Luminosity Function (luminosity + function)

Distribution by Scientific Domains

Kinds of Luminosity Function

  • galaxy luminosity function
  • x-ray luminosity function


  • Selected Abstracts


    Luminosity function of galaxies in rich and poor galaxy clusters

    ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
    J. Krywult
    Abstract Using photometric data from SDSS survey we study the galaxy luminosity function in the 75 rich and poor Abell clusters. The integrated Schechter functions were fitted to unbinned data in the four g, r, i, and z photometric passbands. We find that the luminosity function differs with Abell richness class (R). In all bands the faint-end slope , is steeper in poor clusters than in rich clusters. Moreover, the value of characteristic magnitude M * decreasing with richness class R ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    The variation of the galaxy luminosity function with group properties

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
    Aaron Robotham
    ABSTRACT We explore the shape of the galaxy luminosity function (LF) in groups of different mass by creating composite LFs over large numbers of groups. Following previous work using total group luminosity as the mass indicator, here we split our groups by multiplicity and by estimated virial (group halo) mass, and consider red (passive) and blue (star-forming) galaxies separately. In addition, we utilize two different group catalogues (2PIGG and Yang et al.) in order to ascertain the impact of the specific grouping algorithm and further investigate the environmental effects via variations in the LF with position in groups. Our main results are that LFs show a steepening faint end for early-type galaxies as a function of group mass/multiplicity, with a much suppressed trend (evident only in high mass groups) for late-type galaxies. Variations between LFs as a function of group mass are robust irrespective of which grouping catalogue is used, and broadly speaking what method for determining group ,mass' is used. We find in particular that there is a significant deficit of low-mass passive galaxies in low-multiplicity groups, as seen in high-redshift clusters. Further to this, the variation in the LF appears to only occur in the central regions of systems, and in fact seems to be most strongly dependent on the position in the group relative to the virial radius. Finally, distance,rank magnitude relations were considered. Only the Yang groups demonstrated any evidence of a correlation between a galaxy's position relative to the brightest group member and its luminosity. 2PIGG possessed no such gradient, the conclusion being the friend-of-friend algorithm suppresses the signal for weak luminosity,position trends and the Yang grouping algorithm naturally enhances it. [source]


    The velocity function of gas-rich galaxies

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
    M. A. Zwaan
    ABSTRACT We measure the distribution function of rotational velocities ,(Vc) of late-type galaxies from the HIPASS galaxy catalogue. Previous measurements of the late-type velocity function are indirect, derived by converting the galaxy luminosity function using the relation between galaxy luminosity and rotation velocity (the Tully,Fisher relation). The advantage of H i Parkes All Sky Survey is that space densities and velocity widths are both derived from the same survey data. We find good agreement with earlier inferred measurements of ,(Vc), but we are able to define the space density of objects with Vc as low as 30 km s,1. The measured velocity function is ,flat' (power-law slope ,,,1.0) below Vc, 100 km s,1. We compare our results with predictions based on , cold dark matter simulations and find good agreement for rotational velocities in excess of 100 km s,1, but at lower velocities current models over-predict the space density of objects. At Vc= 30 km s,1, this discrepancy is approximately a factor of 20. [source]


    X-ray groups and clusters of galaxies in the Subaru,XMM Deep Field

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
    A. Finoguenov
    Abstract We present the results of a search for galaxy clusters in the Subaru,XMM Deep Field (SXDF). We reach a depth for a total cluster flux in the 0.5,2 keV band of 2 10,15 erg cm,2 s,1 over one of the widest XMM,Newton contiguous raster surveys, covering an area of 1.3 deg2. Cluster candidates are identified through a wavelet detection of extended X-ray emission. The red-sequence technique allows us to identify 57 cluster candidates. We report on the progress with the cluster spectroscopic follow-up and derive their properties based on the X-ray luminosity and cluster scaling relations. In addition, three sources are identified as X-ray counterparts of radio lobes, and in three further sources, an X-ray counterpart of the radio lobes provides a significant fraction of the total flux of the source. In the area covered by near-infrared data, our identification success rate achieves 86 per cent. We detect a number of radio galaxies within our groups, and for a luminosity-limited sample of radio galaxies we compute halo occupation statistics using a marked cluster mass function. We compare the cluster detection statistics in the SXDF with that in the literature and provide the modelling using the concordance cosmology combined with current knowledge of the X-ray cluster properties. The joint cluster log(N) , log(S) is overpredicted by the model, and an agreement can be achieved through a reduction of the concordance ,8 value by 5 per cent. Having considered the dn/dz and the X-ray luminosity function of clusters, we conclude that to pin down the origin of disagreement a much wider (50 deg2) survey is needed. [source]


    Constraints on modified gravity from the observed X-ray luminosity function of galaxy clusters

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009
    David Rapetti
    ABSTRACT We use measurements of the growth of cosmic structure, as inferred from the observed evolution of the X-ray luminosity function (XLF) of galaxy clusters, to constrain departures from general relativity (GR) on cosmological scales. We employ the popular growth rate parameterization, ,m(z),, for which GR predicts a growth index ,, 0.55. We use observations of the cosmic microwave background (CMB), type Ia supernovae (SNIa) and X-ray cluster gas mass fractions (fgas), to simultaneously constrain the expansion history and energy content of the Universe, as described by the background model parameters: ,m, w and ,k, i.e. the mean matter density, the dark energy equation of state parameter and the mean curvature, respectively. Using conservative allowances for systematic uncertainties, in particular for the evolution of the mass,luminosity scaling relation in the XLF analysis, we find ,= 0.51+0.16,0.15 and ,m= 0.27 0.02 (68.3 per cent confidence limits), for a flat cosmological constant, cold dark matter (,CDM) background model. Allowing w to be a free parameter, we find ,= 0.44+0.17,0.15. Relaxing the flatness prior in the ,CDM model, we obtain ,= 0.51+0.19,0.16. When in addition to the XLF data we use the CMB data to constrain , through the ISW effect, we obtain a combined constraint of ,= 0.45+0.14,0.12 for the flat ,CDM model. Our analysis provides the tightest constraints to date on the growth index. We find no evidence for departures from GR on cosmological scales. [source]


    Are fossil groups a challenge of the cold dark matter paradigm?

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009
    Stefano Zibetti
    ABSTRACT We study six groups and clusters of galaxies suggested in the literature to be ,fossil' systems (i.e. to have luminous diffuse X-ray emission and a magnitude gap of at least 2 mag R between the first and the second ranked member within half of the virial radius), each having good quality X-ray data and Sloan Digital Sky Survey (SDSS) spectroscopic or photometric coverage out to the virial radius. The poor cluster AWM 4 is clearly established as a fossil system, and we confirm the fossil nature of four other systems (RX J1331.5+1108, RX J1340.6+4018, RX J1256.0+2556 and RX J1416.4+2315), while the cluster RX J1552.2+2013 is disqualified as fossil system. For all systems, we present the luminosity functions within 0.5 and 1 virial radius that are consistent, within the uncertainties, with the universal luminosity function of clusters. For the five bona fide fossil systems, having a mass range 2 1013,3 1014 M,, we compute accurate cumulative substructure distribution functions (CSDFs) and compare them with the CSDFs of observed and simulated groups/clusters available in the literature. We demonstrate that the CSDFs of fossil systems are consistent with those of normal observed clusters and do not lack any substructure with respect to simulated galaxy systems in the cosmological , cold dark matter (,CDM) framework. In particular, this holds for the archetype fossil group RX J1340.6+4018 as well, contrary to earlier claims. [source]


    Global properties of the rich cluster ABCG 209 at z, 0.2. Spectroscopic and photometric catalogue

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2008
    A. Mercurio
    ABSTRACT This paper is aimed at giving an overview of the global properties of the rich cluster of galaxies ABCG 209. This is achieved by complementing the already available data with new medium-resolution spectroscopy and near-infrared (NIR) photometry which allow us to (i) analyse in detail the cluster dynamics, distinguishing among galaxies belonging to different substructures and deriving their individual velocity distributions, using a total sample of 148 galaxies in the cluster region, of which 134 belonging to the cluster; (ii) derive the cluster NIR luminosity function; (iii) study the Kormendy relation and the photometric plane of cluster early-type galaxies (ETGs). Finally we provide an extensive photometric (optical and NIR) and spectroscopic data set for such a complex system to be used in further analyses investigating the nature, formation and evolution of rich clusters of galaxies. The present study shows that the cluster is characterized by a very high value of the line-of-sight velocity dispersion: ,v= 1268+93,84 km s,1, that results in a virial mass of Mvir= 2.95+0.80,0.78 1015 h,170 M, within Rvir= 3.42 h,170 Mpc. The analysis of the velocity dispersion profile shows that such high value of ,v is already reached in the central cluster region. There is evidence of three significant substructures, the primary one having a velocity dispersion of ,v= 847+52,49 km s,1, which makes it consistent with mass estimates from weak lensing analyses. This observational scenario confirms that ABCG 209 is presently undergoing strong dynamical evolution with the merging of two or more subclumps. This interpretation is also supported by the detection of a radio halo suggesting that there is a recent or ongoing merging. Cluster ETGs follow a Kormendy relation whose slope is consistent with previous studies both at optical and NIR wavelengths. We investigate the origin of the intrinsic scatter of the photometric plane due to trends of stellar populations, using line indices as indicators of age, metallicity and ,/Fe enhancement. We find that the chemical evolution of galaxies could be responsible for the intrinsic dispersion of the photometric plane. [source]


    Redshifted 21-cm observations of high-redshift quasar proximity zones

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
    J. Stuart B. Wyithe
    ABSTRACT The introduction of low-frequency radio arrays is expected to revolutionize the study of the reionization epoch. Observation of the contrast in redshifted 21-cm emission between a large H ii region and the surrounding neutral intergalactic medium (IGM) will be the simplest and most easily interpreted signature. However, the highest redshift quasars known are thought to reside in an ionized IGM. Using a semi-analytic model we describe the redshifted 21-cm signal from the IGM surrounding quasars discovered using the i -drop-out technique (i.e. quasars at z, 6). We argue that while quasars at z < 6.5 seem to reside in the post-overlap IGM, they will still provide valuable probes of the late stages of the overlap era because the light-travel time across a quasar proximity zone should be comparable to the duration of overlap. For redshifted 21-cm observations within a 32-MHz bandpass, we find that the subtraction of a spectrally smooth foreground will not remove spectral features due to the proximity zone. These features could be used to measure the neutral hydrogen content of the IGM during the late stages of reionization. The density of quasars at z, 6 is now well constrained. We use the measured quasar luminosity function to estimate the prospects for discovery of high-redshift quasars in fields that will be observed by the Murchison Widefield Array. [source]


    Where are the cosmic metals at z, 3?

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
    Jesper Sommer-Larsen
    ABSTRACT The global temperature distribution of the cosmic gas-phase oxygen at z, 3 is determined by combining high-resolution cosmological simulations of individual protogalactic as well as larger regions with the observed, extinction-corrected, rest-frame V -band galaxy luminosity function. The simulations have been performed with three different stellar initial mass functions (IMFs), a Kroupa (K98), a Salpeter (S) and an Arimoto,Yoshii (AY), spanning a range of a factor of 5 in chemical yield and specific supernova type II energy feedback. Gas-phase oxygen is binned according to T as log(T) , 4.0 (,cold'), log(T) , 4.5 (,warm') and log(T) , 5.0, 5.5, 6.0, 6.5, 7.0 (,hot' phases). Oxygen is found to be distributed over all T phases, in particular for the top-heavy AY IMF. But, at variance with previous works, it is found that for the K98 and S IMFs the cold phase is the most important. For these IMFs it contains 47 and 37 per cent, respectively, of all gas-phase oxygen, mainly at fairly high density, nH, 0.1 cm,3. The implications of this in relation to observational damped Ly, absorber studies are discussed. In relation to ,missing metals' it is found that a significant fraction of the oxygen is located in a warm/hot phase that may be very difficult to detect. Moreover, it is found that less than about 20,25 per cent of the cosmic oxygen is associated with galaxies brighter than MV,,22, i.e. the faintest galaxy luminosities probed by current metallicity determinations for Lyman-break galaxies (LBGs). Hence, 75,80 per cent of the oxygen is also in this sense ,missing'. From the LBG-based, ,, 1500 ultraviolet luminosity density history at z, 3, we obtain an essentially IMF-independent constraint on the mean oxygen density at z= 3. We compare this to what is obtained from our models, for the three different IMFs. We find that the K98 IMF is strongly excluded, as the chemical yield is simply too small, the Salpeter is marginally excluded, and the AY matches the constraint well. The K98 IMF can only match the data if the ,, 1500 extinction corrections have been overestimated by factor of ,4, which seems highly unlikely. The yields for K98 are also far too small to match the observational data for C iv. The optimal IMF should have a yield intermediate between the S and AY. [source]


    A deep i -selected multiwaveband galaxy catalogue in the COSMOS field,

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2008
    A. Gabasch
    ABSTRACT In this paper we present a deep and homogeneous i -band-selected multiwaveband catalogue in the COSMOS field covering an area of about 0.7 deg2. Our catalogue with a formal 50 per cent completeness limit for point sources of i, 26.7 comprises about 290 000 galaxies with information in 8 passbands. We combine publicly available u, B, V, r, i, z and K data with proprietary imaging in H band. We discuss in detail the observations, the data reduction, and the photometric properties of the H -band data. We estimate photometric redshifts for all the galaxies in the catalogue. A comparison with 162 spectroscopic redshifts in the redshift range 0 ,z, 3 shows that the achieved accuracy of the photometric redshifts is ,z/(zspec+ 1) , 0.035 with only ,2 per cent outliers. We derive absolute UV magnitudes and investigate the evolution of the luminosity function evaluated in the rest-frame UV (1500 ). There is a good agreement between the luminosity functions derived here and the luminosity functions derived in the FORS Deep Field. We see a similar brightening of M* and a decrease of ,* with redshift. The catalogue including the photometric redshift information is made publicly available. [source]


    Stellar contents and star formation in the young star cluster Be 59

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008
    A. K. Pandey
    ABSTRACT We present UBV Ic CCD photometry of the young open cluster Be 59 with the aim to study the star formation scenario in the cluster. The radial extent of the cluster is found to be ,10 arcmin (2.9 pc). The interstellar extinction in the cluster region varies between E(B,V) , 1.4 to 1.8 mag. The ratio of total-to-selective extinction in the cluster region is estimated as 3.7 0.3. The distance of the cluster is found to be 1.00 0.05 kpc. Using near-infrared (NIR) colours and slitless spectroscopy, we have identified young stellar objects (YSOs) in the open cluster Be 59 region. The ages of these YSOs range between <1 and ,2 Myr, whereas the mean age of the massive stars in the cluster region is found to be ,2 Myr. There is evidence for second-generation star formation outside the boundary of the cluster, which may be triggered by massive stars in the cluster. The slope of the initial mass function, ,, in the mass range 2.5 < M/M,, 28 is found to be ,1.01 0.11 which is shallower than the Salpeter value (,1.35), whereas in the mass range 1.5 < M/M,, 2.5 the slope is almost flat. The slope of the K -band luminosity function is estimated as 0.27 0.02, which is smaller than the average value (,0.4) reported for young embedded clusters. Approximately 32 per cent of H, emission stars of Be 59 exhibit NIR excess indicating that inner discs of the T Tauri star (TTS) population have not dissipated. The Midcourse Space Experiment (MSX) and IRAS-HIRES images around the cluster region are also used to study the emission from unidentified infrared bands and to estimate the spatial distribution of optical depth of warm and cold interstellar dust. [source]


    Black hole growth in hierarchical galaxy formation

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
    Rowena K. Malbon
    ABSTRACT We incorporate a model for black hole growth during galaxy mergers into the semi-analytical galaxy formation model based on ,CDM proposed by Baugh et al. Our black hole model has one free parameter, which we set by matching the observed zero-point of the local correlation between black hole mass and bulge luminosity. We present predictions for the evolution with redshift of the relationships between black hole mass and bulge properties. Our simulations reproduce the evolution of the optical luminosity function of quasars. We study the demographics of the black hole population and address the issue of how black holes acquire their mass. We find that the direct accretion of cold gas during starbursts is an important growth mechanism for lower mass black holes and at high redshift. On the other hand, the re-assembly of pre-existing black hole mass into larger units via merging dominates the growth of more massive black holes at low redshift. This prediction could be tested by future gravitational wave experiments. As redshift decreases, progressively less massive black holes have the highest fractional growth rates, in line with recent claims of ,downsizing' in quasar activity. [source]


    The mass function of , Centauri down to 0.15 M,,

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
    A. Sollima
    ABSTRACT By means of deep FORS1/VLT and ACS/Hubble Space Telescope observations of a wide area in the stellar system , Cen we measured the luminosity function of main-sequence stars down to R= 22.6 and IF814W= 24.5. The luminosity functions obtained have been converted into mass functions and compared with analytical initial mass functions (IMFs) available in the literature. The mass function obtained, reaching M, 0.15 M,, can be well reproduced by a broken power law with indices ,=,2.3 for M > 0.5 M, and ,=,0.8 for M < 0.5 M,. Since the stellar populations of , Cen have been proved to be actually unaffected by dynamical evolution processes, the mass function measured in this stellar system should represent the best approximation of the IMF of a star cluster. The comparison with the MF measured in other Galactic globular clusters suggests that possible primordial differences in the slope of the low-mass end of their MF could exist. [source]


    The DEEP2 galaxy redshift survey: the evolution of the blue fraction in groups and the field

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
    Brian F. Gerke
    ABSTRACT We explore the behaviour of the blue galaxy fraction over the redshift range 0.75 ,z, 1.3 in the DEEP2 Survey, both for field galaxies and for galaxies in groups. The primary aim is to determine the role that groups play in driving the evolution of galaxy colour at high z. In pursuing this aim, it is essential to define a galaxy sample that does not suffer from redshift-dependent selection effects in colour,magnitude space. We develop four such samples for this study: at all redshifts considered, each one is complete in colour,magnitude space, and the selection also accounts for evolution in the galaxy luminosity function. These samples will also be useful for future evolutionary studies in DEEP2. The colour segregation observed between local group and field samples is already in place at z, 1: DEEP2 groups have a significantly lower blue fraction than the field. At fixed z, there is also a correlation between blue fraction and galaxy magnitude, such that brighter galaxies are more likely to be red, both in groups and in the field. In addition, there is a negative correlation between blue fraction and group richness. In terms of evolution, the blue fraction in groups and the field remains roughly constant from z= 0.75 to 1, but beyond this redshift the blue fraction in groups rises rapidly with z, and the group and field blue fractions become indistinguishable at z, 1.3. Careful tests indicate that this effect does not arise from known systematic or selection effects. To further ensure the robustness of this result, we build on previous mock DEEP2 catalogues to develop mock catalogues that reproduce the colour,overdensity relation observed in DEEP2 and use these to test our methods. The convergence between the group and field blue fractions at z, 1.3 implies that DEEP2 galaxy groups only became efficient at quenching star formation at z, 2; this result is broadly consistent with other recent observations and with current models of galaxy evolution and hierarchical structure growth. [source]


    Satellite systems around galaxies in hydrodynamic simulations

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007
    Noam I. Libeskind
    ABSTRACT We investigate the properties of satellite galaxies formed in N -body/SPH simulations of galaxy formation in the ,CDM cosmology. The simulations include the main physical effects thought to be important in galaxy formation and, in several cases, produce realistic spiral discs. In total, a sample of nine galaxies of luminosity comparable to the Milky Way was obtained. At magnitudes brighter than the resolution limit, MV=,12, the luminosity function of the satellite galaxies in the simulations is in excellent agreement with data for the Local Group. The radial number density profile of the model satellites, as well as their gas fractions also match observations very well. In agreement with previous N -body studies, we find that the satellites tend to be distributed in highly flattened configurations whose major axis is aligned with the major axis of the (generally triaxial) dark halo. In two out of three systems with sufficiently large satellite populations, the satellite system is nearly perpendicular to the plane of the galactic disc, a configuration analogous to that observed in the Milk Way. The discs themselves are perpendicular to the minor axis of their host haloes in the inner parts, and the correlation between the orientation of the galaxy and the shape of the halo persists even out to the virial radius. However, in one case the disc's minor axis ends up, at the virial radius, perpendicular to the minor axis of the halo. The angular momenta of the galaxies and their host halo tend to be well aligned. [source]


    A Subaru/Suprime-Cam wide-field survey of globular cluster populations around M87 , I. Observation, data analysis and luminosity function

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
    Naoyuki Tamura
    ABSTRACT In this paper and a companion paper, we report on a wide-field imaging survey of the globular cluster (GC) populations around M87 carried out with Suprime-Cam on the 8.2-m Subaru telescope. Here, we describe the observations, data reduction and data analysis, and present luminosity functions of GC populations around M87 and NGC 4552, another luminous Virgo elliptical in our survey field. The imaging data were taken in the B, V and I bands with a sky coverage of extending from the M87 centre out to ,0.5 Mpc. GC candidates were selected by applying a colour criterion on the B,V and V,I diagram to unresolved objects, which greatly reduces contamination. The data from control fields taken with Subaru/Suprime-Cam were also analysed for subtraction of contamination in the GC sample. These control field data are compatible with those in the M87 field in terms of the filter set (BVI), limiting magnitudes and image quality, which minimize the possibility of introducing any systematic errors into the subtractive correction. We investigate GC luminosity functions (GCLFs) at distances , 10 arcmin (,45 kpc) from the host galaxy centre in detail. By fitting Gaussians to the GCLFs, the V -band turnover magnitude (VTO) is estimated to be 23.62 0.06 and 23.56 0.20 mag for the GC population in M87 and NGC 4552, respectively. The GCLF is found to be a function of GC colour; VTO of the red GC subpopulation (V,I > 1.1) is fainter than that of the blue GC subpopulation (V,I, 1.1) in both M87 and NGC 4552, as expected if the colour differences are primarily due to a metallicity effect, and the mass functions of the two subpopulations are similar. The radial dependence of the GCLF is also investigated for the GC population in M87. The GCLF of each subpopulation at 1 ,R, 5 arcmin is compared to that at 5 ,R, 10 arcmin, but no significant trend with distance is found in the shape of the GCLF. We also estimate GC-specific frequencies (SN) for M87 and NGC 4552. The SN of the M87 GC population is estimated to be 12.5 0.8 within 25 arcmin. The SN value of the NGC 4552 GC population is estimated to be 5.0 0.6 within 10 arcmin. [source]


    The Millennium Galaxy Catalogue: a census of local compact galaxies

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
    J. Liske
    ABSTRACT We use the Millennium Galaxy Catalogue (MGC) to study the effect of compact galaxies on the local field galaxy luminosity function (LF). Here, we observationally define as ,compact' galaxies that are too small to be reliably distinguished from stars using a standard star,galaxy separation technique. In particular, we estimate the fraction of galaxies that are misclassified as stars due to their compactness. We have spectroscopically identified all objects to Bmgc= 20 mag in a 1.14-deg2 subregion of the MGC, regardless of morphology. From these data we develop a model of the high surface brightness (SB) incompleteness and estimate that ,1 per cent of galaxies with Bmgc < 20 mag are misclassified as stars, with an upper limit of 2.3 per cent at 95 per cent confidence. However, since the missing galaxies are preferentially sub- L* their effect on the faint end of the LF is substantially amplified: we find that they contribute ,6 per cent to the total LF in the range ,17 < MB < ,14 mag, which raises the faint end slope , by 0.03+0.02,0.01. Their contribution to the total B -band luminosity density is ,2 per cent. Roughly half of the missing galaxies have already been recovered through spectroscopy of morphologically stellar targets selected mainly by colour. We find that the missing galaxies mostly consist of intrinsically small, blue, star forming, sub- L* objects. In combination with the recent results of Driver et al. we have now demonstrated that the MGC is free from both high- and low-SB selection bias for giant galaxies (MB,,17 mag). Dwarf galaxies, on the other hand, are significantly affected by these selection effects. To gain a complete view of the dwarf population will require both deeper and higher-resolution surveys. [source]


    Where are z= 4 Lyman Break Galaxies?

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
    Results from conditional luminosity function models of luminosity-dependent clustering
    ABSTRACT Using the conditional luminosity function (CLF) , the luminosity distribution of galaxies in a dark matter halo , as a way to model galaxy statistics, we study how z= 4 Lyman Break Galaxies (LBGs) are distributed in dark matter haloes. For this purpose, we measure luminosity-dependent clustering of LBGs in the Subaru/XMM,Newton Deep Field by separating a sample of 16 920 galaxies to three magnitude bins in i, band between 24.5 and 27.5. Our model fits to data show a possible trend for more-luminous galaxies to appear as satellites in more-massive haloes; the minimum halo mass in which satellites appear is 3.9+4.1,3.5 1012, 6.2+3.8,4.9 1012 and 9.6+7.0,4.6 1012 M, (1, errors) for galaxies with 26.5 < i, < 27.5, 25.5 < i, < 26.5 and 24.5 < i, < 25.5 mag, respectively. The satellite fraction of galaxies at z= 4 in these magnitude bins is 0.13,0.3, 0.09,0.22 and 0.03,0.14, respectively, where the 1, ranges account for differences coming from two different estimates of the z= 4 LF from the literature. To jointly explain the LF and the large-scale linear bias factor of z= 4 LBGs as a function of rest UV luminosity requires central galaxies to be brighter in UV at z= 4 than present-day galaxies in same dark matter mass haloes. Moreover, UV luminosity of central galaxies in haloes with total mass greater than roughly 1012 M, must decrease from z= 4 to today by an amount more than the luminosity change for galaxies in haloes below this mass. This mass-dependent luminosity evolution is preferred at more than 3, confidence level compared to a pure-luminosity evolution scenario where all galaxies decrease in luminosity by the same amount from z= 4 to today. The scenario preferred by the data is consistent with the ,downsizing' picture of galaxy evolution. [source]


    A deep kinematic survey of planetary nebulae in the Andromeda galaxy using the Planetary Nebula Spectrograph

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006
    H. R. Merrett
    ABSTRACT We present a catalogue of positions, magnitudes and velocities for 3300 emission-line objects found by the Planetary Nebula Spectrograph in a survey of the Andromeda galaxy, M31. Of these objects, 2615 are found likely to be planetary nebulae (PNe) associated with M31. The survey area covers the whole of M31's disc out to a radius of . Beyond this radius, observations have been made along the major and minor axes, and the Northern Spur and Southern Stream regions. The calibrated data have been checked for internal consistency and compared with other catalogues. With the exception of the very central, high surface brightness region of M31, this survey is complete to a magnitude limit of m5007, 23.75, 3.5 mag into the PN luminosity function. We have identified emission-line objects associated with M31's satellites and other background galaxies. We have examined the data from the region tentatively identified as a new satellite galaxy, Andromeda VIII, comparing it to data in the other quadrants of the galaxy. We find that the PNe in this region have velocities that appear to be consistent with membership of M31 itself. The luminosity function of the surveyed PNe is well matched to the usual smooth monotonic function. The only significant spatial variation in the luminosity function occurs in the vicinity of M31's molecular ring, where the luminosities of PNe on the near side of the galaxy are systematically ,0.2 mag fainter than those on the far side. This difference can be explained naturally by a modest amount of obscuration by the ring. The absence of any difference in luminosity function between bulge and disc suggests that the sample of PNe is not strongly populated by objects whose progenitors are more massive stars. This conclusion is reinforced by the excellent agreement between the number counts of PNe and the R -band light. The number counts of kinematically selected PNe also allow us to probe the stellar distribution in M31 down to very faint limits. There is no indication of a cut-off in M31's disc out to beyond four scalelengths, and no signs of a spheroidal halo population in excess of the bulge out to 10 effective bulge radii. We have also carried out a preliminary analysis of the kinematics of the surveyed PNe. The mean streaming velocity of the M31 disc PNe is found to show a significant asymmetric drift out to large radii. Their velocity dispersion, although initially declining with radius, flattens out to a constant value in the outer parts of the galaxy. There are no indications that the disc velocity dispersion varies with PN luminosity, once again implying that the progenitors of PNe of all magnitudes form a relatively homogeneous old population. The dispersion profile and asymmetric drift results are shown to be mutually consistent, but require that the disc flares with radius if the shape of its velocity ellipsoid remains invariant. [source]


    Cosmic evolution of metal densities: the enrichment of the intergalactic medium

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006
    F. Calura
    ABSTRACT By means of chemo-photometric models for galaxies of different morphological types, we have carried out a detailed study of the history of element production by spheroidal and dwarf irregular galaxies. Spheroidal galaxies suffer a strong and intense star formation episode at early times. In dwarf irregulars, the star formation rate (SFR) proceeds at a low regime but continuously. Both galactic types enrich the intergalactic medium (IGM) with metals by means of galactic winds. We have assumed that the galaxy number density is fixed and normalized to the value of the optical luminosity function observed in the local Universe. Our models allow us to investigate in detail how the metal fractions locked up in stars in spheroids and dwarf irregulars, those present in the interstellar medium (ISM) and those ejected into the IGM have changed with cosmic time. By relaxing the instantaneous recycling approximation and taking into account stellar lifetimes, for the first time we have studied the evolution of the chemical abundance ratios in the IGM and compared our predictions with a set of observations by various authors. Our results indicate that the bulk of the IGM enrichment is due to spheroids, with dwarf irregular galaxies playing a negligible role. Our predictions grossly account for the [O/H] observed in the IGM at high redshift, but overestimate the [C/H]. Furthermore, it appears hard to reproduce the abundance ratios observed in the high-redshift IGM. Some possible explanations are discussed in the text. This is the first attempt to study the abundance ratios in the IGM by means of detailed chemical evolution models which take into account the stellar lifetimes. Numerical simulations adopting our chemical evolution prescriptions could be useful to improve our understanding of the IGM chemical enrichment. [source]


    The properties of Ly, emitting galaxies in hierarchical galaxy formation models

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006
    M. Le Delliou
    ABSTRACT We present detailed predictions for the properties of Ly,-emitting galaxies in the framework of the , cold dark matter cosmology, calculated using the semi-analytical galaxy formation model galform. We explore a model that assumes a top-heavy initial mass function in starbursts and that has previously been shown to explain the sub-millimetre number counts and the luminosity function of Lyman-break galaxies at high redshift. We show that this model, with the simple assumption that a fixed fraction of Ly, photons escape from each galaxy, is remarkably successful at explaining the observed luminosity function of Ly, emitters (LAEs) over the redshift range 3 < z < 6.6. We also examine the distribution of Ly, equivalent widths and the broad-band continuum magnitudes of emitters, which are in good agreement with the available observations. We look more deeply into the nature of LAEs, presenting predictions for fundamental properties such as the stellar mass and radius of the emitting galaxy and the mass of the host dark matter halo. The model predicts that the clustering of LAEs at high redshifts should be strongly biased relative to the dark matter, in agreement with observational estimates. We also present predictions for the luminosity function of LAEs at z > 7, a redshift range that is starting to be be probed by near-infrared surveys and using new instruments such as the Dark Ages Z Lyman Explorer (DAzLE). [source]


    Halo model at its best: constraints on conditional luminosity functions from measured galaxy statistics

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006
    Asantha Cooray
    ABSTRACT Using the conditional luminosity function (CLF; the luminosity distribution of galaxies in a dark matter halo) as the fundamental building block, we present an empirical model for the galaxy distribution. The model predictions are compared with the published luminosity function (LF) and clustering statistics from the Sloan Digital Sky Survey (SDSS) at low redshifts, galaxy correlation functions from the Classifying Objects by Medium-Band Observations 17 (COMBO-17) survey at a redshift of 0.6, the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey at a redshift of unity, the Great Observatories Deep Origins Survey (GOODS) at a redshift around 3 and the Subaru/XMM,Newton Deep Field data at a redshift of 4. The comparison with statistical measurements allows us to constrain certain parameters related to analytical descriptions on the relation between a dark matter halo and its central galaxy luminosity, its satellite galaxy luminosity, and the fraction of early- and late-type galaxies of that halo. With the SDSS r -band LF at Mr < ,17, the lognormal scatter in the central galaxy luminosity at a given halo mass in the central galaxy,halo mass, Lc(M), relation is constrained to be 0.17+0.02,0.01, with 1, errors here and below. For the same galaxy sample, we find no evidence for a low-mass cut-off in the appearance of a single central galaxy in dark matter haloes, with the 68 per cent confidence level upper limit on the minimum mass of dark matter haloes to host a central galaxy, with luminosity Mr < ,17, is 2 1010 h,1 M,. If the total luminosity of a dark matter halo varies with halo mass as Lc(M) (M/Msat),s when M > Msat, using SDSS data, we find that Msat= (1.2+2.9,1.1) 1013 h,1 M, and power-law slope ,s= 0.56+0.19,0.17 for galaxies with Mr < ,17 at z < 0.1. At z, 0.6, the COMBO-17 data allows these parameters for MB < ,18 galaxies to be constrained as (3.3+4.9,3.0) 1013 h,1 M, and (0.62+0.33,0.27), respectively. At z, 4, Subaru measurements constrain these parameters for MB < ,18.5 galaxies as (4.12+5.90,4.08) 1012 h,1 M, and (0.55+0.32,0.35), respectively. The redshift evolution associated with these parameters can be described as a combination of the evolution associated with the halo mass function and the luminosity,halo mass relation. The single parameter well constrained by clustering measurements is the average of the total satellite galaxy luminosity corresponding to the dark matter halo distribution probed by the galaxy sample. For SDSS, ,Lsat,= (2.1+0.8,0.4) 1010 h,2 L,, while for GOODS at z, 3, ,Lsat, < 2 1011 h,2 L,. For SDSS, the fraction of galaxies that appear as satellites is 0.13+0.03,0.03, 0.11+0.05,0.02, 0.11+0.12,0.03 and 0.12+0.33,0.05 for galaxies with luminosities in the r, band from ,22 to ,21, ,21 to ,20, ,20 to ,19 and ,19 to ,18, respectively. In addition to constraints on central and satellite CLFs, we also determine model parameters of the analytical relations that describe the fraction of early- and late-type galaxies in dark matter haloes. We use our CLFs to establish the probability distribution of halo mass in which galaxies of a given luminosity could be found either at halo centres or as satellites. Finally, to help establish further properties of the galaxy distribution, we propose the measurement of cross-clustering between galaxies divided into two distinctly different luminosity bins. Our analysis shows how CLFs provide a stronger foundation to built-up analytical models of the galaxy distribution when compared with models based on the halo occupation number alone. [source]


    The luminosity dependence of the type 1 active galactic nucleus fraction

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005
    Chris Simpson
    ABSTRACT Using a complete, magnitude-limited sample of active galaxies from the Sloan Digital Sky Survey, we show that the fraction of broad-line (type 1) active galactic nuclei (AGNs) increases with luminosity of the isotropically emitted [O iii] narrow emission line. Our results are quantitatively in agreement with, and far less uncertain than, similar trends found from studies of X-ray and radio-selected active galaxies. While the correlation between broad-line fraction and luminosity is qualitatively consistent with the receding torus model, its slope is shallower and we therefore propose a modification to this model where the height of the torus increases slowly with AGN luminosity. We demonstrate that the faint-end slope of the AGN luminosity function steepens significantly when a correction for ,missing' type 2 objects is made, and that this can substantially affect the overall AGN luminosity density extrapolated from samples of more luminous objects. [source]


    The XMM,Newton Needles in the Haystack Survey: the local X-ray luminosity function of ,normal' galaxies

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005
    I. Georgantopoulos
    ABSTRACT In this paper we estimate the local (z < 0.22) X-ray luminosity function of ,normal' galaxies derived from the XMM,Newton Needles in the Haystack Survey. This is an on-going project that aims to identify X-ray-selected normal galaxies (i.e. non-AGN dominated) in the local Universe. We are using a total of 70 XMM,Newton fields covering an area of 11 deg2 which overlap with the Sloan Digital Sky Survey Data Release 2. Normal galaxies are selected on the basis of their resolved optical light profile, their low X-ray-to-optical flux ratio [log (fx/fo) < , 2] and soft X-ray colours. We find a total of 28 candidate normal galaxies to the 0.5,8 keV band flux limit of ,2 10,15 erg cm,2 s,1. Optical spectra are available for most sources in our sample (82 per cent). These provide additional evidence that our sources are bona fide normal galaxies with X-ray emission coming from diffuse hot gas emission and/or X-ray binaries rather than a supermassive black hole. 16 of our galaxies have narrow emission lines or a late-type spectral energy distribution (SED) while the remaining 12 present only absorption lines or an early-type SED. Combining our XMM,Newton sample with 18 local (z < 0.22) galaxies from the Chandra Deep Field North and South surveys, we construct the local X-ray luminosity function of normal galaxies. This can be represented with a Schechter form with a break at L,, 3+1.4,1.0 1041 erg s,1 and a slope of ,, 1.78 0.12. Using this luminosity function and assuming pure luminosity evolution of the form ,(1 +z)3.3 we estimate a contribution to the X-ray background from normal galaxies of ,10,20 per cent (0.5,8 keV). Finally, we derive, for the first time, the luminosity functions for early- and late-type systems separately. [source]


    The abundance and radial distribution of satellite galaxies

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2005
    Frank C. Van Den Bosch
    ABSTRACT Using detailed mock galaxy redshift surveys (MGRSs) we investigate the abundance and radial distribution of satellite galaxies. The mock surveys are constructed using large numerical simulations and the conditional luminosity function (CLF), and are compared against data from the Two Degree Field Galaxy Redshift Survey (2dFGRS). We use Monte Carlo Markov chains to explore the full posterior distribution of the CLF parameter space, and show that the average relation between light and mass is tightly constrained and in excellent agreement with our previous models and with that of Vale & Ostriker. The radial number density distribution of satellite galaxies in the 2dFGRS reveals a pronounced absence of satellites at small projected separations from their host galaxies. This is (at least partly) owing to the overlap and merging of galaxy images in the 2dFGRS parent catalogue. Owing to the resulting close-pair incompleteness we are unfortunately unable to put meaningful constraints on the radial distribution of satellite galaxies; the data are consistent with a radial number density distribution that follows that of the dark matter particles, but we cannot rule out alternatives with a constant number density core. Marginalizing over the full CLF parameter space, we show that in a ,CDM concordance cosmology the observed abundances of host and satellite galaxies in the 2dFGRS indicate a power spectrum normalization of ,8, 0.7. The same cosmology but with ,8= 0.9 is unable to match simultaneously the abundances of host and satellite galaxies. This confirms our previous conclusions based on the pairwise peculiar velocity dispersions and the group multiplicity function. [source]


    Near-infrared imaging observations of the southern massive star-forming region G333.6,0.2

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005
    Takuya Fujiyoshi
    ABSTRACT We present near-infrared broad-band JHK, images of the southern massive star-forming region G333.6,0.2. The slope of the K -luminosity function towards the region (0.24 0.01) is considered to be equivalent to that expected for main-sequence stars in the solar neighbourhood. Point sources with their (H,K) colour greater than 1 are more likely to be located in extended emission and it is suggested that these objects are physically associated with the H ii region. [source]


    Galaxy groups in the Two-degree Field Galaxy Redshift Survey: the luminous content of the groups

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004
    V. R. Eke
    ABSTRACT The Two-degree Field Galaxy Redshift Survey (2dFGRS) Percolation-Inferred Galaxy Group (2PIGG) catalogue of ,29 000 objects is used to study the luminous content of galaxy systems of various sizes. Mock galaxy catalogues constructed from cosmological simulations are used to gauge the accuracy with which intrinsic group properties can be recovered. It is found that a Schechter function is a reasonable fit to the galaxy luminosity functions in groups of different mass in the real data, and that the characteristic luminosity L, is slightly larger for more massive groups. However, the mock data show that the shape of the recovered luminosity function is expected to differ from the true shape, and this must be allowed for when interpreting the data. Luminosity function results are presented in both the bJ and rF wavebands. The variation of the halo mass-to-light ratio, ,, with group size is studied in both of these wavebands. A robust trend of increasing , with increasing group luminosity is found in the 2PIGG data. Going from groups with bJ luminosities equal to 1010 h,2 L, to those 100 times more luminous, the typical bJ -band mass-to-light ratio increases by a factor of 5, whereas the rF -band mass-to-light ratio grows by a factor of 3.5. These trends agree well with the predictions of the simulations which also predict a minimum in the mass-to-light ratio on a scale roughly corresponding to the Local Group. The data indicate that if such a minimum exists, then it must occur at L, 1010h,2 L,, below the range accurately probed by the 2PIGG catalogue. According to the mock data, the bJ mass-to-light ratios of the largest groups are expected to be approximately 1.1 times the global value. Assuming that this correction applies to the real data, the mean bJ luminosity density of the Universe yields an estimate of ,m= 0.26 0.03 (statistical error only). Various possible sources of systematic error are considered, with the conclusion that these could affect the estimate of ,m by a few tens of per cent. [source]


    The mass function of the stellar component of galaxies in the Sloan Digital Sky Survey

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004
    Benjamin Panter
    ABSTRACT Using the moped algorithm, we determine non-parametrically the stellar mass function of 96 545 galaxies from the Sloan Digital Sky Survey Data Release One. By using the reconstructed spectrum due to starlight, we can eliminate contamination from either emission lines or active galactic nuclei components. Our results give excellent agreement with previous works, but extend their range by more than two decades in mass to 107.5,Ms/h,2 M,, 1012. We present both a standard Schechter fit and a fit modified to include an extra, high-mass contribution, possibly from cluster central dominant galaxies. The Schechter fit parameters are ,,= (7.8 0.1) 10,3 h3 Mpc,3, M,= (7.64 0.09) 1010 h,2 M, and ,=,1.159 0.008. Our sample also yields an estimate for the contribution from baryons in stars to the critical density of ,b*h= (2.39 0.08) 10,3, in good agreement with other indicators. Error bars are statistical and a Salpeter initial mass function is assumed throughout. We find no evolution of the mass function in the redshift range 0.05 < z < 0.34, indicating that almost all stars were already formed at z, 0.34 with little or no star formation activity since then and that the evolution seen in the luminosity function must be largely due to stellar fading. [source]


    Lyman break galaxies and the star formation rate of the Universe at z, 6

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003
    Elizabeth R. Stanway
    ABSTRACT We determine the space density of UV-luminous starburst galaxies at z, 6 using deep HST ACS SDSS- i, (F775W) and SDSS- z, (F850LP) and VLT ISAAC J and Ks band imaging of the Chandra Deep Field South. We find eight galaxies and one star with (i,,z,) > 1.5 to a depth of z,AB= 25.6 (an 8, detection in each of the 3 available ACS epochs). This corresponds to an unobscured star formation rate of ,15 h,270 M, yr,1 at z= 5.9, equivalent to L* for the Lyman-break population at z= 3,4 (,,= 0.7, ,M= 0.3). We are sensitive to star-forming galaxies at 5.6 ,z, 7.0 with an effective comoving volume of ,1.8 105h,370 Mpc3 after accounting for incompleteness at the higher redshifts due to luminosity bias. This volume should encompass the primeval subgalactic-scale fragments of the progenitors of about a thousand L* galaxies at the current epoch. We determine a volume-averaged global star formation rate of (6.7 2.7) 10,4h70 M, yr,1 Mpc,3 at z, 6 from rest-frame UV selected starbursts at the bright end of the luminosity function: this is a lower limit because of dust obscuration and galaxies below our sensitivity limit. This measurement shows that at z, 6 the star formation density at the bright end is a factor of ,6 times less than that determined by Steidel et al. for a comparable sample of UV-selected galaxies at z= 3,4, and so extends our knowledge of the star formation history of the Universe to earlier times than previous work and into the epoch where reionization may have occurred. [source]


    Mass segregation in young compact clusters in the Large Magellanic Cloud , III.

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002
    Implications for the initial mass function
    ABSTRACT The distribution of core radii of rich clusters in the Large Magellanic Cloud (LMC) systematically increases in both upper limit and spread with increasing cluster age. Cluster-to-cluster variations in the stellar initial mass function (IMF) have been suggested as an explanation. We discuss the implications of the observed degree of mass segregation in our sample clusters for the shape of the initial mass function. Our results are based on Hubble Space Telescope/WFPC2 observations of six rich star clusters in the LMC, selected to include three pairs of clusters of similar age, metallicity and distance from the LMC centre, and exhibiting a large spread in core radii between the clusters in each pair. All clusters show clear evidence of mass segregation: (i) their luminosity function slopes steepen with increasing cluster radius, and (ii) the brighter stars are characterized by smaller core radii. For all sample clusters, both the slope of the luminosity function in the cluster centres and the degree of mass segregation are similar to each other, within observational errors of a few tenths of power-law slope fits to the data. This implies that their initial mass functions must have been very similar, down to ,0.8,1.0 M,. We therefore rule out variations in the IMF of the individual sample clusters as the main driver of the increasing spread of cluster core radii with cluster age. [source]