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?Integrated absolute magnitude in V Band, MV, vs. MASSCLEAN-derived log?(age/yr) for 920 LMC clusters. The integrated magnitudes are from Hunter et al. (2003) catalog. Dot color and size are further scaled with MASSCLEAN-derived mass. The color scale presented below the plot magnifies the 0?5000?M? range. The mean error is given in the lower right corner.
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We present new age and mass estimates for 920 stellar clusters in the Large Magellanic Cloud (LMC) based on previously published broadband photometry and the stellar cluster analysis package, MASSCLEANage. Expressed in the generic fitting formula, d
2N/dMdt?M
?t
?, the distribution of observed clusters is described by ? = ?1.5 to ?1.6 and ? = ?2.1...
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Context 1
... another representation of the LMC cluster sample is given in Figure 4. Here, we show the integrated magnitudes M V versus log(age/yr). ...
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Citations
... Finally, assuming a mass-to-light ratio (M/L V ) of ∼0.5-1, as appropriate for such a young stellar population (Maraston 1998), the total mass is M ∼ 80-160 M e , compatible with that of a low-mass open cluster (e.g., Piskunov et al. 2008). This value is two to four times smaller than that derived by Popescu et al. (2012), likely because of the different data sets, background decontamination procedure, and mass estimate technique adopted there. ...
In the context of a project aimed at characterizing the dynamical evolution of old globular clusters in the Large Magellanic Cloud, we have secured deep HST/WFC3 images of the massive cluster NGC 1835. In the field of view of the acquired images, at a projected angular separation of approximately 2′ from the cluster, we detected the small stellar system KMK 88-10. The observations provided the deepest color–magnitude diagram ever obtained for this cluster, revealing that it hosts a young stellar population with an age of 600–1000 Myr. The cluster surface brightness profile is nicely reproduced by a King model with a core radius r c = 4″ (0.97 pc), a half-mass radius r hm = 12″ (2.9 pc), and a concentration parameter c ∼ 1.3 corresponding to a truncation radius r t ∼ 81″ (19.5 pc). We also derived its integrated absolute magnitude ( M V = −0.71) and total mass ( M ∼ 80–160 M ⊙ ). The most intriguing feature emerging from this analysis is that KMK 88-10 presents a structure elongated in the direction of NGC 1835, with an intracluster overdensity that suggests the presence of a tidal bridge between the two systems. If confirmed, this would be the first evidence of a tidal capture of a small star cluster by a massive globular.
... The bias also decreases at low ages t < 5 Myr (see fig. 7 in Piskunov at al. 2011). The use of various methods for determining ages in the range of 5 − 10 Myr gives results that differ by an order of magnitude or more (see, e.g., Kim et al. 2012;Popescu, Hanson & Elmegreen 2012;Messa et al. 2018). ...
We present the results of a study of young unresolved stellar groupings (clusters, OB associations, and their complexes) associated with HII regions, based on the coupling of spectroscopic, photometric and H{\alpha} spectrophotometric observations of star formation regions. Along with our own observations, we use a part of the spectroscopic and H{\alpha} data from the literature and open databases. The study is based on the catalogue of 1510 star formation regions with ages ~10-20 Myr in 19 spiral galaxies, compiled by us earlier. We study the morphology of stellar groupings and their relation with the associated H{\alpha} emission region. Extinctions, gas chemical abundances, and sizes of star formation regions are measured. Using numerical SSP models computed for metallicities fixed from observations to intrinsic colours of the studied star formation regions, we estimated ages and masses of stellar population of 400 young stellar groupings. Different relations between observational and physical parameters of the young stellar population in star formation regions are discussed.
... Piskunov et al. 2008). This value is 2-4 times smaller than that derived by Popescu et al. (2012), likely because of the different data-sets, background decontamination procedure, and mass estimate technique adopted there. ...
In the context of a project aimed at characterizing the dynamical evolution of old globular clusters in the Large Magellanic Cloud, we have secured deep HST/WFC3 images of the massive cluster NGC 1835. In the field of view of the acquired images, at a projected angular separation of approximately 2 arcmin from the cluster, we detected the small stellar system KMK88-10. The observations provided the deepest color-magnitude diagram ever obtained for this cluster, revealing that it hosts a young stellar population with an age of 600-1000 Myr. The cluster surface brightness profile is nicely reproduced by a King model with a core radius rc = 4 arcsec (0.97 pc), an half-mass radius rhm = 12 arcsec (2.9 pc), and a concentration parameter c~1.3 corresponding to a truncation radius rt~81 arcsec (19.5 pc). We also derived its integrated absolute magnitude (MV=-0.71) and total mass (M~80-160 Msun). The most intriguing feature emerging from this analysis is that KMK88-10 presents a structure elongated in the direction of NGC 1835, with an intracluster over-density that suggests the presence of a tidal bridge between the two systems. If confirmed, this would be the first evidence of a tidal capture of a small star cluster by a massive globular.
... The OB association LH75, or NGC 2011, has been studied as a cluster using either integrated cluster photometry or resolved stellar photometry. Its age determined from integrated photometry ranges from ∼5 Myr (Hunter et al. 2003) to 14 Myr (Popescu et al. 2012), while its age determined from CMDs of resolved stars is higher, 20 Myr (Kumar et al. 2008) or 25 Myr (Glatt et al. 2010). ...
The supernova remnant (SNR) B0532−67.5 in the Large Magellanic Cloud (LMC) was first diagnosed by its nonthermal radio emission, and its SNR nature was confirmed by the observation of diffuse X-ray emission; however, no optical SNR shell is detected. The OB association LH75, or NGC 2011, is projected within the boundary of this SNR. We have analyzed the massive star population in and around SNR B0532−67.5 using optical photometric data to construct color–magnitude diagrams, using stellar evolutionary tracks to estimate stellar masses, and using isochrones to assess the stellar ages. From these analyses, we find a 20–25 Myr population in LH75 and a younger population less than 10 Myr old to the southwest of LH75. The center of SNR B0532−67.5 is located closer to the core of LH75 than to the massive stars to its southwest. We conclude that the supernova progenitor was probably a member of LH75 with an initial mass of ∼15 M ⊙ . The supernova exploded in an H i cavity excavated by the energy feedback of LH75. The low density of the ambient medium prohibits the formation of a visible nebular shell. Despite the low density in the ambient medium, physical properties of the hot gas within the SNR interior do not differ from SNRs with a visible shell by more than a factor of 2–3. The large-scale H i map shows that SNR B0532−67.5 is projected in a cavity that appears to be connected with the much larger cavity of the supergiant shell LMC-4.
... The OB association LH75, or NGC 2011, has been studied as a cluster using either integrated cluster photometry or resolved stellar photometry. Its age determined from integrated photometry ranges from ∼5 Myr (Hunter et al. 2003) to 14 Myr (Popescu et al. 2012), while its age determined from CMDs of resolved stars is higher, 20 Myr (Kumar et al. 2008) or 25 Myr (Glatt et al. 2010). ...
The supernova remnant (SNR) B0532$-$67.5 in the Large Magellanic Cloud (LMC) was first diagnosed by its nonthermal radio emission and its SNR nature was confirmed by diffuse X-ray emission; however, no optical SNR shell is detected. The OB association LH75, or NGC 2011, is projected within the boundary of this SNR. We have analyzed the massive star population in and around SNR B0532$-$67.5: using optical photometric data to construct color-magnitude diagrams (CMDs), using stellar evolutionary tracks to estimate stellar masses, and using isochrones to assess the stellar ages. From these analyses, we find a 20-25 Myr population in LH75 and a younger population less than 10 Myr old to the southwest of LH75. The center of SNR B0532$-$67.5 is located closer to the core of LH75 than the massive stars to its southwest. We conclude that the SN progenitor was probably a member of LH75 with an initial mass $\sim$15 $M_\odot$. The SN exploded in an H I cavity excavated by the energy feedback of LH75. The low density of the ambient medium prohibits the formation of a visible nebular shell. Despite the low density in the ambient medium, physical properties of the hot gas within the SNR interior do not differ from SNRs with a visible shell by more than a factor of 2-3. The large-scale H I map shows that SNR B0532$-$67.5 is projected in a cavity that appears to be connected with the much larger cavity of the supergiant shell LMC-4.
... To perform this test, we use the catalog of LMC clusters compiled by Baumgardt et al. (2013) and only include the 296 systems inside the HZ09 area. Baumgardt et al. (2013) compiled ages and masses for these clusters measured using either isochrone fitting or broadband spectral energy distribution fitting of data obtained by previous surveys (Pietrzynski & Udalski 2000;Hunter et al. 2003;Mackey & Gilmore 2003;de Grijs & Anders 2006;Milone et al. 2009;Glatt et al. 2010;Popescu et al. 2012). We determine the cluster radii, r c , from their major axis (a) and minor axis (b) reported in Bica et al. (2008) as Bica et al. (2008) note that these are "apparent" sizes (measured as far as the background limit in the images), but they most likely enclose the majority of the cluster mass. ...
The delay-time distribution (DTD) is the occurrence rate of a class of objects as a function of time after a hypothetical burst of star formation. DTDs are mainly used as a statistical test of stellar evolution scenarios for supernova progenitors, but they can be applied to many other classes of astronomical objects. We calculate the first DTD for RR Lyrae variables using 29,810 RR Lyrae from the OGLE-IV survey and a map of the stellar age distribution (SAD) in the Large Magellanic Cloud (LMC). We find that ∼46% of the OGLE-IV RR Lyrae are associated with delay times greater than 8 Gyr (main-sequence progenitor masses less than 1 M o˙), and consistent with existing constraints on their ages, but surprisingly about 51% of RR Lyrae appear to have delay times of 1.2-8 Gyr (main-sequence masses between 1 and 2 M o˙ at LMC metallicity). This intermediate-age signal also persists outside the Bar region, where crowding is less of a concern, and we verified that without this signal the spatial distribution of the OGLE-IV RR Lyrae is inconsistent with the SAD map of the LMC. Since an intermediate-age RR Lyrae channel is in tension with the lack of RR Lyrae in intermediate-age clusters (noting issues with small-number statistics), and noting the age-metallicity constraints on LMC stars, our DTD result possibly indicates that systematic uncertainties may still exist in SAD measurements of old stellar populations, perhaps stemming from the construction methodology or the stellar evolution models used. We describe tests to further investigate this issue. © 2021. The American Astronomical Society. All rights reserved..
... To perform this test, we use the catalog of LMC clusters compiled by Baumgardt et al. (2013) and only include the 296 systems inside the HZ09 area. Baumgardt et al. (2013) compiled ages and masses for these clusters measured using either isochrone fitting or broadband spectral energy distribution fitting of data obtained by previous surveys (Pietrzynski & Udalski 2000;Hunter et al. 2003;Mackey & Gilmore 2003;de Grijs & Anders 2006;Milone et al. 2009;Glatt et al. 2010;Popescu et al. 2012). We determine the cluster radii, r c from their major (a) and minor axes (b) reported in Bica et al. (2008) as r c = (a + b)/4. ...
The delay-time distribution (DTD) is the occurrence rate of a class of objects as a function of time after a hypothetical burst of star formation. DTDs are mainly used as a statistical test of stellar evolution scenarios for supernova progenitors, but they can be applied to many other classes of astronomical objects. We calculate the first DTD for RR Lyrae variables using 29,810 RR Lyrae from the OGLE-IV survey and a map of the stellar-age distribution (SAD) in the Large Magellanic Cloud (LMC). We find that $\sim 46\%$ of the OGLE-IV RR Lyrae are associated with delay-times older than 8 Gyr (main-sequence progenitor masses less than 1 M$_{\odot}$), and consistent with existing constraints on their ages, but surprisingly about $51\%$ of RR Lyrae appear have delay times $1.2-8$ Gyr (main-sequence masses between $1 - 2$ M$_{\odot}$ at LMC metallicity). This intermediate-age signal also persists outside the Bar-region where crowding is less of a concern, and we verified that without this signal, the spatial distribution of the OGLE-IV RR Lyrae is inconsistent with the SAD map of the LMC. Since an intermediate-age RR Lyrae channel is in tension with the lack of RR Lyrae in intermediate-age clusters (noting issues with small-number statistics), and the age-metallicity constraints of LMC stars, our DTD result possibly indicates that systematic uncertainties may still exist in SAD measurements of old-stellar populations, perhaps stemming from the construction methodology or the stellar evolution models used. We described tests to further investigate this issue.
... The effects of stochastic fluctuations on photometric observations of star clusters have been studied by several teams (e.g., Lançon & Mouhcine 2000;Cerviño & Luridiana 2004Piskunov et al. 2009;Popescu & Hanson 2009;Popescu et al. 2012;Fouesneau & Lançon 2010;Fouesneau et al. 2012Fouesneau et al. , 2014Krumholz et al. 2015Krumholz et al. , 2019. These studies have shown that the predicted colour distributions depend strongly on the cluster mass (especially in the near-IR regime) and that they can be significantly non-Gaussian, even for cluster masses exceeding 10 5 . ...
In this second paper of a series on the accuracy and precision of the determination of age and metallicity of simple stellar populations (SSPs) by means of the full spectrum fitting technique, we study the influence of star cluster mass through stochastic fluctuations of the number of stars near the top of the stellar mass function, which dominate the flux in certain wavelength regimes depending on the age. We consider SSP models based on the Padova isochrones, spanning the age range 7.0 $\leq$ log (age/yr) $\leq$ 10.1. Simulated spectra of star clusters in the mass range $10^4 \leq M/M_{\odot} < 10^6$ are compared with SSP model spectra to determine best-fit ages and metallicities using a full-spectrum fitting routine in four wavelength regimes: the blue optical (0.35-0.70 $\mu$m), the red optical (0.6-1.0 $\mu$m), the near-IR (1.0-2.5 $\mu$m), and the mid-IR (2.5-5.0 $\mu$m). We compare the power of each wavelength regime in terms of both the overall precision of age and metallicity determination, and of its dependence on cluster mass. We also study the relevance of spectral resolution in this context by utilizing two different spectral libraries (BaSeL and BT-Settl). We highlight the power of the mid-IR regime in terms of identifying young massive clusters in dusty star forming regions in external galaxies. The spectra of the simulated star clusters and SSPs are made available online to enable follow-up studies by the community.
... We note that the CMD of KMK88 49, not shown in Figure 2, is marginally different from that of field stars in the same area. From the analysis of its integrated colors, Piatti (2017) estimated an age of 500 Myr, while the total mass is estimated by Popescu et al. (2012) to be around 800 M e , also from integrated colors. ...
... For these parameters, the model predicts an ICMF with a low-mass truncation M min = 1.1 × 10 2 M and a maximum cluster mass M max = 4.5 × 10 4 M . fig. 16 of Popescu et al. (2012) for each age bin. The model is normalized to contain the same integrated number of clusters as the observations for each of the two age ranges. ...
... The model is normalized to contain the same integrated number of clusters as the observations for each of the two age ranges. Popescu et al. (2012) observe clusters in the LMC down to the lowest masses available for extragalactic objects, i.e. M ∼ 10 2.6 M for cluster ages <10 Myr. ...
... The solid line and shaded band show the mean and 2.5-97.5 percentile range of Monte Carlo samples drawn from the predicted ICMF, respectively. The points we obtained from the cluster catalogue by Popescu, Hanson & Elmegreen (2012). Open symbols denote clusters below the completeness limit set by the effect of fading. ...
We present a simple physical model for the minimum mass of bound stellar clusters as a function of the galactic environment. The model evaluates which parts of a hierarchically clustered star-forming region remain bound given the time-scales for gravitational collapse, star formation, and stellar feedback. We predict the initial cluster mass functions (ICMFs) for a variety of galaxies and we show that these predictions are consistent with observations of the solar neighbourhood and nearby galaxies, including the Large Magellanic Cloud and M31. In these galaxies, the low minimum cluster mass of ∼102 M⊙ is caused by sampling statistics, representing the lowest mass at which massive (feedback-generating) stars are expected to form. At the high gas density and shear found in the Milky Way’s Central Molecular Zone and the nucleus of M82, the model predicts that a mass >102 M⊙ must collapse into a single cluster prior to feedback-driven dispersal, resulting in narrow ICMFs with elevated characteristic masses. We find that the minimum cluster mass is a sensitive probe of star formation physics due to its steep dependence on the star formation efficiency per free-fall time. Finally, we provide predictions for globular cluster (GC) populations, finding a narrow ICMF for dwarf galaxy progenitors at high redshift, which can explain the high specific frequency of GCs at low metallicities observed in Local Group dwarfs like Fornax and WLM. The predicted ICMFs in high-redshift galaxies constitute a critical test of the model, ideally suited for the upcoming generation of telescopes.
