* Astronomy

Blobrana · L

NGC 4150

Blobrana · L

Title: A WFC3 study of globular clusters in NGC 4150 - an early-type minor merger
Authors: Sugata Kaviraj, R. Mark Crockett, Bradley C. Whitmore, Joseph Silk, Robert W. O'Connell, Rogier A. Windhorst, Max Mutchler, Marina Rejkuba, Sukyoung Yi, Jay A. Frogel, Daniela Calzetti

We combine near-ultraviolet (NUV; 2250 {\AA}) and optical (U, B, V, I) imaging from the Wide Field Camera 3 (WFC3), on board the Hubble Space Telescope (HST), to study the globular cluster (GC) population in NGC 4150, a sub-L* (M_B ~ -18.48 mag) early-type minor-merger remnant in the Coma I cloud. We use broadband NUV-optical photometry from the WFC3 to estimate individual ages, metallicities, masses and line-of-sight extinctions [E_(B-V)] for 63 bright (M_V < -5 mag) GCs in this galaxy. In addition to a small GC population with ages greater than 10 Gyr, we find a dominant population of clusters with ages centred around 6 Gyr, consistent with the expected peak of stellar mass assembly in faint early-types residing in low-density environments. The old and intermediate-age GCs in NGC 4150 are metal-poor, with metallicities less than 0.1 ZSun, and reside in regions of low extinction (E_(B-V) < 0.05 mag). We also find a population of young, metal-rich (Z > 0.3 ZSun) clusters that have formed within the last Gyr and reside in relatively dusty (E_(B-V) > 0.3 mag) regions that are coincident with the part of the galaxy core that hosts significant recent star formation. Cluster disruption models (in which ~80-90% of objects younger than a few 10^8 yr dissolve every dex in time) suggest that the bulk of these young clusters are a transient population.

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Blobrana · L

Elliptical galaxies were once thought to be aging star cities whose star-making heyday was billions of years ago. But new observations with NASA's Hubble Space Telescope are helping to show that elliptical galaxies still have some youthful vigour left, thanks to encounters with smaller galaxies.
Images of the core of NGC 4150, taken in near-ultraviolet light with the sharp-eyed Wide Field Camera 3 (WFC3), reveal streamers of dust and gas and clumps of young, blue stars that are significantly less than a billion years old. Evidence shows that the star birth was sparked by a merger with a dwarf galaxy. The new study helps bolster the emerging view that most elliptical galaxies have young stars, bringing new life to old galaxies. In the large-scale image, the dark strands of dust in the center provide tentative evidence of a recent galaxy merger. The inset image shows a magnified view of the chaotic activity inside the galaxy's core. The blue areas indicate a flurry of recent star birth. The stellar breeding ground is about 1,300 light-years across. The stars in this area are less than a billion years old.
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