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Register a new userThe UV Luminosity Function of Protocluster Galaxies at $zsim4$: the Bright-end Excess and the Enhanced Star Formation Rate Density
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We report the rest-frame ultraviolet luminosity function of $g$-dropout galaxies in 177 protocluster candidates (PC UVLF) at $zsim4$ selected in the Hyper Suprime-Cam Subaru Strategic Program. Comparing with the UVLF of field galaxies at the same redshift, we find that the PC UVLF shows a significant excess towards the bright-end. This excess can not be explained by the contribution of only active galactic nuclei, and we also find that this is more significant in higher dense regions. Assuming that all protocluster members are located on the star formation main sequence, the PC UVLF can be converted into a stellar mass function. Consequently, our protocluster members are inferred to have a 2.8 times more massive characteristic stellar mass than that of the field Lyman break galaxies at the same redshift. This study, for the first time, clearly shows that the enhancement in star formation or stellar mass in overdense regions can generally be seen as early as at $zsim4$. We also estimate the star formation rate density (SFRD) in protocluster regions as $simeq 6-20%$ of the cosmic SFRD, based on the measured PC UVLF after correcting for the selection incompleteness in our protocluster sample. This high value suggests that protoclusters make a non-negligible contribution to the cosmic SFRD at $zsim4$, as previously suggested by simulations. Our results suggest that protoclusters are essential components for the galaxy evolution at $zsim4$.
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We establish a robust statistical description of the star-forming galaxy population at the end of cosmic HI reionization ($5.0le{}zle6.6$) from a large sample of 52 galaxies with spectroscopically confirmed redshifts from the VIMOS UltraDeep Survey. We identify galaxies with Ly$alpha$ either in absorption or in emission, at variance with most spectroscopic samples in the literature where Ly$alpha$ emitters dominate. We find that star-forming galaxies at these redshifts are distributed along a main sequence in the stellar mass vs. SFR plane. We report a flat evolution of the sSFR(z) in 3<z<6 compared to lower redshift measurements. UV-continuum slopes vary with luminosity, with a large dispersion. We determing UV and Ly$alpha$ luminosity functions using V$_{max}$ method and use them to derive star formation rate densities (SFRD). We find that both UV-derived and Ly$alpha$-derived SFRDs are in excellent agreement after correcting Ly$alpha$ luminosity density for IGM absorption. Our new SFRD measurements at a mean redshift z=5.6 confirm the steep decline of the SFRD at z>2. The bright end of the Ly$alpha$ luminosity function has a high number density, indicating a significant star formation activity concentrated in the brightest Ly$alpha$ emitters (LAE) at these redshifts. LAE with EW>25AA ~contribute to about 75% of the total UV-derived SFRD. While our analysis favors a low dust content in 5.0<z<6.6, uncertainties on the dust extinction correction and associated degeneracies in spectral fitting will remain an issue to estimate the total SFRD until future survey extending spectroscopy to the NIR rest-frame spectral domain, e.g. with JWST.
We present estimates of the GALEX NUV and FUV luminosity functions (LFs) of the Coma cluster, over a total area of ~9 deg^2 (~25 Mpc^2), i.e. from the cluster center to the virial radius. Our analysis represents the widest and deepest UV investigation of a nearby cluster of galaxies made to date. The Coma UV LFs show a faint-end slope steeper than the one observed in the local field. This difference, more evident in NUV, is entirely due to the contribution of massive quiescent systems (e.g. ellipticals, lenticulars and passive spirals), more frequent in high density environments. On the contrary, the shape of the UV LFs for Coma star-forming galaxies does not appear to be significantly different from that of the field, consistently with previous studies of local and high redshift clusters. We demonstrate that such similarity is only a selection effect, not providing any information on the role of the environment on the star formation history of cluster galaxies. By integrating the UV LFs for star-forming galaxies (corrected for the first time for internal dust attenuation), we show that the specific star formation rate of Coma is significantly lower than the integrated SSFR of the field and that Coma-like clusters contribute only <7% of the total SFR density of the local universe. Approximately 2/3 of the whole star-formation in Coma is occurring in galaxies with M_star < 10^10 M_sol. The vast majority of star-forming galaxies has likely just started its first dive into the cluster core and has not yet been affected by the cluster environment. The total stellar mass accretion rate of Coma is ~(0.6-1.8) x 10^12 M_sol Gyr^-1, suggesting that a significant fraction of the population of lenticular and passive spirals observed today in Coma could originate from infalling galaxies accreted between z~1 and z~0.
We report on the discovery of three especially bright candidate $z_{phot} gtrsim 8$ galaxies. Five sources were targeted for follow-up with HST/WFC3, selected from a larger sample of 16 bright ($24.8 lesssim Hlesssim25.5$~mag) candidate $zgtrsim 8$ LBGs identified over the 1.6 degrees$^2$ of the COSMOS/UltraVISTA field. These were identified as Y and J dropouts by leveraging the deep (Y-to-$K_{S} sim 25.3-24.8$~mag, $5sigma$) NIR data from the UltraVISTA DR3 release, deep ground based optical imaging from the CFHTLS and Subaru Suprime Cam programs and Spitzer/IRAC mosaics combining observations from the SMUVS and SPLASH programs. Through the refined spectral energy distributions, which now also include new HyperSuprime Cam g, r, i, z and Y band data, we confirm that 3/5 galaxies have robust $z_{phot}sim8.0-8.7$, consistent with the initial selection. The remaining 2/5 galaxies have a nominal $z_{phot}sim2$. However, if we use the HST data alone, these objects have increased probability of being at $zsim9$. Furthermore, we measure mean UV continuum slopes $beta=-1.91pm0.26$ for the three $zsim8-9$ galaxies, marginally bluer than similarly luminous $zsim4-6$ in CANDELS but consistent with previous measurements of similarly luminous galaxies at $zsim7$. The circularized effective radius for our brightest source is $0.9pm0.2$ kpc, similar to previous measurements for a bright $zsim11$ galaxy and bright $zsim7$ galaxies. Finally, enlarging our sample to include the six brightest $zsim8$ LBGs identified over UltraVISTA (i.e., including three other sources from Labbe et al. 2017, in prep.) we estimate for the first time the volume density of galaxies at the extreme bright ($M_{UV}sim-22$~mag) end of the $zsim8$ UV LF. Despite this exceptional result, the still large statistical uncertainties do not allow us to discriminate between a Schechter and a double power-law form.
[Abridged] We present a robust measurement of the rest-frame UV luminosity function (LF) and its evolution during the peak epoch of cosmic star formation at 1<z<3. We use our deep near ultraviolet imaging from WFC3/UVIS on the Hubble Space Telescope (HST) and existing ACS/WFC and WFC3/IR imaging of three lensing galaxy clusters, Abell 2744 and MACSJ0717 from the Hubble Frontier Field survey and Abell 1689. We use photometric redshifts to identify 780 ultra-faint galaxies with $M_{UV}$<-12.5 AB mag at 1<z<3. From these samples, we identified 5 new, faint, multiply imaged systems in A1689. We compute the rest-frame UV LF and find the best-fit faint-end slopes of $alpha=-1.56pm0.04$, $alpha=-1.72pm0.04$ and $alpha=-1.94pm0.06$ at 1.0<z<1.6, 1.6<z<2.2 and 2.2<z<3.0, respectively. Our results demonstrate that the UV LF becomes steeper from zsim1.3 to zsim2.6 with no sign of a turnover down to $M_{UV}=-14$ AB mag. We further derive the UV LFs using the Lyman break dropout selection and confirm the robustness of our conclusions against different selection methodologies. Because the sample sizes are so large, and extend to such faint luminosities, the statistical uncertainties are quite small, and systematic uncertainties (due to the assumed size distribution, for example), likely dominate. If we restrict our analysis to galaxies and volumes above > 50% completeness in order to minimize these systematics, we still find that the faint-end slope is steep and getting steeper with redshift, though with slightly shallower (less negative) values ($alpha=-1.55pm0.06$, $-1.69pm0.07$ and $-1.79pm0.08$ for $zsim1.3$, 1.9 and 2.6, respectively). Finally, we conclude that the faint star-forming galaxies with UV magnitudes of $-18.5<M_{UV}<-12.5$ covered in this study, produce the majority (55%-60%) of the unobscured UV luminosity density at 1<z<3.
Context. Knowing the exact shape of the UV luminosity function of high-redshift galaxies is important in order to understand the star formation history of the early universe. However, the uncertainties, especially at the faint and bright ends of the LFs, are still significant. Aims. In this paper, we study the UV luminosity function of redshift z = 2.5 - 4.5 galaxies in 2.38 deg^2 of ALHAMBRA data with I <= 24. Thanks to the large area covered by ALHAMBRA, we particularly constrain the bright end of the luminosity function. We also calculate the cosmic variance and the corresponding bias values for our sample and derive their host dark matter halo masses. Methods. We use a novel methodology based on redshift and magnitude probability distribution functions (PDFs). This methodology robustly takes into account the uncertainties due to redshift and magnitude errors, shot noise and cosmic variance, and models the luminosity function in two dimensions (z; M_UV ). Results. We find an excess of bright ~ M*_UV galaxies as compared to the studies based on broad-band photometric data. However, our results agree well with the luminosity function of the magnitude-selected spectroscopic VVDS data. We measure high bias values, b ~ 8 - 10, that are compatible with the previous measurements considering the redshifts and magnitudes of our galaxies and further reinforce the real high-redshift nature of our bright galaxies. Conclusions. We call into question the shape of the luminosity function at its bright end; is it a double power-law as suggested by the recent broad-band photometric studies or rather a brighter Schechter function, as suggested by our multi-filter analysis and the spectroscopic VVDS data.
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