Evolution of the galaxy luminosity function in progenitors of fossil groups

Using the semi-analytic models based on the Millennium simulation, we trace back the evolution of the luminosity function of galaxies residing in progenitors of groups classified by the magnitude gap at redshift zero. We determine the luminosity function of galaxies within $0.25R_{200}, 0.5R_{200}$, and $R_{200}$ for galaxy groups/clusters. The bright end of the galaxy luminosity function of fossil groups shows a significant evolution with redshift, with changes in $M^*$ by $\sim$ 1-2 mag between $z\sim0.5$ and $z=0$ (for the central $0.5R_{200}$), suggesting that the formation of the most luminous galaxy in a fossil group has had a significant impact on the $M^{*}$ galaxies e.g. it is formed as a result of multiple mergers of the $M^{*}$ galaxies within the last $\sim5$ Gyr. In contrast, the slope of the faint end, $\alpha$, of the luminosity function shows no considerable redshift evolution and the number of dwarf galaxies in the fossil groups exhibits no evolution, unlike in non-fossil groups where it grows by $\sim25-42\%$ towards low redshifts. In agreement with previous studies, we also show that fossil groups accumulate most of their halo mass earlier than non-fossil groups. Selecting the fossils at a redshift of 1 and tracing them to a redshift 0, we show that $80\%$ of the fossil groups ($10^{13} M_{\odot} h^{-1}<M_{200}<10^{14} M_{\odot} h^{-1}$) will lose their large magnitude gaps. However, about $40\%$ of fossil clusters ($M_{200}>10^{14} M_{\odot} h^{-1}$) will retain their large gaps.Comment: Accepted for publication in A&A. 13 pages, 15 figure

Optically selected fossil groups; X-ray observations and galaxy properties

We report on the X-ray and optical observations of galaxy groups selected from the 2dfGRS group catalog, to explore the possibility that galaxy groups hosting a giant elliptical galaxy and a large optical luminosity gap present between the two brightest group galaxies, can be associated with an extended X-ray emission, similar to that observed in fossil galaxy groups. The X-ray observations of 4 galaxy groups were carried out with Chandra telescope with 10-20 ksec exposure time. Combining the X-ray and the optical observations we find evidences for the presence of a diffuse extended X-ray emission beyond the optical size of the brightest group galaxy. Taking both the X-ray and the optical criteria, one of the groups is identified as a fossil group and one is ruled out because of the contamination in the earlier optical selection. For the two remaining systems, the X-ay luminosity threshold is close to the convention know for fossil groups. In all cases the X-ray luminosity is below the expected value from the X-ray selected fossils for a given optical luminosity of the group. A rough estimation for the comoving number density of fossil groups is obtained and found to be in broad agreement with the estimations from observations of X-ray selected fossils and predictions of cosmological simulations.Comment: Accepted for publication in MNRA

Mining the gap: evolution of the magnitude gap in X-ray galaxy groups from the 3 square degree XMM coverage of CFHTLS

We present a catalog of 129 X-ray galaxy groups, covering a redshift range 0.04<z<1.23, selected in the ~3 square degree part of the CFHTLS W1 field overlapping XMM observations performed under the XMM-LSS project. We carry out a statistical study of the redshift evolution out to redshift one of the magnitude gap between the first and the second brightest cluster galaxies of a well defined mass-selected group sample. We find that the slope of the relation between the fraction of groups and the magnitude gap steepens with redshift, indicating a larger fraction of fossil groups at lower redshifts. We find that 22.2$\pm$6% of our groups at z$\leq$0.6 are fossil groups. We compare our results with the predictions of three semi-analytic models based on the Millennium simulation. The intercept of the relation between the magnitude of the brightest galaxy and the value of magnitude gap becomes brighter with increasing redshift. This trend is steeper than the model predictions which we attribute to the younger stellar age of the observed brightest cluster galaxies. This trend argues in favor of stronger evolution of the feedback from active galactic nuclei at z<1 compared to the models. The slope of the relation between the magnitude of the brightest cluster galaxy and the value of the gap does not evolve with redshift and is well reproduced by the models, indicating that the tidal galaxy stripping, put forward as an explanation of the occurrence of the magnitude gap, is both a dominant mechanism and is sufficiently well modeled

Brightest Group Galaxies : Stellar Mass and Star Formation Rate (paper I)

We study the distribution and evolution of the stellar mass and the star formation rate (SFR) of the brightest group galaxies (BGGs) over 0.04 <z <1.3 using a large sample of 407 X-ray galaxy groups selected from the COSMOS, AEGIS, and XMM-LSS fields. We compare our results with predictions from the semi-analytic models based on the Millennium simulation. In contrast to model predictions, we find that, as the Universe evolves, the stellarmass distribution evolves towards a normal distribution. This distribution tends to skew to low-mass BGGs at all redshifts implying the presence of a star-forming population of the BGGs with M-S similar to 10(10.5) M-circle dot which results in the shape of the stellar mass distribution deviating from a normal distribution. In agreement with the models and previous studies, we find that the mean stellar mass of BGGs grows with time by a factor of similar to 2 between z = 1.3 and z = 0.1, however, the significant growth occurs above z = 0.4. The BGGs are not entirely a dormant population of galaxies, as low-mass BGGs in low-mass haloes are more active in forming stars than the BGGs in more massive haloes, over the same redshift range. We find that the average SFR of the BGGs evolves steeply with redshift and fraction of the passive BGGs increases as a function of increasing stellar mass and halo mass. Finally, we show that the specific SFR of the BGGs within haloes with M-200Peer reviewe

Brightest group galaxies-II : the relative contribution of BGGs to the total baryon content of groups at z <1.3

We performed a detailed study of the evolution of the star formation rate (SFR) and stellar mass of the brightest group galaxies (BGGs) and their relative contribution to the total baryon budget within $R_{200}$ ($f^{BGG}_{b,200}$). The sample comprises 407 BGGs selected from X-ray galaxy groups ($M_{200}=10^{12.8}-10^{14} \;M_{\odot}$) out to $z\sim1.3$ identified in the COSMOS, XMM-LSS, and AEGIS fields. We find that BGGs constitute two distinct populations of quiescent and star-forming galaxies and their mean SFR is $\sim2$ dex higher than the median SFR at $z 2$ dex. The mean (median) of stellar mass of BGGs has grown by $0.3$ dex since $z=1.3$ to the present day. We show that up to $\sim45\%$ of the stellar mass growth in a star-forming BGG can be due to its star-formation activity. With respect to $f^{BGG}_{b,200}$, we find it to increase with decreasing redshift by $\sim0.35$ dex while decreasing with halo mass in a redshift dependent manner. We show that the slope of the relation between $f^{BGG}_{b,200}$ and halo mass increases negatively with decreasing redshift. This trend is driven by an insufficient star-formation in BGGs, compared to the halo growth rate. We separately show the BGGs with the 20\% highest $f^{BGG}_{b,200}$ are generally non-star-forming galaxies and grow in mass by processes not related to star formation (e.g., dry mergers and tidal striping). We present the $M_\star-M_h$ and $M_\star/M_h-M_h$ relations and compare them with semi-analytic model predictions and a number of results from the literature. We quantify the intrinsic scatter in stellar mass of BGGs at fixed halo mass ($\sigma_{log M_{\star}}$) and find that $\sigma_{log M_{\star}}$ increases from 0.3 dex at $z\sim0.2$ to 0.5 dex at $z\sim1.0$ due to the bimodal distribution of stellar mass

Satellite content and quenching of star formation in galaxy groups at z ~ 1.8

We study the properties of satellites in the environment of massive star-forming galaxies at z ~ 1.8 in the COSMOS field, using a sample of 215 galaxies on the main sequence of star formation with an average mass of ~1011M⊙. At z> 1.5, these galaxies typically trace halos of mass ≳1013M⊙. We use optical-near-infrared photometry to estimate stellar masses and star formation rates (SFR) of centrals and satellites down to ~ 6 × 109M⊙. We stack data around 215 central galaxies to statistically detect their satellite halos, finding an average of ~3 galaxies in excess of the background density. We fit the radial profiles of satellites with simple β-models, and compare their integrated properties to model predictions. We find that the total stellar mass of satellites amounts to ~68% of the central galaxy, while spectral energy distribution modeling and far-infrared photometry consistently show their total SFR to be 25-35% of the central's rate. We also see significant variation in the specific SFR of satellites within the halo with, in particular, a sharp decrease at <100 kpc. After considering different potential explanations, we conclude that this is likely an environmental signature of the hot inner halo. This effect can be explained in the first order by a simple free-fall scenario, suggesting that these low-mass environments can shut down star formation in satellites on relatively short timescales of ~0.3 Gyr

Exoplanets prediction in multiplanetary systems

We present the results of a search for additional exoplanets in allmultiplanetary systems discovered to date, employing a logarithmic spacing between planets in our Solar System known as the Titius-Bode (TB) relation. We use theMarkov Chain Monte Carlo method and separately analyse 229 multiplanetary systems that house at least three or more confirmed planets. We find that the planets in similar to 53% of these systems adhere to a logarithmic spacing relation remarkably better than the Solar System planets. Using the TB relation, we predict the presence of 426 additional exoplanets in 229 multiplanetary systems, of which 197 candidates are discovered by interpolation and 229 by extrapolation. Altogether, 47 predicted planets are located within the habitable zone of their host stars, and 5 of the 47 planets have a maximum mass limit of 0.1-2 M-circle plus and a maximum radius lower than 1.25 R-circle plus. Our results and prediction of additional planets agree with previous studies' predictions; however, we improve the uncertainties in the orbital period measurement for the predicted planets significantly.Peer reviewe

The evolution of the radio luminosity function of group galaxies in COSMOS

To understand the role of the galaxy group environment on galaxy evolution, we present a study of radio luminosity functions (RLFs) of group galaxies based on the Karl G. Jansky Very Large Array-COSMOS 3 GHz Large Project. The radio-selected sample of 7826 COSMOS galaxies with robust optical/near-infrared counterparts, excellent photometric coverage, and the COSMOS X-ray galaxy groups (M_200c > 10^13.3 M_0) enables us to construct the RLF of group galaxies (GGs) and their contribution to the total RLF since z ~ 2.3. Using the Markov chain Monte Carlo algorithm, we fit a redshift-dependent pure luminosity evolution model and a linear and power-law model to the luminosity functions. We compare it with past RLF studies from VLA-COSMOS on individual populations of radio-selected star-forming galaxies (SFGs) and galaxies hosting active galactic nuclei (AGN). These populations are classified based on the presence or absence of a radio excess concerning the star-formation rates derived from the infrared emission. We find that the fraction of radio group galaxies evolves by a factor of ~ 3 from z ~ 2 to the present day. The increase in the galaxy group contribution is due to the radio activity in groups being nearly constant at z < 1, while it is declining in the field. We show that massive galaxies inside galaxy groups remain radio active below redshift 1, contrary to the ones in the field. This evolution in the GG RLF is driven mainly by satellite galaxies in groups. Group galaxies associated with SFGs dominate the GG RLF at z_med = 0.3, while at z_med = 0.8, the peak in the RLF, coinciding with a known overdensity in COSMOS, is mainly driven by AGN. The study provides an observational probe for the accuracy of the numerical predictions of the radio emission in galaxies in a group environment.Comment: submitted to A&A; 15 pages, 6 figures, 8 table

Radio galaxies in galaxy groups: Kinematics, scaling relations, and AGN feedback

We investigate the kinematic properties of a large (N = 998) sample of COSMOS spectroscopic galaxy members distributed among 79 groups. We identify the Brightest Group Galaxies (BGGs) and cross-match our data with the VLA-COSMOS Deep survey at 1.4 GHz, classifying our parent sample into radio/non-radio BGGs and radio/non-radio satellites. The radio luminosity distribution spans from $L_R\sim 2\times 10^{21}$ W Hz$^{-1}$ to $L_R\sim 3\times 10^{25}$ W Hz$^{-1}$. A phase-space analysis, performed by comparing the velocity ratio (line-of-sight velocity divided by the group velocity dispersion) with the galaxy-group centre offset, reveals that BGGs (radio and non-radio) are mostly ($\sim$80 per cent) ancient infallers. Furthermore, the strongest ($L_R\gt 10^{23}$ W Hz$^{-1}$) radio galaxies are always found within 0.2$R_{\rm vir}$ from the group centre. Comparing our samples with HORIZON-AGN, we find that the velocities and offsets of simulated galaxies are more similar to radio BGGs than to non-radio BGGs, albeit statistical tests still highlight significant differences between simulated and real objects. We find that radio BGGs are more likely to be hosted in high-mass groups. Finally, we observe correlations between the powers of BGG radio galaxies and the X-ray temperatures, $T_{\rm x}$, and X-ray luminosities, $L_{\rm x}$, of the host groups. This supports the existence of a link between the intragroup medium and the central radio source. The occurrence of powerful radio galaxies at group centres can be explained by Chaotic Cold Accretion, as the AGN can feed from both the galactic and intragroup condensation, leading to the observed positive $L_{\rm R}-T_{\rm x}$ correlation