| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Adamo, Angela, et al.
(författare)
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HIGH-RESOLUTION STUDY OF THE CLUSTER COMPLEXES IN A LENSED SPIRAL AT REDSHIFT 1.5 : CONSTRAINTS ON THE BULGE FORMATION AND DISK EVOLUTION
- 2013
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 766:2, s. 105-
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the clump population of the spiral galaxy Sp 1149 at redshift 1.5. Located behind the galaxy cluster MACS J1149.5+2223, Sp 1149 has been significantly magnified allowing us to study the galaxy on physical scales down to similar to 100 pc. The galaxy cluster frame is among the targets of the Cluster Lensing And Supernova survey with Hubble (CLASH), an ongoing Hubble Space Telescope (HST) Multi-Cycle Treasury program. We have used the publicly available multi-band imaging data set to reconstruct the spectral energy distributions of the clumps in Sp 1149, and derive, by means of stellar evolutionary models, their physical properties. We found that 40% of the clumps observed in Sp 1149 are older than 30 Myr and can be as old as 300 Myr. These are also the more massive (luminous) clumps in the galaxy. Among the complexes in the local reference sample, the star-forming knots in luminous blue compact galaxies could be considered progenitor analogs of these long-lived clumps. The remaining 60% of clumps have colors comparable to local cluster complexes, suggesting a similar young age. We observe that the Sp 1149 clumps follow the M proportional to R-2 relation similar to local cluster complexes, suggesting similar formation mechanisms although they may have different initial conditions (e.g., higher gas surface densities). We suggest that the galaxy is experiencing a slow decline in star formation rate and a likely transitional phase toward a more quiescent star formation mode. The older clumps have survived between 6 and 20 dynamical times and are all located at projected distances smaller than 4 kpc from the center. Their current location suggests migration toward the center and the possibility of being the building blocks of the bulge. On the other hand, the dynamical timescale of the younger clumps is significantly shorter, meaning that they are quite close to their birthplace. We show that the clumps of Sp 1149 may account for the expected metal-rich globular cluster population usually associated with the bulge and thick disk components of local spirals.
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| 3. |
- Adamo, Angela, et al.
(författare)
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Legacy ExtraGalactic UV Survey with The Hubble Space Telescope : Stellar Cluster Catalogs and First Insights Into Cluster Formation and Evolution in NGC 628
- 2017
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Ingår i: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 841:2
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Tidskriftsartikel (refereegranskat)abstract
- We report the large effort that is producing comprehensive high-level young star cluster (YSC) catalogs for a significant fraction of galaxies observed with the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program. We present the methodology developed to extract cluster positions, verify their genuine nature, produce multiband photometry (from NUV to NIR), and derive their physical properties via spectral energy distribution fitting analyses. We use the nearby spiral galaxy NGC 628 as a test case for demonstrating the impact that LEGUS will have on our understanding of the formation and evolution of YSCs and compact stellar associations within their host galaxy. Our analysis of the cluster luminosity function from the UV to the NIR finds a steepening at the bright end and at all wavelengths suggesting a dearth of luminous clusters. The cluster mass function of NGC 628 is consistent with a power-law distribution of slopes similar to-2 and a truncation of a few times 10(5) M-circle dot. After their formation, YSCs and compact associations follow different evolutionary paths. YSCs survive for a longer time frame, confirming their being potentially bound systems. Associations disappear on timescales comparable to hierarchically organized star-forming regions, suggesting that they are expanding systems. We find massindependent cluster disruption in the inner region of NGC 628, while in the outer part of the galaxy there is little or no disruption. We observe faster disruption rates for low mass (<= 10(4) M-circle dot) clusters, suggesting that a massdependent component is necessary to fully describe the YSC disruption process in NGC 628.
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| 4. |
- Adamo, Angela, et al.
(författare)
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On the Origin of the Red Excess in Very Young Super Star Clusters : The Case of SBS 0335-052E
- 2010
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 725:2, s. 1620-1628
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Tidskriftsartikel (refereegranskat)abstract
- The spectral energy distribution analysis of very young unresolved star clusters challenges our understanding of the cluster formation process. Studies of resolved massive clusters in the Milky Way and in the nearby Magellanic Clouds show us that the contribution from photoionized gas is very important during the first Myr of cluster evolution. We present our models which include both a self-consistent treatment of the photoionized gas and the stellar continuum and quantify the impact of such a nebular component on the total flux of young unresolved star clusters. A comparison with other available models is considered. The very young star clusters in the SBS 0335-052E dwarf starburst galaxy are used as a test for our models. Due to the low metallicity of the galactic medium our models predict a longer lasted nebular phase which contributes between 10% and 40% of the total near-infrared (NIR) fluxes at around 10 Myr. We thus propose a possible solution for the observed flux excess in the six bright super star clusters (SSCs) of SBS 0335-052E. Reines et al. showed that the observed cluster fluxes, in the red-optical and NIR range, sit irreconcilably above the stellar continuum models provided. We find that in the age range estimated from the Hα emission we can explain the red excess in all six SSCs as due to nebular emission, which at cluster ages around 10 Myr still affects the NIR wavebands substantially.
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| 5. |
- Adamo, Angela, et al.
(författare)
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Probing cluster formation under extreme conditions : massive star clusters in blue compact galaxies
- 2011
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 417:3, s. 1904-1912
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Tidskriftsartikel (refereegranskat)abstract
- The numerous and massive young star clusters in blue compact galaxies (BCGs) are used to investigate the properties of their hosts. We test whether BCGs follow claimed relations between cluster populations and their hosts, such as the fraction of the total luminosity contributed by the clusters as function of the mean star formation rate (SFR) density, the V-band luminosity of the brightest youngest cluster as related to the mean host SFR and the cluster formation efficiency (i.e. the fraction of star formation happening in star clusters) versus the density of the SFR. We find that BCGs follow the trends, supporting a scenario where cluster formation and environmental properties of the host are correlated. They occupy, in all the diagrams, the regions of higher SFRs, as expected by the extreme nature of the starbursts operating in these systems. We find that the star clusters contribute almost to the 20 per cent of the UV luminosity of the hosts. We suggest that the BCG starburst environment has most likely favoured the compression and collapse of the giant molecular clouds, enhancing the local star formation efficiency, so that massive clusters have been formed. The estimated cluster formation efficiency supports this scenario. BCGs have a cluster formation efficiency comparable to luminous IR galaxies and spiral starburst nuclei (the averaged value is similar to 35 per cent) which is much higher than the 8-10 per cent reported for quiescent spirals and dwarf star-forming galaxies.
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| 6. |
- Adamo, Angela, et al.
(författare)
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Probing Cluster Formation under Extreme Conditions: Super Star Clusters in Blue Compact Galaxies
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The numerous and massive young star clusters in blue compact galaxies (BCG) are used to investigate the properties of their hosts. We test whether BCGs follow claimed relations between the cluster population and their hosts, such as the cluster specific luminosity in the U band, TL(U), and the star formation rate density ΣSFR; the V bandluminosity of the brightest youngest cluster, Mbrightest, and the mean star formation Vrate (SFR); the cluster formation efficiency versus the ΣSFR. We find that BCGs fairly well reproduce the relations, supporting a scenario where cluster formation and environmental properties of the host are correlated. They occupy, in all the diagrams, the regions of higher SFRs, suggesting the extreme nature of the starburst operating in these systems. We suggest that the BCG environment has most likely favoured the compression and collapse of the giant molecular clouds, enhancing the local star formation efficiency, so that massive clusters have been formed. The cluster formation efficiency (i.e., the fraction of star formation happening in star clusters) in BCGs is higher than the 8-10 % reported from quiescent spirals and dwarf starburst galaxies. BCGs have a cluster formation efficiency comparable to luminous IR galaxies and spiral starburst nuclei (the averaged value is ∼ 30 %).
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| 7. |
- Adamo, Angela, et al.
(författare)
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Probing the near-IR flux excess in young star clusters
- 2011
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Konferensbidrag (refereegranskat)abstract
- We report the results of a recent study of young star clusters (YSCs) in luminous blue compact galaxies (BCGs). The age distributions of the YSCs suggest that the starburst episode in Haro 11, ESO 185-IG13, and Mrk 930 started not more than 30-40 Myr ago. A peak of cluster formation only 3 - 4 Myr old is observed, unveiling a unique sample of clusters still partially embedded. A considerable fraction of clusters (30 - 50%), mainly younger than 10 Myr, shows an observed flux excess between 0.8 and 2.2 micron. This so-called near-infrared (NIR) excess is impossible to reproduce even with the most recent spectral synthesis models (that include a self-consistent treatment of the photoionized gas). We have used these YSCs to probe the very early evolution phase of star clusters. In all the three host galaxies, the analysis is limited to the optically brightest objects, i.e., systems that are only partially embedded by their natal cocoons (since deeply embedded clusters are probably too faint to be detected). We discuss possible explanations for this NIR excess, in the context of IR studies of both extragalactic young star clusters and resolved massive star forming regions in the Milky Way and in the nearby Magellanic Clouds.
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| 8. |
- Adamo, Angela, et al.
(författare)
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Probing the role of the galactic environment in the formation of stellar clusters, using M83 as a test bench
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 452:1, s. 246-260
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of the M83 cluster population, covering the disc of the galaxy between radii of 0.45 and 4.5 kpc. We aim to probe the properties of the cluster population as a function of distance from the galactic centre. We observe a net decline in cluster formation efficiency (Gamma, i.e. amount of star formation happening in bound clusters) from about 26 per cent in the inner region to 8 per cent in the outer part of the galaxy. The recovered Gamma values within different regions of M83 follow the same Gamma versus star formation rate density relation observed for entire galaxies. We also probe the initial cluster mass function (ICMF) as a function of galactocentric distance. We observe a significant steepening of the ICMF in the outer regions (from -1.90 +/- 0.11 to -2.70 +/- 0.14) and for the whole galactic cluster population (slope of -2.18 +/- 0.07) of M83. We show that this change of slope reflects a more fundamental change of the 'truncation mass' at the high-mass end of the distribution. This can be modelled as a Schechter function of slope -2 with an exponential cutoff mass (M-c) that decreases significantly from the inner to the outer regions (from 4.00 to 0.25 x 10(5) M-circle dot) while the galactic M-c is approximate to 1.60 x 10(5) M-circle dot. The trends in Gamma and ICMF are consistent with the observed radial decrease of the Sigma (H-2), hence in gas pressure. As gas pressure declines, cluster formation becomes less efficient. We conclude that the host galaxy environment appears to regulate (1) the fraction of stars locked in clusters and (2) the upper mass limit of the ICMF, consistently described by a near-universal slope -2 truncated at the high-mass end.
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| 9. |
- Adamo, Angela, et al.
(författare)
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Star cluster formation and evolution in Mrk 930 : properties of a metal-poor starburst
- 2011
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 415:3, s. 2388-2406
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Tidskriftsartikel (refereegranskat)abstract
- We present the analysis of the large population of star clusters in the blue compact galaxy (BCG) Mrk 930. The study has been conducted by means of a photometric analysis of multiband data obtained with the Hubble Space Telescope (HST). We have reconstructed the spectral energy distributions of the star clusters and estimated the age, mass and extinction for a representative sample. Similar to previous studies of star clusters in BCGs, we observe a very young cluster population with 70 per cent of the systems formed less than 10 Myr ago. In Mrk 930, the peak in the star cluster age distribution at 4 Myr is corroborated by the presence of Wolf-Rayet spectral features, and by the observed optical and infrared (IR) line ratios [OIII]/H beta and [Ne III]/[Ne II]. The recovered extinction in these very young clusters shows large variations, with a decrease at older ages. It is likely that our analysis is limited to the optically brightest objects (i.e. systems only partially embedded in their natal cocoons; the deeply embedded clusters being undetected). We map the extinction across the galaxy using low-resolution spectra and the H alpha-to-H beta ratio, as obtained from ground-based narrow band imaging. These results are compared with the extinction distribution recovered from the clusters. We find that the mean optical extinction derived in the starburst regions is close to the averaged value observed in the clusters [more than 80 per cent of the systems have E(B - V) <= 0.2mag], but locally, do not trace the more extinguished clusters. Previous HST studies of BCGs have revealed a population of young and extremely red super star clusters. We detect a considerable fraction of clusters affected by a red excess also in Mrk 930. The nature of the red excess, which turns up at near-IR wavelengths (I band and longwards), remains unknown. We compare the cluster formation history and the star formation history, the latter derived from the fit of spectral population synthesis models to the spectra. We find a general agreement between the two independently estimated quantities. Using the cluster properties, we perform a study of the host environmental properties. We find that the cluster formation efficiency (the fraction of star formation happening in clusters) is significantly higher, suggesting a key role of the environment for the formation of these massive objects.
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| 10. |
- Adamo, Angela, et al.
(författare)
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Star cluster formation in the most extreme environments: Insights from the HiPEEC survey
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 499:3, s. 3267-3294
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Tidskriftsartikel (refereegranskat)abstract
- We present the Hubble imaging Probe of Extreme Environments and Clusters (HiPEEC) survey. We fit HST NUV to NIR broad-band and H α fluxes to derive star cluster ages, masses, and extinctions and determine the star formation rate (SFR) of six merging galaxies. These systems are excellent laboratories to trace cluster formation under extreme gas physical conditions, rare in the local Universe, but typical for star-forming galaxies at cosmic noon. We detect clusters with ages of 1-500 Myr and masses that exceed 107 M☉. The recent cluster formation history and their distribution within the host galaxies suggest that systems such as NGC 34, NGC 1614, and NGC 4194 are close to their final coalescing phase, while NGC 3256, NGC 3690, and NGC 6052 are at an earlier/intermediate stage. A Bayesian analysis of the cluster mass function in the age interval 1-100 Myr provides strong evidence in four of the six galaxies that an exponentially truncated power law better describes the observed mass distributions. For two galaxies, the fits are inconclusive due to low number statistics. We determine power-law slopes β ∼ −1.5 to −2.0 and truncation masses, Mc, between 106 and a few times 107 M☉, among the highest values reported in the literature. Advanced mergers have higher Mc than early/intermediate merger stage galaxies, suggesting rapid changes in the dense gas conditions during the merger. We compare the total stellar mass in clusters to the SFR of the galaxy, finding that these systems are among the most efficient environments to form star clusters in the local Universe.
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