dominant early-type dwarf galaxy population. Methods. We extend the analysis of colour versus surface brightness binned by stellar mass to higher masses and a wider range of optical colours. The results, in particular at low stellar mass, are compared to predictions of stellar evolution models. Benefitting from larger sample sizes, we also analyse late- and early-type galaxies separately. This analysis is carried out for the Virgo and Fornax clusters, and the colour versus surface brightness relation, as well as other properties of the two clusters’ galaxy populations, are compared. Results. While the colour–surface brightness diagrams are remarkably similar for the two clusters, only the low-mass late-type galaxies are found to have slopes consistent with a fading and reddening following the quenching of star formation. For the early-type galaxies, there are no (or only weak) correlations between colour and surface brightness in all mass bins. Early- and late-type galaxies in both clusters have comparable sizes below a stellar mass of M⋆ ≲ 108 M⊙. The colour and size scaling relations are very similar for the Virgo and Fornax clusters. However, Virgo features a lower fraction of early-type or red galaxies despite its higher mass. Conclusions. The similarity of early-type dwarfs and low-mass late types in size at the masses M⋆ ≲ 108 M⊙ as well as the overall consistency of the colour–surface brightness correlation with fading stellar populations support a scenario of transformation via the quenching of star formation, for example by gas removal. However, the lack of this imprint of an ageing stellar population on the early-type dwarfs themselves calls for some additional explanation. Finally, the Virgo cluster is an atypical cluster with a comparably low fraction of quiescent early-type galaxies at all galaxy masses despite its large cluster mass.

A New Feedback Cycle in the Archetypal Cooling Flow Group NGC 5044

Abstract The fate of cooling gas in the centers of galaxy clusters and groups is still not well understood, as is also the case for the complex process of triggering active galactic nucleus (AGN) outbursts in their central dominant galaxies and the consequent reheating of the gas by the AGN jets. With the largest known reservoir of cold molecular gas of any group-dominant galaxy and three epochs of AGN activity visible as cavities in its hot gas, NGC 5044 is an ideal system in which to study the cooling/AGN feedback cycle at the group scale. We present VLBA observations of NGC 5044 to ascertain the current state of the central AGN. We find a compact core and two small jets aligned almost in the plane of the sky and in the orthogonal direction to the location of cavities. We construct the radio/submillimeter spectral energy distribution over more than 3 orders of magnitude. We find that below 5 GHz, the spectrum is best fit by a self-absorbed continuous injection model representing emission coming from the jets, while the higher frequencies show clear signs of an advection-dominated accretion flow. We derive a black hole mass and accretion rate consistent with independent measurements. We conclude that the age of the jets is much younger than the innermost cavities, marking the start of a new feedback cycle.

The Evolution of the Star-Forming Interstellar Medium Across Cosmic Time

Over the past decade, increasingly robust estimates of the dense molecular gas content in galaxy populations between redshift z = 0 and the peak of cosmic galaxy/star formation ( z ∼ 1–3) have become available. This rapid progress has been possible due to the advent of powerful ground- and space-based telescopes for the combined study of several millimeter to far-IR, line or continuum tracers of the molecular gas and dust components. The main conclusions of this review are as follows: ▪ Star-forming galaxies contained much more molecular gas at earlier cosmic epochs than at the present time. ▪ The galaxy-integrated depletion timescale for converting the gas into stars depends primarily on z or Hubble time and, at a given z, on the vertical location of a galaxy along the star-formation rate versus stellar mass main sequence (MS) correlation. ▪ Global rates of galaxy gas accretion primarily control the evolution of the cold molecular gas content and star-formation rates of the dominant MS galaxy population, which in turn vary with cosmological expansion. Another key driver may be global disk fragmentation in high- z, gas-rich galaxies, which ties local free-fall timescales to galactic orbital times and leads to rapid radial matter transport and bulge growth. The low star-formation efficiency inside molecular clouds is plausibly set by supersonic streaming motions and internal turbulence, which in turn may be driven by conversion of gravitational energy at high z and/or by local feedback from massive stars at low z. ▪ A simple gas regulator model is remarkably successful in predicting the combined evolution of molecular gas fractions, star-formation rates, galactic winds, and gas-phase metallicities.

Exploring the origin of ultra-diffuse galaxies in clusters from their primordial alignment

ABSTRACT We find that the minor axes of the ultra-diffuse galaxies (UDGs) in Abell 2634 tend to be aligned with the major axis of the central dominant galaxy, at a $\gtrsim 95{{\ \rm per\ cent}}$ confidence level. This alignment is produced by the bright UDGs with the absolute magnitudes Mr &amp;lt; −15.3 mag, and outer-region UDGs with R &amp;gt; 0.5R200. The alignment signal implies that these bright, outer-region UDGs are very likely to acquire their angular momenta from the vortices around the large-scale filament before they were accreted into A2634, and form their extended stellar bodies outside of the cluster; in this scenario, the orientations of their primordial angular momenta, which are roughly shown by their minor axes on the images, should tend to be parallel to the elongation of the large-scale filament. When these UDGs fell into the unrelaxed cluster A2634 along the filament, they could still preserve their primordial alignment signal before violent relaxation and encounters. These bright, outer-region UDGs in A2634 are very unlikely to be the descendants of the high-surface-brightness dwarf progenitors under tidal interactions with the central dominant galaxy in the cluster environment. Our results indicate that the primordial alignment could be a useful probe of the origin of UDGs in large-scale structures.