Testing the Bullet Dwarf Collision Scenario in the NGC 1052 Group Through Morphologies and Stellar Populations
Yimeng Tang, Aaron J. Romanowsky, Pieter G. van Dokkum, T. H. Jarrett, Kevin A. Bundy, Maria Luisa Buzzo, Shany Danieli, Jonah S. Gannon, Michael A. Keim, Seppo Laine, Zili Shen
本研究利用哈勃及多波段成像分析 NGC 1052 群尾迹矮星系的形态与恒星族群，发现其年龄更老、金属丰度更高且长轴沿尾迹排列，从而支持子弹矮星系碰撞形成假说。
摘要：
NGC 1052-DF2 和 -DF4 是两个超弥散星系，据报道它们缺乏暗物质，并同属一个星系群。近期研究结果表明，DF2 和 DF4 是一个大型线性矮星系子结构的组成部分，该子结构可能由两个富气星系的高速正面相遇形成，即所谓的子弹矮星系碰撞。基于哈勃空间望远镜的新观测，并结合从 u 波段到中红外的现有成像数据，我们通过研究尾迹矮星系的形态和恒星族群来检验子弹矮星系情景。我们发现，尾迹矮星系与该星系群中的其他矮星系之间没有显著的形态差异；但出人意料的是，这两类星系的测光长轴都与尾迹平行排列。我们发现，与对照样本相比，尾迹矮星系具有显著更老的年龄和更高的金属丰度，这支持了尾迹的独特性。这些观测为任何形成模型提供了关键约束，并且我们认为，目前它们最适合由子弹矮星系碰撞情景解释，预计未来观测还将带来更多强有力的检验。
英文摘要：
NGC 1052-DF2 and -DF4 are two ultra-diffuse galaxies that have been reported as deficient in dark matter and associated with the same galaxy group. Recent findings suggest that DF2 and DF4 are part of a large linear substructure of dwarf galaxies that could have been formed from a high-velocity head-on encounter of two gas-rich galaxies, known as a bullet dwarf collision. Based on new observations from the Hubble Space Telescope, combined with existing imaging from the u band to mid-infrared, we test the bullet dwarf scenario by studying the morphologies and stellar populations of the trail dwarfs. We find no significant morphological differences between the trail dwarfs and other dwarfs in the group, while for both populations, their photometric major axes unexpectedly align parallel with the trail. We find that the trail dwarfs have significantly older ages and higher metallicities than the comparison sample, supporting the distinctiveness of the trail. These observations provide key constraints for any formation model, and we argue that they are currently best explained by the bullet dwarf collision scenario, with additional strong tests anticipated with future observations.
We continue to explore the relationship between globular cluster total number, $N_{\rm GC}$, and central black hole mass, $M_\bullet$, in spiral galaxies. We present here results for the Sab galaxies NGC 3368, NGC 4736 (M 94) and NGC 4826 (M 64), and the Sm galaxy NGC 4395. The globular cluster (GC) candidate selection is based on the ($u^*$ - $i^\prime$) versus ($i^\prime$ - $K_s$) color-color diagram, and $i^\prime$-band shape parameters. We determine the $M_\bullet$ versus $N_{\rm GC}$ correlation for these spirals, plus NGC 4258, NGC 253, M 104, M 81, M 31, and the Milky Way. We also redet…
We present new measurements for the nuclear stellar velocity dispersion $σ_{\ast}$ within sub-arcsecond apertures for 28 nearby galaxies. Our data consist of Space Telescope Imaging Spectrograph (STIS) long-slit spectra obtained with the G750M grating centred on the H$α$ spectral range. We fit the spectra using a library of single stellar population models and Gaussian emission lines, while constraining in most cases the stellar-population content from an initial fit to G430L STIS spectra. We illustrate how these $σ_{\ast}$ measurements can be useful for constraining the mass $M_{\bullet}$ of …
A fully-sampled and hitherto highest resolution and sensitivity observation of neutral hydrogen (HI) in the Leo Triplet (NGC 3628, M 65/NGC 3623, and M 66/NGC 3627) reveals six HI structures beyond the three galaxies. We present detailed results of the morphologies and kinematics of these structures, which can be used for future simulations. In particular, we detect a two-arm structure in the plume of NGC 3628 for the first time, which can be explained by a tidal interaction model. The optical counterpart of the plume is mainly associated with the southern arm. The connecting part (base) of th…
It was recently proposed that the dark matter-deficient ultra-diffuse galaxies DF2 and DF4 in the NGC1052 group could be the products of a "bullet dwarf" collision between two gas-rich progenitor galaxies. In this model DF2 and DF4 formed at the same time in the immediate aftermath of the collision, and a strong prediction is that their globular clusters should have nearly identical stellar populations. Here we test this prediction by measuring accurate F606W-F814W colors from deep HST/ACS imaging. We find that the clusters are extremely homogeneous. The mean color difference between the globu…
We aim to explore the relationship between globular cluster total number, $N_{\rm GC}$, and central black hole mass, $M_\bullet$, in spiral galaxies, and compare it with that recently reported for ellipticals. We present results for the Sbc galaxy NGC 4258, from Canada France Hawaii Telescope data. Thanks to water masers with Keplerian rotation in a circumnuclear disk, NGC 4258 has the most precisely measured extragalactic distance and supermassive black hole mass to date. The globular cluster (GC) candidate selection is based on the ($u^*\ -\ i^\prime$) vs. ($i^\prime\ -\ K_s$) diagram, which…
New Measurements of Distances to Galaxies in the NGC 1052 Field with the Hubble and James Webb Space Telescopes: Testing the Bullet-Dwarf Origin of the Trail
University of California Santa Cruz（加州大学圣克鲁兹分校）；Space Telescope Science Institute（太空望远镜科学研究所）；San José State University（圣何塞州立大学）；Yale University（耶鲁大学）
Kinematic Confirmation of a Remarkable Linear Trail of Galaxies in the NGC 1052 Field, Consistent with Formation in a High-Speed Bullet Dwarf Collision
Yale University（耶鲁大学）；Princeton University（普林斯顿大学）；University of Toronto（多伦多大学）；San Jose State University（圣何塞州立大学）；University of California Santa Cruz（加州大学圣克鲁兹分校）
NGC 4258 is an SABbc Seyfert galaxy, located at a distance of $7.2 \pm 0.3$ Mpc. This object is well known by its nearly edge-on molecular nuclear disc, located between 0.16 and 0.28 pc from the nucleus, whose H$_2$O maser emission allows a very precise measurement of the central supermassive black hole mass ($M_{\bullet}(maser) = 3.78 \pm 0.01 \times 10^7$ Mo). We analyse the emission line properties and the stellar kinematics in a data cube of the central region of NGC 4258, obtained, in the K band, with the Near-Infrared Integral Field Spectrograph, at the Gemini-north telescope. The nuclea…
The rest-frame far-ultraviolet (FUV) morphologies of 8 nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 8, NGC 520, NGC 1068, NGC 3079, NGC 3310, NGC 7673) are compared with 54 galaxies at z ~ 1.5 and 46 galaxies at z ~ 4 observed in the GOODS-ACS field. The nearby sample is artificially redshifted to z ~ 1.5 and 4. We compare the simulated galaxy morphologies to real z ~ 1.5 and 4 UV-bright galaxy morphologies. We calculate the Gini coefficient (G), the second-order moment of the brightest 20% of the galaxy's flux (M_20), and the Sersic index (n). We explore the use of nonparamet…
Recent X-ray observations by Jiang et al. have identified an active galactic nucleus (AGN) in the bulgeless spiral galaxy NGC 3319, located just $14.3\pm1.1\,$Mpc away, and suggest the presence of an intermediate-mass black hole (IMBH; $10^2\leq M_\bullet/\mathrm{M_{\odot}}\leq10^5$) if the Eddington ratios are as high as 3 to $3\times10^{-3}$. In an effort to refine the black hole mass for this (currently) rare class of object, we have explored multiple black hole mass scaling relations, such as those involving the (not previously used) velocity dispersion, logarithmic spiral-arm pitch angle,…
Characterising the Globular Cluster Systems of Three Local Group Dwarf Galaxies: NGC6822, NGC147 and NGC185
University of Edinburgh（爱丁堡大学）；Independent Researcher（独立研究者）；University of Exeter（埃克塞特大学）；University of Cambridge（剑桥大学）；National Research Council Herzberg Astronomy and Astrophysics（国家研究委员会赫茨伯格天文学与天体物理学研究所）；University of California, Berkeley（加州大学伯克利分校）；University of Leicester（莱斯特大学）
We present SMA CO(2-1) observations toward the protostellar jet driven by SVS13A, a variable protostar in the NGC1333 star-forming region. The SMA CO(2-1) images show an extremely high-velocity jet composed of a series of molecular 'bullets'. Based on the SMA CO observations, we discover clear and large systematic velocity gradients, perpendicular to the jet axis, in the blueshifted and redshifted bullets. After discussing several alternative interpretations, such as twin-jets, jet precession, warped disk, and internal helical shock, we suggest that the systematic velocity gradients observed i…
Recent high-quality photometry of many star clusters in the Magellanic Clouds with ages of 1$\,-\,$2 Gyr revealed main sequence turnoffs (MSTOs) that are significantly wider than can be accounted for by a simple stellar population (SSP). Such extended MSTOs (eMSTOs) are often interpreted in terms of an age spread of several $10^8$ yr, challenging the traditional view of star clusters as being formed in a single star formation episode. Li et al. and Bastian & Niederhofer recently investigated the sub-giant branches (SGBs) of NGC 1651, NGC 1806, and NGC 1846, three star clusters in the Large Mag…
We report near-infrared integral field spectroscopic observations of the active galactic nucleus NGC 4151 with archive data from the NIFS-Gemini North Telescope. We have selected best-seeing observations ($\lesssim$0.3 arcsec) that, allied to our methodology of image processing techniques, show structures with spatial resolution comparable to those of the HST. The intricate outflow of NGC 4151 is revisited in light of the results found for NGC 1068, in a previous work, and a very similar dynamic is found: the low-velocity [Fe II] emission depicts the glowing walls of an hourglass structure, wh…
The study of gas-dust interactions occurring in the interstellar medium of a galaxy is essential for understanding various physical processes taking place within it. A comparison of such events at different locations corresponding to diverse astrophysical environments provides more insight into the star-formation as well as dust destruction conditions and time-scales. We present a case study for two galaxies: NGC 3184 and NGC 7793, which are typical examples of a `grand design spiral' and a `flocculent spiral', respectively. We investigate the gas-dust correlations at various spatially resolve…
Metallicity distributions (MDs) of globular clusters (GCs) provide crucial clues for the assembly and star formation history of their host galaxies. GC colors, when GCs are old, have been used as a proxy of GC metallicities. Bimodal GC color distributions (CDs) observed in most early-type galaxies have been interpreted as bimodal MDs for decades, suggesting the presence of merely two GC subpopulations within single galaxies. However, the conventional view has been challenged by a new theory that nonlinear metallicity-to-color conversion can cause bimodal CDs from unimodal MDs. The unimodal MDs…
Dorado is a nearby (17.69 Mpc) strongly evolving galaxy group in the Southern Hemisphere. We are investigating the star formation in this group. This paper provides a FUV imaging of NGC 1533, IC 2038 and IC 2039, which form a substructure, south west of the Dorado group barycentre. FUV CaF2-1 UVIT-Astrosat images enrich our knowledge of the system provided by GALEX. In conjunction with deep optical wide-field, narrow-band Halpha and 21-cm radio images we search for signatures of the interaction mechanisms looking in the FUV morphologies and derive the star formation rate. The shape of the FUV …
We report the discovery of a UV-bright tidal dwarf galaxy candidate in the NGC 4631/4656 galaxy group, which we designate NGC 4656UV. Using survey and archival data spanning from 1.4 GHz to the ultraviolet we investigate the gas kinematics and stellar properties of this system. The HI morphologies of NGC 4656UV and its parent galaxy NGC 4656 are extremely disturbed, with significant amounts of counterrotating and extraplanar gas. From UV-FIR photometry, computed using a new method to correct for surface gradients on faint objects, we find that NGC 4656UV has no significant dust opacity and a b…
Cluster substructure and ram pressure stripping in individual galaxies are among the primary evidence for the ongoing growth of galaxy clusters as they accrete galaxies and groups from their surroundings. We present a multi-wavelength study of the center of the Hydra I galaxy cluster, including exquisite new MeerKAT HI and DECam Halpha imaging which reveal conclusive evidence for ram pressure stripping in NGC 3312, NGC 3314a and NGC 3314b through compressed HI contours, well-defined HI tails, and ongoing star formation in the stripped gas. In particular, we quantify the stripped material in NG…
The ultra-diffuse galaxies DF2 and DF4 in the NGC1052 group share several unusual properties: they both have large sizes, rich populations of overluminous and large globular clusters, and very low velocity dispersions indicating little or no dark matter. It has been suggested that these galaxies were formed in the aftermath of high velocity encounters of gas rich galaxies, events that resemble the collision that created the bullet cluster but on much smaller scales. The gas separates from the dark matter in the collision and subsequent star formation leads to the formation of one or more dark …
The morphology of HII regions around young star clusters provides insight into the timescales and physical processes that clear a cluster's natal gas. We study ~700 young clusters (<10Myr) in three nearby spiral galaxies (NGC 7793, NGC 4395, and NGC 1313) using Hubble Space Telescope (HST) imaging from LEGUS (Legacy ExtraGalactic Ultraviolet Survey). Clusters are classified by their H$α$ morphology (concentrated, partially exposed, no-emission) and whether they have neighboring clusters (which could affect the clearing timescales). Through visual inspection of the HST images, and analysis of a…
We present detailed morphological, photometric, and stellar-kinematic analyses of the central regions of two massive, early-type barred galaxies with nearly identical large-scale morphologies. Both have large, strong bars with prominent inner photometric excesses that we associate with boxy/peanut-shaped (B/P) bulges; the latter constitute ~ 30% of the galaxy light. Inside its B/P bulge, NGC 4608 has a compact, almost circular structure (half-light radius R_e approx. 310 pc, Sérsic n = 2.2) we identify as a classical bulge, amounting to 12.1% of the total light, along with a nuclear star clust…
We present deep Hubble Space Telescope imaging of five faint dwarf galaxies associated with the nearby spiral NGC 253 (D$\approx$3.5 Mpc). Three of these are newly discovered ultra-faint dwarf galaxies, while all five were found in the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS), a Magellan$+$Megacam survey to identify faint dwarfs and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data reach $\gtrsim$3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances, structural par…
We present the unexpected discovery of four ultra diffuse galaxies (UDGs) in a group environment. We recently identified seven extremely low surface brightness galaxies in the vicinity of the spiral galaxy M101, using data from the Dragonfly Telephoto Array. The galaxies have effective radii of $10"-38"$ and central surface brightnesses of $25.6-27.7$ mag arcsec$^{-2}$ in g-band. We subsequently obtained follow-up observations with $HST$ to constrain the distances to these galaxies. Four remain persistently unresolved even with the spatial resolution of $HST$/ACS, which implies distances of $D…
It is still unknown how magnetic field-generation mechanisms could operate in low-mass dwarf galaxies. Here, we present a detailed study of a nearby pure-disk dwarf galaxy NGC 2976. Unlike previously observed dwarf objects, this galaxy possesses a clearly defined disk. For the purpose of our studies, we performed deep multi-frequency polarimetric observations of NGC 2976 with the VLA and Effelsberg radio telescopes. Additionally, we supplement them with re-imaged data from the WSRT-SINGS survey. The magnetic field morphology discovered in NGC 2976 consists of a southern polarized ridge. This s…
We present a scenario for the formation and the morphology of the arrow-shaped dwarf irregular galaxy NGC 1427A in the Fornax Cluster. This galaxy shows intriguing stellar and gaseous tails pointing in different directions for which alternative but not conclusive formation scenarios have been proposed in the literature. We performed N-body/SPH simulations of dwarf galaxies falling into a model of the Fornax cluster, exhibiting a jellyfish-like appearance while undergoing ram-pressure stripping. We noted that some of our models show interesting tail morphologies similar to that of NGC 1427A. In…
NGC 4258 is the galaxy with the most accurate (maser-based) determination for the mass of the supermassive black hole (SMBH) in its nucleus. In this work we present a two-dimensional mapping of the stellar kinematics in the inner 3.0 x 3.0 arcsec = 100 x 100 pc of NGC 4258 using adaptative-optics observations obtained with the Near-Infrared Integral Field Spectrograph of the GEMINI North telescope at a 0.11 arcsec (4 pc) angular resolution. The observations resolve the radius of influence of the SMBH, revealing an abrupt increase in the stellar velocity dispersion within 10 pc from the nucleus…
In most blue compact dwarf (BCD) galaxies, it remains unclear what triggers their bursts of star formation. We study the HI of three relatively isolated BCDs, Mrk 178, VII Zw 403, and NGC 3738, in detail to look for signatures of star formation triggers, such as gas cloud consumption, dwarf-dwarf mergers, and interactions with companions. High angular and velocity resolution atomic hydrogen (H I) data from the Very Large Array (VLA) dwarf galaxy HI survey, Local Irregulars That Trace Luminosity Extremes, The HI Nearby Galaxy Survey (LITTLE THINGS), allows us to study the detailed kinematics an…
We present optical $\textit{BVRI}$ photometry, H$α$ IFU velocity fields, and H$α$ long-slit rotation curves for a sample of four nearby spiral galaxies having a range of morphologies and inclinations. We show that the $\texttt{DiskFit}$ code can be used to model the photometric and kinematic data of these four galaxies and explore how well the photometric data can be decomposed into structures like bars and bulges and to look for non-circular motions in the kinematic data. In general, we find good agreement between our photometric and kinematic models for most parameters. We find the best cons…
Dark matter-deficient twins: FCC 224 and FCC 240 as possible analogues of NGC 1052-DF2 and DF4
Yale University（耶鲁大学）；Swinburne University of Technology（斯威本科技大学）；European Southern Observatory（欧洲南方天文台）；San José State University（圣何塞州立大学）；University of California Santa Cruz（加州大学圣克鲁兹分校）
We present resolved HI synthesis maps from the Very Large Array (VLA) of three interacting dwarf systems: the NGC 3664 dwarf pair, the NGC 3264 dwarf pair, and the UGC 4638 dwarf triplet. All three dwarf systems are captured at various stages of interaction and span a range of environments. We detect clear hallmarks of tidal interactions through the presence of HI bridges, and diffuse HI extensions that surround the dwarfs. We overlay the HI data on Pan-STARRS r-band images and find further evidence of tidal interactions through coincident distorted HI and tidal stellar features in NGC 3264 an…
We report the photometric properties of 16 dwarf galaxies, 15 of which are newly identified, in the Western halo of the nearby giant elliptical galaxy NGC5128. All candidates are found at projected distances $\sim\!100\!-\!225$kpc from their giant host, with luminosities $-10.82\!\leq\!M_V/{\rm mag}\!\leq\!-7.42$ and effective radii $4''\!\leq\!r_{\rm eff}\!\leq\!17''$ (or $75\!\leq\!r_{\rm eff}/{\rm pc}\!\leq\!300$ at the distance of NGC5128). We compare to other low-mass dwarf galaxies in the local universe and find them to populate the faint/compact extension of the size-luminosity relation…
We present detailed analysis of color-magnitude diagrams of NGC2403, obtained from a deep (m<28) Hubble Space Telescope (HST) Wide Field Planetary Camera 2 observation of the outer disk of NGC2403, supplemented by several shallow (m<26) HST Advanced Camera for Surveys fields. We derive the spatially resolved star formation history of NGC2403 out to 11 disk scale lengths. In the inner portions of the galaxy, we compare the recent star formation rates (SFRs) we derive from the resolved stars with those measured using GALEX FUV + Spitzer 24-micron fluxes, finding excellent agreement between the m…
We present the first results of a wide-field mapping survey of the M81 group conducted with Hyper Suprime-Cam on the Subaru Telescope. Our deep photometry reaches $\sim2$ magnitudes below the tip of the red giant branch (RGB) and reveals the spatial distribution of both old and young stars over an area of $\sim 100\times115$ kpc at the distance of M81. The young stars ($\sim30-160$ Myr old) closely follow the neutral hydrogen distribution and can be found in a stellar stream between M81 and NGC\,3077 and in numerous outlying stellar associations, including the known concentrations of Arp's Loo…
The star formation history of NGC 2276: Comparison between SED modeling and hydrodynamical simulations
University of Zagreb（萨格勒布大学）；INAF–Padova Astronomical Observatory（意大利国家天体物理研究所帕多瓦天文台）；Universidad Tecnica Federico Santa Maria（费德里科·Santa María理工大学）；Millenium Nucleus for Galaxies (MINGAL)（星系千年核心（MINGAL））；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）；Waterloo Centre for Astrophysics, University of Waterloo（滑铁卢大学天体物理中心）；Department of Physics & Astronomy, University of Waterloo（滑铁卢大学物理与天文系）；Georgia Institute of Technology（佐治亚理工学院）；INAF–Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）
We investigate the stellar disk structure of six nearby edge-on spiral galaxies using high-resolution JHKs-band images and 3D radiative transfer models. To explore how mass and environment shape spiral disks, we selected galaxies with rotational velocities between 69 < Vrot < 245 km/sec, and two with unusual morphologies. We find a wide diversity of disk structure. Of the fast-rotating (Vrot > 150 km/sec) galaxies, only NGC 4013 has the super-thin+thin+thick nested disk structure seen in NGC 891 and the Milky Way, albeit with decreased oblateness, while NGC 1055, a disturbed massive spiral gal…
We present the first multi-frequency VLBI images of PKS 2254-367, a Giga-hertz Peaked Spectrum (GPS) radio source hosted by the nearby galaxy IC 1459 (D=20.5 Mpc). PKS 2254-367 and the radio source in NGC 1052 (PKS 0238-084; D=17.2 Mpc) are the two closest GPS radio sources to us, far closer than the next closest example, PKS 1718-649 (D=59 Mpc). As such, IC 1459 and NGC 1052 offer opportunities to study the details of the pc-scale radio sources as well as the environments that the radio sources inhabit, across the electromagnetic spectrum. Given that some models for the origin and evolution o…
It has been suggested that a trail of diffuse galaxies, including two dark matter deficient galaxies (DMDGs), in the vicinity of NGC1052 formed because of a high-speed collision between two gas-rich dwarf galaxies, one bound to NGC1052 and the other one on an unbound orbit. The collision compresses the gas reservoirs of the colliding galaxies, which in turn triggers a burst of star formation. In contrast, the dark matter and pre-existing stars in the progenitor galaxies pass through it. Since the high pressures in the compressed gas are conducive to the formation of massive globular clusters (…
High-resolution Hubble Space Telescope optical observations have been used to analyze the stellar population and the structure of the poorly investigated bulge globular cluster NGC 6316. We constructed the first high-resolution reddening map in the cluster direction, which allowed us to correct the evolutionary sequences in the color magnitude diagram (CMD) for the effects of differential reddening. A comparison between the CMDs of NGC 6316 and 47 Tucanae revealed strikingly similar stellar populations, with the two systems basically sharing the same turn-off, sub-giant branch, and horizontal …
Context: Pre-merger interactions between galaxies can induce significant changes in the morphologies and kinematics of the stellar and ISM components. Large amounts of gas and stars are often found to be disturbed or displaced as tidal debris. This debris then evolves, sometimes forming stars and occasionally tidal dwarf galaxies. Here we present results from our HI study of Arp 65, an interacting pair hosting extended HI tidal debris. Aims: In an effort to understand the evolution of tidal debris produced by interacting pairs of galaxies, including in situ star and tidal dwarf galaxy formatio…
AGN-driven outflows are believed to play an important role in regulating the growth of galaxies mostly via negative feedback. However, their effects on their hosts are far from clear, especially for low and moderate luminosity Seyferts. To investigate this issue, we have obtained cold molecular gas observations, traced by the CO(2-1) transition, using the NOEMA interferometer of five nearby (distances between 19 and 58 Mpc) Seyfert galaxies. The resolution of approx. 0.3-0.8 arcsec (approx. 30-100 pc) and field of view of NOEMA allowed us to study the CO(2-1) morphology and kinematics in the n…
The molecular gas of four ram pressure stripped galaxies in the core of the Hydra I cluster
Instituto de Astrofísica de Andalucía (CSIC)（安达卢西亚天体物理研究所）；European Southern Observatory（欧洲南方天文台）；Chalmers University of Technology（查尔姆斯理工大学）；ASTRON, the Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）；University of Cape Town（开普敦大学）；South African Astronomical Observatory（南非天文台）；Universidad Técnica Federico Santa María（弗雷德里科·圣玛丽亚技术大学）；Millennium Nucleus for Galaxies (MINGAL)（银河系千年核）；Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester（曼彻斯特大学物理与天文学院乔德雷克银行天体物理学中心）；United Kingdom SKAO Regional Centre (UKSRC)（英国SKAO区域中心）；Finnish Centre for Astronomy with ESO, (FINCA)（芬兰ESO天文中心）
We report the results of Gemini/GMOS long-slit spectroscopic observations along the major and minor axes of the central galaxies in two fossil groups, SDSS J073422.21+265133.9 and SDSS J075828.11+374711.8 (the NGC 2484 group). Spatially resolved kinematics and stellar population parameters (ages, metallicities and $α$-element abundance ratios) derived using ~20 Lick indices are presented. Despite remarkable similarities in their morphologies, photometric properties (luminosity and colour) and kinematics, the two galaxies exhibit significantly different stellar population parameters. SDSS J0734…
The formation of very young massive clusters or "starburst" clusters is currently one of the most widely debated topic in astronomy. The classical notion dictates that a star cluster is formed in-situ in a dense molecular gas clump followed by a substantial residual gas expulsion. On the other hand, based on the observed morphologies of many young stellar associations, a hierarchical formation scenario is alternatively suggested. A very young (age $\approx$ 1 Myr), massive ($>10^4M_\odot$) star cluster like the Galactic NGC 3603 young cluster (HD 97950) is an appropriate testbed for distinguis…
