Young Star Cluster Candidates Research Articles

The Age Dependence of Mid-infrared Emission around Young Star Clusters

Abstract Using the star cluster catalogs from the Hubble Space Telescope program Legacy Extragalactic UV survey (LEGUS) and 8 μm images from the IRAC camera on the Spitzer Space Telescope for five galaxies within 5 Mpc, we investigate how the 8 μm dust luminosity correlates with the stellar age on the 30–50 pc scale of star-forming regions. We construct a sample of 97 regions centered at local peaks of 8 μm emission, each containing one or more young star cluster candidates from the LEGUS catalogs. We find a tight anticorrelation with a Pearson correlation coefficient of r = −0.84 ± 0.05 between the mass-normalized dust-only 8 μm luminosity and the age of stellar clusters younger than 1 Gyr; the 8 μm luminosity decreases with increasing age of the stellar population. Simple assumptions on a combination of stellar and dust emission models reproduce the observed trend. We also explore how the scatter of the observed trend depends on assumptions of stellar metallicity, polycyclic aromatic hydrocarbon (PAH) abundance, fraction of stellar light absorbed by dust, and instantaneous versus continuous star formation models. We find that variations in stellar metallicity have little effect on the scatter, while PAH abundance and the fraction of dust-absorbed light bracket the full range of the data. We also find that the trend is better explained by continuous star formation, rather than instantaneous burst models. We ascribe this result to the presence of multiple star clusters with different ages in many of the regions. Upper limits of the dust-only 8 μm emission as a function of age are provided.

Globular clusters in the stellar stream surrounding the Milky Way analogue NGC 5907

ABSTRACT We study the globular clusters (GCs) in the spiral galaxy NGC 5907 well-known for its spectacular stellar stream – to better understand its origin. Using wide-field Subaru/Suprime-Cam gri images and deep Keck/DEIMOS multi-object spectroscopy, we identify and obtain the kinematics of several GCs superimposed on the stellar stream and the galaxy disc. We estimate the total number of GCs in NGC 5907 to be 154 ± 44, with a specific frequency of 0.73 ± 0.21. Our analysis also reveals a significant, new population of young star cluster candidates found mostly along the outskirts of the stellar disc. Using the properties of the stream GCs, we estimate that the disrupted galaxy has a stellar mass similar to the Sagittarius dwarf galaxy accreted by the Milky Way, i.e. $\sim 10^8~\rm M_\odot$.

Imaging of star clusters in unperturbed spiral galaxies with the Advanced Camera for Surveys

We present results from ACS and WFPC observations in the low luminosity galaxy NGC 45. We identified 28 young star cluster candidates. While the exact values of age, mass, and extinction depend somewhat on the choice of SSP models, we find no young clusters with masses higher than a few 1000 Msun for any model choice. We derive the luminosity function of young star clusters and find a slope of alpha=-1.94+-0.28. We also identified 19 old globular clusters and we estimate a specific frequency of globular clusters of S_N=1.4-1.9 which is significantly higher than observed for other late-type galaxies (e.g. SMC, LMC, M33). Most of these globular clusters appear to belong to a metal-poor population, although they coincide spatially with the location of the bulge of NGC 45.

New nearby young star cluster candidates within 200 pc

AbstractI briefly describe two new young star cluster candidates found within 200 pc of the Sun, associated with the 4th-magnitude stars μ Oph and 32 Ori. The μ Oph group (d ≃ 170pc) has a space motion and age (~120± 25 Myr) suspiciously similar to the Pleiades, but lies in the opposite side of the sky behind ~0.9 mag of visual extinction in Ophiuchus. The 32 Ori group is a nearby (d ≃ 90 pc) loose aggregate of ~25-Myr-old post-T Tauri stars co-moving with the massive binary 32 Ori (B5V+B7V) in northern Orion. The 32 Ori group accounts for part of the population of “isolated” Li-rich RASS pre-MS stars in northern Orion.

The nearest extreme starburst: bubbles, young star clusters and outflow in the merger NGC 3256

We have studied the extreme starburst in the infrared merger NGC 3256. We detect four galactic bubbles (using ESO New Technology Telescope and Hubble Space Telescope WFPC2 Hα images). These shells would be associated with previous supernova explosions. The first analysis of the spatial distribution of young star cluster candidates shows that more than 90 per cent of them are located in a complex starburst structure, including some of the bubble walls, three nuclei and three blue asymmetrical spiral arms. We have made a kinematic study of the ionized gas in the core of the main optical nucleus, performed with HST STIS spectra. The shape of the rotation curve and the emission-line profile can be explained by the presence in the core of young star clusters with outflow. Any low-luminosity active galactic nucleus associated with this core would have a mass less than 107 M⊙. It is also probable that the compact X-ray and radio emission of ULX(7)N – the source coincident with the main optical nucleus – is the result of a few recent supernova remnants.

E+A Galaxies and the Formation of Early‐Type Galaxies atz ∼ 0

E+A galaxies, whose spectra have deep Balmer absorption lines but no significant [O II] emission, are the best candidates for an evolutionary link between star-forming, gas-rich galaxies and quiescent, gas-poor galaxies. However, their current morphologies are not well known. We present Hubble Space Telescope WFPC2 observations of the five bluest E+A galaxies (z ~ 0.1) in the sample of Zabludoff and coworkers to study whether their detailed morphologies are consistent with late- to early-type evolution and to determine what drives that evolution. The morphologies of four galaxies are disturbed, indicating that a galaxy-galaxy merger is at least one mechanism that leads to the E+A phase. Two-dimensional image fitting shows that the E+As are generally bulge-dominated systems, even though at least two E+As may have underlying disks. In the fundamental plane, E+As stand apart from the E/S0 galaxies mainly because of their high effective surface brightness. Fading of the young stellar population and the corresponding increase in their effective radii will cause these galaxies to migrate toward the locus of E/S0 galaxies. E+As have profiles qualitatively like those of normal power-law early-type galaxies but have higher surface brightnesses. This result provides the first direct evidence supporting the hypothesis that power-law elliptical galaxies form via gas-rich mergers. In total, at least four E+As are morphologically consistent with early-type galaxies. We detect compact sources, possibly young star clusters, associated with the galaxies. These sources are much brighter (MR ~ -13) than Galactic globular clusters, have luminosities consistent with the brightest clusters in nearby starburst galaxies, and have blue colors consistent with the ages estimated from the E+A galaxy spectra (several 108 yr). Further study of such young star cluster candidates might provide the elusive chronometer needed to break the age/burst-strength degeneracy for these postmerger galaxies.

Identification and Analysis of Young Star Cluster Candidates in M31

We present a method for finding clusters of young stars in M31 using broadband WFPC2 data from the HST data archive. Applying our identification method to 13 WFPC2 fields, covering an area of ~60 arcmin2, has revealed 79 new candidate young star clusters in these portions of the M31 disk. Most of these clusters are small (≲5 pc), young (~10-200 Myr) star groups located within large OB associations. We have estimated the reddening values and the ages of each candidate individually by fitting isochrones to the stellar photometry. We provide a catalog of the candidates including rough approximations of their reddenings and ages. We also look for patterns of cluster formation with galactocentric distance, but our rough estimates are not precise enough to reveal any clear patterns.