Intermediate-Age Globular Clusters in Four Galaxy Merger Remnants

Globular clusters (GCs) are some of the most visible tracers of the merging and accretion history of galaxy halos. Metal-poor GCs, in particular, are thought to arrive in massive galaxies largely through dry, minor merging events, but it is rare to see a direct connection between GCs and visible stellar streams. NGC 474 is a post-merger early-type galaxy with dramatic fine structures made of concentric shells and radial streams that have been more clearly revealed by deep imaging. We present a study of GCs in NGC 474 to better establish the relationship between merger-induced fine structure and the GC system. We find that many GCs are superimposed on visible streams and shells, and about 35% of GCs outside 3R e,galaxy are located in regions of fine structure. The spatial correlation between the GCs and fine structure is significant at the 99.9% level, showing that this correlation is not coincidental. The colors of the GCs on the fine structures are mostly blue, and we also find an intermediate-color population that is dominant in the central region, and which will likely passively evolve to have colors consistent with a traditional metal-rich GC population. The association of the blue GCs with fine structures is direct confirmation that many metal-poor GCs are accreted onto massive galaxy halos through merging events, and that progenitors of these mergers are sub-L ⋆ galaxies.

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“…Several observational studies also support this formation scenario (e.g. Whitmore et al 1993;Sikkema et al 2006;Trancho et al 2014).…”

Section: Introductionmentioning

confidence: 75%

Globular Clusters as Tracers of Fine Structure in the Dramatic Shell Galaxy NGC 474

Lim

Peng

Duc

et al. 2017

ApJ

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“…The galaxy with the highest L X (gas)/SFR in our sample, NGC 1700, does not appear in Figure 16, due to the lack of FUV data. However, based on optical photometry, the stellar population age in NGC 1700 is estimated to be 1 − 2 Gyrs (Trancho et al 2014) or ∼3 Gyrs (Brown et al 2000).…”

Section: X (Gas)/sfr Vs Stellar Population Agementioning

confidence: 99%

“…Arp 222 has a very low FIR luminosity (10 8.71 L ⊙ ) relative to its K band luminosity (10 11.12 L ⊙ ), thus it is now a relatively quiescent galaxy. However, high resolution optical and IR images revealed the presence of intermediate-age (1 − 2 Gyr) globular clusters in Arp 222 (Trancho et al 2014), suggesting a starburst in the past.…”

Section: 78±mentioning

confidence: 99%

“…Based on optical BVI imaging, Brown et al (2000) suggest an age for the younger stellar population in NGC 1700 of about 3 Gyrs. Using HST and Gemini optical and IR, Trancho et al (2014) concluded that NGC 1700 hosts globular clusters with intermediate ages (1 − 2 Gyr). The optical radial profile provides evidence for a stellar disk in the interior (Franx, Illingworth, & Heckman 1989;Goudfrooij et al 1994).…”

Section: Mrk 231 (Iras 12540+5708)mentioning

confidence: 99%

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Diffuse X-Ray-emitting Gas in Major Mergers

Smith

Campbell

Struck

et al. 2018

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Using archived data from the Chandra X-ray telescope, we have extracted the diffuse Xray emission from 49 equal-mass interacting/merging galaxy pairs in a merger sequence, from widely separated pairs to merger remnants. After removal of contributions from unresolved point sources, we compared the diffuse thermal X-ray luminosity from hot gas (L X (gas)) with the global star formation rate (SFR). After correction for absorption within the target galaxy, we do not see strong trend of L X (gas)/SFR with SFR or merger stage for galaxies with SFR > 1 M ⊙ yr −1 . For these galaxies, the median L X (gas)/SFR is 5.5 × 10 39 ((erg s −1 )/M ⊙ yr −1 )), similar to that of normal spiral galaxies. These results suggest that stellar feedback in star forming galaxies reaches an approximately steady state condition, in which a relatively constant fraction of about 2% of the total energy output from supernovae and stellar winds is converted into X-ray flux. Three late-stage merger remnants with low SFRs and high K band luminosities (L K ) have enhanced L X (gas)/SFR; their UV/IR/optical colors suggest that they are post-starburst galaxies, perhaps in the process of becoming ellipticals. Systems with L K < 10 10 L ⊙ have lower L X (gas)/SFR ratios than the other galaxies in our sample, perhaps due to lower gravitational fields or lower metallicities. We see no relation between L X (gas)/SFR and Seyfert activity in this sample, suggesting that feedback from active galactic nuclei is not a major contributor to the hot gas in our sample galaxies.

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“…It presents a remarkably steep age gradient from a central ∼1.5 Gyr (Sánchez-Blázquez et al 2007;Reda et al 2007) to ∼10 Gyr close to 1R e ; it also has a steep metallicity gradient (Reda et al 2007). Its GCS was studied by Sikkema et al (2006) using HST/ACS, finding a sizeable blue population consistent with a young-to-intermediate GC population (see also Trancho et al 2014). -NGC 3962 is part of the sample of Smith et al (2004) of field ellipticals without companions, as confirmed by Madore et al (2004), and no signs of any tidal disturbance (Tal et al 2009).…”

Section: Galaxy Samplementioning

confidence: 99%

Isolated ellipticals and their globular cluster systems

Salinas

Alabi

Richtler

2015

A&A

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As tracers of star formation, galaxy assembly, and mass distribution, globular clusters have provided important clues to our understanding of early-type galaxies. But their study has been mostly constrained to galaxy groups and clusters where early-type galaxies dominate, leaving the properties of the globular cluster systems (GCSs) of isolated ellipticals as a mostly uncharted territory. We present Gemini-South/GMOS g i observations of five isolated elliptical galaxies: NGC 3962, NGC 2865, IC 4889, NGC 2271, and NGC 4240. Photometry of their GCSs reveals clear color bimodality in three of them, but remains inconclusive for the other two. All the studied GCSs are rather poor with a mean specific frequency S N ∼ 1.5, independently of the parent galaxy luminosity. Considering information from previous work as well, it is clear that bimodality and especially the presence of a significant, even dominant, population of blue clusters occurs at even the most isolated systems, which casts doubts on a possible accreted origin of metal-poor clusters, as suggested by some models. Additionally, we discuss the possible existence of ultra-compact dwarfs around the isolated elliptical NGC 3962.

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Intermediate-Age Globular Clusters in Four Galaxy Merger Remnants

Cited by 18 publications

References 42 publications

Globular Clusters as Tracers of Fine Structure in the Dramatic Shell Galaxy NGC 474

Globular Clusters as Tracers of Fine Structure in the Dramatic Shell Galaxy NGC 474

Diffuse X-Ray-emitting Gas in Major Mergers

Isolated ellipticals and their globular cluster systems

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