Showing papers on "Photometry (optics) published in 2008"

The Seventh Data Release of the Sloan Digital Sky Survey

Abstract: This paper describes the Seventh Data Release of the Sloan Digital Sky Survey (SDSS), marking the completion of the original goals of the SDSS and the end of the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most of the roughly 2000 deg^2 increment over the previous data release lying in regions of low Galactic latitude. The catalog contains five-band photometry for 357 million distinct objects. The survey also includes repeat photometry over 250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A coaddition of these data goes roughly two magnitudes fainter than the main survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2 in the Northern Galactic Cap, closing the gap that was present in previous data releases. There are over 1.6 million spectra in total, including 930,000 galaxies, 120,000 quasars, and 460,000 stars. The data release includes improved stellar photometry at low Galactic latitude. The astrometry has all been recalibrated with the second version of the USNO CCD Astrograph Catalog (UCAC-2), reducing the rms statistical errors at the bright end to 45 milli-arcseconds per coordinate. A systematic error in bright galaxy photometr is less severe than previously reported for the majority of galaxies. Finally, we describe a series of improvements to the spectroscopic reductions, including better flat-fielding and improved wavelength calibration at the blue end, better processing of objects with extremely strong narrow emission lines, and an improved determination of stellar metallicities. (Abridged)

GMASS Ultradeep Spectroscopy of Galaxies at 1.4<z<2. II. Superdense passive galaxies: how did they form and evolve ?

Abstract: We combine ultradeep optical spectroscopy from the GMASS project ("Galaxy Mass Assembly ultradeep Spectroscopic Survey") with GOODS multi-band photometry and HST imaging to study a sample of passive galaxiesat 1.39 2. These galaxies have morphologies that are predominantly compact and spheroidal.However, their sizes (R_e 1, and absent if R_e 2. The results are compared with theoretical models and the main implications discussed in the framework of massive galaxy formation and evolution.

Two bright submillimeter galaxies in a z=4.05 proto-cluster in GOODS-North, and accurate radio-infrared photometric redshifts

Abstract: We present the serendipitous discovery of z=4.05 molecular gas CO emission lines with the IRAM Plateau de Bure interferometer coincident with GN20 and GN20.2, two luminous submillimeter galaxies (SMGs) in the Great Observatories Origins Deep Survey North field (GOODS-N). These are among the most distant submillimeter-selected galaxies reliably identified through CO emission and also some of the most luminous known. In terms of CO to bolometric luminosities, stellar mass and star formation rates (SFRs), these newly discovered z>4 SMGs are similar to z~1.5-3 SMGs studied to date. These z~4 SMGs have much higher specific SFRs than typical B-band dropout Lyman break galaxies at the same redshift. The stellar mass-SFR correlation for normal galaxies does not seem to evolve much further, between z~2 and z~4. A significant z=4.05 spectroscopic redshift spike is observed in GOODS-N, and a strong spatial overdensity of B-band dropouts and IRAC selected z>3.5 galaxies appears to be centered on the GN20 and GN20.2 galaxies. This suggests a proto-cluster structure with total mass ~10^14 Msun. Using photometry at mid-IR, submm and radio wavelengths, we show that reliable photometric redshifts (Dz/(1+z)~0.1) can be derived for SMGs over 1 3.5 starbursts, regardless of their submm/mm emission [abridged].

A Steep Faint-End Slope of the UV Luminosity Function at z~2-3: Implications for the Global Stellar Mass Density and Star Formation in Low Mass Halos

Abstract: We use the deep ground-based optical photometry of the Lyman Break Galaxy (LBG) Survey to derive robust measurements of the faint-end slope (alpha) of the UV LF at redshifts 1.9 2000 spectroscopic redshifts and ~31000 LBGs in 31 spatially-independent fields over a total area of 3261 arcmin^2. These data allow us to select galaxies to 0.07L* and 0.10L* at z~2 and z~3, respectively. A maximum likelihood analysis indicates steep values of alpha(z=2)=-1.73+/-0.07 and alpha(z=3)=-1.73+/-0.13. This result is robust to luminosity dependent systematics in the Ly-alpha equivalent width and reddening distributions, is similar to the steep values advocated at z>4, and implies that ~93% of the unobscured UV luminosity density at z~2-3 arises from sub-L* galaxies. With a realistic luminosity dependent reddening distribution, faint to moderately luminous galaxies account for >70% and >25% of the bolometric luminosity density and present-day stellar mass density, respectively, when integrated over 1.9 2 contrasts with the shallower value inferred locally, suggesting that the evolution in the faint-end slope may be dictated simply by the availability of low mass halos capable of supporting star formation at z<2. [Abridged]

Photometric redshift and classification for the XMM-COSMOS sources

Abstract: We present photometric redshifts and spectral energy distribution (SED) classifications for a sample of 1542 optically identified sources detected with XMM in the COSMOS field. Our template fitting classifies 46 sources as stars and 464 as non-active galaxies, while the remaining 1032 require templates with an AGN contribution. High accuracy in the derived photometric redshifts was accomplished as the result of 1) photometry in up to 30 bands with high significance detections, 2) a new set of SED templates including 18 hybrids covering the far-UV to mid-infrared, which have been constructed by the combination of AGN and non-active galaxies templates, and 3) multi-epoch observations that have been used to correct for variability (most important for type 1 AGN). The reliability of the photometric redshifts is evaluated using the sub-sample of 442 sources with measured spectroscopic redshifts. We achieved an accuracy of $\sigma_{\Delta z/(1+z_{spec})} = 0.014$ for i$_{AB}^*<$22.5 ($\sigma_{\Delta z/(1+z_{spec})} \sim0.015$ for i$_{AB}^*<$24.5). The high accuracies were accomplished for both type 2 (where the SED is often dominated by the host galaxy) and type 1 AGN and QSOs out to $z=4.5$. The number of outliers is a large improvement over previous photometric redshift estimates for X-ray selected sources (4.0% and 4.8% outliers for i$_{AB}^*<$22.5 and i$_{AB}^*<$24.5, respectively). We show that the intermediate band photometry is vital to achieving accurate photometric redshifts for AGN, whereas the broad SED coverage provided by mid infrared (Spitzer/IRAC) bands is important to reduce the number of outliers for normal galaxies.

The Sloan Digital Sky Survey-II Photometry and Supernova IA Light Curves from the 2005 Data

Abstract: We present ugriz light curves for 146 spectroscopically-confirmed or spectroscopically-probable Type Ia supernovae (SNe) from the 2005 season of the Sloan Digital Sky Survey-II Supernova (SN) survey. The light curves have been constructed using a photometric technique that we call scene modeling, which is described in detail here; the major feature is that SN brightnesses are extracted from a stack of images without spatial resampling or convolution of the image data. This procedure produces accurate photometry along with accurate estimates of the statistical uncertainty, and can be used to derive photometry taken with multiple telescopes. We discuss various tests of this technique that demonstrate its capabilities. We also describe the methodology used for the calibration of the photometry, and present calibrated magnitudes and fluxes for all of the spectroscopic SNe Ia from the 2005 season.

SiFTO: An Empirical Method for Fitting SNe Ia Light Curves

Abstract: We present SiFTO, a new empirical method for modeling type Ia supernovae (SNe Ia) light curves by manipulating a spectral template. We make use of high-redshift SN observations when training the model, allowing us to extend it bluer than rest frame U. This increases the utility of our high-redshift SN observations by allowing us to use more of the available data. We find that when the shape of the light curve is described using a stretch prescription, applying the same stretch at all wavelengths is not an adequate description. SiFTO therefore uses a generalization of stretch which applies different stretch factors as a function of both the wavelength of the observed filter and the stretch in the rest-frame B band. We compare SiFTO to other published light-curve models by applying them to the same set of SN photometry, and demonstrate that SiFTO and SALT2 perform better than the alternatives when judged by the scatter around the best fit luminosity distance relationship. We further demonstrate that when SiFTO and SALT2 are trained on the same data set the cosmological results agree.

Galactic Globular and Open Clusters in the Sloan Digital Sky Survey. I. Crowded Field Photometry and Cluster Fiducial Sequences in ugriz

Abstract: We present photometry for globular and open cluster stars observed with the Sloan Digital Sky Survey (SDSS). In order to exploit the over 100 million stellar objects with -->r < 22.5 mag observed by SDSS, we need to understand the characteristics of stars in the SDSS ugriz filters. While star clusters provide important calibration samples for stellar colors, the regions close to globular clusters, where the fraction of field stars is smallest, are too crowded for the standard SDSS photometric pipeline to process. To complement the SDSS imaging survey, we reduce the SDSS imaging data for crowded cluster fields using the DAOPHOT/ALLFRAME suite of programs and present photometry for 17 globular clusters and three open clusters in a SDSS value-added catalog. Our photometry and cluster fiducial sequences are on the native SDSS 2.5 m ugriz photometric system, and the fiducial sequences can be directly applied to the SDSS photometry without relying on any transformations. Model photometry for red giant branch and main-sequence stars obtained by Girardi et al. cannot be matched simultaneously to fiducial sequences; their colors differ by ~0.02-0.05 mag. Good agreement (0.02 mag in colors) is found with Clem et al. empirical fiducial sequences in u'g'r'i'z' when using the transformation equations in Tucker et al.

Galactic Globular and Open Clusters in the Sloan Digital Sky Survey. I. Crowded Field Photometry and Cluster Fiducial Sequences in ugriz

Abstract: We present photometry for globular and open cluster stars observed with the Sloan Digital Sky Survey (SDSS). In order to exploit over 100 million stellar objects with r < 22.5 mag observed by SDSS, we need to understand the characteristics of stars in the SDSS ugriz filters. While star clusters provide important calibration samples for stellar colors, the regions close to globular clusters, where the fraction of field stars is smallest, are too crowded for the standard SDSS photometric pipeline to process. To complement the SDSS imaging survey, we reduce the SDSS imaging data for crowded cluster fields using the DAOPHOT/ALLFRAME suite of programs and present photometry for 17 globular clusters and 3 open clusters in a SDSS value-added catalog. Our photometry and cluster fiducial sequences are on the native SDSS 2.5-meter ugriz photometric system, and the fiducial sequences can be directly applied to the SDSS photometry without relying upon any transformations. Model photometry for red giant branch and main-sequence stars obtained by Girardi et al. cannot be matched simultaneously to fiducial sequences; their colors differ by ~0.02-0.05 mag. Good agreement (< ~0.02 mag in colors) is found with Clem et al. empirical fiducial sequences in u'g'r'i'z' when using the transformation equations in Tucker et al.

Clustered and Triggered Star Formation in W5: Observations with Spitzer

Abstract: We present images and initial results from our extensive Spitzer Space Telescope imaging survey of the W5 H II region with the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS). We detect dense clusters of stars, centered on the O stars HD 18326, BD +60 586, HD 17505, and HD 17520. At 24 μm, substantial extended emission is visible, presumably from heated dust grains that survive in the strongly ionizing environment of the H II region. With photometry of more than 18,000 point sources, we analyze the clustering properties of objects classified as young stars by their IR spectral energy distributions (a total of 2064 sources) across the region using a minimal-spanning-tree algorithm. We find ~40%-70% of infrared excess sources belong to clusters with ≥10 members. We find that within the evacuated cavities of the H II regions that make up W5, the ratio of Class II to Class I sources is ~7 times higher than for objects coincident with molecular gas as traced by -->12CO emission and near-IR extinction maps. We attribute this contrast to an age difference between the two locations and postulate that at least two distinct generations of star formation are visible across W5. Our preliminary analysis shows that triggering is a plausible mechanism to explain the multiple generations of star formation in W5 and merits further investigation.

A Golden Standard Type Ia Supernova SN 2005cf: Observations from the Ultraviolet to the Near-Infrared Wavebands

Abstract: We present extensive photometry at ultraviolet (UV), optical, and near-infrared (NIR) wavelengths, as well as dense sampling of optical spectra, for the normal type Ia supernova (SN Ia) 2005cf. From the well-sampled light curves, we find that SN 2005cf reached a B-band maximum at 13.63+/-0.02 mag, with an observed luminosity decline rate dm_15(B) = 1.05+/-0.03 mag. The correlations between the decline rate and various color indexes, recalibrated on the basis of an expanded SN Ia sample, yielded E(B-V)_host=0.09+/-0.03 mag for SN2005cf. The UV photometry was obtained with the HST and the Swift Ultraviolet/Optical Telescope, and the results match each other to within 0.1-0.2 mag. The UV light curves show similar evolution to the broadband U, with an exception in the 2000-2500 Angstrom spectral range (corresponding to the F220W/uvm2 filters), where the light curve appears broader and much fainter than that on either side (likely owing to the intrinsic spectral evolution). Combining the UV data with the ground-based optical and NIR data, we establish the generic UV-optical-NIR bolometric light curve for SN 2005cf and derive the bolometric corrections in the absence of UV and/or NIR data. The overall spectral evolution of SN 2005cf is similar to that of a normal SN Ia, but with variety in the strength and profile of the main feature lines. The spectra at early times displayed strong, detached high-velocity (HV) features in the Ca II H&K doublet and NIR triplet. Similar HV features may exist in the SiII 6355 absorption line which evolved rapidly from a flat-bottomed feature in the earliest phase to a triangular shape one week before maximum, and may be common in other normal SNe Ia. The possible origin of the HV absorption features is briefly discussed (abridged).

Measuring the Fraction of Obscured Quasars by the Infrared Luminosity of Unobscured Quasars

Abstract: Recent work has suggested that the fraction of obscured AGNs declines with increasing luminosity, but it has been difficult to quantify this trend. Here we attempt to measure this fraction as a function of luminosity by studying the ratio of mid-infrared to intrinsic nuclear bolometric luminosity in unobscured AGNs. Because the mid-infrared is created by dust reprocessing of shorter wavelength nuclear light, this ratio is a diagnostic of -->fobsc, the fraction of solid angle around the nucleus covered by obscuring matter. In order to eliminate possible redshift dependences while also achieving a large dynamic range in luminosity, we have collected archival 24 μm MIPS photometry from objects with -->z ~ 1 in the Sloan Digital Sky Survey, the Great Observatories Origins Deep Survey, and the Cosmic Evolution Survey. To measure the bolometric luminosity for each object, we used archival optical data supplemented by GALEX data. We find that the mean ratio of 24 μm to bolometric luminosity decreases by a factor of ~3 in the -->Lbol = 1044–3 × 1047 ergs s -->−1 range, but there is also a large scatter at constant -->Lbol. Using radiation transfer solutions for model geometries, we show how the IR/bolometric ratio relates to -->fobsc and compare these values with those obtained from samples of X-ray-selected AGNs. Although we find approximate agreement, our method indicates somewhat higher values of -->fobsc, particularly in the middle range of luminosities, suggesting that there may be a significant number of heavily obscured AGNs missed by X-ray surveys.

Balancing the Energy Budget between Star-Formation and AGN in High Redshift Infrared Luminous Galaxies

Abstract: (abridged) We present deep Spitzer mid-infrared spectroscopy, along with 16, 24, 70, and 850um photometry, for 22 galaxies located in GOODS-N. The sample spans a redshift range of 0.6 25) sources. We find that IR luminosities derived by fitting local SEDs with 24um photometry alone are well matched to those when additional mid-infrared spectroscopic and longer wavelength photometric data is used for galaxies having z 3x10^12 L_sun. However, for galaxies in the redshift range between 1.4 3x10^12 L_sun, IR luminosities are overestimated by an average factor of ~5 when SED fitting with 24um photometry alone. This result arises partly due to the fact that high redshift galaxies exhibit PAH EQWs that are large compared to local galaxies of similar luminosities. Using improved estimates for the IR luminosities of these sources, we investigate whether their IR emission is found to be in excess relative to that expected based on extinction corrected UV SFRs, possibly suggesting the presence of an obscured AGN. Through a spectral decomposition of IRS spectroscopic data, we are able to isolate the fraction of IR luminosity arising from an AGN as opposed to star formation activity. This fraction is only ~30% of the total IR luminosity among the entire sample, on average. Of the sources identified as having mid-infrared excesses, half are accounted for by using proper bolometric corrections while half show the presence of obscured AGN. We do not find evidence for evolution in the FIR-radio correlation over this redshift range, although the SMGs have IR/radio ratios which are, on average, ~3 times lower than the nominal value.

Absolute physical calibration in the infrared

Abstract: We determine an absolute calibration for the Multiband Imaging Photometer for Spitzer 24 μm band and recommend adjustments to the published calibrations for Two Micron All Sky Survey (2MASS), Infrared Array Camera (IRAC), and IRAS photometry to put them on the same scale. We show that consistent results are obtained by basing the calibration on either an average A0V star spectral energy distribution (SED), or by using the absolutely calibrated SED of the Sun in comparison with solar-type stellar photometry (the solar analog method). After the rejection of a small number of stars with anomalous SEDs (or bad measurements), upper limits of ~1.5% root mean square (rms) are placed on the intrinsic infrared (IR) SED variations in both A-dwarf and solar-type stars. These types of stars are therefore suitable as general-purpose standard stars in the IR. We provide absolutely calibrated SEDs for a standard zero magnitude A star and for the Sun to allow extending this work to any other IR photometric system. They allow the recommended calibration to be applied from 1 to 25 μm with an accuracy of ~2%, and with even higher accuracy at specific wavelengths such as 2.2, 10.6, and 24 μm, near which there are direct measurements. However, we confirm earlier indications that Vega does not behave as a typical A0V star between the visible and the IR, making it problematic as the defining star for photometric systems. The integration of measurements of the Sun with those of solar-type stars also provides an accurate estimate of the solar SED from 1 through 30 μm, which we show agrees with theoretical models.

Exploring the substellar temperature regime down to ∼550 K

Abstract: We report the discovery of three very late T dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS) Third Data Release: ULAS J101721.40+011817.9 (ULAS1017), ULAS J123828.51+095351.3 (ULAS1238) and ULAS J133553.45+113005.2 (ULAS1335). We detail optical and near-infrared photometry for all three sources, and mid-infrared photometry for ULAS1335. We use near-infrared spectra of each source to assign spectral types T8p (ULAS1017), T8.5 (ULAS1238) and T9 (ULAS1335) to these objects. ULAS1017 is classed as a peculiar T8 (T8p) due to appearing as a T8 dwarf in the J-band, whilst exhibiting H and K-band flux ratios consistent with a T6 classification. Through comparison to BT-Settl model spectra we estimate that ULAS1017 has 750K T8 dwarfs to the rest of the T dwarf sequence, the suggestion of the Y0 spectral class for these objects is premature. Comparison of model spectra with that of ULAS1335 suggest a temperature below 600K, possibly combined with low-gravity and/or high-metallicity. We find ULAS1335 to be extremely red in near to mid-infrared colours, with H [4.49] = 4.34 ± 0.04 . This is the reddest near to mid-infrared colour yet observed for a T dwarf. The near to mid-infrared spectral energy distribution of ULAS1335 further supports Teff < 600K, and we estimate Teff � 550 600K for ULAS1335. We estimate that ULAS1335 has an age of 0.6–5.3 Gyr, a mass of 15–31 MJ and lies at a distance of 8–12 pc.

Ground-based CCD astrometry with wide-field imagers

Abstract: Context. The solar-age open cluster M 67 (C0847+120, NGC 2682) is a touchstone in studies of the old Galactic disk. Despite its outstanding role, the census of cluster membership for M 67 at fainter magnitudes and their properties are not well-established. Aims. Using proprietary and archival ESO data, we have obtained astrometric, photometric, and radial velocities of stars in a 34 × 33 arcmin 2 field centered on the old open cluster M 67. Methods. The two-epoch archival observations separated by 4 years and acquired with the Wide-Field Imager at the 2.2 m MPG/ESO telescope were reduced with our new astrometric techniques, as described in the first paper in this series. The same observations served to derive calibrated BVI photometry in M 67. Radial velocities were measured using the archival and new spectroscopic data obtained at the VLT. Results. We have determined relative proper motions and membership probabilities for ∼2400 stars. The precision of proper motions for optimally exposed stars is 1.9 mas yr −1 , gradually degrading down to ∼ 5m as yr −1 at V = 20. Our relatively precise proper motions at V > 16 were first obtained in this magnitude range for M 67. Radial velocities were measured for 211 stars in the same field. We also present a detailed comparison with recent theoretical isochrones from several independent groups. Conclusions. For the M 67 area, we provide positions, calibrated BVI photometry, relative proper motions, membership probabilities, and radial velocities. We demonstrate that ground-based CCD mosaic observations just a few years apart are producing proper motions, allowing reliable membership determination. We have produced a catalog that is electronically available to the astronomical community.

Discovery of a T Dwarf Binary with the Largest Known J-Band Flux Reversal

Abstract: We present Keck laser guide star observations of two T2.5 dwarfs - 2MASS J11061197+2754225 & 2MASS J14044941-3159329 - using NIRC2 on Keck-II and find 2MASS J14044941-3159329 to be a 0.13" binary. This system has a secondary that is 0.45 mags brighter than the primary in J-band but 0.49 mags fainter in H-band and 1.13 mags fainter in Ks-band. We use this relative photometry along with near-infrared synthetic modeling performed on the integrated light spectrum to derive component types of T1 for the primary and T5 for the secondary. Optical spectroscopy of this system obtained with Magellan/LDSS-3 is also presented. This is the fourth L/T transition binary to show a flux reversal in the 1-1.2 micron regime and this one has the largest flux reversal. Unless the secondary is itself an unresolved binary, the J-band magnitude difference between the secondary and primary shows that the J-band "bump" is indeed a real feature and not an artifact caused by unresolved binarity.

The Invisibles: A Detection Algorithm to Trace the Faintest Milky Way Satellites

Abstract: [Abridged] A specialized data mining algorithm has been developed using wide-field photometry catalogues, enabling systematic and efficient searches for resolved, extremely low surface brightness satellite galaxies in the halo of the Milky Way (MW). Tested and calibrated with the Sloan Digital Sky Survey Data Release 6 (SDSS-DR6) we recover all fifteen MW satellites recently detected in SDSS, six known MW/Local Group dSphs in the SDSS footprint, and 19 previously known globular and open clusters. In addition, 30 point source overdensities have been found that correspond to no cataloged objects. The detection efficiencies of the algorithm have been carefully quantified by simulating more than three million model satellites embedded in star fields typical of those observed in SDSS, covering a wide range of parameters including galaxy distance, scale-length, luminosity, and Galactic latitude.

MOST detects variability on τ Bootis A possibly induced by its planetary companion

Abstract: Context. There is considerable interest in the possible interaction between parent stars and giant planetary companions in 51 Peg-type systems. Aims. We shall demonstrate from MOST satellite photometry and Call K line emission that there has been a persistent, variable region on the surface of r Boo A, which tracked its giant planetary companion for some 440 planetary revolutions and lies ∼68° (Φ = 0.8) in advance of the sub-planetary point. Methods. The light curves are folded on a range of periods centered on the planetary orbital period, and phase-dependent variability is quantified by Fourier methods and by the mean absolute deviation (MAD) of the folded data for both the photometry and the Call K line reversals. Results. The region varies in brightness on the time scale of a rotation by ∼1 mmag. In 2004 it resembled a dark spot of variable depth, while in 2005 it varied between bright and dark. The 2004 light curve gives a spot rotation period of 3.5 ± 0.7 d compared to the known planetary orbital period of 3.3125 d. The amplitude spectrum of the 2005 light curve shows no marked peak at the orbital period but the mean absolute deviation (MAD) of the light curve has a well-defined maximum (half width ∼0.15 d) centered on the orbital frequency. Over the 123 planetary orbits spanned by the photometry, the variable region detected in 2004 and in 2005 are synchronized to the planetary orbital period within 0.0015 d. The Call K line in 2001, 2002, and 2003 also shows enhanced K-line variability centered on Φ = 0.8, extending coverage to some 440 planetary revolutions. Conclusions. The apparently constant rotation period of the variable region and its rapid variation make an explanation in terms of conventional star spots unlikely. The lack of complementary variability at Φ = 0.3 and the detection of the variable region so far in advance of the sub-planetary point excludes tidal excitation, but the combined photometric and Call K line reversal results make a good case for an active region induced magnetically on the surface of T Boo A by its planetary companion.

The SCUBA HAlf Degree Extragalactic Survey (SHADES) - VII. Optical/IR photometry and stellar masses of sub-millimeter galaxies

Abstract: We present estimates of the photometric redshifts, stellar masses and star formation histories of sources in the SCUBA HAlf Degree Extragalactic Survey (SHADES). This paper describes the 60 SCUBA sources detected in the Lockman Hole covering an area of ~320 square arcmin. Using photometry spanning the B band to 8um, we find that the average SCUBA source forms a significant fraction of its stars in an early period of star formation and that most of the remainder forms in a shorter more intense burst around the redshift it is observed. This trend does not vary significantly with source redshift but the exact ratio of early to late mass is quite sensitive to the way extinction is treated in the modelling. However, the sources show a clear increase in stellar mass with redshift, consistent with downsizing. In terms of SED types, only two out of the 51 sources we have obtained photometric redshifts for are best fit by a quasar-like spectral energy distribution, with approximately 80 per cent of the sources being best fit with late-type spectra (Sc, Im and starburst). By including photometry at 850um, we conclude that the average SCUBA source is forming stars at a rate somewhere between 6 and 30 times the rate implied from the rest-frame optical in a dust obscured burst and that this burst creates 15-65 per cent of the total stellar mass. Using a simplistic calculation, we estimate from the average star formation history that between one in five and one in 15 bright (L_* +2 mag < L_optical < L_* -1 mag) galaxies in the field over the interval 0 < z < 3 will at some point in their lifetime experience a similar energetic dusty burst of star formation. Finally, we compute the evolution of the star formation rate density and find it peaks around z=2.

MOST detects variability on tau Bootis possibly induced by its planetary companion

Abstract: (abridged) There is considerable interest in the possible interaction between parent stars and giant planetary companions in 51 Peg-type systems. We demonstrate from MOST satellite photometry and Ca II K line emission that there has been a persistent, variable region on the surface of tau Boo A which tracked its giant planetary companion for some 440 planetary revolutions and lies ~68deg (phi=0.8) in advance of the sub-planetary point. The light curves are folded on a range of periods centered on the planetary orbital period and phase dependent variability is quantified by Fourier methods and by the mean absolute deviation (MAD) of the folded data for both the photometry and the Ca II K line reversals. The region varies in brightness on the time scale of a rotation by ~1 mmag. In 2004 it resembled a dark spot of variable depth, while in 2005 it varied between bright and dark. Over the 123 planetary orbits spanned by the photometry the variable region detected in 2004 and in 2005 are synchronised to the planetary orbital period within 0.0015 d. The Ca II K line in 2001, 2002 and 2003 also shows enhanced K-line variability centered on phi=0.8, extending coverage to some 440 planetary revolutions. The apparently constant rotation period of the variable region and its rapid variation make an explanation in terms of conventional star spots unlikely. The lack of complementary variability at phi=0.3 and the detection of the variable region so far in advance of the sub-planetary point excludes tidal excitation, but the combined photometric and Ca II K line reversal results make a good case for an active region induced magnetically on the surface of tau Boo A by its planetary companion.

Spitzer Observations of the z = 2.73 Lensed Lyman Break Galaxy: MS 1512?cB58

Abstract: We present Spitzer infrared (IR) photometry and spectroscopy of the lensed Lyman break galaxy (LBG) MS 1512–cB58 at z = 2.73. The large (factor ~30) magnification allows for the most detailed IR study of an L☉_(UV)(z = 3) LBG to date. Broadband photometry with IRAC (3-10 μm), IRS (16 μm), and MIPS (24, 70, and 160 μm) was obtained, as well as IRS spectroscopy spanning 5.5-35 μm. A fit of stellar population models to the optical/near-IR/IRAC photometry gives a young age (~9 Myr), forming stars at ~98 M⊙ yr^(-1), with a total stellar mass of ~10^9 M☉ formed thus far. The existence of an old stellar population with twice the stellar mass cannot be ruled out. IR spectral energy distribution fits to the 24 and 70 μm photometry, as well as previously obtained submillimeter/millimeter data give an intrinsic IR luminosity L_(IR) = (1–2) × 10^(11) L☉ and a star formation rate (SFR) ~20-40 M☉yr^(−1). The ultraviolet (UV) derived SFR is ~3-5 times higher than the SFR determined using L_(IR) or L_(Hα) because the red UV spectral slope is significantly overpredicting the level of dust extinction. This may suggest that the assumed Calzetti starburst obscuration law is not valid in young LBGs. We detect strong line emission from polycyclic aromatic hyrdrocarbons (PAHs) at 6.2, 7.7, and 8.6 μm. The line ratios are consistent with ratios observed in both local and high-redshift starbursts. Both the PAH and rest-frame 8 μm luminosities predict the total LIR based on previously measured relations in starbursts. Finally, we do not detect the 3.3 μm PAH feature. This is marginally inconsistent with some PAH emission models, but still consistent with PAH ratios measured in many local star-forming galaxies.

Biases and Uncertainties in Physical Parameter Estimates of Lyman Break Galaxies from Broad-band Photometry

Abstract: We investigate the biases and uncertainties in estimates of physical parameters of high-redshift Lyman break galaxies (LBGs), such as stellar mass, mean stellar population age, and star formation rate (SFR), obtained from broad-band photometry. By combining LCDM hierarchical structure formation theory, semi-analytic treatments of baryonic physics, and stellar population synthesis models, we construct model galaxy catalogs from which we select LBGs at redshifts z ~ 3.4, 4.0, and 5.0. The broad-band spectral energy distributions (SEDs) of these model LBGs are then analysed by fitting galaxy template SEDs derived from stellar population synthesis models with smoothly declining SFRs. We compare the statistical properties of LBGs' physical parameters -- such as stellar mass, SFR, and stellar population age -- as derived from the best-fit galaxy templates with the intrinsic values from the semi-analytic model. We find some trends in these distributions: first, when the redshift is known, SED-fitting methods reproduce the input distributions of LBGs' stellar masses relatively well, with a minor tendency to underestimate the masses overall, but with substantial scatter. Second, there are large systematic biases in the distributions of best-fit SFRs and mean ages, in the sense that single-component SED-fitting methods underestimate SFRs and overestimate ages. We attribute these trends to the different star formation histories predicted by the semi-analytic models and assumed in the galaxy templates used in SED-fitting procedure, and to the fact that light from the current generation of star-formation can hide older generations of stars. These biases, which arise from the SED-fitting procedure, can significantly affect inferences about galaxy evolution from broadband photometry.

The SCUBA HAlf Degree Extragalactic Survey (SHADES) – VII. Optical/IR photometry and stellar masses of submillimetre galaxies

Abstract: We present estimates of the photometric redshifts, stellar masses and star formation histories of sources in the Submillimetre Common-User Bolometer Array (SCUBA) HAlf Degree Extragalactic Survey (SHADES). This paper describes the 60 SCUBA sources detected in the Lockman Hole covering an area of ∼320 arcmin 2 . Using photometry spanning the B band to 8 μm, we find that the average SCUBA source forms a significant fraction of its stars in an early period of star formation and that most of the remainder forms in a shorter more intense burst around the redshift it is observed. This trend does not vary significantly with source redshift. However, the sources show a clear increase in stellar mass with redshift, consistent with downsizing. In terms of spectral energy distribution types, only two out of the 51 sources we have obtained photometric redshifts for are best fitted by a quasar-like spectrum, with approximately 80 per cent of the sources being best fitted with late-type spectra (Sc, Im and starburst). By including photometry at 850 μm, we conclude that the average SCUBA source is forming stars at a rate somewhere between 6 and 30 times the rate implied from the rest-frame optical in a dust obscured burst and that this burst creates 15‐65 per cent of the total stellar mass. Using a simplistic calculation, we estimate from the average star formation history that between one in five and one in 15 bright (L∗ + 2 < Loptical < L∗ − 1 mag) galaxies in the field over the interval 0 < z < 3 will at some point in their lifetime

Photometric redshifts for weak lensing tomography from space: the role of optical and near infrared photometry

Abstract: We study in detail the photometric redshift requirements needed for tomographic weak gravitational lensing in order to measure accurately the dark energy equation of state. In particular, we examine how ground-based photometry (u, g, r, i, z, y) can be complemented by space-based near-infrared (near-IR) photometry (J, H), e.g. onboard the planned DUNE satellite. Using realistic photometric redshift simulations and an artificial neural network photo-z method we evaluate the figure of merit for the dark energy parameters (w0, wa). We consider a DUNE-like broad optical filter supplemented with ground-based multiband optical data from surveys like the Dark Energy Survey, Pan-STARRS and LSST. We show that the dark energy figure of merit would be improved by a factor of 1.3‐1.7 if IR filters are added onboard DUNE. Furthermore we show that with IR data catastrophic photo-z outliers can be removed effectively. There is an interplay between the choice of filters, the magnitude limits and the removal of outliers. We draw attention to the dependence of the results on the galaxy formation scenarios encoded into the mock galaxies, e.g. the galaxy reddening. For example, very deep u-band data could be as effective as the IR. We also find that about 10 5 ‐10 6 spectroscopic redshifts are needed for calibration of the full survey.

Complex organic materials in the circumstellar disk of hr 4796a

Abstract: We combine HST NICMOS imaging photometry of the HR 4796A disk at previously unobserved wavelengths between 1.71-2.22 μm with reprocessed archival observations to produce a measure of the dust's scattering efficiency as a function of wavelength. The spectrum of the dust, synthesized from the seven photometric measures, is characterized by a steep red slope increasing from 0.5 to 1.6 μm followed by a flattening of the spectrum at wavelengths >1.6 μm. We fit the spectrum with a model population of dust grains made of tholins, materials composed of complex organic materials seen throughout the outer parts of our solar system. The presence of organic material around a star that may be in the later stages of giant planet formation implies that the basic building blocks for life may be common in planetary systems.

Robust Machine Learning Applied to Astronomical Datasets III: Probabilistic Photometric Redshifts for Galaxies and Quasars in the SDSS and GALEX

Abstract: We apply machine learning in the form of a nearest neighbor instance-based algorithm (NN) to generate full photometric redshift probability density functions (PDFs) for objects in the Fifth Data Release of the Sloan Digital Sky Survey (SDSS DR5). We use a conceptually simple but novel application of NN to generate the PDFs - perturbing the object colors by their measurement error - and using the resulting instances of nearest neighbor distributions to generate numerous individual redshifts. When the redshifts are compared to existing SDSS spectroscopic data, we find that the mean value of each PDF has a dispersion between the photometric and spectroscopic redshift consistent with other machine learning techniques, being sigma = 0.0207 +/- 0.0001 for main sample galaxies to r < 17.77 mag, sigma = 0.0243 +/- 0.0002 for luminous red galaxies to r < ~19.2 mag, and sigma = 0.343 +/- 0.005 for quasars to i < 20.3 mag. The PDFs allow the selection of subsets with improved statistics. For quasars, the improvement is dramatic: for those with a single peak in their probability distribution, the dispersion is reduced from 0.343 to sigma = 0.117 +/- 0.010, and the photometric redshift is within 0.3 of the spectroscopic redshift for 99.3 +/- 0.1% of the objects. Thus, for this optical quasar sample, we can virtually eliminate 'catastrophic' photometric redshift estimates. In addition to the SDSS sample, we incorporate ultraviolet photometry from the Third Data Release of the Galaxy Evolution Explorer All-Sky Imaging Survey (GALEX AIS GR3) to create PDFs for objects seen in both surveys. For quasars, the increased coverage of the observed frame UV of the SED results in significant improvement over the full SDSS sample, with sigma = 0.234 +/- 0.010. We demonstrate that this improvement is genuine. [Abridged]

The impact of Spitzer infrared data on stellar mass estimates – and a revised galaxy stellar mass function at 0 < z < 5

Abstract: Aims. We estimate stellar masses of galaxies in the high redshift universe with the intention of determining the influence of newly available Spitzer/IRAC infrared data on the analysis. Based on the results, we probe the mass assembly history of the universe. Methods. We use the GOODS-MUSIC catalog, which provides multiband photometry from the U-filter to the 8 µm Spitzer band for almost 15 000 galaxies with either spectroscopic (for ≈7% of the sample) or photometric redshifts, and apply a standard model fitting technique to estimate stellar masses. We than repeat our calculations with fixed photometric redshifts excluding Spitzer photometry and directly compare the outcomes to look for systematic deviations. Finally we use our results to compute stellar mass functions and mass densities up to redshift z = 5. Results. We find that stellar masses tend to be overestimated on average if further constraining Spitzer data are not included into the analysis. Whilst this trend is small up to intermediate redshifts z < 2.5 and falls within the typical error in mass, the deviation increases strongly for higher redshifts and reaches a maximum of a factor of three at redshift z ≈ 3.5. Thus, up to intermediate redshifts, results for stellar mass density are in good agreement with values taken from literature calculated without additional Spitzer photometry. At higher redshifts, however, we find a systematic trend towards lower mass densities if Spitzer/IRAC data are included.

Properties of dusty tori in active galactic nuclei – I. The case of SWIRE/SDSS quasars

Abstract: We derive the properties of dusty tori in active galactic nuclei from the comparison of observed spectral energy distributions (SEDs) of SDSS quasars and a precomputed grid of torus models. The observed SEDs comprise SDSS photometry, Two-Micron All-Sky Survey J, H and K data, whenever available, and mid-infrared (mid-IR) data from the Spitzer Wide-area InfraRed Extragalactic Survey. The adopted model is that of Fritz, Franceschini & Hatziminaoglou. The fit is performed by standard chi(2)-minimization; the model, however, can be a multicomponent comprising a stellar and a starburst component, whenever necessary. Models with low equatorial optical depth, tau(9.7), were allowed as well as 'traditional' models with tau(9.7) >= 1.0, corresponding to A(V) >= 22 and the results were compared. Fits using high optical depth tori models only produced dust more compactly distributed than in the configuration where all tau(9.7) models were permitted. Tori with decreasing dust density with the distance from the centre were favoured while there was no clear preference for models with or without angular variation of the dust density. The computed outer radii of the tori are of some tens of parsecs large but can reach, in a few cases, a few hundreds of parsecs. The mass of dust, M-Dust, and IR luminosity, L-IR, integrated in the wavelength range between 1 and 1000 mu m, do not show significant variations with redshift, once the observational biases are taken into account. Objects with 70-mu m detections, representing 25 per cent of the sample, are studied separately and the starburst contribution (whenever present) to the IR luminosity can reach, in the most extreme but very few cases, 80 per cent.

High-Precision Photometry of Extreme KBO 2003 EL61

Abstract: We present high-precision, time-resolved, visible and near-infrared photometry of the large (diameter ~ 2500 km) Kuiper belt object (136108) 2003 EL61. The new data confirm rapid rotation at period P = 3.9155 ± 0.0001 h with a peak-to-peak photometric range of ΔmR = 0.29 ± 0.02 mag and further show subtle but reproducible color variations with rotation. Rotational deformation of 2003 EL61 alone would give rise to a symmetric light curve free of color variations. The observed photometric deviations from the best-fit equilibrium model show the existence of a large surface region with an albedo and color different from the mean surface of 2003 EL61. We explore constraints on the nature of this anomalous region set by the existing data.