Keywords

We present ALMA CO (1−0) observations toward the dust lane of the nearest elliptical and radio galaxy, NGC 5128 (Centaurus A), with high angular resolution (∼1'', or 18 pc), including information from large to small spatial scales and total flux. We find a total molecular gas mass of 1.6 × 10⁹ M_⊙ and reveal the presence of filamentary components more extended than previously seen, up to a radius of 4 kpc. We find that the global star formation rate is ∼1 M_⊙ yr⁻¹, which yields a star formation efficiency (SFE) of 0.6 Gyr⁻¹ (depletion time τ = 1.5 Gyr), similar to those in disk galaxies. We show the most detailed view to date (40 pc resolution) of the relation between molecular gas and star formation within the stellar component of an elliptical galaxy, from a scale of several kiloparsecs to the circumnuclear region close to the powerful radio jet. Although on average the SFEs are similar to those of spiral galaxies, the circumnuclear disk (CND) presents SFEs of 0.3 Gyr⁻¹, lower by a factor of 4 than the outer disk. The low SFE in the CND is in contrast to the high SFEs found in the literature for the circumnuclear regions of some nearby disk galaxies with nuclear activity, probably as a result of larger shear motions and longer active galactic nucleus feedback. The higher SFEs in the outer disk suggest that only central molecular gas or filaments with sufficient density and strong shear motions will remain in ∼1 Gyr, which will later result in the compact molecular distributions and low SFEs usually seen in other giant ellipticals with cold gas.

Winds from asymptotic giant branch (AGB) stars not only provide mass and energy return, but also produce dust grains in massive elliptical galaxies. Due to the fast stellar velocity, the wind is thought to form a comet-like tail, similar to Mira in the Local Bubble. Many massive elliptical galaxies and cluster centrals host extended dusty cold filaments. We carry out both analytical and numerical studies of the interaction between an AGB wind and the surrounding hot gas. We find that the cooling time of the tail is inversely proportional to the ambient pressure. In the absence of cooling, or in low-pressure environments (e.g., the outskirts of elliptical galaxies), AGB winds are quickly mixed into the hot gas, and all the AGB winds have a similar appearance and head-to-tail ratio. In high-pressure environments, such as the Local Bubble and the central regions of massive elliptical galaxies, some of the gas in the mixing layer between the stellar wind and the surrounding hot gas can cool efficiently and cause the tail to become longer. Our simulated tail of Mira itself has a similar length and velocity to that observed, and appears similar to the simulated AGB tail in the central regions of massive galaxies. While confirmation awaits future studies, we speculate that instead of thermal instability, the induced condensation at the mixing layer of AGB winds may be the origin of cold filaments in massive galaxies and galaxy clusters. This naturally explains the existence of dust and polycyclic aromatic hydrocarbon in the filaments.

We present observations using the Atacama Large Millimeter/submillimeter Array of the CO(2−1), HCN(3−2), and HCO⁺(3−2) lines in the nearby radio galaxy/brightest cluster galaxy (BCG) NGC 1275 with a spatial resolution of ∼20 pc. In previous observations, the CO(2−1) emission was detected as radial filaments lying in the east–west direction on a kiloparsec scale. We resolved the inner filament and found that it cannot be represented by a simple infalling stream on a sub-kiloparsec scale. The observed complex nature of the filament resembles the cold gas structure predicted by numerical simulations of cold chaotic accretion. Within the central 100 pc, we detected a rotational disk of molecular gas whose mass is ∼10⁸ M_⊙. This is the first evidence of the presence of a massive cold gas disk on this spatial scale for BCGs. A crude estimate suggests that the accretion rate of the cold gas can be higher than that of hot gas. The disk rotation axis is approximately consistent with the radio-jet axis. This probably suggests that the cold gas disk is physically connected to the innermost accretion disk, which is responsible for jet launching. We also detected absorption features in the HCN(3−2) and HCO⁺(3−2) spectra against the radio continuum emission mostly radiated by a jet of size ∼1.2 pc. The absorption features are blueshifted from the systemic velocity by ∼300–600 km s⁻¹, suggesting the presence of outflowing gas from the active galactic nucleus (AGN). We discuss the relation of the AGN feeding with cold accretion, the origin of blueshifted absorption, and an estimate of the black hole mass using molecular gas dynamics.

Using the photometric data from the Next Generation Fornax Survey, we find a significant radial alignment signal among the Fornax dwarf galaxies. For the first time, we report that the radial alignment signal of nucleated dwarfs is stronger than that of non-nucleated ones at the 2.4σ confidence level, and the dwarfs located in the outer region (R > R_vir/3; R_vir is the Fornax virial radius) show a slightly stronger radial alignment signal than those in the inner region (R < R_vir/3) at the 1.5σ level. We also find that the significance of the radial alignment signal is independent of the luminosities or sizes of the dwarfs.

We present long-slit and panoramic spectroscopy of extended gaseous disks in 18 S0 galaxies, mostly in groups. The gas has often decoupled kinematics: at least five galaxies demonstrate strongly inclined large-scale ionized gas disks, seven galaxies reveal circumnuclear polar disks, and in NGC 2551 the ionized gas, although confined to the main plane, counterrotates the stars. The gas excitation analysis reveals ionization by young stars in 12 of 18 S0 galaxies; current star formation in these galaxies is confined to ring-like zones coinciding with their UV rings. Gas oxygen abundances in the rings are around 0.7 Z_⊙ and correlate neither with the ring radius nor with the metallicity of the stellar population. By applying tilted ring analysis to the velocity fields, we have traced the gas rotation plane lines of nodes along the radius. We find that current star formation proceeds usually where the gas lies strictly in the stellar disk planes and rotates circularly; the sense of the gas rotation does not matter (the counterrotating gas in NGC 2551 forms stars). In the galaxies without current star formation the extended gaseous disks either are in steady-state quasi-polar orientation or were acquired recently through the misaligned external filaments provoking shock-like excitation. Our data imply a crucial difference of the accretion regime in S0s with respect to spirals: the geometry of gas accretion in S0s is typically off-plane.

We examine the role of environment on the in situ star formation (SF) hosted by the progenitors of the most massive galaxies in the present-day universe, the brightest cluster galaxies (BCGs), from z ∼ 3 to present in the COSMOS field. Progenitors are selected from the COSMOS field using a stellar mass cut motivated by the evolving cumulative comoving number density of progenitors within the Illustris simulation, as well as the Millennium-II simulation and a constant comoving number density method for comparison. We characterize each progenitor using far-ultraviolet–far-infrared observations taken from the COSMOS field and fitting stellar, dust, and active galactic nucleus components to their spectral energy distributions. Additionally, we compare the SF rates of our progenitor sample to the local density maps of the COSMOS field to identify the effects of environment. We find that BCG progenitors evolve in three stages, starting with an in situ SF-dominated phase (z > 2.25). This is followed by a phase until z ∼ 1.25 where mass growth is driven by in situ SF and stellar mass deposited by mergers (both gas rich and poor) on the same order of magnitude independent of local environment. Finally, at low redshift dry mergers are the dominant stellar mass generation process. We also identify this final transition period as the time when progenitors quench, exhibiting quiescent NUVrJ colors.

We present results on the rest-frame H-band luminosity functions (LFs) of red-sequence galaxies in seven clusters at 1.0 < z < 1.3 from the Gemini Observations of Galaxies in Rich Early Environments Survey. Using deep GMOS $z^{\prime}$ and IRAC 3.6 μm imaging, we identify red-sequence galaxies and measure their LFs down to ${M}_{H}\sim {M}_{H}^{* }+(2.0-3.0)$. By stacking the entire sample, we derive a shallow faint-end slope of $\alpha \sim -{0.35}_{-0.15}^{+0.15}$ and ${M}_{H}^{* }\sim -{23.52}_{-0.17}^{+0.15}$, suggesting that there is a deficit of faint red-sequence galaxies in clusters at high redshift. By comparing the stacked red-sequence LF of our sample with a sample of clusters at z ∼ 0.6, we find an evolution of the faint end of the red sequence over the ∼2.6 Gyr between the two samples, with the mean faint-end red-sequence luminosity growing by more than a factor of 2. The faint-to-luminous ratio of our sample (${0.78}_{-0.15}^{+0.19}$) is consistent with the trend of decreasing ratio with increasing redshift proposed in previous studies. A comparison with the field shows that the faint-to-luminous ratios in clusters are consistent with those in the field at z ∼ 1.15 and exhibit a stronger redshift dependence. Our results support the picture that the buildup of faint red-sequence galaxies occurs gradually over time and suggest that faint cluster galaxies, similar to bright cluster galaxies, already experience the quenching effect induced by the environment at z ∼ 1.15.

We present a catalog of the 1525 most optically luminous galaxies from the Sloan Digital Sky Survey with r-band luminosity L_r > 8L* and redshift z < 0.3, including 84 super spirals, 15 super lenticulars, 14 super post-merger galaxies, and 1400 giant ellipticals. With mass in stars of 10^11.3–10¹²M_⊙, super spirals and lenticulars are the most massive disk galaxies currently known. The specific star formation rates of super spirals place them on or below the star-forming main sequence. They must have formed stars at a high rate throughout their history in order to grow their massive, gigantic stellar disks and maintain their blue u − r integrated colors. Their disks are red on the inside and blue on the outside, consistent with inside-out growth. They tend to have small bulge-to-total (B/T) r-band luminosity ratios, characteristic of disk building via minor mergers and cold accretion. A large percentage of super disk galaxies (41%) have double nuclei, double disks, or other signatures of ongoing mergers. Most (72%) are found in moderate- to low-density environments, while the rest are found at the outskirts of clusters. It is likely that super spirals survive in these environments because they continue to accrete cold gas and experience only minor mergers at late times, by virtue of their enormous masses and angular momenta. We suggest that super post-mergers are the product of super spiral major mergers and may be the precursors of some giant elliptical galaxies found in low-density environments. We present two new gravitational lens candidates in an appendix.

We use observations from the GEMINI-N/GMOS integral field spectrograph (IFS) to obtain spatially resolved stellar kinematics of the central ∼1 kpc of 20 early-type galaxies (ETGs) with stellar masses greater than 10^11.7 M_⊙ in the MASSIVE survey. Together with observations from the wide-field Mitchell IFS at McDonald Observatory in our earlier work, we obtain unprecedentedly detailed kinematic maps of local massive ETGs, covering a scale of ∼0.1–30 kpc. The high (∼120) signal-to-noise ratio of the GMOS spectra enables us to obtain two-dimensional maps of the line-of-sight velocity and velocity dispersion σ, as well as the skewness h₃ and kurtosis h₄ of the stellar velocity distributions. All but one galaxy in the sample have σ(R) profiles that increase toward the center, whereas the slope of σ(R) at one effective radius (R_e) can be of either sign. The h₄ is generally positive, with 14 of the 20 galaxies having positive h₄ within the GMOS aperture and 18 having positive h₄ within 1R_e. The positive h₄ and rising σ(R) toward small radii are indicative of a central black hole and velocity anisotropy. We demonstrate the constraining power of the data on the mass distributions in ETGs by applying Jeans anisotropic modeling (JAM) to NGC 1453, the most regular fast rotator in the sample. Despite the limitations of JAM, we obtain a clear χ² minimum in black hole mass, stellar mass-to-light ratio, velocity anisotropy parameters, and circular velocity of the dark matter halo.

Rings in S0s are enigmatic features that can, however, betray the evolutionary paths of particular galaxies. We have undertaken long-slit spectroscopy of five lenticular galaxies with UV-bright outer rings. The observations have been made with the Southern African Large Telescope to reveal the kinematics, chemistry, and ages of the stellar populations and the gas characteristics in the rings and surrounding disks. Four of the five rings are also bright in the Hα emission line, and the spectra of the gaseous rings extracted around the maxima of the Hα equivalent width reveal excitation by young stars betraying current star formation in the rings. The integrated level of this star formation is 0.1–0.2 ${M}_{\odot }$ yr⁻¹, with the outstanding value of 1 ${M}_{\odot }$ yr⁻¹ in NGC 7808. The difference of chemical composition between the ionized gas of the rings, which demonstrate nearly solar metallicity, and the underlying stellar disks, which are metal-poor, implies recent accretion of the gas and star formation ignition; the star formation history estimated by using different star formation indicators implies that the star formation rate decreases with an e-folding time of less than 1 Gyr. In NGC 809, where the UV ring is well visible but the Hα emission line excited by massive stars is absent, the star formation has already ceased.