Faint-end Upturn Research Articles

Galaxy Populations in Groups and Clusters: Evidence for a Characteristic Stellar Mass Scale at M ∗ ∼ 109.5 M ⊙

We use the DR9 of the DESI legacy imaging survey and SDSS galaxy groups to measure the conditional luminosity function (CLF) for groups with halo mass M h ≥ 1012 M ⊙ and redshift 0.01 ≤ z ≤ 0.08, down to a limiting r-band magnitude of M r = −10 to −12. For given halo masses we measure the CLF for the total populations and for the red and blue populations classified using the (g − z) color. We find a clear faint-end upturn in the CLF of red satellites, with a slope α ≈ −1.8, which is almost independent of halo mass. This faint-end upturn is not seen for the blue and total populations. Our stellar population synthesis modeling shows that (g − z) provides a clean red/blue division and that red group galaxies defined by (g − z) are all dominated by old stellar populations. The fraction of old galaxies as a function of galaxy luminosity shows a minimum at M r ∼ −18, corresponding to M * ∼ 109.5 M ⊙. This scale is independent of halo mass and is comparable to the characteristic luminosity at which galaxies show a dichotomy in surface brightness and size, suggesting that the dichotomy in the old fraction and in galaxy structure may have a common origin. The rising of the old fraction at the faint end for Milky Way (MW)−sized halos is in good agreement with the quenched fraction measured for the MW/M31 system and from the ELVES survey. We discuss the implications of our results for the formation and evolution of low-mass galaxies and for the stellar mass functions of low-mass galaxies to be observed at high redshift.

The luminosity of cluster galaxies in the Cluster-EAGLE simulations

ABSTRACT We computed the luminosity of simulated galaxies of the c-eagle project, a suite of 30 high-resolution zoom-in simulations of galaxy clusters based on the eagle simulation. The AB magnitudes are derived for different spectral bands, from ultraviolet to infrared, using the simple stellar population modelling based on the E-MILES stellar spectra library. We take into account obscuration due to dust in star forming regions and diffuse interstellar medium. The g − r colour–stellar mass diagram, at z = 0.1, presents a defined red sequence, reaching g − r ≃ 0.8, 0.05 dex redder than eagle at high masses, and a well populated blue cloud, when field galaxies are included. The clusters’ inner regions are dominated by red-sequence galaxies at all masses, although a non-negligible amount of blue galaxies are still present. We adopt Bayesian inference to compute the clusters LFs, testing for statistical significance of both single and double Schechter functions. The multicolour LFs at z = 0 show a knee luminosity that peaks in the infrared and increases with the cluster’s mass. The faint-end is weakly dependent on colour and mass and shows an upturn in the optical, bounded between −1.25 and −1.39, just moderately steeper than the field. The simulations reproduce, within the observational errors, the spectroscopic LFs of the Hercules and Abell 85 clusters, including their faint end upturn. c-eagle LFs are in broad agreement with observed LFs taken from SDSS and XXL surveys, up to z = 0.67, showing a rather flat faint end when the observational constrains are taken into account.

The galaxy luminosity function in groups and clusters: the faint-end upturn and the connection to the field luminosity function

We characterize the luminosity functions of galaxies residing in $z\sim0$ groups and clusters over the broadest ranges of luminosity and mass reachable by the Sloan Digital Sky Survey. Our measurements cover four orders of magnitude in luminosity, down to about $M_r=-12$ mag or $L=10^7\,L_\odot$, and three orders of magnitude in halo mass, from $10^{12}$ to $10^{15} \, {\rm M}_\odot$. We find a characteristic scale, $M_r\sim-18$ mag or $L\sim10^9\, L_\odot$, below which the slope of the luminosity function becomes systematically steeper. This trend is present for all halo masses and originates mostly from red satellites. This ubiquitous faint-end upturn suggests that it is formation, rather than halo-specific environmental effect, that plays a major role in regulating the stellar masses of faint satellites. We show that the satellite luminosity functions can be described in a simple manner by a double Schechter function with amplitudes scaling with halo mass over the entire range of observables. Combining these conditional luminosity functions with the dark matter halo mass function, we accurately recover the entire field luminosity function over 10 visual magnitudes and reveal that satellite galaxies dominate the field luminosity function at magnitudes fainter than $-17$. We find that the luminosity functions of blue and red satellite galaxies show distinct shapes and we present estimates of the stellar mass fraction as a function of halo mass and galaxy type. Finally, using a simple model, we demonstrate that the abundances and the faint-end slopes of blue and red satellite galaxies can be interpreted in terms of their formation history, with two distinct modes separated by some characteristic time.

The luminosity function of the NoSOCS galaxy cluster sample

We present the analysis of the luminosity function of a large sample of galaxy clusters from the Northern Sky Optical Cluster Survey, using latest data from the Sloan Digital Sky Survey. Our global luminosity function (down to M_r<= -16) does not show the presence of an upturn at faint magnitudes, while we do observe a strong dependence of its shape on both richness and cluster-centric radius, with a brightening of M^* and an increase of the dwarf to giant ratio with richness, indicating that more massive systems are more efficient in creating/retaining a population of dwarf satellites. This is observed both within physical (0.5 R_200) and fixed (0.5 Mpc) apertures, suggesting that the trend is either due to a global effect, operating at all scales, or to a local one but operating on even smaller scales. We further observe a decrease of the relative number of dwarf galaxies towards the cluster center; this is most probably due to tidal collisions or collisional disruption of the dwarfs since merging processes are inhibited by the high velocity dispersions in cluster cores and, furthermore, we do not observe a strong dependence of the bright end on the environment. We find indication that the dwarf to giant ratio decreases with increasing redshift, within 0.07<z<0.2. We also measure a trend for stronger suppression of faint galaxies (below M^*+2) with increasing redshift in poor systems, with respect to more massive ones, indicating that the evolutionary stage of less massive galaxies depends more critically on the environment. Finally we point out that the luminosity function is far from universal; hence the uncertainties introduced by the different methods used to build a composite function may partially explain the variety of faint-end slopes reported in the literature as well as, in some cases, the presence of a faint-end upturn.

THE FAINT END OF THE GALAXY LUMINOSITY FUNCTION IN A1689: A STEEP RED FAINT END UPTURN AT z = 0.18

We present a deep and wide $I$ luminosity function for galaxies in Abell 1689 ($z=0.183$) from a mosaic of HST WFPC2 images covering $10'$ on the side. The main result of this work is the detection of a steep upturn in the dwarf galaxy LF, with $\alpha \sim -2$. The dwarf to giant ratio appears to increase outwards, but this is because giant galaxies are missing in the cluster outskirts, indicating luminosity segregation. The red sequence LF has the same parameters, within errors, as the total LF, showing that the faint end upturn consists of red quiescent galaxies. We speculate that the upturn is connected to the `filling-in' of the red sequence at $z < 0.4$ and may represent the latest installment of `downsizing' as the least massive galaxies are being quenched at the present epoch.

Detailed cluster mass and light profiles of A1703, A370 and RXJ1347−11 from deep Subaru imaging

Weak lensing work can be badly compromised by unlensed foreground and cluster members which dilute the true lensing signal. We show how the lensing amplitude in multi-colour space can be harnessed to securely separate cluster members from the foreground and background populations for three massive clusters, A1703 (z=0.258), A370 (z=0.375) and RXJ1347-11 (z=0.451) imaged with Subaru. The luminosity functions of these clusters when corrected for dilution, show similar faint-end slopes, \alpha ~= -1.0, with no marked faint-end upturn to our limit of M_R ~= -15.0, and only a mild radial gradient. In each case, the radial profile of the M/L ratio peaks at intermediate radius, ~=0.2r_{vir}, at a level of 300-500(M/L_R)_\odot, and then falls steadily towards ~100(M/L_R)_{\odot} at the virial radius, similar to the mean field level. This behaviour is likely due to the relative paucity of central late-type galaxies, whereas for the E/S0-sequence only a mild radial decline in M/L is found for each cluster. We discuss this behaviour in the context of detailed simulations where predictions for tidal stripping may now be tested accurately with observations.

THE LUMINOSITY FUNCTION OF GALAXIES TOMBgVriz∼ –14 INz∼ 0.3 CLUSTERS

We present deep composite luminosity functions (LFs) in B, g, V, r, i, and z for six clusters at 0.14 – 16, as is locally observed. If the faint-end upturn is real, the steepening of the LF must be due to a newly infalling population of faint dwarf galaxies.

The cluster galaxy luminosity function at z= 0.3: a recent origin for the faint-end upturn?

We derive deep luminosity functions (LFs) (to M z = -15) for galaxies in Abell 1835 (z = 0.25) and AC 114 (z = 0.31), and compare these with the local z' LF for 69 clusters. The data show that the faint-end upturn, the excess of galaxies above a single Schechter function at M z < -17, does not exist in the higher redshift clusters. This suggests that the faint-end upturn galaxies have been created recently, by infall into clusters of star-forming field populations or via tidal disruption of brighter objects.

RASS-SDSS Galaxy cluster survey

We analyze the Luminosity Functions (LFs) of a subsample of 69 clusters from the RASS-SDSS galaxy cluster catalog. When calculated within the cluster physical sizes, given by r 200 or r 500 , all the cluster LFs appear to have the same shape, well fitted by a composite of two Schechter functions with a marked upturn and a steepening at the faint-end. Previously reported cluster-to-cluster variations of the LF faint-end slope are due to the use of a metric cluster aperture for computing the LF of clusters of different masses. We determine the composite LF for early- and late-type galaxies, where the typing is based on the galaxy u - r colors. The late-type LF is well fitted by a single Schechter function with a steep slope (α = -2.0 in the r band, within r 200 ). The early-type LF instead cannot be fitted by a single Schechter function, and a composite of two Schechter functions is needed. The faint-end upturn of the global cluster LF is due to the early-type cluster galaxies. The shape of the bright-end tail of the early-type LF does not seem to depend upon the local galaxy density or the distance from ihe cluster center. The late-type LF shows a significant variation only very near the cluster center. On the other hand, the faint-end tail of the early-type LF shows a significant and continuous variation with the environment. We provide evidence that the process responsible for creating the excess population of dwarf early type galaxies in clusters is a threshold process that occurs when the density exceeds ∼500 times the critical density of the Universe. We interpret our results in the context of the harassment scenario where faint early-type cluster galaxies are predicted to be the descendants of tidally-stripped late-type galaxies.

RASS-SDSS galaxy cluster survey. A ubiquitous dwarf galaxy population in clusters

We analyze the Luminosity Functions (LFs) of a subsample of 69 clusters from the RASS-SDSS galaxy cluster catalog. When calculated within the cluster physical sizes, given by r200 or r500, all the cluster LFs appear to have the same shape, well fitted by a composite of two Schechter functions with a marked upturn and a steepening at the faint-end. Previously reported cluster-to-cluster variations of the LF faint-end slope are due to the use of a metric cluster aperture for computing the LF of clusters of different masses. We determine the composite LF for early- and late-type galaxies, where the typing is based on the galaxy u-r colors. The late-type LF is well fitted by a single Schechter function with a steep slope (alpha=-2.0 in the r band, within r200}). The early-type LF instead cannot be fitted by a single Schechter function, and a composite of two Schechter functions is needed. The faint-end upturn of the global cluster LF is due to the early-type cluster galaxies. The shape of the bright-end tail of the early-type LF does not seem to depend upon the local galaxy density or the distance from the cluster center. The late-type LF shows a significant variation only very near the cluster center. On the other hand, the faint-end tail of the early-type LF shows a significant and continuous variation with the environment. We provide evidence that the process responsible for creating the excess population of dwarf early type galaxies in clusters is a threshold process that occurs when the density exceeds ~500 times the critical density of the Universe. We interpret our results in the context of the 'harassment' scenario, where faint early-type cluster galaxies are predicted to be the descendants of tidally-stripped late-type galaxies.