Luminosity function

The Cometary Globules (CGs) are characterized by compact, dusty heads with long faintly luminous tails extending on one side and narrow bright rims on the other side. There exists a sizable population of such CGs in the Gum Nebula, distributed over a region -80 parsec in radius with their tails pointing away from an apparent common center. Some of the heads have embedded young stars. In the region bounded by the CGs there are a few massive hot stars, including £ Puppis believed to be the most luminous star in the southern sky. It has been conjectured that the morphological appearance of the CGs may be due to the influence of these stars. In order to understand the kinematics and the origin of the system, a study was undertaken using the first rotational transition of the carbon monoxide molecule. The study consisted of 12 CO observations of the heads and the tails of the CGs. In addition, the Globule No. 22 was mapped in both 12 CO and 13 CO. An analysis of this data has led to the following findings: (1) The system of CGs is expanding with respect to a common morphological center at -12 km s -1 . The expansion age is -6 Myr. (2) Some of the tails show systematic velocity gradients. If the tails were formed due to the enlongation resulting from these velocity gradients then the estimated stretching age is -3 Myr. In order to clarify whether the observed star formation in this region is externally triggered, an analysis of the locations of the embedded young stellar objects (YSOs, identified from the Infra-Red Astronomy Satellite data) in the dark clouds in the Gum-Vela region was undertaken. This study has shown that the YSOs have a statistically significant tendency to fall on the sides of dark clouds facing the morphological center rather than the far sides, supporting external triggering. From the above analysis we come to the following conclusions: (1) The rough agreement between the expansion age and the tail-stretching age suggests a common origin for the expansion and the formation of the tails. The presence of young stars of comparable ages in the heads of some of the globules suggests that the processes responsible for the expansion may have also triggered star formation in them. (2) The radiation pressure from the hot stars in the central region or the stellar winds from them cannot account for the momentum of the expanding globules. It is more likely that the rocket effect arising out of the one-sided heating and the consequent anisotropic ablation of the globules supplied the necessary momentum. All the conclusions mentioned above can be reconciled easily if one argues that they are casually connected and have a common origin. The main apparent obstacle to such a unified picture for the system of CGs in the Gum Nebula is that although there appears to be a morphological center, there are no identifiable objects, say, massive stars, presently located at or near this morphological center. However, the most dominant star in the central region £ Puppis has a large space motion in a direction which suggests that it was close to the morphological center half a million years ago. We suggest that f Puppis had a massive companion which exploded near this center. Thus until roughly half a million years ago there must have been a massive binary system (£ Puppis and its companion) near the center of the system of CGs. The combined effect of the ultraviolet radiation and the stellar wind from this binary, as well as from other stars in the neighborhood, must have resulted in much of the molecular material in the vicinity being blown away except the numerous regions of enhanced density (<condensations) in the original molecular cloud. Continued effect of the radiation and stellar winds resulted in these condensations being set in motion, as well as developing cometary tails. The thesis also involved the development of a wide-band mechanically tuned local oscillator using the Gunn diode for use with the 10.4-m millimeter-wave-radio telescope at the Raman Research Institute. This provides sufficient power to efficiently operate two cryogenic Schottky mixers (dual polarization) and tunes over the frequency range 75-115 GHz covering most of the 3 mm atmospheric transmission window (W-band). Rotational transitions of many astrophysically important molecules including CO fall in this range.

We present the results from a new search for candidate galaxies at z ≈ 8.5–11 discovered over the 850 arcmin2 area probed by the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS). We use a photometric-redshift selection including both Hubble and Spitzer Space Telescope photometry to robustly identify galaxies in this epoch at H 160 &lt; 26.6. We use a detailed vetting procedure, including screening against persistence and stellar contamination, and the inclusion of ground-based imaging and follow-up Hubble Space Telescope imaging to build a robust sample of 11 candidate galaxies, three presented here for the first time. The inclusion of Spitzer/IRAC photometry in the selection process reduces contamination, and yields more robust redshift estimates than Hubble alone. We constrain the evolution of the rest-frame ultraviolet luminosity function via a new method of calculating the observed number densities without choosing a prior magnitude bin size. We find that...

We report the discovery of two faint ultracool companions to the nearby (d∼17.9 pc) young G2V star HD 130948 (HR 5534, HIP 72567) using the Hokupa’a adaptive optics instrument mounted on the Gemini North 8-meter telescope. Both objects have the same common proper motion as the primary star as seen over a 7 month baseline and have near-IR photometric colors that are consistent with an early-L classification. Near-IR spectra taken with the NIRSPEC AO instrument on the Keck II telescope reveal K I lines, FeH, and H2O bandheads. Based on these spectra, we determine that both objects have spectral type dL2 with an uncertainty of 2 spectral subclasses. The position of the new companions on the H-R diagram in comparison with theoretical models is consistent with the young age of the primary star (&lt;0.8 Gyr) estimated on the basis of X-ray activity, lithium abundance and fast rotation. HD 130948B and C likely constitute a pair of young contracting brown dwarfs with an orbital period of ab...

The identification of young star groupings (YSG) in the three spiral galaxies NGC 3377A, NGC 3507, NGC 4394 is obtained by mean of the statistical method described in Paper I. We find 83, 90, 185 YSGs, respectively. An identification map of YSGs, as well as their size distribution, their B-luminosity function and their surface luminosity density radial behaviour are presented and compared. These data, in addition to those in Paper I, constitute a first sample suitable for seeking correlations among properties of galaxies and their YSGs, which we briefly discuss here.

This thesis presents a study of the radio luminosity function and the evolution of galaxies in the Abell 2256 cluster (z=0.058, richness class 2). Using the NED database and VLA deep data with an rms sensitivity of 18µ Jy.beam -1 , we identified 257 optical galaxies as members of A2256, of which 83 are radio galaxies. Since A2256 is undergoing a cluster-cluster merger, it is a good candidate to study the radio activity of galaxies in the cluster. We calculated the Univariate and Bivariate radio luminosity functions for A2256, and compared the results to studies on other clusters. We also used the SDSS parameter fracDev to roughly classify galaxies as spirals and ellipticals, and investigated the distribution and structure of galaxies in the cluster. We found that most of the radio galaxies in A2256 are faint, and are distributed towards the outskirts of the cluster. On the other hand, almost all very bright radio galaxies are ellipticals which are located at the center of the cluster. We also found there is an excess in the number of radio spiral galaxies in A2256 compared to the number of radio ellipticals, counting down to a radio luminosity of log(luminosity) = 20.135

We present Spitzer IRS low resolution, mid-IR spectra of a sample of 25 high luminosity QSOs at 2 < z < 3.5. When combined with archival IRS observations of local, low luminosity type-I active galactic nuclei (AGNs), the sample spans five orders of magnitude in luminosity. We find that the continuum dust thermal emission at λ rest = 6.7 µm is correlated with the optical luminosity, following the non-linear relation λL λ (6.7 µm) ∝ λL λ (5100 Å) 0.82 . We also find an anti correlation between λL λ (6.7 µm)/λL λ (5100 Å) and the [Oiii]λ5007 line luminosity. These effects are interpreted as a decreasing covering factor of the circumnuclear dust as a function of luminosity. Such a result is in agreement with the decreasing fraction of absorbed AGNs as a function of luminosity recently found in various surveys. In particular, while X-ray surveys find a decreasing covering factor of the absorbing gas as a function of luminosity, our data provides an independent and complementary confirmation by finding a decreasing covering factor of dust. We clearly detect the silicate emission feature in the average spectrum, but also in four individual objects. These are the silicate emission in the most luminous objects obtained so far. When combined with the silicate emission observed in local, low luminosity type-I AGNs, we find that the silicate emission strength is correlated with luminosity. The silicate strength of all type-I AGNs also follows a positive correlation with the black hole mass and with the accretion rate. The Polycyclic Aromatic Hydrocarbon (PAH) emission features, expected from starburst activity, are not detected in the average spectrum of luminous, high-z QSOs. The upper limit inferred from the average spectrum points to a ratio between PAH luminosity and QSO optical luminosity significantly lower than observed in lower luminosity AGNs, implying that the correlation between star formation rate and AGN power saturates at high luminosities.

Broad-band optical observations of the extraordinarily bright optical afterglow of the intense gamma-ray burst GRB 991208 started ∼2.1 days after the event and continued until 4 Apr. 2000. The flux decay constant of the optical afterglow in the R-band is -2.30 ± 0.07 up to ∼5 days, which is very likely due to the jet effect, and it is followed by a much steeper decay with constant -3.2 ± 0.2, the fastest one ever seen in a GRB optical afterglow. A negative detection in several all-sky films taken simultaneously with the event, that otherwise would have reached naked eye brightness, implies either a previous additional break prior to ∼2 days after the occurrence of the GRB (as expected from the jet effect) or a maximum, as observed in GRB 970508. The existence of a second break might indicate a steepening in the electron spectrum or the superposition of two events, resembling GRB 000301C. Once the afterglow emission vanished, contribution of a bright underlying supernova was found on the basis of the late-time R-band measurements, but the light curve is not sufficiently well sampled to rule out a dust echo explanation. Our redshift determination of z = 0.706 indicates that GRB 991208 is at 3.7 Gpc (for H0 = 60 km s -1 Mpc -1 , Ω0 = 1 and Λ0 = 0), implying an isotropic energy release of 1.15 10 53 erg which may be relaxed by beaming by a factor >10 2 . Precise astrometry indicates that the GRB coincides within 0.2 with the host galaxy, thus supporting a massive star origin. The absolute magnitude of the galaxy is MB = -18.2, well below the knee of the galaxy luminosity function and we derive a star-forming rate of (11.5 ± 7.1) M yr -1 , which is much larger than the present-day rate in our Galaxy. The quasisimultaneous broad-band photometric spectral energy distribution of the afterglow was determined ∼3.5 day after the burst (Dec. 12.0) implying a cooling frequency νc below the optical band, i.e. supporting a jet model with p = -2.30 as the index of the power-law electron distribution.

We derive transformation equations between GALEX and UBV colours by using the reliable data of 556 stars. We present two sets of equations: as a function of (only) luminosity class and as a function of both luminosity class and metallicity. The metallicities are provided from the literature, while the luminosity classes are determined by using the PARSEC mass tracks in this study. Small colour residuals and high squared correlation coefficients promise accurate derived colours. The application of the transformation equations to 70 stars with reliable data shows that the metallicity plays an important role in estimation of more accurate colours.

Local extremely metal-poor galaxies (XMPs) are of particular astrophysical interest since they allow us to look into physical processes characteristic of the early universe, from the assembly of galaxy disks to the formation of stars in conditions of low metallicity. Given the luminosity-metallicity relationship, all galaxies fainter than M r ;-13 are expected to be XMPs. Therefore, XMPs should be common in galaxy surveys. However, they are not common, because several observational biases hamper their detection. This work compares the number of faint XMPs in the SDSS-DR7 spectroscopic survey with the expected number, given the known biases and the observed galaxy luminosity function (LF). The faint end of the LF is poorly constrained observationally, but it determines the expected number of XMPs. Surprisingly, the number of observed faint XMPs (∼10) is overpredicted by our calculation, unless the upturn in the faint end of the LF is not present in the model. The lack of an upturn can be naturally understood if most XMPs are central galaxies in their low-mass dark matter halos, which are highly depleted in baryons due to interaction with the cosmic ultraviolet background and to other physical processes. Our result also suggests that the upturn toward low luminosity of the observed galaxy LF is due to satellite galaxies.

THESEUS is an ESA space based project, which aims to explore the early universe by unveiling a complete census of Gamma-ray Burst (GRB) population in the first billion years. This goal is expected to be realized by the combined observations of its three instruments on board: the Soft X-ray Imager (SXI), the X and Gamma Imaging Spectrometer (XGIS), and the InfraRed Telescope (IRT). This last one will identify, localise, and study the afterglow of the GRBs detected by SXI and XGIS, and about 40% of its time will be devoted to an all-sky photometric survey, which will certainly detect a relevant number of extragalactic sources, including Quasars. In this paper, we focus on the capability of IRT-THESEUS Telescope to observe Quasars and, in particular, Quasars lensed by foreground galaxies. In our analysis we consider the recent results for the Quasar Luminosity Function (QLF) in the infrared band based on the Spitzer Space Telescope imaging survey. In order to estimate the number of len...

Oxygen to iron abundance ratios of metal-poor stars provide information on nucleosynthesis yields from massive stars which end in Type II supernova explosions. Using a standard model of chemical evolution of the Galaxy we have reproduced the solar neighborhood abundance data and estimated the oxygen and iron yields of genuine SN II origin. The estimated yields are compared with the theoretical yields to derive the relation between the lower and upper mass limits in each generation of stars and the IMF slope. Independently of this relation, we furthermore derive the relation between the lower mass limit and the IMF slope from the stellar mass to light ratio in the solar neighborhood. These independent relations unambiguously determine the upper mass limit of m u = 50 ± 10 M and the IMF slope index of 1.3 -1.6 above 1 M . This upper mass limit corresponds to the mass beyond which stars end as black holes without ejecting processed matter into the interstellar medium. We also find that the IMF slope index below 0.5 M cannot be much shallower than 0.8.

We present Globular Cluster Luminosity Functions for four ellipticals and one S0-Galaxy in the Fornax cluster of galaxies, derived from CCD photometry in V and I. The averaged turnover magnitudes are V T O = 23.80 ± 0.06 mag and I T O = 22.39 ± 0.05 mag, respectively. We derive a relative distance modulus (m -M ) F ornax -(m -M ) M87 = 0.08 ± 0.09 mag using the turnover of M87 based on HST data.

The front page illustrates the essence of this work, under the directives given by the University Design Guidelines, which seem to be very preoccupied with bubbles. The lower bubble displays a snapshot from a cosmological simulation at the time when the Universe was two and a half billion years old. The region is some 13 million lightyears across. Roughly one thousand galaxies float around in this volume, organized in beautiful filamentary structures, separated by huge voids of nothingness. Zooming in on one of the little dots, the middle bubble shows a pencil drawing of a few galaxies, slightly smeared out with my finger to create the effect of gaseous nebulae, and subsequently color-inverted. The upper bubble shows the closest zoom-in, symbolizing the fact that this work is predominantly numerical. In the simulations, the physical properties of the galaxies are represented by millions of numbers arranged in a threedimensional irregular matrix of cells. Two different projections of this matrix are shown in red and cyan, respectively, generating an anaglyph image which can be viewed with a pair of 3D glasses (although in the printed version the cyan may come out a bit too dark). In between the cells is seen a few lines from the computer code.

We have initiated a survey using the newly commissioned X-shooter spectrograph to target candidate relatively metal-rich damped Lyα absorbers (DLAs). Our rationale is that highmetallicity DLAs due to the luminosity-metallicity relation likely will have the most luminous galaxy counterparts. In addition, the spectral coverage of X-shooter allows us to search for not only Lyα emission, but also rest-frame optical emission lines. We have chosen DLAs where the strongest rest-frame optical lines ([O II], [O III], Hβ and Hα) fall in the nearinfrared atmospheric transmission bands. In this first paper resulting from the survey, we report on the discovery of the galaxy counterpart of the z abs = 2.354 DLA towards the z = 2.926 quasar Q 2222-0946. This DLA is amongst the most metal-rich z > 2 DLAs studied so far at comparable redshifts and there is evidence for substantial depletion of refractory elements on to dust grains. We measure metallicities from Zn II, Si II, Ni II, Mn II and Fe II of -0.46 ± 0.07, -0.51 ± 0.06, -0.85 ± 0.06, -1.23 ± 0.06 and -0.99 ± 0.06, respectively. The galaxy is detected in the Lyα, [O III] λλ4959, 5007 and Hα emission lines at an impact parameter of about 0.8 arcsec (6 kpc at z abs = 2.354). Based on the Hα line, we infer a star formation rate of 10 M yr -1 , which is a lower limit due to the possibility of slit loss. Compared to the recently determined Hα luminosity function for z = 2.2 galaxies, the DLAgalaxy counterpart has a luminosity of L ∼ 0.1L * Hα . The emission-line ratios are 4.0 (Lyα/Hα) and 1.2 ([O III]/Hα). In particular, the Lyα line shows clear evidence for resonant scattering effects, namely an asymmetric, redshifted (relative to the systemic redshift) component and a much weaker blueshifted component. The fact that the blueshifted component is relatively weak indicates the presence of a galactic wind. The properties of the galaxy counterpart of this DLA are consistent with the prediction that metal-rich DLAs are associated with the most luminous of the DLA-galaxy counterparts.

Taking advantage of recent Hubble Space Telescope (HST) data for field stars in the region of the Galactic globular cluster NGC 6397, we tested the predictions of several Galactic models with star counts reaching a largely unexplored range of magnitudes, down to V , 26:5: After updating the input stellar V 2 I colours, we found that the two-component Bahcall± Soneira (B&S) model can be put into satisfactory agreement with observations for suitable choices of disc/spheroid luminosity functions (LFs). However, if one assumes the disc LF of Gould, Bahcall and Flynn together with the spheroid LF of Gould, Flynn and Bahcall, there is no way to reconcile the predicted and observed V-magnitude distribution. We also analysed the agreement between observed and predicted magnitude and colour distributions for two selected models with a thick disc component. Even in this case there are suitable combinations of model parameters and faint-magnitude LFs that can give a reasonable agreement with observational star counts in both magnitude and colour. However, the abovequoted combination of Gould et al. LFs again gives predictions in clear disagreement with observations.

We present a robust measurement and analysis of the rest-frame ultraviolet (UV) luminosity functions at z = 4 to 8. We use deep Hubble Space Telescope imaging over the CANDELS/GOODS fields, the Hubble Ultra Deep Field and the Hubble Frontier Field deep parallel observations near the Abell 2744 and MACS J0416.1-2403 clusters. The combination of these surveys provides an effective volume of 0.6-1.2 ×10 6 Mpc 3 over this epoch, allowing us to perform a robust search for faint (M UV = -18) and bright (M UV < -21) highredshift galaxies. We select candidate galaxies using a well-tested photometric redshift technique with careful screening of contaminants, finding a sample of 7446 candidate galaxies at 3.5 < z < 8.5, with >1000 galaxies at z ≈ 6 -8. We measure both a stepwise luminosity function for candidate galaxies in our redshift samples, as well as a Schechter function, using a Markov Chain Monte Carlo analysis to measure robust uncertainties. At the faint end our UV luminosity functions agree with previous studies, yet we find a higher abundance of UV-bright candidate galaxies at z ≥ 6. Our best-fit value of the characteristic magnitude M * UV is consistent with -21 at z ≥ 5, different than that inferred based on previous trends at lower redshift, and brighter at ∼2σ significance than previous measures at z = 6 and 7 . At z = 8, a single powerlaw provides an equally good fit to the UV luminosity function, while at z = 6 and 7, an exponential cutoff at the bright end is moderately preferred. We compare our luminosity functions to semi-analytical models, and find that the lack of evolution in M * UV is consistent with models where the impact of dust attenuation on the bright end of the luminosity function decreases at higher redshift, though a decreasing impact of feedback may also be possible. We measure the evolution of the cosmic star-formation rate (SFR) density by integrating our observed luminosity functions to M UV = -17, correcting for dust attenuation, and find that the SFR density declines proportionally to (1+z) -4.3±0.5 at z > 4, consistent with observations at z ≥ 9. Our observed luminosity functions are consistent with a reionization history that starts at z 10, completes at z > 6, and reaches a midpoint (x HII = 0.5) at 6.7 < z < 9.4. Finally, using a constant cumulative number density selection and an empirically derived rising star-formation history, our observations predict that the abundance of bright z = 9 galaxies is likely higher than previous constraints, though consistent with recent estimates of bright z ∼ 10 galaxies.

We present new HST/WFPC2 observations of 20 fields centered around T Tauri stars in the Chamaeleon I star forming region. Images have been obtained in the F631N ([OI]λ6300), F656N (Hα) and F673N ([SII]λλ6716, 6731) narrowband filters, plus the Johnson V-band equivalent F547M filter. We detect 31 T Tauri stars falling within our fields. We discuss the optical morphology of 10 sources showing evidence of either binarity, circumstellar material, or mass loss. We supplement our photometry with a compilation of optical, infrared and sub-millimeter data from the literature, together with new sub-mm data for three objects, to build the Spectral Energy Distributions (SED) of 19 single sources. Using an SED model fitting tool, we self-consistently estimate a number of stellar and disk parameters, while mass accretion rates are directly derived from our Hα photometry. We find that bolometric luminosities derived from dereddened optical data tend to be underestimated in systems with high α 2-24 IR spectral index, suggesting that disks seen nearly edge-on may occasionally be interpreted as low luminosity (and therefore more evolved) sources. On the other hand, the same α 2-24 IR spectral index, a tracer of the amount of dust in the warmer layers of the circumstellar disks, and the mass accretion rate appear to decay with the isocronal stellar age, suggesting that the observed age spread (≃ 0.5 -5 Myr) within the cluster is real. Our sample contains a few outliers that may have dissipated their circumstellar disks on shorter time-scale.

The Hubble Space Telescope (HST) Treasury Program on the Orion Nebula Cluster has used 104 orbits of HST time to image the Great Orion Nebula region with the Advanced Camera for Surveys (ACS), the Wide-Field/Planetary Camera 2 (WFPC2) and the Near Infrared Camera and Multi Object Spectrograph (NICMOS) instruments in 11 filters ranging from the U-band to the H-band equivalent of HST. The program has been intended to perform the definitive study of the stellar component of the ONC at visible wavelengths, addressing key questions like the cluster IMF, age spread, mass accretion, binarity and cirumstellar disk evolution. The scanning pattern allowed to cover a contiguous field of approximately 600 square arcminutes with both ACS and WFPC2, with a typical exposure time of approximately 11 minutes per ACS filter, corresponding to a point source depth AB(F435W) = 25.8 and AB(F775W)=25.2 with 0.2 magnitudes of photometric error. We describe the observations, data reduction and data products...

The aim of this paper is to investigate a possible contribution of the rotation-powered pulsars and pulsar wind nebulae to the population of ultraluminous X-ray sources (ULXs). We first develop an analytical model for the evolution of the distribution function of pulsars over the spin period and find both the steady-state and the time-dependent solutions. Using the recent results on the X-ray efficiency dependence on pulsar characteristic age, we then compute the X-ray luminosity function (XLF) of rotation-powered pulsars. In a general case, it has a broken power-law shape with a high-luminosity cutoff, which depends on the distributions of the birth spin period and the magnetic field. Using the observed XLF of sources in the nearby galaxies and the condition that the pulsar XLF does not exceed that, we find the allowed region for the parameters describing the birth period distribution. We find that the mean pulsar period should be greater than 10-40 ms. These results are consistent with the constraints obtained from the X-ray luminosity of core-collapse supernovae. We estimate that the contribution of the rotation-powered pulsars to the ULX population is at a level exceeding 3 per cent. For a wide birth period distribution, this fraction grows with luminosity and above 10 40 erg s -1 pulsars can dominate the ULX population.

In fitting galactic rotation curves to data, most standard theories make use of a single exponential disk approximation of the gas distribution to account for the HI synthesis data observed at various radio telescope facilities. We take a sample of surface brightness profiles from The HI Nearby Galaxy Survey (THINGS), and apply both single disk exponentials and Multi-Disk exponentials, and use these various models to see how the modelling procedure changes the Newtonian prediction of the mass of the galaxy. Since the missing mass problem has not been fully explained in large spiral galaxies, different modelling procedures could account for some of the missing matter.

Galactic evolution is studied in a field in the centre of the LMC Bar. We obtain data of high quality with the HST WFPC2 and uvby photometry. To match the photometric accuracy and make use of the potential of the uvby system in terms of evolutionary parameters and chemical abundance, we need adequate calibration of the data observed. Conversion of the observing system into that of the international uvby system is made from observations of reference stars in cluster fields. These fields are first observed with a ground based telescope together with selected sets of standard stars for the uvby system. This way, the cluster field reference stars are tied into the international uvby system. Subsequently, the reference stars are observed with the HST WFPC2 used with its set of uvby filters, thus providing final system conversion. We here discuss the observations and present some initial results.

We present the Macquarie/AAO/Strasbourg Hα Planetary Nebula Catalogue (MASH) of over 900 true, likely and possible new Galactic planetary nebulae (PNe) discovered from the AAO/UKST Hα survey of the southern Galactic plane. The combination of depth, resolution, uniformity and areal coverage of the Hα survey has opened up a hitherto unexplored region of parameter space permitting the detection of this significant new PN sample. Away from the Galactic bulge the new PNe are typically more evolved, of larger angular extent, of lower surface brightness and more obscured (i.e. extinguished) than those in most previous surveys. We have also doubled the number of PNe in the Galactic bulge itself and although most are compact, we have also found more evolved examples. The MASH catalogue represents the culmination of a seven-year programme of identification and confirmatory spectroscopy. A key strength is that the entire sample has been derived from the same, uniform observational data. The 60 per cent increase in known Galactic PNe represents the largest ever incremental sample of such discoveries and will have a significant impact on many aspects of PN research. This is especially important for studies at the faint end of the PN luminosity function which was previously poorly represented.

Aims. We produce a clean and well-characterised catalogue of objects within 100 pc of the Sun from the Gaia Early Data Release 3. We characterise the catalogue through comparisons to the full data release, external catalogues, and simulations. We carry out a first analysis of the science that is possible with this sample to demonstrate its potential and best practices for its use. Methods. Theselection of objects within 100 pc from the full catalogue used selected training sets, machine-learning procedures, astrometric quantities, and solution quality indicators to determine a probability that the astrometric solution is reliable. The training set construction exploited the astrometric data, quality flags, and external photometry. For all candidates we calculated distance posterior probability densities using Bayesian procedures and mock catalogues to define priors. Any object with reliable astrometry and a non-zero probability of being within 100 pc is included in the catalogue. Re...

The age and dynamics of the young LMC clusters SL 666 and NGC 2098 were investigated using CCD observations obtained with the 3.9m Anglo-Australian Telescope. SL 666 was found to have an age of 1 -1.25 × 10 8 yr, while NGC 2098 is somewhat younger, with an age of 6.3 -7.9×10 7 yr. In the case of SL 666 the good quality of the acquired data allowed the construction of the main sequence luminosity function as a function of radius, which revealed mass segregation, also confirmed from star counts. Since the age of SL 666 is significantly lower than the mean relaxation time of at least 5 × 10 8 yr calculated for this cluster and since the mass range of the cluster members does not permit us to assume faster energy equipartition, the observed mass segregation seems to be due to the way stars form in the cluster. Indications on a star formation scenario are examined. Disruption time is also discussed and there is strong evidence that the cluster is bound. NGC 2098 shows strong evidence of mass segregation, but further observations are needed in this case.

We present results on over 100 high-redshift quasars found in the Sloan Digital Sky Survey (SDSS), using automated selection algorithms applied to SDSS imaging data and with spectroscopic confirmation obtained during routine spectroscopic operations of the Sloan 2.5-m telescope. The SDSS spectra cover the wavelength range 3900 -9200 Å at a spectral resolution of 1800, and have been obtained for 116 quasars with redshifts greater than 3.94; 92 of these objects were previously uncataloged, significantly increasing the current tally of published z > 4 quasars. The paper also reports observations of five additional new z > 4.6 quasars; all were found from the SDSS imaging survey and spectroscopically confirmed with data from the Apache Point Observatory's 3.5-m telescope. The i ′ magnitudes of the quasars range from 18.03 to 20.56. Of the 97 new objects in this paper, 13 are Broad Absorption Line quasars. Five quasars, including one object at a redshift of 5.11, have 20 cm peak flux densities greater than 1 mJy. Two of the quasars, both at z ≈ 4.5, have very weak emission lines; one of these objects is a radio source. Nineteen of the newly-discovered objects have redshifts above 4.6, and the maximum redshift is z=5.41; among objects reported to date, the latter is the third highest redshift AGN, and penultimate in redshift among luminous quasars.

We present preliminary measurements of the b J and K-band luminosity functions (LFs) of field galaxies obtained from optical and Kband imaging of a sample of galaxies selected from the Stromlo-APM Redshift Survey. The b J LF is consistent with that previously published from photographic data. The K-band LF has been estimated over a range of 12 magnitudes and is reasonably well fit by a Schechter function with faint-end slope α = -1.2.

We present preliminary results of a neutral hydrogen (HI) redshift survey to find low surface brightness (LSB) galaxies in the very nearby universe. Our sample consists of all galaxies in the APM catalog ) with a mean surface brightness of µ ≥ 24 mag/arcsec 2 , down to a magnitude limit of b j ≤ 17. With the Parkes 64m radiotelescope 35 objects were detected at v < 4300 km s -1 . The resulting luminosity function, HI mass function, and for the first time field mass function are presented. It is found that LSBs make a negligible contribution to the overall integrated luminosity, HI mass, and total mass contained in galaxies.

We describe modifications to the joint stepwise maximum likelihood method of Cole (2011) in order to simultaneously fit the GAMA-II galaxy luminosity function (LF), corrected for radial density variations, and its evolution with redshift. The whole sample is reasonably well-fit with luminosity (Q) and density (P ) evolution parameters Q, P ≈ 0.8, 1.7. Red galaxies show larger luminosity but smaller density evolution than blue galaxies, as expected.

Aims. We aim to study the 250 µm luminosity function (LF) down to much fainter luminosities than achieved by previous efforts. Methods. We developed a modified stacking method to reconstruct the 250 µm LF using optically selected galaxies from the SDSS survey and Herschel maps of the GAMA equatorial fields and Stripe 82. Our stacking method not only recovers the mean 250 µm luminosities of galaxies that are too faint to be individually detected, but also their underlying distribution functions. Results. We find very good agreement with previous measurements in the overlapping luminosity range. More importantly, we are able to derive the LF down to much fainter luminosities (∼25 times fainter) than achieved by previous studies. We find strong positive luminosity evolution L * 250 (z) ∝ (1 + z) 4.89±1.07 and moderate negative density evolution Φ * 250 (z) ∝ (1 + z) -1.02±0.54 over the redshift range 0.02 < z < 0.5.

We present a combined analysis of the low-mass initial mass function (IMF) for seven star-forming regions. We first demonstrate that the ratios of stars to brown dwarfs are consistent with a single underlying IMF. By assuming that the underlying IMF is the same for all seven clusters and by combining the ratio of stars to brown dwarfs from each cluster, we constrain the shape of the brown dwarf IMF and find it to be consistent with a lognormal IMF. This provides the strongest constraint yet that the substellar IMF turns over ( ,

We use the Herschel-Astrophysical Terahertz Large Area Survey (ATLAS) science demonstration data to investigate the star formation properties of radio-selected galaxies in the GAMA-9h field as a function of radio luminosity and redshift. Radio selection at the lowest radio luminosities, as expected, selects mostly starburst galaxies. At higher radio luminosities, where the population is dominated by active galactic nuclei (AGN), we find that some individual objects are associated with high far-infrared luminosities. However, the far-infrared properties of the radio-loud population are statistically indistinguishable from those of a comparison Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

The nature of galaxy structures on large scales is a key observational prediction for current models of galaxy formation. The Sloan Digital Sky Survey (SDSS) and the 2dF galaxy survey have revealed a number of structures on 40-150 h -1 Mpc scales at low redshifts, and some even larger ones. To constrain galaxy number densities, luminosities, and stellar populations in large structures at higher redshift, we have investigated two sheet-like structures of galaxies at z = 0.8 and 1.3 spanning 150 h -1 comoving Mpc embedded in large quasar groups (LQGs) extending over at least 200 h -1 Mpc. We present first results of an analysis of these sheet-like structures using two contiguous 1 deg Galaxy Evolution Explorer (GALEX) fields (FUV and NUV) cross-correlated with optical data from the SDSS. We derive a sample of 462 Lyman break galaxy (LBG) candidates coincident with the sheets. Using the GALEX and SDSS data, we show that the overall average spectral energy distribution of a LBG galaxy at z ∼ 1 is flat (in f λ ) in the rest-frame wavelength range from 1500 Å to 4000 Å, implying evolved populations of stars in the LBGs. From the luminosity functions we get indications for overdensities in the two LQGs compared to their foreground regions. Similar conclusions come from the calculation of the 2-point correlation function, showing a 2σ overdensity for the LBGs in the z ∼ 0.8 LQG on scales of 1.6 to 4.8 Mpc, indicating similar correlation scales for our LBG sample as their z ∼ 3 counterparts.

The Macquarie/AAO/Strasbourg Hα Planetary Nebula Catalogue (MASH) of nearly 1000 new Galactic Planetary Nebulae (PNe) discovered from the AAO/UKST Hα survey of the southern Galactic plane is now essentially complete. The survey's excellent combination of resolution, uniformity, areal coverage and depth has enabled detection of this unprecedented new PN sample. MASH PNe are typically more evolved, obscured, of larger angular extent, and of lower surface brightness than those in most previous surveys. The number of PNe in the Galactic bulge has also been doubled. Though most of these are quite compact, more evolved examples have been found. The MASH catalogue represents a seven year programme of discovery and spectroscopic confirmation and will form the basis for significant studies. A key strength is that the whole sample has been obtained from the same, uniform survey data. The 75% increase in known Galactic PNe represents the largest single increase in such discoveries. MASH PNe will have a significant impact on many aspects of PNe research, especially for studies at the extremes of the luminosity function which were previously poorly represented.

We use high spatial resolution maps of stellar mass and infrared flux of the Large Magellanic Cloud (LMC) to calibrate a conversion between 3.6 and 4.5 µm fluxes and stellar mass, M * = 10 5.65 F 2.85 3.6 F -1.85 4.5 D 0.05 2 M ⊙ , where fluxes are in Jy and D is the luminosity distance to the source in Mpc, and to provide an approximate empirical estimate of the fractional internal uncertainty in M * of 0.3 N/10 6 , where N is the number of stars in the region. We find evidence that young stars and hot dust contaminate the measurements, but attempts to remove this contamination using data that is far superior than what is generally available for unresolved galaxies resulted in marginal gains in accuracy. The scatter among mass estimates for regions in the LMC is comparable to that found by previous investigators when modeling composite populations, and so we conclude that our simple conversion is as precise as possible for the data and models currently available. Our results allow for a reasonably bottom-heavy initial mass function, such as Salpeter or heavier, and moderately disfavor lighter versions such as a diet-Salpeter or Chabrier initial mass function.

This paper reports updated results on our systematic mining of the DENIS database for nearby very cool M-dwarfs (M 6V-M 8V, 2.0 ≤ I -J ≤ 3.0, photometric distance within 30 pc), initiated by Phan-Bao et al. (2001, hereafter Paper I). We use M dwarfs with well measured parallaxes (HIP, GCTP, ...) to calibrate the DENIS (M I , I -J) colour-luminosity relationship. The resulting distance error for single dwarfs is about 25%. Proper motions, as well as B and R magnitudes, were measured on archive Schmidt plates for those stars in the DENIS database that meet the photometric selection criteria. We then eliminate the giants by a Reduced Proper Motion cutoff, which is significantly more selective than a simple proper motion cutoff. It greatly reduces the selection bias against low tangential velocity stars, and results in a nearly complete sample. Here we present new data for 62 red dwarf candidates selected over 5700 square degrees in the DENIS database. 26 of those originate in the 2100 square degrees analysed in Paper I, with improved parameters here, and 36 were found in 3600 additional square degrees. 25 of those are new nearby dwarfs. We determine from that sample of 62 stars a stellar density for 12.0 ≤ M I ≤ 14.0 of Φ I cor = (2.2 ± 0.4) × 10 -3 stars pc -3 mag -1 . This value is consistent with photometric luminosity functions measured from deeper and smaller-field observations, but not with the nearby star luminosity function. In addition we cross-identified the NLTT and DENIS catalogues to find 15 similar stars, in parts of the sky not yet covered by the colour-selected search. We present distance and luminosity estimates for these 15 stars, 10 of which are newly recognized nearby dwarfs. A similar search in Paper I produced 4 red dwarf candidates, and we have thus up to now identified a total of 35 new nearby late-M dwarfs.

We present the first results of a survey for high-redshift, z ≥ 6, quasars using izY multicolour photometric observations from the Dark Energy Survey (DES). Here we report the discovery and spectroscopic confirmation of the z AB , Y AB = 20.2, 20.2 (M 1450 = -26.5) quasar DES J0454-4448 with a redshift of z = 6.09±0.02 based on the onset of the Ly α forest and an H I near zone size of 4.1 +1.1 -1.2 proper Mpc. The quasar was selected as an i-band drop out with i-z = 2.46 and z AB < 21.5 from an area of ∼300 deg 2 . It is the brightest of our 43 candidates and was identified for spectroscopic follow-up solely based on the DES i-z and z-Y colours. The quasar is detected by WISE and has W1 AB = 19.68. The discovery of one spectroscopically confirmed quasar with 5.7 < z < 6.5 and z AB ≤ 20.2 is consistent with recent determinations of the luminosity function at z ∼ 6. DES when completed will have imaged ∼5000 deg 2 to Y AB = 23.0 (5σ point source) and we expect to discover 50-100 new quasars with z > 6 including 3-10 with z > 7 dramatically increasing the numbers of quasars currently known that are suitable for detailed studies.

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 square degrees, we compute the luminosity function of galaxies in the r * band over a range -23 < M r * < -16 (for h = 1). The result is well-described by a Schechter function with parameters φ * = (1.46±0.12)×10 -2 h 3 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) × 10 8 hL Mpc -3 . We find that the surface brightness selection threshold has a negligible impact for M r * < -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 R GKC -band or b j -band using these Petrosian magnitudes, we obtain luminosity densities 2 times that found by the Las Campanas Redshift Survey in R GKC and 1.4 times that found by the Two-degree Field Galaxy Redshift Survey in b j . 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.

The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed investigations of the distribution of luminous and non-luminous matter in the Universe: a photometrically and astrometrically calibrated digital imaging survey of π steradians above about Galactic latitude 30 • in five broad optical bands to a depth of g ∼ 23 m , and a spectroscopic survey of the approximately 10 6 brightest galaxies and 10 5 brightest quasars found in the photometric object catalog produced by the imaging survey. This paper summarizes the observational parameters and data products of the SDSS, and serves as an introduction to extensive technical on-line documentation.

We report the detection of 239 trans-Neptunian objects discovered through the ongoing New Horizons survey for distant minor bodies being performed with the Hyper Suprime-Cam mosaic imager on the Subaru Telescope. These objects were discovered in images acquired with either the r2 or the recently commissioned EB-gri filter using shift and stack routines. Due to the extremely high stellar density of the search region downstream of the spacecraft, new machine learning techniques had to be developed to manage the extremely high false-positive rate of bogus candidates produced from the shift and stack routines. We report discoveries as faint as r2 ∼ 26.5. We highlight an overabundance of objects found at heliocentric distances R ≳ 70 au compared to expectations from modeling of the known outer solar system. If confirmed, these objects betray the presence of a heretofore-unrecognized abundance of distant objects that can help explain a number of other observations that otherwise remain at odds with the known Kuiper Belt, including detections of serendipitous stellar occultations, and recent results from the Student Dust Counter on board the New Horizons spacecraft.

We briefly describe our on-going investigation of the near-IR luminosity-metallicity relationship for dwarf irregular galaxies in nearby groups of galaxies. The motivations of the project and the observational databases are introduced, and a preliminary result is presented. The 12 + log(O/H) vs. H plane must be populated with more low-luminosity galaxies before a definite conclusion can be drawn.

We present JHK observations of Leo I and Leo II dwarf spheroidal galaxies obtained with the WFCAM@UKIRT. The wide field of view and the good photometric quality of the camera led to the first high-precision NIR photometric catalogue obtained so far for these two galaxies. With high-precision photometry we could isolate the foreground Galactic population and disentangle oxygen-and carbon-rich AGB stars. Our data are compared with predictions of the most recent theoretical AGB models.

We describe the HST ACS Coma cluster Treasury survey, a deep twopassband imaging survey of one of the nearest rich clusters of galaxies, the Coma cluster (Abell 1656). The survey was designed to cover an area of 740 arcmin 2 in regions of different density of both galaxies and intergalactic medium within the cluster. The ACS failure of January 27th 2007 leaves the survey 28% complete, with 21 ACS pointings (230 arcmin 2 ) complete, and partial data for a further 4 pointings (44 arcmin 2 ). Predicted survey depth for 10σ detections for optimal photometry of point sources is g ′ = 27.6 in the F475W filter, and I C =26.8 mag in F814 (AB magnitudes). Initial simulations with artificially injected point sources show 90% recovered at magnitude limits of g ′ = 27.55 and I C = 26.65. For extended sources, the predicted 10σ limits for a 1 arcsecond 2 region are g ′ = 25.8 mag arcsec -2 and I C = 25.0 mag arcsec -2 . We highlight several motivating science goals of the survey, including study of the faint end of the cluster galaxy luminosity function, structural parameters of dwarf galaxies, stellar populations and their effect on colors and color gradients, evolution of morphological components in a dense environment, the nature of ultra compact dwarf galaxies, and globular cluster populations of cluster galaxies of a range of luminosities and types. This survey will also provide a local rich USA.

We revise the scenario of the formation of Galactic globular clusters (GCs) by adding the observed detailed chemical composition of their different stellar generations to the set of their global parameters. We exploit the unprecedented set of homogeneous abundances of more than 1200 red giants in 19 clusters, as well as additional data from literature, to give a new definition of bona fide GCs, as the stellar aggregates showing the Na-O anticorrelation. We propose a classification of GCs according to their kinematics and location in the Galaxy in three populations: disk/bulge, inner halo, and outer halo. We find that the luminosity function of GCs is fairly independent of their population, suggesting that it is imprinted by the formation mechanism only marginally affected by the ensuing evolution. We show that a large fraction of the primordial population should have been lost by the proto-GCs. The extremely low Al abundances found for the primordial population of massive GCs indicate a very fast enrichment process before the formation of the primordial population. We suggest a scenario for the formation of GCs that includes at least three main phases: i) the formation of a precursor population (likely due to the interaction of cosmological structures similar to those that led to the formation of dwarf spheroidals, but residing at smaller Galactocentric distances, with the early Galaxy or with other structures); ii) the triggering of a long episode of star formation (the primordial population) from the precursor population; and iii) the formation of the current GC, mainly within a cooling flow formed by the slow winds of a fraction of the primordial population. The precursor population is very effective in raising the metal content in massive and/or metal-poor (mainly halo) clusters, while its rôle is minor in small and/or metal-rich (mainly disk) ones. Finally, we use principal component analysis and multivariate relations to study the phase of metal enrichment from first to second generation. We conclude that most of the chemical signatures of GCs may be ascribed to a few parameters, the most important being metallicity, mass, and cluster age. Location within the Galaxy (as described by the kinematics) also plays some rôle, while additional parameters are required to describe their dynamical status.