A universal ultraviolet-optical colour-colour-magnitude relation of galaxies

Although the optical colour-magnitude diagram of galaxies allows one to select red sequence objects, neither can it be used for galaxy classification without additional observational data such as spectra or high-resolution images, nor to identify blue galaxies at unknown redshifts. We show that adding the near ultraviolet colour to the optical CMD reveals a tight relation in the three-dimensional colour-colour-magnitude space smoothly continuing from the "blue cloud" to the "red sequence". We found that 98 per cent of 225,000 low-redshift (Z<0.27) galaxies follow a smooth surface g-r=F(M,NUV-r) with a standard deviation of 0.03-0.07 mag making it the tightest known galaxy photometric relation. There is a strong correlation between morphological types and integrated NUV-r colours. Rare galaxy classes such as E+A or tidally stripped systems become outliers that occupy distinct regions in the 3D parameter space. Using stellar population models for galaxies with different SFHs, we show that (a) the (NUV-r, g-r) distribution is formed by objects having constant and exponentially declining SFR with different characteristic timescales; (b) colour evolution for exponentially declining models goes along the relation suggesting its weak evolution up-to a redshift of 0.9; (c) galaxies with truncated SFHs have very short transition phase offset from the relation thus explaining the rareness of E+A galaxies. This relation can be used as a powerful galaxy classification tool when morphology remains unresolved. Its mathematical consequence is the photometric redshift estimates from 3 broad-band photometric points. This approach works better than most existing photometric redshift techniques applied to multi-colour datasets. Therefore, the relation can be used as an efficient selection technique for galaxies at intermediate redshifts (0.3<Z<0.8) using optical imaging surveys.Comment: 15 pages, 10 figures, accepted to MNRAS. This is an updated version that addresses referee's remarks. All relations have been recomputed using Petrosian magnitudes. The best-fitting relations in the electronic form are available at the project web-page: http://specphot.sai.msu.ru/galaxies

ESO Imaging Survey. The Stellar Catalogue in the Chandra Deep Field South

(abridged) Stellar catalogues in five passbands (UBVRI) over an area of approximately 0.3 deg^2, comprising about 1200 objects, and in seven passbands (UBVRIJK) over approximately 0.1 deg^2, comprising about 400 objects, in the direction of the Chandra Deep Field South are presented. The 90% completeness level of the number counts is reached at approximately U = 23.8, B = 24.0, V = 23.5, R = 23.0, I = 21.0, J = 20.5, K = 19.0. A scheme is presented to select point sources from these catalogues, by combining the SExtractor parameter CLASS_STAR from all available passbands. Probable QSOs and unresolved galaxies are identified by using the previously developed \chi^2-technique (Hatziminaoglou et al 2002), that fits the overall spectral energy distributions to template spectra and determines the best fitting template. The observed number counts, colour-magnitude diagrams, colour-colour diagrams and colour distributions are presented and, to judge the quality of the data, compared to simulations based on the predictions of a Galactic Model convolved with the estimated completeness functions and the error model used to describe the photometric errors of the data. The resulting stellar catalogues and the objects identified as likely QSOs and unresolved galaxies with coordinates, observed magnitudes with errors and assigned spectral types by the $\chi^2$-technique are presented and are publicly available.Comment: Paper as it will appear in print. Complete figures and tables can be obtained from: http://www.eso.org/science/eis/eis_pub/eis_pub.html. Astronomy & Astrophysics, accepted for publicatio

CLASH: Photometric redshifts with 16 HST bands in galaxy cluster fields

The Cluster Lensing And Supernovae survey with Hubble (CLASH) is an Hubble Space Telescope (HST) Multi-Cycle Treasury program observing 25 massive galaxy clusters. CLASH observations are carried out in 16 bands from UV to NIR to derive accurate and reliable estimates of photometric redshifts. We present the CLASH photometric redshifts and study the photometric redshift accuracy of the arcs in more detail for the case of MACS1206.2-0847. We use the publicly available Le Phare and BPZ photometric redshift codes on 17 CLASH galaxy clusters. Using Le Phare code for objects with StoN>=10, we reach a precision of 3%(1+z) for the strong lensing arcs, which is reduced to 2.4%(1+z) after removing outliers. For galaxies in the cluster field the corresponding values are 4%(1+z) and 3%(1+z). Using mock galaxy catalogues, we show that 3%(1+z) precision is what one would expect from the CLASH photometry when taking into account extinction from dust, emission lines and the finite range of SEDs included in the photo-z template library. We study photo-z results for different aperture photometry and find that the SExtractor isophotal photometry works best. Le Phare and BPZ give similar photo-z results for the strong lensing arcs as well as galaxies of the cluster field. Results are improved when optimizing the photometric aperture shape showing an optimal aperture size around 1" radius giving results which are equivalent to isophotal photometry. Tailored photometry of the arcs improve the photo-z results.Comment: Accepted in A&A on nov 201

The Physical Properties of Galaxies with Unusually Red Mid-Infrared Colours

The goal of this paper is to investigate the physical nature of galaxies in the redshift range $0.02<z<0.15$ that have strong excess emission at mid-IR wavelengths and to determine whether they host a population of accreting black holes that cannot be identified using optical emission lines. We show that at fixed stellar mass $M_*$ and $D_n(4000)$, the distribution of [3.4]-[4.6] $\mu$m (WISE W1-W2 band) colours is sharply peaked, with a long tail to much redder W1-W2 colours. We introduce a procedure to pull out the red outlier population based on a combination of three stellar population diagnostics. When compared with optically-selected AGN, red outliers are more likely to be found in massive galaxies, and they tend to have lower stellar mass densities, younger stellar ages and higher dust content than optically-selected AGN hosts. They are twice as likely to be detected at radio wavelengths. We examine W1-W2 colour profiles for a subset of the nearest, reddest outliers and find that most are not centrally peaked, indicating that the hot dust emission is spread throughout the galaxy. We find that radio luminosity is the quantity that is most predictive of a redder central W1-W2 colour. Radio-loud galaxies with centrally concentrated hot dust emission are almost always morphologically disturbed, with compact, unresolved emission at 1.4 Ghz. Eighty percent of such systems are identifiable as AGN using optical emission line diagnostics.Comment: 12 pages, 15 figures, accepted in MNRA

Photometric Redshift Estimation Using Spectral Connectivity Analysis

The development of fast and accurate methods of photometric redshift estimation is a vital step towards being able to fully utilize the data of next-generation surveys within precision cosmology. In this paper we apply a specific approach to spectral connectivity analysis (SCA; Lee & Wasserman 2009) called diffusion map. SCA is a class of non-linear techniques for transforming observed data (e.g., photometric colours for each galaxy, where the data lie on a complex subset of p-dimensional space) to a simpler, more natural coordinate system wherein we apply regression to make redshift predictions. As SCA relies upon eigen-decomposition, our training set size is limited to ~ 10,000 galaxies; we use the Nystrom extension to quickly estimate diffusion coordinates for objects not in the training set. We apply our method to 350,738 SDSS main sample galaxies, 29,816 SDSS luminous red galaxies, and 5,223 galaxies from DEEP2 with CFHTLS ugriz photometry. For all three datasets, we achieve prediction accuracies on par with previous analyses, and find that use of the Nystrom extension leads to a negligible loss of prediction accuracy relative to that achieved with the training sets. As in some previous analyses (e.g., Collister & Lahav 2004, Ball et al. 2008), we observe that our predictions are generally too high (low) in the low (high) redshift regimes. We demonstrate that this is a manifestation of attenuation bias, wherein measurement error (i.e., uncertainty in diffusion coordinates due to uncertainty in the measured fluxes/magnitudes) reduces the slope of the best-fit regression line. Mitigation of this bias is necessary if we are to use photometric redshift estimates produced by computationally efficient empirical methods in precision cosmology.Comment: Resubmitted to MNRAS (11 pages, 8 figures

Assessing the accuracy of Hartree-Fock-Bogoliubov calculations by use of mass relations

The accuracy of three different sets of Hartree-Fock-Bogoliubov calculations of nuclear binding energies is systematically evaluated. To emphasize minor fluctuations, a second order, four-point mass relation, which almost completely eliminates smooth aspects of the binding energy, is introduced. Applying this mass relation yields more scattered results for the calculated binding energies. By examining the Gaussian distributions of the non-smooth aspects which remain, structural differences can be detected between measured and calculated binding energies. Substructures in regions of rapidly changing deformation, specifically around $(N,Z)=(60,40)$ and $(90,60)$, are clearly seen for the measured values, but are missing from the calculations. A similar three-point mass relation is used to emphasize odd-even effects. A clear decrease with neutron excess is seen continuing outside the experimentally known region for the calculations.Comment: 13 pages, 9 figures, published versio

Kinematic outliers in the LMC: constraints on star-star microlensing

Although a decade of microlensing searches towards the Large Magellanic Cloud (LMC) has detected 13-25 possible microlensing events, the nature and the location of the lenses, being either halo machos or LMC stars, remains a subject of debate. The star-star lensing models generically predict the existence of a small population (more than about 5 percent of stars with a spatial and kinematic distribution different from the thin, young disc of the LMC. Here we present the results of a large spectroscopic survey of the LMC, consisting of more than 1300 radial velocities measured accurately with the 2dF instrument. In this large sample, no evidence is found for any extraneous population over the expected LMC and Galactic components. Any additional, kinematically distint, population can only be present at less than the 1 percent level. We discuss the significance of this finding for the LMC self-lensing models.Comment: MNRAS accepted, to be published 2003. 6pp w/ 10 eps fig, references updated to match proo

Estimating Photometric Redshifts for X-ray sources in the X-ATLAS field, using machine-learning techniques

We present photometric redshifts for 1,031 X-ray sources in the X-ATLAS field, using the machine learning technique TPZ (Carrasco Kind & Brunner 2013). X-ATLAS covers 7.1 deg2 observed with the XMM-Newton within the Science Demonstration Phase (SDP) of the H-ATLAS field, making it one of the largest contiguous areas of the sky with both XMMNewton and Herschel coverage. All of the sources have available SDSS photometry while 810 have additionally mid-IR and/or near-IR photometry. A spectroscopic sample of 5,157 sources primarily in the XMM/XXL field, but also from several X-ray surveys and the SDSS DR13 redshift catalogue, is used for the training of the algorithm. Our analysis reveals that the algorithm performs best when the sources are split, based on their optical morphology, into point-like and extended sources. Optical photometry alone is not enough for the estimation of accurate photometric redshifts, but the results greatly improve when, at least, mid-IR photometry is added in the training process. In particular, our measurements show that the estimated photometric redshifts for the X-ray sources of the training sample, have a normalized absolute median deviation, n_mad=0.06, and the percentage of outliers, eta=10-14 percent, depending on whether the sources are extended or point-like. Our final catalogue contains photometric redshifts for 933 out of the 1,031 X-ray sources with a median redshift of 0.9.Comment: 10 pages, 13 figures, A&A accepte

Classical T-Tauri stars with VPHAS+: II: NGC 6383 in Sh 2-012

This paper presents optical ($ugri$H$\alpha$)-infrared ($JHK$s,3.6--8.0$\mu$m) photometry, and $Gaia$ astrometry of 55 Classical T-Tauri stars (CTTS) in the star-forming region Sh 2-012, and it's central cluster NGC 6383. The sample was identified based on photometric H$\alpha$ emission line widths, and has a median age of 2.8$\pm$1.6 Myr, with a mass range between 0.3-1 $M_{\odot}$. 94% of CTTS with near-infrared cross-matches fall on the near-infrared T-Tauri locus, with all stars having mid-infrared photometry exhibiting evidence for accreting circumstellar discs. CTTS are found concentrated around the central cluster NGC 6383, and towards the bright rims located at the edges of Sh 2-012. Stars across the region have similar ages, suggestive of a single burst of star formation. Mass accretion rates ($\dot{M}_{\textrm{acc}}$) estimated via H$\alpha$ and $u$-band line intensities show a scatter (0.3 dex) similar to spectroscopic studies, indicating the suitability of H$\alpha$ photometry to estimate $\dot{M}_{\textrm{acc}}$. Examining the variation of $\dot{M}_{\textrm{acc}}$ with stellar mass ($M_{\ast}$), we find a smaller intercept in the $\dot{M}_{\textrm{acc}}$-$M_{\ast}$ relation than oft-quoted in the literature, providing evidence to discriminate between competing theories of protoplanetary disc evolution.Comment: Accepted for publication in MNRAS; 12 pages, 9 figures; Table 1 is published in electronic form only along with the source cod