Reanalysis of the spectrum of the z=10 galaxy

In a recent paper Pello et al. reported observations of a faint galaxy, gravitationally lensed by the galaxy cluster Abell 1835. Deep J-band spectroscopy revealed a weak emission line near 1.34 microns, detected in two spectra with different central wavelengths. The line was interpreted as Lyman-alpha at redshift z=10.0. This interpretation is supported by the broad-band photometric spectral energy distribution, and by the location of the galaxy close to the lens critical line for this redshift. We have reanalysed the two spectra, just released from the data archive. Our analysis includes allowance for wavelength shifts due to transverse drift of the object in the slit. We do not detect a significant emission line at the reported location, or nearby, at either grating setting, nor in the combined spectrum. We provide a possible explanation for the reported detection as due to spurious positive flux introduced in the sky-subtraction stage as a result of variable hot pixels. We provide our final reduced 2D frame, and corresponding error array.Comment: 4 pages, 1 figure. To appear in A&A Letters. Added possible explanation for reported emission line as due to variable hot pixel

X-ray selected starbursts in the GOODS-North

We investigate claims that recent deep X-ray surveys are detecting starbursts at cosmologically interesting redshifts (z=0-1). We combine X-ray data from the 2Ms CDF-North with multi-wavelength observations from GOODS to build the SEDs (UV, optical, IR) of X-ray sources in this field. These are fit with model templates providing an estimate of the total IR luminosity of each source. We then exploit the correlation between IR and X-ray luminosities for star-forming galaxies, established in the local Universe, to select sources that are dominated by star-formation. This approach is efficient in discriminating normal galaxies from AGN over a wide range of SFRs. The resulting sample consists of 45 X-ray selected star-forming systems at a median redshift z~0.5, the majority of which (60%) are LIRGs or ULIRGs. This sample is least affected by incompleteness and AGN contamination and is well suited for cosmological studies. We quantify the X-ray evolution of these sources by constructing their differential, 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, are indeed finding the starburst galaxy population that drives the rapid evolution of the global SFR density in the range z~0-1. Our analysis also reveals a separate population of IR-faint X-ray sources. These include old galaxies but also systems that are X-ray luminous for their stellar mass compared to local E/S0. We argue that these may be post-starbursts that will, over time, become fainter at X-rays and will eventually evolve into early-type systems (e.g. E/S0).Comment: Accepted for publication in MNRA

The spatial clustering of ultraluminous infrared galaxies over 1.5 < z < 3

We present measurements of the spatial clustering of galaxies with stellar masses 1011 M, infrared luminosities 1012 L, and star formation rates 200 M yr-1 in two redshift intervals: 1.5 &lt; z &lt; 2.0 and 2 &lt; z &lt; 3. Both samples cluster moderately strongly, with spatial correlation lengths of r0 = 6.14 B1 0.84 h-1 Mpc for the 2 &lt; z &lt; 3 sample and r0 = 5.36 B1 1.28 h-1 Mpc for the 1.5 &lt; z &lt; 2.0 sample. These clustering amplitudes are consistent with both populations residing in dark matter halos with masses of 7 C 1012 M, which is comparable to that seen for optical QSOs at the same epochs. We infer that a minimum dark matter halo mass is an important factor for all forms of luminous, obscured activity in galaxies at z &gt; 1, both starbursts and active galactic nuclei. Adopting plausible models for the growth of dark matter halos with redshift, the halos hosting the 2 &lt; z &lt; 3 sample will likely host poor to rich clusters of galaxies at z = 0, whereas the halos hosting the 1.5 &lt; z &lt; 2.0 sample will likely host L* elliptical galaxies or poor clusters at z = 0. We conclude that ultraluminous infrared galaxies (ULIRGs) at z 2.5 likely signpost stellar buildup in galaxies that will reside in clusters at z = 0 and that ULIRGs at z 1.7 signpost stellar buildup in sources that will either become L* elliptical galaxies or reside in poor clusters at z = 0

The SCUBA Half Degree Extragalactic Survey (SHADES) - III : Identification of radio and mid-infrared counterparts to submillimetre galaxies

Peer reviewe

Specific star-formation and the relation to stellar mass from 0<z<2 as seen in the far-infrared at 70 and 160mu

We use the Spitzer Wide-area InfraRed Extragalactic Legacy Survey (SWIRE) to explore the specific star-formation activity of galaxies and their evolution near the peak of the cosmic far-infrared (FIR) background at 70 and 160um. We use a stacking analysis to determine the mean FIR properties of well defined subsets of galaxies at flux levels well below the FIR catalogue detection limits of SWIRE and other Spitzer surveys. We tabulate the contribution of different subsets of galaxies to the FIR background at 70um and 160um. These long wavelengths provide a good constraint on the bolometric, obscured emission. The large area provides good constraints at low z and in finer redshift bins than previous work. At all redshifts we find that the specific FIR Luminosity (sLFIR) decreases with increasing mass, following a trend L_FIR/M* propto M_* ^beta with beta =-0.38\pm0.14. This is a more continuous change than expected from the {Delucia2007} semi-analytic model suggesting modifications to the feedback prescriptions. We see an increase in the sLFIR by about a factor of ~100 from 0<z<2 and find that the sLFIR evolves as (1+z)^alpha with alpha=4.4\pm0.3 for galaxies with 10.5 < log M*/Msun < 12. This is considerably steeper than the {Delucia2007} semi-analytic model (alpha \sim 2.5). When separating galaxies into early and late types on the basis of the optical/IR spectral energy distributions we find that the decrease in sLFIR with stellar mass is stronger in early type galaxies (beta ~ -0.46), while late type galaxies exhibit a flatter trend (beta \sim -0.15). The evolution is strong for both classes but stronger for the early type galaxies. The early types show a trend of decreasing strength of evolution as we move from lower to higher masses while the evolution of the late type galaxies has little dependence on stellar mass. We suggest that in late-type galaxies we are seeing a consistently declining sSFR..Comment: v2 Update doesn't change the content of the paper, but now includes data files for the plots Fig 5-13 (all.plotdat, spi.plotdat and ell.plotdat on arXiv package

Clustering of galaxies at 3.6 microns in the Spitzer Wide-area Infrared Extragalactic legacy survey

We investigate the clustering of galaxies selected in the 3.6 micron band of the Spitzer Wide-area Infrared Extragalactic (SWIRE) legacy survey. The angular two-point correlation function is calculated for eleven samples with flux limits of S_3.6 > 4-400 mujy, over an 8 square degree field. The angular clustering strength is measured at >5-sigma significance at all flux limits, with amplitudes of A=(0.49-29)\times10^{-3} at one degree, for a power-law model, A\theta^{-0.8}. We estimate the redshift distributions of the samples using phenomological models, simulations and photometric redshifts, and so derive the spatial correlation lengths. We compare our results with the GalICS (Galaxies In Cosmological Simulations) models of galaxy evolution and with parameterized models of clustering evolution. The GalICS simulations are consistent with our angular correlation functions, but fail to match the spatial clustering inferred from the phenomological models or the photometric redshifts. We find that the uncertainties in the redshift distributions of our samples dominate the statistical errors in our estimates of the spatial clustering. At low redshifts (median z<0.5) the comoving correlation length is approximately constant, r_0=6.1\pm0.5h^{-1} Mpc, and then decreases with increasing redshift to a value of 2.9\pm0.3h^{-1} Mpc for the faintest sample, for which the median redshift is z=1. We suggest that this trend can be attributed to a decrease in the average galaxy and halo mass in the fainter flux-limited samples, corresponding to changes in the relative numbers of early- and late-type galaxies. However, we cannot rule out strong evolution of the correlation length over 0.5<z<1.Comment: 14 pages, 9 (colour) figures. Published in MNRA

On the use of photometric redshifts for X-ray selected AGNs

(Abridged) In this paper we present photometric redshift estimates for a sample of X-ray selected sources detected in the wide field (~2 deg^2), bright [f_{X} (0.5-8 keV)~10^{-14} cgs] XMM-Newton/2dF survey. Unlike deeper X-ray samples comprising a large fraction of sources with colours dominated by the host galaxy, our bright survey primarily probes the QSO X-ray population. Therefore photometric redshift methods employing both galaxy and QSO templates need to be used. We employ the photometric redshift technique of Hatziminaoglou, Mathez & Pello (2000) using 5-band photometry from the SDSS. We separate our X-ray sources according to their optical profile to point-like and extended. We apply QSO and galaxy templates to the point-like and extended sources respectively. X-ray sources associated with Galactic stars are identified and discarded from our point-like sample on the basis of their low X-ray--to--optical flux ratio and their broad band colours that are best fit by stellar templates. Comparison of our results with spectroscopic redshifts available, allows calibration of our method and estimation of the photometric redshift accuracy. For ~70 per cent of the point-like sources photometric redshifts are correct within dz <= 0.3 (or ~75 per cent have dz/(1+z) <= 0.2), and the rms scatter is estimated to be sigma_z = 0.30. For the optically extended objects the photometric redshifts work only in the case of red (g - r > 0.5 mag) sources yielding dz <= 0.15 and dz/(1+z) <= 0.2 for 73 and 93 per cent respectively. However, we find that the above photometric redshift technique does not work in the case of extended sources with blue colours (g - r < 0.5): such sources cannot be fit successfully by QSO or galaxy templates, or any linear combination of the two.Comment: Replaced due to extended revision; 11 pages, 4 figures; Accepted in A&