D. Calzetti, K. E. Johnson, A. Adamo, J. S. Gallagher, J. E. Andrews, L. J. Smith, G. C. Clayton, J. C. Lee, E. Sabbi, L. Ubeda, H. Kim, J. E. Ryon, D. Thilker,… 展开作者
D. Calzetti, K. E. Johnson, A. Adamo, J. S. Gallagher, J. E. Andrews, L. J. Smith, G. C. Clayton, J. C. Lee, E. Sabbi, L. Ubeda, H. Kim, J. E. Ryon, D. Thilker, S. N. Bright, E. Zackrisson, R. C. Kennicutt, S. E. de Mink, B. C. Whitmore, A. Aloisi, R. Chandar, M. Cignoni, D. Cook, D. A. Dale, B. G. Elmegreen, D. M. Elmegreen, A. S. Evans, M. Fumagalli, D. A. Gouliermis, K. Grasha, E. K. Grebel, M. R. Krumholz, R. Walterbos, A. Wofford, T. M. Brown, C. Christian, C. Dobbs, A. Herrero, L. Kahre, M. Messa, P. Nair, A. Nota, G. Oestlin, A. Pellerin, E. Sacchi, D. Schaerer, M. Tosi
备注：
67 pages; 11 figures; 7 tables. Accepted for publication in the Astrophysical Journal
The nearby dwarf starburst galaxy NGC5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the `radio nebula'). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC5253 with wavelength coverage from 1500 Ang to 1.9 micron in 13 filters. These include H-alpha, P-beta, and P-alpha, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the 9 optically brightest clusters (M_V < -8.8) and the two young radio nebula clusters. The clusters have ages ~1-15 Myr and masses ~1x10^4 - 2.5x10^5 M_sun. The clusters' spatial location and ages indicate that star formation has become more concentrated towards the radio nebula over the last ~15 Myr. The most massive cluster is in the radio nebula; with a mass 2.5x10^5 M_sun and an age ~1 Myr, it is 2-4 times less massive and younger than previously estimated. It is within a dust cloud with A_V~50 mag, and shows a clear nearIR excess, likely from hot dust. The second radio nebula cluster is also ~1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.
We resolve a significant fraction of globular clusters (GCs) in NGC 4921, the brightest spiral galaxy in Coma. Also we find a number of extended bright star clusters (star complexes) in the spur region of the arms. The latter are much brighter and bluer than those in the normal star-forming region, being as massive as 3x10^5 M_odot. The color distribution of the GCs in this galaxy is found to be bimodal. The turnover magnitudes of the luminosity functions (LF) of the blue (metal-poor) GCs (0.70<(V-I)<1.05) in the halo are estimated to be V(max) =27.11+-0.09 mag and I(max)=26.21+-0.11 mag. We o…
We investigate the stellar kinematics and line strength indices in the outer halos of brightest cluster galaxies (BCGs) in the Coma cluster to obtain the outer halo V_rot and sigma profiles and to derive constraints on the formation history of these objects. Methods: We analyzed absorption lines in deep, medium-resolution, long-slit spectra in the wavelength range ~ 4500 - 5900 Angstrom, out to ~50 kpc for NGC 4874 and ~65 kpc for NGC 4889, probing regions with a surface brightness down to mu_R ~24 mag/arcsec^2. Results: These data provide stellar velocity and velocity dispersion profiles alon…
We investigate the spatial regularity in the distribution of the young stellar population along spiral arms of three late type spiral galaxies: NGC 895, NGC 5474, and NGC 6946. This study is based on an analysis of photometric properties of spiral arms using {\it GALEX} ultraviolet, optical UBVRI, Halpha, and 8mum {IRAC} infrared surface photometry data. Using the Fourier analysis approach, we found features of spatial regularity or quasi-regularity in the distribution of the young stellar population or (and) regular chains of star formation regions in all arms of NGC 895, NGC 5474, and NGC 69…
We present high-resolution (synthesised beam size 0."088x0."083 or 25x23 pc$^2$) Atacama Large Millimetre/submillimetre Array (ALMA) $^{12}$CO(2-1) line and 236 GHz continuum observations, as well as 5 GHz enhanced Multi-Element Radio Linked Interferometer Network (e-MERLIN) continuum observations, of NGC 0708; the brightest galaxy in the low-mass galaxy cluster Abell 262. The line observations reveal a turbulent, rotating disc of molecular gas in the core of the galaxy, and a high-velocity, blue-shifted feature ~0."4 (~113 pc) from its centre. The sub-millimetre continuum emission peaks at th…
Context. We investigate the stellar population and the origin of diffuse light around brightest cluster galaxies. Aims. We study the stellar population of the dynamically hot stellar halo of NGC 3311, the brightest galaxy in the Hydra I cluster, and that of photometric substructures in the diffuse light to constrain the origin of these components. Methods. We analyze absorption lines in medium-resolution, long-slit spectra in the wavelength range 4800-5800 angstrom obtained with FORS2 at the Very Large Telescope. We measure the equivalent width of Lick indices out to 20 kpc from the center of …
The recent star formation history (SFH) in the outer disk of NGC 300 is presented through the analysis of color magnitude diagrams (CMDs). We analyze resolved stellar photometry by creating CMDs from four Hubble Space Telescope fields containing a combination of images from the Advanced Camera for Surveys and the UVIS imager aboard the Wide Field Camera 3. From the best models of these CMDs, we derive the SFH in order to extract the young stellar component for the past 200 Myrs. We find that the young stellar disk of NGC 300 is unbroken out to at least ${\sim}$8 scale lengths (including an upp…
We report the serendipitous young Large Magellanic Cloud cluster, NGC 1971, exhibits an extended main-sequence turnoff (eMSTO) possibly originated by mostly a real age spread. We used CT1 Washington photometry to produce a colour-magnitude diagram (CMD) with the fiducial cluster features. From its eMSTO, we estimated an age spread of ~ 170 Myr (observed age range 100-280 Myr), once observational errors, stellar binarity, overall metalicity variations and stellar rotation effects were subtracted in quadrature from the observed age width.
Spectra of the intermediate age star cluster NGC 1978 and the dwarf irregular galaxies NGC 55 and NGC 3109 that span the 0.7 to 1.1um wavelength interval are discussed. The NGC 1978 spectra are used to examine stochastic effects on the integrated red light from an intermediate age cluster. The removal of either the brightest M giant or the brightest C star from the co-added NGC 1978 spectrum has minor effects on the equivalent withs of the Ca triplet. The most robust signature of C stars in the integrated cluster spectrum at these wavelengths is the CN band head near 0.79um. The equivalent wid…
We use deep Chandra X-ray Observatory observations to examine the coronae of the two brightest cluster galaxies in the Coma cluster of galaxies, NGC 4874 and NGC 4889. We find that NGC 4889 hosts a central depression in X-ray surface brightness consistent with a cavity or pair of cavities of radius 0.6 kpc. If the central cavity is associated with an AGN outburst and contains relativistic material, its enthalpy should be around 5x10^55 erg. The implied heating power of this cavity would be around an order of magnitude larger than the energy lost by X-ray emission. It would be the smallest and …
We study photometric properties, chemical abundances and sizes of star formation regions in the two principal arms of the galaxy NGC 628 (M74). The GALEX ultraviolet, optical UBVRI, and H-alpha? surface photometry data are used, including those obtained with the 1.5-m telescope of the Maidanak Observatory. The thirty brightest star formation regions in ultraviolet light located in the spiral arms of NGC 628 are identified and studied. We find that the star formation regions in one (longer) arm are systematically brighter and larger than the regions in the other (shorter) arm. However, both lum…
The relative contribution of various physical processes to the spatial and temporal distribution of molecular clouds and star-forming regions in the disks of galaxies has not been fully studied. The spatial regularity in the distribution of the young stellar population in spiral and ring structures is a good test to study this contribution. We investigate photometric properties of the ring and spiral arms in the barred spiral galaxy NGC 6217 based on analysis of GALEX ultraviolet, optical UBVRI and Halpha surface photometry data. The ring in the galaxy is located near the corotation area. A sp…
We present new deep photometry of the globular cluster system (GCS) around NGC 6166, the central supergiant galaxy in Abell 2199. HST data from the ACS and WFC3 cameras in F475W, F814W are used to determine the spatial distribution of the GCS, its metallicity distribution function (MDF), and the dependence of the MDF on galactocentric radius and on GC luminosity. The MDF is extremely broad, with the classic red and blue subpopulations heavily overlapped, but a double-Gaussian model can still formally match the MDF closely. The spatial distribution follows a Sersic-like profile detectably to a …
Images and spectra of the open cluster NGC 3105 have been obtained with GMOS on Gemini South. The (i', g'-i') color-magnitude diagram (CMD) constructed from these data extends from the brightest cluster members to g'~23. This is 4 - 5 mag fainter than previous CMDs at visible wavelengths and samples cluster members with sub-solar masses. Assuming a half-solar metallicity, comparisons with isochrones yield a distance of 6.6+/-0.3 kpc. An age of at least 32 Myr is found based on the photometric properties of the brightest stars, coupled with the apparent absence of pre-main sequence stars in the…
The conventional picture of coeval, chemically homogeneous, populous star clusters -- known as `simple stellar populations' (SSPs) -- is a view of the past. Photometric and spectroscopic studies reveal that almost all ancient globular clusters in the Milky Way and our neighbouring galaxies exhibit star-to-star light-element abundance variations, typically known as 'multiple populations' (MPs). Here, we analyse photometric $\it Hubble$ $\it Space$ $\it Telescope$ observations of three young ($<$2 Gyr-old) Large and Small Magellanic Cloud clusters, NGC 411, NGC 1718 and NGC 2213. We measure the …
This paper shows a technique for searching for bright massive stars in galaxies beyond the Local Group. To search for massive stars, we used the results of stellar photometry of the Hubble Space Telescope images using the DAOPHOT and DOLPHOT packages. The results of such searches are shown on the example of the galaxies DDO68, M94 and NGC1672. In the galaxy DDO68 the LBV star changes its brightness, and in M94 massive stars can be identified by the excess in the H$α$ band. For the galaxy NGC1672, we measured the distance for the first time by the TRGB method, which made it possible to determin…
High-resolution spectroscopic observations were taken of 29 extended main sequence turn-off (eMSTO) stars in the young ($\sim$200 Myr) LMC cluster, NGC 1866 using the Michigan/Magellan Fiber System and MSpec spectrograph on the Magellan-Clay 6.5-m telescope. These spectra reveal the first direct detection of rapidly rotating stars whose presence has only been inferred from photometric studies. The eMSTO stars exhibit H-alpha emission (indicative of Be-star decretion disks), others have shallow broad H-alpha absorption (consistent with rotation $\gtrsim $150 km s$^{-1}$), or deep H-alpha core a…
We present the results of our study of starforming regions in the lenticular galaxy NGC 4324. During a complex analysis of multiwavelength observational data -- the narrow-band emission-line images obtained with the 2.5-m telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University and the archival images in the broad bands of the SDSS, GALEX and WISE surveys -- we have detected young starforming complexes (clumps) located in the inner ring of the lenticular galaxy NGC 4324, and we have established a regular pattern of their distribution…
We studied 102 star forming regions in seven spiral galaxies (NGC 628, NGC 783, NGC 2336, NGC 6217, NGC 6946, NGC 7331, and NGC 7678) on the basis of complex spectroscopic, photometric (UBVRI) and spectrophotometric (H alpha line) observations. Using data on the chemical composition and absorption in HII regions, obtained from spectroscopic observations, and using evolutionary models, we estimated physical parameters (ages and masses) of young stellar groupings embedded in HII regions. We found that the gas extinction, A(gas), which determined from the Balmer decrement, does not correspond in …
The very young open cluster (OC) NGC 2244 in the Rosette Nebula was studied with field-star-decontaminated 2MASS photometry, which shows the main-sequence (MS) stars and an abundant pre-MS (PMS) population. Fundamental and structural parameters were derived with colour-magnitude diagrams (CMDs), stellar radial density profiles (RDPs) and mass functions (MFs). Most previous studies centred NGC 2244 close to the bright K0V star 12 Monocerotis, which is not a cluster member. Instead, the near-IR RDP indicates a pronounced core near the O5 star HD 46150. We derive an age within 1--6 Myr, an absorp…
Small kinematically-decoupled stellar discs with scalelengths of a few tens of parsec are known to reside in the centre of galaxies. Different mechanisms have been proposed to explain how they form, including gas dissipation and merging of globular clusters. Using archival Hubble Space Telescope imaging and ground-based integral-field spectroscopy, we investigated the structure and stellar populations of the nuclear stellar disc hosted in the interacting SB0 galaxy NGC 1023. The stars of the nuclear disc are remarkably younger and more metal rich with respect to the host bulge. These findings …
In the first few Myr the massive stars dynamically interact, produce runaways and affect the initial binary population. Observing and interpreting the dynamics of young massive clusters is key to our understanding of the star formation process and predicting the outcome of stellar evolution. We have studied NGC6611 in the Eagle Nebula (M16), a young massive cluster hosting 19 O stars. We used Gaia EDR3 data to determine the membership, age, cluster dynamics and the kinematics of the massive stars including runaways. The membership analysis yields 137 members located at a mean distance of 1706 …
NGC 4839 is the brightest galaxy (cD) of the NGC 4839 group at $R\approx 1$ Mpc in the south-west of the Coma cluster, which is known to be falling into Coma. However, it has been controversial whether it is in the first phase of infall or in the second phase of infall after passing the Coma center. We present a wide field study of globular clusters (GCs) in NGC 4839 and its environment based on Hyper Suprime-Cam $gr$ images in the Subaru archive. We compare the GC system of NGC 4839 with that of NGC 4816, which is the brightest member (S0) of the nearby group and lies at a similar distance in…
Astrophysical parameters (age, reddening, distance, radius, luminosity function, mass function, total mass, relaxation time and mass segregation) have been estimated for open clusters NGC 2571, NGC 6802, Koposov 53 and Be 89 by using the Two Micron All Sky Survey (2MASS) photometry. We analyse the color-magnitude diagrams and stellar radial density profiles. We have found that NGC 2571 is the youngest one having young main sequence stars while Be 89 is the oldest cluster.
Recently, Li et al. (2016) claimed to have found evidence for multiple generations of stars in the intermediate age clusters NGC 1783, NGC 1696 and NGC 411 in the Large and Small Magellanic Clouds (LMC/SMC). Here we show that these young stellar populations are present in the field regions around these clusters and are not likely associated with the clusters themselves. Using the same datasets, we find that the background subtraction method adopted by the authors does not adequately remove contaminating stars in the small number Poisson limit. Hence, we conclude that their results do not provi…
We use deep images acquired with the Advanced Camera for Surveys (ACS) on board of the Hubble Space Telescope (HST) in the filters F555W and F814W to characterize the properties of NGC 376, a young star cluster located in the wing of the Small Magellanic Cloud (SMC). Using isochrone fitting we derive for NGC 376 an age of 28+/-7 Myr, in good agreement with previous studies. The high spatial resolution ACS data allow us to determine the center of gravity of the cluster and to construct extended surface brightness and radial density profiles. Neither of these profiles can be fitted with a theore…
The aim of this work is to investigate the characteristics of the young stellar population in the spiral galaxy NGC 247. In particular, we focused our attention in its hierarchical clustering distributions and the properties of the smallest groups. We used multiband Hubble Space Telescope (HST) data from three fields covering more than half of NGC 247 to select the young population. Then, through the path linkage criterion (PLC), we found compact young star groups, and estimated their fundamental parameters, such as their stellar densities, sizes, amount of members and luminosity function (LF)…
We use integrated-light spectroscopic observations to measure metallicities and chemical abundances for two extragalactic young massive star clusters (NGC1313-379 and NGC1705-1). The spectra were obtained with the X-Shooter spectrograph on the ESO Very Large Telescope. We compute synthetic integrated-light spectra, based on colour-magnitude diagrams for the brightest stars in the clusters from Hubble Space Telescope photometry and theoretical isochrones. Furthermore, we test the uncertainties arising from the use of Colour Magnitude Diagram (CMD) +Isochrone method compared to an Isochrone-Only…
We present integrated-light spectra of 8 Young Massive Clusters (YMCs) in the metal-rich spiral galaxy NGC 5236 (M 83). The observations were taken with the X-Shooter spectrograph on the ESO Very Large Telescope. Through the use of theoretical isochrones and synthetic integrated-light (IL) spectra we derive metallicities and study the radial metallicity gradient observed through these young populations. For the inner regions of the galaxy we observe a relatively shallow metallicity gradient of $-$0.37 $\pm$0.29 dex R$_{25}^{-1}$, agreeing with chemical evolution models with an absence of infal…
We analyze spectroscopic observations of five young massive clusters (YMCs) in the barred spiral galaxy NGC 1313 to obtain detailed abundances from their integrated light. Our sample of YMCs was observed with the X-Shooter spectrograph on the Very Large Telescope (VLT). We make use of theoretical isochrones to generate synthetic integrated-light spectra, iterating on the individual elemental abundances until converging on the best fit to the observations. We measure abundance ratios for [Ca/Fe], [Ti/Fe], [Mg/Fe], [Cr/Fe], and [Ni/Fe]. We estimate an Fe abundance gradient of $-$0.124 $\pm$ 0.03…
ALMA observations of CO(1-0) emission in the interacting galaxies IC 2163 and NGC 2207 are used to determine the properties of molecular clouds and their association with star-forming regions observed with the Hubble Space Telescope. Half of the CO mass is in 249 clouds each more massive than 4.0x10^5Mo. The mass distribution functions for the CO clouds and star complexes in a galactic-scale shock front in IC 2163 both have a slope on a log-log plot of -0.7, similar to what is observed in Milky Way clouds. The molecular cloud mass function is steeper in NGC 2207. The CO distribution in NGC 220…
The blue compact dwarf galaxy NGC 5253 hosts a very young central starburst. The center contains intense radio thermal emission from a massive ultracompact H II region (or "supernebula") and two massive and very young super star clusters (SSCs), which are seen at optical and infrared wavelengths. The spatial correspondence between these three objects over an area of < 0.5 arcsec is very uncertain, and it is usually assumed that one of the optically-detected SSCs coincides with the supernebula. Using the Gaia Data Release 2 catalog, we improve the absolute astrometry of Hubble Space Telescope u…
We present high resolution (R = 75,000-100,000) mid-infrared spectra of the high-mass embedded young star IRS 1 in the NGC 7538 star-forming region. Absorption lines from many rotational states of C2H2, 13C12CH2, CH3, CH4, NH3, HCN, HNCO, and CS are seen. The gas temperature, column density, covering factor, line width, and Doppler shift for each molecule are derived. All molecules were fit with two velocity components between -54 and -63 km/s. We find high column densities (~ 10e16 cm^2) for all the observed molecules compared to values previously reported and present new results for CH3 and …
Using the Oxford Short Wavelength Integral Field specTrograph (SWIFT), we trace radial variations of initial mass function (IMF) sensitive absorption features of three galaxies in the Coma cluster. We obtain resolved spectroscopy of the central 5kpc for the two central brightest-cluster galaxies (BCGs) NGC4889, NGC4874, and the BCG in the south-west group NGC4839, as well as unresolved data for NGC4873 as a low-$σ_*$ control. We present radial measurements of the IMF-sensitive features sodium NaI$_{\rm{SDSS}}$, calcium triplet CaT and iron-hydride FeH0.99, along with the magnesium MgI0.88 and …
As a case study to understand the coevolution of Brightest Cluster Galaxies (BCGs) and their host clusters, we investigate the BCGs in dynamically young and old clusters, Abell 1139 (A1139) and Abell 2589 (A2589). We analyze the pixel color-magnitude diagrams (pCMDs) using deep g- and r-band images, obtained from the Canada-France-Hawaii Telescope observations. After masking foreground/background objects and smoothing pixels in consideration of the observational seeing size, detailed pCMD features are compared between the two BCGs. (1) While the overall shapes of the pCMDs are similar to those…
We present a study of the young population in the starburst galaxy NGC 253. In particular, we focused our attention on searching young star groups, obtaining their main properties and studying their hierarchical organization. For this task, we used multiband images and their corresponding photometric data obtained with the Advanced Camera for Surveys of the Hubble Space Telescope (ACS/HST). We have first derived the absorption affecting the different regions of the galaxy. Then, we applied an automatic and objective searching method over the corrected data in order to detect young star groups.…
We have analyzed two epochs of HST/WFPC2 observations of the young Galactic starburst cluster in NGC 3603 with the aim to study its internal dynamics and stellar population. Relative proper motions measured over 10.15 yrs of more than 800 stars enable us to distinguish cluster members from field stars. The best-fitting isochrone yields Av=4.6-4.7 mag, a distance of 6.6-6.9 kpc, and an age of 1 Myr for NGC 3603 Young Cluster (NYC). We identify pre-main-sequence/main-sequence transition stars located in the short-lived radiative-convective gap, which in the NYC occurs in the mass range 3.5-3.8 M…
Currently there are two competing scenarios to explain the origin of the stellar population in globular clusters (GCs). The main difference between them is whether or not multiple events of star formation took place within GCs. In this paper we present the star formation history (SFH) of Cluster 1, a massive young cluster in NGC 34 $(\sim10^7\mbox{ M}_\odot)$. We use DynBaS, a spectrum fitting algorithm, to retrieve the SFH and find that Cluster 1 is consistent with a single stellar population of solar metallicity with an age of $100\pm30$ Myr and a mass of $1.9\pm0.4\times10^7\mbox{ M}_\odot$…
Multiple stellar populations (MPs) representing star-to-star light-element abundance variations are common in nearly all ancient Galactic globular clusters. Here we provide the strongest evidence yet that the populous, ~ 1.7 Gyr-old Large Magellanic Cloud cluster NGC 2173 also exhibits light-element abundance variations. Thus, our results suggest that NGC 2173 is the youngest cluster for which MPs have been confirmed to date. Our conclusion is based on the distinct bifurcation at the tip of its red-giant branch in high-quality color--magnitude diagrams generated from Hubble Space Telescope ima…
Using high-resolution data sets obtained with the Hubble Space Telescope, we investigate the radial distributions of the F-type main-sequence binary fractions in the massive young Large Magellanic Cloud star clusters NGC 1805 and NGC 1818. We apply both an isochrone-fitting approach and chi^2 minimization using Monte Carlo simulations, for different mass-ratio cut-offs, q, and present a detailed comparison of the methods' performance. Both methods yield the same radial binary fraction profile for the same cluster, which therefore supports the robustness and applicability of either method to yo…
We present HK spectra of three sources located in the N66 region of the Small Magellanic Cloud. The sources display prominent stellar Br Gamma and extended H2 emission, and exhibit infrared excesses at lambda > 2 micron. Based on their spectral features, and photometric spectral energy distributions, we suggest that these sources are massive young stellar objects (mYSOs). The findings are interpreted as evidence of on-going high mass star formation in N66.
The recent discovery of double main sequences in the young, massive star cluster NGC 1856 has caught significant attention. The observations can be explained by invoking two stellar generations with different ages and metallicities or by a single generation of stars composed of two populations characterized by different rotation rates. We analyzed the number ratios of stars belonging to both main-sequence components in NGC 1856 as a function of radius. We found that their number ratios remain approximately unchanged from the cluster's central region to its periphery, indicating that both compo…
Recent discoveries have put the picture of stellar clusters being simple stellar populations into question. In particular, the color-magnitude diagrams of intermediate age (1-2 Gyr) massive clusters in the Large Magellanic Cloud (LMC) show features that could be interpreted as age spreads of 100-500 Myr. If multiple generations of stars are present in these clusters then, as a consequence, young (<1 Gyr) clusters with similar properties should have age spreads of the same order. In this paper we use archival Hubble Space Telescope (HST) data of eight young massive LMC clusters (NGC 1831, NGC 1…
Bifurcated patterns of blue straggler stars in their color--magnitude diagrams have atracted significant attention. This type of special (but rare) pattern of two distinct blue straggler sequences is commonly interpreted as evidence of cluster core-collapse-driven stellar collisions as an efficient formation mechanism. Here, we report the detection of a bifurcated blue straggler distribution in a young Large MagellanicCloud cluster, NGC 2173. Because of the cluster's low central stellar number density and its young age, dynamical analysis shows that stellar collisions alone cannot explain the …
A primordial group of open clusters containing NGC 6871 is confirmed and described through Gaia DR3 data and the previous literature. It is a star-forming complex containing at least six young OCs, including Teutsch 8, FSR 198 and Biurakan 2. Two nearby OCs (Casado 82 and Casado-Hendy 1) are newly identified and studied in detail and found to be also members of the cited group. The parameters of the components are sufficiently similar to postulate the case of at least six clusters born from a single GMC. None of the cluster pairs of the group seems to be an authentic binary cluster, with the p…
We present multiwavelength linear polarimetric observations of 104 stars towards the region of young open cluster NGC 6823. The polarization towards NGC 6823 is dominated by foreground dust grains and we found the evidence for the presence of several layers of dust towards the line of sight. The first layer of dust is located approximately within 200 pc towards the cluster, which is much closer to the Sun than the cluster (~ 2.1 kpc). The radial distribution of the position angles for the member stars are found to show a systematic change while the polarization found to reduce towards the oute…
High-resolution spectral analysis is performed for the first time in evolved stars of two young open clusters: NGC 4609 and NGC 5316, of about 80 and 100 Myr in age, respectively, and turn-off masses above 5 Msun. Stellar evolution models predict an extra-mixing event in evolved stars, which follows the first dredge-up and happens later on the red giant branch. However, it is still not understood how this process affects stars of different masses. In this study, we determine abundances of the mixing sensitive elements carbon and nitrogen, carbon isotope 12C/13C ratios, as well as 20 other elem…
Understanding how distinct, near-spherical gas-free clusters of very young, massive stars shape out of vast, complex clouds of molecular hydrogen is one of the biggest challenges in astrophysics. A popular thought dictates that a single gas cloud fragments into many new-born stars which, in turn, energize and rapidly expel the residual gas to form a gas-free cluster. This study demonstrates that the above classical paradigm remarkably reproduces the well-observed central, young cluster (HD 97950) of the Galactic NGC 3603 star-forming region, in particular, its shape, internal motion and the ma…
Aims. We present positions and velocities for 796 planetary nebulae (PNe) in the Fornax Brightest Cluster Galaxy NGC 1316 (Fornax A). The planetary nebulae and existing kinematics are used to explore the rotation of this merger remnant and constrain dynamical models. Methods. Using FORS2 on the VLT, the PN velocities were measured using a counter-dispersed slitless-spectroscopy technique that produced the largest-to-date sample outside of the Local Group. Spherical, non-rotating, constant-anisotropy Jeans models were con- strained by observations of the planetary nebulae and existing integrate…
Images recorded with the Gemini South Adaptive Optics Imager (GSAOI) and corrected for atmospheric seeing by the Gemini Multiconjugate Adaptive Optics System (GeMS) are used to investigate the stellar contents of the young outer Galactic disk clusters Haffner 17, NGC 2401, and NGC 3105. Ages estimated from the faint end of the main sequence (MS) and the ridgeline of the pre-main sequence (PMS) on the (K, J-K) color-magnitude diagrams are consistent with published values that are based on the MS turn-off, with the GSAOI data favoring the younger end of the age range for NGC 2401 in the literatu…
The stellar contents of the open clusters King 12, NGC 7788, and NGC 7790 are investigated using MegaCam images. Comparisons with isochrones yield an age < 20 Myr for King 12, 20--40 Myr for NGC 7788, and 60 -- 80 Myr for NGC 7790 based on the properties of stars near the main sequence turn-off (MSTO) in each cluster. The reddening of NGC 7788 is much larger than previously estimated. The luminosity functions (LFs) of King 12 and NGC 7788 show breaks that are attributed to the onset of pre-main sequence (PMS) objects, and comparisons with models of PMS evolution yield ages that are consistent …
NGC 1980 is a young cluster that is located about 0.5 degrees south of the Orion Nebula Cluster (ONC). Recent studies by Bouy et al. and Pillitteri et al. have suggested that NGC 1980 contains an older population of stars compared to a much younger ONC, and that it belongs to a foreground population that may be located in front of the Orion A molecular gas by as much as 40 pc. In this work we present low-resolution spectra towards 148 young stars found towards the NGC 1980 region. We determine the spectral types of these stars, examine accretion signatures and measure the extinction towards th…
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…
We present the results of an infrared photometric survey performed with NICS@TNG in the nearby starburst galaxy NGC 4214. We derived accurate integrated JK magnitudes of 10 young massive clusters and compared them with the already available Hubble Space Telescope ultraviolet colors. These clusters are located in the combined ultraviolet-infrared colors planes on well defined sequences, whose shapes allow a precise determination of their age. By means of the comparison with suitable stellar evolution models we estimated ages, metallicities, reddening and masses of these clusters. All the analyz…
Nearly all the star clusters with ages of ~1-2 Gyr in both Magellanic Clouds exhibit an extended main-sequence turn off (eMSTO) whose origin is under debate. The main scenarios suggest that the eMSTO could be either due to multiple generations of stars with different ages or to coeval stellar populations with different rotation rates. In this paper we use Hubble-Space-Telescope images to investigate the ~80-Myr old cluster NGC1755 in the LMC. We find that the MS is split with the blue and the red MS hosting about the 25% and the 75% of the total number of MS stars, respectively. Moreover, the …
High-resolution observations in the near infrared show star clusters around the active galactic nucleus (AGN) of the Seyfert 1 NGC2110, along with a 90 x 35 pc bar of shocked gas material around its nucleus. These are seen for the first time in our imaging and gas kinematics of the central 100pc with the Keck OSIRIS instrument with adaptive optics. Each of these clusters is 2-3 times brighter than the Arches cluster close to the centre of the Milky Way. The core star formation rate (SFR) is 0.3 M$_\odot$/yr. The photoionized gas (He I) dynamics imply an enclosed mass of 3-4 x 10$^8$ M$_\odot$.…
