Photometric Luminosity Functions Research Articles

Subaru FOCAS survey of z = 7-7.1 Lyα emitters: a test for z≳ 7 Lyα photometric luminosity functions

Recent observations of z >~ 7 Ly{\alpha} emitters (LAEs) have derived a variety of Ly{\alpha} luminosity functions (LFs) with contradictory results, evolution or non-evolution from z <~ 6, the epoch after reionization. This could be because most of z >~ 7 LFs comprise photometric candidates and might include some contaminations. We conducted the Subaru Telescope Faint Object Camera And Spectrograph narrowband NB980 ({\lambda}c ~ 9800A, FWHM ~ 100A) imaging and spectroscopy survey of z=7-7.1 LAEs to compare its "contamination-free" result with z >~ 7 photometric Ly{\alpha} LFs previously derived. We imaged the Subaru Deep Field and the sky around a cluster MS 1520.1+3002 and found one LAE candidate, but spectroscopy did not reveal Ly{\alpha} though deep enough to detect it. We calculated the expected number of LAEs in our survey, using five z=7 and three z=7.7 Ly{\alpha} LFs from recent surveys. Seven of them are consistent with null detection (0.1^{+1.8}_{-0.1}-1.1^{+2.2}_{-1.0} LAEs) within errors including Poisson statistics and cosmic variance, but average values (0.7-1.1 LAEs) predicted from one z=7 and two z=7.7 LFs among the seven indicate nearly a single detection. The remaining one z=7 LF predicts 3.0^{+3.2}_{-2.0} LAEs. As to z=7, the discrepancy likely comes from different LAE selection criteria. For z=7.7, there are two possibilities; (1) If z=7.7 LAEs are somehow brighter in Ly{\alpha} luminosity than lower redshift LAEs, z=7.7 LF is observed to be similar to or higher than lower redshift LFs even if attenuated by neutral hydrogen. (2) All/most of the z=7.7 candidates are not LAEs. This supports the decline of LF from z ~ 6 to 7.7 and reionization at z ~ 6-7.7.

Fossil groups origins

The most accepted scenario for the origin of fossil groups (FGs) is that they are galaxy associations in which the merging rate was fast and efficient. These systems have assembled half of their mass at early epoch of the Universe, subsequently growing by minor mergers. They could contain a fossil record of the galaxy structure formation. We have started a project in order to characterize a large sample of FGs. In this paper we present the analysis of the fossil system RX J105453.3+552102. Optical deep images were used for studying the properties of the brightest group galaxy and for computing the photometric luminosity function of the group. We have also performed a detail dynamical analysis of the system based on redshift data for 116 galaxies. This galaxy system is located at z=0.47, and shows a quite large line-of-sight velocity dispersion \sigma_{v}~1000 km/s. Assuming the dynamical equilibrium, we estimated a virial mass of M ~ 10^{15} h_{70} M_{\odot}. No evidence of substructure was found within 1.4 Mpc radius. We found a statistically significant departure from Gaussianity of the group members velocities in the most external regions of the group. This could indicate the presence of galaxies in radial orbits in the external region of the group. We also found that the photometrical luminosity function is bimodal, showing a lack of M_{r} ~ -19.5 galaxies. The brightest group galaxy shows low Sersic parameter (n~2) and a small peculiar velocity. Indeed, our accurate photometry shows that the difference between the brightest and the second brightest galaxies is 1.9 mag in the r-band, while the classical definition of FGs is based on a magnitude gap of 2. We conclude that this fossil system does not follow the empirical definition of FGs. Nevertheless, it is a massive, old and undisturbed galaxy system with little infall of L^{*} galaxies since its initial collapse.

New neighbours

This paper reports updated results on our systematic mining of the DENIS database for nearby very cool M-dwarfs (M6V-M8V, 2.0<I-J<3.0, photometric distance within 30 pc), We calibrate the DENIS (M_I, I-J) colour-luminosity relationship from M dwarfs with well measured parallaxes (HIP, GCTP,...), obtaining distance errors for single dwarfs of 25%. Using proper motions measured on archive Schmidt plates for stars that meet the photometric selection criteria, we eliminate the giants by a Reduced Proper Motion cutoff, which is significantly more selective than a simple proper motion cutoff. 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 2.2(+-0.4)E-3 stars/pc^3/mag. 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.

New neighbours: IV. 30 DENIS late-M dwarfs between 15 and 30 parsecs

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 (MI, 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 cuto ff .I t 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 ≤ MI ≤ 14. 0o f ΦI 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.

Determination of the Low-Mass Star Mass Function in the Galactic Disk

We use the theoretical mass-luminosity relationship derived recently for low-mass stars (Chabrier, Baraffe, & Plez) to determine the lower end of the stellar mass function in the Galactic disk from observed luminosity functions. The age and metallicity spreads characteristic of the disk population are carefully examined. The mass function (MF) is shown to rise monotonically with decreasing mass and is reasonably well described by a power law n(m) ∝ m-α with α ≈ 2 ± 0.5 from ~0.6 M☉ down to the hydrogen-burning limit. Bimodal MFs, as derived in previous studies, are shown to be due to unresolved binaries in the photometric luminosity function, as suggested previously by Kroupa and coworkers. Such a rising MF suggests a substantial amount of brown dwarfs in the Galactic disk. The local density of main-sequence stars is found to be ρ* = 4.2 ± 0.8 × 10-2 M☉ pc-3, which corresponds to a surface density Σ* = 28.5 ± 6 M☉ pc-2, including the thick-disk contribution. The expected number of brown dwarfs is examined within the context of the OGLE and MACHO microlensing experiments. Although the contribution of brown dwarfs to the disk-mass budget is likely to be larger than previously thought, it still lacks in reproducing the observed optical depth.

Are the nearby and photometric stellar luminosity functions different ?

view Abstract Citations (39) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Are the nearby and photometric stellar luminosity functions different ? Kroupa, Pavel Abstract The stellar luminosity function derived from the sample of stars within 5.2-20 pc is the nearby luminosity function. The luminosity function obtained from deep low spatial resolution surveys to distances of typically 100-200 pc is the photometric luminosity function. We obtain and tabulate a best estimate of the parent distribution from which Malmquist-corrected photometric luminosity functions are sampled. This is presently the most accurate and precise available estimate of the true distribution of stars with absolute magnitude for Mν < 16.5, as derived from low-resolution surveys. Using rigorous statistical analysis, we find that the hypothesis that the nearby and photometric luminosity functions estimate the same parent luminosity function can be discarded with 99% confidence or better for Mν > 13, Mbol > 10. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176394 arXiv: arXiv:astro-ph/9505128 Bibcode: 1995ApJ...453..350K Keywords: Astrophysics E-Print: 14 pages, plain TeX, figures available on request, ApJ (to appear in Nov.1 issue of Part I) full text sources arXiv | ADS | Related Materials (11) Part 1: 1990MNRAS.244...76K Part 2: 1991MNRAS.251..293K Part 3: 1992AJ....103.1602K Part 4: 1993MNRAS.262..545K Part 6: 1995ApJ...453..358K Part 7: 2001MNRAS.322..231K Part 8: 2002Sci...295...82K Part 9: 2004MNRAS.348..187W Part 10: 2004A&A...426...75M Part 11: 2006MNRAS.373..295P Part 12: 2007ApJ...671..767T

Unification of the nearby and photometric stellar luminosity functions

view Abstract Citations (63) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Unification of the nearby and photometric stellar luminosity functions Kroupa, Pavel Abstract We introduce a model Galactic field low-mass stellar population that has a proportion of binary systems as observed, with a mass ratio distribution consistent with observational constraints. The model single-star and system luminosity function agrees with the nearby and the Malmquist-corrected photometric luminosity function, respectively. We tabulate the model luminosity functions in the photometric V, I, and K bands, and in bolometric magnitudes. Unresolved binary systems are thus a natural explanation for the difference between the nearby and photometric luminosity functions. A local overdensity of faint stars need not be postulated to account for the difference and is very unlikely. We stress that the nearby luminosity function can only be used to weakly constrain the stellar mass function below 0.5 Msun because of the small sample size. The photometric luminosity function can only be used to put lower limits on the stellar mass function because most binary systems are not resolved. Taken together, however, the nearby and photometric stellar luminosity function data do not imply a mass function with a peak at a mass of 0.2-0.3 Msun. Instead, the data are consistent with a power-law mass function between 0.08 Msun and 0.5 Msun. We urge researchers to use only star count data that are properly corrected for all contributions to cosmic scatter, photometric uncertainties, and unresolved binaries, and to be aware of the severe limitations of theoretical mass-luminosity relations for low-mass stars, when drawing conclusions about structure in the stellar mass function. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176395 arXiv: arXiv:astro-ph/9506037 Bibcode: 1995ApJ...453..358K Keywords: Astrophysics E-Print: 19 pages, plain TeX, figures available on request, to appear in Nov.1 issue of Part I of ApJ full text sources arXiv | ADS | Related Materials (11) Part 1: 1990MNRAS.244...76K Part 2: 1991MNRAS.251..293K Part 3: 1992AJ....103.1602K Part 4: 1993MNRAS.262..545K Part 5: 1995ApJ...453..350K Part 7: 2001MNRAS.322..231K Part 8: 2002Sci...295...82K Part 9: 2004MNRAS.348..187W Part 10: 2004A&A...426...75M Part 11: 2006MNRAS.373..295P Part 12: 2007ApJ...671..767T