AB Magnitude Research Articles

PAU, a fully depleted mosaic imager with narrow band filters

The PAU Survey studies the existence and properties of dark energy from the observations of redshift space distortions and weak lensing magnification from galaxy cross-correlations as main cosmological probes. The PAU Team is building an instrument, PAUCam, equipped with fully depleted CCD detectors, designed to be mounted at the prime focus of the 4.2 m diameter William Herschel Telescope (WHT) in La Palma. Simulations indicate that PAUCam at the WHT will be able to image about 2 square degrees per night in 40 narrow-band filters plus six wide-band filters to an AB magnitude depth of i ∼ 22.5, providing low-resolution (R ∼ 50) photometric spectra for around 30,000 galaxies, 5,000 stars and 1,000 quasars per square degree. Accurate photometric calibration of the PAU data is vital to achieve the survey science goals. This calibration is challenging due to the large and unusual filter set. We outline the data management pipelines being developed for the survey, both for nightly data reduction and co-addition of multiple epochs, with emphasis on the photometric calibration strategies. We also describe the main tests and results in the characterization of our Hamamatsu fully depleted detectors.

A 7 deg2 survey for galaxy-scale gravitational lenses with the HST imaging archive★

We present the results of a visual search for galaxy-scale gravitational lenses in nearly 7 square degrees of Hubble Space Telescope (HST) images. The dataset comprises the whole imaging data ever taken with the Advanced Camera for Surveys (ACS) in the filter F814W (I-band) up to August 31st, 2011, i.e. 6.03 square degrees excluding the field of the Cosmic Evolution Survey (COSMOS) which has been the subject of a separate visual search. In addition, we have searched for lenses in the whole Wide Field Camera 3 (WFC3) near-IR imaging dataset in all filters (1.01 square degrees) up to the same date. Our primary goal is to provide a sample of lenses with a broad range of different morphologies and lens-source brightness contrast in order estimate a lower limit to the number of galaxy-scale strong lenses in the future Euclid survey in its VIS band. Our criteria to select lenses are purely morphological as we do not use any colour or redshift information.The final candidate selection is very conservative hence leading to a nearly pure but incomplete sample. We find 49 new lens candidates: 40 in the ACS images and 9 in the WFC3 images. Out of these, 16 candidates are secure lenses owing to their striking morphology, 21 more are very good candidates, and 12 more have morphologies compatible with gravitational lensing but also compatible with other astrophysical objects. It is therefore insensitive to cosmic variance and allows to estimate the number of galaxy-scale strong lenses on the sky for a putative survey depth, which is the main result of the present work. Because of the incompleteness of the sample, the estimated lensing rates should be taken as lower limits. Using these, we anticipate that a 15 000 square degrees space survey such as Euclid will find at least 60 000 galaxy-scale strong lenses down to a limiting AB magnitude of I = 24.5 (10-sigma) or I = 25.8 (3-sigma).

Recalibrating the Wide-field Infrared Survey Explorer (WISE) W4 Filter

AbstractWe present a revised effective wavelength and photometric calibration for the Wide-field Infrared Survey Explorer W4 band, including tests of empirically motivated modifications to its pre-launch laboratory-measured relative system response curve. We derived these by comparing measured W4 photometry with photometry synthesised from spectra of galaxies and planetary nebulae. The difference between measured and synthesised photometry using the pre-launch laboratory-measured W4 relative system response can be as large as 0.3 mag for galaxies and 1 mag for planetary nebulae. We find the W4 effective wavelength should be revised upward by 3.3%, from 22.1 to 22.8 μm, and the W4 AB magnitude of Vega should be revised from mW4 = 6.59 to mW4 = 6.66. In an attempt to reproduce the observed W4 photometry, we tested three modifications to the pre-launch laboratory-measured W4 relative system response curve, all of which have an effective wavelength of 22.8 μm. Of the three relative system response curve models tested, a model that matches the laboratory-measured relative system response curve, but has the wavelengths increased by 3.3% (or ≃ 0.73 μm) achieves reasonable agreement between the measured and synthesised photometry.

HIGH- n HYDROGEN RECOMBINATION LINES FROM THE FIRST GALAXIES

We investigate the prospects of blind and targeted searches in the radio domain (10 MHz to 1 THz) for high-n hydrogen recombination lines from the first generation of galaxies, at z < 10. The expected optically thin spontaneous alpha-line luminosities are calculated as a function of the absolute AB magnitude of a galaxy at 1500 angstrom. For a blind search, semi-empirical luminosity functions are used to calculate the number of galaxies whose expected flux densities exceed an assumed detectability threshold. Plots of the minimum sky area, within which at least one detectable galaxy is expected at a given observing frequency, in the fiducial instantaneous passband of 10^4 km/s, allow to assess the blind search time necessary for detection by a given facility. We show that the chances for detection are the highest in the mm and submm domains, but finding spontaneous emission in a blind search, especially from redshifts z >> 1, is a challenge even with powerful facilities, such as ALMA and SKA. The probability of success is higher for a targeted search of lines with principal quantum number n ~ 10 in Lyman-break galaxies amplified by gravitational lensing. Detection of more than one hydrogen line in such a galaxy will allow for line identification and a precise determination of the galaxy's redshift.

LUMINOUS SUPERNOVA-LIKE UV/OPTICAL/INFRARED TRANSIENTS ASSOCIATED WITH ULTRA-LONG GAMMA-RAY BURSTS FROM METAL-POOR BLUE SUPERGIANTS

Metal-poor massive stars may typically end up their lives as blue supergiants (BSGs). Gamma-ray bursts (GRBs) from such progenitors could have ultra-long duration of relativistic jets. For example Population III (Pop III) GRBs at z ~ 10-20 might be observable as X-ray rich events with a typical duration of T_90 ~ 10^4(1+z) sec. Recent GRB111209A at z = 0.677 has an ultra long duration of T_90 ~ 2.5*10^4 sec so that it have been suggested that the progenitor might be a metal-poor BSGs in the local universe. Here, we suggest luminous UV/optical/infrared emissions associated with such a new class of GRB from metal poor BSGs. Before the jet head breaks out the progenitor envelope, the energy injected by the jet is stored in a hot-plasma cocoon, which finally emerges and expands as a baryon-loaded fireball. We show that the photospheric emissions from the cocoon fireball could be intrinsically very bright (L_peak ~ 10^(42-44) erg/sec) in UV/optical bands (E_peak ~ 10 eV) with a typical duration of ~ 100 days in the rest frame. Such cocoon emissions from Pop III GRB might be detectable in infrared bands at ~ years after Pop III GRBs at up to z ~ 15 by up-coming facilities like JWST. We also suggest that GRB111209A might have been rebrightening in UV/optical bands up to an AB magnitude of < 26. The cocoon emissions from local metal-poor BSGs might have been already observed as luminous supernovae without GRB since they can be seen from the off-axis direction of the jet.

The North Ecliptic Pole Wide survey of AKARI: a near- and mid-infrared source catalog

We present a photometric catalog of infrared (IR) sources based on the North Ecliptic PoleWide field (NEP-Wide) survey of AKARI, which is an infrared space telescope launched by Japan. The NEP-Wide survey covered 5.4 deg2 area, a nearly circular shape centered on the North Ecliptic Pole, using nine photometric filter-bands from 2 - 25 {\mu}m of the Infrared Camera (IRC). Extensive efforts were made to reduce possible false objects due to cosmic ray hits, multiplexer bleeding phenomena around bright sources, and other artifacts. The number of detected sources varied depending on the filter band: with about 109,000 sources being cataloged in the near-IR bands at 2 - 5 {\mu}m, about 20,000 sources in the shorter parts of the mid-IR bands between 7 - 11 {\mu}m, and about 16,000 sources in the longer parts of the mid-IR bands, with \sim 4,000 sources at 24 {\mu}m. The estimated 5? detection limits are approximately 21 magnitude (mag) in the 2 - 5 {\mu}m bands, 19.5 - 19 mag in the 7 - 11 {\mu}m, and 18.8 - 18.5 mag in the 15 - 24 {\mu}m bands in the AB magnitude scale. The completenesses for those bands were evaluated as a function of magnitude: the 50% completeness limits are about 19.8 mag at 3 {\mu}m, 18.6 mag at 9 {\mu}m, and 18 mag at 18 {\mu}m band, respectively. To construct a reliable source catalog, all of the detected sources were examined by matching them with those in other wavelength data, including optical and ground-based near-IR bands. The final band-merged catalog contains about 114,800 sources detected in the IRC filter bands. The properties of the sources are presented in terms of the distributions in various color-color diagrams.

The DRD2 C957T polymorphism and the Attentional Blink—A genetic association study

The Attentional Blink phenomenon (AB) describes a transient deficit in temporally selective visual attention regarding the processing of the second of two target stimuli in a rapid serial visual presentation (RSVP) task. The AB is a very prominent paradigm in the Cognitive Neurosciences that has been extensively studied by diverse psychophysiological techniques such as EEG or fMRI. Association studies from molecular genetics are scarce although the high heritability of higher cognitive functioning is proven. Only one seminal study reported an association between AB magnitude and the dopamine receptor D2 (DRD2) C957T polymorphism (Colzato et al., 2011). This functional polymorphism influences striatal D2 receptor binding affinity and thereby the efficacy of dopaminergic neurotransmission which is important for working memory and attentional processes. Colzato et al. (2011) reported that DRD2 C957T T/T-carriers exhibit a significant smaller AB than C-allele carriers. In the present study this influence of the DRD2 SNP on the AB could not be replicated in N=211 healthy participants. However, a significantly larger lag 1 sparing was observed for homozygous T/T-carriers. Moreover, carriers of at least one T-allele showed a significantly poorer performance in the identification of T1. In general, these results support the notion of a role of the dopaminergic system on the AB. However, as our results do not parallel previous findings the exact nature of this influence and its dependence on task parameters will have to be examined in further genetic association studies.

NORTH ECLIPTIC POLE WIDE SURVEY

The North Ecliptic Pole (NEP) Wide survey covered about 5.4 deg², a nearly circular area centered on the NEP, using nine passbands of InfraRed Camera (IRC). We present the photometric properties of the data sets, and the nature of the sources detected in this field. The number of detected sources varied according to the filter band: with about 109,000 sources in the NIR, about 20,000 sources in the MIR-S, and about 16,000 sources seen in the MIR-L channel. The 5¾ detection limits are about 21 mag in the NIR and 19.5 ? 18.5 mag in the MIR bands in terms of the AB magnitude. 50% completeness levels are about 19.8 mag at 3 ㎛, 18.6 mag at 9 ㎛, and 18 mag at 18 ㎛ band (in AB magnitude), respectively. In order to validate the detected sources, all of them are confirmed by matching tests with those in other bands. The ‘star-like’ sources, defined by the high stellarity and magnitude cut from the optical ancillary data, appear statistically to have a high probability of being stars. The nature of the various types of extragalactic sources in this field are discussed using the color-color diagrams of the NIR and MIR bands with the redshift tracks of galaxies providing useful guidelines.

NEAR-INFRARED SURVEY OF THE GOODS-NORTH FIELD: SEARCH FOR LUMINOUS GALAXY CANDIDATES ATz≳ 6.5,

We present near-infrared (NIR; J & Ks) survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field. The publicly available imaging data were obtained using the MOIRCS instrument on the 8.2m Subaru and the WIRCam instrument on the 3.6m Canada-France-Hawaii Telescope (CFHT). These observations fulfill a serious wavelength gap in the GOODS-N data - i.e., lack of deep NIR observations. We combine the Subaru/MOIRCS and CFHT/WIRCam archival data to generate deep J and Ks band images, covering the full GOODS-N field (~169 sq. arcmin) to an AB magnitude limit of ~25 mag (3sigma). We applied z'-band dropout color selection criteria, using the NIR data generated here. We have identified two possible Lyman Break Galaxy (LBG) candidates at z\gtrsim6.5 with J\lesssim24.5. The first candidate is a likely LBG at z\sim6.5 based on a weak spectral feature tentatively identified as Lyalpha line in the deep Keck/DEIMOS spectrum, while the second candidate is a possible LBG at z\sim7 based on its photometric redshift. These z'-dropout objects, if confirmed, are among the brightest such candidates found so far. At z\gtrsim6.5, their star formation rate is estimated as 100-200 solar mass per year. If they continue to form stars at this rate, they assemble a stellar mass of ~5x10^10 solar mass after about 400 million years, becoming the progenitors of massive galaxies observed at z\sim5. We study the implication of the z'-band dropout candidates discovered here, in constraining the bright-end of the luminosity function and understanding the nature of high redshift galaxies.

A FULLY IDENTIFIED SAMPLE OF AEGIS20 MICROJANSKY RADIO SOURCES

Infrared 3.6 to 8 micron images of the Extended Groth Strip yield plausible counterpart identifications for all but one of 510 radio sources in the AEGIS20 S(1.4 GHz) > 50 micro-Jy sample. This is the first such deep sample that has been effectively 100% identified. Achieving the same identification rate at R-band would require observations reaching R_AB > 27. Spectroscopic redshifts are available for 46% of the sample and photometric redshifts for an additional 47%. Almost all of the sources with 3.6 micron AB magnitudes brighter than 19 have spectroscopic redshifts z < 1.1, while fainter objects predominantly have photometric redshifts with 1 \lapprox z \lapprox 3. Unlike more powerful radio sources that are hosted by galaxies having large stellar masses within a relatively narrow range, the AEGIS20 counterparts have stellar masses spanning more than a factor of 10 at z \sim 1. The sources are roughly 10--15% starbursts at z \lapprox 0.5 and 20--25% AGNs mostly at z > 1 with the remainder of uncertain nature.

PANORAMIC SURVEY OF Lyα EMITTERS ATz= 3.1

We present the results of the extensive narrowband survey of Lyα emission-line objects at z = 3.1 in the 1.38 deg2 area surrounding the high-density region of star-forming galaxies at z = 3.09 in the SSA22 field, as well as in the 1.04 deg2 area of the three separated general blank fields. In total, of 2161 Lyα emitters, there are 1394 in the SSA22 fields and 767 in the general fields detected at the narrowband AB magnitude limit of 25.73, which corresponds to the line flux of ≈1.8 × 10−17 erg s−1 cm−2 or the luminosity of ≈1.5 × 1042 erg s−1 at z = 3.1, above the observed equivalent-width threshold, ≈190 Å. The average surface number density of the emitters at z = 3.1 in the general fields above the thresholds is 0.20 ± 0.01 arcmin−2. The SSA22 high-density region at z = 3.09, whose peak local density is six times that of the average, is found to be the most prominent outstanding structure in the whole surveyed area and is firmly identified as a robust "protocluster." We also compared the overdensity of the 100 arcmin2 and 700 arcmin2 areas which contain the protocluster with the expected fluctuation of the dark matter as well as those of the model galaxies in cosmological simulations. We found that the peak height values of the overdensity are 8–10 and 3–4 times the expected standard deviations for the counts of Lyα emitters at z = 3.1 in the corresponding volume, respectively. We conclude that the structure at z = 3.09 in the SSA22 field is a very significant and rare density peak up to the scale of ≈60 Mpc.

Evolution of the observed Lyαluminosity function fromz= 6.5 toz= 7.7: evidence for the epoch of reionization?

Aims. Ly-alpha emitters (LAEs) can be detected out to very high redshifts during the epoch of reionization. The evolution of the LAE luminosity function with redshift is a direct probe of the Ly-alpha transmission of the intergalactic medium (IGM), and therefore of the IGM neutral-hydrogen fraction. Measuring the Ly-alpha luminosity function (LF) of LAEs at redshift z = 7.7 therefore allows us to constrain the ionizing state of the Universe at this redshift. Methods. We observed three 7.5'x7.5' fields with the HAWK-I instrument at the VLT with a narrow band filter centred at 1.06 $\mu$m and targeting LAEs at redshift z ~ 7.7. The fields were chosen for the availability of multiwavelength data. One field is a galaxy cluster, the Bullet Cluster, which allowed us to use gravitational amplification to probe luminosities that are fainter than in the field. The two other fields are subareas of the GOODS Chandra Deep Field South and CFHTLS-D4 deep field. We selected z=7.7 LAE candidates from a variety of colour criteria, in particular from the absence of detection in the optical bands. Results. We do not find any LAE candidates at z = 7.7 in ~2.4 x 10^4 Mpc^3 down to a narrow band AB magnitude of ~ 26, which allows us to infer robust constraints on the Ly-alpha LAE luminosity function at this redshift. Conclusions. The predicted mean number of objects at z = 6.5, derived from somewhat different LFs of Hu et al. (2010), Ouchi et al. (2010), and Kashikawa et al. (2011) are 2.5, 13.7, and 11.6, respectively. Depending on which of these LFs we refer to, we exclude a scenario with no evolution from z = 6.5 to z = 7.7 at 85% confidence without requiring a strong change in the IGM Ly-alpha transmission, or at 99% confidence with a significant quenching of the IGM Ly-alpha transmission, possibly from a strong increase in the high neutral-hydrogen fraction between these two redshifts.

KECK SPECTROSCOPY OF LYMAN-BREAK GALAXIES AND ITS IMPLICATIONS FOR THE UV-CONTINUUM AND Lyα LUMINOSITY FUNCTIONS ATz&gt; 6

We present Keck spectroscopic observations of z>6 Lyman-break galaxy (LBG) candidates in the Subaru Deep Field (SDF). The candidates were selected as i'-dropout objects down to z'=27 AB magnitudes from an ultra-deep SDF z'-band image. With the Keck spectroscopy we identified 19 LBGs with prominent Ly_alpha emission lines at 6< z < 6.4. The median value of the Ly_alpha rest-frame equivalent widths (EWs) is ~50 A, with four EWs >100 A. This well-defined spectroscopic sample spans a UV-continuum luminosity range of -21.8< M_{UV}<-19.5 (0.6~5 L*_{UV}) and a Ly_alpha luminosity range of (0.3~3) x 10^{43} erg s^{-1} (0.3~3 L*_ {Ly_alpha}). We derive the UV and Ly_alpha luminosity functions (LFs) from our sample at <z>~6.2 after we correct for sample incompleteness. We find that our measurement of the UV LF is consistent with the results of previous studies based on photometric LBG samples at 5<z<7. Our Ly_alpha LF is also generally in agreement with the results of Ly_alpha-emitter surveys at z~5.7 and 6.6. This study shows that deep spectroscopic observations of LBGs can provide unique constraints on both the UV and Ly_alpha LFs at z>6.

FAR-ULTRAVIOLET NUMBER COUNTS OF FIELD GALAXIES

The far-ultraviolet (FUV) number counts of galaxies constrain the evolution of the star-formation rate density of the universe. We report the FUV number counts computed from FUV imaging of several fields including the Hubble Ultra Deep Field, the Hubble Deep Field North, and small areas within the GOODS-North and -South fields. These data were obtained with the Hubble Space Telescope Solar Blind Channel of the Advance Camera for Surveys. The number counts sample a FUV AB magnitude range from 21-29 and cover a total area of 15.9 arcmin^2, ~4 times larger than the most recent HST FUV study. Our FUV counts intersect bright FUV GALEX counts at 22.5 mag and they show good agreement with recent semi-analytic models based on dark matter "merger trees" by Somerville et al. (2011). We show that the number counts are ~35% lower than in previous HST studies that use smaller areas. The differences between these studies are likely the result of cosmic variance; our new data cover more lines of sight and more area than previous HST FUV studies. The integrated light from field galaxies is found to contribute between 65.9 +/-8 - 82.6 +/-12 photons/s/cm^2/sr/angstrom to the FUV extragalactic background. These measurements set a lower limit for the total FUV background light.

Discovery of a possibly old galaxy at z= 6.027, multiply imaged by the massive cluster Abell 383

Abstract We report the discovery of a unique z= 6.027 galaxy, multiply imaged by the cluster Abell 383 and detected in new Hubble Space Telescope ACS and WFC3 imaging, as well as in Warm Spitzer observations. This galaxy was selected as a pair of i-dropouts; its suspected high redshift was confirmed by the measurement of a strong Lyman a line in both images using Keck/DEIMOS. Combining Hubble and Spitzer photometry after correcting for contamination by line emission (estimated to be a small effect), we identify a strong Balmer break of 1.5 mag. Taking into account the magnification factor of 11.4 ± 1.9 (2.65 ± 0.17 mag) for the brightest image, the unlensed AB magnitude for the source is 27.2 ± 0.05 in the H band, corresponding to a 0.4 L* galaxy, and 25.7 ± 0.08 at 3.6 µm. The UV slope is consistent with β∼ 2.0, and from the rest-frame UV continuum we measure a current star formation rate of 2.4 ± 1.1 M⊙ yr-1. The unlensed half-light radius is measured to be 300 pc, from which we deduce a star-forming surface density of ∼10 M⊙ yr-1 kpc-2. The Lyman α emission is found to be extended over ∼3 arcsec along the slit, corresponding to ∼5 kpc in the source plane. This can be explained by the presence of a much larger envelope of neutral hydrogen around the star-forming region. Finally, fitting the spectral energy distribution (SED) using seven photometric data points with simple SED models, we derive the following properties: very little reddening, an inferred stellar mass of M*= 6 × 109 M⊙, and an inferred age of ∼800 Myr (corresponding to a redshift of formation of ∼18). The star formation rate of this object was likely much stronger in the past than at the time of observation, suggesting that we may be missing a fraction of galaxies at z∼ 6 which have already faded in rest-frame UV wavelengths.

Reionization and feedback in overdense regions at high redshift

Observations of galaxy luminosity function at high redshifts typically focus on fields of view of limited sizes preferentially containing bright sources. These regions possibly are overdense and hence biased with respect to the globally averaged regions. Using a semi-analytic model based on Choudhury & Ferrara (2006) which is calibrated to match a wide range of observations, we study the reionization and thermal history of the universe in overdense regions. The main results of our calculation are: (i) Reionization and thermal histories in the biased regions are markedly different from the average ones because of enhanced number of sources and higher radiative feedback. (ii) The galaxy luminosity function for biased regions is markedly different from those corresponding to average ones. In particular, the effect of radiative feedback arising from cosmic reionization is visible at much brighter luminosities. (iii) Because of the enhanced radiative feedback within overdense locations, the luminosity function in such regions is more sensitive to reionization history than in average regions. The effect of feedback is visible for absolute AB magnitude $M_{AB} \gtrsim -17$ at $z=8$, almost within the reach of present day observations and surely to be probed by JWST. This could possibly serve as an additional probe of radiative feedback and hence reionization at high redshifts.

SUPERNOVA PTF 09UJ: A POSSIBLE SHOCK BREAKOUT FROM A DENSE CIRCUMSTELLAR WIND

Type-IIn supernovae (SNe IIn), which are characterized by strong interaction of their ejecta with the surrounding circumstellar matter (CSM), provide a unique opportunity to study the mass-loss history of massive stars shortly before their explosive death. We present the discovery and follow-up observations of an SN IIn, PTF 09uj, detected by the Palomar Transient Factory (PTF). Serendipitous observations by Galaxy Evolution Explorer (GALEX) at ultraviolet (UV) wavelengths detected the rise of the SN light curve prior to the PTF discovery. The UV light curve of the SN rose fast, with a timescale of a few days, to a UV absolute AB magnitude of about −19.5. Modeling our observations, we suggest that the fast rise of the UV light curve is due to the breakout of the SN shock through the dense CSM (n ≈ 1010 cm−3). Furthermore, we find that prior to the explosion the progenitor went through a phase of high mass-loss rate (∼0.1 M☉ yr−1) that lasted for a few years. The decay rate of this SN was fast relative to that of other SNe IIn.

Quick Minds Slowed Down: Effects of Rotation and Stimulus Category on the Attentional Blink

BackgroundMost people show a remarkable deficit to report the second of two targets when presented in close temporal succession, reflecting an attentional restriction known as the ‘attentional blink’ (AB). However, there are large individual differences in the magnitude of the effect, with some people showing no such attentional restrictions.Methodology/Principal FindingsHere we present behavioral and electrophysiological evidence suggesting that these ‘non-blinkers’ can use alphanumeric category information to select targets at an early processing stage. When such information was unavailable and target selection could only be based on information that is processed relatively late (rotation), even non-blinkers show a substantial AB. Electrophysiologically, in non-blinkers this resulted in enhanced distractor-related prefrontal brain activity, as well as delayed target-related occipito-parietal activity (P3).Conclusion/SignificanceThese findings shed new light on possible strategic mechanisms that may underlie individual differences in AB magnitude and provide intriguing clues as to how temporal restrictions as reflected in the AB can be overcome.

TWO LENSED LYMAN-α EMITTING GALAXIES ATz∼ 5

We present observations of two strongly lensed $z\sim5$ Lyman-$\alpha$ Emitting (LAE) galaxies that were discovered in the Sloan Giant Arcs Survey (SGAS). We identify the two sources as SGAS J091541+382655, at $z=5.200$, and SGAS J134331+415455 at $z=4.994$. We measure their AB magnitudes at $(i,z)=(23.34\pm0.09,23.29\pm0.13$) mags and $(i,z)=(23.78\pm0.18,24.24^{+0.18}_{-0.16}$) mags, and the rest-frame equivalent widths of the Lyman-$\alpha$ emission at $25.3\pm4.1$\AA~and $135.6\pm20.3$\AA~for SGAS J091541+382655 and SGAS J134331+415455, respectively. Each source is strongly lensed by a massive galaxy cluster in the foreground, and the magnifications due to gravitational lensing are recovered from strong lens modeling of the foreground lensing potentials. We use the magnification to calculate the intrinsic, unlensed Lyman-$\alpha$ and UV continuum luminosities for both sources, as well as the implied star formation rates (SFR). We find SGAS J091541+382655 and SGAS J134341+415455 to be galaxies with (L$_{Ly-\alpha}$, L$_{UV})\leq(0.6$L$_{Ly-\alpha}^{*}, 2$L$_{UV}^{*}$) and (L$_{Ly-\alpha}$, L$_{UV})=(0.5$L$_{Ly-\alpha}^{*}, 0.9$L$_{UV}^{*}$), respectively. Comparison of the spectral energy distributions (SEDs) of both sources against stellar population models produces estimates of the mass in young stars in each galaxy: we report an upper limit of M$_{stars} \leq 7.9^{+3.7}_{-2.5} \times 10^{7}$ M$_{\sun} h_{0.7}^{-1}$ for SGAS J091531+382655, and a range of viable masses for SGAS J134331+415455 of $2\times10^{8}$ M$_{\sun} h_{0.7}^{-1} <$ M$_{stars} < 6\times10^{9}$ M$_{\sun} h_{0.7}^{-1}$.

“DARK” GRB 080325 IN A DUSTY MASSIVE GALAXY ATz∼ 2

We present optical and near infrared observations of GRB 080325 classified as a "Dark GRB". Near-infrared observations with Subaru/MOIRCS provided a clear detection of afterglow in Ks band, although no optical counterpart was reported. The flux ratio of rest-wavelength optical to X-ray bands of the afterglow indicates that the dust extinction along the line of sight to the afterglow is Av = 2.7 - 10 mag. This large extinction is probably the major reason for optical faintness of GRB 080325. The J - Ks color of the host galaxy, (J - Ks = 1.3 in AB magnitude), is significantly redder than those for typical GRB hosts previously identified. In addition to J and Ks bands, optical images in B, Rc, i', and z' bands with Subaru/Suprime-Cam were obtained at about one year after the burst, and a photometric redshift of the host is estimated to be z_{photo} = 1.9. The host luminosity is comparable to L^{*} at z \sim 2 in contrast to the sub-L^{*} property of typical GRB hosts at lower redshifts. The best-fit stellar population synthesis model for the host shows that a large dust extinction (Av = 0.8 mag) attributes to the red nature of the host and that the host galaxy is massive (M_{*} = 7.0 \times 10^{10} Msun) which is one of the most massive GRB hosts previously identified. By assuming that the mass-metallicity relation for star-forming galaxies at z \sim 2 is applicable for the GRB host, this large stellar mass suggests the high metallicity environment around GRB 080325, consistent with inferred large extinction.