Sustained formation of progenitor globular clusters in a giant elliptical galaxy

Abstract

Globular clusters (GCs) are thought to be ancient relics from the early formative phase of galaxies, although their physical origin remains uncertain 1, 2. GCs are most numerous around massive elliptical galaxies, where they can exhibit a broad colour dispersion, suggesting a wide metallicity spread 3. Here, we show that many thousands of compact and massive (∼5 × 10 3-3 × 10 6 M ☉) star clusters have formed at an approximately steady rate over, at least, the past ∼1 Gyr around NGC 1275, the central giant elliptical galaxy of the Perseus cluster. Beyond ∼1 Gyr, these star clusters are indistinguishable in broadband optical colours from the more numerous GCs. Their number distribution exhibits a similar dependence with 2119-M-001-026-. T. B. thanks HKU for generous support from the Visiting Research Professor Scheme. Contributions J. L. supervised the project, and wrote the paper. E. W. and Y. O. conducted the technical aspects of the work. T. B. and E. M. initiated the project, and participated in the interpretation of the results.

Temporally and Spatially Extended Star Formation in the Brightest Cluster Galaxy of MACS\,J0329.7$-$0211 at $z=0.45$: Implications for Stellar Growth

“…Their overall distribution in color-color space suggests a collection of unextincted SSPs having a range of ages spanning a few Myr to a few 100 Myr. The lack of apparent dust extinction is consistent with that observed for young star clusters over the same age range in NGC 1275 (Lim et al 2020), where the vast majority of star clusters lie next to rather than within the emission-line nebula associated with that galaxy. Note the weak dependence on the colors of the evolutionary tracks with metallicity: as a consequence, our best-fit model SEDs to the measured SEDs do not permit a strong constraint on metallicity (over, at least, the range 0.4-1.0 Z ).…”

“…Finally, a prominent blue filament north-northwest of the BCG center (indicated by an arrow) can be seen in the (F105W−F160W) color image but not the (F435W−F160W) nor (F775W−F160W) color images; this feature corresponds to line emission from a gaseous nebula, which is commonly found in BCGs at the centers of cool-core clusters. Such emission-line nebulae are not always spatially coincident with young stars (e.g., Canning et al 2010Canning et al , 2014Lim et al 2020), if any are indeed present. Because features such as the emissionline nebula appear only in a restricted number of filters, we did not impose an intensity threshold for computing the color images; as a consequence, regions with neighbouring pixels that very randomly between blue and red correspond to noise.…”

“…The nebula is multi-phase, containing not just atomic/ionic gas seen in optical emission lines, but also ionized gas seen in X-rays, and a counterpart in molecular gas seen in the rotational-vibrational line of H 2 in the IR (Lim et al 2012) and as traced in CO (Salomé et al 2006;Lim et al 2008;Salomé et al 2008;Ho et al 2009;Salomé et al 2011). NGC 1275 is the only star-forming BCG sufficiently close for individual star clusters to be observable (and even marginally resolved): this galaxy has formed thousands of star clusters having masses ranging from ∼10 4 M , imposed by the observational detection threshold, up to ∼10 6 M , thus spanning the same mass range as globular clusters, at an essentially constant rate of ∼ 0.1 M yr −1 over at least the past 1 Gyr, beyond which the relatively young star clusters cannot be distinguished from the even more numerous globular clusters in this galaxy (Lim et al 2020). Although the bulk of the molecular gas is located at a projected radius of 10 kpc from the center of NGC 1275, the majority of the newly-formed star clusters are located much further out in close association with the outer gas filaments.…”

“…Although the bulk of the molecular gas is located at a projected radius of 10 kpc from the center of NGC 1275, the majority of the newly-formed star clusters are located much further out in close association with the outer gas filaments. Beginning their free-fall from far beyond the strong tidal fields at the inner region of the BCG, the more massive star clusters ( 10 5 M ) are likely to survive a Hubble time, whereas the more numerous star clusters having lower masses are more easily tidally disrupted to help grow the galaxy in, especially, stellar size (see a more detailed discussion in Lim et al 2020, as well as earlier arguments by Conselice et al 2001).…”

The PIPER Survey: I. An Initial Look at the Intergalactic Globular Cluster Population in the Perseus Cluster

“…NGC 1275 is uniquely interesting because GC systems have never been explored in a galaxy with such extreme, high-activity conditions. If, for example, its GCS turns out to have high specific frequency (number of GCs per unit galaxy luminosity) as is the usual case for BCGs (Harris et al 2017c), it would support the view that the current spec-tacular AGN and star-forming activity including young (< 1 Gyr) star clusters in its inner 20 kpc (Carlson et al 1998;Canning et al 2010Canning et al , 2014Lim et al 2019) is only an add-on to a dominant early formation epoch. ( 4) At the opposite end of the dwarf-galaxy structural scale from the UDGs are the Ultra-Compact Dwarfs (UCDs).…”