Hubble Space Telescope Images Research Articles

Surface Brightness Evolution of Galaxies in the CANDELS GOODS Fields up to z ∼ 6: High-z Galaxies Are Unique or Remain Undetected

Abstract We investigate the rest-frame ultraviolet (UV, λ ∼ 2000 Å) surface brightness (SB) evolution of galaxies up to z ∼ 6 using a variety of deep Hubble Space Telescope (HST) imaging. UV SB is a measure of the density of emission from mostly young stars and correlates with an unknown combination of star formation rate, initial mass function, cold gas mass density, dust attenuation, and the size evolution of galaxies. In addition to physical effects, the SB is, unlike magnitude, a more direct way in which a galaxy’s detectability is determined. We find a very strong evolution in the intrinsic SB distribution that declines as , decreasing by 4–5 mag arcsec−2 between z = 6 and z = 1. This change is much larger than expected in terms of the evolution in UV luminosity, sizes, or dust extinction, and we demonstrate that this evolution is “unnatural” and due to selection biases. We also find no strong correlation between mass and UV SB. Thus, deep HST imaging is unable to discover all of the most massive galaxies in the distant universe. Through simulations we show that only ∼15% of galaxies that we can detect at z = 2 would be detected at high z. We furthermore explore possible origins of high-SB galaxies at high z by investigating the relationship between intrinsic SB and star formation rates. We conclude that ultra–high-SB galaxies are produced by very gas-rich dense galaxies that are in a unique phase of evolution, possibly produced by mergers. Analogs of such galaxies do not exist in the relatively nearby universe.

Long tidal tails in merging galaxies and their implications

ABSTRACT We investigate the properties of long tidal tails using the largest to date sample of 461 merging galaxies with $\log (M_\ast /\rm M_\odot)\ge 9.5$ within 0.2 ≤ z ≤ 1 from the COSMOS survey in combination with Hubble Space Telescope imaging data. Long tidal tails can be briefly divided into three shape types: straight (41 per cent), curved (47 per cent), and plume (12 per cent). Their host galaxies are mostly at late stages of merging, although 31 per cent are galaxy pairs with projected separations d > 20 kpc. The high formation rate of straight tidal tails needs to be understood as the projection of curved tidal tails accounts for only a small fraction of the straight tails. We identify 165 tidal dwarf galaxies (TDGs), yielding a TDG production rate of 0.36 per merger. Combined with a galaxy merger fraction and a TDG survival rate from the literature, we estimate that ∼5 per cent of local dwarf galaxies (DGs) are of tidal origin, suggesting the tidal formation is not an important formation channel for the DGs. About half of TDGs are located at the tip of their host tails. These TDGs have stellar masses in the range of $7.5\le \log (M_\ast /\rm M_\odot)\le 9.5$ and appear compact with half-light radii following the M*–Re relation of low-mass elliptical galaxies. However, their surface brightness profiles are generally flatter than those of local disc galaxies. Only 10 out of 165 TDGs have effective radii larger than 1.5 kpc and would qualify as unusually bright ultradiffuse galaxies.

Morphometry as a probe of the evolution of jellyfish galaxies: evidence of broadening in the surface brightness profiles of ram-pressure stripping candidates in the multicluster system A901/A902

ABSTRACT We explore the morphometric properties of a group of 73 ram-pressure stripping candidates in the A901/A902 multicluster system, at z∼ 0.165, to characterize the morphologies and structural evolution of jellyfish galaxies. By employing a quantitative measurement of morphometric indicators with the algorithm morfometryka on Hubble Space Telescope (F606W) images of the galaxies, we present a novel morphology-based method for determining trail vectors. We study the surface brightness profiles and curvature of the candidates and compare the results obtained with two analysis packages, morfometryka and iraf/ellipse on retrieving information of the irregular structures present in the galaxies. Our morphometric analysis shows that the ram-pressure stripping candidates have peculiar concave regions in their surface brightness profiles. Therefore, these profiles are less concentrated (lower Sérsic indices) than other star-forming galaxies that do not show morphological features of ram-pressure stripping. In combination with morphometric trail vectors, this feature could both help identify galaxies undergoing ram-pressure stripping and reveal spatial variations in the star formation rate.

The Velocity Dispersion Function for Quiescent Galaxies in Nine Strong-lensing Clusters

Abstract We measure the central stellar velocity dispersion function for quiescent galaxies in a set of nine northern clusters in the redshift range 0.18 < z < 0.29 and with strong lensing arcs in Hubble Space Telescope images. The velocity dispersion function links galaxies directly to their dark matter halos. From dense SDSS and MMT/Hectospec spectroscopy, we identify 222–463 spectroscopic members in each cluster. We derive physical properties of cluster members including redshift, , and central stellar velocity dispersion and we include a table of these measurements for 3419 cluster members. We construct the velocity dispersion functions for quiescent galaxies with > 1.5 and within R 200. The cluster velocity dispersion functions all show excesses at σ ≳ 250 km s−1 compared to the field velocity dispersion function. The velocity dispersion function slope at large velocity dispersion (σ > 160 km s−1) is steeper for more massive clusters, consistent with the trend observed for cluster luminosity functions. The spatial distribution of galaxies with large velocity dispersion at radii larger than R 200 further underscores the probable major role of dry mergers in the growth of massive cluster galaxies during cluster assembly.

The Elusive Distance Gradient in the Ultrafaint Dwarf Galaxy Hercules: A Combined Hubble Space Telescope and Gaia View

Abstract The ultrafaint dwarf galaxy Hercules has an extremely elongated morphology with both photometric overdensities and kinematic members at large radii, suggesting that it may be tidally disrupting due to a previous close encounter with the Milky Way. To explain its observational peculiarities, we present a deep Hubble Space Telescope (HST) imaging study of Hercules and its surrounding regions and investigate its tidal history through a careful search for a distance gradient along its stretched body. Our off-center HST data clearly resolve a main sequence, showing that the stellar extension seen along the major axis of Hercules is genuine, not a clump of background galaxies. Utilizing Gaia DR2 data, we clean the region around the Hercules of field contamination, and find four new plausible member stars, all of which are located on the outskirts of the dwarf galaxy. We update the distance to Hercules, and find 130.6 ± 6.1 kpc ( ) for the main body, which is consistent with earlier estimates in the literature. While we find no conclusive evidence for a distance gradient, our work demonstrates that constraining a distance gradient in such a faint system is not trivial, and the possible thickness of the dwarf along the line of sight and field contamination make it harder to make decisive conclusions even with these high-precision data. Future studies coupled with tailored theoretical models are needed to understand the true nature of Hercules and of tidal distortion observables in ultrafaint galaxies in general.

Mapping the Escape Fraction of Ionizing Photons Using Resolved Stars: A Much Higher Escape Fraction for NGC 4214

Abstract We demonstrate a new method for measuring the escape fraction of ionizing photons using Hubble Space Telescope imaging of resolved stars in NGC 4214, a local analog of high-redshift starburst galaxies that are thought to be responsible for cosmic reionization. Specifically, we forward model the UV through near-IR spectral energy distributions of ∼83,000 resolved stars to infer their individual ionizing flux outputs. We constrain the local escape fraction by comparing the number of ionizing photons produced by stars to the number that are either absorbed by dust or consumed by ionizing the surrounding neutral hydrogen in individual star-forming regions. We find substantial spatial variation in the escape fraction (0%–40%). Integrating over the entire galaxy yields a global escape fraction of 25 − 15 + 16 %. This value is much higher than previous escape fractions of zero reported for this galaxy. We discuss the sources of this apparent tension and demonstrate that the viewing angle and 3D interstellar medium geometric effects are the cause. If we assume that NGC 4214 has no internal dust, like many high-redshift galaxies, we find an escape fraction of 59% (an upper limit for NGC 4214). This is the first nonzero escape fraction measurement for UV-faint (M FUV = −15.9) galaxies at any redshift and supports the idea that starburst UV-faint dwarf galaxies can provide a sufficient number of ionizing photons to the intergalactic medium.

Emission-line Data Cubes of the HH 32 Stellar Jet

Abstract We analyze data cubes of over 60 emission lines in the HH 32 stellar jet acquired with the Keck Cosmic Web Imager (KCWI). The data cover the less explored blue portion of the spectrum between 3586 and 6351 Å and have both high spectral (R ∼ 10,000) and spatial (≲1″) resolution. The study includes all three major ionization states of oxygen, three Balmer lines, multiple lines of Fe ii and Fe iii, and the first data cubes ever acquired for important unblended diagnostic lines such as He ii λ4686, Ca i λ3933, and Mg i] λ4571. The data cubes generally sort according to excitation and have a relatively continuous progression from the highest-excitation ions (He ii, O iii) through the intermediate-excitation ions (O i and H i) to the lowest-excitation ions (Ca ii and Mg i). Merging the KCWI cubes with Hubble Space Telescope images leads to several new insights about the flow, including evidence for bow shocks, partial bow shocks, spur shocks, Mach disks, jet deflection shocks, a wiggling jet, and potential shock precursors. The most surprising result is that one of the velocity components of Fe ii in the Mach disk suddenly increases in flux relative to other lines by a factor of two, implying that the Mach disk vaporizes dust in the jet. Hence, jets must accelerate or entrain dust to speeds of over 300 km s−1 without destroying the grains.

The Sizes of z ∼ 9−10 Galaxies Identified in the Brightest of Reionizing Galaxies (BoRG) Survey

Abstract Redshift z = 9–10 object selection is the effective limit of Hubble Space Telescope (HST) imaging capability, even when confirmed with Spitzer. If only a few photometry data points are available, it becomes attractive to add criteria based on their morphology in these J- and H-band images. One could do so through visual inspection, a size criterion, or alternate morphometrics. We explore a vetted sample of Brightest of Reionizing Galaxies (BoRG) z ∼ 9 and z ∼ 10 candidate galaxies and the object rejected by Morishita+ to explore the utility of a size criterion in z = 9–10 candidate selection. A stringent, point-spread function (PSF)-corrected effective radius criterion ( ) would result in the rejection of 65%–70% of the interlopers visually rejected by Morishita et al. It may also remove up to ∼20% of bona fide brightest ( ) z = 9 or 10 candidates from a BoRG selected sample based on the Mason et al. luminosity functions, assuming the Holwerda et al. size–luminosity relation. We argue that including a size constraint in lieu of a visual inspection may serve in wide-field searches for these objects in, e.g., Euclid or HST archival imaging with the understanding that some brightest ( ) candidates may be missed. The sizes of the candidates found by Morishita et al. follow the expected size distribution of z ∼ 9 for bright galaxies, consistent with the log normal in Shibuya et al. and single objects. Two candidates show high star formation surface density ( ) and all merit further investigation and follow-up observations.

HST Proper Motions of NGC 147 and NGC 185: Orbital Histories and Tests of a Dynamically Coherent Andromeda Satellite Plane

Abstract We present the first proper-motion (PM) measurements for the dwarf elliptical galaxies NGC 147 and NGC 185, two satellite galaxies of M31, using multiepoch Hubble Space Telescope (HST) imaging data with time baselines of ∼8 yr. For each galaxy, we take an error-weighted average of measurements from HST Advanced Camera for Surveys/WFC and Wide Field Camera 3/UVIS to determine the PMs. Our final results for the PMs are (μ W, μ N)N147 = (−0.0232, 0.0378) ± (0.0143, 0.0146) mas yr−1 for NGC 147 and (μ W, μ N)N185 = (−0.0242, 0.0058) ± (0.0141, 0.0147) mas yr−1 for NGC 185. The 2D direction of motion for NGC 147 about M31 is found to be aligned with its tidal tails. The 3D positions and velocities of both galaxies are transformed into a common M31-centric coordinate system to study the detailed orbital histories of the combined M31+NGC 147+NGC 185 system via numerical orbit integration. We find that NGC 147 (NGC 185) had its closest passage to M31 0.3–0.5 Gyr (≳1.6 Gyr) within the past 6 Gyr at distances of ∼70 kpc (70–260 kpc). The pericentric times of NGC 147/NGC 185 correlate qualitatively well with the presence/absence of tidal tails seen around the galaxies. Our PMs show that the orbital poles of NGC 147, as well as NGC 185, albeit to a lesser degree, agree within the uncertainties with the normal of the Great Plane of Andromeda (GPoA). These are the first measurements of the 3D angular momentum vector of any satellite identified as original GPoA members. Our results strengthen the hypothesis that the GPoA may be a dynamically coherent entity. We revisit previous claims that NGC 147 and NGC 185 are binary galaxies and conclude that it is very unlikely that the two galaxies were ever gravitationally bound to each other.

In the Trenches of the Solar–Stellar Connection. I. Ultraviolet and X-Ray Flux–Flux Correlations across the Activity Cycles of the Sun and Alpha Centauri AB

Abstract This study focuses on high-energy proxies of stellar magnetic activity over long-term starspot cycles of three low-activity Sun-like stars: α Centauri A (HD 128620: G2 V), α Cen B (HD 128621: K1 V), and the Sun itself. Data sets include: daily solar ultraviolet irradiance spectra and X-ray fluxes from the Solar Radiation and Climate Experiment, during recent sunspot Cycles 23 and 24; Interface Region Imaging Spectrograph long-slit stigmatic imaging of solar Mg ii h (2803 Å) and k (2796 Å) in quiet and active regions; and Hubble Space Telescope Imaging Spectrograph ultraviolet, and Chandra X-ray, campaigns on α Cen AB. Established stellar “flux–flux” relations, for example X-rays (T ∼ 1 MK) versus Mg ii (T ∼ 8000 K), showed increasing power-law slopes with increasing formation temperature, but these give way on the Sun to bent power laws, and surprising inversions in the activity hierarchy: Si iii is more “active” (steeper power laws) than N v, despite the latter’s four times higher formation temperature. The Sun’s flux–flux behavior, nevertheless, remarkably parallels its low-activity solar twin α Cen A. In contrast, the cooler, somewhat more active, K dwarf companion displays correlations more in line with the previous stellar paradigm. The new flux–flux relations offer a way to vet numerical spectral simulations and proxy-based irradiance models, and extrapolate solar global activity indices into regimes below or above the grasp of contemporary records, or to exoplanet hosts at the low end of the Sun-like activity ladder.

Discovery of molecular gas fueling galaxy growth in a protocluster at z = 1.7

Based on ALMA Band 3 observations of the CO(2→1) line transition, we report the discovery of three new gas-rich (MH2 ∼ 1.5 − 4.8 × 1010 M⊙) galaxies in an overdense region at z = 1.7 that already contains eight spectroscopically confirmed members. This leads to a total of 11 confirmed overdensity members within a projected distance of ∼1.15 Mpc and in a redshift range of Δz = 0.012. Under simple assumptions, we estimate that the system has a total mass of ≥3 − 6 × 1013 M⊙, and show that it will likely evolve into a ≳1014 M⊙ cluster at z = 0. The overdensity includes a powerful Compton-thick Fanaroff-Riley type II (FRII) radio galaxy, around which we discovered a large molecular gas reservoir (MH2 ∼ 2 × 1011 M⊙). We fit the FRII resolved CO emission with a 2D Gaussian model with a major (minor) axis of ∼27 (∼17) kpc, which is a factor of ∼3 larger than the optical rest-frame emission. Under the assumption of a simple edge-on disk morphology, we find that the galaxy interstellar medium produces a column density toward the nucleus of ∼5.5 × 1023 cm−2. A dense interstellar medium like this may then contribute significantly to the total nuclear obscuration measured in the X-rays (NH, X ∼ 1.5 × 1024 cm−2) in addition to a small, paresec-scale absorber around the central engine. The velocity map of this source unveils a rotational motion of the gas that is perpendicular to the radio jets. All ALMA sources have a dust-reddened counterpart in deep Hubble Space Telescope images (bands i, z, H), while we do not detect any molecular gas reservoir around the known UV-bright, star-forming members discovered by MUSE. This highlights the capability of ALMA of tracing gas-rich members of the overdensity. For the MUSE sources, we derive 3σ upper limits to the molecular gas mass of MH2 ≤ 2.8 − 4.8 × 1010 M⊙. We derive star formation rates in the range ∼5 − 100 M⊙ yr−1 for the three new ALMA sources. The FRII is located at the center of the projected spatial distribution of the structure members, and its velocity offset from the peak of the redshift distribution is well within the velocity dispersion of the structure. All this, coupled with the large amount of gas around the FRII, its stellar mass of ∼3 × 1011 M⊙, star formation rate of ∼200 − 600 M⊙ yr−1, and powerful radio-to-X-ray emission, suggests that this source is the likely progenitor of the future brightest cluster galaxy.

The ALPINE–ALMA [C ii] Survey: Size of Individual Star-forming Galaxies at z = 4–6 and Their Extended Halo Structure

Abstract We present the physical extent of [C ii] 158 μm line-emitting gas from 46 star-forming galaxies at z = 4–6 from the ALMA Large Program to INvestigate C ii at Early Times (ALPINE). Using exponential profile fits, we measure the effective radius of the [C ii] line ( ) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum ( ) from Hubble Space Telescope images. The effective radius exceeds by factors of ∼2–3, and the ratio of increases as a function of M star. We do not find strong evidence that the [C ii] line, rest-frame UV, and far-infrared (FIR) continuum are always displaced over ≃1 kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended [C ii] component over 10 kpc scales detected at 4.1σ–10.9σ beyond the size of rest-frame UV and FIR continuum. One object has tentative rotating features up to ∼10 kpc, where the 3D model fit shows the rotating [C ii]-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended [C ii] line structure have high star formation rate, high stellar mass (M star), low Lyα equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Lyα line), as compared to galaxies without such extended [C ii] structures. Although we cannot rule out the possibility that a selection bias toward luminous objects may be responsible for such trends, the star-formation-driven outflow also explains all these trends. Deeper observations are essential to test whether the extended [C ii] line structures are ubiquitous to high-z star-forming galaxies.

The OH Megamaser galaxy IRAS11506−3851: an AGN and star formation revealed by multiwavelength observations

ABSTRACT We present Gemini Multi-Object Spectrograph (GMOS) Integral Field Unit (IFU), Hubble Space Telescope (HST), and Very Large Array (VLA) observations of the OH Megamaser (OHM) galaxy IRAS 11506−3851. The HST images reveal an isolated spiral galaxy and the combination with the GMOS-IFU flux distributions and VLA data allow us to identify a partial ring of star-forming regions surrounding the nucleus with a radius of ≈ 500 pc. While this ring shows starburst excitation and low velocity dispersion, the region internal to the ring shows higher excitation and velocity dispersion values, with values increasing towards its borders at ≈ 240 pc from the nucleus, resembling a projected bubble. The enhanced excitation and velocity dispersion of this bubble surrounds a 8.5-GHz radio emission structure, supporting its origin in a faint active galactic nucleus (AGN) that is mostly shocking the surrounding gas via a plasma ejection seen in radio at the present stage. This is the fourth of the 5 OHM galaxies we have studied so far (from our sample of 15 OHM) for which GMOS-IFU data indicate the presence of a previously unknown faint AGN at the nucleus, consistent with the hypothesis that OHM galaxies harbour recently triggered AGN.

High‐Spatiotemporal Resolution Observations of Jupiter Lightning‐Induced Radio Pulses Associated With Sferics and Thunderstorms

AbstractJupiter lightning discharges produce various kinds of phenomena including radio wave pulses at different frequencies. On 6 April 2019, the Juno Waves instrument captured an extraordinary series of radio pulses at frequencies below 150 kHz on timescales of submilliseconds. Quasi‐simultaneous multi‐instrument data show that the locations of their magnetic footprints are very close to the locations of ultrahigh frequency (UHF) sferics recorded by the Juno MWR instrument. Hubble Space Telescope images show that the signature of active convection includes cloud‐free clearings, in addition to the convective towers and deep water clouds that were also recognized in previous spacecraft observations of lightning source regions. Furthermore, the detections of 17 very low frequency/low‐frequency (VLF/LF) radio pulses suggest a minimum duration of lightning processes on the order of submilliseconds. These observations provide new constraints on the physical properties of Jupiter lightning.

Performing Point-spread Function Fitting with Photutils on Hubble Space Telescope Images

Abstract The low mass end of the Initial Mass Function (IMF) is a component of star formation that is not well understood. By analyzing Hubble Space Telescope (HST) images of star-forming regions, we aimed to provide data to constrain the shape of the low-mass IMF. We performed point-spread function (PSF) fitting using the Astropy Photutils package v0.6 on shallow HST Wide Field Camera 3 images taken in filters F110W, F139M, and F160W with the goal of identifying low mass stars and brown dwarfs. Residual images from our PSF fitting routine showed that fainter sources were effectively fit while fits to the brighter sources left residuals. Despite this, analysis confirmed that our PSF magnitudes are consistent with aperture magnitudes and mostly have smaller errors; 85%–100% of the flux was captured by the PSF fitting in most cases. PSF fitting of WFC3-IR images using Photutils shows promise for precise photometry.

The Morphology–Density Relationship in 1 < z < 2 Clusters

Abstract The morphology–density relationship states that dense cosmic environments such as galaxy clusters have an overabundance of quiescent elliptical galaxies, but it is unclear at which redshift this relationship is first established. We study the morphology of four clusters with 1.2 < z < 1.8 using Hubble Space Telescope imaging and the morphology computation code statmorph. By comparing the median morphology of cluster galaxies to CANDELS field galaxies using Monte Carlo analysis, we find that two out of four clusters (at z = 1.19 and 1.75) have an established morphology–density relationship with more than 3σ significance. Approximately 50% of the galaxies in these clusters are bulge-dominated, compared to ∼30% in the field, and they are significantly more compact. This result is more significant for low-mass galaxies with , showing that low-mass galaxies are affected the most in clusters. We also find an intriguing system of two z ≈ 1.45 clusters at a unusually small 2D separation of 3′ and 3D separation of ≈73 Mpc that exhibit no morphology–density relationship but have enhanced merger signatures. We conclude that the environmental mechanism responsible for the morphology–density relationship is (1) already active as early as z = 1.75; (2) forms compact, bulge-dominated galaxies; and (3) affects primarily low-mass galaxies. However, there is a significant degree of intracluster variance that may depend on the larger cosmological environment in which the cluster is embedded.

Color Gradients along the Quiescent Galaxy Sequence: Clues to Quenching and Structural Growth

Abstract This Letter examines how the sizes, structures, and color gradients of galaxies change along the quiescent sequence. Our sample consists of ∼400 quiescent galaxies at 1.0 ≤ z ≤ 2.5 and in three CANDELS fields. We exploit deep multi-band Hubble Space Telescope imaging to derive accurate mass profiles and color gradients, then use an empirical calibration from rest-frame UVJ colors to estimate galaxy ages. We find that—contrary to previous results—the youngest quiescent galaxies are not significantly smaller than older quiescent galaxies at fixed stellar mass. These “post-starburst” galaxies only appear smaller in half-light radii because they have systematically flatter color gradients. The strength of color gradients in quiescent galaxies is a clear function of age, with older galaxies exhibiting stronger negative color gradients (i.e., redder centers). Furthermore, we find that the central mass surface density Σ1 is independent of age at fixed stellar mass, and only weakly depends on redshift. This finding implies that the central mass profiles of quiescent galaxies do not significantly change with age; however, we find that older quiescent galaxies have additional mass at large radii. Our results support the idea that building a massive core is a necessary requirement for quenching beyond z = 1, and indicate that post-starburst galaxies are the result of a rapid quenching process that requires structural change. Furthermore, our observed color gradient and mass profile evolution supports a scenario where quiescent galaxies grow inside-out via minor mergers.

Structural parameters for the globular-cluster-like objects in NGC 1052-DF2

ABSTRACT Recently, van Dokkum et al. have found an ultra-diffuse galaxy NGC 1052-DF2 with little or no dark matter, based on a spectroscopic study of its 11 constituent globular-cluster-like objects. In this paper, we analyse these 11 objects using Hubble Space Telescope imaging. We derive the structural parameters for each object by fitting the surface brightness profiles to three different models. Our results indicate that these objects are better fitted by the Wilson model than by the King and Sérsic models. Using the distance of D = 20 Mpc to NGC 1052-DF2 obtained by van Dokkum et al., these 11 objects have half-light radii in the range from ∼11 to ∼16 pc. These values are much larger than for normal globular clusters in the Milky Way, and are comparable to the sizes of an extended star cluster and of a typical ultra-compact dwarf. The half-light radii obtained here are larger than those obtained by van Dokkum et al. and Trujillo et al. The offset of the differences between the half-light radii of van Dokkum et al. and ours is 6.17 pc, and the offset of the differences between the half-light radii of Trujillo et al. and ours is 4.99 pc. Our half-light radii are, on average, 11.74 pc, which corresponds to 53 and 43 per cent larger than those obtained by van Dokkum et al. and Trujillo et al., respectively. The Rh versus MV diagram shows that these objects occupy the same areas of extended star clusters and ultra-compact dwarfs. Using the distance of D = 13 Mpc obtained by Trujillo et al., there are still five objects that do not lie in the area of normal globular clusters in the Milky Way. So, we suggest that these globular-cluster-like objects in NGC 1052-DF2 are not normal globular clusters like those in the Milky Way.

The Carnegie Supernova Project II

We present optical and near-infrared broadband photometry and optical spectra of AT 2014ej from the Carnegie Supernova Project-II. These observations are complemented with data from the CHilean Automatic Supernova sEarch, the Public ESO Spectroscopic Survey of Transient Objects, and from the Backyard Observatory Supernova Search. Observational signatures of AT 2014ej reveal that it is similar to other members of the gap-transient subclass known as luminous red novae (LRNe), including the ubiquitous double-hump light curve and spectral properties similar to that of LRN SN 2017jfs. A medium-dispersion visual-wavelength spectrum of AT 2014ej taken with the Magellan Clay telescope exhibits a P Cygni Hα feature characterized by a blue velocity at zero intensity of ≈110 km s−1 and a P Cygni minimum velocity of ≈70 km s−1. We attribute this to emission from a circumstellar wind. Inspection of pre-outbust Hubble Space Telescope images yields no conclusive progenitor detection. In comparison with a sample of LRNe from the literature, AT 2014ej lies at the brighter end of the luminosity distribution. Comparison of the ultra-violet, optical, infrared light curves of well-observed LRNe to common-envelope evolution models from the literature indicates that the models underpredict the luminosity of the comparison sample at all phases and also produce inconsistent timescales of the secondary peak. Future efforts to model LRNe should expand upon the current parameter space we explore here and therefore may consider more massive systems and a wider range of dynamical timescales.

New H i observations of KK 69. Is KK 69 a dwarf galaxy in transition?

We present new HI data of the dwarf galaxy KK 69, obtained with the Giant Metrewave Radio Telescope (GMRT) with a signal-to-noise ratio that almost double previous observations. We carried out a Gaussian spectral decomposition and stacking methods to identify the cold neutral medium (CNM) and the warm neutral medium (WNM) of the HI gas. We found that 30% of the total HI gas, which corresponds to a mass of approx. 10^7 Mo, is in the CNM phase. The distribution of the HI in KK 69 is not symmetric. Our GMRT HI intensity map of KK 69 overlaid onto a Hubble Space Telescope image reveals an offset of approx. 4 kpc between the HI high-density region and the stellar body, indicating it may be a dwarf transitional galaxy. The offset, along with the potential truncation of the HI body, are evidence of interaction with the central group spiral galaxy NGC 2683, indicating the HI gas is being stripped from KK 69. Additionally, we detected extended HI emission of a dwarf galaxy member of the group as well as a possible new galaxy located near the north-eastern part of the NGC 2683 HI disk.