Luminosity function

The Millennium Galaxy Catalogue (MGC) provides a structural database comprising 10,095 well resolved galaxies drawn from a 37.5 sq degree region of sky, with B_{MGC} < 20.0 mag and 96.1 per cent spectroscopic completeness. The data are being used to investigate a number of diverse topics including: the nearby galaxy merger rate (via close pairs and asymmetry); dust attenuation; bulge and disc luminosity functions; the luminosity size relations; the supermassive black hole mass function; galaxy bimodality; the space-density of high and low surface brightness galaxies; blue spheroids; and the B-band luminosity function. Plans to extend the MGC in area (200 sq deg), depth (K_{Vega}=16.5 mag), resolution (0.5'') and wavelength (u-K) are underway.

In the course of its commissioning observations, the Sloan Digital Sky Survey (SDSS) has produced one of the largest redshift samples of galaxies selected from CCD images. Using 11,275 galaxies complete to r*=17.6 over 140 deg2, we compute the luminosity function of galaxies in the r* band over a range -23<Mr*<-16 (for h=1). The result is well-described by a Schechter function with parameters φ*=(1.46+/-0.12)×10-2 h3 Mpc-3, M*=-20.83+/-0.03, and α=-1.20+/-0.03. The implied luminosity density in r* is j~(2.6+/-0.3)×108h Lsolar Mpc-3. We find that the surface brightness selection threshold has a negligible impact for Mr*<-18. Using subsets of the data, we measure the luminosity function in the u*, g*, i*, and z* bands as well; the slope at low luminosities ranges from α=-1.35 to α=-1.2. We measure the bivariate distribution of r* luminosity with half-light surface brightness, intrinsic g*-r* color, and morphology. In agreement with previous studies, we find that high surface brightness, red, highly concentrated galaxies are on average more luminous than low surface brightness, blue, less concentrated galaxies. An important feature of the SDSS luminosity function is the use of Petrosian magnitudes, which measure a constant fraction of a galaxy's total light regardless of the amplitude of its surface brightness profile. If we synthesize results for RGKC band or bj band using these Petrosian magnitudes, we obtain luminosity densities 2 times that found by the Las Campanas Redshift Survey in RGKC and 1.4 times that found by the Two Degree Field Galaxy Redshift Survey in bj. However, we are able to reproduce the luminosity functions obtained by these surveys if we also mimic their isophotal limits for defining galaxy magnitudes, which are shallower and more redshift dependent than the Petrosian magnitudes used by the SDSS. Based on observations obtained with the Sloan Digital Sky Survey.

We study the properties of the fossil cluster RX J1416.4+2315 through g' and i'-band imaging and spectroscopy of 25 member galaxies. The system is at a mean redshift of 0.137 and has a velocity dispersion of 584 km s^-1. Superimposed onto one quadrant of the cluster field there is a group of five galaxies at a mean redshift of 0.131, which, if included as part of the cluster, increases the velocity dispersion to 846 km/s. The central object of RX J1416.4+2315 is a normal elliptical galaxy, with no cD envelope. The luminosity function of the system, estimated by the number counts, and statistical background correction, in the range -22.6< M_g'< -16.6, is well fitted by a Schechter function with M_g'^* = -21.2 +/- 0.8 and alpha = -1.2 +/- 0.2 (H_0 = 70 km s^-1 Mpc^-1, Omega_M=0.3, Omega_Lambda=0.7). The luminosity function obtained from the spectroscopically confirmed members in both g' and i' bands agrees with the photometric results. The mass of the system, M 0.9 \times 10^14 h^-1_70 M_sun, its M/L of 445 h_70 M_sun/L_B_sun and L_X of 11 10^43 h^-2_70 ergs s^-1 (bolometric) suggest that this system is the second example of known fossil cluster, after RX J1552.2+2013, confirmed in the literature.

The photometric data of Kalużny (1988) was used in conjunction with the proper motion measurements of USNOB1.0 catalog (Monet et al. 2003) to refine and complete the main physical properties of the faint open cluster NGC 1193. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The study of brown dwarfs and extrasolar giant planets is very much germane to understanding the occurrence and properties of planetary systems, the baryonic content and chemical evolution of the cosmos, and the relationship (in both genesis and physical properties) between stars and objects not massive enough ever to become stars. By detecting and characterizing brown dwarfs and giant planets, we extend our knowledge of the cosmos from the ubiquitous macroscale of stars ever closer to the instinctively ...

In this paper, using 2MASS photometry, we study the structural and dynamical properties of four young star clusters viz. King 16, NGC 1931, NGC 637 and NGC 189. For the clusters King 16, NGC 1931, NGC 637 and NGC 189, we obtain the limiting radii of 7′, 12′, 6′ and 5′ which correspond to linear radii of 3.6 pc, 8.85 pc, 3.96 pc and 2.8 pc respectively. The reddening values E(B−V) obtained for the clusters are 0.85, 0.65–0.85, 0.6 and 0.53 and their true distances are 1786 pc, 3062 pc, 2270 pc and 912 pc respectively. Ages of the clusters are 6 Myr, 4 Myr, 4 Myr and 10 Myr respectively. We compare their structures, luminosity functions and mass functions (φ(M)=dN/dM ∝ M −(1+χ)) to the parameter τ=t age /t relax to study the star formation process and the dynamical evolution of these clusters. We find that, for our sample, mass seggregation is observed in clusters or their cores only when the ages of the clusters are comparable to their relaxation times (τ≥1). These results suggest mass seggregation due to dynamical effects. The values of χ, which characterize the overall mass functions for the clusters are 0.96±0.11, 1.16±0.18, 0.55±0.14 and 0.66±0.31 respectively. The change in χ as a function of radius is a good indicator of the dynamical state of clusters.

Observations of the extraordinarily bright optical afterglow (OA) of GRB 991208 started 2.1 d after the event. The flux decay constant of the OA in the R-band is -2.30 +/- 0.07 up to 5 d, which is very likely due to the jet effect, and after that it is followed by a much steeper decay with constant -3.2 +/- 0.2, the fastest one ever seen in a GRB OA. A negative detection in several all-sky films taken simultaneously to the event implies either a previous additional break prior to 2 d after the occurrence of the GRB (as expected from the jet effect). The existence of a second break might indicate a steepening in the electron spectrum or the superposition of two events. Once the afterglow emission vanished, contribution of a bright underlying SN is found, but the light curve is not sufficiently well sampled to rule out a dust echo explanation. Our determination of z = 0.706 indicates that GRB 991208 is at 3.7 Gpc, implying an isotropic energy release of 1.15 x 10E53 erg which may be relaxed by beaming by a factor > 100. Precise astrometry indicates that the GRB coincides within 0.2" with the host galaxy, thus given support to a massive star origin. The absolute magnitude is M_B = -18.2, well below the knee of the galaxy luminosity function and we derive a star-forming rate of 11.5 +/- 7.1 Mo/yr. The quasi-simultaneous broad-band photometric spectral energy distribution of the afterglow is determined 3.5 day after the burst (Dec 12.0) implying a cooling frequency below the optical band, i.e. supporting a jet model with p = -2.30 as the index of the power-law electron distribution.

We determine the number counts and z=0-5 luminosity function for a well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey (SDSS). We conservatively define the most uniform statistical sample possible, consisting of 15,343 quasars within an effective area of 1622 deg2 that was derived from a parent sample of 46,420 spectroscopically confirmed broad-line quasars in the 5282 deg2 of imaging data from SDSS Data Release 3. The sample extends from i=15 to 19.1 at z<~3 and to i=20.2 for z>~3. The number counts and luminosity function agree well with the results of the Two Degree Field QSO Redshift Survey (2QZ) at redshifts and luminosities at which the SDSS and 2QZ quasar samples overlap, but the SDSS data probe to much higher redshifts than does the 2QZ sample. The number density of luminous quasars peaks between redshifts 2 and 3, although uncertainties in the selection function in this range do not allow us to determine the peak redshift more precisely. Our best-fit model has a flatter bright-end slope at high redshift than at low redshift. For z<2.4 the data are best fit by a redshift-independent slope of β=-3.1 [Φ(L)~Lβ]. Above z=2.4 the slope flattens with redshift to β>~-2.37 at z=5. This slope change, which is significant at the >~5 σ level, must be accounted for in models of the evolution of accretion onto supermassive black holes.

We have used the WFPC2 camera of the Hubble Space Telescope to obtain deep F814W images of a blank field in the Virgo Cluster located 41 arcmin northwest of M87. We perform star counts in that field, and in another Virgo field observed by Ferguson, Tanvir & von Hippel (1998), and show that, when compared to the Hubble Deep Field North and South, the Virgo Cluster contains an excess of objects with magnitudes I > 27. We attribute this excess to a population of intracluster red-giant branch (IC-RGB) stars. By modeling the luminosity function of these stars, we show that the tip of the Virgo RGB is at I = 27.31 +0.27/-0.17 and that the cluster contains a small, but significant, excess of stars that are up to ~1 mag brighter than this tip. If this luminous component is due entirely to stars on the asymptotic giant branch (AGB), it implies an age for the population of > 2 Gyr; if foreground RGB stars contribute to the luminous tail, then the derived age for the stars is older still. The luminosity function also suggests that most of the intracluster stars are moderately metal-rich (-0.8 < [Fe/H] <-0.2), a result consistent with that expected from stars that have been tidally stripped from intermediate luminosity galaxies. Additionally, a comparison with the planetary nebulae in our field also supports this view, although the existence of a more metal-poor population (from stripped dwarfs) cannot be ruled out. Our derived average surface brightness, mu_I = 27.9 +0.3/-0.5 mag/arcsec^2 for Virgo's diffuse component suggests that intracluster stars contribute 10% to 20% of the cluster's total I-band luminosity.

We have studied the globular cluster systems of seven giant, edge-on spiral galaxies using Hubble Space Telescope imaging in V and I. The galaxy sample covers the Hubble types Sa to Sc, allowing us to study the variation of the properties of globular cluster systems along the Hubble sequence. The photometry reaches ~1.5 mag beyond the turn-over magnitude of the globular cluster luminosity function for each galaxy. Specific frequencies of globular clusters (SN values) were evaluated by comparing the numbers of globular clusters found in our WFPC2 pointings with those in our Milky Way that would be detected in the same spatial region if placed at the distance of the target galaxies. Results from this method were found to be consistent with the more commonly used method of constructing radial distribution functions of globular clusters. The SN values of spirals with B/T<~ 0.3 (i.e. spirals with a Hubble type later than about Sb) are consistent with a value of SN= 0.55 +/- 0.25. We suggest that this population of globular clusters represents a `universal', old halo population that is present around each galaxy. Most galaxies in our sample have SN values that are consistent with a scenario in which globular cluster systems are made up of (i) the aforementioned halo population plus (ii) a population that is associated with bulges, which grows approximately linearly with the mass of the bulge. Such scenarios include the `merger scenario' for the formation of elliptical galaxies as well as the `multi-phase collapse' scenario, but it seems inconsistent with the `secular evolution' scenario of Pfenniger & Norman, in which bulges are formed from disc stars by means of the redistribution of angular momentum through bar instabilities and/or minor perturbations. However, there is one bulge-dominated spiral galaxy in our sample (NGC7814) with a low SN value that is consistent with those of the latest-type spirals. This means that the `secular evolution' scenario can still be viable for some bulge-dominated spirals. Thus, our results suggest that the formation histories of galaxy bulges of early-type spirals can be significantly different from one galaxy to another.

Details are presented of the H i Jodrell All Sky Survey (HIJASS). HIJASS is a blind neutral hydrogen (H i) survey of the northern sky (δ > 22°), being conducted using the multibeam receiver on the Lovell Telescope (full width at half-maximum beamwidth 12 arcmin) at Jodrell Bank. HIJASS covers the velocity range −3500 to 10 000 km s−1, with a velocity resolution of 18.1 km s−1 and spatial positional accuracy of ∼2.5 arcmin. Thus far about 1115 deg2 of sky have been surveyed. The average rms noise during the early part of the survey was around 16 mJy beam−1. Following the first phase of the Lovell Telescope upgrade (in 2001), the rms noise is now around 13 mJy beam−1. We describe the methods of detecting galaxies within the HIJASS data and of measuring their H i parameters. The properties of the resulting H i-selected sample of galaxies are described. Of the 222 sources so far confirmed, 170 (77 per cent) are clearly associated with a previously catalogued galaxy. A further 23 sources (10 per cent) lie close (within 6 arcmin) to a previously catalogued galaxy for which no previous redshift exists. A further 29 sources (13 per cent) do not appear to be associated with any previously catalogued galaxy. The distributions of peak flux, integrated flux, H i mass and cz are discussed. We show, using the HIJASS data, that H i self-absorption is a significant, but often overlooked, effect in galaxies with large inclination angles to the line of sight. Properly accounting for it could increase the derived H i mass density of the local Universe by at least 25 per cent. The effect that this will have on the shape of the H i mass function will depend on how self-absorption affects galaxies of different morphological types and H i masses. We also show that galaxies with small inclinations to the line of sight may also be excluded from H i-selected samples, since many such galaxies will have observed velocity widths that are too narrow for them to be distinguished from narrow-band radio-frequency interference. This effect will become progressively more serious for galaxies with smaller intrinsic velocity widths. If, as we might expect, galaxies with smaller intrinsic velocity widths have smaller H i masses, then compensating for this effect could significantly steepen the faint-end slope of the derived H i mass function.

This paper describes the Hubble Space Telescope imaging data products and data reduction procedures for the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). This survey is designed to document the evolution of galaxies and black holes at $z\sim1.5-8$, and to study Type Ia SNe beyond $z>1.5$. Five premier multi-wavelength sky regions are selected, each with extensive multiwavelength observations. The primary CANDELS data consist of imaging obtained in the Wide Field Camera 3 / infrared channel (WFC3/IR) and UVIS channel, along with the Advanced Camera for Surveys (ACS). The CANDELS/Deep survey covers \sim125 square arcminutes within GOODS-N and GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a total of \sim800 square arcminutes across GOODS and three additional fields (EGS, COSMOS, and UDS). We summarize the observational aspects of the survey as motivated by the scientific goals and present a detailed description of the data reduction procedures and products from the survey. Our data reduction methods utilize the most up to date calibration files and image combination procedures. We have paid special attention to correcting a range of instrumental effects, including CTE degradation for ACS, removal of electronic bias-striping present in ACS data after SM4, and persistence effects and other artifacts in WFC3/IR. For each field, we release mosaics for individual epochs and eventual mosaics containing data from all epochs combined, to facilitate photometric variability studies and the deepest possible photometry. A more detailed overview of the science goals and observational design of the survey are presented in a companion paper.