Giant Galaxies Research Articles

Galaxy populations in the Hydra I cluster from the VEGAS survey

In this work, we extend the catalog of low-surface brightness (LSB) galaxies, including ultra-diffuse galaxy (UDG) candidates, within ≈0.4Rvir of the Hydra I cluster of galaxies based on deep images from the VST Early-type GAlaxy Survey (VEGAS). The new galaxies were found by applying an automatic detection tool and carrying out additional visual inspections of g and r band images. This led to the detection of 11 UDGs and 8 more LSB galaxies. For all of them, we assessed the cluster membership using the color–magnitude relation derived for early-type giant and dwarf galaxies in Hydra I. The UDGs and new LSB galaxies found in Hydra I span a wide range of central surface brightness (22.7 ≲ μ0, g ≲ 26.5 mag arcsec−2), effective radius (0.6 ≲ Re ≲ 4.0 kpc), and color (0.4 ≤ g − r ≤ 0.9 mag), and have stellar masses in the range ∼5 × 106 − 2 × 108 M⊙. The 2D projected distribution of both galaxy types is similar to the spatial distribution of dwarf galaxies, with over-densities in the cluster core and north of the cluster center. They have similar color distribution and comparable stellar masses to the red dwarf galaxies. Based on photometric selection, we identify a total of nine globular cluster (GC) candidates associated to the UDGs and four to the LSB galaxies, with the highest number of candidates in an individual UDG being three. We find that there are no relevant differences between dwarfs, LSB galaxies, and UDGs: the structural parameters (i.e., surface brightness, size, color, and n-index) and GC content of the three classes have similar properties and trends. This finding is consistent with UDGs being the extreme LSB tail of the size–luminosity distribution of dwarfs in this environment.

Investigation of intra-day variability of the radio galaxy 3C 84 (Perseus A) flux density in centimeter range on the RT-32 VIRAC (Latvia) and RT-32 NSFCTC (Ukraine) radio telescopes

Extragalactic radio source 3C 84 (also known as Perseus A) is the active nucleus of the giant galaxy NGC 1275, the largest in the Perseus galaxy cluster (Abell 426). It is one of the brightest X-ray galaxy clusters. The nucleus of galaxy NGC 1275 (Seyfert II type) is a powerful radio source in the Northern Sky (flux density at frequency 8 GHz is about 30 Jy). 3C 84 has a long-term variability in the radio band, with a “wave-like” change in the flux density on a time scale of several decades. The purpose of our work was to search for and study the properties and features of the appearance of fast variability of the 3C 84 radio source in the centimeter radio range. For this, as part of the international Ukrainian–Latvian cooperation between the Institute of Radio Astronomy NAS of Ukraine and the Ventspils International Radio Astronomy Centre, many observation sessions were performed (October 2020 – September 2021) at the 32-m radio telescopes in Ukraine (Zolochiv) and Latvia (Irbene), with additional observations at the 16-m radio telescope (Irbene). As a result, the following main results were obtained: the 3C 84 radio source exhibits manifestations of episodic intraday variability, with characteristic times, usually in the range 3–8 hours, as well as “calm phases”, when there is no significant variability, and the source flux density does not change over several observation sessions. The most likely cause of this variability could be interstellar scintillations, but some quasi-simultaneous observations of 3C 84 carried out at the 32-m radio telescopes in Ukraine and Latvia showed the presence of a correlation in cross-Fourier spectra, with a characteristic time about 6 hours. In addition, the appearance of 3C 84 flux variability with characteristic times from 1–3 hours to several tens of minutes were recorded, which were not associated with radiointerference or hardware effects. They were detected in observations both in Ukraine and in Latvia, in different seasons of the year.

Galactic mass-to-light ratios with superfluid dark matter

Context. We make rotation curve fits to test the superfluid dark matter model. Aims. In addition to verifying that the resulting fits match the rotation curve data reasonably well, we aim to evaluate how satisfactory they are with respect to two criteria, namely, how reasonable the resulting stellar mass-to-light ratios are and whether the fits end up in the regime of superfluid dark matter where the model resembles modified Newtonian dynamics (MOND). Methods. We fitted the superfluid dark matter model to the rotation curves of 169 galaxies in the SPARC sample. Results. We found that the mass-to-light ratios obtained with superfluid dark matter are generally acceptable in terms of stellar populations. However, the best-fit mass-to-light ratios have an unnatural dependence on the size of the galaxy in that giant galaxies have systematically lower mass-to-light ratios than dwarf galaxies. A second finding is that the superfluid often fits the rotation curves best in the regime where the superfluid’s force cannot resemble that of MOND without adjusting a boundary condition separately for each galaxy. In that case, we can no longer expect superfluid dark matter to reproduce the phenomenologically observed scaling relations that make MOND appealing. If, on the other hand, we consider only solutions whose force approximates MOND well, then the total mass of the superfluid is in tension with gravitational lensing data. Conclusions. We conclude that even the best fits with superfluid dark matter are still unsatisfactory for two reasons. First, the resulting stellar mass-to-light ratios show an unnatural trend with galaxy size. Second, the fits do not end up in the regime that automatically resembles MOND, and if we force the fits to do so, the total dark matter mass is in tension with strong lensing data.

The Accurate Mass Distribution of M87, the Giant Galaxy with Imaged Shadow of Its Supermassive Black Hole, as a Portal to New Physics

Abstract The very careful Event Horizon Telescope estimate of the mass of the supermassive black hole at the center of the giant cD galaxy M87, allied with recent high-quality photometric and spectroscopic measurements, yields a proper dark/luminous mass decomposition from the galaxy center to its virial radius. That provides us with decisive information on crucial cosmological and astrophysical issues. The dark and the standard matter distributions in a wide first time detected galaxy region under the supermassive black hole gravitational control. The well-known supermassive black hole mass versus stellar dispersion velocity relationship at the highest galaxy masses implies an exotic growth of the former. This may be the first case in which one can argue that the supermassive black hole mass growth was also contributed by the dark matter component. A huge dark matter halo core in a galaxy with inefficient baryonic feedback is present and consequently constrains the nature of the dark halo particles. The unexplained entanglement between dark/luminous structural properties, already emerged in disk systems, also appears.

H i Gas Playing Hide-and-seek around a Powerful FRI-type Quasar at z ∼ 2.1

Abstract We present optical spectroscopic and milliarcsecond-scale radio continuum observations of the quasar M1540–1453 (z em = 2.104 ± 0.002) that show associated H i 21 cm absorption at z abs = 2.1139. At subkiloparsec scales, the powerful radio source with 1.4 GHz luminosity of 5.9 × 1027 W Hz−1 shows Fanaroff–Riley class I morphology caused by the interaction with dense gas within 70 pc of the active galactic nucleus (AGN). Interestingly, while there are indications for the presence of absorption from low-ionization species like Fe ii, Si ii, and Si iii in the optical spectrum, the expected strong damped Lyα absorption is not detected at the redshift of the H i 21 cm absorber. In comparison to typical high-z quasars, the Lyα emission line is much narrower. The “ghostly” nature of the H i Lyα absorber partially covering the broad-line region of extent 0.05 pc and the detection of widespread H i 21 cm absorption covering the diffuse radio source (extent >425 pc) imply the presence of a large clumpy H i halo, which may have been blown by the jet–interstellar medium (ISM) interaction. Further observations are needed to confirm the ghostly nature of the Lyα absorber and obtain a better understanding of the role played by the jet–ISM interaction in shaping the radio morphology of this powerful AGN. The study showcases how joint radio and optical analysis can shed light on the gaseous environment and origin of radio morphology in AGNs at high redshifts, when these are still the assembly sites of giant galaxies.

Hunting for massive black holes in dwarf galaxies

Despite traditional thinking, an appreciable population of massive black holes may be lurking in dwarf galaxies. Prior to the last decade, nearly all massive black holes were found in the nuclei of giant galaxies and the existence of massive black holes in dwarf galaxies was highly controversial. The field has now been transformed with a growing community of researchers working on a variety of observational studies and theoretical models of dwarf galaxies hosting massive black holes. Work in this area is not only important for a holistic understanding of dwarf galaxy evolution and feedback, but it may just tell us how the first "seeds" of massive black holes formed in the early Universe. In this Perspective, I discuss the current state of the field as well as future prospects. I also present new insights on the demographics of nearby dwarf galaxies, which can be used to help constrain the black hole occupation/active fraction as a function of mass and dwarf galaxy type.

An extreme case of galaxy and cluster co-evolution at z = 0.7

ABSTRACT We report the discovery of eMACS J0252.4−2100 (eMACS J0252), a massive and highly evolved galaxy cluster at z = 0.703. Our analysis of Hubble Space Telescope imaging and VLT/MUSE and Keck/DEIMOS spectroscopy of the system finds a high-velocity dispersion of 1020$^{+180}_{-190}$ km s−1 and a high (if tentative) X-ray luminosity of (1.2 ± 0.4) × 1045 erg s−1 (0.1–2.4 keV). As extreme is the system’s brightest cluster galaxy, a giant cD galaxy that forms stars at a rate of between 85 and 300 M⊙ yr−1 and features an extended halo of diffuse [O ii] emission, as well as evidence of dust. Its most remarkable properties, however, are an exceptionally high ellipticity and a radially symmetric flow of gas in the surrounding intracluster medium, potential direct kinematic evidence of a cooling flow. A strong-lensing analysis, anchored by two multiple-image systems with spectroscopic redshifts, finds the best lens model to consist of a single cluster-scale halo with a total mass of (1.9 ± 0.1) × 1014 M⊙ within 250 kpc of the cluster core and, again, an extraordinarily high ellipticity of e = 0.8. Although further, in-depth studies across the electromagnetic spectrum (especially in the X-ray regime) are needed to conclusively determine the dynamical state of the system, the properties established so far suggest that eMACS J0252 must have already been highly evolved well before z ∼ 1, making it a prime target to constrain the physical mechanisms and history of the co-evolution or dark-matter haloes and baryons in the era of cluster formation.

Rotation curves and scaling relations of extremely massive spiral galaxies

ABSTRACT We study the kinematics and scaling relations of a sample of 43 giant spiral galaxies that have stellar masses exceeding $10^{11} \, {\rm M}_\odot$ and optical discs up to 80 kpc in radius. We use a hybrid 3D–1D approach to fit 3D kinematic models to long-slit observations of the H α-$\rm{[N\, \small {II}]}$ emission lines and we obtain robust rotation curves of these massive systems. We find that all galaxies in our sample seem to reach a flat part of the rotation curve within the outermost optical radius. We use the derived kinematics to study the high-mass end of the two most important scaling relations for spiral galaxies: the stellar/baryonic mass Tully–Fisher relation and the Fall (mass-angular momentum) relation. All galaxies in our sample, with the possible exception of the two fastest rotators, lie comfortably on both these scaling relations determined at lower masses, without any evident break or bend at the high-mass regime. When we combine our high-mass sample with low-mass data from the Spitzer Photometry & Accurate Rotation Curves catalogue, we find a slope of α = 4.25 ± 0.19 for the stellar Tully–Fisher relation and a slope of γ = 0.64 ± 0.11 for the Fall relation. Our results indicate that most, if not all, of these rare, giant spiral galaxies are scaled up versions of less massive discs and that spiral galaxies are a self-similar population of objects up to the very high-mass end.

The dwarf galaxy population in nearby clusters from the KIWICS survey

ABSTRACT We analyse a sample of 12 galaxy clusters, from the Kapteyn IAC WEAVE INT Cluster Survey (KIWICS) looking for dwarf galaxy candidates. By using photometric data in the r and g bands from the Wide Field Camera (WFC) at the 2.5-m Isaac Newton Telescope (INT), we select a sample of bright dwarf galaxies (M$_r\, \le$ −15.5 mag) in each cluster and analyse their spatial distribution, stellar colour, and as well as their Sérsic index and effective radius. We quantify the dwarf fraction inside the R200 radius of each cluster, which ranges from ∼0.7 to ∼0.9. Additionally, when comparing the fraction in the inner region with the outermost region of the clusters, we find that the fraction of dwarfs tends to increase going to the outer regions. We also study the clustercentric distance distribution of dwarf and giant galaxies (M$_r\, \lt $ −19.0 mag), and in half of the clusters of our sample, the dwarfs are distributed in a statistically different way as the giants, with the giant galaxies being closer to the cluster centre. We analyse the stellar colour of the dwarf candidates and quantify the fraction of blue dwarfs inside the R200 radius, which is found to be less than ∼0.4, but increases with distance from the cluster centre. Regarding the structural parameters, the Sérsic index for the dwarfs we visually classify as early-type dwarfs tends to be higher in the inner region of the cluster. These results indicate the role that the cluster environment plays in shaping the observational properties of low-mass haloes.

The central region of the enigmatic Malin 1

Malin 1, being a class of giant low surface galaxies, continues to surprise us even today. The HST/F814W observation has shown that the central region of Malin 1 is more like a normal SB0/a galaxy, while the rest of the disk has the characteristic of a low surface brightness system. The AstroSat/UVIT observations suggest scattered recent star formation activity all over the disk, especially along the spiral arms. The central \(9''\) (\(\sim 14\,\hbox {kpc}\)) region, similar to the size of the Milky Way’s stellar disk, has a number of far-UV clumps—indicating recent star-formation activity. The high resolution UVIT/F154W image reveals far-UV emission within the bar region (\(\sim 4\,\hbox {kpc}\))—suggesting the presence of hot, young stars in the bar. These young stars from the bar region are perhaps responsible for producing the strong emission lines such as H\(\alpha \), [Oii] seen in the SDSS spectra. Malin 1B, a dwarf early-type galaxy, is interacting with the central region and probably responsible for inducing the recent star-formation activity in this galaxy.

Globular Cluster Systems of Massive Compact Elliptical Galaxies in the Local Universe: Evidence for Relic Red Nuggets?

Abstract Nearby massive compact elliptical galaxies (MCEGs) are strong candidates for relic galaxies (i.e., local analogs of red nuggets at high redshifts). It is expected that the globular cluster (GC) systems of relic galaxies are dominated by red (metal-rich) GCs. NGC 1277 is known as a unique example of such a galaxy in the previous study. In this study, we search for GCs in 12 nearby MCEGs at distances of ≲100 Mpc from the Hubble Space Telescope/Wide Field Camera 3 F814W(I 814)/F160W(H 160) archival images. We find that most of these MCEGs host a rich population of GCs with a color range of . The fractions of their red GCs range from f RGC = 0.2 to 0.7 with a mean of f RGC = 0.48 ± 0.14. We divide the MCEG sample into two groups: one in clusters and the other in groups/fields. The mean red GC fraction of the cluster MCEGs is 0.60 ± 0.06, which is 0.2 larger than the value of the group/field MCEGs, 0.40 ± 0.10. The value for the cluster MCEGs is ∼0.3 larger than the mean value of giant early-type galaxies with similar stellar mass in the Virgo Cluster (f RGC = 0.33 ± 0.13). Our results show that most of the MCEGs in our sample are indeed relic galaxies. This further implies that a majority of the red GCs in MCEGs are formed early in massive galaxies and that most MCEGs in the local universe have rarely undergone mergers after they became red nuggets about 10 Gyr ago.

The role of the elaphrocentre in void galaxy formation

ABSTRACT Voids may affect galaxy formation via weakening mass infall or increasing disk sizes, which could potentially play a role in the formation of giant low surface brightness galaxies (LSBGs). If a dark matter halo forms at the potential hill corresponding to a void of the cosmic web, which we denote the ‘elaphrocentre’ in contrast to a barycentre, then the elaphrocentre should weaken the infall rate to the halo when compared to infall rates towards barycentres. We investigate this hypothesis numerically. We present a complete software pipeline to simulate galaxy formation, starting from a power spectrum of initial perturbations and an N-body simulation through to merger-history-tree based mass infall histories. The pipeline is built from well-established, free-licensed cosmological software packages, and aims at highly portable long-term reproducibility. We find that the elaphrocentric accelerations tending to oppose mass infall are modest. We do not find evidence of location in a void or elaphrocentric position weakening mass infall towards a galaxy. However, we find indirect evidence of voids influencing galaxy formation: while void galaxies are of lower mass compared to galaxies in high-density environments, their spin parameters are typically higher. For a fixed mass, the implied disc scale length would be greater. Tangential accelerations in voids are found to be high and might significantly contribute to the higher spin parameters. We find significantly later formation epochs for void galaxies; this should give lower matter densities and may imply lower surface densities of disc galaxies. Thus, void galaxies have higher spin parameters and later formation epochs; both are factors that may increase the probability of forming LSBGs in voids.

Giant Galaxies from the Universe's Childhood Challenge Cosmic Origin Stories

Giant Galaxies from the Universe's Childhood Challenge Cosmic Origin Stories

A mid-life crisis of the Universe? A giant red disk galaxy at z = 0.76

A mid-life crisis of the Universe? A giant red disk galaxy at z = 0.76

Black Hole Factories May Hide at Cores of Giant Galaxies

Black Hole Factories May Hide at Cores of Giant Galaxies

A giant central red disk galaxy at redshift z = 0.76: Challenge to theories of galaxy formation

We report a giant red central disk galaxy in the XMM-LSS north region. The region is covered with a rich variety of multiband photometric and spectroscopic observations. Using the photometric data of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) and spectroscopic observation of the Baryon Oscillation Spectroscopic Survey (BOSS), we find that the galaxy has a stellar mass of $\sim 10^{11.6}$ times of the solar mass $M_\odot$. The galaxy has a red color and has an old stellar population, and thus its star formation has stopped. With the photometric image data of Hyper Suprime-Cam (HSC) Subaru Strategic Program, we demonstrate that its luminosity profile is perfectly described by a S\'ersic form with $n=1.22$ indicating disk morphology. We also analyze its environment based on the VIMOS Public Extragalactic Redshift Survey (VIPERS) photometric catalog, and find that its close neighbors are all less massive, indicating that our observed galaxy is sitting at the center of its host halo. Existence of the giant red central disk galaxy seriously challenges the current standard paradigm of galaxy formation, as there is no known physical mechanism to explain the quenching of its star formation. This conclusion is supported by state-of-the-art hydrodynamical simulations of galaxy formation.

Observational insights on the origin of giant low surface brightness galaxies

ABSTRACT Giant low surface brightness galaxies (gLSBGs) with dynamically cold stellar discs reaching the radius of 130 kpc challenge currently considered galaxy formation mechanisms. We analyse new deep long-slit optical spectroscopic observations, archival optical images, and published Hi and optical spectroscopic data for a sample of seven gLSBGs, for which we performed mass modelling and estimated the parameters of dark matter haloes assuming the Burkert dark matter density profile. Our sample is not homogeneous by morphology, parameters of stellar populations, and total mass, however, six of seven galaxies sit on the high-mass extension of the baryonic Tully–Fisher relation. In UGC 1382, we detected a global counterrotation of the stellar high surface brightness (HSB) disc with respect to the extended LSB disc. In UGC 1922 with signatures of a possible merger, the gas counterrotation is seen in the inner disc. Six galaxies host active galactic nuclei, three of which have the estimated black hole masses substantially below those expected for their (pseudo-)bulge properties suggesting poor merger histories. Overall, the morphology, internal dynamics, and low star formation efficiency in the outer discs indicate that the three formation scenarios shape gLSBGs: (i) a two-stage formation when an HSB galaxy is formed first and then grows an LSB disc by accreting gas from an external supply; (ii) an unusual shallow and extended dark matter halo; (iii) a major merger with fine-tuned orbital parameters and morphologies of the merging galaxies.

Evolution of Stellar Feedback in H ii Regions

Abstract Stellar feedback is needed to produce realistic giant molecular clouds and galaxies in simulations, but due to limited numerical resolution, feedback must be implemented using sub-grid models. Observational work is an important means to test and anchor these models, but limited studies have assessed the relative dynamical role of multiple feedback modes, particularly at the earliest stages of expansion when H ii regions are still deeply embedded. In this paper, we use multiwavelength (radio, infrared, and X-ray) data to measure the pressures associated with direct radiation (P dir), dust-processed radiation (P IR), photoionization heating (P H II ), and shock-heating from stellar winds (P X) in a sample of 106 young, resolved H ii regions with radii ≲0.5 pc to determine how stellar feedback drives their expansion. We find that the P IR dominates in 84% of the regions and that the median P dir and P H II are smaller than the median P IR by factors of ≈6 and ≈9, respectively. Based on the radial dependences of the pressure terms, we show that H ii regions transition from P IR-dominated to P H II -dominated at radii of ∼3 pc. We find a median trapping factor of f trap ∼ 8 without any radial dependence for the sample, suggesting this value can be adopted in sub-grid feedback models. Moreover, we show that the total pressure is greater than the gravitational pressure in the majority of our sample, indicating that the feedback is sufficient to expel gas from the regions.

The WISSH quasars project

Context. Sources at the brightest end of the quasi-stellar object (QSO) luminosity function, during the peak epoch in the history of star formation and black hole accretion (z ∼ 2−4, often referred to as “Cosmic noon”) are privileged sites to study the cycle of feeding & feedback processes in massive galaxies. Aims. We aim to perform the first systematic study of cold gas properties in the most luminous QSOs, by characterising their host-galaxies and environment. These targets exhibit indeed widespread evidence of outflows at nuclear and galactic scales. Methods. We analyse ALMA, NOEMA and JVLA observations of the far-infrared continuum, CO and [CII] emission lines in eight QSOs (bolometric luminosity LBol ≳ 3 × 1047 erg s−1) from the WISE-SDSS selected hyper-luminous (WISSH) QSOs sample at z ∼ 2.4−4.7. Results. We report a 100% emission line detection rate and a 80% detection rate in continuum emission, and we find CO emission to be consistent with the steepest CO ladders observed so far. Sub-millimetre data reveal presence of (one or more) bright companion galaxies around ∼80% of WISSH QSOs, at projected distances of ∼6−130 kpc. We observe a variety of sizes for the molecular gas reservoirs (∼1.7−10 kpc), mostly associated with rotating disks with disturbed kinematics. WISSH QSOs typically show lower CO luminosity and higher star formation efficiency than infrared matched, z ∼ 0−3 main-sequence galaxies, implying that, given the observed SFR ∼170−1100 M⊙ yr−1, molecular gas is converted into stars in ≲50 Myr. Most targets show extreme dynamical to black-hole mass ratios Mdyn/MBH ∼ 3−10, two orders of magnitude smaller than local relations. The molecular gas fraction in the host-galaxies of WISSH is lower by a factor of ∼10−100 than in star forming galaxies with similar M*. Conclusions. Our analysis reveals that hyper-luminous QSOs at Cosmic noon undergo an intense growth phase of both the central super-massive black hole and of the host-galaxy. These systems pinpoint the high-density sites where giant galaxies assemble, where we show that mergers play a major role in the build-up of the final host-galaxy mass. We suggest that the observed low molecular gas fraction and short depletion timescale are due to AGN feedback, whose presence is indicated by fast AGN-driven ionised outflows in all our targets.

Search and analysis of giant radio galaxies with associated nuclei (SAGAN)

Radio galaxies with jets of relativistic particles are usually hosted by massive elliptical galaxies with active nuclei powered by accretion of interstellar matter onto a supermassive black hole. In some rare cases (< 5%), their jets drive the overall structure to sizes larger than 700 kpc, and they are called giant radio galaxies (GRGs). A very small fraction of the population of such radio galaxies contains molecular and atomic gas in the form of rings or discs that can fuel star formation. The origin of this gas is not well known; it has sometimes been associated with a minor merger with a gas-rich disc galaxy (e.g. Centaurus A) or cooling of material from a hot X-ray atmosphere (e.g. cooling flows). The giant radio jets might be the extreme evolution of these objects, and they can teach us about the radio galaxy evolution. We selected 12 targets from a catalogue of 820 GRGs that are likely to be in a gas-accretion and star formation phase. The targets were selected from the mid-infrared to contain heated dust. We report here the results of IRAM-30m observations, the molecular gas content, and the star formation efficiency, and we discuss the origin of the gas and disc morphology. Three out of our 12 targets are detected, and for the others, we report significant upper limits. We combine our three detections and upper limits with four additional detected GRGs from the literature to discuss the results. Most of the GRG targets belong to the main sequence, and a large fraction are in the passive domain. Their star formation efficiency is comparable to normal galaxies, except for two galaxies that are deficient in molecular gas with a short (∼200 Myr) depletion time, and a quiescent gas-rich giant spiral galaxy. In general, the depletion time is much longer than the lifetime of the giant radio jet.