Host galaxies of bright high redshift quasars: Luminosities and colours

We present the results of a near-infrared imaging study of high redshift (z~3) quasars using the ESO-VLT. Our targets were selected to have luminosities among the highest known (absolute magnitude M_B <~ -28. We searched for resolved structures underlying the bright point-source nuclei by comparing the QSO images with stars located in the same fields. Two QSOs (HE2348-1444 at z=2.904 and HE2355-5457 at z=2.933) are clearly resolved in K_S, and with somewhat lower significance also in H; one object is resolved only in K_S. At these redshifts, H and K_S correspond almost exactlly to rest-frame B and V, respectively, with virtually no K-correction. We also report briefly the non-detection of some additional QSOs. The detected host galaxies are extremely luminous with M_V ~ -25. Their rest-frame B-V colours, however, are close to zero in the Vega system, indicating substantial contributions from young stars and a stellar mass-to-light ratio below 1 (in solar units). Tentatively converting M_V and B-V into rough estimates of stellar masses, we obtain values of M_star in the range of several 10^11 M_sun, placing them within the high-mass range of recent high-redshift galaxy surveys. We present optical spectra and use CIV line width measurements to predict virial black hole masses, obtaining typical values of M_bh ~ 5x10^9 M_sun. With respect to the known correlation between host galaxy luminosity L_V(host) and M_bh, our measurements reach to higher luminosities and redshifts than previous studies, but are completely consistent with them. Comparing our objects with the local (z~0) M_bh - M_bulge relation and taking also the low stellar mass-to-light ratios into account, we find tentative evidence for an excess in the M_bh/M_bulge mass ratio at z~3.Comment: 9 pages, 7 figures, accepted for publication in A&

Epistasis between the MHC and the RCAα block in primary Sjögren syndrome

ObjectiveThe RCA alpha block (Regulators of Complement Activation, 1q32) contains critical complement regulatory genes such as CR1 and MCP. This study examined RCA alpha block haplotype associations with both disease susceptibility and diversification of the anti-Ro/La autoantibody response in primary Sjögren syndrome (pSS).Methods115 patients with pSS and 98 controls were included in the study. 93 of 109 (85%) of the patients with pSS were seropositive for Ro/La autoantibodies. The Genomic Matching Technique (GMT) was used to define RCA alpha block ancestral haplotypes (AH).ResultsRCA alpha block haplotypes, AH1 and AH3, were both associated with autoantibody-positive pSS (p = 0.0003). Autoantibody associations with both HLA DR3 and DR15 have been previously defined. There was an epistatic interaction (p = 0.023) between RCA alpha AH1 and HLA DR3, and this genotypic combination was present in 48% of autoantibody-positive patients with pSS compared with 8% of controls. This epistasis is most simply attributable to an interaction between C4 and its receptor, CR1, encoded within the RCA alpha block. Both DR3 and a relative C4 deficiency are carried on the major histocompatibility complex 8.1 ancestral haplotype. Only four of 92 (4%) autoantibody-positive patients with pSS did not carry any risk RCA alpha or HLA haplotype, compared with 36 of 96 (38%) controls, and there were differences in haplotype frequencies within autoantibody subsets of pSS.ConclusionsNormal population variation in the RCA alpha block, in addition to the major histocompatibility complex, contributes genetic susceptibility to systemic autoimmune disease and the autoantibody response. This finding provides evidence for the role of regulation of complement activation in disease pathogenesis.S. Lester, C. McLure, J. Williamson, P. Bardy, M. Rischmueller, R. L. Dawkin

A robust sample of galaxies at redshifts 6.0<z<8.7: stellar populations, star-formation rates and stellar masses

We present the results of a photometric redshift analysis designed to identify z>6 galaxies from the near-IR HST imaging in three deep fields (HUDF, HUDF09-2 & ERS). By adopting a rigorous set of criteria for rejecting low-z interlopers, and by employing a deconfusion technique to allow the available IRAC imaging to be included in the candidate selection process, we have derived a robust sample of 70 Lyman-break galaxies (LBGs) spanning the redshift range 6.0<z<8.7. Based on our final sample we investigate the distribution of UV spectral slopes (beta), finding a variance-weighted mean value of =-2.05 +/- 0.09 which, contrary to some previous results, is not significantly bluer than displayed by lower-redshift starburst galaxies. We confirm the correlation between UV luminosity and stellar mass reported elsewhere, but based on fitting galaxy templates featuring a range of star-formation histories, metallicities and reddening we find that, at z>=6, the range in mass-to-light ratio (M*/L_UV) at a given UV luminosity could span a factor of ~50. Focusing on a sub-sample of twenty-one candidates with IRAC detections at 3.6-microns we find that L* LBGs at z~6.5 have a median stellar mass of M* = (2.1 +/- 1.1) x 10^9 Msun and a median specific star-formation rate of 1.9 +/- 0.8 Gyr^-1. Using the same sub-sample we have investigated the influence of nebular continuum and line emission, finding that for the majority of candidates (16 out of 21) the best-fitting stellar-mass estimates are reduced by less than a factor of 2.5. Finally, a detailed comparison of our final sample with the results of previous studies suggests that, at faint magnitudes, several high-redshift galaxy samples in the literature are significantly contaminated by low-redshift interlopers (abridged).Comment: 35 pages, 22 figures, replaced to match version accepted by MNRAS, minor changes onl

Constraining Lyman-alpha spatial offsets at 3<z<5.53<z<5.5 from VANDELS slit spectroscopy

We constrain the distribution of spatially offset Lyman-alpha emission (Ly$\alpha$) relative to rest-frame ultraviolet emission in $\sim300$ high redshift ($3<z<5.5$) Lyman-break galaxies (LBGs) exhibiting Ly$\alpha$ emission from VANDELS, a VLT/VIMOS slit-spectroscopic survey of the CANDELS Ultra Deep Survey and Chandra Deep Field South fields (${\simeq0.2}~\mathrm{deg}^2$ total). Because slit spectroscopy compresses two-dimensional spatial information into one spatial dimension, we use Bayesian inference to recover the underlying Ly$\alpha$ spatial offset distribution. We model the distribution using a 2D circular Gaussian, defined by a single parameter $\sigma_{r,\mathrm{Ly}\alpha}$, the standard deviation expressed in polar coordinates. Over the entire redshift range of our sample ($3<z<5.5$), we find $\sigma_{r,\mathrm{Ly}\alpha}=1.70^{+0.09}_{-0.08}$ kpc ($68\%$ conf.), corresponding to $\sim0.25$ arcsec at $\langle z\rangle=4.5$. We also find that $\sigma_{r,\mathrm{Ly}\alpha}$ decreases significantly with redshift. Because Ly$\alpha$ spatial offsets can cause slit-losses, the decrease in $\sigma_{r,\mathrm{Ly}\alpha}$ with redshift can partially explain the increase in the fraction of Ly$\alpha$ emitters observed in the literature over this same interval, although uncertainties are still too large to reach a strong conclusion. If $\sigma_{r,\mathrm{Ly}\alpha}$ continues to decrease into the reionization epoch, then the decrease in Ly$\alpha$ transmission from galaxies observed during this epoch might require an even higher neutral hydrogen fraction than what is currently inferred. Conversely, if spatial offsets increase with the increasing opacity of the IGM, slit losses may explain some of the drop in Ly$\alpha$ transmission observed at $z>6$. Spatially resolved observations of Ly$\alpha$ and UV continuum at $6<z<8$ are needed to settle the issue.Comment: Submitted to MNRA

The VANDELS survey: Dust attenuation in star-forming galaxies at z=3−4\mathbf{z=3-4}

We present the results of a new study of dust attenuation at redshifts $3 < z < 4$ based on a sample of $236$ star-forming galaxies from the VANDELS spectroscopic survey. Motivated by results from the First Billion Years (FiBY) simulation project, we argue that the intrinsic spectral energy distributions (SEDs) of star-forming galaxies at these redshifts have a self-similar shape across the mass range $8.2 \leq$ log$(M_{\star}/M_{\odot}) \leq 10.6$ probed by our sample. Using FiBY data, we construct a set of intrinsic SED templates which incorporate both detailed star formation and chemical abundance histories, and a variety of stellar population synthesis (SPS) model assumptions. With this set of intrinsic SEDs, we present a novel approach for directly recovering the shape and normalization of the dust attenuation curve. We find, across all of the intrinsic templates considered, that the average attenuation curve for star-forming galaxies at $z\simeq3.5$ is similar in shape to the commonly-adopted Calzetti starburst law, with an average total-to-selective attenuation ratio of $R_{V}=4.18\pm0.29$. We show that the optical attenuation ($A_V$) versus stellar mass ($M_{\star}$) relation predicted using our method is consistent with recent ALMA observations of galaxies at $2<z<3$ in the \emph{Hubble} \emph{Ultra} \emph{Deep} \emph{Field} (HUDF), as well as empirical $A_V - M_{\star}$ relations predicted by a Calzetti-like law. Our results, combined with other literature data, suggest that the $A_V - M_{\star}$ relation does not evolve over the redshift range $0<z<5$, at least for galaxies with log$(M_{\star}/M_{\odot}) \gtrsim 9.5$. Finally, we present tentative evidence which suggests that the attenuation curve may become steeper at log$(M_{\star}/M_{\odot}) \lesssim 9.0$.Comment: 16 pages, 12 figures, accepted for publication in MNRA

The VANDELS survey: Dust attenuation in star-forming galaxies at z=3−4\mathbf{z=3-4}

We present the results of a new study of dust attenuation at redshifts $3 < z < 4$ based on a sample of $236$ star-forming galaxies from the VANDELS spectroscopic survey. Motivated by results from the First Billion Years (FiBY) simulation project, we argue that the intrinsic spectral energy distributions (SEDs) of star-forming galaxies at these redshifts have a self-similar shape across the mass range $8.2 \leq$ log$(M_{\star}/M_{\odot}) \leq 10.6$ probed by our sample. Using FiBY data, we construct a set of intrinsic SED templates which incorporate both detailed star formation and chemical abundance histories, and a variety of stellar population synthesis (SPS) model assumptions. With this set of intrinsic SEDs, we present a novel approach for directly recovering the shape and normalization of the dust attenuation curve. We find, across all of the intrinsic templates considered, that the average attenuation curve for star-forming galaxies at $z\simeq3.5$ is similar in shape to the commonly-adopted Calzetti starburst law, with an average total-to-selective attenuation ratio of $R_{V}=4.18\pm0.29$. We show that the optical attenuation ($A_V$) versus stellar mass ($M_{\star}$) relation predicted using our method is consistent with recent ALMA observations of galaxies at $2<z<3$ in the \emph{Hubble} \emph{Ultra} \emph{Deep} \emph{Field} (HUDF), as well as empirical $A_V - M_{\star}$ relations predicted by a Calzetti-like law. Our results, combined with other literature data, suggest that the $A_V - M_{\star}$ relation does not evolve over the redshift range $0<z<5$, at least for galaxies with log$(M_{\star}/M_{\odot}) \gtrsim 9.5$. Finally, we present tentative evidence which suggests that the attenuation curve may become steeper at log$(M_{\star}/M_{\odot}) \lesssim 9.0$.Comment: 16 pages, 12 figures, accepted for publication in MNRA

The VANDELS survey: A strong correlation between Lyα\alpha equivalent width and stellar metallicity at 3≤z≤5\mathbf{3\leq z \leq 5}

We present the results of a new study investigating the relationship between observed Ly$\alpha$ equivalent width ($W_{\lambda}$(Ly$\alpha$)) and the metallicity of the ionizing stellar population ($Z_{\star}$) for a sample of $768$ star-forming galaxies at $3 \leq z \leq 5$ drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame $W_{\lambda}$(Ly$\alpha$) across the range -58 \unicode{xC5} \lesssim $W_{\lambda}$(Ly$\alpha$) \lesssim 110 \unicode{xC5} we determine $Z_{\star}$ from full spectral fitting of composite far-ultraviolet (FUV) spectra and find a clear anti-correlation between $W_{\lambda}$(Ly$\alpha$) and $Z_{\star}$. Our results indicate that $Z_{\star}$ decreases by a factor $\gtrsim 3$ between the lowest $W_{\lambda}$(Ly$\alpha$) quartile ($\langle$$W_{\lambda}$(Ly$\alpha$)\rangle=-18\unicode{xC5}) and the highest $W_{\lambda}$(Ly$\alpha$) quartile ($\langle$$W_{\lambda}$(Ly$\alpha$)\rangle=24\unicode{xC5}). Similarly, galaxies typically defined as Lyman Alpha Emitters (LAEs; $W_{\lambda}$(Ly$\alpha$) >20\unicode{xC5}) are, on average, metal poor with respect to the non-LAE galaxy population ($W_{\lambda}$(Ly$\alpha$) \leq20\unicode{xC5}) with $Z_{\star}$$_{\rm{non-LAE}}\gtrsim 2 \times$ $Z_{\star}$$_{\rm{LAE}}$. Finally, based on the best-fitting stellar models, we estimate that the increasing strength of the stellar ionizing spectrum towards lower $Z_{\star}$ is responsible for $\simeq 15-25\%$ of the observed variation in $W_{\lambda}$(Ly$\alpha$) across our sample, with the remaining contribution ($\simeq 75-85\%$) being due to a decrease in the HI/dust covering fractions in low $Z_{\star}$ galaxies.Comment: 10 pages, 6 figures, MNRAS accepte