The peculiar spiral NGC 2782 is the result of a minor merger with a mass ratio ~4: 1 occurring ~200 Myr ago. This merger produced a molecular and H I-rich, optically bright eastern tail and an H ...I-rich, optically faint western tail. Non-detection of CO in the western tail by Braine et al. suggested that star formation had not yet begun. However, deep UBVR and H alpha narrowband images show evidence of recent star formation in the western tail, though it lacks massive star clusters and cluster complexes. Using Herschel PACS spectroscopy, we discover 158 mu m CII emission at the location of the three most luminous H alpha sources in the eastern tail, but not at the location of the even brighter H alpha source in the western tail. The western tail is found to have a normal star formation efficiency (SFE), but the eastern tail has a low SFE. The lack of CO and CII emission suggests that the western tail H II region may have a low carbon abundance and be undergoing its first star formation. The western tail is more efficient at forming stars, but lacks massive clusters. We propose that the low SFE in the eastern tail may be due to its formation as a splash region where gas heating is important even though it has sufficient molecular and neutral gas to make massive star clusters. The western tail, which has lower gas surface density and does not form high-mass star clusters, is a tidally formed region where gravitational compression likely enhances star formation.
Superstar clusters are young, compact star clusters found in the central regions of interacting galaxies. Recently, they have also been reported to preferentially form in certain tidal tails, but not ...in others. In this paper, we have used 21-cm H i maps and the Hubble Space Telescope Wide Field Planetary Camera 2 images of eight tidal tail regions of four merging galaxy pairs to compare the kiloparsec scale H i distribution with the location of superstar clusters found from the optical images. For most of the tails, we find that there is an increase in superstar cluster density with increasing projected H i column density, such that the star cluster density is highest when log NH i≳ 20.6 cm−2, but equal to the background count rate at lower H i column density. However, for two tails (NGC 4038/39 Pos A and 3921), there is no significant star cluster population despite the presence of gas at high column density. This implies that the NH i threshold is a necessary but not sufficient condition for cluster formation. Gas volume density is likely to provide a more direct criterion for cluster formation, and other factors such as gas pressure or strength of encounter may also have an influence. Comparison of H i thresholds needed for formation of different types of stellar structures await higher resolution H i and optical observations of larger numbers of interacting galaxies.
This work examines star formation in the debris associated with collisions of dwarf and spiral galaxies. While the spectacular displays of major mergers are famous (e.g., NGC 4038/9, "The ...Antennae''), equal mass galaxy mergers are relatively rare compared to minor mergers (mass ratio <0.3) Minor mergers are less energetic than major mergers, but more common in the observable universe and, thus, likely played a pivotal role in the formation of most large galaxies. Centers of mergers host vigorous star formation from high gas density and turbulence and are surveyed over cosmological distances. However, the tidal debris resulting from these mergers have not been well studied. Such regions have large reservoirs of gaseous material that can be used as fuel for subsequent star formation but also have lower gas density. Tracers of star formation at the local and global scale have been examined for three tidal tails in two minor merger systems. These tracers include young star cluster populations, H-alpha, and CII emission. The rate of apparent star formation derived from these tracers is compared to the gas available to estimate the star formation efficiency (SFE). The Western tail of NGC 2782 formed isolated star clusters while massive star cluster complexes are found in the UGC 10214 ("The Tadpole'') and Eastern tail of NGC 2782. Due to the lack of both observable CO and CII emission, the observed star formation in the Western tail of NGC 2782 may have a low carbon abundance and represent only the first round of local star formation. While the Western tail has a normal SFE, the Eastern tail in the same galaxy has an low observed SFE. In contrast, the Tadpole tidal tail has a high observed star formation rate and a corresponding high SFE. The low SFE observed in the Eastern tail of NGC 2782 may be due to its origin as a splash region where localized gas heating is important. However, the other tails may be tidally formed regions where gravitational compression likely dominates and enhances the local star formation.
Star clusters in tidal debris Rodruck, Michael; Charlton, Jane; Borthakur, Sanchayeeta ...
Monthly notices of the Royal Astronomical Society,
09/2023, Letnik:
526, Številka:
2
Journal Article
Recenzirano
ABSTRACT
We present results of a Hubble Space Telescope (HST) UBVI-band study of star clusters in tidal tails, using new WFC3 and ACS imaging to complement existing WFPC2 data. We survey 12 tidal ...tails across seven merging systems, deriving ages and masses for 425 star cluster candidates (SCCs). The stacked mass distribution across all systems follows a power law of the form dN/dM ∝ Mβ, with β = −2.02 ± 0.15, consistent with what is seen in other star-forming environments. GALEX and Swift UV imaging provide star formation rates (SFRs) for our tidal tails, which when compared with ages and masses of our SCCs, allows for a determination of the cluster formation efficiency (CFE). We find the CFE increases with increasing SFR surface density, matching the theoretical model. We confirm this fit down at SFR densities lower than previously measured (log ΣSFR (M⊙ yr−1 kpc−2) ≈ −4.2), as related to the CFE. We determine the half-light radii for a refined sample of 57 SCCs with our HST WFC3 and ACS imaging, and calculate their dynamical age, finding the majority of them to be gravitationally bound. We also provide evidence of only low-mass (<104 M⊙) cluster formation in our nearest galaxy, NGC 1487, consistent with the theory that this system is a dwarf merger.
We have developed an observing programme using deep, multiband imaging to probe the chaotic regions of tidal tails in search of an underlying stellar population, using NGC 3256's 400 Myr twin tidal ...tails as a case study. These tails have different colours of u - g = 1.05 plus or minus 0.07 and r - i = 0.13 plus or minus 0.07 for NGC 3256W, and u - g = 1.26 plus or minus 0.07 and r - i = 0.26 plus or minus 0.07 for NGC 3256E, indicating different stellar populations. These colours correspond to simple stellar population ages of 288... and 841... Myr for NGC 3256W and NGC 3256E, respectively, suggesting that NGC 3256W's diffuse light is dominated by stars formed after the interaction, while light in NGC 3256E is primarily from stars that originated in the host galaxy. Using a mixed stellar population model, we break our diffuse light into two populations: one at 10 Gyr, representing stars pulled from the host galaxies, and a younger component, whose age is determined by fitting the model to the data. We find similar ages for the young populations of both tails (195... and 170... Myr for NGC 3256W and NGC 3256E, respectively), but a larger percentage of mass in the 10 Gyr population for NGC 3256E (98... per cent versus 90... per cent). Additionally, we detect 31 star cluster candidates in NGC 3256W and 19 in NGC 2356E, with median ages of 141 and 91 Myr, respectively. NGC 3256E contains several young (<10 Myr), low-mass objects with strong nebular emission, indicating a small, recent burst of star formation. (ProQuest: ... denotes formulae/symbols omitted.)
How does the tidal debris of minor galaxy mergers contribute to structures in spiral galaxies or in the intergalactic medium? While major mergers are known to create structures such as tidal dwarf ...galaxies and star clusters within their tidal debris, less is known about minor mergers (mass ratios between a dwarf galaxy and disk galaxy of less than one-third) and their tidal debris. This work surveys 6 nearby minor mergers using optical broad-band and H-alpha narrow-band imaging to characterize star formation in their tidal debris. Young star clusters with ages less than the dynamical age of the tidal tails are found in all 6 mergers, indicating that the star clusters formed in situ. Even if minor mergers contribute less tidal debris per interaction than major mergers, they are more common and possibly contribute structure to all types of galaxies and to the intergalactic medium throughout the history of the universe.
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