Integrated Luminosity Function Research Articles

HiZELS: a high-redshift survey of Hα emitters - I. The cosmic star formation rate and clustering atz= 2.23★

We present results from a near-infrared narrow-band survey of emission-line galaxies at z = 2.23, using the Wide Field Camera on the United Kingdom Infrared Telescope. The H2S1 narrow-band filter ( �c = 2.121µm) we employ selects the Hemission line redshifted to z = 2.23, and is thus suitable for selecting 'typical' star forming g alaxies and active galactic nuclei at this epoch. The pilot study was undertaken in the well studied Cosmological Evolution Survey field (COSMOS) and is already the largest near-infrar ed narrow-band survey at this depth, with a line flux limit of FH� � 10 −16 erg s −1 cm −2 over 0.60 square degrees, probing �220× 10 3 Mpc 3 (co-moving) down to a limiting star formation rate of �30M⊙ yr −1 (3�). In this paper we present the results from our pilot survey and evaluate the Hluminosity function and estimate the clustering properties of Hemitters at z = 2.23 from 55 detected galaxies. The integrated luminosity function is used to est imate the volume averaged star formation rate at z = 2.23: �SFR = 0.17 +0.16 −0.09M⊙ yr −1 Mpc −3 for LH� > 10 42 erg s −1 . For the first time, we use the Hstar-formation tracer to reliably constrainSFR out to z = 2.23 demonstrating the rapid increase inSFR out to this redshift as well as confirming the flattening inSFR betweenz � 1-2. In addition to the luminosity distribution, we analyse t he clustering properties of these galaxies. Using the 2-point angular correlation function, !(�), we estimate a real space correlation length of r0 = 4.2 +0.4 −0.2 h −1 Mpc. In comparison to models of clustering which take into account bias evolution, we estimate that these galaxies are hosted by dark matter halos of mass Mhalo � 10 12 M⊙ consistent with the progenitors of the Milky

Extended star formation history of the star cluster NGC 2154 in the Large Magellanic Cloud

The colour-magnitude diagram (CMD) of the intermediate-age Large Magellanic Cloud star cluster NGC 2154 and its adjacent field has been analysed using Padova stellar models to determine the cluster's fundamental parameters and its star formation history. Deep BR CCD photometry, together with synthetic CMDs and integrated luminosity functions, has allowed us to infer that the cluster experienced an extended star formation period of about 1.2 Gyr, which began approximately 2.3 Gyr ago and ended 1.1 Gyr ago. However, the physical reality of such a prolonged period of star formation is questionable, and could be the result of inadequacies in the stellar evolutionary tracks themselves. A substantial fraction of binaries (70 per cent) seems to exist in NGC 2154.

Three clusters of the SMC from ACS/WFC HST archive data: NGC 265, K 29 and NGC 290 and their field population

Aims. We determine the age, metallicity and initial mass function of three clusters, namely NGC 265, K 29, NGC 290, located in the main body of the Small Magellanic Cloud. In addition, we derive the history of star formation in the companion fields. Methods. We make use of ACS/WFC HST archive data. For the clusters, the age and metallicity are derived fitting the integrated luminosity function with single synthetic stellar population by means of the x 2 minimization. For the companion fields, the history of star formation is derived using the x 2 minimization together with the downhill-simplex method. Results. For the clusters we find the following ages and metallicities: NGC 265 has log(Age) = 8.5 ± 0.3 yr and metallicity 0.004 ± 0.003 (or [Fe/H] = -0.62); K 29 has log(Age) = 8.2 ± 0.2 yr and metallicity Z = 0.003 ± 0.002 (or [Fe/H] = -0.75); NGC 290 has log(Age) = 7.8 ± 0.5 yr and metallicity 0.003 ± 0.002 (or [Fe/H] = -0.75). The superior quality of the data allows the study of the initial mass function down to M ∼ 0.7 M ⊙ . The initial mass function turns out to be in agreement with the standard Kroupa model. The comparison of the NGC 265 luminosity function with the theoretical ones from stellar models both taking overshoot from the convective core into account and neglecting it, seems to suggest that a certain amount of convective overshoot is required. However, this conclusion is not a strong one because this cluster has a certain amount of mass segregation which makes it difficult to choose a suitable area for this comparison. The star formation rate of the field population presents periods of enhancements at 300-400 Myr, 3-4 Gyr and finally 6 Gyr. However it is relatively quiescent at ages older than 6 Gyr. This result suggests that at older ages, the tidal interaction between the Magellanic Clouds and the Milky Way was not able to trigger significant star formation events.

Photometric binary content in intermediate/old open clusters

The stellar evolutionary models by Bertelli et al. ([CITE]) have been used to generate synthetic colour–magnitude diagrams (CMDs) of open clusters. A comparison of the synthetic integrated luminosity function (ILF) and synthetic colour distribution with the corresponding observed distributions is used to estimate the photometric binary content in three intermediate age open clusters, which is found to be about 30% in these clusters.

NGC 1866: A workbench for stellar evolution

The young LMC cluster NGC 1866 represents the ideal laboratory for testing stellar evolutionary models: in particular, it can be used to discriminate among classical stellar models, in which the extension of the convective regions is fixed by the classical Schwarzschild criterion, from models with overshooting, in which an ``extra-mixing'' is considered to take place beyond the classical limit of the convective zone. Addressing this subject in a recent work, Testa et al. (1999) reached the conclusion that the classical scheme for the treatment of convection represents a good and sufficient approximation for convective interiors. Using their own data, we repeat here the analysis. First we revise the procedure followed by Testa et al. (1999) to correct the data for completeness, second we calculate new stellar models with updated physical input for both evolutionary schemes, finally we present many simulations of the colour-magnitude diagrams and luminosity functions of the cluster using the ratio of the integrated luminosity function of main sequence stars to the number of giants as the normalization factor of the simulations. We also take into account several possible physical agents that could alter the color-magnitude diagram and the luminosity function: they are unresolved binary stars, dispersion in the age, stochastic effects in the initial mass function. Their effect is analyzed separately, with the conclusion that binary stars have the largest impact. The main result of this study is that the convective overshoot hypothesis (together with a suitable percentage of unresolved binaries) is really needed to fully match the whole pattern of data. The main drawback of the classical models is that they cannot reproduce the correct ratio of main sequence to post-main sequence stars.

Probing the faint end of the Galaxy luminosity function at $\vec{z}=$ 3 with Lyαemission

We present spectroscopic observations obtained with the ESO Very Large Telecope (VLT) of seven candidate Ly-alpha emitting galaxies in the field of the radio quiet Q1205-30 at z=3.04 previously detected with deep narrow band imaging. Based on equivalent widths and limits on line ratios we confirm that all seven objects are Ly-alpha emitting galaxies. Deep images also obtained with the VLT in the B and I bands show that five of the seven galaxies have very faint continuum fluxes (I(AB) approx. 26.8 and B(AB) approx. 27.3). The star formation rates of these seven galaxies estimated from the rest-frame UV continuum around 2000AA, as probed by the I-band detections, as well as from the Ly-alpha luminosities, are 1-4 M_sun yr^{-1}. This is 1-3 orders of magnitude lower than for other known populations of star-forming galaxies at similar redshifts (the Lyman-Break galaxies and the sub-mm selected sources). The inferred density of the objects is high, 16+-4 per arcmin^2 per unit redshift. This is consistent with the integrated luminosity function for Lyman-Break galaxies down to R=27 if the fraction of Ly-alpha emitting galaxies is approx. 70% at the faint end of the luminosity function. However, if this fraction is 20% as reported for the bright end of the luminosity function then the space density in this field is significantly larger (by a factor of 3.5) than expected from the luminosity function for Lyman-Break galaxies in the HDF-North. This would be an indication that at least some radio quiet QSOs at high redshift reside in overdense environments or that the faint end slope of the high redshift luminosity function has been underestimated. These observations show that Ly-alpha emission is an efficient method by which to probe the faint end of the luminosity function at high redshifts.

The Large Magellanic Cloud Globular Cluster NGC 1866: New Data, New Models, New Analysis

We present a new deep (down to V ~ 24) photometry of a wide region (~6' × 6') around the Large Magellanic Cloud globular cluster NGC 1866. Our sample is much larger (by more than a factor of 3) than any previous photometry and with a main sequence (MS) that may be considered complete, down to at least 3 mag below the brightest MS star; such an occurrence allows a meaningful and robust comparison with various theoretical scenarios produced by means of models computed with the evolutionary code FRANEC. Both age and present-day mass function slope, α, are derived by a fit to the available MS and by the use of the parameter Δσ, which is simply the difference, in σ, between the observed and the predicted integrated MS luminosity functions. Our main conclusions are as follows: (1) The adoption of standard models (i.e., computed by adopting the Schwarzschild criterion to fix the border of the convective core) allows a fair fit to the MS for an age of the order of 100–140 Myr and a present-day mass function having a slope α between 2.3 and 1.9, the exact values depending on the adopted distance modulus. It is moreover possible to reproduce the average He clump luminosity while the total number of stars predicted in the He clump is twice the observed value; this means that we reobtain and confirm the first finding of Becker & Mathews, according to whom the simple adoption of a classical scenario leads to a neat discrepancy concerning the prediction of the number of stars in the He clump. (2) The adoption of models computed by increasing the size of the convective core by a certain amount—i.e., 0.25Hp—leads to a fair fit to the MS only for a visual distance modulus (m - M)V 18.6, an age t 200 Myr, and a mass function slope α 2.2. In this case, the total number of He clump stars is well reproduced, although the luminosity function of the He clump itself is predicted to be systematically less luminous than observed. The previous conclusions are based on the assumption that there is no appreciable population of binaries in NGC 1866. Though there are not yet sufficient data on the frequency of binary systems in these clusters, we analyze how the previous scenarios would change if a consistent (30%) population of binary systems were present in the cluster. This choice is based on the fact that a fraction of binaries of the order of 30% has already been found in NGC 1818, a cluster similar to NGC 1866. The inclusion of a 30% binary population leads to the following additional conclusions: (3) The adoption of the standard models now leads to a good fit to the entire luminosity function—i.e., MS, turnoff, and He clump stars—for a visual distance modulus (m - M)V = 18.8, an age t 100 Myr, and a mass function slope α 2.4, thus largely removing the classical discrepancy between observed and predicted number of stars in the He-burning clump. The quoted visual distance modulus constrains the unreddened distance modulus (m - M)0 within 18.50 and 18.62, depending on the reddening (whose most common values available in the literature range from 0.05 to 0.10). (4) At variance with the last point, the fit obtained by using models computed with an enlarged convective core gets worse when a binary component is taken into account. This is because of the fact that the presence of binary systems increases the existing discrepancy between the observed and predicted clump luminosity, since the He clump is predicted to be even less luminous than in absence of binaries. As a consequence of this analysis, we think that the next step toward a proper understanding of NGC 1866 and similar clusters, must include the accurate determination of the frequency of binary systems, which we hope will be performed with the incoming Cycle 8 Hubble Space Telescope observations of NGC 1866.

Multicolor CCD Photometry and Stellar Evolutionary Analysis of NGC 1907, NGC 1912, NGC 2383, NGC 2384, and NGC 6709 Using Synthetic Color-Magnitude Diagrams

We present the first CCD photometric observations of NGC 2383 and NGC 2384 in B, V, R, and I, NGC 1912, NGC 6709 in B, V, and I and NGC 1907 in B and V passbands, reaching down to a limiting magnitude of V ~ 20 mag for ~3300 stars put together. The results of the spectroscopic observations of 43 bright stars in the field of NGC 1912, NGC 2383, NGC 2384, and NGC 6709 are also presented. The color-magnitude diagrams (CMDs) of the clusters in V versus B-V, V versus V-R, and V versus V-I are presented. The distances and reddening to these clusters are determined using the cluster CMDs. The distances to the clusters NGC 1907, NGC 1912, NGC 2383, NGC 2384, and NGC 6709 are 1785 ± 260, 1820 ± 265, 3340 ± 490, 2925 ± 430, and 1190 ± 175 pc, respectively. Some gaps in the cluster main sequence have been identified. We have compared the observed color-magnitude diagrams of these four open clusters with the synthetic ones derived from one classical and two overshoot stellar evolutionary models. Overshoot models estimate older ages for clusters when compared to the classical models. The age of the clusters estimated using the isochrones of Bertelli et al. are 400, 250, 400, 20, and 315 Myr for the clusters NGC 1907, NGC 1912, NGC 2383, NGC 2384, and NGC 6709, respectively. A comparison of the synthetic color-magnitude diagrams with the observed ones indicates that the overshoot models should be preferred. The comparison of integrated luminosity functions do not clearly indicate as to which model is to be preferred. The values of the mass function slopes estimated for the clusters are x = 1.7 ± 0.15 for NGC 1912 (mass range: 1.7–3.9 M⊙) and NGC 6709 (1.7–3.4 M⊙), x = 1.3 ± 0.15 for NGC 2383 (1.7–3.1 M⊙), and x = 1.0 ± 0.15 for NGC 2384 (2.0–14.0). The present age estimates show that the closely located cluster pair NGC 1912 + NGC 1907 have similar ages, indicating that they may have born together, making them a good candidate to be a binary open cluster.

The NGC 1399 Globular Cluster System: Washington Photometry Revisited

A new analysis and discussion of Washington CCD photometry for some 500 globular cluster candidates associated with the Fornax cluster cD galaxy NGC 1399 are presented. The image handling in this work includes improved methods for the removal of both the galaxy halo and fringing effects over that employed in a previous work of ours. The analysis of the globular cluster candidates inside an annular region between 05 and 4' from the galaxy center using two-color diagrams shows a clear bimodal distribution for objects fainter than T1 = 21.0 (V ≈ 21.5). The modal colors of the globular clusters belonging to the red population are coincident, within the measuring uncertainties, with those of the galaxy halo. In turn, the average integrated colors of the blue population are comparable to those of the bluest non–star-forming low surface brightness galaxies in Fornax. Red clusters appear more centrally concentrated than the blue clusters. A new determination of the integrated luminosity function turnover (T1 = 23.24) leads to a distance modulus for NGC 1399 of V0 - MV = 31.02 ± 0.2. The total number of globular clusters, combined with our preliminary photometry of the galaxy halo, leads to an overall specific frequency SN = 5.6 ± 1.0, which is considerably lower than previous estimates available in the literature. We note that these last values have been based on an extrapolation of aperture photometry of the inner regions of the galaxy.

Synthetic luminosity functions of galaxies in different environments

AbstractAdopting luminosity functions of various morphological types of galaxies and galaxy populations for different environments characterized by the density, the overall differential and integrated luminosity functions of Hubble mix in different dense regions have been obtained. The calculated overall luminosity functions show a weak dependence on the density. Although there is a satisfactory agreement between the calculated overall luminosity functions and the observed distributions of samples of corresponding densities, the observed data are too uncertain in order to confirm the expected density dependence.

The Luminosity Function and Structure of the Coma Cluster

view Abstract Citations (129) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Luminosity Function and Structure of the Coma Cluster Abell, G. O. Abstract The luminosity function of the galaxies in the Coma cluster is determined by a procedure of extrafocal photographic photometry. The logarithmic integrated luminosity function rises sharply with increasing magnitude through the interval m = 11.6 to 14.5, and then slowly for greater magnitudes to the limit m = 19.4. The data suggest a moderate increase in the slope of the function for magnitudes fainter than m = 17.5. The cluster is found, in projection, to be ellipsoidal in shape, centered at (1950) a = 12h56m9 = +280141. To the limit m = 18.3 the cluster is estimated to have 1525 member galaxies. The brighter galaxies in the inner part of the cluster have a distribution resembling that of the isothermal polytrope, but there is no marked segregation of bright and faint galaxies, as would be required for complete statistical sequilibrium. The luminosity of the cluster is estimated at 2 x 1018 L0. The mass-to-light ratio (in solar units) is found probably not to exceed 122. Subject headings: galaxies: clusters of - galaxies: photometry Publication: The Astrophysical Journal Pub Date: April 1977 DOI: 10.1086/155159 Bibcode: 1977ApJ...213..327A full text sources ADS | data products NED (96)