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Register a new userSearch for Galaxies at z>4 from a Deep Multicolor Survey
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E. Giallongo
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We present deep BVrI multicolor photometry in the field of the quasar BR1202-07 (z_{em}=4.694) aimed at selecting field galaxies at z>4. We compare the observed colors of the galaxies in the field with those predicted by spectral synthesis models including UV absorption by the intergalactic medium and we define a robust multicolor selection of galaxies at z>4. We provide spectroscopic confirmation of the high redshift QSO-companion galaxy (z=4.702) selected by our method. The first estimate of the surface density of galaxies in the redshift interval 4<z<4.5 is obtained for the same field, corresponding to a comoving volume density of ~ 10^{-3}$ Mpc$^{-3}. This provides a lower limit to the average star formation rate of the order of 10^{-2} Mo/yr/Mpc^{-3} at z~ 4.25.
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Motivated by the claimed discovery of a very massive galaxy (HUDF-JD2; M~5x10^11 Msun) at extreme redshift (z = 6.5) within the Hubble Ultra Deep Field (HUDF) (Mobasher et al. 2005), we have completed a systematic search for comparably massive galaxies with z > 4 among the 2688 galaxies in our K < 23.5 (AB) catalogue within the CDFS/GOODS-South field. This search was conducted using redshift estimates based on the recently-completed, uniquely-deep 11-band imaging in this 125 square arcmin field, ~25 times larger than the NICMOS HUDF. Initial spectral fitting, based on published catalogue SExtractor photometry, led us to conclude that at least 2669 of the galaxies in our sample lie at z < 4. We carried out a detailed investigation of the 19 remaining z > 4 candidates, performing aperture photometry on all images, and including marginal detections and formal non-detections in the fitting process. This led to the rejection of a further 13 galaxies to lower redshift. Moreover, subjecting HUDF-JD2 to the same analysis, we find that it lies at z ~ 2.2, rather than the extreme redshift favoured by Mobasher et al. (2005). The 6 remaining candidates appear to be credible examples of galaxies in the redshift range z = 4 - 6, with plausible stellar ages. However, refitting with allowance for extreme values of extinction we find that, even for these objects, statistically acceptable solutions can be found at z < 3. Moreover, the recently-released Spitzer MIPS imaging in GOODS-South has revealed that 5 of our 6 final z > 4 candidates are detected at 24 microns. We conclude that there is no convincing evidence for any galaxy with M > 3 x 10^11 Msun, and z > 4 within the GOODS-South field (abridged).
We study the clustering properties of about 1200 z~4 Lyman Break Galaxy (LBG) candidates with i<26 which are selected by color from deep BRi imaging data of a 618 arcmin^2 area in the Subaru/XMM-Newton Deep Field taken with Subaru Prime Focus Camera. The contamination and completeness of our LBG sample are evaluated, on the basis of the Hubble Deep Field North (HDFN) objects, to be 17% and 45%, respectively. We derive the angular correlation function over theta = 2-1000, and find that it is fitted fairly well by a power law, omega(theta)=A_omega theta^{-0.8}, with A_omega = 0.71 +/- 0.26. We then calculate the correlation length r0 (in comoving units) of the two-point spatial correlation function xi(r) = (r/r0)^{-1.8} from A_omega using the redshift distribution of LBGs derived from the HDFN, and find r0=2.7 (+0.5/-0.6) h^{-1} Mpc in a Lambda-dominated universe (Omega_m=0.3 and Omega_Lambda=0.7). This is twice larger than the correlation length of the dark matter at z~4 predicted from an analytic model by Peacock & Dodds but about twice smaller than that of bright galaxies predicted by a semi-analytic model of Baugh et al. We find an excess of omega(theta) on small scales (theta < 5) departing from the power law fit over 3 sigma significance levels. Interpreting this as due to galaxy mergers, we estimate the fraction of galaxies undergoing mergers in our LBG sample to be 3.0 +/- 0.9%, which is significantly smaller than those of galaxies at intermediate redshifts.
We present a result of a blind search for [CII] 158 $mu$m emitters at $zsim 4.5$ using ALMA Cycle~0 archival data. We collected extra-galactic data covering at 330-360 GHz (band~7) from 8 Cycle~0 projects from which initial results have been already published. The total number of fields is 243 and the total on-source exposure time is 19.2 hours. We searched for line emitters in continuum-subtracted data cubes with spectral resolutions of 50, 100, 300 and 500 km/s. We could not detect any new line emitters above a 6-$sigma$ significance level. This result provides upper limits to the [CII] luminosity function at $zsim 4.5$ over $L_{rm [CII]} sim 10^8 - 10^{10} L_{odot}$ or star formation rate, SFR $sim$ 10-1000 M$_{^odot}$/yr. These limits are at least 2 orders of magnitude larger than the [CII] luminosity functions expected from the $z sim 4$ UV luminosity function or from numerical simulation. However, this study demonstrates that we would be able to better constrain the [CII] luminosity function and to investigate possible contributions from dusty galaxies to the cosmic star-formation rate density by collecting Cycle~1+2 archival data as the ALMA Patchy Deep Survey.
We present the results of a narrow-band survey of QSO fields at redshifts that place the [OIII](5007) emission line in the 1% 2.16micron filter. We have observed 3 square arcminutes and detected one emission line candidate object in the field around PC 1109+4642. We discuss the possibilities that this object is a star-forming galaxy at the QSO redshift, z_em=3.313 or a Seyfert galaxy. In the former case, we infer a star formation rate of 170 Msun/yr for this Kprime=21.3 object. The galaxy has a compact but resolved morphology, with a FWHM=0.6arcs, or 4.2kpc at z=3.313 (H_0=50 km/s/Mpc and q_0=0.5). The comoving density of such objects in QSO environments appears to be 0.0033Mpc^3, marginally lower (<= 3sigma) than the density observed for Halpha-emitters in absorption-line fields at z~2.5, but similar to the density of Lyman Break Galaxies at z~3. If on the other hand, most of the line emission is [OIII] from a Seyfert 2 nucleus at z=3.31, then the high inferred volume density could imply a large evolution in the Seyfert 2 luminosity function from the current epoch. We find the field containing the object to also contain many faint extended objects in the Kprime image, but little significant excess over the expected number-magnitude relation. We discuss the implication of the emission line being a longer wavelength line at a lower redshift.
To understand how strong emission line galaxies (ELGs) contribute to the overall growth of galaxies and star formation history of the universe, we target Strong ELGs (SELGs) from the ZFOURGE imaging survey that have blended (Hb+[OIII]) rest-frame equivalent widths of >230A and 2.5<zphot<4.0. Using Keck/MOSFIRE, we measure 49 redshifts for galaxies brighter than Ks=25 mag as part of our Multi-Object Spectroscopic Emission Line (MOSEL) survey. Our spectroscopic success rate is ~53% and zphot uncertainty is sigma_z= [Delta(z)/(1+z)]=0.0135. We confirm 31 ELGs at 3<zspec<3.8 and show that Strong ELGs have spectroscopic rest-frame [OIII]5007A equivalent widths of 100-500A and tend to be lower mass systems [log(Mstar/Msun)~8.2-9.6] compared to more typical star-forming galaxies. The Strong ELGs lie ~0.9 dex above the star-forming main-sequence at z~3.5 and have high inferred gas fractions of fgas~>60%, i.e. the inferred gas masses can easily fuel a starburst to double stellar masses within ~10-100 Myr. Combined with recent results using ZFOURGE, our analysis indicates that 1) strong [OIII]5007A emission signals an early episode of intense stellar growth in low mass (Mstar<0.1M*) galaxies and 2) many, if not most, galaxies at z>3 go through this starburst phase. If true, low-mass galaxies with strong [OIII]5007A emission (EW_rest>200A) may be an increasingly important source of ionizing UV radiation at z>3.
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