Morphometric analysis of brightest cluster galaxies

2020 ◽  
Vol 498 (3) ◽  
pp. 4433-4449
Author(s):  
J Cougo ◽  
S B Rembold ◽  
F Ferrari ◽  
A L P Kaipper

ABSTRACT We study the build-up of the stellar mass of brightest cluster galaxies (BCGs) at z < 0.1 as a function of their morphological type. Morphometric parameters for 1216 BCGs were obtained from the SDSS DR12 r-band images with the code morfometryka. We show that the morphometric parameters are efficient to separate BCGs into cD galaxies, conventional ellipticals, disc-dominated BCGs, and merging objects. We propose a simple classification scheme using two concentration indices, C1 and C2, and the spirality σψ. We then investigate how the stellar masses of BCGs and the velocity dispersions of their parent haloes relate to their morphological properties. We find that BCGs with larger envelope contributions are more massive than BCGs in other classes and more common in massive clusters. The stellar mass and the halo velocity dispersion correlate for all classes, suggesting that environmental effects are important for BCGs of any morphology. At fixed parent halo mass, we detect a continuous mass excess up to $\sim 60{{\ \rm per\ cent}}$ from pure E galaxies to extreme cD galaxies, while the inner regions of such cDs present only $\sim 40{{\ \rm per\ cent}}$ of the mass of an E galaxy. We interpret our findings in a scenario where different BCGs have developed their mass through an asymmetric combination of distinct processes, so that present-time cD galaxies have grown in mass mainly through minor merging and tidal stripping from satellite galaxies, while elliptical BCGs evolve mainly through processes like major merging.

2019 ◽  
Vol 14 (S353) ◽  
pp. 257-258
Author(s):  
S. I. Loubser

AbstractWe study the stellar and dynamical masses, as well as the stellar populations, of brightest cluster galaxies (BCGs) located in 32 massive clusters, and for a sub-sample of these use the results to place constraints on the Initial Mass Function (IMF). We measure the spatially-resolved stellar population properties of the BCGs, such as recent star formation episodes, and use it to predict their stellar mass-to-light ratios (ϒ*POP). We find that ∼60 per cent of the BCGs have constant ϒ*POP over the radial range (<15 kpc). We also use the stellar and dynamical mass profiles to derive the stellar mass-to-light ratio from dynamics (ϒ*DYN, see Loubser, these proceedings). We directly compare ϒ*POP with ϒ*DYN, and find that for most BCGs, a Salpeter IMF is needed to explain their properties, but we also find a small subset of BCGs for which a Kroupa-like IMF is needed to explain their properties.


2020 ◽  
Vol 500 (3) ◽  
pp. 4153-4165
Author(s):  
S I Loubser ◽  
H Hoekstra ◽  
A Babul ◽  
Y M Bahé ◽  
M Donahue

ABSTRACT We use stellar and dynamical mass profiles, combined with a stellar population analysis, of 32 brightest cluster galaxies (BCGs) at redshifts of 0.05 ≤$z$ ≤ 0.30, to place constraints on their stellar initial mass function (IMF). We measure the spatially resolved stellar population properties of the BCGs, and use it to derive their stellar mass-to-light ratios ($\Upsilon _{\star \rm POP}$). We find young stellar populations (&lt;200 Myr) in the centres of 22 per cent of the sample, and constant $\Upsilon _{\star \rm POP}$ within 15 kpc for 60 per cent of the sample. We further use the stellar mass-to-light ratio from the dynamical mass profiles of the BCGs ($\Upsilon _{\star \rm DYN}$), modelled using a multi-Gaussian expansion and Jeans Anisotropic Method, with the dark matter contribution explicitly constrained from weak gravitational lensing measurements. We directly compare the stellar mass-to-light ratios derived from the two independent methods, $\Upsilon _{\star \rm POP}$ (assuming some IMF) to $\Upsilon _{\star \rm DYN}$ for the subsample of BCGs with no young stellar populations and constant $\Upsilon _{\star \rm POP}$. We find that for the majority of these BCGs, a Salpeter (or even more bottom-heavy) IMF is needed to reconcile the stellar population and dynamical modelling results although for a small number of BCGs, a Kroupa (or even lighter) IMF is preferred. For those BCGs better fit with a Salpeter IMF, we find that the mass-excess factor against velocity dispersion falls on an extrapolation (towards higher masses) of known literature correlations. We conclude that there is substantial scatter in the IMF amongst the highest mass galaxies.


2020 ◽  
Vol 496 (3) ◽  
pp. 2591-2604 ◽  
Author(s):  
Taizo Okabe ◽  
Masamune Oguri ◽  
Sébastien Peirani ◽  
Yasushi Suto ◽  
Yohan Dubois ◽  
...  

ABSTRACT We study shapes and alignments of 45 dark matter (DM) haloes and their brightest cluster galaxies (BCGs) using a sample of 39 massive clusters from Hubble Frontier Field (HFF), Cluster Lensing And Supernova survey with Hubble (CLASH), and Reionization Lensing Cluster Survey (RELICS). We measure shapes of the DM haloes by strong gravitational lensing, whereas BCG shapes are derived from their light profiles in Hubble Space Telescope images. Our measurements from a large sample of massive clusters presented here provide new constraints on DM and cluster astrophysics. We find that DM haloes are on average highly elongated with the mean ellipticity of 0.482 ± 0.028, and position angles of major axes of DM haloes and their BCGs tend to be aligned well with the mean value of alignment angles of 22.2 ± 3.9 deg. We find that DM haloes in our sample are on average more elongated than their BCGs with the mean difference of their ellipticities of 0.11 ± 0.03. In contrast, the Horizon-AGN cosmological hydrodynamical simulation predicts on average similar ellipticities between DM haloes and their central galaxies. While such a difference between the observations and the simulation may well be explained by the difference of their halo mass scales, other possibilities include the bias inherent to strong lensing measurements, limited knowledge of baryon physics, or a limitation of cold DM.


2020 ◽  
Vol 493 (4) ◽  
pp. 4607-4621 ◽  
Author(s):  
Douglas Rennehan ◽  
Arif Babul ◽  
Christopher C Hayward ◽  
Connor Bottrell ◽  
Maan H Hani ◽  
...  

Abstract The current consensus on the formation and evolution of the brightest cluster galaxies is that their stellar mass forms early ($z$ ≳ 4) in separate galaxies that then eventually assemble the main structure at late times ($z$ ≲ 1). However, advances in observational techniques have led to the discovery of protoclusters out to $z$ ∼ 7. If these protoclusters assemble rapidly in the early Universe, they should form the brightest cluster galaxies much earlier than suspected by the late-assembly picture. Using a combination of observationally constrained hydrodynamical and dark-matter-only simulations, we show that the stellar assembly time of a sub-set of brightest cluster galaxies occurs at high redshifts ( $z$ &gt; 3) rather than at low redshifts ($z$ &lt; 1), as is commonly thought. We find, using isolated non-cosmological hydrodynamical simulations, that highly overdense protoclusters assemble their stellar mass into brightest cluster galaxies within ∼1 Gyr of evolution – producing massive blue elliptical galaxies at high redshifts ($z$ ≳ 1.5). We argue that there is a downsizing effect on the cluster scale wherein some of the brightest cluster galaxies in the cores of the most-massive clusters assemble earlier than those in lower mass clusters. In those clusters with $z$ = 0 virial mass ≥ 5 × 1014 M⊙, we find that $9.8{{\ \rm per\ cent}}$ have their cores assembly early, and a higher fraction of $16.4{{\ \rm per\ cent}}$ in those clusters above 1015 M⊙. The James Webb Space Telescope will be able to detect and confirm our prediction in the near future, and we discuss the implications to constraining the value of σ8.


2020 ◽  
Vol 635 ◽  
pp. A32 ◽  
Author(s):  
G. Castignani ◽  
F. Combes ◽  
P. Salomé ◽  
J. Freundlich

The mechanisms governing the stellar mass assembly and star formation history of brightest cluster galaxies (BCGs) are still being debated. By means of new and archival molecular gas observations we investigate the role of dense megaparsec-scale environments in regulating the fueling of star formation in distant BCGs, through cosmic time. We observed in CO with the IRAM 30 m telescope two star-forming BCGs belonging to SpARCS clusters, namely, 3C 244.1 (z = 0.4) and SDSS J161112.65+550823.5 (z = 0.9), and compared their molecular gas and star formation properties with those of a compilation of ∼100 distant cluster galaxies from the literature, including nine additional distant BCGs at z  ∼  0.4 − 3.5. We set robust upper limits of MH2 <  1.0 × 1010 M⊙ and < 2.8 × 1010 M⊙ to their molecular gas content, respectively, and to the ratio of molecular gas to stellar mass M(H2)/M⋆ ≲ 0.2 and depletion time τdep ≲ 40 Myr of the two targeted BCGs. They are thus among the distant cluster galaxies with the lowest gas fractions and shortest depletion times. The majority (64%±15% and 73%±18%) of the 11 BCGs with observations in CO have lower M(H2)/M⋆ values and τdep, respectively, than those estimated for main sequence galaxies. Statistical analysis also tentatively suggests that the values of M(H2)/M⋆ and τdep for the 11 BCGs deviates, with a significance of ∼2σ, from those of the comparison sample of cluster galaxies. A morphological analysis for a subsample of seven BCGs with archival HST observations reveals that 71%±17% of the BCGs are compact or show star-forming components or substructures. Our results suggest a scenario where distant star-forming BCGs assemble a significant fraction ∼16% of their stellar mass on the relatively short timescale ∼τdep, while environmental mechanisms might prevent the replenishment of gas feeding the star formation. We speculate that compact components also favor the rapid exhaustion of molecular gas and ultimately help to quench the BCGs. Distant star-forming BCGs are excellent targets for ALMA and for next-generation telescopes such as the James Webb Space Telescope.


2016 ◽  
Vol 460 (3) ◽  
pp. 2862-2874 ◽  
Author(s):  
Sabine Bellstedt ◽  
Chris Lidman ◽  
Adam Muzzin ◽  
Marijn Franx ◽  
Susanna Guatelli ◽  
...  

2013 ◽  
Vol 771 (1) ◽  
pp. 61 ◽  
Author(s):  
Yen-Ting Lin ◽  
Mark Brodwin ◽  
Anthony H. Gonzalez ◽  
Paul Bode ◽  
Peter R. M. Eisenhardt ◽  
...  

1999 ◽  
Vol 186 ◽  
pp. 407-407
Author(s):  
A. Aragón-Salamanca ◽  
C.M. Baugh ◽  
G. Kauffmann

We analyze the K-band Hubble diagram for a sample of brightest cluster galaxies (BCGs) in the redshift range 0 < z < 1. We confirm that the scatter in the absolute magnitudes of the galaxies is small (0.3 magnitudes). The BCGs exhibit very little luminosity evolution in this redshift range: if q0 = 0.0 we detect no luminosity evolution; for q0 = 0.5 we measure a small negative evolution (i.e., BCGs were about 0.5 magnitudes fainter at z = 1 than today). If the mass in stars of these galaxies had remained constant over this period of time, substantial positive luminosity evolution would be expected: BCGs should have been brighter in the past since their stars were younger. A likely explanation for the observed zero or negative evolution is that the stellar mass of the BCGs has been assembled over time through merging and accretion, as expected in hierarchical models of galaxy formation. The colour evolution of the BCGs is consistent with that of an old stellar population (zform > 2) that is evolving passively. We can thus use evolutionary population synthesis models to estimate the rate of growth in stellar mass for these systems. We find that the stellar mass in a typical BCG has grown by a factor ≃ 2 since z ≃ 1 if q0 = 0.0 or by factor ≃ 4 if q0 = 0.5. These results are in remarkably good agreement with the predictions of semi-analytic models of galaxy formation and evolution set in the context of a hierarchical scenario for structure formation.


2014 ◽  
Vol 446 (1) ◽  
pp. 1107-1114 ◽  
Author(s):  
Takahiro Inagaki ◽  
Yen-Ting Lin ◽  
Hung-Jin Huang ◽  
Bau-Ching Hsieh ◽  
Naoshi Sugiyama

Sign in / Sign up

Export Citation Format

Share Document