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Register a new userEvidence for Significant Growth in the Stellar Mass of Brightest Cluster Galaxies over the Past 10 Billion Years
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Using new and published data, we construct a sample of 160 brightest cluster galaxies (BCGs) spanning the redshift interval 0.03 < z < 1.63. We use this sample, which covers 70% of the history of the universe, to measure the growth in the stellar mass of BCGs after correcting for the correlation between the stellar mass of the BCG and the mass of the cluster in which it lives. We find that the stellar mass of BCGs increase by a factor of 1.8 between z=0.9 and z=0.2. Compared to earlier works, our result is closer to the predictions of semi-analytic models. However, BCGs at z=0.9, relative to BCGs at z=0.2, are still a factor of 1.5 more massive than the predictions of these models. Star formation rates in BCGs at z~1 are generally to low to result in significant amounts of mass. Instead, it is likely that most of the mass build up occurs through mainly dry mergers in which perhaps half of the mass is lost to the intra-cluster medium of the cluster.
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We constrain the evolution of the brightest cluster galaxy plus intracluster light (BCG+ICL) using an ensemble of 42 galaxy groups and clusters that span redshifts of z = 0.05-1.75 and masses of $M_{500,c}=2times10^{13}-10^{15}$ M$_odot$ Specifically, we measure the relationship between the BCG+ICL stellar mass $M_star$ and $M_{500,c}$ at projected radii 10 < r < 100 kpc for three different epochs. At intermediate redshift (z = 0.40), where we have the best data, we find $M_starpropto M_{500,c}^{0.48pm0.06}$. Fixing the exponent of this power law for all redshifts, we constrain the normalization of this relation to be $2.08pm0.21$ times higher at z = 0.40 than at high redshift (z = 1.55). We find no change in the relation from intermediate to low redshift (z = 0.10). In other words, for fixed $M_{500,c}$, $M_star$ at 10 < r < 100 kpc increases from z = 1.55 to z = 0.40 and not significantly thereafter. Theoretical models predict that the physical mass growth of the cluster from z = 1.5 to z = 0 within $r_{500,c}$ is a factor of 1.4, excluding evolution due to definition of $r_{500,c}$. We find that $M_star$ within the central 100 kpc increases by a factor of 3.8 over the same period. Thus, the growth of $M_star$ in this central region is more than a factor of two greater than the physical mass growth of the cluster as a whole. Furthermore, the concentration of the BCG+ICL stellar mass, defined by the ratio of stellar mass within 10 kpc to the total stellar mass within 100 kpc, decreases with increasing $M_{500,c}$ at all redshift. We interpret this result as evidence for inside-out growth of the BCG+ICL over the past ten Gyrs, with stellar mass assembly occuring at larger radii at later times.
We use the IllustrisTNG simulations to investigate the evolution of the mass-metallicity relation (MZR) for star-forming cluster galaxies as a function of the formation history of their cluster host. The simulations predict an enhancement in the gas-phase metallicities of star-forming cluster galaxies (10^9< M_star<10^10 M_sun) at z<1.0 in comparisons to field galaxies. This is qualitatively consistent with observations. We find that the metallicity enhancement of cluster galaxies appears prior to their infall into the central cluster potential, indicating for the first time a systematic chemical pre-processing signature for {it infalling} cluster galaxies. Namely, galaxies which will fall into a cluster by z=0 show a ~0.05 dex enhancement in the MZR compared to field galaxies at z<0.5. Based on the inflow rate of gas into cluster galaxies and its metallicity, we identify that the accretion of pre-enriched gas is the key driver of the chemical evolution of such galaxies, particularly in the stellar mass range (10^9< M_star<10^10 M_sun). We see signatures of an environmental dependence of the ambient/inflowing gas metallicity which extends well outside the nominal virial radius of clusters. Our results motivate future observations looking for pre-enrichment signatures in dense environments.
We study the evolution of the scaling relations between maximum circular velocity, stellar mass and optical half-light radius of star-forming disk-dominated galaxies in the context of LCDM-based galaxy formation models. Using data from the literature combined with new data from the DEEP2 and AEGIS surveys we show that there is a consistent observational and theoretical picture for the evolution of these scaling relations from zsim 2 to z=0. The evolution of the observed stellar scaling relations is weaker than that of the virial scaling relations of dark matter haloes, which can be reproduced, both qualitatively and quantitatively, with a simple, cosmologically-motivated model for disk evolution inside growing NFW dark matter haloes. In this model optical half-light radii are smaller, both at fixed stellar mass and maximum circular velocity, at higher redshifts. This model also predicts that the scaling relations between baryonic quantities evolve even more weakly than the corresponding stellar relations. We emphasize, though, that this weak evolution does not imply that individual galaxies evolve weakly. On the contrary, individual galaxies grow strongly in mass, size and velocity, but in such a way that they move largely along the scaling relations. Finally, recent observations have claimed surprisingly large sizes for a number of star-forming disk galaxies at z sim 2, which has caused some authors to suggest that high redshift disk galaxies have abnormally high spin parameters. However, we argue that the disk scale lengths in question have been systematically overestimated by a factor sim 2, and that there is an offset of a factor sim 1.4 between Halpha sizes and optical sizes. Taking these effects into account, there is no indication that star forming galaxies at high redshifts (zsim 2) have abnormally high spin parameters.
We examine the star formation properties of group and field galaxies in two surveys, the Sloan Digital Sky Survey (SDSS; at z ~ 0.08) and the Group Environment and Evolution Collaboration (GEEC; at z ~ 0.4). Using UV imaging from the GALEX space telescope, along with optical and, for GEEC, near infrared photometry, we compare the observed spectral energy distributions to large suites of stellar population synthesis models. This allows us to accurately determine star formation rates and stellar masses. We find that star forming galaxies of all environments undergo a systematic lowering of their star formation rate between z=0.4 and z=0.08 regardless of mass. Nonetheless, the fraction of passive galaxies is higher in groups than the field at both redshifts. Moreover, the difference between the group and field grows with time and is mass-dependent, in the sense the the difference is larger at low masses. However, the star formation properties of star forming galaxies, as measured by their average specific star formation rates, are consistent within the errors in the group and field environment at fixed redshift. The evolution of passive fraction in groups between z=0.4 and z=0 is consistent with a simple accretion model, in which galaxies are environmentally affected 3 Gyrs after falling into a ~ 10E13 Msun group. This long timescale appears to be inconsistent with the need to transform galaxies quickly enough to ensure that star forming galaxies appear similar in both the group and field, as observed.
We measure the stellar mass function (SMF) of galaxies in the COSMOS field up to $zsim6$. We select them in the near-IR bands of the COSMOS2015 catalogue, which includes ultra-deep photometry from UltraVISTA-DR2, SPLASH, and Subaru/Hyper-SuprimeCam. At $z>2.5$ we use new precise photometric redshifts with error $sigma_z=0.03(1+z)$ and an outlier fraction of $12%$, estimated by means of the unique spectroscopic sample of COSMOS. The increased exposure time in the DR2, along with our panchromatic detection strategy, allow us to improve the stellar mass completeness at high $z$ with respect to previous UltraVISTA catalogues. We also identify passive galaxies through a robust colour-colour selection, extending their SMF estimate up to $z=4$. Our work provides a comprehensive view of galaxy stellar mass assembly between $z=0.1$ and 6, for the first time using consistent estimates across the entire redshift range. We fit these measurements with a Schechter function, correcting for Eddington bias. We compare the SMF fit with the halo mass function predicted from $Lambda$CDM simulations. We find that at $z>3$ both functions decline with a similar slope in the high-mass end. This feature could be explained assuming that the mechanisms that quench star formation in massive haloes become less effective at high redshift; however further work needs to be done to confirm this scenario. Concerning the SMF low-mass end, it shows a progressive steepening as moving towards higher redshifts, with $alpha$ decreasing from $-1.47_{-0.02}^{+0.02}$ at $zsimeq0.1$ to $-2.11_{-0.13}^{+0.30}$ at $zsimeq5$. This slope depends on the characterisation of the observational uncertainties, which is crucial to properly remove the Eddington bias. We show that there is currently no consensus on the method to quantify such errors: different error models result in different best-fit Schechter parameters. [Abridged]
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