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ABSTRACT We investigate the spectroscopic properties of 85 brightest cluster galaxies (BCGs) and their companions observed with the SDSS MaNGA integral field unit. Galaxy redshifts are between 0.08 < z < 0.15, allowing for a field-of-view up to 80 × 80 kpc. For the main galaxies: the average age of the BCG cores is 7.66$$\, \pm \,$$1.36 Gyr with no significant gradient out to $$2\, R_ {e}$$; the average metallicity of the BCG cores is $$[Z/H]=0.23\, \pm \, 0.03$$ with a negative gradient of Δ[Z/H]/Δ(R/Re) = –0.14$$\, \pm \, 0.09$$ which flattens beyond $$1.2\, R_ {e}$$. Velocity dispersion gradients are mostly flat, but a few positive slopes are seen in the most massive galaxies. Emission lines are present in 12 of the BCGs, most often confined to the central $$\sim 2\,$$ kpc with emission line ratios well-described by a LINER or AGN excitation source. There are 78 companion galaxies identified and 9 have nebular emission lines that indicate recent star formation. The companions with flux ratios of 4:1 and 20:1 within 30 kpc of their BCG’s core are studied. The companion galaxies have a median age of 7.65$$\, \pm \,$$1.55 Gyr and are high-metallicity systems, with a median [Z/H] = 0.17 ± 0.07. Close spectroscopic companions with higher merging probabilities have an average merging time of 0.5 ± 0.2 Gyr. The average merger rate is 0.08$$\, \pm \, 0.12 \,$$ Gyr−1 for 4:1 companions and 0.26$$\, \pm \, 0.22 \,$$ Gyr−1 for 20:1 companions, allowing for an increase in mass of 2.3$$\, \pm \,$$3.4 per cent Gyr−1 and 3.5$$\, \pm \,$$3.2 per cent Gyr−1, respectively.
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Clocking the formation of today’s largest galaxies: wide field integral spectroscopy of brightest cluster galaxies and their surroundings
ABSTRACT The formation and evolution of local brightest cluster galaxies (BCGs) is investigated by determining the stellar populations and dynamics from the galaxy core, through the outskirts and into the intracluster light (ICL). Integral spectroscopy of 23 BCGs observed out to $$4\, r_{e}$$ is collected and high signal-to-noise regions are identified. Stellar population synthesis codes are used to determine the age, metallicity, velocity, and velocity dispersion of stars within each region. The ICL spectra are best modelled with populations that are younger and less metal-rich than those of the BCG cores. The average BCG core age of the sample is $$\rm 13.3\pm 2.8\, Gyr$$ and the average metallicity is $$\rm [Fe/H] = 0.30\pm 0.09$$, whereas for the ICL the average age is $$\rm 9.2\pm 3.5\, Gyr$$ and the average metallicity is $$\rm [Fe/H] = 0.18\pm 0.16$$. The velocity dispersion profile is seen to be rising or flat in most of the sample (17/23), and those with rising values reach the value of the host cluster’s velocity dispersion in several cases. The most extended BCGs are closest to the peak of the cluster’s X-ray luminosity. The results are consistent with the idea that the BCG cores and inner regions formed quickly and long ago, with the outer regions and ICL forming more recently, and continuing to assemble through minor merging. Any recent star formation in the BCGs is a minor component, and is associated with the cluster cool core status.
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- Award ID(s):
- 1814375
- PAR ID:
- 10126257
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 491
- Issue:
- 2
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 2617-2638
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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