Great Observatories Origins Deep Survey-North Research Articles

Galaxies of the z ∼ 2 Universe. I. Grism-selected Rest-frame Optical Emission-line Galaxies

Abstract Euclid, the Wide Field Infrared Survey Telescope, and the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) will make emission-line selected galaxies the largest observed constituent in the z > 1 universe. However, we only have a limited understanding of the physical properties of galaxies selected via their Lyα or rest-frame optical emission lines. To address this problem, we present the basic properties of ∼2000 All-Wavelength Extended Groth Strip International Survey, Cosmological Evolution Survey, Great Observatories Origins Deep Survey-North, Great Observatories Origins Deep Survey-South, and Ultra Deep Survey galaxies identified in the redshift range 1.90 < z < 2.35 via their [O ii], Hβ, and [O iii] emission lines in the 3D-Hubble Space Telescope survey. For these z ∼ 2 galaxies, [O iii] is generally much brighter than [O ii] and Hβ, with typical rest-frame equivalent widths of several hundred Angstroms. Moreover, these strong emission-line systems span an extremely wide range of stellar mass (∼3 dex), star formation rate (∼2 dex), and [O iii] luminosity (∼2 dex). Comparing the distributions of these properties to those of continuum-selected galaxies, we find that emission-line galaxies have systematically lower stellar masses and lower optical/UV dust attenuations. These measurements lay the groundwork for an extensive comparison between these rest-frame optical emission-line galaxies and Lyα emitters identified in the HETDEX survey.

Near-infrared Survey and Photometric Redshifts in the Extended GOODS-North Field

Abstract We present deep J- and H-band images in the extended Great Observatories Origins Deep Survey-North field covering an area of 0.22 deg2. The observations were taken using WIRCam on the 3.6 m Canada–France–Hawaii Telescope. Together with the reprocessed K s-band image, the 5σ limiting AB magnitudes (in 2″ diameter apertures) are 24.7, 24.2, and 24.4 AB mag in the J, H, and K s bands, respectively. We also release a multiband photometry and photometric redshift catalog containing 93,598 sources. For non-X-ray sources, we obtained a photometric redshift accuracy σ NMAD = 0.036 with an outlier fraction η = 7.3%. For X-ray sources, which are mainly active galactic nuclei (AGNs), we cross-matched our catalog with the updated 2M-CDFN X-ray catalog from Xue et al. and found that 658 out of 683 X-ray sources have counterparts. GALEX UV data are included in the photometric redshift computation for the X-ray sources to give σ NMAD = 0.040 with η = 10.5%. Our approach yields more accurate photometric redshift estimates compared to previous works in this field. In particular, by adopting AGN–galaxy hybrid templates, our approach delivers photometric redshifts for the X-ray counterparts with fewer outliers compared to the 3D-Hubble Space Telescope catalog, which fit these sources with galaxy-only templates.

FIGS—Faint Infrared Grism Survey: Description and Data Reduction

Abstract The Faint Infrared Grism Survey (FIGS) is a deep Hubble Space Telescope (HST) WFC3/IR (Wide Field Camera 3 Infrared) slitless spectroscopic survey of four deep fields. Two fields are located in the Great Observatories Origins Deep Survey-North (GOODS-N) area and two fields are located in the Great Observatories Origins Deep Survey-South (GOODS-S) area. One of the southern fields selected is the Hubble Ultra Deep Field. Each of these four fields were observed using the WFC3/G102 grism (0.8 μm–1.15 μm continuous coverage) with a total exposure time of 40 orbits (≈100 kilo-seconds) per field. This reaches a continuum depth of AB magnitudes and probes emission lines to . This paper details the four FIGS fields and the overall observational strategy of the project. A detailed description of the Simulation Based Extraction (SBE) method used to extract and combine over 10,000 spectra of over 2000 distinct sources brighter than mag is provided. High fidelity simulations of the observations is shown to significantly improve the background subtraction process, the spectral contamination estimates, and the final flux calibration. This allows for the combination of multiple spectra to produce a final high quality, deep, 1D spectra for each object in the survey.

IDENTIFICATION OF z ≳ 2 Herschel 500 μm SOURCES USING COLOR DECONFUSION

ABSTRACT We present a new method to search for candidate z ≳ 2 Herschel 500 μm sources in the Great Observatories Origins Deep Survey-North field using a S 500 μm/S 24 μm “color deconfusion” technique. Potential high-z sources are selected against low-redshift ones from their large 500 to 24 μm flux density ratios. By effectively reducing the contribution from low-redshift populations to the observed 500 μm emission, we are able to identify counterparts to high-z 500 μm sources whose 24 μm fluxes are relatively faint. The recovery of known z ≳ 4 starbursts confirms the efficiency of this approach in selecting high-z Herschel sources. The resulting sample consists of 34 dusty star-forming galaxies at z ≳ 2. The inferred infrared luminosities are in the range 1.5 × 1012–1.8 × 1013 L ⊙, corresponding to dust-obscured star formation rates (SFRs) of ∼260–3100 M ⊙ yr−1 for a Salpeter initial mass function. Comparison with previous SCUBA 850 &mgr; m ?> -selected galaxy samples shows that our method is more efficient at selecting high-z dusty galaxies, with a median redshift of z = 3.07 ± 0.83 ?> and with 10 of the sources at z ≳ 4. We find that at a fixed luminosity, the dust temperature is ∼5 K cooler than that expected from the T d − L IR ?> relation at z ≲ ?> 1, though different temperature selection effects should be taken into account. The radio-detected subsample (excluding three strong active galactic nucleus) follows the far-infrared (far-IR)/radio correlation at lower redshifts, and no evolution with redshift is observed out to z ∼ 5 ?> , suggesting that the far-IR emission is star formation dominated. The contribution of the high-z Herschel 500 μm sources to the cosmic SFR density is comparable to that of (sub)millimeter galaxy populations at z ∼ 2.5 ?> and at least 40% of the extinction-corrected UV samples at z ∼ 4 ?> . Further investigation into the nature of these high-z dusty galaxies will be crucial for our understanding of the star formation histories and the buildup of stellar mass at the earliest cosmic epochs.

STAR FORMATION RATE AND EXTINCTION IN FAINTz∼ 4 LYMAN BREAK GALAXIES

We present a statistical detection of 1.5 GHz radio continuum emission from a sample of faint z~4 Lyman-break galaxies (LBGs). LBGs are key tracers of the high-redshift star formation history and important sources of UV photons that ionized the intergalactic medium in the early universe. In order to better constrain the extinction and intrinsic star formation rate (SFR) of high-redshift LBGs, we combine the latest ultradeep Karl G. Jansky Very Large Array 1.5 GHz radio image and the Hubble Space Telescope Advance Camera for Surveys (ACS) optical images in the Great Observatories Origins Deep Survey-North. We select a large sample of 1771 z~4 LBGs from the ACS catalogue using $\bband$-dropout color criteria. Our LBG samples have $\iband$~25-28 (AB), ~0-3 magnitudes fainter than M*_UV at z~4. In our stacked radio images, we find the LBGs to be point-like under our 2" angular resolution. We measure their mean 1.5 GHz flux by stacking the measurements on the individual objects. We achieve a statistical detection of $S_{1.5GHz}$=0.210+-0.075 uJy at ~3 sigma, first time on such a faint LBG population at z~4. The measurement takes into account the effects of source size and blending of multiple objects. The detection is visually confirmed by stacking the radio images of the LBGs, and the uncertainty is quantified with Monte Carlo simulations on the radio image. The stacked radio flux corresponds to an intrinsic SFR of 16.0+-5.7 M/yr, which is 2.8X the SFR derived from the rest-frame UV continuum luminosity. This factor of 2.8 is in excellent agreement with the extinction correction derived from the observed UV continuum spectral slope, using the local calibration of meurer99. This result supports the use of the local calibration on high-redshift LBGs for deriving the extinction correction and SFR, and also disfavors a steep reddening curve such as that of the Small Magellanic Cloud.

The ALHAMBRA Survey: Bayesian photometric redshifts with 23 bands for 3 deg2

The Advance Large Homogeneous Area Medium-Band Redshift Astronomical (ALHAMBRA) survey has observed eight different regions of the sky, including sections of the Cosmic Evolution Survey (COSMOS), DEEP2, European Large-Area Infrared Space Observatory Survey (ELAIS), Great Observatories Origins Deep Survey North (GOODS-N), Sloan Digital Sky Survey (SDSS) and Groth fields using a new photometric system with 20 optical, contiguous ∼300-Å filters plus the JHKs bands. The filter system is designed to optimize the effective photometric redshift depth of the survey, while having enough wavelength resolution for the identification of faint emission lines. The observations, carried out with the Calar Alto 3.5-m telescope using the wide-field optical camera Large Area Imager for Calar Alto (LAICA) and the near-infrared (NIR) instrument Omega-2000, represent a total of ∼700 h of on-target science images. Here we present multicolour point-spread function (PSF) corrected photometry and photometric redshifts for ∼438 000 galaxies, detected in synthetic F814W images. The catalogues are complete down to a magnitude I ∼ 24.5 AB and cover an effective area of 2.79 deg2. Photometric zero-points were calibrated using stellar transformation equations and refined internally, using a new technique based on the highly robust photometric redshifts measured for emission-line galaxies. We calculate Bayesian photometric redshifts with the Bayesian Photometric Redshift (bpz)2.0 code, obtaining a precision of δz/(1 + zs) = 1 per cent for I < 22.5 and δz/(1 + zs) = 1.4 per cent for 22.5 < I < 24.5. The global n(z) distribution shows a mean redshift 〈z〉 = 0.56 for I < 22.5 AB and 〈z〉 = 0.86 for I < 24.5 AB. Given its depth and small cosmic variance, ALHAMBRA is a unique data set for galaxy evolution studies.

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.

Cosmic Star-Formation Activity at z = 2.2 Probed by H α Emission-Line Galaxies

Abstract We present a pilot narrow-band survey of H$\alpha$ emitters at z$=$ 2.2 in the Great Observatories Origins Deep Survey North (GOODS-N) field with MOIRCS instrument on the Subaru Telescope. The survey reached a 3$\ \sigma$ limiting magnitude of 23.6 (NB209), which corresponds to a 3$\ \sigma$ limiting line flux of 2.5 $\times$ 10$^{-17}\ $erg s$^{-1}\ $cm$^{-2}$ over a 56 arcmin$^2$ contiguous area (excluding a shallower area). From this survey, we have identified eleven H$\alpha$ emitters and one AGN at z$=$ 2.2 on the basis of narrow-band excesses and photometric redshifts. We obtained spectra for seven out of the new objects, including one AGN; also, an emission line above 3$\ \sigma$ was detected from all of them. We estimated star-formation rates (SFR) and stellar masses ($M_{\mathrm{star}}$) for individual galaxies. The average SFR and $M_{\mathrm{star}}$ are 27.8$\ M_{\odot}\ $yr$^{-1}\ $ and 4.0 $\times$ 10$^{10}\ M_\odot$, respectively. Their specific star-formation rates negatively correlate with their stellar masses. Fitting to a Schechter function yields the H$\alpha$ luminosity function with log$L$$=$ 42.82, log$\phi$$=$$-$2.78, and $\alpha$$=$$-$1.37. The average star-formation rate density in the survey volume is estimated to be 0.31$\ M_{\odot}\ $yr$^{-1}\ $Mpc$^{-3}$ according to the Kennicutt relation between the H$\alpha$ luminosity and the star-formation rate. We compared our H$\alpha$ emitters at z$=$ 2.2 in GOODS-N with narrow-band line emitters in other fields and clusters to see their time evolution and environmental dependence. We found that the star-formation activity is rapidly reduced from z$=$ 2.5 to z$=$ 0.8 in the cluster environment, while it only moderately changed in the field environment. This result suggests that the time scale of galaxy formation differs among different environments, and the star-forming activities in high density regions eventually overtake those in lower-density regions as a consequence of “galaxy-formation bias” at high redshifts.

HerMES: SPIRE detection of high-redshift massive compact galaxies in GOODS-N field

Abstract We have analysed the rest-frame far-infrared properties of a sample of massive (M★ &amp;gt; 1011 M⊙) galaxies at 2 ≲z≲ 3 in the Great Observatories Origins Deep Survey-North (GOODS-N) field using the Spectral and Photometric Imaging Receiver (SPIRE) instrument aboard the Herschel Space Observatory. To conduct this analysis we take advantage of the data from the Herschel Multi-tiered Extragalactic Survey (HerMES) key programme. The sample comprises 45 massive galaxies with structural parameters characterized with HST NICMOS-3. We study detections at submm Herschel bands, together with Spitzer 24-μm data, as a function of the morphological type, mass and size. We find that 26/45 sources are detected at MIPS 24 μm and 15/45 (all MIPS 24-μm detections) are detected at SPIRE 250 μm, with disc-like galaxies more easily detected. We derive star formation rates (SFRs) and specific star formation rates (sSFRs) by fitting the spectral energy distribution of our sources, taking into account non-detections for SPIRE and systematic effects for MIPS derived quantities. We find that the mean SFR for the spheroidal galaxies (∼50–100 M⊙ yr−1) is substantially (a factor ∼3) lower than the mean value presented by disc-like galaxies (∼250–300 M⊙ yr−1).

Evolution of dust temperature of galaxies through cosmic time as seen by Herschel★

We study the dust properties of galaxies in the redshift range 0.1 ≲z≲ 2.8 observed by the Herschel Space Observatory in the field of the Great Observatories Origins Deep Survey-North as part of the PACS Extragalactic Probe (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES) key programmes. Infrared (IR) luminosity (LIR) and dust temperature (Tdust) of galaxies are derived from the spectral energy distribution fit of the far-IR (FIR) flux densities obtained with the PACS and SPIRE instruments onboard Herschel. As a reference sample, we also obtain IR luminosities and dust temperatures of local galaxies at z < 0.1 using AKARI and IRAS data in the field of the Sloan Digital Sky Survey. We compare the LIR–Tdust relation between the two samples and find that the median Tdust of Herschel-selected galaxies at z≳ 0.5 with LIR≳ 5 × 1010 L⊙ appears to be 2–5 K colder than that of AKARI-selected local galaxies with similar luminosities, and the dispersion in Tdust for high-z galaxies increases with LIR due to the existence of cold galaxies that are not seen among local galaxies. We show that this large dispersion of the LIR−Tdust relation can bridge the gap between local star-forming galaxies and high-z submillimetre galaxies (SMGs). We also find that three SMGs with very low Tdust (≲20 K) covered in this study have close neighbouring sources with similar 24-μm brightness, which could lead to an overestimation of FIR/(sub)millimetre fluxes of the SMGs.

VERY LARGE ARRAY 1.4 GHz OBSERVATIONS OF THE GOODS-NORTH FIELD: DATA REDUCTION AND ANALYSIS

We describe deep, new, wide-field radio continuum observations of the Great Observatories Origins Deep Survey -- North (GOODS-N) field. The resulting map has a synthesized beamsize of ~1.7" and an r.m.s. noise level of ~3.9uJy/bm near its center and ~8uJy/bm at 15', from phase center. We have cataloged 1,230 discrete radio emitters, within a 40' x 40' region, above a 5-sigma detection threshold of ~20uJy at the field center. New techniques, pioneered by Owen & Morrison (2008), have enabled us to achieve a dynamic range of 6800:1 in a field that has significantly strong confusing sources. We compare the 1.4-GHz (20-cm) source counts with those from other published radio surveys. Our differential counts are nearly Euclidean below 100uJy with a median source diameter of ~1.2". This adds to the evidence presented by Owen & Morrison (2008) that the natural confusion limit may lie near ~1uJy. If the Euclidean slope of the counts continues down to the natural confusion limit as an extrapolation of our log N - log S, this indicates that the cutoff must be fairly sharp below 1uJy else the cosmic microwave background temperature would increase above 2.7K at 1.4 GHz.

ULTRADEEP K S IMAGING IN THE GOODS-N

We present an ultradeep Ks-band image that covers 0.5*0.5 deg^2 centered on the Great Observatories Origins Deep Survey-North (GOODS-N). The image reaches a 5 \sigma depth of Ks(AB) = 24.45 in the GOODS-N region, which is as deep as the GOODS-N Spitzer Infrared Array Camera (IRAC) 3.6 \mu m image. We present a new method of constructing IRAC catalogs that uses the higher spatial resolution Ks image and catalog as priors and iteratively subtracts fluxes from the IRAC images to estimate the IRAC fluxes. Our iterative method is different from the \chi^2 approach adopted by other groups. We verified our results using data taken in two different epochs of observations, as well as by comparing our colors with the colors of stars and with the colors derived from model spectral energy distributions (SEDs) of galaxies at various redshifts. We make available to the community our WIRCam Ks-band image and catalog (94951 objects in 0.25 deg^2), the Interactive Data Language (IDL) pipeline used for reducing the WIRCam images, and our IRAC 3.6 to 8.0 \mu m catalog (16950 objects in 0.06 deg^2 at 3.6 \mu m). With this improved Ks and IRAC catalog and a large spectroscopic sample from our previous work, we study the color-magnitude and color-color diagrams of galaxies. We compare the effectiveness of using Ks and IRAC colors to select active galactic nuclei (AGNs) and galaxies at various redshifts. We also study a color selection of z = 0.65--1.2 galaxies using the Ks, 3.6 \mu m, and 4.5 \mu m bands.

An AzTEC 1.1 mm survey of the GOODS-N field - II. Multiwavelength identifications and redshift distribution

We present results from a multi-wavelength study of 29 sources (false detection probabilities <5%) from a survey of the Great Observatories Origins Deep Survey-North field at 1.1mm using the AzTEC camera. Comparing with existing 850um SCUBA studies in the field, we examine differences in the source populations selected at the two wavelengths. The AzTEC observations uniformly cover the entire survey field to a 1-sigma depth of ~1mJy. Searching deep 1.4GHz VLA, and Spitzer 3--24um catalogues, we identify robust counterparts for 21 1.1mm sources, and tentative associations for the remaining objects. The redshift distribution of AzTEC sources is inferred from available spectroscopic and photometric redshifts. We find a median redshift of z=2.7, somewhat higher than z=2.0 for 850um-selected sources in the same field, and our lowest redshift identification lies at a spectroscopic redshift z=1.1460. We measure the 850um to 1.1mm colour of our sources and do not find evidence for `850um dropouts', which can be explained by the low-SNR of the observations. We also combine these observed colours with spectroscopic redshifts to derive the range of dust temperatures T, and dust emissivity indices $\beta$ for the sample, concluding that existing estimates T~30K and $\beta$~1.75 are consistent with these new data.

THE NATURE OF GROWING BULGES WITHIN z &lt; 1.3 GALAXY DISKS IN THE GOODS-N FIELD

We analyze central surface brightness mu_0, nuclear and global colors of intermediate redshift disk galaxies. On an apparent-diameter limited sample of 398 galaxies from ACS/HST Great Observatories Origins Deep Survey North (GOODS-N), we find 131 galaxies with bulges and 214 without. Up to z ~ 0.8, blue, star-forming nuclei are found in galaxies with low mu_0 only; all high-mu_0 nuclei show red, passive colors, so that nuclear and global (U - B) colors strongly correlate with central surface brightness, as found in the local Universe. At 0.8 < z < 1.3, a fraction ~ 27% of the high-surface brightness nuclei show blue colors, and positive nuclear color gradients. The associated nuclear star formation must lead to bulge growth inside disks. Population modeling suggests that such blue bulges evolve into local pseudobulges rather than classical bulges. We do not find evidence for rejuvenation of classical bulges at the sampled z. High luminosity AGNs become common at 0.8 < z < 1.3, perhaps pointing to a role of AGN in the growth or star formation truncation of bulges.

ULTRADEEP NEAR-INFRARED OBSERVATIONS OF GOODS 850-5,

GOODS 850-5 is a hyperluminous radio-faint submillimeter source in the Great Observatories Origins Deep Survey-North. Although it is generally agreed that GOODS 850-5 is at a high redshift, z 4, its exact redshift is unknown. While its stellar spectral energy distribution (SED) suggests z ~ 6, its radio/far-IR (FIR) SED suggests a lower redshift of z ~ 4. To better constrain its stellar SED and redshift, we carried out nano-Jansky sensitivity ultradeep near-IR (NIR) observations between 1.2 and 2.1 μm with the Hubble Space Telescope and the 8 m Subaru Telescope. Even with such great depths we did not detect GOODS 850-5, and the results show that it is an extremely curious source. Between the Ks and 3.6 μm bands, its spectral slope is greater than 3 times that of an extremely red object, and the flux ratio between the two bands is greater than 8 times that of Lyman breaks. It is quite challenging to explain this unusually red color without a Lyman break (which would imply z > 17). It requires a large amount (M ~ 1011.5 M ☉) of reddened old stars at z ~ 6, coexisting with an even more extinguished violent ~2400-4400 M ☉ yr–1 starburst, which does not have any associated detectable rest-frame UV radiation. We discuss the discrepancy between the NIR and radio/FIR photometric redshifts. We conclude that GOODS 850-5 is at least at z > 4 and is more likely at z 6. We describe the unusual properties of GOODS 850-5, including its SED and formation history, and we discuss the implications of such massive z > 6 galaxies.

X-ray selected starbursts in the Great Observatories Origins Deep Survey-North

We investigate claims that recent ultra-deep X-ray surveys are detecting starbursts at cosmologically interesting redshifts (z= 0–1). We combine X-ray data from the 2 Ms Chandra Deep Field-North and multiwavelength observations obtained as part of the Great Observatories Origins Deep Survey (GOODS)-North to build the Spectral Energy Distributions (UV, optical, infrared) of X-ray sources in this field. These are fit with model templates providing an estimate of the total infrared luminosity (3–1000 μm) of each source. We then exploit the tight correlation between infrared and X-ray luminosities for star-forming galaxies, established in the local Universe, to select sources that are dominated by star formation rather than supermassive black hole accretion. This approach is efficient in discriminating normal galaxies from active galactic nuclei (AGN) over a wide range of star formation rates, from quiescent systems to starbursts. The above methodology results in a sample of 45 X-ray selected star-forming systems at a median redshift z≈ 0.5, the majority of which (60 per cent) are either luminous or ultraluminous infrared galaxies. This sample is least affected by incompleteness and residual AGN contamination and is therefore well suited for cosmological studies. We quantify the X-ray evolution of these sources by constructing their differential X-ray counts, dN/dS, and comparing them with evolving luminosity function models. The results are consistent with luminosity evolution of the form (1 +z)p with p≈ 2.4. This is similar to the evolution rate of star-forming galaxies selected at other wavelengths, suggesting that the deep X-ray surveys, like the Chandra Deep Field-North, are indeed finding the starburst galaxy population that drives the rapid evolution of the global star formation rate density in the range z≈ 0–1. Our analysis also reveals a separate population of infrared-faint X-ray sources at moderate z. These include old galaxies but also systems that are X-ray luminous for their stellar mass compared to local ellipticals. We argue that these may be post-starbursts that will, over time, become fainter at X-ray wavelengths and will eventually evolve into early-type systems (i.e. E/S0).

MOIRCS Deep Survey. I: DRG Number Counts

Abstract We used very deep near-infrared imaging data taken with the Multi-Object InfraRed Camera and Spectrograph (MOIRCS) on the Subaru Telescope to investigate the number counts of Distant Red Galaxies (DRGs). We observed a $4' \times 7'$ field in the Great Observatories Origins Deep Survey-North (GOODS-N), and our data reached $J=24.6$ and $K=23.2$ ($5\,\sigma$, Vega magnitude). The surface density of DRGs selected by $J-K \gt 2.3 J-K \gt 2.3$ is $2.35 \pm 0.31 \,\mathrm{arcmin}^{-2}$ at $K &amp;lt; 22$ and $3.54 \pm 0.38 \,\mathrm{arcmin}^{-2}$ at $K &amp;lt; 23$, respectively. These values are consistent with those in the GOODS-South and FIRES. Our deep and wide data suggest that the number counts of DRGs turn over at $K \sim 22$, and the surface density of the faint DRGs with $K \gt 22$ is smaller than that expected from the number counts at the brighter magnitude. The result indicates that while there are many bright galaxies at $2 &amp;lt; z &amp;lt; 4$ with the relatively old stellar population and/or heavy dust extinction, the number of faint galaxies with a similar red color is relatively small. Different behavior patterns of the number counts of the DRGs and bluer galaxies with $2 &amp;lt; z_{\mathrm{phot}} &amp;lt; 4$ at $K \gt 22$ suggest that the mass-dependent color distribution, where most of the low-mass galaxies are blue, while more massive galaxies tend to have redder colors, had already been established at that epoch.

Star Formation Rates and Stellar Masses in z ~ 1 Gamma-Ray Burst Hosts

We analyse 4.5, 8 and 24 um band Spitzer images of six gamma ray burst host galaxies at redshifts close to 1. We constrain their star formation rates (SFR) based on the entire available spectral energy distribution rather than the 24 um band only. Further, we estimate their stellar masses (M*) based on rest frame K band luminosities. Our sample spans a wide range of galaxy properties: derived SFRs range from less than 10 to a few hundred solar masses per year; values of M* range from 10^9 to 10^10 Mo with a median of 5.6 x 10^9 Mo. Comparing the specific star formation rate (PHI = SFR/M*) of our sample as a function of M* to other representative types of galaxies (distant red galaxies, Ly-alpha emitters, Lyman break galaxies, submillimeter galaxies and z ~ 2 galaxies from the Great Observatories Origins Deep Survey-North field), we find that gamma ray burst hosts are among those with the highest PHI.

On the cross-correlation of sub-mm sources and optically selected galaxies

Bright submillimetre (sub-mm) galaxies are expected to arise in massive highly biased haloes, and hence exhibit strong clustering. We argue that a valuable tool for measuring these clustering properties is the cross-correlation of sub-mm galaxies with faint optically selected sources. We analyse populations of sub-mm detected and optical galaxies in the Great Observatories Origins Deep Survey-North (GOODS-N) survey area. Using optical/infrared photometric-redshift information, we search for correlations induced by two separate effects: (i) cosmic magnification of background sub-mm sources by foreground dark matter haloes traced by optical galaxies at lower redshifts and (ii) galaxy clustering due to sub-mm and optical sources tracing the same population of haloes where their redshift distributions overlap. Regarding cosmic magnification, we find no detectable correlation. Our null result is consistent with a theoretical model for the cosmic magnification, and we show that a dramatic increase in the number of sub-mm sources will be required to measure the effect reliably. Regarding clustering, we find evidence at the 3.5σ level for a cross-correlation between sub-mm and optical galaxies analysed in identical photometric redshift slices. The data hint that the sub-mm sources have an enhanced bias parameter compared to the optically selected population (with a significance of 2σ). The next generation of deep sub-mm surveys can potentially perform an accurate measurement of each of these cross-correlations, adding a new set of diagnostics for understanding the development of massive structure in the Universe.

The Kinematics of Morphologically Selectedz ∼ 2 Galaxies in the GOODS‐North Field

We present near-IR spectra of Hα emission from 13 galaxies at z ~ 2 in the Great Observatories Origins Deep Survey-North (GOODS-N) field. The galaxies were selected primarily because they appear to have elongated morphologies, and slits were aligned with the major axes (as determined from the rest-frame UV emission) of 11 of the 13. If the galaxies are elongated because they are highly inclined, alignment of the slit and major axis should maximize the observed velocity and reveal velocity shear, if present. In spite of this alignment, we see spatially resolved velocity shear in only two galaxies. We show that the seeing makes a large difference in the observed velocity spread of a tilted emission line, and use this information to place limits on the velocity spread of the ionized gas of the galaxies in the sample: we find that all 13 have v0.5 ≤ 110 km s-1, where v0.5 is the velocity shear (half of the velocity range of a tilted emission line) that would be observed under our best seeing conditions of ~05. When combined with previous work, our data also indicate that aligning the slit along the major axis does not increase the probability of observing a tilted emission line. We then focus on the one-dimensional velocity dispersion σ, which is much less affected by the seeing, and see that the elongated subsample exhibits a significantly lower velocity dispersion than galaxies selected at random from our total Hα sample, not higher as one might have expected. We also see some evidence that the elongated galaxies are less reddened than those randomly selected using only UV colors. Both of these results are contrary to what would be expected if the elongated galaxies were highly inclined disks. It is at least as likely that the galaxies' elongated morphologies are due to merging subunits.